Encyclopedia of Ocean Engineering 9789811069451, 9789811069468, 9789811069475

Citation preview

Weicheng Cui Shixiao Fu Zhiqiang Hu Editors

Encyclopedia of Ocean Engineering

Encyclopedia of Ocean Engineering

Weicheng Cui • Shixiao Fu • Zhiqiang Hu Editors

Encyclopedia of Ocean Engineering With 1737 Figures and 126 Tables

Editors Weicheng Cui School of Engineering Westlake University Hangzhou, Zhejiang, China

Shixiao Fu School of Naval Architecture, Ocean and Civil Engineering Shanghai Jiao Tong University Shanghai, China

Zhiqiang Hu Marine, Offshore and Subsea Technology Group School of Engineering Newcastle University Newcastle upon Tyne, UK

ISBN 978-981-10-6945-1 ISBN 978-981-10-6946-8 (eBook) ISBN 978-981-10-6947-5 (print and electronic bundle) https://doi.org/10.1007/978-981-10-6946-8 © Springer Nature Singapore Pte Ltd. 2022 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

Although the planet on which we live is called Earth, more than 70% of her surface is covered by the ocean. With the constant increase of human population, people are striving to develop more living space in the ocean and take advantage of its resources. However, there is no doubt that during this process humans will meet many technological challenges and must find ways to protect the ocean environment, on purpose of reaching a sustainable and harmonious lifestyle with the ocean. To achieve this goal, we must know the ocean, gather sufficient knowledge about the ocean, and treat the ocean in a respectful and cautious manner, because otherwise, any violent and reckless exploration behavior that harms the ocean will lead to unaffordable consequences to humanity. Therefore, to understand the ocean and to master the fundamental technology relating to its development is of critical importance, especially this year when humanity is truly beginning to experience the obvious temperature rise due to global warming. The writing of this encyclopedia, Ocean Engineering, has three aims. Firstly, to provide a useful introductory reading reference for people interested in, but not delving into, the field of ocean engineering. Secondly, to provide necessary scientific and technological knowledge for people who are delving into some specific aspects in ocean engineering and want to do interdisciplinary extensions. Thirdly, to contribute within our scope in helping people find sustainable and harmonious ways to develop and protect the ocean. This encyclopedia discusses the main categories of fundamental knowledge on ocean engineering, which are extensively covered in 21 parts, including the parts on conventional naval architecture and offshore engineering such as ship design and offshore decommissioning; the parts on ocean exploration such as underwater engineering, AUV/ROV, and polar engineering; the parts on harvesting of ocean resources such as deepwater mining and on utilizing the ocean space such as very large floating structures (VLFS) and aquaculture engineering; and the parts on sustainable ocean development such as offshore renewable energy, green shipping, and ocean environmental protection. This encyclopedia contains numerous illustrations and examples to make it easy to understand. With the publication of this encyclopedia, Ocean Engineering, the editorial team wants to thank all those who have contributed to it. Please forgive us for not being able to name all the section editors here since they are specified in the next page, but we would like to convey sincere appreciations to our excellent section editors (SEs). You have done great work, and the time and effort spent v

vi

Preface

in organizing and reviewing entries is much appreciated. Besides, please let us acknowledge every author’s contribution. We would not be able to begin without the help of all our brilliant authors. Finally, we are also very grateful to the Springer Nature supporting team. Thank you for always being there for this encyclopedia. The experience of working together in this 3-year project leaves an indelible impression on us. Westlake University, Hangzhou, China Shanghai Jiao Tong University, Shanghai, China Newcastle University, Newcastle upon Tyne, United Kingdom May 2022

Weicheng Cui, Ph.D. (Editor) Shixiao Fu, Ph.D. (Editor) Zhiqiang Hu, Ph.D. (Editor)

Table of Contents

Alternative Fuel for Ship Propulsion Analysis of Renewable Energy Devices Application of Image Processing in Ice–Structure Interaction Aquaculture Structures: Experimental Techniques Aquaculture Structures: Numerical Methods Arctic Pipeline Atmospheric Diving Suit (ADS) Autonomous Underwater Vehicle (AUV) AUV/ROV/HOV Control Systems AUV/ROV/HOV Hydrostatics AUV/ROV/HOV Propulsion System AUV/ROV/HOV Resistance AUV/ROV/HOV Stability Auxiliary Icebreaking Methods Beaching Bearing Capacity of Spudcans Big Data-Based Decision Support Systems Biodiversity Conservation Block Assembly Line Block Erection Technology Bucket Foundations Buffer Station Cable Capacity of Suction Anchor Catenary Anchor Leg Mooring Catenary Mooring Central Monitoring System Christmas Tree Collector and Crusher Complete and Partial Dismantling Compliant Tower Platform Computational Fluid Dynamics in AUV/ROV/ HOV Hydrodynamics

Concept Design Concrete Platform Connectors of VLFS Cutting Technology of Steel Damage Stability Dead Ship Condition Decommissioning of Fixed Platform Decommissioning of Floating Platforms Decommissioning of Offshore Oil and Gas Installations Decommissioning of Subsea Facilities Deep Sea Mining Deep Submergence Rescue Vehicle (DSRV) Deep Tow System Deep-Ocean Assessment and Reporting of Tsunamis (DART) BUOY Design of Mooring System Design of Pipelines and Risers Design of Renewable Energy Devices Design of Submersibles Design Rules and Standards Design Spiral Detailed Design Diving of Anchors Doppler Velocity Log for Navigation System in Underwater Vehicle Drag Anchors Ductile-Brittle Transition of Sea Ice Under Uniaxial Compression and Its Engineering Applications Dynamic Analysis Method Dynamic Behavior and Fatigue Dynamic Ice Loads and Structural Responses Dynamic Positioning in Ice vii

viii

Economic Assessment Empirical Design Energy Efficiency Regulations from IMO Environmental Impact Assessment System Environmental Perception for Underwater Vehicles Eutrophication Excessive Accelerations Experimental Investigation of Offshore Renewable Energy Experimental Techniques for VLFS Exploitation of Gas Hydrates Explosive Removal External Turret External Turret Single Point Mooring System Fatigue of Mooring Lines Fiber Optic Hydrophone Fiber-Optic Cable Field Development Fishing Ships Flexible Pipes and Umbilicals Flexural Strength of Sea Ice FLNG Floating Bridge Fluid Effects During Iceberg-Structure Interactions Forming Technology of Profiles Forming Technology of Steel Hull Plates FPSO Future Trend on the Design, Building, and Operation of Ships for Energy Efficiency Glider Global Buckling of Offshore Pipelines Global Navigation Satellite System (GNSS) Buoy Green Tides Harmful Algal Blooms Heave Plate High-Performance Ship Homotopy Analysis Method Human Factors in Ship Design Human Factors in the Role of Energy Efficiency Human Occupied Vehicle (HOV) Hybrid Remotely Operated Vehicle (HROV)/ Autonomous and Remotely Operated Vehicle (ARV) Hydrodynamic Design Hydrodynamics for Subsea Systems

Table of Contents

Hydroelasticity Theory Ice Breaking Vessel Ice Management in Offshore Operations Ice Tank Test Iceberg Scouring Ice-Induced Vibration and Noise of Ships Impact of Maritime Transport In Situ Permeability Measured Using Piezopenetrometers Installation and Decommissioning Installation of Offshore Pipelines Installation of Spudcans Intact, Damage, and Dynamic Stability of Floating Structures Integrated Navigation Intelligent Control Algorithms in Underwater Vehicles Internal Turret Single-Point Mooring (SPM) System Introduction to Shipbuilding (Shipyard) Inventory of Hazardous Materials Jacket Platform Jack-Up Platforms Jellyfish Bloom Launching Technology Lifting System Local/Global Buckling and Propagation Long Baseline Underwater Acoustic Location Technology Long-Term Storage Luxury Cruises Maneuverability of Polar Vessel Marine Ecological Red Line Marine Operations Marine Protected Areas in Areas Beyond National Jurisdiction Mega-Float Meteorological Monitoring and Measurement Buoy Microplastics Mineral Processing and Metallurgy Modern Aquaculture Structures Modification for Reuse Monopile Foundations in Offshore Wind Farm Moored Ship in Ice Mooring Anchor Mooring Connector

Table of Contents

Mooring Lines Mooring System Mooring System of Renewable Energy Devices Multidisciplinary Design Optimization (MDO) Navigation Buoy Navigation of Polar Vessel Net Structures: Biofouling and Antifouling Net Structures: Design Net Structures: Hydrodynamics New Technologies in Auxiliary Propulsions Nonexplosive Removal Numerical Simulation Floe Ice–Sloping Structure Interactions Numerical Simulation of Ice-Going Ships Numerical Tank Obstacle Avoidance Technology for Underwater Vehicle Ocean Thermal Energy Conversion Offshore In Situ Penetrometers Offshore Pile Driving Offshore Structure Design Under Ice Loads Offshore Vessel Offshore Wind Turbine-Ice Interactions Offshore Wind Turbines On-Bottom Stability of Submarine Pipelines Open Water Test Optical Compass Optimal Design Painting Technology Parametric Rolling Photoelectric Detection Technology in Underwater Vehicles Physical Properties of Sea Ice Pile Capacity Pipeline Soil Interactions Piping Technology Polar Acoustics Polar Communications Polar Materials Polar Merchant Vessel Polar Offshore Engineering Polar Propulsion Polar Research Vessel Power Take-Off System Power Transmission and Distribution Preliminary Design Probabilistic Aspects for Ice Loads on Ships

ix

Profiling Float Pure Loss of Stability Recycling Regulations Reefing Reliability and Safety in Offshore Engineering Reliability-Based Design (RBD) Remotely Operated Vehicle (ROV) Remotely Operated Vehicle (ROV) in Subsea Engineering Rescue Bell Research Ship Resistance of Polar Vessel Resource Assessment Risk-Based Design for Ship and Offshore Structures ROV Dynamic Positioning Safety of Offshore Platforms Salinity Gradient Power Conversion Second Generation Intact Stability Criteria Semi-submersible Platform Semisubmersible Vehicle Autopilot Control System Service Ships Shallow Foundations Shear Strength Ship Construction and Operation Impact on Energy Efficiency Ship Design Process Ship Electrical Design Ship Hull Lofting and Marking-Off Ship Machinery Design Ship Navigation System Ship Operational Environment Ship Overall Design Ship Propulsion System Ship Recycling Ship Recycling Facility Plan Ship Recycling Plan Ship Structural Design Ship-Fitting Design Ship-Iceberg Interactions Short Pile and Uplifting Capacity Simultaneous Localization and Mapping Single Anchor Leg Mooring Single-Point Mooring Size Effect and High-Pressure Zone of Sea Ice Sloping Structure: Floe Ice Interactions

x

Sloping Structure–Level Ice Interactions Soft YOKE Single Point Mooring System Sonar Technology SPAR Platform Spatial Variability Special Marine Vehicle Spread Mooring System Static Analysis Method Station-Keeping System for VLFS Steel Pipelines and Risers Steel Pretreatment Structural Analysis and Design of VLFS Structural Characteristics of Polar Engineering Structural Design Submarine Submersible Subsea Connector Subsea Equipment Installation Technology Subsea Hazards Subsea Production System Suction Piles Surface Buoy Surface Mineral Storage and Dump Surface Warships Surf-Riding and Broaching Taut Mooring Technical and Economical Barriers on Green Energy Utilization in Shipping Tension-Leg platform Thermal Insulation Thruster-Assisted Mooring

Table of Contents

Tidal and Ocean Current Turbines Towing Tank Test Traditional Aquaculture Structures Transport Ship Tropical Atmosphere Ocean (TAO) Buoy Tsunami Warning Buoy Ultra-short Baseline Underwater Acoustic Location Technology Umbilical Cable Underwater Acoustic Communication Underwater Acoustic Sensor Network Underwater Driving Subsystem Underwater Information Sensing Technology Underwater Lander Underwater Mining System Underwater Welding Very Large Floating Structures (VLFS): Overview Vortex Shedding and VIV Suppression Water Surface Support (Layout and Recovery) System Wave Energy Converters Wave Energy Utilization Buoy Wave Measurement Buoy Wave-Ice Interactions Welding Technology Winch Wind Tunnel Test Winterization of Polar Engineering

About the Editors

Weicheng Cui School of Engineering Westlake University Hangzhou, Zhejiang, China Associate Editor, Journal of Ship Mechanics, Shipbuilding of China Editorial Board Member, Marine Structures, Ocean Engineering, Ships and Offshore Structures, Journal of Marine Science and Technology, Journal of Engineering for the Maritime Environment, Journal of Marine Science and Application, Journal of marine science and engineering Weicheng Cui joined Westlake University (WU) as a chair professor in September 2018, 1 month before its founding ceremony. The founding mission of WU is to become a global leader in frontier scientific research and a reformer in higher education in China. Dr. Cui’s current research interests include (1) development of robotic fish-type submersibles and (2) fundamental research on the generalization of general system theory (GST) into theory of everything (TOE) for complex systems. He got his B.Sc. from the Department of Engineering Mechanics at Tsinghua University in 1986 and his Ph.D. from the University of Bristol, England, in 1990. From 1990 to 1993, he did his postdoctoral research in the Department of Aerospace Engineering at the University of Bristol. He made some contributions in the aspects of measurement of interlaminar shear strength, nonlinear effect and size effect of the delamination strength, and the delamination mechanism for composite materials. xi

xii

About the Editors

From February 1993 to May 1999, he worked at China Ship Scientific Research Center (CSSRC), and from June 1999 to September 2002, he was appointed as the Changjiang Professor at Shanghai Jiao Tong University. During these two periods, he mainly engaged in research in ship structural mechanics. He had made some contributions in the areas of the prediction of the ultimate strength of intact and damaged ship structures, fatigue strength assessment of ship structures, and reliability-based analysis and design of ship structures. From October 2002 to March 2013, he worked at CSSRC again. Dr. Cui was the project leader and first deputy chief designer of Jiaolong deep manned submersible. He made some contributions in the application of multidisciplinary design optimization method and the establishment of a rational design standard for the manned cabin. Because of his outstanding contribution to the Jiaolong manned submersible development project, he won the Blancpain Hans Hass Fifty Fathoms Award, the First Prize in National Science and Technology Progress, and many honorary titles such as “The National Excellent Science and Technology Workers,” “The Deep Diving Hero” awarded by the Central Committee and the State Council, and the first batch of scholars of the National Innovation Talent Award. From March 2013 to September 2018, he worked at Shanghai Ocean University, and from September 2018 onward, he has been working at Westlake University. He served as the project leader and chief designer of the Rainbowfish Challenging the Challenger Deep project from 2013 to 2020. In 2016, he was named one of “China’s Top Ten Science Stars” by Nature. He is currently an editorial board member of six international journals, and the associate editorin-chief of both Shipbuilding of China and the Journal of Ship Mechanics. He has published more than 400 papers in SCI and EI journals, being selected in Elsevier’s list of China’s Highly Cited Researchers continuously from 2017 to 2019.

About the Editors

xiii

Shixiao Fu School of Naval Architecture, Ocean and Civil Engineering Shanghai Jiao Tong University Shanghai, China Associate Editor, Marine Structures, Journal of Offshore Mechanics and Arctic Engineering, Proceeding of the Institute of Civil Engineers-Marine Engineering Editorial Board Member, Journal of Hydrodynamics, China Ocean Engineering (in Chinese) Shixiao Fu got Bachelor and MSc degrees from DaLian University of Technology, and received his Ph.D. from Shanghai Jiao Tong University (SJTU) in 2005. In the next 2 years, he did his postdoctoral research at CeSOS, Norwegian University of Science and Technology (NTNU). He joined the faculty of Shanghai Jiao Tong University in 2008, served as a professor from 2009 to 2018, and was appointed as a distinguished professor in 2019. Professor Fu has been selected as the Academician of the Norwegian Academy of Technological Sciences in 2020, and was granted China National Funds for Distinguished Young Scientists in 2018. Professor Fu is now the vice director of the State Key Laboratory of Ocean Engineering at Shanghai Jiao Tong University, and the dean of the Research School of Polar and Deep Sea Technologies (joint research school between SJTU and Second Institute of Oceanography). He is also the associate editor of Marine Structures and the Journal of Offshore Mechanics and Arctic Engineering. Professor Fu’s research interests include hydroelasticity of floating bridges/tunnels and large-scale fish cage, vortex-induced vibration of flexible structures, experimental methods of force feedback control, and hybrid full-scale model testing.

xiv

About the Editors

Zhiqiang Hu Marine, Offshore and Subsea Technology Group School of Engineering Newcastle University Newcastle upon Tyne, UK Associate Editor, Ocean Engineering Zhiqiang Hu received his Ph.D. in naval architecture and ocean engineering from Shanghai Jiao Tong University in 2008 and had been working in Shanghai Jiao Tong University until 2016. He joined Newcastle University in 2016 and has been the Lloyds Professor of Offshore Engineering since 2018. Professor Hu has plenty of lecturing and research experience in offshore renewable energy, offshore hydrodynamics, structural dynamics, and basin experiment testing. Professor Hu has published approximately 100 scientific papers and currently is the deputy editor of the journal Ocean Engineering.

About the Section Editors

Hongwei An Department of Civil Environmental and Mining School of Engineering University of Western Australia Perth, WA, Australia

Weicheng Cui School of Engineering Westlake University Hangzhou, Zhejiang, China

Zunfeng Du Department of Naval Architecture and Ocean Engineering School of Civil Engineering Tianjin University Tianjin, China

xv

xvi

About the Section Editors

Menglan Duan College of Safety and Ocean Engineering China University of Petroleum-Beijing (CUP) Beijing, China

Shixiao Fu School of Naval Architecture, Ocean and Civil Engineering Shanghai Jiao Tong University Shanghai, China

Zhen Gao Norwegian University of Science and Technology Trondheim, Norway

Terry Griffiths Oceans Graduate School The University of Western Australia Perth, WA, Australia

About the Section Editors

xvii

Min Gu China Ship Scientific Research Center (CSSRC) Wuxi, China

Zhiqiang Hu Marine, Offshore and Subsea Technology Group School of Engineering Newcastle University Newcastle upon Tyne, UK

Shunying Ji State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of Technology Dalian, China

Zhe Jiang Hadal Science and Technology Center Shanghai Ocean University Shanghai, China

xviii

About the Section Editors

Xiangyang Li China Ocean Mineral Resources R&D Association (COMRA) Beijing, China

Yujun Liu School of Naval Architecture and Ocean Engineering Dalian University of Technology Dalian, China

Zhenhui Liu Front End Engineering Aker Solutions ASA Trondheim, Norway

Jiang Lu China Ship Scientific Research Center Wuxi, Jiangsu, China

About the Section Editors

xix

Wenjun Lu Sustainable Arctic Marine and Coastal Technology Research Centre Norwegian University of Science and Technology Trondheim, Norway The Norwegian Academy of Science and Letters Trondheim, Norway

Wengang Mao Department of Mechanics and Maritime Sciences Chalmers University of Technology Gothenburg, Sweden

Wanan Sheng SW MARE Marine Technology Cork, Ireland

Changhui Song School of Engineering Westlake University Hangzhou, China

xx

About the Section Editors

Liping Sun College of Shipbuilding and Ocean Engineering Harbin Engineering University Harbin, Heilongjiang, China

Yinghui Tian Department of Infrastructure Engineering The University of Melbourne Melbourne, VIC, Australia

Chunsheng Wang Laboratory of Marine Ecosystem and Biogeochemistry Second Institute of Oceanography State Oceanic Administration Hangzhou, China

Yanzhuo Xue College of Shipbuilding Engineering Harbin Engineering University Harbin, China

About the Section Editors

xxi

A-Man Zhang College of Shipbuilding and Ocean Engineering Harbin Engineering University Harbin, Heilongjiang, China

Contributors

Chen An School of Safety and Ocean Engineering, China University of Petroleum (Beijing), Beijing, China Hongwei An Department of Civil Environmental and Mining, School of Engineering, University of Western Australia, Perth, WA, Australia Xinglan Bai School of Naval Architecture and Maritime, Zhejiang Ocean University, Zhoushan, The People’s Republic of China Chunwei Bi State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China Shuxia Bu China Ship Scientific Research Center (CSSRC), Wuxi, China Jing Cai College of Automation, Harbin Engineering University, Harbin, China Yang Cao China Ship Scientific Research Center, Shanghai, China Wei Chai Departments of Naval Architecture, Ocean and Structural Engineering, School of Transportation, Wuhan University of Technology, Wuhan, China Department of Marine Technology, Norwegian University of Science and Technology, Trondheim, Norway Cheng Chen College of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, China Guo-Qing Chen College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Hao Chen Zhejiang University – Westlake University Joint Training, Zhejiang University, Hangzhou, China Ji-Kang Chen College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Lu Chen Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China Miao Chen College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China xxiii

xxiv

Quanzhen Chen Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China Shaohua Chen Yichang Research Institute of Testing Technology, Yichang, China Xi Chen China Ship Development and Design Centre, Wuhan, China Xiaodong Chen State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, China Xin Chen College of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, China Xujun Chen College of Field Engineering, The Army Engineering University of PLA, Nanjing, China Yunsai Chen Department of Technology, National Deep Sea Center of China, Qingdao, Shandong, China Jianhua Cheng College of Automation, Harbin Engineering University, Harbin, China Jinping Cheng Hong Kong University of Science and Technology, Hong Kong, China Tianhu Cheng State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China L. F. Chernogor V. N. Karazin Kharkiv National University, Kharkiv, Ukraine Jilong Chu China Ship Scientific Research Center (CSSRC), Wuxi, China Wen-Hua Chu College of Marine Sciences, Shanghai Ocean University, Shanghai, Shanghai, China Jie Cui College of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, China Weicheng Cui School of Engineering, Westlake University, Hangzhou, Zhejiang, China Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China Ye Cui College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin, China Guoliang Dai School of Civil Engineering, Southeast University, Nanjing, China Shuang Ling Dai Key Laboratory of Marine Mineral Resources, Ministry of Natural Resources, Guangzhou, China Guangzhou Marine Geological Survey, Guangzhou, China

Contributors

Contributors

xxv

Chen Dandong China Ship Development and Design Center, Wuhan City, China Shaocheng Di College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Wenbin Dong Senior Engineer Technical Advisory of Offshore Structures, DNV GL AS, Høvik, Oslo, Norway Xinguang Du Intelligent Equipment Engineering Technology Center, China Ship Scientific Research Center (CSSRC), Shanghai, China Zunfeng Du Department of Naval Architecture and Ocean Engineering, School of Civil Engineering, Tianjin University, Tianjin, China QingFeng Duan School of Safety and Ocean Engineering, China University of Petroleum (Beijing), Beijing, China Menglan Duan College of Safety and Ocean Engineering, China University of Petroleum-Beijing (CUP), Beijing, China Wen-Yang Duan College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Mike Efthymiou Indian Ocean Marine Research Centre, The University of Western Australia, Crawley, WA, Australia Junkai Feng College of Safety and Ocean Engineering, China University of Petroleum (Beijing), Beijing, China Linyong Feng Beijing General Research Institute of Mining and Metallurgy Technology Group, Beijing, China Xiaowei Feng Fugro Australia Marine Pty Ltd, Perth, WA, Australia Yan Feng College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Zhengping Feng School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China Dengfeng Fu State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Guangming Fu Department of Offshore Oil and Gas Engineering, China University of Petroleum (East China), Qingdao, Shandong, China Shixiao Fu School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China Shaowei Gan Overseas Technology Center, China Classification Society, Singapore, Singapore Cong Gao College of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, China

xxvi

Fu-ping Gao Institute of Mechanics, Chinese Academy of Sciences, Beijing, China Huan Gao Shanghai Electric Cable Research Institute, Shanghai, China Lei Gao Shanghai Rainbowfish Deepsea Equipment & Technology Co. Ltd, Shanghai, China Liang-Tian Gao College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Xifeng Gao State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Zhen Gao Norwegian University of Science and Technology, Trondheim, Norway Lin Gong Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China Terry Griffiths Oceans Graduate School, The University of Western Australia, Perth, WA, Australia Min Gu China Ship Scientific Research Center (CSSRC), Wuxi, China Fukun Gui National Engineering Research Center for Marine Aquaculture, Zhejiang Ocean University, Zhejiang, China Chunyu Guo Harbin Engineering University, Harbin, China Fengwei Guo DNVGL, Oslo, Norway Hong Guo China National Offshore Oil Corporation, Beijing, China Qiang Guo College of Information and Communication Engineering, Harbin Engineering University, Harbin, China Ruiyan Guo College of Safe and Off-shore Engineering, China University of Petroleum – Beijing, Beijing, China Ying Guo State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University, Tianjin, China Feng-Lei Han College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Duochang He Zhuzhou CRRC Times Electric CO., LTD, Zhuzhou, Hunan, China Yankang He Intelligent Transportation Systems Research Center, Wuhan University of Technology, Wuhan, China

Contributors

Contributors

xxvii

Li Hongtao Offshore Engineering Technology Center of China Classification Society, Tianjin, China Wu Hongyun Seabed Mining Department of Changsha Institute of Mining Research, Changsha, China Muhammad Shazzad Hossain Centre for Offshore Foundation Systems (COFS), Oceans Graduate School, The University of Western Australia, Crawley, WA, Australia Cun Hu Research Center of Offshore Geotechnical Engineering, Research Institute of Tsinghua University in Shenzhen, Shenzhen, China Haitao Hu Department of Engineering Mechanics, Dalian University of Technology, Dalian, China Qing Hu School of Marine Engineering and Technology, Sun Yat-sen University, Zhuhai, China Yong Hu Shanghai Jiaotong University, ShangHai, China School of Transportation, Wuhan University of Technology, Wuhan, China Zhen Hu China Ship Scientific Research Center (CSSRC), Wuxi, China Ting Huang Hohai University, Nanjing, Jiangsu, China Wei Huang Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China Yan Huang State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Da Hui School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China Kim Hyunwook School of naval architecture and ocean engineering, Dalian university of technology, Dalian, Liaoning, China Kazuhiro Iijima Department of Naval Architecture and Ocean Engineering, Osaka University, Osaka, Japan Shunying Ji State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, China Hui Jia College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Zhike Jia Engineering Technology, CNOOC Energy Technology & Services Limited, Tianjin, China Xun Xiong Jiang Beijing General Research Institute of Mining and Metallurgy Technology Group, Beijing, China Zhe Jiang Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China

xxviii

Zhiyu Jiang Department of Engineering Sciences, University of Agder, Grimstad, Norway Guo-Yong Jin College of Power and Energy Engineering, Harbin Engineering University, Harbin, China Haiyan Jin Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China Lei Ju College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Zhuang Kang College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Youngho Kim Centre for Offshore Foundation Systems (COFS), Oceans Graduate School, The University of Western Australia, Crawley, WA, Australia Xiao Lang Department of Mechanics and Maritime Sciences, Chalmers University of Technology, Gothenburg, Sweden Chengfeng Li State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Dewang Li Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China Feng Li College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Hai-Chao Li College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, China Hongtao Li Offshore Engineering Technology Center of China Classification Society, Tianjin, China Sustainable Arctic Marine and Coastal Technology (SAMCoT), Centre for Research-based Innovation (CRI), Norwegian University of Science and Technology, Trondheim, Norway Hui Li College of Mechanical and Energy Engineering, Jimei University, Xiamen, China College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Jinhui Li Department of Civil and Environmental Engineering, Harbin Institute of Technology at Shenzhen, Shenzhen, P. R. China Junrong Li China Classification Society Wuhan Research and Institute, Wuhan, Hubei province, China Liang Li Department of Naval Architecture and Ocean Engineering, University of Strathclyde, Glasgow, UK

Contributors

Contributors

xxix

Lin Li Department of Mechanical and Structural Engineering and Materials Science, University of Stavanger, Stavanger, Norway Mian Li UM-SJTU Joint Institute, Shanghai Jiao Tong University, Shanghai, China Mingfang Li Wuhan University of Science and Technology, Wuhan, China Peiyong Li School of transportation, Wuhan University of Technology, Wuhan, China Qiuhua Li Changsha Mining and Metallurgy Research Institute Co., Ltd., Changsha, People’s Republic of China Rui Li School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China Ruipeng Li School of Engineering, Westlake University, Hangzhou, China Shuai Li State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China Song-Jie Li College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Xiangyang Li China Ocean Mineral Resources R&D Association (COMRA), Beijing, China Xiaodong Li Yichang Research Institute of Testing Technology, Yichang, China Xinzheng Li Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology (Qingdao), Qingdao, China University of Chinese Academy of Sciences, Beijing, China Xueyou Li School of Civil Engineering, Sun Yat-sen University, Guangzhou, P. R. China Yan Li State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University, Tianjin, China Zhijun Li State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China Lian Lian School of Oceanography, Shanghai Jiao Tong University, Shanghai, China State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China

xxx

Xu Liang Institute of Marine Structures and Ship Architecture, Zhejiang University, Zhoushan, Zhejiang, China Kang-Ping Liao College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Qiang Lin China Ship Science Research Center (CSSRC), Shanghai, China Zhiliang Lin School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China Sun Liqiang Tianjin University, Tianjin, China Guijie Liu College of Engineering, Ocean University of China, Qingdao, China Hongbin Liu Hong Kong University of Science and Technology, Hong Kong, China Junfeng Liu Shanghai Jiao Tong University, Shanghai, China Kun Liu Department of Technology, National Deep Sea Center of China, Qingdao, Shandong, China Liqin Liu State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Ning Liu School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China Pengfei Liu School of Engineering, Newcastle University, Newcastle upon Tyne, UK Renwei Liu College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Run Liu State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Shewen Liu Nava Architecture and Ocean Engineering College, Dalian Maritime University, Dalian, China Tao Liu China Ship Scientific Research Center, Wuxi, China Wenlong Liu Department of Infrastructure Engineering, The University of Melbourne, Melbourne, VIC, Australia Xiaodong Liu Institute of Acoustics, Chinese Academy of Sciences, Beijing, China Yujun Liu School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China Zhenhui Liu Front End Engineering, Aker Solutions ASA, Trondheim, Norway Xue Long Nava Architecture and Ocean Engineering College, Dalian Maritime University, Dalian, China

Contributors

Contributors

xxxi

Jiang Lu China Ship Scientific Research Center (CSSRC), Wuxi, China Wenjun Lu Sustainable Arctic Marine and Coastal Technology Research Centre, Norwegian University of Science and Technology, Trondheim, Norway The Norwegian Academy of Science and Letters, Trondheim, Norway Yang Lu College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Xiaofeng Luo China Classification Society, Wuhan Rules & Research Institute, Wuhan, China Yong Luo Shanghai Jiao Tong University, Shanghai, China Haining Lyu School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China Gang Ma Harbin Engineering University, Harbin, Heilongjiang, China Lu Ma College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin, China Qian Ma American Bureau of Shipping, Houston, TX, USA Shan Ma College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Xiafei Ma Shanghai Jiao Tong University, Shanghai Jiao Tong University Underwater Engineering Insititute Co., Ltd., Shanghai, China Xuewen Ma College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Wengang Mao Department of Mechanics and Maritime Sciences, Chalmers University of Technology, Gothenburg, Sweden Dong-Qing Miao College of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, China Baoyu Ni College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Wen-Chi Ni College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Mac Darlington Uche Onuoha College of Safety and Ocean Engineering, China University of Petroleum Beijing, Beijing, People’s Republic of China Fu-Zhen Pang College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Wei Ping Shanghai Jiao Tong University, Shanghai Jiao Tong University Underwater Engineering Insititute Co., Ltd., Shanghai, China Dongsheng Qiao State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning, China

xxxii

Gang Qiao College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin, China Aohan Qin China Classification Society Wuhan Rules & Research Institute, Wuhan, China Jun Qin Marine Design & Research Institute of China (MARIC), Shanghai, China Ting Qu National Engineering Research Centre for Marine Aquaculture, Institute of Innovation & Application, Zhejiang Ocean University, Zhoushan, China Zhen Ren Tianjin Jinhang Institute of Technical Physics, Tianjin, China Igor Rychlik Department of Mathematical Sciences, Chalmers University of Technology, Gothenburg, Sweden Junji Sawamura Naval Architecture and Ocean Engineering, Osaka University, Osaka, Japan Yugao Shen Department of Marine Technology, Centre for Autonomous Marine Operations and Systems (AMOS), Norwegian University of Science and Technology (NTNU), Trondheim, Norway Wanan Sheng SW MARE Marine Technology and Consultation, Cork, Ireland Wei Shi Deepwater Engineering Research Center, Dalian University of Technology, Dalian, Liaoning, China State Key Laboratory of Coast and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning, China Changhui Song School of Engineering, Westlake University, Hangzhou, China Ming Song Department of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, China Xiancang Song College of Engineering, Ocean University of China, Qingdao, China Biao Su SINTEF Ocean, Trondheim, Norway Dong Sun Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China Fengsheng Sun School of Navigation and Naval Architecture, Dalian Ocean University, Dalian, China Kai Sun State Key Laboratory of Structure Analysis of Industrial Equipment, Dalian University of Technology, Dalian, China Liping Sun College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China

Contributors

Contributors

xxxiii

Pengfei Sun Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China Zhe Sun School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China Yougang Tang Tianjin University, Tianjin, China Zongyong Tang Yichang Testing Technique Research Institute, Yichang, China Yinghui Tian Department of Infrastructure Engineering, The University of Melbourne, Melbourne, VIC, Australia F. Tong School of Civil, Environmental and Mining Engineering, The University of Western Australia, Perth, WA, Australia Anliang Wang Marine Disaster Forecasting and Warning Division, National Marine Environmental Forecasting Center, Beijing, China Biao Wang Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China Chao Wang Harbin Engineering University, Harbin, China Chong Wang School of Transportation, Wuhan University of Technology, Wuhan, China Chunhui Wang Harbin Engineering University, Harbin, China Dong Wang Ocean University of China, Qingdao, China Enhao Wang State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Hongwei Wang Harbin Engineering University, Harbin, China Ji Wang School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China Jinlong Wang College of Safety and Ocean Engineering, China University of Petroleum, Beijing, China Junrong Wang College of Engineering, Ocean University of China, Qingdao, China Liyuan Wang State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University, Tianjin, China Pengbin Wang Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China Fourth Institute of Oceanography, Ministry of Natural Resources, Beihai, China Qingkai Wang State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China Shoujun Wang CIMC Raffles Offshore Ltd, Yantai, China

xxxiv

Shuai Wang China Ship Scientific Research Center, Wuxi, China Shuqing Wang College of Engineering, Ocean University of China, Qingdao, China Tianhua Wang China Ship Scientific Research Center (CSSRC), Wuxi, China Xian-Zhong Wang Departments of Naval Architecture, Ocean and Structural Engineering, School of Transportation, Wuhan University of Technology, Wuhan, People’s Republic of China Yanhui Wang School of Mechanical Engineering, Tianjin University, Tianjin, China Yongfeng Wang School of Safety and Ocean Engineering, China University of Petroleum (Beijing), Beijing, China Yi Wang College of Safe and Off-shore Engineering, China University of Petroleum – Beijing, Beijing, China Yingying Wang China Ship Scientific Research Center, Wuxi, China School of Safety and Ocean Engineering, China University of Petroleum (Beijing), Beijing, China Yongkui Wang College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Zhen Wang DNV AS, Høvik, Norway Zongling Wang Key Laboratory of Marine Eco-Environmental Science and Technology, First Institute of Oceanography, Ministry of Natural Resources (MNR), Qingdao, China Laboratory of Marine Ecology and Environmental Science, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, China Cheng Long Wei Key Laboratory of Marine Mineral Resources, Ministry of Natural Resources, Guangzhou, China Guangzhou Marine Geological Survey, Guangzhou, China Zhaoyu Wei School of Oceanography, Shanghai Jiao Tong University, Shanghai, China State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China Baoshan Wu China Ship Scientific Research Center (CSSRC), Wuxi, China Fang-Guang Wu College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Gang Wu Marine Design and Research Institute of China, Shanghai, China Baoshan Wu: deceased.

Contributors

Contributors

xxxv

Hongyun Wu Seabed Mining Department of, Changsha Institute of Mining Research, Changsha, China Qigang Wu College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Wenxiang Wu National Center of Water Transport Safety, Wuhan University of Technology, Wuhan, China Gongkui Xiao Department of Chemical Engineering, The University of Western Australia, Perth, WA, Australia Hong Xiao Engineering Department, Hunan Kenon Explosive Engineering Co., Ltd., Changsha, People’s Republic of China Jie Xiao Key Laboratory of Marine Eco-Environmental Science and Technology, First Institute of Oceanography, Ministry of Natural Resources (MNR), Qingdao, China Laboratory of Marine Ecology and Environmental Science, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, China Yin Xiao Changsha Mining and Metallurgy Research Institute Co., Ltd., Changsha, People’s Republic of China Jianhang Xin Piping Division, Hualu Engineering and Technology Co., Ltd, Xi’an, China En-Hui Xu Departments of Naval Architecture, Ocean and Structural Engineering, School of Transportation, Wuhan University of Technology, Wuhan, People’s Republic of China Ning Xu Marine Dynamic Division, National Marine Environmental Monitoring Center, Dalian, China Pengfei Xu Institute of Marine Vehicle and Underwater Technology, Hohai University, Nanjing, China Shengwen Xu State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China Wanhai Xu State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Wei Xu College of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, China Wei-Jun Xu College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Yuwang Xu School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China

xxxvi

Yanzhuo Xue College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Hongsheng Yan School of Civil Engineering, Tianjin University, Tianjin, China Jun Yan State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian, China Yue Yan State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Jianmin Yang School of Marine Engineering and Technology, Sun Yat-sen University, Guangzhou, China College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin, China Shaoqiong Yang School of Mechanical Engineering, Tianjin University, Tianjin, China Xiaoyan Yang School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China Zhixun Yang College of Mechanical and Electrical, Harbin Engineering University, Harbin, China Jing-Zheng Yao College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Guanqiong Ye Ocean College, Zhejiang University, Zhoushan, China Jiangzhou Ye Shanghai Jiao Tong University, Shanghai, China Tian-Gui Ye College of Power and Energy Engineering, Harbin Engineering University, Harbin, China Xi Ye Marine Design & Research Institute of China (MARIC), Shanghai, China Jingwei Yin College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin, China Xipeng Ying Department of Engineering Mechanics, Dalian University of Technology, Dalian, China Liwei Yu College of Engineering, Ocean University of China, Qingdao, China Long Yu Dalian University of Technology, Dalian, China Yang Yu China Institute of Marine Technology & Economy, Beijing, China College of Safety and Ocean Engineering, China University of Petroleum, Beijing, China

Contributors

Contributors

xxxvii

Li-Hao Yuan College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Ying-Fei Zan College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Jiangning Zeng Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China Ocean College, Zhejiang University, Zhoushan, China Ke Zeng China Ship Scientific Research Center (CSSRC), Wuxi, China Lingdong Zeng College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Xiaguang Zeng College of Safety and Ocean Engineering, China University of Petroleum, Beijing, China A-Man Zhang College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Chi Zhang Intelligent Transportation Systems Research Center, Wuhan University of Technology, Wuhan, China Chunfang Zhang Ocean College, Zhejiang University, Zhoushan, China Dongdong Zhang Ocean College, Zhejiang University, Zhoushan, China Di Zhang Intelligent Transportation Systems Research Center, Wuhan University of Technology, Wuhan, China Gui-Yong Zhang School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China Hailong Zhang National Engineering Research Centre for Marine Aquaculture, Institute of Innovation & Application, Zhejiang Ocean University, Zhoushan, China Heyue Zhang Dalian University of Technology, Dalian, China Jinfei Zhang Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China Mingyang Zhang Intelligent Transportation Systems Research Center, Wuhan University of Technology, Wuhan, China Pei Zhang State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University, Tianjin, China Qin Zhang Department of Marine Technology, Norwegian University of Science and Technology, Trondheim, Norway Qing Zhang College of Automation, Harbin Engineering University, Harbin, China

xxxviii

Shiyuan Zhang State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China Xinhu Zhang School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an, Shaanxi, China Xuelei Zhang Key Laboratory of Marine Eco-Environmental Science and Technology, First Institute of Oceanography, Ministry of Natural Resources (MNR), Qingdao, China Laboratory of Marine Ecology and Environmental Science, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, China Yu Zhang College of Safety and Ocean Engineering, China University of Petroleum-Beijing (CUP), Beijing, China Zhongwu Zhang College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin, China Baihui Zhao Shanghai Jiao Tong University, Shanghai, China Bin-Bin Zhao College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Dong Sheng Zhao School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China Liang Zhao Formerly, Centre for Offshore Foundation Systems and ARC Centre of Excellence for Geotechnical Science and Engineering, University of Western Australia, Perth, WA, Australia Min Zhao State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China Qiaosheng Zhao Department of Hydrodynamic Research, China Ship Science Research Center, Wuxi, China Xueliang Zhao School of Civil Engineering, Southeast University, Nanjing, China Yong Zhao Naval and Ocean engineering college, Dalian Maritime University, Dalian, People’s Republic of China Yu-Xin Zhao College of Automation, Harbin Engineering University, Harbin, Heilongjiang, China Yunpeng Zhao State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China Hao Zheng Changsha Mining and Metallurgy Research Institute Co., Ltd., Changsha, People’s Republic of China Jingbin Zheng Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, College of Environmental Science and Engineering, Ocean University of China, Qingdao, China Miaozhuang Zheng China Institute for Marine Affairs, Ministry of Natural Resources, Beijing, China

Contributors

Contributors

xxxix

Qiumeng Zheng College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Zhenming Zheng Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China Guoqiang Zhou China Classification Society Wuhan Research and Institute, Wuhan, Hubei province, China Ke Zhou Shanghai Jiao Tong University, Shanghai, China Li Zhou Jiangsu University of Science and Technology, Zhenjiang, China Mi Zhou College of Civil Engineering and Transportation, South China University of Technology, Guangzhou, China Qingji Zhou School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Singapore Haiming Zhu Department of Naval Architecture and Ocean Engineering, School of Civil Engineering, Tianjin University, Tianjin, China Jianbo Zhu Zhuzhou CRRC Times Electric CO., LTD, Zhuzhou, Hunan, China Xiaomeng Zhu College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China Feng-Xuan Zhuo College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China Li Zou School of Naval Architecture, Dalian University of Technology, Dalian, People’s Republic of China

A

Accidental Loads ▶ Offshore Structure Design Under Ice Loads

Acoustic Correlation Current Profiler (ACCP) ▶ Underwater Information Sensing Technology

Acoustic Positioning System (APS) ▶ Integrated Navigation

Acoustic Synthetic Baseline (ASBL) ▶ Long Baseline Underwater Acoustic Location Technology

Acoustic Deep Tow System ▶ Deep Tow System

Acoustic Towed System ▶ Deep Tow System

Acoustic Doppler Current Profiler (ADCP)

Active Sonar

▶ Underwater Information Sensing Technology

▶ Sonar Technology

Acoustic Modems

Ad Hoc Network

▶ Underwater Acoustic Sensor Network

▶ Underwater Acoustic Sensor Network

© Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

2

Advanced Control

Advanced Control

Alternative Fuel

▶ Intelligent Control Algorithms in Underwater Vehicles

▶ Ship Construction and Operation Impact on Energy Efficiency

AEM - Anion-Exchange Membrane

Alternative Fuel for Ship Propulsion

▶ Salinity Gradient Power Conversion

Shaowei Gan Overseas Technology Center, China Classification Society, Singapore, Singapore

Aerodynamic Drag ▶ Wind Tunnel Test

Air Emissions ▶ Impact of Maritime Transport ▶ Ship Propulsion System

AIS (Automatic Identification System) ▶ Ship Navigation System

Alarm Pheromone-Assisted Ant Colony System (AP-ACS) ▶ Obstacle Avoidance Technology for Underwater Vehicle

ALS – Accidental Limit States ▶ Design of Renewable Energy Devices

Synonyms Fuel cell; Hydrogen; Liquefied natural gas (LNG); Liquefied petroleum gas (LPG); Methanol

Definition Alternative fuels for ship propulsion mean fuels which serve, at least partly, as a substitute for conventional fossil oil sources, normally heavy fuel oil (HFO), in the energy supply to shipping and which have the potential to contribute to its decarbonization and enhance the environmental performance of the shipping sector.

Driving Force for Alternative Fuels Ships are a relatively fuel-efficient means of moving cargoes: for equivalent weights and distances, carbon dioxide emissions from shipping are considerably lower than air freight and road transport. At its best, emissions from shipping also undercut rail transport. This can be used as a rough proxy for transport costs and helps to illustrate the crucial role of international shipping in supporting global commerce, carrying as it does an estimated 90% of world trade. However, at the same time, the huge shipping quantity also makes shipping such a significant contributor to air pollution in terms of SOx and NOx emission, as well as

Alternative Fuel for Ship Propulsion

greenhouse gas emissions (accounting for 3% of global greenhouse gas emissions). International Maritime Organization (IMO) and national environmental agencies have realized the impact of emission from shipping and therefore issued regulations and policies that drastically reduce emissions emanating from marine sources (IMO 2016; EU 2014, etc.). In particular, with the decision of IMO to limit the sulfur content of ship fuel from 1 January 2020 to 0.5% worldwide, more than 70,000 ships will be affected by the regulation. In addition, stricter limits on sulfur dioxide (SOx) emissions are already in place in Emission Control Areas (ECAs) in Europe and the Americas, and new control areas are being established in ports and coastal areas in China. While these practical challenges related to sulfur reduction are knocking at the door, there is an accelerating worldwide trend toward pushing down CO2 and nitrogen oxides (NOx) and particle emissions. In April 2018, IMO’s Marine Environment Protection Committee (MEPC), at its 72nd session, adopted an initial strategy on the reduction of greenhouse gas emissions from ships, setting out a vision to reduce GHG emissions from international shipping and phase them out, as soon as possible in this century. The vision confirms IMO’s commitment to reducing GHG emissions from international shipping, and, more specifically, under the identified “levels of ambition,” the initial strategy envisages for the first time a reduction in total GHG emissions from international shipping which, it says, should peak as soon

3

as possible and to reduce the total annual GHG emissions by at least 50% by 2050 compared to 2008 while, at the same time, pursuing efforts toward phasing them out entirely. The strategy includes a specific reference to “a pathway of CO2 emissions reduction consistent with the Paris Agreement temperature goals.” The initial strategy represents a framework setting out the future vision for international shipping, the levels of ambition to reduce GHG emissions and guiding principles, and includes candidate short-, mid-, and long-term further measures with possible timelines and their impacts on States. A time map of actions from maritime authorities to promote greener shipping industry is presented in Fig. 1 (DNV GL 2019). The strategy also identifies barriers and supportive measures including capacity building, technical cooperation, and research and development (R&D). Many ship operators, with present-day propulsion plants and marine fuels, cannot meet these new regulations without installing expensive exhaust after-treatment equipment or switching to more expensive marine fuels (such as MGO) or alternative fuels with properties that reduce engine emissions below mandated limits, all of which impact bottom-line profits (IMO 2016). The impact of these new national and international regulations on the shipping industries worldwide has brought alternative fuels to the forefront as a means for realizing compliance. The alternative fuels industry has grown dramatically for both liquid and gaseous fuels. In this context, the gradual adoption of alternative fuels

Alternative Fuel for Ship Propulsion, Fig. 1 Shipping becomes greener and more complex (Courtesy of DNV GL 2019)

A

4

by shipping would have a significant positive immediate environmental impact.

Basic Introduction to Alternative Fuels There is a long list of alternative fuels that can be used in shipping. Among the proposed alternative fuels for shipping, LNG, methanol, hydrogen (particularly for use in fuel cells), and liquefied petroleum gas (LPG) are identified as the most promising solutions. All these fuels are virtually sulfurfree and can be used for compliance with sulfur content regulations, which is considered as the most urgent challenge for shipping. They can be used either in combination with conventional, oilbased marine fuels, thus covering only part of a vessel’s energy demand, or to completely replace conventional fuels for some ships. The type of alternative fuel selected and the proportion of conventional fuel substituted will have a direct impact on the vessel’s emissions, including GHG, NOx, and SOx. Each of these alternative fuels has advantages and disadvantages from the standpoint of the shipping industry. One common challenge, however, posed by the adoption of most alternative fuels are their physicochemical characteristics, typically with associated low flashpoints, higher volatilities, different energy content per unit mass, and, in some cases, even toxicity. The adoption and entry into force of the draft International Code of Safety for Ships using gases or other lowflashpoint fuels (IGF Code), along with proposed amendments to make the code mandatory under SOLAS, by IMO Maritime Safety Committee 95 (MSC 95), on 11 June 2015, was a decisive step forward in addressing those challenges, at the regulatory level. The IGF Code includes mandatory provisions for the arrangement, installation, control, and monitoring of machinery, equipment, and systems using low-flashpoint fuels, such as liquefied natural gas (LNG), to minimize the risk to the ship, its crew, and the environment, having regard to the nature of the fuels involved. LNG has been the first focus of the IGF Code; however, provisions for methyl/ethyl alcohols, fuels cells, and low-flashpoint oil fuels are still being drafted as interim guidelines.

Alternative Fuel for Ship Propulsion

Key Applications Liquefied Natural Gas (LNG) LNG is a cryogenic fuel that is maintained at approximately
260  F (
162  C) at atmospheric pressure. The advantage of cooling and liquefying the fuel is that the volume is decreased approximately 600 times as compared to the gas. This advantage improves the energy density significantly for LNG. As a result, when compared to diesel fuel, LNG has about 2/3 as much energy on a volume basis and almost 90% as much energy on a weight basis. Natural gas consists primarily of methane, and typical composition is presented in Table 1 (Kolwzan and Narewski 2012). The LNG fuel has a higher hydrogen-to-carbon ratio compared to oil-based fuels, which results in lower specific CO2 emissions (kg of CO2/kg of fuel). In addition, LNG is a clean fuel, containing no sulfur; this eliminates the SOX emissions and almost eliminates the emissions of particulate matter. Additionally, the NOX emissions are reduced by up to 90% due to reduced peak temperatures in the combustion process. Unfortunately, one of drawbacks of the use of LNG is the so-called methane slip during the valves overlap period for most four-stroke gas engines that is leading to the increase of the emissions of methane (CH4), hence reducing the net global warming benefit from 25% to about 15%. LNG as a liquid is not flammable or explosive. As any gas it has a flammability range. This range for LNG gas is between 5% and 15% when mixed with air. An explosion can only occur when the gas is in an enclosed space with air, the mixture is between 5 and 15%, and an ignition source is present. As with any flammable substance, proper design, regulations, and personnel training are needed to maintain a safe environment. Another major hazard for LNG as marine is that a spill of a cryogenic-like LNG

Alternative Fuel for Ship Propulsion, Table 1 Typical composition of natural gas in % Methane 94

Ethane 4.7

Propane 0.8

Butane 0.2

Nitrogen 0.3

Alternative Fuel for Ship Propulsion

5

could result in structural damage of ships’ hull, deck, and other steel structures near the ship. Serious injuries could occur when LNG gets in contact with the human body. An LNG fuel system onboard ships normally can be divided into four subsystems, namely,

LNG bunkering system, LNG storage system, fuel gas supply system (FGSS), and gas consumption installation system. Figure 2 shows the typical arrangement of low-pressure and highpressure LNG fuel system onboard ships (McGill et al. 2013; DNV GL 2019).

a LNG Gas Gly-col water LT- water

Bunkering

pre-cooling sprinkler

evaporator GVU

PBU

Engine

master valve

Tank connection space Hear exchanger

b

Damper

Glykol/water circuit

HP pump(s)

GVU HP evaporator GVU LP evaporator GVU Fuel Gas Preparation Unit GVU Bunker station

Tank Dome

LP pump(s)

Alternative Fuel for Ship Propulsion, Fig. 2 (a) Typical LNG fuel system (with low-pressure gas supply) onboard ships. (b) Typical LNG fuel system (with high-pressure gas supply) onboard ships

A

6

LNG is typically stored in highly insulated, spherical, or cylindrical tanks at low pressures (normally 1.05~5 bars). Fitting these tanks on a ship is quite feasible but requires some protection measures to reduce the risk of gas release due to collision with other ships or grounding. A detailed summary of various LNG fuel storage tanks is presented in Fig. 3. Depending on the chosen gas engines, both high-pressure (HP) and low-pressure (LP) FGSS are available. For LP FGSS, LNG extracted from LNG fuel tank by pump or pressure build-up unit, and then vaporized and heated by glycol water, finally supplied to gas engines. For HP FGSS, LNG is firstly pressurized and then vaporized, which this is quite different from LNG carriers, because pressurizing liquid is much easier than gas. Gas engines, gas turbines, and LNG storage and processing systems have been available for land installations for decades. LNG sea transport by LNG carrier also has a history going back to the middle of the last century. Developments to use LNG fuel in general shipping began early in the current century. Today, the technology required for using LNG as ship fuel is readily available. Piston engines and gas turbines, several LNG storage tank types, and process equipment are also commercially available.

Alternative Fuel for Ship Propulsion

Redundancy of fuel gas system shall be considered in particular for pure LNG-fueled ships; IGF Code stipulates that for single fuel installations, the fuel supply system shall be arranged with full redundancy and segregation all the way from the fuel tanks to the consumer, so that a leakage in one system does not lead to an unacceptable loss of power. In this regard, one pure gas engine with two fuel supply systems or two pure gas engines that each with one independent fuel supply system are both acceptable. Conversion from diesel to LNG propulsion is possible, but the LNG is mainly relevant for newly constructed ships, since substantial modification of engines, the related piping, and allocation of extra storage capacity is required. LNG presents hazards that are different than conventional marine fuels, like heavy fuel oil (HFO) and marine gas oil (MGO). If released at normal ambient temperatures and pressures, it will form a flammable vapor, so the release of LNG or natural gas should be prevented at all time. Furthermore, in its liquid phase, LNG is cold enough that it can cause ordinary steel to become brittle and crack, so any contact with steel structures and decks should be avoided. Because of these hazards and others that can occur, safety and the prevention of leakage need

Alternative Fuel for Ship Propulsion, Fig. 3 Different LNG fuel storage tank types according to IGF Code

Alternative Fuel for Ship Propulsion

to be among the primary objectives in the design, construction, and operation of LNG-fueled ships. The three primary safety objectives for LNG fuel system onboard a ship are as follows: • Prevent the occurrence of any hazardous release of gas or liquid. • In the event of a release, prevent or contain any hazardous situations. • If a hazardous incident does occur, limit the consequences and harmful effects. A potential disadvantage to using LNG is space. Since gas weighs more, volume-wise it requires more space as compared to bunker oil. The farther the journey, the equally larger amount of storage space is required. So far, tanks are designed to be built in the cargo spaces of the ships for using gas as fuel. This is a major setback for the ship operators in terms of freight earned by the cargo. Engineers and architects are working toward developing systems that would make room for storing LNG. This could be anywhere on the vessel, above deck, in the superstructures, beneath the cargo containers, astern of the vessel, etc., and this would also call for extra insulation, piping, and steelwork as far as construction of the vessels is concerned. LNG fuel surely holds a promising future in the shipping industry. However, only time can tell as to how well it becomes an integral part of the shipping industry in the days to come.

Methanol/Methyl Alcohol Methanol, with the chemical structure CH3OH, is the simplest alcohol with the lowest carbon content and highest hydrogen content of any liquid fuel. Methanol is a liquid between 176 and 338 K (
93 to +65  C) at atmospheric pressure; it is a basic building block for hundreds of essential chemical commodities that contribute to our daily lives, such as building materials, plastic packaging, paints, and coatings. It is also a transport fuel and a hydrogen carrier for fuel cells (SSPA 2015). Methanol can be produced from several different feedstock resources, mainly natural gas or

7

coal, but also from renewable resources like black liquor from pulp and paper mills, forest thinning or agricultural waste, and even directly from CO2 that is captured from power plants. When produced from natural gas, a combination of steam reforming and partial oxidation is typically applied, with an energy efficiency up to about 70% (defined as energy stored in the methanol versus energy provided by natural gas). Renewable methanol is produced from pulp mill residue in Sweden, waste in Canada, and from CO2 emissions at a small commercial plant in Iceland. As an alternative liquid fuel, methanol is cleanburning, biodegradable, and sulfur-free. The only PM produced from burning methanol is from the pilot fuel (usually diesel). Methanol is able to meet the increasingly stringent emission reduction requirement such as the global sulfur limit of 0.5% by 2020 for the international shipping and acting as potential candidate to meet further greenhouse gas reduction targets. Major OEMs have shown methanol can meet Tier III NOx requirements with the aid of emulsification. There are two main options for using methanol as fuel in conventional ship engines: in a twostroke diesel-cycle engine or in a four-stroke, lean-burn Otto-cycle engine. Similar to LPG, only a single two-stroke diesel engine is currently commercially available, the MAN ME-LGI series, which is now in operation on methanol tankers. Wärtsilä four-stroke engines are in operation onboard the passenger ferry Stena Germanica. Another possibility would be to use methanol in fuel cells. A test installation has been running on the Viking Line ferry MS Mariella since 2017. Methanol is a liquid fuel and can be stored in standard fuel tanks for liquid fuels, with certain modifications to accommodate its low-flashpoint properties and the requirements currently under development for the IGF Code at the IMO. Fuel tanks should be provided with an arrangement for safe inert gas purging and gas freeing. Typical methanol fuel system onboard a ship can be divided into the following system elements: • Bunkering of methanol • Storage of methanol onboard

A

8

Alternative Fuel for Ship Propulsion

Alternative Fuel for Ship Propulsion, Fig. 4 Schematic overview of the methanol fuel system

• Methanol handling and processing toward the main engine • Combustion of methanol in the main engine • Methanol handling and processing after the main engine

requires additional considerations during use to limit inhalation exposure and skin contact.

Figure 4 shows a typical arrangement of a methanol fuel system, which includes the Purge return system, cooling oil system in the main marine engine, while the methanol fuel is pumped through the fuel service tank, low-flashpoint fuel supply system and fuel valve train, and finally entering the engine system. Different piping types are used in the fuel transmit system. However, there are still some essential challenges for methanol as a marine fuel. Methanol has about half of the energy density of conventional fossil fuels, which means that more fuel storage space will be required onboard a vessel as compared to conventional fuels; this also means cargo space loss for a ship with specified dimension. The second challenge is that, as methanol is corrosive to some materials, materials selection for tank coatings, piping, seals, and other components must consider compatibility. In addition, methanol is classed as toxic so

Hydrogen (H2) is a colorless, odorless, and nontoxic gas. For use on ships, it can either be stored as a cryogenic liquid, as compressed gas, or chemically bound. The boiling point of hydrogen is very low: 20 K (
253  C) at 1 bar. It is possible to liquefy hydrogen at temperatures up to 33 K (
240  C) by increasing the pressure toward the “critical pressure” for hydrogen, which is 13 bar. The energy density per mass (LHV of 120 MJ/kg) is approximately three times the energy density of HFO. The volumetric density of liquefied H2 (LH2) (71 kg/m3) is only 7% that of HFO. This results in approximately five times the volume compared to the same energy stored in the form of HFO. When stored as a compressed gas, its volume is roughly 10 to 15 times (depending on the pressure [700 to 300 bar]) the volume of the same amount of energy when stored as HFO.

Hydrogen

Alternative Fuel for Ship Propulsion

Hydrogen is an energy carrier and a widely used chemical commodity. It can be produced from various energy sources, such as by electrolysis of renewables or by reforming natural gas. Today, nearly all hydrogen is produced from natural gas. For applications in the transport sector, production by reforming from natural gas is currently the most common method. If the resulting CO2 would be captured, this could result in a zero-emission value chain for shipping. When used in combination with marine fuel cells, the emissions associated with other marine fuels could be minimized or eliminated entirely. If H2 is generated using renewable energy, nuclear power, or natural gas with carbon capture and storage, zero-emission ships are possible. Power generation systems based on H2 may eventually be an alternative to today’s fossil-fuelbased systems. While fuel cells are considered the key technology for hydrogen, other applications are also under consideration, including gas turbines or internal combustion engines in stand-alone operation or in arrangements incorporating fuel cells. Hydrogen-fueled internal combustion engines for marine applications are said to be less efficient than diesel engines. Hydrogen-fueled piston engines for ships are not available in the market. On land development is ongoing. Possibly larger-scale industrial and maritime applications combined with waste heat recovery solutions might be better suited for high-temperature technologies such as solid oxide fuel cells (SOFC) or even industrial systems using molten carbonate fuel cells. Fuel cells combined with batteries (and possibly super capacitors) adding peak-shaving effects are a promising option. Even proton-exchange membrane fuel cells (PEMFC), thanks to their flexible materials, could improve fuel cell lifetime significantly when protected against the harshest load gradients. SOFC must be applied in a hybrid environment using peak-shaving technology to be a realistic alternative for shipping. Regarding the marine application, the European Commission FCSHIP study concluded in 2004 that the use of fuel cells in ships was feasible, with the usual caveats about availability and fuel supply. The subsequent METHAPU project sets out to

9

evaluate solid oxide fuel cell technology running on methanol for ship auxiliary power. For example, a 20 KW fuel cell system from Finnish company Wärtsilä was installed on the deck of the car carrier MV Undine. The 2009–2010 trial showed that the use of fuel cell technology and an alternative fuel poses no more of a risk to a commercial vessel than conventional equipment and fuel, laying the foundation for further deployment. The FellowSHIP project has tested fuel cell technology integrated with a ship’s propulsion system. In September 2009, a 330 KW molten carbonate fuel cell from MTU Onsite Energy was installed onboard the Viking Lady, an LNGfueled ship with gas-electric propulsion system, without the need for pre-reforming. During the trial, the fuel cell logged 18,500 successful operating hours, providing supplementary power to the ship at an electrical efficiency of over 52% at full load. The next phase of FellowSHIP, now underway, is installing a battery pack for energy storage to create a true hybrid propulsion system for the Viking Lady. Backed by the Norwegian Maritime Authority (NMA) and led by shipbuilder Fiskerstrand (seen Fig. 5), the HYBRIDShips innovation project aims to have a pilot version of a hybrid hydrogen/batterypowered ferry operational by 2020. HYBRIDShips will establish the knowledge base necessary to build zero-emission propulsion systems for larger vessels and longer voyages. The pilot ferry will be the world’s first such hybrid to combine hydrogen fuel cell power working alongside batteries. In 2018 June, ABB and Ballard Power Systems decided to jointly develop zero-emission fuel cell power plant for shipping industry as in Fig. 6. The two companies propose to develop an electrical generating capacity of 3 MW (4000 horsepower) module and fit within a single module no bigger in size than a traditional marine engine running on fossil fuels. Typically, a fuel cell power installation is shown as in Fig. 7. The IMO has looked at fuel cells as part of its Carriage of Cargoes and Containers Sub-Committee, with a view to include safety provisions in the International Code of Safety for Ships using gases or other lowflashpoint fuels (IGF) code.

A

10

Alternative Fuel for Ship Propulsion

Alternative Fuel for Ship Propulsion, Fig. 5 Project of hydrogen-powered ferry in Norway (Courtesy of Fiskerstrand)

Alternative Fuel for Ship Propulsion, Fig. 6 The installation of proton-exchange membrane fuel cells onboard ship (Courtesy of ABB)

Liquefied Petroleum Gas (LPG) Liquefied petroleum gas (LPG) is any mixture of propane and butane in liquid form. In the USA, the term LPG is generally associated with propane. Specific mixtures of butane and propane are used to achieve desired saturation, pressure, and temperature characteristics. Propane is gaseous under ambient conditions, with a boiling point of
42  C. It can be handled as a liquid by

applying moderate pressure (8.4 bar at 20  C). Butane can be found in two forms: n-butane or isobutane, which have a boiling point of
0.5  C and
12, respectively. Since both isomers have higher boiling points than propane, they can be liquefied at lower pressure. Regarding land-based storage, propane tanks are equipped with safety valves to keep the pressure below 25 bar. LPG fuel tanks are larger than oil tanks due to the lower density of LPG.

Alternative Fuel for Ship Propulsion

11

A

Alternative Fuel for Ship Propulsion, Fig. 7 Components of a typical fuel cell power installation

There are two main sources of LPG: it occurs as a by-product of oil and gas production or as a by-product of oil refinery. It is also possible to produce LPG from renewable sources, for example, as a by-product of renewable diesel production. Basically, there are three main options for using LPG as ship fuel: • In a two-stroke diesel-cycle engine • In a four-stroke, lean-burn Otto-cycle engine • In a gas turbine Currently, only a single two-stroke diesel engine model is commercially available, the MAN ME-LGI series. In 2017, a Wartsila fourstroke engine was commissioned for stationary power generation (34SG series). This engine had to be derated to maintain a safe knock margin. An alternative technology offered by Wartsila consists in the installation of a gas reformer to turn

LPG and steam into methane by mixing them with CO2 and hydrogen. This mixture can then be used in a regular gas or dual-fuel engine without derating. LPG can be stored under pressure or refrigerated. It will not always be available in the temperature and pressure range a ship can handle. Therefore, the bunkering vessel and the ship to be bunkered must carry the necessary equipment and installations for safe bunkering. A pressurized LPG fuel tank is the preferred solution due to its simplicity and because the vessel can bunker more easily using either pressurized tanks or semirefrigerated tanks without major modifications. The cost of installing LPG systems onboard a vessel (e.g., internal combustion engine, fuel tanks, process system) is roughly half that of an LNG system if pressurized type C tanks are used in both cases. This is because there is no need for special materials that can handle cryogenic temperatures. On large ships, the cost difference

12

between LNG and LPG systems is lower if the LPG is stored in pressurized type C tanks, which are more expensive than large prismatic tanks. Alternatively, LPG can be stored at low temperatures in low-pressure tanks, which require thermal insulation.

Cross-References ▶ Future Trend on the Design, Building, and Operation of Ships for Energy Efficiency

References DNV GL (2019) Assessment of selected alternative fuels and technologies in shipping. Oslo, Norway EU (2014) Directive 2014/94/EU of the European Parliament and of the Council of 22 October 2014 on the deployment of alternative fuels infrastructure Text with EEA relevance, Official Journal of the European Union, 28.10.2014, pp 1–20 IMO (2016) Study of the use of methanol as marine fuel – environmental benefits, technology readiness and economic feasibility, MEPC 69/INF.10 Kolwzan K, Narewski M (2012) Alternative fuels for marine applications. Latv J Chem 4:398–406 McGill R, Remley WB, Winther K (2013) A report from the IEA advanced motor fuels implementing agreement, alternative fuels for marine applications. https://www. iea-amf.org/app/webroot/files/file/Annex%20Reports/ AMF_Annex_41.pdf SSPA (2015) Study on the use of ethyl and methyl alcohol as alternative fuels in shipping, Final Report Version 20151204.5, Report prepared for the European Maritime Safety Agency

American Petroleum Institute (API)

Analysis of Renewable Energy Devices Zhiyu Jiang1 and Wei Shi2,3 1 Department of Engineering Sciences, University of Agder, Grimstad, Norway 2 Deepwater Engineering Research Center, Dalian University of Technology, Dalian, Liaoning, China 3 State Key Laboratory of Coast and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning, China

Synonyms BEM – Blade element momentum; CFD – Computational fluid dynamics; DLL – Dynamic-link library; FEM – Finite element method; GDW – Generalized dynamic wake theory; HAWT – Horizontal-axis wind turbine; MBS – Multibody simulation; ME – Morison’s equation; OWT – Offshore wind turbine

Definition Analysis refers to the application of scientific and engineering principles and processes to reveal the properties of a system.

Introduction

American Petroleum Institute (API) ▶ Christmas Tree ▶ Installation of Offshore Pipelines

Analog-to-Digital (A/D) ▶ Underwater Acoustic Communication

Renewable energy devices may operate in complex internal and external conditions, and engineering analysis is a key element of the design process. Because of the sophisticated physics associated with specific renewable energy devices, simplified analysis is often not adequate for a full understanding of the system behavior. With the advent of information and digital technologies, analysis at various fidelity levels can be achieved using simulation tools. To reduce the computational costs and to validate the accuracy of simulation tools, significant efforts have been invested from both industry and academia.

Analysis of Renewable Energy Devices Analysis of Renewable Energy Devices, Fig. 1 Schematic of a spar floating wind turbine and a jacket-supported offshore wind turbine

13

Turbulent wind field

A Blade

Tower Irregular waves

Transition piece

Jacket

Mooring line

Spar platform

This chapter will focus on the analysis of renewable energy devices that operate in offshore environments. Such devices may experience hydrodynamic and aerodynamic load actions and have large dynamic motions and structural deformations. Figure 1 (left) presents an example of a floating wind turbine which is originally designed for the North Sea environments (Nielsen 2013). A bottom-fixed offshore wind turbine (OWT) is shown in Fig. 1 (right) which is intended for intermediate water depths below 50 m. At the design stage, dynamic response analysis must be performed to assess the power production quality, blade deflections in extreme wind conditions, platform pitch motions, mooring line dynamics, and so forth (Jiang et al. 2018).

Hydrostatic Analysis Traditionally, hydrostatic analysis deals with naval architectures including ships and offshore

Leg pile

drilling units. To ensure safety of such floating installations, classification authorities (DNV GL 2013; ABS 2018) dictate that all offshore units have positive metacentric height in calm water position for afloat conditions and intact stability and damage stability be checked. Thus, hydrostatic analysis is also involved when renewable energy devices are supported on floating foundations. As shown in Fig. 2, a spar buoy has a simple geometry with a draft of T has hydrostatic pressure (p) acting on the submerged hull. The pressure is a function of the submerged depth. After a static heel within certain range, the buoy should be able to return to its equilibrium position with the assistance of the restoring moment created by the buoyancy and gravity forces. Details of hydrostatics can be found in Biran and Pulido (2013). Note that hydrostatic analysis can be among the first steps in dimensioning the floating platforms. Luan et al. (2016) checked the intact stability of a semisubmersible wind turbine (Fig. 3) considering the overturning moment from

14

Analysis of Renewable Energy Devices

Hydrodynamic Analysis

Analysis of Renewable Energy Devices, Fig. 2 Schematic of a buoy and hydrostatic pressure

For renewable energy devices that are subjected to ocean waves and currents, hydrodynamic load can be an important source of excitation. Both viscous effects and potential flow effects (Faltinsen 1993) may play a role in determining the wave-induced loads and motions on certain types of renewable energy devices including wind turbines and wave energy converters. Figure 5 (upper) shows a vertical cylinder with diameter D that stands on the seabed, and an incident wave with wavelength of l and wave height of H is propagating toward the cylinder. Based on Fig. 5 (lower), it is possible to judge which wave forces are of greater significance to the structure. If the cylinder is slender with large l/D ratio, then viscous forces are prominent due to flow separation. For wind turbines supported by jacket or monopile foundations, the hydrodynamic forces acting on the foundations can often be represented by Morison’s equation (ME); see Morison et al. (1950). Suppose that the slender structure can be divided into many strips, the hydrodynamic force per unit length normal to each strip can be expressed as f s ¼ rCM

pD2 pD2 x€w
rðCM
1Þ
€ 4 4 1

1 þ rCD Dðx_w

_ 1 Þjx_ w

_ 1 j 2

Analysis of Renewable Energy Devices, Fig. 3 Illustration of the 5-MW CSC wind turbine (Luan et al. 2016)

aerodynamic loads and the righting moment by hydrostatic pressure. As shown in Fig. 4, the area under the righting moment curve (f) is relatively large compared to the area under the design overturning moment (straight line), and large safety margin is indicated. Similar analyses can also be found in the works of Lefebvre and Collu (2012) and Karimirad and Michailides (2015).

ð1Þ

where r is the density of seawater, D is the diameter of the slender structure, CM is the mass coefficient, and CD is the drag coefficient, x_ w and x€w are the velocity and acceleration of water particles at the strip center, and
_ 1 and
€1 are the velocity and acceleration of the strip. In Eq. (1), CM and CD are dependent on the Reynolds number, the Keulegan-Carpenter number, and surface roughness. Reference values are given by offshore standards (NORSOK 2007; DNV 2010). As the strip velocity and acceleration are included in Eq. (1), this equation is also applicable to moving structures. Note that although the ME has been widely applied by industry and academia, this equation ignores lift forces, slamming forces, and axial Froude-Krylov forces.

Analysis of Renewable Energy Devices

15

Analysis of Renewable Energy Devices, Fig. 4 Intact stability analysis of the 5-MW-CSC, f, heeling angle; RMC, righting moment curve; DOM, design overturning moment curve (Luan et al. 2016)

Analysis of Renewable Energy Devices, Fig. 5 Importance of mass, viscous, and diffraction forces on marine structures (Faltinsen 1993)

Hydrodynamic analysis of monopile-type wind turbines using the ME can be found in Veldkamp and Van Der Tempel (2005), Shirzadeh et al. (2013), and Jiang (2018). For monopile foundations supporting 10-megawatt (MW) wind turbines, the diameter can reach 10 m (Velarde 2016), and the ME is not necessarily applicable

A

for short waves. For jacket-type wind turbines, the tubular members have relatively small diameters. For example, the maximum leg diameters of traditional jackets supporting 5-MW wind turbines generally do not exceed 2 m (Chen et al. 2016; Dong et al. 2011). Thus, the hydrodynamic loads are drag-dominated for extreme waves, and the ME is well-suited for the analysis. Shi et al. (2013a, b) performed dynamic loads analysis of jacket-type wind turbines extensively and applied the ME during the hydrodynamic analysis. The ME has also been considered in the hydrodynamic analysis of floating platforms including spar buoy (Jonkman 2007; Jiang et al. 2013b), tension leg platform (Bachynski and Moan 2012), as well as mooring systems (Kvittem et al. 2012). For floating renewable energy devices supported by large-volume structures, the diffraction effects are important, and potential flow theory is often used. Potential flow theory is realized numerically through the panel method (boundary element method), which solves the boundary-value problem for the interaction of wave-waves with prescribed motions in finite and infinite water depth (Lee 1995). Figure 6 schematizes a twobody wave energy converter which produces power using the relative heave motion between the torus and the float. A panel model is shown of the submerged parts. For a low-order panel method, the velocity potential is constant over the panel, and the diagonal length of the panel mesh is

16

Analysis of Renewable Energy Devices

Analysis of Renewable Energy Devices, Fig. 6 Schematic of a twobody wave energy converter and the panel model (Muliawan et al. 2013a)

recommended to be below 1/6 of the smallest wavelength analyzed (DNV 2010). Potential theory assumes ideal flow and ignores viscous effects. For floating structures with sharp corners, viscous effects may be more important, and Morison-type elements can be applied in time-domain simulations to complement the potential-flow solution. Kvittem et al. (2012) adopted this approach for a semisubmersible wind turbine with heave damping plates. The panel method is a frequency-domain approach applicable to weakly nonlinear hydrodynamic problems. If there is highly nonlinear interaction between waves and floating bodies, analytical approaches (Faltinsen et al. 2004), the time-domain boundary element approaches (Schløer et al. 2016; Salehyar et al. 2017), or computational fluid dynamics methods (Li and Yu 2012) can be used. Chella et al. (2012) presented an overview of the wave impact forces on OWT substructures. Saletti (2018) studied the bottom slamming phenomenon for a combined wind and wave energy converter. Additionally, a wave theory must be involved to calculate the wave kinematics which is closely correlated with the hydrodynamic loads. The linear wave theory, or the airy wave theory (Airy 1841; Craik 2004), is the simplest solution for the flow field and is only applicable for smallamplitude waves. Figure 7 shows the applicability

of various wave theories. Here, H denotes wave height, T is wave period, d is water depth, and L0 is wavelength. Details on wave kinematics can be found in Dean and Dalrymple (1991).

Aerodynamic and Aeroelastic Analysis For renewable energy devices that are exposed to wind loads, analysis of wind effect is indispensable. Wind turbines are particularly designed to harness the kinetic energy from the wind, and modern wind turbine blades are long and slender. For horizontal-axis wind turbines (HAWTs), the longest blade announced approaches 90 m for an 8-MW wind turbine (LM Wind Power 2018). Such flexible blades may experience large deformation under the combined effect of wind excitations, centrifugal forces, gravitational forces, and control actions. Aerodynamic analysis helps to understand the behavior of the airflow and the forces acting on the blades and the performance of the wind turbine. The classical blade element moment (BEM) was initially proposed by Glauert (1983) and modified for wind turbine analysis. The basic assumption of the BEM theory is that the force of a blade element is solely responsible for the change of axial momentum of the air which passes through the annulus swept by the elements, and there is no radial interaction between the

Analysis of Renewable Energy Devices

17

Analysis of Renewable Energy Devices, Fig. 7 Applicability of wave theories (Sarpkaya 2010)

flows through contiguous annuli (Burton et al. 2011). BEM can be used to calculate the steady loads, the thrust, and the power of HAWTs. A simple BEM algorithm to find the axial and tangential induction factors is presented in Hansen (2008). A BEM algorithm with improved convergence rate is presented in Ning (2014). The classical BEM needs to be corrected by Prandtl’s tip loss factor and Glauert correction to get reasonably good results, as compared to the measurements. Due to unsteadiness of the wind seen by the rotor, the classical BEM cannot realistically capture the aeroelastic behavior of wind turbines, and the unsteady BEM method should be considered. The unsteady BEM, albeit still efficient, considers the time behavior of loads and power by the dynamic wake model and the dynamic change of angle of attack by the dynamic stall model (Hansen 2008). Further, physical phenomena like wake meandering can also be incorporated as engineering corrections to BEM (Larsen et al. 2013). The BEM theory considers uniform pressure distribution across a rotor plane. Unlike BEM, the generalized dynamic wake (GDW) method, also

A

known as the acceleration potential method, allows for a more general distribution of pressure across a rotor plane and includes inherent modeling of the dynamic wake effect, tip losses, and skewed wake aerodynamics (Moriarty and Hansen 2005). However, the GDW method was developed for lightly loaded rotors at high wind speeds, and the induced velocities are small relative to the mean inflow velocity. Detailed descriptions of the GDW theory can be found in Pitt and Peters (1980) and Suzuki (2000). Over the past decades, computational fluid dynamics (CFD) has been widely used in aerodynamic analysis of rotors, and actuator disc and actuator line methods are special types of CFD methods (Hansen and Aagaard Madsen 2011). Krogstad and Eriksen (2013) presented a summary of different computational methods that were applied to predict the performance and wake development of a tested model wind turbine. De Vaal et al. (2014) used the actuator disc model to study the effect of surge motion of a floating wind turbine on rotor thrust and induced velocity. Wen et al. (2018) applied the free vortex method to study the power coefficient

18

overshoot of a floating wind turbine in surge oscillations. Aeroelastic analysis refers to the type of analysis that deals with the interaction between the inertial, elastic, and aerodynamic forces when the structure is exposed to a fluid flow. For commercial wind turbines, stall-induced vibrations and classical flutter are two categories of instabilities that have been observed for stall- and pitchregulated wind turbines, respectively. Hansen (2003, 2007) presented a state-of-the-art review on aeroelastic stability analysis of wind turbines.

Integrated Dynamic Analysis A complex renewable energy system may comprise structural components, mechanical parts, electrical devices, and control systems. Modeling and simulation of such systems can be achieved by using numerical methods such as multibody simulation (MBS) or finite element method (FEM). Integrated dynamic analysis of renewable energy devices under external load conditions is usually performed in the time domain and Analysis of Renewable Energy Devices, Fig. 8 Modularized computational flowchart for floating wind turbine simulation (Jiang et al. 2013a)

Analysis of Renewable Energy Devices

provides global and structural responses. For OWTs, the integrated dynamic analysis is also addressed as aero-hydro-servo-elastic analysis (Jonkman et al. 2008) as aerodynamics, hydrodynamics, servo dynamics, and structural dynamics are involved in the analysis. Figure 8 illustrates the computational flowchart of an integrated dynamic analysis in the HAWC2 program (Larsen 2009). As shown, user-specified control actions including mechanical system faults can be added to the main program via external dynamiclink libraries (DLLs) written in a programming language. For HAWTs, blade pitch control and generator torque control are also achieved through DLLs. There exist many engineering challenges with regard to modeling complexity, coupling of different submodules, nonlinear responses, and time-domain efficiency; see Butterfield et al. (2007). Global motions and structural responses are two main aspects of concern. The global motions refer to the horizontal displacement and rotation of structural members or bodies. For floating wind turbines, rigid body motions of the floating platforms under dynamic loading can provide insights

Analysis of Renewable Energy Devices

into system dynamics. Nielsen et al. (2006) conducted dynamic response analysis of the floating wind turbine concept HYWIND under wind, wave, and current conditions and compared the simulated and experimental decay tests of tower pitch angle. Pereya et al. (2018) analyzed the nacelle acceleration and platform pitch motion of the TetraSpar floating wind turbine. Such global motion responses, albeit not stated explicitly, can form design constraints for drivetrain components. Kurniawan et al. (2012) performed modeling and global motion analysis of a pitching wave energy converter and discussed dynamics of such a system with different hydraulic components. Muliawan et al. (2013b) conducted dynamic response analysis of a combined wind-wave energy converter and uncovered positive synergy between the two floating bodies by global motion analysis. Shi et al. (2016) developed an ice load force module for an aero-hydro-servo-elastic program and identified important response characteristics of a monopile-type wind turbine under combined ice and wave loads. From an integrated dynamic analysis, structural responses are available. To ensure structural integrity of renewable energy devices, the structural responses need be checked against possible failure modes including fatigue and ultimate limit states. Dong et al. (2011) checked the long-term fatigue damage of tubular joints of a jacket-type OWT (see Fig. 1 right) after performing integrated dynamic

Analysis of Renewable Energy Devices, Fig. 9 Illustration of a wind turbine gearbox (Image source: (Jiang et al. 2014a), courtesy of National Renewable Energy Laboratory)

19

analysis. Jiang et al. (2015) analyzed the shortterm fatigue damage of mooring lines of a floating wind turbine during shutdown. Wei et al. (2014) calculated the structural capacity of jacket support structure of an OWT under extreme wind and wave loading.

Analysis of Mechanical Components For many renewable energy devices, mechanical components are widely used to transfer the energy to the generator side. Figure 9 demonstrates a three-stage gearbox of a 750-kilowatt stallregulated wind turbine. The gearbox has one planetary stage and two parallel stages. High failure rates of gearbox components have been observed for the wind industry since its inception (McNiff et al. 1991), and analysis of mechanical components sometimes requires knowledge of both external loading conditions from the rotor side and internal conditions like friction, oil viscosity, and lubricant temperature (Harris and Kotzalas 2007). Numerical methods like FEM and MBS are useful tools for modeling the detailed setup of mechanical components and to study the internal responses under dynamic conditions. Using FEM and MBS, Xing and Moan (2013) showed that the main shaft non-torque loads can substantially contribute to the bearing loads and gear displacements. Dong et al. (2012) investigated gear

A

20

contact fatigue in a wind turbine drivetrain using a decoupled analysis approach. Jiang et al. (2014a) proposed using multilevel integrated analysis for contact fatigue analysis of planetary bearings. Nejad et al. (2014, 2016) analyzed dynamic load effects of a drivetrain components and performed reliability analysis of wind turbine gears. Hydraulic components including valves, pumps, accumulators, pipelines, and motors are also mechanical components that have been suggested for use in wave energy converters and wind turbines. Analysis of hydraulic systems often involves mathematical modeling and numerical simulations. Henderson (2006) presented both numerical simulation and laboratory tests of the hydraulic system employed in the Pelamis wave energy converter. Yang et al. (2010) investigated the wear damage in the piston ring and cylinder bore of a heaving-buoy wave energy converter. Numerical simulations of hydraulic transmission of wind turbines can be found in the works of Jiang et al. (2014b), Yang et al. (2015), Buhagiar et al. (2016), and Buhagiar and Sant (2017).

Code Verification and Validation A multitude of design codes have been developed and extensively used for analysis of renewable energy devices. In general, many design codes adopt simplified physical representations of actual systems with reduced degrees of freedom but account for most prominent system features. Before being put into use, a new code should be verified against other state-of-the-art codes with adequate model fidelity levels or validated against experimental results. Larsen et al. (2013) showed good comparison between HAWC2 and the CFD code EllipSys3D for aerodynamic forces on a blade. Extensive benchmark work usually involves international collaboration among various academic and industrial partners. Passon et al. (2007) introduced the first international investigation and verification of aeroelastic codes for OWTs. Modeling capabilities of offshore environment, structural modeling, and rotor aerodynamics were compared among nine design codes for

Analysis of Renewable Energy Devices

four different support structures. Later, code-tocode verifications were conducted of other types of foundations with an increased number of participants and additional load cases; see Jonkman et al. (2008), Popko et al. (2012), and Vorpahl et al. (2014). Experiments at model scale or full-scale testing are other effective means of code verification. Discrepancies in results between model testing and numerical codes are not uncommon, especially for renewable energy devices that have both aerodynamic and hydrodynamic excitations, because similarity between inertia and viscous forces of the models cannot be achieved simultaneously. Li and Calisal (2010) developed numerical codes using a discrete vortex method for vertical axis tidal current turbines and verified the two- and three-dimensional codes with experiments. Preliminary verification of a wave energy converter design tool with experimental wave tank results is presented in Ruehl et al. (2014). Coulling et al. (2013) verified a numerical model constructed in the design code FAST (Jonkman and Buhl 2005) with 1/50th-scale model test data for a semisubmersible floating wind turbine system. Luan et al. (2018) compared the simulated sectional responses of a semisubmersible using a nonlinear finite element code SIMO-Riflex with the 1/30th-scale model test results.

Cross-References ▶ Design of Renewable Energy Devices ▶ Design Rules and Standards

References Airy GB (1841) Tides and waves. Encyclopaedia Metropolitana, London, 5, p 241 American Bureau of Shipping (ABS) (2018) Rules for building and classing mobile offshore drilling units, Part 3, Hull construction and equipment. Houston Bachynski EE, Moan T (2012) Design considerations for tension leg platform wind turbines. Mar Struct 29(1):89–114 Biran A, Pulido RL (2013) Ship hydrostatics and stability. Butterworth-Heinemann, Oxford, UK

Analysis of Renewable Energy Devices Buhagiar D, Sant T (2017) Modelling of a novel hydropneumatic accumulator for large-scale offshore energy storage applications. J Energy Storage 14:283–294 Buhagiar D, Sant T, Bugeja M (2016) A comparison of two pressure control concepts for hydraulic offshore wind turbines. J Dyn Syst Meas Control 138(8):081007 Burton T, Jenkins N, Sharpe D, Bossanyi E (2011) Wind energy handbook. Wiley, Chichester Butterfield CP, Musial W, Jonkman J, Sclavounos P, Wayman L (2007) Engineering challenges for floating offshore wind turbines. National Renewable Energy Laboratory, CO, USA Chella MA, Tørum A, Myrhaug D (2012) An overview of wave impact forces on offshore wind turbine substructures. Energy Procedia 20:217–226 Chen I-W, Wong B-L, Lin Y-H, Chau S-W, Huang H-H (2016) Design and analysis of jacket substructures for offshore wind turbines. Energies 9(4):264 Coulling AJ, Goupee AJ, Robertson AN, Jonkman JM, Dagher HJ (2013) Validation of a FAST semi-submersible floating wind turbine numerical model with DeepCwind test data. J Renewable Sustainable Energy 5(2):023116 Craik AD (2004) The origins of water wave theory. Annu Rev Fluid Mech 36:1–28 De Vaal J, Hansen ML, Moan T (2014) Effect of wind turbine surge motion on rotor thrust and induced velocity. Wind Energy 17(1):105–121 Dean RG, Dalrymple RA (1991) Water wave mechanics for engineers and scientists, vol 2. World Scientific Publishing, Singapore DNV (2010) Recommended Practice DNV-RP-C205 Environmental conditions and environmental loads. Høvik, Norway DNV GL (2013) Offshore standard DNVGL-OS-C301 Stability and watertight integrity. Høvik, Norway Dong W, Moan T, Gao Z (2011) Long-term fatigue analysis of multi-planar tubular joints for jacket-type offshore wind turbine in time domain. Eng Struct 33(6):2002–2014 Dong W, Xing Y, Moan T (2012) Time domain modeling and analysis of dynamic gear contact force in a wind turbine gearbox with respect to fatigue assessment. Energies 5(11):4350–4371 Faltinsen OM (1993) Sea loads on ships and offshore structures, vol 1. Cambridge University Press, UK Faltinsen OM, Landrini M, Greco M (2004) Slamming in marine applications. J Eng Math 48(3–4):187–217 Glauert H (1983) The elements of aerofoil and airscrew theory. Cambridge University Press, UK Hansen MH (2003) Improved modal dynamics of wind turbines to avoid stall-induced vibrations. Wind Energy 6(2):179–195 Hansen MH (2007) Aeroelastic instability problems for wind turbines. Wind Energy 10(6):551–577 Hansen MOL (2008) Aerodynamics of wind turbines, 2nd edn. Earthscan, London Hansen MOL, Aagaard Madsen H (2011) Review paper on wind turbine aerodynamics. Trans ASME-I-J Fluids Eng 133(11):114001

21 Harris TA, Kotzalas MN (2007) Rolling bearing analysis: essential concepts of bearing technology, 5th edn. CRC Press/Taylor & Francis Group, Boca Raton Henderson R (2006) Design, simulation, and testing of a novel hydraulic power take-off system for the Pelamis wave energy converter. Renew Energy 31(2):271–283 Jiang Z (2018) The impact of a passive tuned mass damper on offshore single-blade installation. J Wind Eng Ind Aerodyn 176:65–77 Jiang Z, Karimirad M, Moan T (2013a) Dynamic response analysis of wind turbines under blade pitch system fault, grid loss, and shutdown events. Wind Energy 17(9):1385–1409 Jiang Z, Karimirad M, Moan T (2013b) Response analysis of parked spar-type wind turbine considering bladepitch mechanism fault. Int J Offshore Polar Eng 23(02):120–128 Jiang Z, Xing Y, Guo Y, Moan T, Gao Z (2014a) Long-term contact fatigue analysis of a planetary bearing in a landbased wind turbine drivetrain. Wind Energy 18(4):591–611 Jiang Z, Yang L, Gao Z, Moan T (2014b) Numerical simulation of a wind turbine with a hydraulic transmission system. Energy Procedia 53:44–55 Jiang Z, Moan T, Gao Z (2015) A comparative study of shutdown procedures on the dynamic responses of wind turbines. J Offshore Mech Arct Eng 137(1):011904 Jiang Z, Zhu X, Hu W (2018) Modeling and analysis of offshore floating wind turbines. In: Advanced wind turbine technology. Springer, New York, USA, pp 247–280 Jonkman J (2007) Dynamics modeling and loads analysis of an offshore floating wind turbine, Technical report no. NREL/TP-500-41958, National Renewable Energy Lab.(NREL), Golden Jonkman J, Buhl Jr, ML (2005) FAST user’s guide. National Renewable Energy Laboratory, Golden, Technical report no. NREL/EL-500-38230 Jonkman J, Butterfield S, Passon P, Larsen T, Camp T, Nichols J, Azcona J, Martinez A (2008) Offshore code comparison collaboration within IEAwind annex XXIII: phase II results regarding monopile foundation modeling. Technical report no. NREL/CP-500-47534, National Renewable Energy Lab.(NREL), Golden Karimirad M, Michailides C (2015) V-shaped semisubmersible offshore wind turbine: an alternative concept for offshore wind technology. Renew Energy 83:126–143 Krogstad P-Å, Eriksen PE (2013) “Blind test” calculations of the performance and wake development for a model wind turbine. Renew Energy 50:325–333 Kurniawan A, Pedersen E, Moan T (2012) Bond graph modelling of a wave energy conversion system with hydraulic power take-off. Renew Energy 38(1):234–244 Kvittem MI, Bachynski EE, Moan T (2012) Effects of hydrodynamic modelling in fully coupled simulations of a semi-submersible wind turbine. Energy Procedia 24:351–362 Larsen TJ (2009) How 2 HAWC2, the user’s manual. Risø National Laboratory, Technical University of Denmark, Roskilde

A

22 Larsen TJ, Madsen HA, Larsen GC, Hansen KS (2013) Validation of the dynamic wake meander model for loads and power production in the Egmond aan Zee wind farm. Wind Energy 16(4):605–624 Lee C-H (1995) WAMIT theory manual. Massachusetts Institute of Technology, Department of Ocean Engineering. Boston, USA Lefebvre S, Collu M (2012) Preliminary design of a floating support structure for a 5 MW offshore wind turbine. Ocean Eng 40:15–26 Li Y, Calisal SM (2010) Three-dimensional effects and arm effects on modeling a vertical axis tidal current turbine. Renew Energy 35(10):2325–2334 Li Y, Yu Y-H (2012) A synthesis of numerical methods for modeling wave energy converter-point absorbers. Renew Sust Energ Rev 16(6):4352–4364 LM Wind Power, The worlds’s longest blade. https://www. lmwindpower.com/en/stories-and-press/stories/news-fr om-lm-places/record-breaking-lm-88-4-blade. Accessed 18 Oct 2018 Luan C, Gao Z, Moan T (2016) Design and analysis of a braceless steel 5-MW semi-submersible wind turbine. In: ASME 2016 35th international conference on Ocean, Offshore and Arctic Engineering, American Society of Mechanical Engineers, pp V006T009A052V006T009A052 Luan C, Gao Z, Moan T (2018) Comparative analysis of numerically simulated and experimentally measured motions and sectional forces and moments in a floating wind turbine hull structure subjected to combined wind and wave loads. Eng Struct 177:210–233 McNiff BP, Musial WD, Errichello R (1991) Variations in gear fatigue life for different wind turbine braking strategies. Solar Energy Research Institute, Golden Moriarty PJ, Hansen AC (2005) AeroDyn theory manual. Technical report NREL/TP-500-36881, National Renewable Energy Laboratory, Golden Morison J, Johnson J, Schaaf S (1950) The force exerted by surface waves on piles. J Pet Technol 2(5):149–154 Muliawan MJ, Gao Z, Moan T, Babarit A (2013a) Analysis of a two-body floating wave energy converter with particular focus on the effects of power take-off and mooring systems on energy capture. J Offshore Mech Arct Eng 135(3):031902 Muliawan MJ, Karimirad M, Moan T (2013b) Dynamic response and power performance of a combined spartype floating wind turbine and coaxial floating wave energy converter. Renew Energy 50:47–57 Nejad AR, Gao Z, Moan T (2014) On long-term fatigue damage and reliability analysis of gears under wind loads in offshore wind turbine drivetrains. Int J Fatigue 61:116–128 Nejad AR, Jiang Z, Gao Z, Moan T (2016) Drivetrain load effects in a 5-MW bottom-fixed wind turbine under blade-pitch fault condition and emergency shutdown. J Phys Conf Ser, vol 11. IOP Publishing, p 112011 Nielsen FG (2013) Hywind-Deep offshore wind operational experience. 10th Deep Sea Offshore Wind R&D conference, Trondheim Nielsen FG, Hanson TD, Skaare B (2006) Integrated dynamic analysis of floating offshore wind turbines.

Analysis of Renewable Energy Devices In: Proceedings of 25th international conference on offshore mechanics and arctic engineering, pp OMAE2006-92291, Hamburg Ning SA (2014) A simple solution method for the blade element momentum equations with guaranteed convergence. Wind Energy 17(9):1327–1345 NORSOK (2007) Standard N-003: actions and action effects. Standards Norway, Lysaker Passon P, Kühn M, Butterfield S, Jonkman J, Camp T Larsen TJ (2007) OC3—Benchmark Exercise of Aero-Elastic Offshore Wind Turbine Codes, conference paper NREL/CP-500-41930. The European academy of wind energy special topic conference: the science of making torque from wind, University of Denmark, Lyngby, p 012071 Pereya BT, Jiang Z, Gao Z, Anderson MT, Stiesdal H (2018) Parametric study of a counter weight suspension system for the tetraspar floating wind turbine. In: Proceedings of the ASME 2018 international offshore wind technical conference, IOWTC 2018, San Francisco Pitt DM, Peters DA (1980) Theoretical prediction of dynamic-inflow derivatives. Sixth European rotorcraft and powered lift aircraft forum, Bristol Popko W, Vorpahl F, Zuga A, Kohlmeier M, Jonkman J, Robertson A, Larsen TJ, Yde A, Sætertrø K, Okstad KM (2012) Offshore code comparison collaboration continuation (OC4), phase 1-results of coupled simulations of an offshore wind turbine with jacket support structure. In: Proceedings of the twenty-second international offshore and polar engineering conference. Rhodes, Greece Ruehl K, Michelen C, Kanner S, Lawson M, Yu Y-H (2014) Preliminary verification and validation of WECSim, an open-source wave energy converter design tool. In: Proceedings of the ASME 2014 33rd international conference on ocean, offshore and arctic engineering, San Francisco, USA, American Society of Mechanical Engineers, pp V09BT09A040-V009BT009A040 Salehyar S, Li Y, Zhu Q (2017) Fully-coupled time-domain simulations of the response of a floating wind turbine to non-periodic disturbances. Renew Energy 111:214–226 Saletti M (2018) Comparative numerical and experimental study of the global responses of the spar-toruscombination in extreme waves due to the bottom slamming effect. Master thesis, Department of Marine Technology, Norwegian University of Science and Technology, Trondheim, Norway Sarpkaya T (2010) Wave forces on offshore structures. Cambridge University Press, New York Schløer S, Bredmose H, Bingham HB (2016) The influence of fully nonlinear wave forces on aero-hydroelastic calculations of monopile wind turbines. Mar Struct 50:162–188 Shi W, Park H, Chung C, Baek J, Kim Y, Kim C (2013a) Load analysis and comparison of different jacket foundations. Renew Energy 54:201–210 Shi W, Park H, Han J, Na S, Kim C (2013b) A study on the effect of different modeling parameters on the dynamic response of a jacket-type offshore wind turbine in the Korean Southwest Sea. Renew Energy 58:50–59

Application of Image Processing in Ice–Structure Interaction Shi W, Tan X, Gao Z, Moan T (2016) Numerical study of ice-induced loads and responses of a monopile-type offshore wind turbine in parked and operating conditions. Cold Reg Sci Technol 123:121–139 Shirzadeh R, Devriendt C, Bidakhvidi MA, Guillaume P (2013) Experimental and computational damping estimation of an offshore wind turbine on a monopile foundation. J Wind Eng Ind Aerodyn 120:96–106 Suzuki A (2000) Application of dynamic inflow theory to wind turbine rotors. Doctoral thesis, The University of Utah Velarde J (2016) Design of monopile foundations to support the DTU 10 MW offshore wind turbine. Master thesis, Department of Marine Technology, Norwegian University of Science and Technology Veldkamp H, Van Der Tempel J (2005) Influence of wave modelling on the prediction of fatigue for offshore wind turbines. Wind Energy 8(1):49–65 Vorpahl F, Strobel M, Jonkman JM, Larsen TJ, Passon P, Nichols J (2014) Verification of aero-elastic offshore wind turbine design codes under IEA wind task XXIII. Wind Energy 17(4):519–547 Wei K, Arwade SR, Myers AT (2014) Incremental windwave analysis of the structural capacity of offshore wind turbine support structures under extreme loading. Eng Struct 79:58–69 Wen B, Tian X, Dong X, Peng Z, Zhang W (2018) On the power coefficient overshoot of an offshore floating wind turbine in surge oscillations. Wind Energy 21(11):1076–1091 Xing Y, Moan T (2013) Multi-body modelling and analysis of a planet carrier in a wind turbine gearbox. Wind Energy 16(7):1067–1089 Yang L, Hals J, Moan T (2010) Analysis of dynamic effects relevant for the wear damage in hydraulic machines for wave energy conversion. Ocean Eng 37(13): 1089–1102 Yang L, Jiang Z, Gao Z, Moan T (2015) Dynamic analysis of a floating wind turbine with a hydraulic transmission system. In: Proceedings of the twenty-fifth international ocean and polar engineering conference, Hawaii, USA

23

Antifreeze of the Polar Ocean Platform ▶ Winterization of Polar Engineering

APAL ▶ Mineral Processing and Metallurgy

API – American Petroleum Institute ▶ Pile Capacity

API (American Petroleum Institute) ▶ Offshore Pile Driving

Appendage Resistance ▶ AUV/ROV/HOV Resistance

Application of Image Processing in Ice–Structure Interaction Anchor Shackle ▶ Mooring Connector

Qin Zhang Department of Marine Technology, Norwegian University of Science and Technology, Trondheim, Norway

Introduction

Ant Colony System (ACS) ▶ Obstacle Avoidance Technology for Underwater Vehicle

The understanding of Arctic physical processes and sustainable exploration, exploitation, and management of Arctic resources require more

A

24

Application of Image Processing in Ice–Structure Interaction

detailed, precise, and continuous measurements of sea ice parameters. Because various types of ice are in the ice-covered regions and the sizes of the ice floes can range from about 1 meter to kilometers, the temporally and spatially continuous field observations of sea ice are necessary for marine activities. One of the best ways of observing the ice conditions in the oceans is by using aerial or nautical imagery. The use of cameras as sensors on mobile sensor platforms (e.g., unmanned vehicles) will aid the development of sea ice observation. It has the potential of continuous measurements with high precision, which is particularly important for providing detailed localized information of sea ice to ensure safe operations of structures in ice-covered regions (Haugen et al. 2011). The collected ice images or videos must be analyzed by dedicated computer algorithms to extract useful ice information to dynamic ice estimators and for decision support in Arctic offshore engineering. Therefore, this article introduces image processing algorithms for providing the ice parameters that are important factors in the analysis of ice–structure interaction in an ice field. These useful ice parameters include ice concentration, ice types, ice floe size, and floe size distribution, and they are defined as follows. Ice Concentration Ice concentration (IC) is the ratio of ice on unit area of sea surface; it has been identified as one of the most influencing parameters on the magnitude of experienced forces during model tests (van der Werff et al. 2012; Comfort et al. 1999). To obtain ice concentration from a visual ice image, only the visible ice can be considered, including brash ice, and submerged ice if visible in the image. With the image area, the height of image taken above the ice sheet, and the segmentation which is the identification of the ice from water, the actual area of sea ice and sea surface can be derived. However, the actual domain area is not necessary for calculating ice concentration. In simplified terms, ice concentration from a digital visual image is defined as the area of sea surface covered by visible ice observable in the 2D visual image taken vertically from above, as a fraction of the

whole sea surface domain area. Hence, it is the ratio of the number of pixels of visible ice to the total number of pixels within the image domain. Note that the domain area is an effective area within the image, excluding land or other nonrelevant areas. The ice concentration is then given by (Zhang et al. 2012a) IC ¼ f ðimage area, height above ice sheet, segmentationÞ Area of all visible ice Actual domain area No:of pixels of visible ice in image domain ¼ Total no:of pixels in image domain

¼

:

ð1Þ Ice Types Sea ice is any form of ice found at sea which has originated from the freezing of sea water. Different types of sea ice have different physical properties. Since one generally assumes that brash ice has a dampening effect in models for calculating ice pressure and ice forces, it may be more convenient to estimate the distribution between three classes, that is, the ratio of ice floes, the ratio of brash ice, and the ratio of water. As defined (Løset et al. 2006): • Floe is any relatively flat piece of sea ice 20 m or more across. It is subdivided according to horizontal extent. A giant flow is over 10 km across; a vast floe is 2–10 km across; a big floe is 500–2000 m across; a medium floe is 100–500 m across; and a small floe is 20–100 m across. • Ice cake is any relatively flat piece of sea ice less than 20 m across. • Brash ice is accumulations of floating ice made up of fragments not more than 2 m across and the wreckage of other forms of ice. It is common between colliding floes or in regions where pressure ridges have collapsed. • Slush is snow which is saturated and mixed with water on land or ice surfaces or as a viscous floating mass in water after heavy snowfall. For simplicity, the size of sea ice piece is the only criterion to distinguish ice floe and brash ice

Application of Image Processing in Ice–Structure Interaction

in this research. That is, any relatively flat piece of sea ice 2 m or more across is considered as “ice floe,” while any relatively flat piece of sea ice less than 2 m across is considered as “brash ice (piece).” And the rest of ice pixels, e.g., single ice pixels or the ice pieces that are too small to be treated as brash ice, are considered as “slush.” Ice Floe Size and Floe Size Distribution The estimation of ice floe size and floe size distribution among the “ice floes” gives an important set of parameters from ice images. In image processing, the ice floe size can be determined by the number of pixels in the identified floe. If the focal length f and camera height are available, the actual size in SI unit of the ice floes and floe size distribution can also be calculated (Lu and Li 2010) by converting the image pixel size to its SI unit size.

Image Processing Methods A digital image is a numeric representation of a two-dimensional picture, and it is composed of pixels which are the smallest individual elements in the image. A pixel holds quantized values that represent the color or gray level of the image at a particular point. Ice Pixel Detection Ice concentration, as defined, is a binary decision of each pixel to determine whether it belongs to the class “ice” or to the class “water.” From Eq. 1, it is clear that the detection of the ice pixels from water pixels is crucial to obtaining the ice concentration from an ice image. Otsu Thresholding

The pixels in the same region have similar intensity. Based on that sea ice is whiter than open water, ice pixels have higher intensity values than those belonging to water in a uniform illumination ice image. Thus, the thresholding, which is based on the pixel’s gray-level to turn a grayscale image into a binary image (whose pixels have only two possible intensity values, e.g., “0” and “1”), is a natural way to segment ice regions from water regions.

25

Assuming that an object is brighter than the background, the object and background pixels have intensity levels grouped into two dominant modes. A threshold value T is chosen to separate an image into an “object region” and a “background region.” Individual pixels are marked as “object” pixels if their value is greater than the threshold value and as “background” pixels otherwise, that is:
gðx, yÞ ¼

1

if f ðx, yÞ > T

0

if f ðx, yÞ  T

ð2Þ

where g(x, y) and f (x, y) are the pixel values located in the xth column and yth row of the binary and grayscale image, respectively. Then, the grayscale image is turned into a binary image. The key of thresholding method is how to select the threshold value. The Otsu thresholding method (Otsu 1975) is one of the most common automatic threshold segmentation algorithms. It requires that the histogram (the distribution of gray value) is bimodal and the illumination is uniform. In this method, the histogram of the image is divided into two classes (i.e., the pixels are classified as either foreground or background), and the goal is to find the threshold value that minimizes the within-class variance, given by (Otsu 1975) s2w ðT Þ ¼ o1 ðT Þs21 ðT Þ þ o2 ðT Þs22 ðT Þ

ð3Þ

where o1 and o2 are the probabilities of the two classes separated by a threshold T and s1 and s2 are the variances of these two classes. The threshold with the maximum between-class variance also has the minimum within-class variance. The between-class variance is given by (Otsu 1975) s2b ðT Þ ¼ o1 ðT Þðm1 ðT Þ
mðT ÞÞ2 þ o2 ðT Þðm2 ðT Þ
mðT ÞÞ2 ffi o1 ðT Þo2 ðT Þðm1 ðT Þ
m2 ðT ÞÞ2

ð4Þ where m1 and m2 are the means of these two classes and m(T) ¼ o1(T)m1(T) + o2(T)m2(T). This expression can also be used to find the best threshold and to update the threshold value iteratively.

A

26

Application of Image Processing in Ice–Structure Interaction

K-means Clustering

Clustering is a statistical data analysis method that divides a data set into many groups (Basak et al. 1988), and it has been widely used in image segmentation, especially classifying the objects into many groups. This method is based on the mathematical distance measure between individual observations and groups of observations to find hidden structures in unlabeled data and assign the unlabeled data into groups, so that the data in one group are more similar to each other than to those in other groups. Among various clustering algorithms, k-means is one of the simplest but most popular clustering algorithms. The goal of k-means clustering is to minimize the within-cluster sum of distance to partition a set of data into k clusters (MacQueen 1967). The step-by-step algorithm for this method in image segmentation is described below: Step 1: For image processing, a set of gray levels is given: f ðx1 , y1 Þ, f ðx2 , y2 Þ,   , f ðxn , yn Þ:

ð5Þ

Step 2: Partition this set into k clusters:   f i ðx1 , y1 Þ, f i ðx2 , y2 Þ,   , f i xni , yni

i

¼ 1, 2,   , k:

ð6Þ

Step 3: Calculate the local means of each cluster: ci ¼

ni 1 X f ðx , y Þ ni m¼1 i m m

i ¼ 1, 2,   , k: ð7Þ

Step 4: Gray level f(xj, yj) (j ¼ 1, 2, . . ., n) belongs to set p (p ¼ 1, 2, . . ., k) if it has the shortest distance to set p than any other sets:     j f x j , y j
cp jj f x j , y j
ci j ¼ 1, 2,   , k:

i ð8Þ

Iterate Steps 3 and 4 until the local means are unchanged.

Ice Floe Boundary Detection In image processing, the detection of ice floe boundaries can be used to distinguish individual ice floes. With the individual ice floe identification result, ice floe characteristics, such as location, area, perimeter, and shape measurements of each ice floe, together with the floe size distribution can thereby be estimated. Thus, ice floe boundary detection is a vital for extracting information of ice floes from ice images. In an actual ice-covered environment, especially in marginal ice zone (MIZ), ice floes typically touch each other, and the edges between touching floes may be difficult to identify in digital images. This issue significantly affects the analysis of individual ice floe properties and floe size distribution. Among various floe boundary detection methods, for example, derivative boundary detection (Zhang et al. 2012a, b), morphology-based method (Zhang et al. 2012a, b; Banfield 1991; Banfield and Raftery 1992), watershed-based algorithms (Blunt et al. 2012; Zhang et al. 2013), etc., the GVF (gradient vector flow) snake-based approach (Zhang et al. 2015; Zhang and Skjetne 2015) is the most advanced method nowadays. The GVF snake algorithm (Xu and Prince 1998) is an extension of the traditional snake (also known as active contours) algorithm (Kass et al. 1988) (the details of the traditional and GVF snake algorithms can be found in “Appendix A”). It has a good capability in the detection of weak boundaries. However, proper initial contours (an initial contour is a starting set of snake points for the evolution) are required by the GVF snake algorithm in ice floe boundary detection, especially when detecting the boundaries of massive ice floes. For each ice floe, it was showed that the initial contour close to the actual floe boundary, located inside the floe and centered as close to the ice floe center, is most effective (Zhang and Skjetne 2015). To accomplish the requirements of the initial contour without manual interaction, an automatic contour initialization algorithm based on the distance transform (the details of the distance transform can be found in “Appendix B”) and its regional maxima (a regional maximum is a connected component of pixels with a value

Application of Image Processing in Ice–Structure Interaction Application of Image Processing in Ice– Structure Interaction, Fig. 1 Contour initialization algorithm

0 0 0 0 0 0 0 0

0 1 1 1 0 0 0 0

0 1 1 1 1 1 0 0

0 1 1 1 1 1 0 0

0 1 1 1 1 1 1 0

(a) Binary image matrix.

greater than any of its neighbors) is concluded as follows (Zhang and Skjetne 2014, 2015): Step 1: Convert the ice image into binary image after separating the ice from the water, in which case the pixels with value “1” indicate ice and pixels with value “0” indicate water; see Fig. 1a. Step 2: Perform the distance transform to the binary image, and find the regional maxima shown as the green numerals in Fig. 1b. Step 3: Merge the regional maxima into a big one if they have a short distance to each other, and then find the “seeds” that are centers of the regional maxima (including the merged ones), shown as red “+” in Figs. 1b and 2b. Step 4: Initialize the circular-shaped contours located at the seeds with the radii selected according to the pixel value at the seeds in the distance map; see the blue circles in Figs. 1b and 2b.

After initializing the contours, the GVF snake algorithm is run on each contour to detect the floe boundary. By superimposing all the detected boundaries over the binarized ice image, it allows to separate touching ice floes and thereby be able to identify individual floes, as shown in Fig. 2.

27

0 1 1 1 1 1 1 0

0 0 1 1 1 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 1 1 1 0 0 0 0

0 1 2 2 1 1 0 0

0 1 2 3 2 1 0 0

0 1 2 3 3 2 1 0

0 1 2 2 2 1 1 0

0 0 1 1 1 0 0 0

0 0 0 0 0 0 0 0

(b)Distance transform of Fig. 1(a), regional maximum, seed, and initial contour.

Floe Shape Enhancement Some segmented floes may contain holes or smaller ice floes inside after boundary detection, and the shape of the segmented ice floe is rough. To smoothen the shape of the ice floe, morphological cleaning is used after ice floe boundary detection. Morphological cleaning is a combination of first morphological closing and then morphological opening (Soh et al. 1998) on an image. Assume A is a binary image and B is a chosen structuring element (a structuring element is a shape that is used to probe an input image and draw conclusions on how the structuring element fits or misses the shapes in the input image. It can be represented as a matrix of 1 s, indicating the points that belong to the structuring element, and 0 s indicating otherwise); the morphological closing of A by B, denoted A • B, is a dilation followed by an erosion (the details of dilation and erosion operations can be found in “Appendix C”): A • B ¼ ð A  BÞ  B

ð9Þ

where Å and  denote dilation and erosion, respectively. The morphological closing is the complement of the union of all translations of B that do not overlap A. It tends to smooth the contours of objects, generally joins narrow breaks, fills long thin gulfs, and fills holes smaller than the structuring element as seen in Fig. 3b.

A

28

Application of Image Processing in Ice–Structure Interaction

Application of Image Processing in Ice– Structure Interaction, Fig. 2 Touching ice floe separation based on GVF snake

(a) Sea ice f loe image.

(b) Binary image with initial contours.

(c) separation result, individual floes are labeled in different colors.

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 1 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 1 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 0 0 0 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 0 0 0

0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

(a) Binary image.

(b) Closing of (a).

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

(c) Opening of (b). Application of Image Processing in Ice–Structure Interaction, Fig. 3 Morphological cleaning by using a 2 2 square structuring element

The morphological opening of A by B, denoted A ∘ B, is an erosion followed by a dilation: A∘B ¼ ðA  BÞ  B:

ð10Þ

The morphological opening is the union of all the translations of B that fit entirely within A. It

can remove complete regions of an object that cannot contain the structuring element, smooths object contours, breaks thin connections, and removes thin protrusions as shown in Fig. 3c. To ensure that smaller ice floes contained in larger floes are removed, the morphological cleaning should be performed on smaller floes

Application of Image Processing in Ice–Structure Interaction

29

Application of Image Processing in Ice– Structure Interaction, Fig. 4 Ice shape enhancement

A

(a) Ice floe image with speckle.

(b) Boudary detection result of Fig. 4(a).

(c) Shape enhancement result of 4(b).

Application of Image Processing in Ice–Structure Interaction, Table 1 Managed ice conditions in the test runs, target values (full scale) Run no. 5100 5200 5300 5400

IC [%] 86 70 70 86

Floe size 1 (45%) [m] 0.50 0.50 0.25 0.25

first. Thus, the shape enhancement includes following two steps (Zhang and Skjetne 2014): Step 1: Arrange all the segmented ice floes from small to large. Step 2: Perform the morphological cleaning to the arranged ice floes in sequence. The shape enhancement result is shown in Fig. 4c.

Applications in Arctic Offshore Engineering Model Ice Image Processing Applications Before performing an analysis at full scale, the dynamic positioning (DP) experiments in model ice at the Hamburg Ship Model Basin (HSVA) in May 2011 allow for the testing of relevant image processing algorithms. This section shows the applications of the image processing techniques for determining important ice parameters from model ice data in the model-scale ice–structure analysis.

Floe size 2 (40%) [m] 1.00 1.00 0.50 0.50

Floe size 3 (15%) [m] 1.50 1.50 0.75 0.75

In these DP experients, a managed ice condition was obtained by cutting the level ice layer into predefined ice floe shapes, and the behavior of two different model ships (an Arctic drillship and a polar research vessel) in a broken-ice field was studied. Four different types of ice fields were tested, varying in ice concentration and ice floe size distribution, as shown in Table 1. The model ice image data provided from the experiments includes two complete overview pictures from run nos. 5100 and 5200 and the videos of each of the four model test runs (see Table 1). The overall tank images were retrieved by stitching 28 top view pictures taken before execution of the model tests, showing a complete overview of the ice floe distribution in the ice tank, as seen in Fig. 5. The videos captured the local conditions around the fixed model vessel with a constant heading of 180 during each run by a top view video camera moving along with the carriage and model, as seen in Fig. 6. The four model ice videos are more than 24 min long with a frame rate of 25 fps. Since a video is composed from a sequence of frames, by gathering the result for each analyzed frame, the model ice parameters over time are retrieved. Before applying the algorithms to these videos, one frame per second is

30

Application of Image Processing in Ice–Structure Interaction

Application of Image Processing in Ice–Structure Interaction, Fig. 5 Overall tank image for run no. 5100. Target ice concentration of 86%

Application of Image Processing in Ice–Structure Interaction, Table 2 Ice concentrations derived from different methods Methods Run no. 5100 Run no. 5200

Application of Image Processing in Ice–Structure Interaction, Fig. 6 One frame in the original video. Run no. 5400

found sufficient, and each frame was fed to the program for further processing (Zhang et al. 2012b). Ice Concentration

Both Otsu thresholding and k-means clustering methods have been used to determine the ice concentration in model basin for run nos. 5100 and 5200. The analysis results are compared with the target ice concentration values, as presented in Table 2. Because the intensity values of all the model ice pixels are significantly higher than water pixels, both methods give similar result (Zhang et al. 2012b) and are both effective, as shown in Fig. 7. When analyzing the ice concentrations in the vicinity of the model ship, the impediments around the tank in the videos are removed, and the vessel in the middle bottom of the tank is eliminated by a black rectangle, as seen in Fig. 8a. Then, the Otsu’s and the k-means

Target value (%) 86 70

Otsu (%) 83.17 62.50

K-means (%) 82.86 62.00

methods are applied in the video processing to calculate the ice concentration as a function of time. Figure 9 shows the variation of the calculated ice concentration in time for all test runs based on the Otsu’s method, and the average ice concentrations after reaching the limiting values in all test runs are summarized in Table 3. Reduced ice concentration in the initial part of the test runs (before convergence) is related to the model ship positioning. It is an unwanted phenomenon, since it reduces the effective length of the ice tank. In all test runs, it was observed that the ice concentration in the near vicinity of the model was reaching a limiting value of approximately 80–89%, irrespective of the starting ice concentrations and floe sizes. This phenomenon can be explained by the tank’s wall effect. That is, the ice floes were compacted by the model ship toward the end of the basin, such that the ice concentration asymptotically approached a limiting value. Within the image analysis results, the time series of the ice concentration have been compared with the absolute total hull forces that were measured during the tests to investigate the relation between the ice concentration and the hull forces (see Fig. 10, for instance) (van der Werff et al. 2012). Further investigations are under consideration.

Application of Image Processing in Ice–Structure Interaction

31

Application of Image Processing in Ice– Structure Interaction, Fig. 7 Ice pixel detection for run no. 5100

A (a) Otsu thresholding method, IC = 83.17%, Threshold = 84.

(b) K-means method, 2 clusters, IC = 82.86%.

Application of Image Processing in Ice– Structure Interaction, Fig. 8 Frames of run no. 5100 at 816 s and ice detection

(a) Pre-processed frame.

(b) Otsu, IC = 87.26%, threshold = 100.

Model Ice Floe Monitoring

In one of the model ice tests as seen in Fig. 11a, the ice floes were modeled square shapes with predefined side lengths, and the largest floe has an area less than a predefined value. To evolve the GVF snake algorithm effectively for identifying ice floe boundaries, an automatic initial contour initialization method was introduced in section “Ice Floe Boundary Detection.”. However, it is difficult for the contour initialization method to initialize the contours for each square-shaped ice floe as shown in Fig. 11b, so that the GVF snake algorithm is unable to find all floe boundaries and many floes still touch each other as shown in Fig. 11c. Thus, an additional round of contour initialization and segmentation is required.

(c) K-means, IC = 86.91%.

In this model ice test, although these model ice floes are not perfect squares, most of the floes could be approximated as rectangles with a length-to-width ratio less than the given threshold. Based on the characteristics of these rectangle-shaped model ice floes, the following three criteria can be used to determine whether it is necessary to initialize the contours and conduct a second segmentation (Zhang et al. 2015): • The ice floe area is less than a given threshold. • The ice floe has a convex shape (it could be done by determining if the ratio between the floe area and its minimum bounding polygon area is larger than the threshold).

32

Application of Image Processing in Ice–Structure Interaction

Application of Image Processing in Ice– Structure Interaction, Fig. 9 Time-varying IC of run nos. 5100–5400 based on Otsu thresholding

Run no. 5100

Run no. 5200

Run no. 5300

Run no. 5400

100,00 % 90,00 % 80,00 %

Ice concentration

70,00 % 60,00 % 50,00 % 40,00 % 30,00 % 20,00 % 10,00 % 0,00 % 1

201

401

601

801

1001

1201

1401

Time (s)

Application of Image Processing in Ice–Structure Interaction, Table 3 Average IC after reaching saturation in all test runs 5100 200 88.93%

Application of Image Processing in Ice– Structure Interaction, Fig. 10 Hull force and ice concentration time series for run no. 5100 (high IC, large floes)

5200 300 80.39%

5300 600 81.69%

5400 300 84.83%

90

force (N)

Total hull force Ice concentration

80

0,92

70

0,9

60

0,88

50

0,86

40

0,84

30

0,82

900

1000

1100

1200

time (s)

1300

1400

1500

0,8

concentration (–)

Run no. Start time (s) Average IC

Application of Image Processing in Ice–Structure Interaction

33

Application of Image Processing in Ice– Structure Interaction, Fig. 11 Crowded model ice floe segmentation

A (a) Model ice image with crowded f loes.

(b) Initializing the contours once.

(d) Initializing the contours twice.

• The length-to-width ratio of the minimum bounding rectangle of the ice floe is less than the threshold. Note that these criteria are designed for segmenting the rectangular-shaped crowded model ice floes only. For crowded model ice floes with other shapes, the criteria can be replaced by the corresponding shape criteria. After a segmentation step, the algorithm will stop if all the segmented floes satisfy these criteria. Otherwise, the algorithm must find the floes that do not satisfy any of these criteria, find their seeds, initialize new contours, and perform the segmentation again (e.g., seen in Fig. 11d, e). After several segmentation steps, some segmented floes may still not satisfy the criteria. This is mainly because the boundaries of those floes are too weak to be detected. However, the total number of segmented floes will converge to a final solution. Therefore, the algorithm is made to stop if the total number of floes segmented after steps N and N + 1 are equal, in combination with an absolute stop criterion.

(c) Results after first round.

(e) Final result.

Finally, the ice shape enhancement algorithm is performed on the overall segmented model ice floe image to obtain the final model ice floe identification result. Figure 12 presents an example showing the crowded model ice floe identification result from Fig. 5 and the corresponding floe size distribution of an overall ice tank image (Zhang et al. 2015). This model ice floe identification algorithm has been applied to an ice surveillance video to monitor the maximum floe size entering the protected vessel from a physical ice management operation, as seen in Fig. 13b. The maximum floe size for each frame is calculated as a function of time as seen in Fig. 14. Based on this result, a warning can be sent to the risk management system if the estimated risk based on the maximum floe size is too large.

Sea Ice Image Processing Applications The Norwegian University of Science and Technology (NTNU) expedition Oden Arctic Technology Research Cruise 2015 (OATRC’15) was

34

Application of Image Processing in Ice–Structure Interaction 5878 1798 1113 710 424 202 20

(a) Ice floe identification. The floe positions, found by averaging the positions of the pixels of each floe, are denoted using black dots.

Frequency

300

5952

250

2081

200

996

1398

710

150

488

100

307 153

50

20

0

0

1000

2000

3000

4000

5000

6000

Floe size (pixel number)

(b) Floe size distribution histogram. Application of Image Processing in Ice–Structure Interaction, Fig. 12 Crowded model ice floe image identification and floe size distribution from Fig. 5

Application of Image Processing in Ice– Structure Interaction, Fig. 13 Model ice video processing

(a) Pre-processed frame at 965s.

carried out in the Arctic region in September 2015. During the research cruise, one of the helicopter flight missions was to capture ice conditions in the marginal ice zone (MIZ). The images contain valuable ice information in the MIZ. In this section, several methods are sequentially presented with an example to demonstrate an automated procedure for ice floe and brash ice identification, their numerical representation, and forthcoming ice field generation.

(b) Segmentation result of (a).

Sea Ice Image Processing

Most of the ice, we called “light ice,” can be identified by Otsu thresholding method. However, the “dark ice,” whose pixel intensity values are close to water pixels, may be lost. To determine more ice pixels, the k-means clustering method is used to divide the image into three or more clusters, considering the cluster with the lowest average intensity value to be water and the other clusters to be ice. The “dark ice” is then obtained

Application of Image Processing in Ice–Structure Interaction

35

4

x 10

Maximum Floe Area (pixel number)

3

A

2.5 2 1.5 1 0.5 0

0

200

600

400

800

1000

Time (s) Application of Image Processing in Ice–Structure Interaction, Fig. 14 Maximum floe size entering the protected vessel

Application of Image Processing in Ice– Structure Interaction, Fig. 15 Sea ice image processing result

(a) Sea ice image.

(b) “Light ice” extracted by the thresholding method.

(c) Ice extraction using the k-means method with 3 clusters.

(d) “Dark ice” found by subtracting Fig. 15(c) from Fig. 15(c).

by comparing the difference between Otsu threshold detection result and k-means clustering detection result, as seen in Fig. 15d. Thereafter, the GVF snake-based floe boundary detection method is run on the image layers of “light ice” and “dark ice” to individually derive “light ice” segmentation and “dark ice” segmentation. Collecting all the segmented ice pieces from both “light ice” and “dark ice” layers, the shape enhancement is then performed to complete the identification. According to section “Ice

Types,” the identified ice pieces are simply distinguished into ice floes and brash ice by defining a brash ice threshold parameter (e.g., number of pixels or area). Then the remaining of detected ice pixels, most of which are the detected boundary pixels between the touching floes, are considered to be “slush.” The sea ice image processing result is then four layers of ice floes (58.00%), brash ice (4.85%), slush (21.21%), and water (15.94%). The processed result of Fig. 15a can be found in Fig. 16, where a total of 2888 ice floes

36

Application of Image Processing in Ice–Structure Interaction

Application of Image Processing in Ice– Structure Interaction, Fig. 16 Sea ice image processing result of Fig. 15a

(a) Layer of “ice f loes”.

(b) Layer of “brash ice”.

(c) Layer of “slush”.

(d) Layer of “water”.

and 3452 brash ice pieces are identified from Fig. 15a. Sea Ice Numerical Modeling

Based on the image processing results, the identified ice floes and brash ice pieces are further simplified for the numerical simulation of the ice–structure interaction. In this modification, each sea ice floe is represented by a bounding polygon, and the brash ice pieces were reshaped by circular disks of equivalent area (Zhang 2015). Figure 17 shows an example of sea ice modeling for Fig. 15a. A close-up view of a few ice floes and brash ice in the middle of Fig. 15a is given in Fig. 18, with the blue boundaries of the polygons/ circles superimposed on top of the original segmented ice pixels. It is obvious to see that the polygonized floes will not be smaller than the actual identified floes and may overlap with other floes and brash ice pieces. Identifying the overlaps of floe-floe, floe-brash, and brash-brash is important when using the identified ice floes and brash ice as a starting condition for the initialization of an ice field in a numerical simulation for ice–structure interactions (Lubbad et al. 2015). To indicate these overlaps, an “overlap flag” is added to each polygonized floe to record the serial number of the floes and brash ice pieces with which the current floe overlaps and the “overlap flags” of

(a) Polygon f itting to ice f loes in Fig. 16(a).

(b) Circle f itting to brash ice in Fig. 16(b).

Application of Image Processing in Ice–Structure Interaction, Fig. 17 Sea ice modeling for Fig. 15a

brash-brash and brash-floe are also registered in this modeling (Zhang and Skjetne 2018). Ice Field Generation

The numerical representation of sea ice is utilized to generate its corresponding ice field to bridge the

Application of Image Processing in Ice–Structure Interaction

gap between a natural ice field and its numerical applications, e.g., simulations involving ice– structure interactions. A major challenge of utilizing the digitalized ice field is overlaps among ice floes and brash ice. These overlaps are the consequence of both the input image’s visual noise (e.g., the foggy bottom-left corner) and inaccuracies introduced by the adopted image processing technique (e.g., the procedure to polygonize the segmented ice floes). A non-smooth discrete

Application of Image Processing in Ice–Structure Interaction, Fig. 18 A close-up view of floe ice, brash ice, and their corresponding simplifications in modeling

Initial phase, ice floes:

without overlap

with overlap

37

element method (DEM) is adopted to resolve all the overlaps among different bodies and assign basic physics to each ice floe and brash ice (Zhang and Skjetne 2018; Zhang 2020). Ice floes are treated as discrete bodies after importing the ice field’s numerical representation into the non-smooth DEM-based simulator, and floe pairs involving overlap are labeled with red color in Fig. 19a. Afterward, for each calculation iteration, the collision detection algorithm identifies existing contacts; and the collision responses are calculated and applied to eliminate the overlaps. Figure 19b shows one snapshot of the ice field domain, within which overlaps are gradually resolved. Notably, for saving computation resources, not all the ice floes are involved in the calculation of each iteration. For ice floes without overlap and that are far away from the overlapped ice floe clusters, they are in “sleeping mode” in the adopted algorithm (see Fig. 19b). Figure 19a shows that ice floes in the ice field’s bottom-left corner have more overlaps. This is mainly because of the input image’s visual noises.

Calculation phase, ice floes:

sleeping;

active with overlap active without overlap

(a) Initial phase of the ice floe field with overlap.

(b) Calculation phase of the ice f loe field with overlap.

(c) All overlaps are resolved.

(d) Finally generated ice f loe f ield.

Application of Image Processing in Ice–Structure Interaction, Fig. 19 Ice floe field generation

A

38

Application of Image Processing in Ice–Structure Interaction

Application of Image Processing in Ice– Structure Interaction, Fig. 20 Ice field generation with both floe ice and brash ice

(a) Initial ice condition with overlaps.

(b) Final ice condition without overlaps.

Nevertheless, applying the above non-smooth DEM calculation procedures, all the overlaps are eventually resolved in Fig. 19c, and its corresponding final ice field is shown in Fig. 19d. After resolving the overlaps, the exact location of each ice floe in Figs. 19d and 17a is not the same, but with only minor differences. On the other hand, each ice floe’s shape and size and the overall ice field’s ice mass are conserved. Similarly, brash ice can be imported into the same non-smooth DEM-based simulator and be treated as discrete bodies. From a non-smooth DEM calculation’s point of view, the simplification of each brash ice as a disk with equivalent area makes the collision detection and consequent collision response calculation much easier comparing to arbitrary polygons. Given the amount of brash ice and its relatively small mass, this simplification is reasonable and has been adopted in previous studies (Konno 2009; Konno et al. 2011, 2013). For the current demonstration, the identified brash ice in Fig. 16b and its numerical representation in Fig. 17b are additionally imported to the ice field in Fig. 19a. This is illustrated in Fig. 20a, which shows relatively much more overlaps. An enlarged view within the field center is also

presented. The circular disk-shaped bodies are the brash ice representations. It is computationally efficient to make the circular disk-shaped simplification for brash ices. For the current ice field composition, i.e., 58.00% ice floe and 4.85% brash ice, the calculation time to resolve all overlaps for the cases with and without brash ice poses no significant difference. In both cases, the bottleneck for calculation time is on the overlap resolution in the bottom-left corner’s large ice floes. However, it is expected that as the amount of brash ice increases, the calculation time would also increase, which eventually becomes the decisive bottleneck for the calculation. To certain point, it might be more efficient to model brash ice as a continuum, e.g., a viscous flow, which is governed by conservation laws as a material collection.

Conclusion Various image processing techniques have been introduced in this entry to extract useful ice information from the collected ice image data to support the estimation of ice forces that are critical to marine operations in the Arctic. The introduced

Application of Image Processing in Ice–Structure Interaction

methods have been applied to both model and sea ice image data to give some results applicable for ice engineering. More results and better information of ice from visual images will be investigated by further development of these image processing techniques.

Appendix A Traditional and GVF Snake Algorithms

39

image noise, the external energy is defined as (Kass et al. 1988) Eext ¼
j∇Gs ðx, yÞ Iðx, yÞj2

where ∇Gs(x, y) is a two-dimensional Gaussian function with a standard deviation s and “ ” denotes convolution. To minimize the energy E, a snake must satisfy the Euler equation: 00

Traditional Snake Algorithm A traditional snake is a curve C(s) ¼ (x(s),y(s)) with the normalized arc length s  [0,1] that moves through the spatial domain of an image to minimize the sum of the internal and external energy, given by

E¼

ð1 0

aC00 ðsÞ
bC00 ðsÞ
∇Eext ¼ 0:

ð11Þ

where Eint is the internal energy Eint ¼

  1 2 2 ajC0 ðsÞj þ bjC00 ðsÞj 2

ð12Þ

where α and β are weight parameters that control the snake’s tension and rigidity, respectively. C0 (s) denotes the first derivatives of C(s) with respect to s, making the snake act as a membrane, and C00 (s) denotes the second derivatives, making the snake act as a thin plate. Eext is the external energy defined in the image domain. It attracts snakes to salient features in the image, such as boundaries. To find boundaries in a grayscale image, I(x, y), the image gradient is typically chosen as the external energy (Kass et al. 1988): Eext ¼
j∇Iðx, yÞj where ∇Iðx, yÞ ¼



@I @I @x , @y

2

ð13Þ

 is the image gradient

that represents a directional change in the brightness of the image with the gradient angle y ¼  @I @I arctan @y = @x . When also considering the

ð15Þ

Let Fint ¼ αC00(s)
βC0000(s) denote the internal force and Fext ¼
∇ Eext denote the external force. Then Eq. 15 can be written as the force balance: Fint þ Fext ¼ 0:

ðEint ðCðsÞÞ þ Eext ðCðsÞÞÞds

ð14Þ

ð16Þ

The internal and external forces are defined such that the snake will conform to an object boundary (or other desired features) within an image. The internal force Fint discourages stretching and bending, while the external potential force Fext pulls the snake toward the desired image boundaries. Eq. 16 implies that the initial curve given in the snake algorithm will move under the influence of internal forces from the curve itself and external forces computed from the image data until the internal and external forces reach equilibrium. To find a solution for Eq. 15, C(s) is treated as a discrete system of normalized arc length s and time t: @Cðs, tÞ 00 ¼ aC00 ðs, tÞ
bC00 ðs, tÞ
∇Eext : ð17Þ @t When the solution C(s,t) becomes stationary, tends to zero, the energy E reaches a minimum, and the curve converges toward the target boundary. The traditional snake algorithm is able to detect weak boundaries. However, there are two key limitations: the capture range of the external force fields is limited, and it is difficult for the

@Cðs, tÞ @t

A

40

Application of Image Processing in Ice–Structure Interaction

snake to progress into boundary concavities. The traditional snake algorithm is, therefore, sensitive to the initial contour, and the initial contour should be somewhat close to the true boundary. GVF Snake Algorithm To overcome the limitations of the traditional snake algorithm, the GVF snake algorithm introduces a spatial diffusion of the gradient of an edge map (which is derived from the image data) to expand the capture range of external force fields from boundary regions to homogeneous regions (Xu and Prince 1998). The GVF is defined to be the vector field v(x, y) ¼ (u(x, y), v(x, y)) that minimizes the energy functional: ϵ¼

ð ðh   i m u2x þ u2y þ v2x þ v2y þ j∇f j2 jv
∇f j2 dxdy

ð18Þ where ux, uy, vx, and vy are the derivatives of the vector field, m is a parameter that controls the balance between the first and second term in the integrand, and f is an edge map (which could be the image gradient |∇I(x, y)|2) that is larger near the edges of objects in the image. In Eq. 18, j ∇ fj becomes large close to the object boundaries, in which case the second term dominates the integrand and is minimized by v ¼ ∇ f. Otherwise, j ∇ fj is small, and the first term dominates the integrand to ensure that the external force field varies slowly and still acts in the homogeneous regions. The GVF field can be found by solving the Euler equations:

  m∇2 u
ðu
f x Þ f 2x þ f 2y ¼ 0

ð19aÞ

   m∇2 v
v
f y f 2x þ f 2y ¼ 0:

ð19bÞ

A solution to Eq. 19a and Eq. 19b can be obtained by introducing a time variable, t, and finding the steady-state solution of the following partial differential equations: ut ðx,y,t Þ ¼ m∇2 uðx,y,t Þ
ðuðx,y,t Þ
  : (20a) f x ðx,yÞ f x ðx,yÞ2 þ f y ðx,yÞ2 vt ðx,y,t Þ ¼ m∇2 vðx,y,t Þ
ðvðx,y,t Þ
  : (20b) f y ðx,yÞ f x ðx,yÞ2 þ f y ðx,yÞ2 Compared to the external force field in the traditional snake model having only fx and fy, the new vector fields, u and v in the GVF, are derived using an iterative method to find a solution for fx and fy. The result is that the capture range is effectively enlarged, as seen Fig. 21. Therefore, the GVF snake releases the requirements of the initial contour, so that the initial contour no longer needs to be as close to the true boundary.

Appendix B Distance Transform Given a binary image f (x, y), whose elements only have values of “0” and “1,” the pixels with a value of “0” indicate the background, while the pixels with a value of “1” indicate the object. Let B ¼ {(x, y)|f (x,y) ¼ 0} be the set of background pixels and O ¼ {(x,y)|f (x, y) ¼ 1} be the set of object pixels. The distance transform of a binary

Application of Image Processing in Ice– Structure Interaction, Fig. 21 External forces

(a) Original image

(b) Traditional external force

(c) GVF external force

Application of Image Processing in Ice–Structure Interaction

Ac ¼ fwjw Ag:

image f, D(x, y) is the minimum distance from each pixel in f to the background B, that is:
Dðx, yÞ ¼

0

if ðx, yÞ  B

min b  B d ½ðx, yÞ, b if ðx, yÞ  O ð21Þ

where d[(x, y), b] is some distance measure between pixel (x, y) and b (Rosenfeld and Pfaltz 1968).

Appendix C Dilation and Erosion A dilation operation “grows” or “thickens” objects by adding pixels to the object boundaries. The mathematical definition of dilation of A by B is defined as follows (Gonzalez et al. 2003): n   o A  B ¼ zj Bb \ A 6¼ ; z

ð22Þ

where (B)z is the translation of B by the point z ¼ (z1, z2), defined as ðBÞz ¼ fb þ zjb  Bg

ð23Þ

and Bb is the reflection of B, defined as Bb ¼ fwj
w  Bg:

ð24Þ

The output of dilation is a binary image having a value of 1 at each location of the origin of the structuring element, such that the reflected and translated structuring element overlaps at least one 1-valued pixel in the input image. An erosion operation “shrinks” or “thins” objects by removing pixels on object boundaries. The mathematical definition of erosion A by B is as follows (Gonzalez et al. 2003):   A  B ¼ zjðBÞz \ Ac 6¼ ;

ð25Þ

where Ac is the complement of A (0-valued pixels set to 1-valued and 1-valued pixels set to 0-valued, for a binary image), defined as

41

ð26Þ

The output of erosion is a binary image having a value of 1 at each location of the origin of the structuring element, such that the element overlaps only 1-valued pixels of the input image (i.e., it does not overlap any of the image background).

References Banfield J (1991) Automated tracking of ice floes: a stochastic approach. IEEE Trans Geosci Remote Sens 29(6):905–911 Banfield JD, Raftery AE (1992) Ice floe identification in satellite images using mathematical morphology and clustering about principal curves. J Am Stat Assoc 87(417):7–16 Basak SC, Magnuson V, Niemi G, Regal R (1988) Determining structural similarity of chemicals using graphtheoretic indices. Discret Appl Math 19(1):17–44 Blunt J, Garas V, Matskevitch D, Hamilton J, Kumaran K et al (2012) Image analysis techniques for high arctic deepwater operation support. In: OTC Arctic technology conference, offshore technology conference Comfort G, Singh S, Spencer D (1999) Evaluation of ice model test data for moored structures. Technical report, PERD/CHC Gonzalez RC, Woods RE, Eddins SL (2003) Digital image processing using MATLAB. Prentice-Hall, Upper Saddle River Haugen J, Imsland L, Løset S, Skjetne R (2011) Ice observer system for ice management operations. In: Proceeding of the 21st international ocean and polar engineering conference, Maui Kass M, Witkin A, Terzopoulos D (1988) Snakes: active contour models. Int J Comput Vis 1(4):321–331 Konno A (2009) Resistance evaluation of ship navigation in brash ice channels with physically based modeling. In: Proceedings of the international conference on port and ocean engineering under arctic conditions Konno A, Saitoh O, Watanabe Y (2011) Numerical investigation of effect of channel condition against ships resistance in brash ice channels. In: Proceedings of the international conference on port and ocean engineering under arctic conditions Konno A, Nakane A, Kanamori S (2013) Validation of numerical estimation of brash ice channel resistance with model test. In: Proceedings of the international conference on port and ocean engineering under arctic conditions Løset S, Shkhinek KN, Gudmestad OT, Høyland KV (2006) Actions from ice on Arctic offshore and coastal structures. LAN, St. Petersburg Lu P, Li Z (2010) A method of obtaining ice concentration and floe size from shipboard oblique sea ice images. IEEE Trans Geosci Remote Sens 48(7):2771–2780

A

42 Lubbad R, Løset S et al (2015) Time domain analysis of floe ice interactions with floating structures. In: OTC Arctic technology conference, offshore technology conference MacQueen J (1967) Some methods for classification and analysis of multivariate observations. In: Proceedings of the fifth Berkeley symposium on mathematical statistics and probability, California, USA, vol 1, pp 281–297 Otsu N (1975) A threshold selection method from graylevel histograms. Automatica 11(285–296):23–27 Rosenfeld A, Pfaltz JL (1968) Distance functions on digital pictures. Pattern Recogn 1(1):33–61 Soh LK, Tsatsoulis C, Holt B (1998) Identifying ice floes and computing ice floe distributions in SAR images. In: Analysis of SAR data of the polar oceans. Springer, Berlin, pp 9–34 van der Werff S, Haase A, Huijsmans R, Zhang Q (2012) Influence of the ice concentration on the ice loads on the hull of a ship in a managed ice field. In: ASME 2012 31st international conference on ocean, offshore and Arctic engineering, American Society of Mechanical Engineers, pp 563–569 Xu C, Prince JL (1998) Snakes, shapes, and gradient vector flow. IEEE Trans Image Process 7(3):359–369 Zhang Q (2015) Image processing for ice parameter identification in ice management. PhD thesis, Norwegian University of Science and Technology Zhang Q (2020) Image processing for sea ice parameter identification from visual images, Chap 12. In: Chen CH (ed) Handbook of pattern recognition and computer vision, 3rd edn. World Scientific, Singapore Zhang Q, Skjetne R (2014) Image techniques for identifying sea-ice parameters. Model Identif Control 35(4):293–301. https://doi.org/10.4173/mic.2014.4.6 Zhang Q, Skjetne R (2015) Image processing for identification of sea-ice floes and the floe size distributions. IEEE Trans Geosci Remote Sens 53(5): 2913–2924 Zhang Q, Skjetne R (2018) Sea ice image processing with MATLAB ®. CRC Press/Taylor & Francis, Milton Zhang Q, Skjetne R, Løset S, Marchenko A (2012a) Digital image processing for sea ice observation in support to Arctic DP operation. In: Proceedings of 31st international conference on ocean, offshore and Arctic engineering, OMAE2012-83860, ASME, Rio de Janeiro Zhang Q, van der Werff S, Metrikin I, Løset S, Skjetne R (2012b) Image processing for the analysis of an evolving broken-ice field in model testing. In: Proceedings of 31st international conference on ocean, offshore and Arctic engineering, OMAE2012-84117, ASME, Rio de Janeiro Zhang Q, Skjetne R, Su B (2013) Automatic image segmentation for boundary detection of apparently connected sea-ice floes. In: Proceedings of the 22nd international conference on port and ocean engineering under Arctic conditions, Espoo

Approximate Technology Zhang Q, Skjetne R, Metrikin I, Løset S (2015) Image processing for ice floe analyses in broken-ice model testing. Cold Reg Sci Technol 111:27–38

Approximate Technology ▶ Multidisciplinary Design Optimization (MDO)

Aquaculture Structures: Experimental Techniques Shixiao Fu1, Yuwang Xu1,2 and Tianhu Cheng2 1 School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China 2 State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China

Synonyms Force oscillation experiment; Seakeeping experiment; Towing experiment

Definition Various experimental techniques for aquaculture structures have been developed for different purposes. Towing and force oscillation tests on an integrated fish cage system or a single fish net plane are utilized to investigate the mathematical models of the hydrodynamic force coefficients in current and waves, respectively, which are an essential input for numerical simulations. Such experiments can also be implemented in a circulating water channel, which can produce uniform and oscillatory currents. Seakeeping experiment technologies for aquaculture structures in waves and currents are also very popular and have mainly been used for the analysis of the dynamic performance of integrated structures; these technologies can provide important verification data for numerical methods.

Aquaculture Structures: Experimental Techniques

43

Scientific Fundamentals Experimental Techniques for Aquaculture Structures in Current In a towing test, an integrated fish cage model or a fish net panel model is installed beneath a towing carriage driven by servo motors. The carriage normally runs at a constant velocity to simulate the pure current in a real sea state. The main purpose is to investigate the hydrodynamic force or deformation for integrating a gravity fish cage or the drag forces of a fish net or semi-submersible fish cage. The circulating water channel test is an alternative approach to the towing test in the simulation of current. The difference is that the model is fixed, and a current with a constant velocity is generated in the water channel. Experimental Study of a Fish Net Panel in Current

An integrated fish cage can be assumed to be a combination of a number of independent net panels. The drag force on a net cage is then given as the sum of the drag forces on the different net panels. One of the most popular towing experiments on a fish net panel model was conducted by Aarsnes, Rudi, and Løland (Aarsnes et al. 1990). These researchers investigated the flow through and around fish net panels and derived the mathematical function of the drag and lift force coefficient for the screen model with the relation of the solidity ratio and incident current angle:   CD ¼ 0:04 þ
0:04 þ 0:33Sn þ 6:54Sn2
4:88Sn3 cos y   CL ¼
0:05Sn þ 2:3Sn2
1:76Sn3 sin 2y

ð1Þ Here, θ refers to the angle between the vector of the fish net plane and the current direction. Sn represents the solidity ratio. The drag and lift forces acting on the fish net panel can then be calculated as 1 1 FD ¼ rCD AU 2 ; FL ¼ rCL AU 2 2 2

ð2Þ

where A is the projected area of the net panel and U represents the current velocity.

Experimental studies of fish net panels have also been investigated by many other researchers. Tsukrov et al. (2011) performed an experimental study of the hydrodynamic forces of copper nets with different solidities, as shown in Fig. 1. Swift et al. (2006) conducted a field test of the drag forces acting on both clean and biofouled net panels. The field testing apparatus is shown in Figs. 2 and 3. Experimental Study of an Integrated Fish Cage in Current

Towing experiments with integrated fish cages, for instance, a gravity fish cage or a semisubmersible fish cage, have been conducted by many researchers. The main purpose also includes the investigation of the deformation of the fish net, which is slightly different from that in a towing test of the fish net panel. Lader and Enerhaug (2005) carried out an experiment of a gravity fish cage with a scale ratio of 1:7.1 in uniform current in a water channel driven by four impellers, as shown in Fig. 4. Three different sets of weights with cylindrical shapes made of steel were used in the experiment. The tension in the mooring lines was measured by load cells, and simultaneously, the deformation of the cylindrical net was captured by cameras. The dependency between the forces and the geometry and the effects of the weights on it were the main focus. Kristiansen et al. (2015) performed a model test of a floating fish cage in current in a towing tank, as shown in Fig. 5. The current was simulated by running a towing carriage in calm water. Experimental Techniques of Aquaculture Structures in Waves Experimental Study of Hydrodynamic Forces on a Fish Net Panel in Waves

Uncertainties exist if the empirical formula that was developed based on towing experimental data is utilized for predicting the hydrodynamic forces acting on a fish net in waves. Therefore, many researchers have conducted experimental investigations on the hydrodynamics of fish nets in waves. In the experiment, the fish net panel is normally pretensioned in a rectangular steel

A

44

Aquaculture Structures: Experimental Techniques

Aquaculture Structures: Experimental Techniques, Fig. 1 Experiment apparatus on the hydrodynamic forces of copper nets with different solidities (Tsukrov et al. 2011)

hydrodynamic forces acting on the net panel are measured simultaneously. Compared with the model in the current-only case, two new key parameters should be considered, i.e., the Keulegan–Carpenter (KC) number and wave steepness. These parameters can be written as KC ¼

Aquaculture Structures: Experimental Techniques, Fig. 2 Field test apparatus on the drag forces acting on both clean and biofouled net panels (Swift et al. 2006)

framework and then fixed in a water channel. By generating regular or random waves, the wave elevation before and after the net and the

pH H , s¼ D L

ð3Þ

where H and L refer to the wave height and wavelength, respectively, and D represents the net twine diameter. Song (2006) performed an experimental study on the effect of horizontal regular waves on fish net panels, as shown in Fig. 6. By using dual series relations, a least squares approximation, and a multiple stepwise regression analysis, this scholar established an empirical relation between the horizontal wave force and the wave period and wave height. Lader et al. (2007) conducted a very similar experiment and measured the forces acting on

Aquaculture Structures: Experimental Techniques

45

Aquaculture Structures: Experimental Techniques, Fig. 3 A biofouled net panel (Swift et al. 2006)

net panels with three different solidity ratios when exposed to five different regular wave cases, as shown in Fig. 7. The measurements were compared with three different empirical load models, i.e., a simple drag model, the Aarsnes model, and the Tsukrov model. The simple drag model yielded the best results for two of the net cases for the horizontal forces, while the Aarsnes model gave the best results for the high solidity net. For the vertical force, the Tsukrov model provided the best results.

A

Experimental Study of Hydrodynamic Forces on a Semi-Submerged Cylinder in Waves

In addition to the fish net, the gravity fish cage also contains a floating collar, which is the main structure resisting wave loads. Slender structures float on the free water surface and continuously undergo locomotion and elastic deformation in waves and current. Although the floating collar is usually made of a circular cylinder and substantial experimental data based on Morison equations are available for the circular cylinder’s

Aquaculture Structures: Experimental Techniques, Fig. 4 Deformation of the net cylinder for different weigh configurations and current velocities in a water channel (Lader and Enerhaug 2005)

46 Aquaculture Structures: Experimental Techniques

Aquaculture Structures: Experimental Techniques

47

A

Aquaculture Structures: Experimental Techniques, Fig. 5 Deformation of the gravity fish cage from towing test in calm water (Kristiansen et al. 2015)

Aquaculture Structures: Experimental Techniques, Fig. 6 Experimental study of fish net panels in regular waves (Song 2006)

hydrodynamic coefficients, it is still difficult to accurately predict the hydrodynamic forces on the floating collar due to its particularities compared with the fully immersed circular cylinder, i.e., the free surface effect.

To understand the hydrodynamic characteristics of floating cylinders, Kristiansen and Faltinsen (2008) conducted research on wave loads on a fixed circular cylinder and the heave and sway motion of a floating cylinder in regular

48

Aquaculture Structures: Experimental Techniques

Aquaculture Structures: Experimental Techniques, Fig. 7 Experiment study of hydrodynamic forces acting on net panel under regular wave (Lader et al. 2007)

Aquaculture Structures: Experimental Techniques, Fig. 8 Experimental study on the wave loads on a cylinder (Kristiansen and Faltinsen 2008)

waves in a wave flume shown in Figs. 8, 9, and 10. In such experiments, the circular cylinder segment model can be fixed or elastically restrained by mooring lines with a specified water depth. As the model is fixed, the main objective is to focus on nonlinear effects such as wave overtopping on the models and how such events influence the wave loads. The experiment makes significant

contributions to the design of gravity fish cages with partially submerged floating collars. Experimental Study of the Dynamic Response of Fish Cages in Waves

Experimental studies of the dynamic response of a whole fish cage model in waves are essential for the design of aquaculture structures. A physical

Aquaculture Structures: Experimental Techniques

49

A

Aquaculture Structures: Experimental Techniques, Fig. 9 Photos of a partially submerged cylinder in waves (Kristiansen 2010)

Aquaculture Structures: Experimental Techniques, Fig. 10 Model test of gravity fish cages containing floating tubes (Shen et al. 2018)

model normally contains the fish cage, and the mooring system is arranged in an ocean basin. Regular or irregular waves can be generated by wave makers. The motions of the fish cage model and the tensions in the mooring lines were measured, providing important test data to validate the accuracy of the numerical methods. The procedure is quite similar to that for traditional marine structures. The main difference is the existence of a super-flexible fish net. The physical model of traditional marine structures, such as ocean

platforms or ships, is considered to be a rigid body, and wave actions are dominated by diffraction and mass forces. However, the fish net encounters very large deformations, and the viscous force is dominant. Many researchers have conducted various experimental studies on the wave-induced response of different types of fish cages, such as the gravity fish cage, semi-submersible fish cage, and closed flexible cage. Nygaard (2013) carried out a model test of gravity fish cages containing

50

Aquaculture Structures: Experimental Techniques

Aquaculture Structures: Experimental Techniques, Fig. 11 Model test of a gravity fish cage (Shen et al. 2018)

Aquaculture Structures: Experimental Techniques, Fig. 12 Model test of a semi-submersible fish cage (Zhao et al. 2019)

floating tubes, an elastic sinker tube, a cylindrical net cage, and a mooring system with a scale ratio of 1:16 in irregular wave, regular wave, and current-only cases, as shown in Figs. 10 and 11. Eight linear accelerometers were arranged to capture the deformation of the floating tubes. In addition, axial force transducers were used to measure

the tensions in the mooring lines. Zhao et al. (2019) performed an experimental study of the hydrodynamic characteristics of a semi-submersible fish cage in waves with different wavelengths, as shown in Fig. 12. The motion response and the mooring line tension are measured and used to verify the rationality of the numerical model.

Aquaculture Structures: Experimental Techniques

51

A

Aquaculture Structures: Experimental Techniques, Fig. 13 Model test of a closed flexible bag (Lader et al. 2017)

Lader et al. (2017) investigated the behavior of closed flexible bags experimentally which is a very new and novel design proposed due to increasing environmental considerations as salmon lice, escape of farmed fish, and release of nutrients. Three different bag shapes with a scale ratio of 1: 30 in Fig. 13 were studied: cylindrical, spherical, and elliptical. The response in vertical direction and the tension in the mooing line were measured simultaneously. The deformation of the bag was only recorded qualitatively by using cameras in the test, and no quantitative data were derived from the images. Forced Oscillation Experiment of Aquaculture Structures It is hard to get large KC number as real sea state via traditional wave making method. Currently, two ways are available for this problem: one is to force the model harmonically oscillating in still water; another is to fix the model in the oscillatory flow in a U-shaped water tunnel. The latter one is very creative and widely used for the fully immerged cylinder in oscillatory flow. Yet for the cylinder floating on the free surface, e.g., floating collars of the fish farming structures, the waves and current will be always co-existent (where current generally maintains a quite large velocity and hence becomes non-negligible); thus, the wave making and overtopping on the cylinder should be taken into consideration. As the U-shaped water tunnel cannot simulate the free

surface, the first experimental method is presently introduced. Specifically, the forced oscillation of the cylinder fixed on the free surface is used to simulate the water particle motions around the floating cylinder in waves; and the forward towing of the cylinder is used to simulate the steady current speed, so that the effect of the wave making and overtopping can be easily achieved in the experiment. Fu et al. (2013) and Ren et al. (2019) investigated the hydrodynamic characteristics of the segment model of a floating collar and floater-net system in oscillatory and steady flows through forced oscillation experiments in a towing tank, as shown in Fig. 14. The Reynolds number is from 0.5 105 to 7.5 105, and the KC number varies from 6.28 to 37.70. The effects of KC number, Reynolds number, reduced velocity, and overtopping phenomenon on the drag and inertia force coefficients are studied. Also, hydrodynamic forces on the floater and net are compared in detail to analyze their respective contributions to the total drag force.

Key Applications Experiment of a Fish Net Panel in Waves and Current An extensive model test of a single net panel in current-only and combined wave and current conditions was performed by J.V. Aarsnes, H. Rudi,

52

Aquaculture Structures: Experimental Techniques

Aquaculture Structures: Experimental Techniques, Fig. 14 Forced oscillation experiment of a partially submerged floating collar (Fu et al. 2013; Ren et al. 2019) Aquaculture Structures: Experimental Techniques, Fig. 15 Model test of a single net panel (Løland 1991)

rotatable net panel

Fx

Fy

force transducer

current

stift frame

and G. Loland (Aarsnes et al. 1990) at the Ocean Basin Laboratory of Marintek. The experimental apparatus is shown in Fig. 15. The tests were run in a towing tank by mounting the physical model with six different incident angles on the towing carriage. Three different constant towing speeds were used. A full-scale net with dimensions of 1.5 1.5 m and six different solidity ratios was used. A total of 108 possible combinations were carried out for the current-only condition. In the combined wave and current condition, different wave heights, wave periods, and current velocities were used. During the test, the hydrodynamic

exchangeable net panel 1.5x 1.5 m

forces acting on the net panel in the normal and tangential directions were measured, which were named the drag and lift forces. By using the experimental data, the drag and lift force coefficients can then be derived by using, for instance, the least squares method, and the empirical relations between the hydrodynamic force coefficients, and the solidity ratios and incident angle can be established, as shown in Eq. 1. As the flow passes through the fish net, the velocity decreases significantly due to the shielding effect. The quantification of the velocity

Aquaculture Structures: Experimental Techniques

reduction is very important for the numerical analysis of the whole fish cage. Therefore, in the model test of the single net panel, the velocity distribution behind the net was also measured, as shown in Fig. 16. An empirical function between the current velocity reduction factor and the drag coefficient was proposed.

53

Experiment of a Gravity Fish Cage in Waves and Current A model test of a gravity fish cage was carried out by Nygaard et al. at the Ocean Basin Laboratory of Marintek as shown in Figs. 17 and 18. The physical model featured all the main components in a real full-scale gravity fish cage used in

Aquaculture Structures: Experimental Techniques, Fig. 16 Experimental apparatus on the velocity distribution behind a net panel (Løland 1991)

Aquaculture Structures: Experimental Techniques, Fig. 17 The experimental arrangement of a gravity fish cage (Shen et al. 2018)

Aquaculture Structures: Experimental Techniques, Fig. 18 From left to right: the gravity fish cage model, the floating collars, the elastic sinker tube, and the buoy (Shen et al. 2018)

A

54

Norway, including the floating collars, a fish net cage, an elastic sinker tube, a center point weight, and a mooring system. The mooring system is quite complex and is composed of bridle lines, anchor lines, mooring frame lines, buoys, coupling plates, and anchor lines. The scale ratio is 1:16, and Froude scaling with geometric similarity except for the net twines was adopted. For the net twines, the diameter is too small, and the geometric similarity is almost impossible to satisfy. Only the solidity ratio was designed to be the same as the real-scale structure to ensure the similarity of the hydrodynamic forces acting on the fish net. A comprehensive measurement system was arranged during the experiment, which includes eight linear accelerometers, fourteen force transducers, and three wave gauges. The tension forces in the bridle lines, anchor lines, ropes connecting the buoy and coupling plate, ropes connecting the sinker tube and net, and ropes in the net cage were measured simultaneously. Furthermore, the motion response and the deformation of the floating collar were captured by using accelerometers. The dynamic response of the gravity fish cage under long-crested irregular Aquaculture Structures: Experimental Techniques, Fig. 19 The experimental apparatus for forced oscillation of a floater-net system (Fu et al. 2014)

Aquaculture Structures: Experimental Techniques

waves, regular waves, and current-only cases was studied. Force Oscillation Experiment of Floater-Net System A forced oscillation experiment of floater-net system was carried out by Fu et al. (2014) in a towing tank in Shanghai Ship and Shipping Research Institute in China, which is 192 m long, 10 m wide, and 4.2 m deep; and the maximum velocity of the towing carriage is 9 m/s. The experimental apparatus includes the towing carriage, the forced oscillation apparatus, and a cylinder model, as shown in Fig. 19. The horizontal track length is 3.5 m and the diameter of cylinder is 0.25 m. The 2 m long smooth cylinder model is manufactured by polypropylene material and installed on the forced oscillation apparatus, passing through two three-component force transducers in use to measure the hydrodynamic force of the floater-net system, as shown in Fig. 2. The model will harmonically oscillate in horizontal direction driven by a servo motor. Oscillating displacement and velocity are controlled according to the experimental design and measured by the encoders of the servo-motor.

Aquaculture Structures: Experimental Techniques

55

A

Aquaculture Structures: Experimental Techniques, Fig. 20 The arrangement of the measurement system (Fu et al. 2014)

The net is manufactured by nylon material and is 2 m wide and 3.5 m length. The netting is knotless with a mesh size of 20 mm and twine thickness of 2 mm. Mounted as square meshes, the solidity ratio of the netting is 0.4. The net structure is supported by a slender steel rod which is installed on three-component force transducers used to measure the force of net structure, as shown in Fig. 20.

Cross-References ▶ Aquaculture Structures: Numerical Methods ▶ Modern Aquaculture Structures ▶ Net Structures: Biofouling and Antifouling ▶ Net Structures: Design ▶ Net Structures: Hydrodynamics ▶ Traditional Aquaculture Structures

References Aarsnes JV, Rudi H, Løland G (1990) Current forces on cage, net deflection. In: Engineering for offshore fish farming. T. Telford, London Fu S, Xu Y, Hu K, Zhang Y (2013) Experimental investigation on hydrodynamics of floating cylinder in oscillatory and steady flows by forced oscillation test. Mar Struct 34:41–55

Fu S, Xu Y, Hu K (2014) Experimental investigation on hydrodynamic of a fish cage floater-net system in oscillatory and steady flows by forced oscillation tests. J Ship Res 58 Kristiansen D (2010) Wave induced effects on floater of aquaculture plants. PhD. Norwegian University of Science and Technology Kristiansen D, Faltinsen OM (eds) (2008) 27th international conference on offshore mechanics and arctic engineering, Estoril Kristiansen D, Lader P, Jensen Ø, Fredriksson D (2015) Experimental study of an aquaculture net cage in waves and current. China Ocean Eng 29:325–340 Lader PF, Enerhaug B (2005) Experimental investigation of forces and geometry of a net cage in uniform flow. IEEE J Ocean Eng 30:79–84 Lader PF, Olsen A, Jensen A, Sveen JK, Fredheim A, Enerhaug B (2007) Experimental investigation of the interaction between waves and net structures – damping mechanism. Aquac Eng 37:100–114 Lader PF, Fredriksson DW, Volent Z, Decew JC, Rosten TW, Strand IMJJoOM, Engineering A (2017) Wave Response of Closed Flexible Bags. J Offshore Mech Arctic Eng 139:051301.051301–051301.051309 Løland (1991) Current forces on and flow through fish farms. The Norwegian Institute of Technology Nygaard I (2013) Merdforsøk. kapasitets-tester. interaksjon mellom not og utspilingssystem. Tech Rep. Norsk Marinteknisk Forskningsinstitutt AS Ren H, Xu Y, Zhang M, Deng S, Li S, Fu S, Sun H (2019) Hydrodynamic forces on a partially submerged cylinder at high Reynolds number in a steady flow. Appl Ocean Res 88:160–169 Shen Y, Greco M, Faltinsen OM, Nygaard I (2018) Numerical and experimental investigations on mooring loads

56 of a marine fish farm in waves and current. J Fluids Struct 79:115–136 Song W (2006) Experimental study on the effect of horizontal waves on netting panels. Fisheries Science Swift MR, Fredriksson DW, Unrein A, Fullerton B, Patursson O, Baldwin K (2006) Drag force acting on biofouled net panels. Aquac Eng 35:292–299 Tsukrov I, Drach A, DeCew J (eds) (2011) 30th international conference on ocean, offshore and arctic engineering. Rotterdam, The Netherlands Zhao Y, Guan C, Bi C, Liu H, Cui Y (2019) Experimental investigations on hydrodynamic responses of a semisubmersible offshore fish farm in waves. J Marine Sci Eng 7

Aquaculture Structures: Numerical Methods Yugao Shen1 and Yuwang Xu2,3 1 Department of Marine Technology, Centre for Autonomous Marine Operations and Systems (AMOS), Norwegian University of Science and Technology (NTNU), Trondheim, Norway 2 School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China 3 State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China

Synonyms Computational fluid dynamics (CFD); Finite element method (FEM); Hydroelasticity theory; Modal superposition method; Morison-force model; Screen-force model

Definition For aquaculture structures, numerical analysis with proper methods is essential for safe structural design. In a numerical method for aquaculture system, a structural model and a hydrodynamicforce model are needed to describe the structure and evaluate the loads on the structure, respectively. A typical fish-farm system comprises different components, and numerical method for each individual component is required.

Aquaculture Structures: Numerical Methods

Scientific Fundamentals Traditional Fish-Farm Concepts There exist a variety of fish-farm concepts, and these concepts can be classified in different ways. For example, Loverich and Gace (1997) classified sea cages into four types based on the structural means used to hold the shape of the cage, i.e., gravity cages, anchor-tension cages, semi-rigid cages, and rigid cages. The gravity cages are by far the most widely used concepts in the fish farming industry and thus are explained in detail here. They rely on the force of gravity to maintain net volume, by providing a surface buoyancy system and an underwater weighting system for the net. There exist different materials and geometries of the buoyancy system. The most commonly used are the circular plastic floaters and the interconnected hinged steel floaters, as shown in Fig. 1. The cage with circular plastic floaters has been widely investigated; thus a detailed description is given here. The cage typically comprises a floating collar, a net cage, a sinker tube, and a mooring system. The floating collar provides buoyancy for the whole system and is common with two nearly semi-submerged concentric circular tubes. The two tubes are held together by steel brackets. The usage of the net is to protect the fish from predators and provide a suitable habitat. The net is highly flexible, so it will experience deformation when subjected to external loads from waves and current. A bottom weight ring (sinker tube) is often attached to the cage bottom to ensure sufficient volume of the net cage. In reality, there exist multiple cages at real sites with cages arranged in mooring grid in single or double rows. This will have an influence, for instance, on the steady inflow (current) due to the shadowing effects from the upstream cages, compared with a single cage system. The mooring system normally used by the circular cages is a square-shaped grid system held on the seabed with an array of mooring lines. The mooring lines include the anchors, ground chains, ropes and related shackles, and buoys (Shen 2018).

Aquaculture Structures: Numerical Methods

57

A

Aquaculture Structures: Numerical Methods, Fig. 1 Left: circular plastic cage. Right: hinged square steel cages. (Source: www.akvagroup.com/news/image-gallery)

Novel Fish-Farm Concepts There exit multiple challenges for the fish-farm industry nowadays. One of the big problems has been the rise of sea lice. It has become increasingly serious as the sea lice have become more resistant to chemicals used to treat them. Escaped fish is another concern. In addition, due to limited nearshore area and increasing impact to the local ecosystem, the aquaculture industry is trying to move the marine fish farms from nearshore to more exposed sea regions where waves and current are stronger. To meet the challenges faced by the fish-farm industry, new fish-farm designs are emerging. Closed fish-cage concepts are proposed to have a better control over the water quality and especially to avoid the problem of salmon lice. New open-cage fish-farm concepts are also under development to operate in more exposed sea regions or even in open sea, by combining the best of existing technology and solutions from the Norwegian fish farming industry and the offshore oil and gas sector (Shen 2018). Historical Development (Traditional Fish Farms) Many numerical and experimental investigations have been performed during the past decades to examine the behavior of traditional aquaculture fish farms under waves and current. The fact that the netting may have ten million meshes limits the implementation of computational fluid dynamics (CFD) and complete structural modeling. Therefore, rational simplifications are often needed. Important literatures for the modeling of the

different components of a traditional fish-farm system will be introduced. The focus will be on the structural and hydrodynamic modeling of the floating collar and the net cage. The Floating Collar

The floating collar of a sea-cage is typically composed of two concentric elastic pipes interconnected by brackets and a handrail. The structure is often modeled into a single or double column pipe without the handrail. When estimating the hydrodynamic loads on the floater, rigid body is commonly assumed and strip theory is adopted, disregarding important three-dimensional (3D) flow, frequencydependency hydrodynamic coefficients, as well as nonlinear effects in steep waves. Modified Morison’s equation (Brebbia and Walker 1979) was widely employed to calculate the load on each collar segment (see Fig. 2), for example, by Huang et al. (2006), Zhao et al. (2007a), Dong et al. (2010a), and Cifuentes and Kim (2017). Dong et al. (2010b) tried to incorporate the elasticity of the floater into the modeling and proposed an analytical method to analyze the elastic deformations of a circular ring in waves. The governing equations of six degree-offreedom rigid-body motions and elastic deformations were obtained according to Euler’s laws and curved beam theory. Faltinsen (2011) pointed out that the diffraction and radiation effects may matter for the response of the floater. He derived an analytical formula for the added mass for different modal of an elastic floater based on a slender body theory

58

Aquaculture Structures: Numerical Methods

Aquaculture Structures: Numerical Methods, Fig. 2 Left: a sketch of the float-collar system. Right: a sketch of the float collar mini-segment (Dong et al. 2010a)

and rigid free-surface condition. Li and Faltinsen (2012) calculated the vertical added mass, damping and wave excitation loads on an elastic semi-submersible torus based on low-frequency slender-body theory. They found that threedimensional (3D) flow, hydroelasticity, and strong hydrodynamic frequency dependency matter on the scale of the torus. The structural response of the floater was modeled using the principle of modal superposition. The numerical model from Li and Faltinsen (2012) was further adopted to investigate vertical accelerations of a moored floating elastic torus without netting in regular waves (Li et al. 2016, 2018b), an aquaculture net cage with floater in regular waves and current (Kristiansen and Faltinsen 2015), and a realistic marine fish farm in waves (both regular and irregular) and current (Shen et al. 2018). Commercial structural software could also serve as an alternative tool to investigate the deformation of the floating collar. For example, Fu et al. (2007) used the extended threedimensional (3D) hydroelasticity theory to predict the hydroelastic response of flexible floating interconnected structures, including displacement and bending moments under various conditions. The finite element method (FEM) solver ABAQUS was used as the eigen-solver. Fu and Moan (2012) applied the same theory in the frequency domain to predict the dynamic response of the 5-by-2 floating fish-farm collars in regular waves. Liu et al. (2019) evaluated the structural

strength and failure for floating collar of a singlepoint mooring fish cage based on FEM solver ANSYS. Computational fluid dynamics (CFD) calculations were also performed to calculate the hydrodynamic loads on the floater. For instance, Kristiansen (2010) presented model test results in two-dimensional (2D) flow conditions of a semi-submerged floater without netting in regular waves and validated a CIP (Constrained Interpolation Profile)-based finite difference method that solved Navier-Stokes equations for laminar flow. Similar approach was implemented by Bardestani (2017) to investigate the snap loads in the netting in two-dimensional conditions in waves. The Sinker Tube

The sinker tube can be modeled in a similar way as the floating collar. For instance, the structure can be described by the curved beam equations, and the hydrodynamic loads can be estimated by the modified Morison’s equation (Shen et al. 2018). The Net Cage

In order to analyze a net in current and waves, one needs a structural model and a hydrodynamic force model. In structural analysis of nets, it is difficult to fully simulate the strong fluid–structure interaction between moving seawater and the highly flexible net. To reduce complexity, the nets are often represented by some equivalent

Aquaculture Structures: Numerical Methods

structural elements, e.g., truss, beam, cable, or spring elements. To guarantee that equivalent twine has the same drag force, buoyancy, gravity, and stiffness as the original netting, the equivalent element is given a certain length and diameter such that it has the same projected area as the physical net it represents. In this way, the number of twines can be reduced to a great extent. For the hydrodynamic loads acting on the net, although computational power has increased significantly, it is still not practical to apply CFD approach to simulate the full nets system with order of ten million. Two main types of hydrodynamic-force models are typically applied to predict viscous loads on nets, i.e., Morison model and screen model. The first method is to model the net as individual knots and twines, calculating the total drag on the net as sum of the drag contributions of individual elements, without considering the interaction between twines. Morison’s equation is used to calculate the crossflow force on each twine based on cross-flow principle. There are two limitations for the Morison model: (1) a drag model based on the crossflow principle cannot be justified when the inflow angle is larger than about 450 and (2) the interaction between the twines is not accounted for. The second method is to assume that the net is made of surface elements with properties accounting for the underlying twine and knot structure. The hydrodynamic force is decomposed into a normal and a tangential force component on the net panel (Kristiansen and Faltinsen 2012).

59

The Morison-force model: The literatures described next applied Morison-force model with different structural modeling. Theret (1993) proposed an original 3D numerical model for modeling fishing nets in steady current using rigid cylindrical bar/truss elements. Bessonneau and Marichal (1998) generalized the method proposed by Theret (1993) to investigate the steady shape of submerged trawl nets. The rigid net twines were further divided into two subelements, allowing the twines to buckle/loose when subjected to compression (see Fig. 3). The mesh grouping method was proposed to reduce the number of unknowns in which several actual meshes were grouped into a fictitious equivalent mesh having the same specific mass, apparent weight, and approximately the same drag resistance. Li et al. (2006) developed a numerical model, based on a mass-spring method (see Fig. 4) to investigate the hydrodynamic behavior of submerged plane nets in current. The method is similar to Bessonneau and Marichal (1998), except considering also the netting elasticity. The fishing nets were modeled as a series of lumped point masses that were interconnected with springs without mass. The model was validated and applied to several other problems, such as a three-dimensional cage with rigid floater in current (Zhao et al. 2007a), in combined regular waves and current (Zhao et al. 2007b) and in irregular waves (Dong et al. 2010a). The method was also implemented to the analysis of

Aquaculture Structures: Numerical Methods, Fig. 3 Decomposition of rigid elements of diamond mesh nettings (Bessonneau and Marichal 1998)

A

60

Aquaculture Structures: Numerical Methods

Aquaculture Structures: Numerical Methods, Fig. 4 The schematic diagram of the mass-spring model (Li et al. 2006)

hydrodynamic behavior of multiple cages in combined wave-current flow (Xu et al. 2013). Similar strategy was chosen by Lee et al. (2008) to simulate a fish cage system subjected to current and waves. Tsukrov et al. (2003) showed that hydrostatic and hydrodynamic forces exerted on the moving netting, including wave and current-related water motion, cannot be exactly represented by equivalent structural elements. They developed a special consistent net element to model net panels or their parts. The method was further applied, for instance, to the analysis of a four-cage grid mooring for open ocean aquaculture (Fredriksson et al. 2003, 2004), the prediction of the dynamic response of a single-point moored submersible fish cage under currents (DeCew et al. 2010), and the evaluation the distribution of tension in a two-dimensional net panel (Fredriksson et al. 2014). Commercial FEM program could also be used to analyze the deformation of the net twines. For example, Gignoux and Messier (1999) proposed an algorithm based on the introduction of the mapping coefficient and successfully applied the model to aquaculture nets using ABAQUS/Aqua beam elements. Moe et al. (2010) used ABAQUS to analyze the deformation of a net cage in currents. ABAQUS was also employed to analyze nonlinear hydroelastic of an aquaculture system, subjected to current, regular, and irregular waves (Li et al. 2013a, b).

The screen-force model: The literatures next describe the development of screen-force models, which are gaining increasingly attention. Schubauer et al. (1950) derived theoretical models based on experimental data for the normal and tangential forces acting on screens inclined to steady ambient flow. The examined inclination angle varies between 0 and 45 . Milne (1972) derived an empirical formula for the drag coefficient of plane nets in a steady current as a function of net geometry. Løland (1991) presented empirical formulas for the drag and lift on planar net panels, known as Løland’s formulas. The drag and lift coefficients were given as function of solidity ratio and inflow angle for a limited range of solidity ratio (0.13–0.317). The solidity ratio of a screen is the ratio of the area projected by the screen on a plane parallel to the screen, to the total area contained within the frame of the screen. The inflow angle is the angle between current velocity and the normal direction of net panel. The coefficients in the formulas were determined by curve fitting experimental data from Rudi et al. (1988) obtained by towing net panels. Lader et al. (2003) proposed a dynamic model for 3D net structures exposed to waves and current, based on a super-element formulation. In the method, the net structure was divided into foursided super-elements interconnected in each corner node (see Fig. 5). The hydrodynamic and structural forces were calculated on each super-

Aquaculture Structures: Numerical Methods

61

A

Aquaculture Structures: Numerical Methods, Fig. 5 Super-element. Left: element area. Right: the structural model of the element. Node numbers are indicated in circles and spring numbers in squares (Lader et al. 2003)

element, and the total forces were collected in each node where the equations of motion were solved. The hydrodynamic forces on each superelement were calculated based on empirical formulas from Løland (1991). The structural forces were calculated by assuming that each element consists of six nonlinear springs, interconnecting each node to the other three. The super-element method was further utilized to calculate the responses of a flexible net sheet in waves and current (Lader and Fredheim 2006). Huang et al. (2006) developed a numerical model to simulate the dynamic properties of a net cage system in current based on a screenforce method. In their model the net cage was divided into several plane surface elements to calculate the external forces. The external force was calculated on each element and then equally distributed to its nodes. The drag and lift force coefficient for the net plane was based on the Løland’s formulas (Løland 1991). The screen model proposed by Løland (1991) was further generalized by Kristiansen and Faltinsen (2012), taking into account also the effect of Reynolds number, i.e., the force components on a panel are functions of solidity ratio, inflow angle, and Reynolds number. The relevant Reynolds number is that based on the physical twine diameter. A uniform turbulent wake was assumed inside the cage based on the theoretical

formula proposed by Løland (1991) for cross-flow past a plane net, leading to a flow reduction in the rear part of the net cage. The dynamic elastic truss model by Marichal (2003) was used to describe the net structure. The screen-force model was further adopted to investigate an aquaculture net cage with floater in regular waves and current (Kristiansen and Faltinsen 2015), a realistic marine fish farm in waves (both regular and irregular) and current (Shen et al. 2018), the influence of well boat on aquaculture system (Shen et al. 2019a, b), and the influence of fish in a net cage on mooring loads (He et al. 2018). Recently, Cheng et al. (2020) presented a systematic review of hydrodynamic models for the net cage, including five Morison models and six screen models. All the models were incorporated into a general finite element (FE) solver for comparison purpose and suggestions for selection of suitable hydrodynamic models were provided. Computational fluid dynamics (CFD): With the increasing computer resources, growing attention is paid to implement the computational fluid dynamic (CFD) approach to evaluate the flow inside and around a fish cage. During CFD simulations, the net is modeled as a porous media with the influence of the net represented by a resistance term, neglecting the detailed geometry of the net structure. The corresponding resistance coefficients can be obtained from empirical formulas

62

(Morison model and screen model) or laboratory experiments. For instance, Shim et al. (2009) investigated the flow through and around a circular cylinder cage using the commercial software Fluent. The net and frame were represented by a porous jump boundary condition, and the pressure drop coefficients were determined through towing tests. Similar approach was adopted by Patursson et al. (2010) and Zhao et al. (2013) to model the flow around a fixed net panel. Attempts have also been made to take the influence of the structural deformation into consideration by coupling the structural model with the porous media model to achieve fluid–structure interaction (FSI) analysis (see Bi et al. (2014a, b) and Yao et al. (2016) for the net under steady current and Chen and Christensen (2017) and Bi et al. (2017) for the net under waves). The Mooring System

The complete set-up of the mooring system typically comprises ropes and chains, with buoys to support all mooring lines. The buoys are floating circular cylinders and can be modeled by classical seakeeping theory (see Endresen et al. (2014)). Ropes and chains can be treated in a similar way as the net and modeled as elastic trusses/beams with correct diameter, weight, and stiffness. The hydrodynamic forces on the mooring lines can be estimated by a modified Morison’s equation based on the cross-flow principle (Shen 2018). Historical Development (Novel Fish Farms) As mentioned, the expansion of nearshore fish farming becomes difficult due to limited space and increased environmental impact. This drives the growth of offshore fish farming. Several new open-cage fish-farm concepts have been designed and tested to operate in offshore sites. Closed fishcage concepts are also under development to get rid of salmon lice. Important numerical investigations performed recently for these concepts will be described in the following. Open-Cage Fish Farm

To withstand large wave actions, offshore fish farms are generally with large floating structures,

Aquaculture Structures: Numerical Methods

constructed from steel. These structures can in many ways be compared to platforms from oil and gas industry. Thus, numerical analyses can be conducted through a combination of the same kind of procedures as for offshore platforms and the approach for the fish net. Bore and Fossan (2015) performed ultimate and fatigue limit state analyses of ocean farming’s rigid offshore aquaculture structure. The concept consists of a twelve-sided, cylindrically shaped frame with a net attached to (stretched over) the sides and bottom. This makes up the hull and the fish cage. A Morison model was used for calculation of hydrodynamic forces on all the components. Similar structure was considered by Shi (2019), but with slight modification to operate in Chinese ocean. Morison equation was applied to estimate the viscous loads on slender members. For the pontoon with large dimension, the radiation and diffraction effects may matter; thus the corresponding hydrodynamic forces were evaluated based on a linear potential theory. Li and Ong (2017) presented a preliminary study of a rigid semi-submersible fish farm for open seas. The farm comprises a lower and upper pontoon with vertical and diagonal bracing in between. The net cage is connected with the lower pontoon and is totally submerged to avoid large wave loads close to the surface. The linear hydrodynamic properties for support structures using different composite models with panel and Morison elements were computed. The nets were simplified as rigid slender elements. This simplification neglects the net deformations and may overestimate the hydrodynamic forces and viscous effects from the nets. Based on the hydrodynamic analysis, linearized frequency-domain and coupled timedomain analysis were performed to predict the extreme motions of the support structure and the extreme tensions in the mooring lines. Similar approach was followed by Li et al. (2018a) to investigate a vessel-shaped offshore fish farm under various wave and current conditions. The effect of current velocity reduction due to shielding effects from upstream cages was also discussed.

Aquaculture Structures: Numerical Methods

Closed-Cage Fish Farm

Closed fish cages can be divided into flexible cages, semi-flexible cages, and rigid. They have typically a vertical symmetry axis at rest. The water inside a closed cage causes statically destabilizing roll and pitch moments. Waveinduced sloshing (interior wave motion) becomes an issue as well-known from many engineering applications. Since marine applications involve relatively large excitation amplitudes, resonant sloshing can involve important nonlinear freesurface effects. The viscous boundary layer damping is very small. However, if breaking waves occur, the associated hydrodynamic damping is not negligible (Faltinsen and Shen 2018). Linear response of a 2D closed flexible fish cage in waves was investigated by Strand and Faltinsen (2019). The motion of the membrane was represented as the sum of rigid body motions and Fourier series with zero displacement at the attachment to the floater. Linear frequencydomain potential flow theory of incompressible water was used both for the interior and external flows. Strong coupling between elastic modes and rigid body motions was observed. The approach was extended to investigate linear wave-induced dynamic structural stress of a 2D semi-flexible closed fish cage (Strand and Faltinsen 2020). They compared a quasi-static analysis with a fully coupled hydroelastic analysis to examine the soundness of assuming that the stresses in the structure is quasi-static. They found that the necessity of performing a hydroelastic analysis depends on the stiffness of the structure. Kristiansen et al. (2018) conducted a numerical and experimental study on the seakeeping behavior of a floating closed rigid fish cage with cylindrical shape. The focus was on effects of sloshing on the coupled motions and mooring loads. Dedicated scaled model tests of closed cages in waves were presented and compared with numerical simulations using linear potential theory in frequency domain. The results showed that the influence of sloshing on the rigid body motion was significant. Mean wave loads were also affected by sloshing. Similar

63

cage concept was examined by Tan et al. (2019). The sloshing inside the cage was described by the single-dominant nonlinear multimodal theory presented in Faltinsen and Timokha (2009). They demonstrated that the nonlinear swirling waves due to the interactions between different sloshing modes could only be explained by a proper nonlinear theory.

Cross-References ▶ Aquaculture Structures: Experimental Techniques ▶ Modern Aquaculture Structures ▶ Net Structures: Hydrodynamics ▶ Traditional Aquaculture Structures

References Bardestani M (2017) A two-dimensional numerical and experimental study of a floater with net and sinker tube in waves and current Bessonneau J, Marichal D (1998) Study of the dynamics of submerged supple nets (applications to trawls). Ocean Eng 25(7):563–583 Bi C-W, Zhao Y-P, Dong G-H, Xu T-J, Gui F-K (2014a) Numerical simulation of the interaction between flow and flexible nets. J Fluids Struct 45:180 Bi C-W, Zhao Y-P, Dong G-H, Zheng Y-N, Gui F-K (2014b) A numerical analysis on the hydrodynamic characteristics of net cages using coupled fluidstructure interaction model. Aquac Eng Bi C-W, Zhao Y-P, Dong G-H, Xu T-J, Gui F-K (2017) Numerical study on wave attenuation inside and around a square array of biofouled net cages. Aquac Eng 78:180–189 Bore PT, Fossan PA (2015) Ultimate-and fatigue limit state analysis of a rigid offshore aquaculture structure. NTNU Brebbia CA, Walker S (1979) Dynamic analysis of offshore structures. Newnes-Butterworths, London Chen H, Christensen ED (2017) Development of a numerical model for fluid-structure interaction analysis of flow through and around an aquaculture net cage. Ocean Eng 142:597–615 Cheng H, Li L, Aarsæther KG, Ong MC (2020) Typical hydrodynamic models for aquaculture nets: a comparative study under pure current conditions. Aquac Eng 90:102070 Cifuentes C, Kim MH (2017) Hydrodynamic response of a cage system under waves and currents using a Morisonforce model. Ocean Eng 141:283–294

A

64 DeCew J, Tsukrov I, Risso A, Swift M, Celikkol B (2010) Modeling of dynamic behavior of a single-point moored submersible fish cage under currents. Aquac Eng 43(2):38–45 Dong G-H, Xu T-J, Zhao Y-P, Li Y-C, Gui F-K (2010a) Numerical simulation of hydrodynamic behavior of gravity cage in irregular waves. Aquac Eng 42(2): 90–101 Dong G-H, Hao S-H, Zhao Y-P, Zong Z, Gui F-K (2010b) Elastic responses of a flotation ring in water waves. J Fluids Struct 26(1):176–192 Endresen PC, Birkevold J, Føre M, Fredheim A, Kristiansen D, Lader P (2014) Simulation and Validation of a Numerical Model of a Full Aquaculture NetCage System. ASME 2014 33rd international conference on ocean. Offshore and Arctic Engineering, American Society of Mechanical Engineers Faltinsen O (2011) Hydrodynamic aspects of a floating fish farm with circular collar. The 26th international workshop on water waves and floating bodies (IWWFB) (April 17–20, 2011), Athens Faltinsen OM, Shen Y (2018) Wave and current effects on floating fish farms. J Mar Sci Appl 17(3):284–296 Faltinsen OM, Timokha AN (2009) Sloshing Fredriksson DW, Palczynski MJ, Irish JD, Swift MR, Celikkol B (2003) Fluid dynamic drag modeling of a central spar cage. In: Open ocean aquaculture: from research to commercial reality. World Aquaculture Society, Baton Rouge, pp 151–168 Fredriksson DW, DeCew J, Swift MR, Tsukrov I, Chambers MD, Celikkol B (2004) The design and analysis of a four-cage grid mooring for open ocean aquaculture. Aquac Eng 32(1):77–94 Fredriksson D, DeCew J, Lader P, Volent Z, Jensen Ø, Willumsen F (2014) A finite element modeling technique for an aquaculture net with laboratory measurement comparisons. Ocean Eng 83:99–110 Fu S, Moan T (2012) Dynamic analyses of floating fish cage collars in waves. Aquac Eng 47:7–15 Fu S, Moan T, Chen X, Cui W (2007) Hydroelastic analysis of flexible floating interconnected structures. Ocean Eng 34(11):1516–1531 Gignoux H, Messier RH (1999) “Computational modeling for fin-fish aquaculture net pens.” Oceanic engineering international. St. John’s, NF 3(1):12–22 He Z, Faltinsen OM, Fredheim A, Kristiansen T (2018) The influence of fish on the mooring loads of a floating net cage. J Fluids Struct 76:384–395 Huang C-C, Tang H-J, Liu J-Y (2006) Dynamical analysis of net cage structures for marine aquaculture: numerical simulation and model testing. Aquac Eng 35(3): 258–270 Kristiansen D (2010) Wave induced effects on floaters of aquaculture plants. Department of Marine Technology. Norwegian University of Science and Technology, Trondheim Kristiansen T, Faltinsen OM (2012) Modelling of current loads on aquaculture net cages. J Fluids Struct 34: 218–235

Aquaculture Structures: Numerical Methods Kristiansen T, Faltinsen OM (2015) Experimental and numerical study of an aquaculture net cage with floater in waves and current. J Fluids Struct 54:1–26 Kristiansen D, Lader P, Endresen PC, Aksnes V (2018) Numerical and experimental study on the seakeeping behavior of floating closed rigid fish cages. ASME 2018 37th international conference on ocean. Offshore and Arctic Engineering, American Society of Mechanical Engineers Lader PF, Fredheim A (2006) Dynamic properties of a flexible net sheet in waves and current – a numerical approach. Aquac Eng 35(3):228–238 Lader PF, Enerhaug B, Fredheim A, Krokstad J (2003) Modelling of 3D net structures exposed to waves and current. 3rd international conference on Hydroelasticity in marine technology Lee C-W, Kim Y-B, Lee G-H, Choe M-Y, Lee M-K, Koo K-Y (2008) Dynamic simulation of a fish cage system subjected to currents and waves. Ocean Eng 35(14–15):1521–1532 Li P, Faltinsen OM (2012) Wave induced response of an elastic circular collar of a floating fish Farm. In Proceedings of 10th international conference on hydrodynamics 2: 58–64 Li L, Ong MC (2017) A preliminary study of a rigid semisubmersible fish farm for open seas. Proceedings of the Asme 36th international conference on ocean, Offshore and Arctic Engineering, 2017, vol 9 Li Y-C, Zhao Y-P, Gui F-K, Teng B (2006) Numerical simulation of the hydrodynamic behaviour of submerged plane nets in current. Ocean Eng 33(17): 2352–2368 Li L, Fu S, Xu Y (2013a) Nonlinear hydroelastic analysis of an aquaculture fish cage in irregular waves. Mar Struct 34:56–73 Li L, Fu S, Xu Y, Wang J, Yang J (2013b) Dynamic responses of floating fish cage in waves and current. Ocean Eng 72:297–303 Li P, Faltinsen OM, Lugni C (2016) Nonlinear vertical accelerations of a floating torus in regular waves. J Fluids Struct 66:589–608 Li L, Jiang Z, Vangdal Høiland A, Chen Ong M (2018a) Numerical analysis of a vessel-shaped offshore fish farm. J Offshore Mech Arct Eng 140(4) Li P, Faltinsen OM, Greco M (2018b) Wave-induced accelerations of a fish-farm elastic floater: experimental and numerical studies. J Offshore Mech Arct Eng 140(1) Liu H-Y, Huang X-H, Wang S-M, Hu Y, Yuan, T.-p. and Guo, G.-X. (2019) Evaluation of the structural strength and failure for floating collar of a single-point mooring fish cage based on finite element method. Aquac Eng 85:32–48 Løland, G. (1991). Current forces on and flow through fish farms, division of marine hydrodynamics, the Norwegian Institute of Technology Loverich GF, Gace L (1997) The effect of currents and waves on several classes of offshore sea cages. Charting Future Ocean Farm 1998:131–144

Arctic Pipeline Marichal D (2003) Cod-end numerical study. In: Taylor E (ed) Proceedings of the 3rd international conference on Hydroelasticity in marine technology, Oxford, UK, ISBN: 0-952-62081-2, Paper: P2003-3 proceedings Milne PH (1972) Fish and shellfish farming in coastal waters Moe H, Fredheim A, Hopperstad O (2010) Structural analysis of aquaculture net cages in current. J Fluids Struct 26(3):503–516 Patursson Ø, Swift MR, Tsukrov I, Simonsen K, Baldwin K, Fredriksson DW, Celikkol B (2010) Development of a porous media model with application to flow through and around a net panel. Ocean Eng 37(2–3):314–324 Rudi H, Løland G, Furunes I (1988) Experiments with nets; forces on and flow trough net panels and cage systems. MT 51 F88 215 Schubauer GB, Spangenberg WG, Klebanoff P (1950) Aeodynamic characteristics of damping screens. DTIC Document Shen Y (2018) Operational limits for floating-collar fish farms in waves and current, without and with well-boat presence. Department of Marine Technology. Norwegian University of Science and Technology, Trondheim Shen Y, Greco M, Faltinsen OM, Nygaard I (2018) Numerical and experimental investigations on mooring loads of a marine fish farm in waves and current. J Fluids Struct 79:115–136 Shen Y, Greco M, Faltinsen OM (2019a) Numerical study of a well boat operating at a fish farm in long-crested irregular waves and current. J Fluids Struct 84:97–121 Shen Y, Greco M, Faltinsen OM (2019b) Numerical study of a well boat operating at a fish farm in current. J Fluids Struct 84:77–96 Shi L (2019) Dynamic analysis of semi-submersible offshore fish farm operated in China East Sea. NTNU Shim K, Klebert P, Fredheim A (2009) Numerical investigation of the flow through and around a net cage. ASME 2009 28th international conference on ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers Strand IM, Faltinsen OM (2019) Linear wave response of a 2D closed flexible fish cage. J Fluids Struct 87:58–83 Strand IM, Faltinsen OM (2020) Linear wave-induced dynamic structural stress analysis of a 2D semi-flexible closed fish cage. J Fluids Struct 94:102909 Tan Y, Shao Y, Read R (2019) Coupled motion and sloshing analysis of a rigid cylindrical closed fish cage in regular waves. ASME 2019 38th international conference on ocean. Offshore and Arctic Engineering Theret F (1993) Étude de l’équilibre des surfaces réticulées placées dans un courant uniforme: application aux chaluts, Nantes Tsukrov I, Eroshkin O, Fredriksson D, Swift MR, Celikkol B (2003) Finite element modeling of net panels using a consistent net element. Ocean Eng 30(2):251–270 Xu T-J, Zhao Y-P, Dong G-H, Li Y-C, Gui F-K (2013) Analysis of hydrodynamic behaviors of

65 multiple net cages in combined wave–current flow. J Fluids Struct 39:222–236 Yao Y, Chen Y, Zhou H, Yang H (2016) Numerical modeling of current loads on a net cage considering fluid– structure interaction. J Fluids Struct 62:350–366 Zhao Y-P, Li Y-C, Dong G-H, Gui F-K, Teng B (2007a) Numerical simulation of the effects of structure size ratio and mesh type on three-dimensional deformation of the fishing-net gravity cage in current. Aquac Eng 36(3):285–301 Zhao Y-P, Li Y-C, Dong G-H, Gui F-K, Teng B (2007b) A numerical study on dynamic properties of the gravity cage in combined wave-current flow. Ocean Eng 34(17):2350–2363 Zhao Y-P, Bi C-W, Dong G-H, Gui F-K, Cui Y, Guan C-T, Xu T-JJOE (2013) Numerical simulation of the flow around fishing plane nets using the porous media model. Ocean Eng 62:25–37

Arbitrary Lagrangian-Eulerian (ALE) ▶ Suction Piles

Arctic Pipeline Yi Wang1 and Yongfeng Wang2 1 College of Safe and Off-shore Engineering, China University of Petroleum – Beijing, Beijing, China 2 School of Safety and Ocean Engineering, China University of Petroleum (Beijing), Beijing, China

Synonyms The Arctic Pole pipeline; The North Pole pipeline

Definition Arctic pipelines refer to pipelines that pass through a permafrost, where the soil or rock remains below 0  C throughout the year and the formation is sufficiently cooled during the winter to form a layer that persists throughout the summer.

A

66

Introduction The Arctic has enormous resources in permafrost, which need to be developed by being highly aware of the possibility of environmental damage. Permafrost currently accounts for about a quarter of the Earth’s land area. Figure 1 shows the distribution of permafrost regions in Alaska, which have large areas of permafrost (Larsen et al. 2008). Arctic pipelines refer to pipelines that pass through a permafrost, where the soil or rock remains below 0  C throughout the year, and the formation is sufficiently cooled during the winter to form a layer that persists throughout the summer. The main characteristics of arctic pipelines are determined by the climatic conditions pertaining to a given territory, which are described below, and it may be noted that some of these features can be encountered in territories outside of the polar circle, low radiation balance, summer average zero temperature, annual average subzero temperature, large areas of permafrost, wet lands, and an abundance of swamps in plains. Normally, Arctic pipelines are pipelines transporting gas and oil from production sites to the facilities. What’s more, arctic pipeline applications also include unprocessed well fluid and utility lines, processed oil and gas pipelines, combined offshore/overland pipeline systems, subsea field developments, cables, and umbilicals. Arctic Pipeline, Fig. 1 Arctic areas of Alaska permafrost coverage (Yong Bai et al. 2014)

Arctic Pipeline

The configurations of arctic pipelines include single-walled steel pipe, pipe-in-pipe, flexible pipe and pipe-in-HDPE pipe, etc. Following BP’s discovery of oil in Prudhoe Bay oil field near the Arctic Ocean coast in 1968, the Northstar Pipeline was proposed. This pipeline construction was the first long pipeline construction in Arctic area; prior to this project, only short pipelines were built only in areas such as Siberia and Norman Wells on the Mackenzie River in Canada. With the development of technology and the rise of oil price in the early of the twenty-first century, lots of Arctic pipeline projects were constructed in recent years.

Advancement of Arctic Pipeline Design Technologies In the Arctic pipeline design, it requires emerging technologies to balance between the efficient and economical design and installation of pipelines in the Arctic. Some early analyses used to evaluate Arctic loads on pipelines apply to those specific projects; but as industry enters more severe Arctic conditions, advancements need to continue to ensure a proper balance between safety and economics. Expanding international knowledge about Arctic conditions, improvements in material behavior, advances in analytical techniques,

Arctic Pipeline

and broad acceptance of progressive design concepts, such as strain-based design and the implementation of reliable Arctic operational strategies, enable the consideration and development of other offshore Arctic prospects (Paulin and Caines 2016). Probabilistic Design Approaches Based on historical data from a given area and water depth, an ice scouring or structural scour depth statistic assessment can be used to predict extreme ice wash or structural scouring depth at a particular acceptable risk level. However, probabilistic analysis which only considers numerical statistical modeling does not evaluate methods for obtaining data, ice wash, or structural washout depth resolution cutoffs, effects of dynamic environmental activities, pipe and scour direction, scour or flush recurrence rate, pipe length, and other factors. In many instances, gouging is considered the most important loading condition for offshore pipeline design, but it is also considered the most uncertain in terms of predictability (Liberty Energy Project 2017) (Fig. 2). Finite Element Methods When a buried pipeline is subjected to a large deformation load, the strain in the pipe wall may be higher than that allowed by conventional design specifications based on linear pipe behavior. In fact, pipeline behavior is nonlinear due to Arctic Pipeline, Fig. 2 The results of prediction on 1 year

67

the potential for large deflections and plastic material properties. Therefore, it is necessary to complete the limit state by including geometric and material nonlinearity, strain-based design. Finite element analysis allows modeling nonlinearities in material, geometry, and tube-soil interactions; it has been used to assess the integrity of pipelines in environmental loading events, such as ice scouring, permafrost melt settlement, frost heave, bulge buckling, and free span of structural scour. INTECSEA, for example, has developed in-house subroutines for the CEL Advanced Constitutive soil models that more realistically simulate the soil behavior based on critical state soil mechanics theory. These models can address dilation issues and hardening/softening behavior of the soil which results in more accurate estimation of subgouge deformations under ice scour loads. An example of a resultant axial strain due to deformation is shown in Fig. 3.

Industry Regulations, Standards, and Codes Following regulations, standards, and codes are widely used in offshore Arctic pipeline design. Arctic Specific Regulations 1. ISO 19906 (2010 Edition) Petroleum and Natural Gas Industries-Arctic Offshore Structures

A

68

Arctic Pipeline

Arctic Pipeline, Fig. 3 Axial strains due to subgouge deformations

2. API RP 2N (2015 Edition) Planning, Designing, and Constructing Structures and Pipelines for Arctic Conditions 3. 30 CFR Parts 250, 254, and 550 Federal Arctic Rule-Oil and Gas and Sulphur Operations on the Outer Continental Shelf-Requirements for Exploratory Drilling on the Arctic Outer Continental Shelf US Federal and State Regulations 1. 49 CFR Part 192 (2011 Edition) Transportation of Natural and Other Gas by Pipeline: Minimum Federal Safety Standards; 2. 49 CFR Part 195 (2017 Edition) Transportation of Hazardous Liquids by Pipeline General Pipeline Design Regulations 1. API RP 1111 (2015 Edition) Design, Construction, Operation and Maintenance of Offshore Hydrocarbon Pipelines (Limit State Design) 2. CSA Z662-15 (2016 Edition) Oil and Gas Pipeline Systems 3. ASME B31.4 (2016 Edition) Pipeline Transportation Systems for Liquids and Slurries/ ASME 31.8 (2016 Edition) Gas Transmission and Distribution Piping Systems 4. DNVGL-ST-F101 (2017 Edition) Submarine Pipeline Systems

5. ISO 13623 (2017 Edition) Petroleum and Natural Gas Industries-Pipeline Transportation 6. RMRS 2-020301-005 (2017 Edition) Rules for the Classification and Construction of Subsea Pipelines

Existing Arctic Pipelines The existing Arctic pipeline projects include singlewalled project: Northstar (Alaska), Varandey Oil Terminal (Russian Pechora Sea), Baydaratskaya Bay Pipeline, Crossing (Russian Kara Sea), Sakhalin 1 (Russian Sea of Okhotsk), Sakhalin 2 (Russian Sea of Okhotsk), Kashagan (Russian North Caspian), and pipe-in-pipe project: Drake Project (Canadian Arctic Archipelago), Oooguruk (Alaska), Nikaitchuq (Alaska), and Liberty Proposal (Alaska). They provide important experience base for designing, installing, and operating future offshore Arctic pipelines. Figure 4 shows the location of these projects. Figure 5 provides design details for the three operational Alaskan offshore pipelines/flowline bundles. Northstar The Northstar pipelines which production commenced in October 2001 were designed for ice

Arctic Pipeline

69

A

Arctic Pipeline, Fig. 4 Alaskan offshore projects

keel gouging using empirical methods. Limit state strain criteria were developed for design of noncyclic pipeline displacements settlement, with allowable strain levels established based on the pipe dimensions and material grade. The pipeline system was made up of a single-walled oil pipeline and a single-walled injection gas pipeline; they were installed in a common trench which the maximum design burial depths reach 7 ft below seabed to top of pipe between, with winter construction using conventional onshore equipment (Paulin et al. 2001) (Fig. 6). Oooguruk Natural Resources Alaska Inc.developed the Oooguruk field on the Alaskan North Slope, using a buried three-phase flowline following a pipe-in-pipe design approach from the gravel island to shore, which includes 12 in by 16in PIP production, 8.625 in OD water injection, 6.625 in OD gas, and 2 in OD AHF line (Lanan et al. 2008). The pipe-in-pipe concept was chosen for the purpose of insulating the production flowline. An added benefit of the vacuum annulus was its

availability as a leak detection system for the offshore production flowline (Fig. 7). Nikaitchuq Eni Petroleum Corporation developed the Nikaitchuq field located south of Spy Island in the Beaufort Sea. Produced fluids are transported to shore from the Spy Island drill site via a buried three-phase flowline to a production facility located at Oliktok Point. The Nikaitchuq flowline bundle is made up of a 14 inch by 18 inch PIP flowline carrying produced fluids, a 12 in OD water injection line, a 6in OD spare flowline, and a 2 inch by 4 inch PIP Arctic heating fuel line. The PIP concept was mainly chosen for the purpose of insulating the flowline, with the added benefit of allowing annular monitoring for leak detection (Paulin et al. 2001) (Fig. 8).

Arctic Pipeline Design Challenges Pipeline configurations for Arctic pipeline design, thermal insulation, and trenching requirements

BUNDLE SPACER

OOOGURUK FLOWLINE BUNDLE

RADIATION BARRIER

P-I-P SPACER

14” PRODUCED FLUIDS LINE

18” STEEL OUTER PIPE

FIBER OPTIC CABLE

8” WATER INJECTION LINE WITH 1.7” POLYURETHANE FOAM, 0.2” POLYETHYLENE, AND 1” CONCRETE COATING

6” GAS LINE

BUNDLE STRAP

Arctic Pipeline, Fig. 5 Alaskan offshore pipelines/flowline bundles design details (Lanan et al. 2015)

RADIATION BARRIER

P-I-P SPACER

10” OIL PIPELINE

12” PRODUCED FLUIDS LINE

BUNDLE SPACER

LEOS TUBE

NORTHSTAR PIPELINE BUNDLE

BUNDLE STRAP

10” GAS PIPELINE

16” STEEL OUTER PIPE

FIBER OPTIC CABLE

2” ARCTIC HEATING FUEL LINE

2” ARCTIC HEATING FUEL LINE

NIKAITCHUQ FLOWLINE BUNDLE

BUNDLE SPACER

12” WATER INJECTION LINE WITH 1.6” POLYURETHANE FOAM, 0.2” POLYETHYLENE, AND 1” CONCRETE COATING

6” SPARE LINE

BUNDLE STRAP

4” STEEL OUTER PIPE

70 Arctic Pipeline

Arctic Pipeline

71

A

Arctic Pipeline, Fig. 6 BP Alaska Northstar Gravel Island (Paulin et al. 2001)

Arctic Pipeline, Fig. 7 Oooguruk bundle details (Lanan et al. 2008)

72

Arctic Pipeline

Arctic Pipeline, Fig. 8 Nikaitchuq Spy Island drill site (Paulin et al. 2001)

are affected by Arctic environmental load conditions. The main features of pipeline design in the Arctic or Arctic environment include pipeline environmental loads and extreme state design under extreme load conditions, resulting from ice scour. Ice scouring is often referred to as the geological term for long and narrow ditches on the sea floor, caused by the grounding of fast ice, fast ice, and pack ice. The differences between arctic pipelines and other conventional pipelines include operating temperature; geotechnical loads, resulting from thaw settlement and frost heave; construction surface disturbance impacts on permafrost terrain; seasonal constrains on construction and maintenance activities; and civil construction techniques in permafrost. The differences due to the climate conditions and ice coverage require the consideration of certain challenges in the design of arctic pipelines, which include ice scouring, strudel scouring,

permafrost thaw settlement, frost heave, pipesoil interaction, monitoring and leak detection in the Arctic, and construction and installation techniques. What’s more, ice scouring, strudel scouring, and permafrost thaw settlement phenomenon are shown in Figs. 9, 10, and 11, respectively. Based on the existing development and research of Arctic pipelines, probabilistic design method and finite element analysis method are used to predict the design principles and layout of Arctic pipelines. Firstly, the probability design method is used to estimate the reliability range of the design of the Arctic pipeline, and then the finite element analysis method is used to accurately calculate and evaluate the reliability of the design of the Arctic pipeline within the reliability range. Through a lot of calculation and comparative analysis, the design principles and layout of the Arctic pipeline are summarized.

Arctic Pipeline Arctic Pipeline, Fig. 9 Ice keel scouring over a pipeline

Arctic Pipeline, Fig. 10 Strudel scour over a pipeline

Arctic Pipeline, Fig. 11 Thaw settlement and frost heave

73

A

74

The differences due to the climate conditions and ice coverage require the consideration of certain challenges in the design of arctic pipelines, while include: Ice gouging or icebergs in shallow water Strudel scour Frost heave Permafrost thaw settlement Upheaval buckling The main concerning limit states to be investigated during the design of arctic pipelines are two types of limit states. One is the limit state of the rupture of a pipe wall that causes leakage of hydrocarbons, in which the ultimate limit state is thresholds beyond which pressure containment, safety, or the environment is threatened. Another one is the limit state of accident conditions where the pipeline no longer meets one or more design requirements. The serviceability limit states are reached, and the normal operations are restricted, which leads to economic damage to the operator. The goal of the limit state design is to verify the adequacy of the pipeline design against limit states and failure modes relevant to the events. The criteria from DNV OS-F101 and API RP 1111 may be considered. Criteria from these references are based mostly on the risk principles and limit state methodology. The following limit states are to be considered for the design of arctic pipelines: compressive strain limit states for local buckling, tensile strain limit states for strain capacity, and fracture. Arctic Pipeline Design Procedure The arctic pipeline design for frost heave and thaw settlement may be carried out through an iterative process in the following steps: 1. Hydraulic analysis for establishing the relationships among the pipe size, material grade, wall thickness, operating temperature, and pressure profiles. 2. Geothermal analysis to predict the potential for frost heave and thaw settlement by using an operating temperature profile. A range of route conditions based on the statistics in terrain analysis are considered as well.

Arctic Pipeline

3. Structural modeling to predict pipeline strain and displacement distributions resulting from predicted frost heave and thaw settlement effects over time. 4. Determination of the pipe’s capability to sustain the strain and displacement through the analysis of finite element modeling and fullscale test results. 5. Comparison between the strain demands over time with the strain capacity to ensure the pipeline integrity. 6. Testing and checking the heave frost and thaw settlement displacements and freeze bulb growth to assess the environmental impacts. 7. Evaluation of the following factors to the design and maintenance of the arctic pipeline, such as temperature limits, material grade of pipeline, pipeline size, and wall thickness. 8. Repeating Step 1 until Step 7 as required. Arctic pipeline designs also need to include parameters such as ice impact, gouging by icebergs or ice keels, assessment of uncertainty related to ice scour events, and ice-soil-pipe interaction. Future Arctic pipeline design principles and layout can be predicted on the existing Arctic pipeline development and research.

References 49 CFR Part 195 (2017) Transportation of hazardous liquids by pipeline. Code of Federal Regulations API Recommended Practice 1111 (2015) Design, construction, operation, and maintenance of offshore hydrocarbon pipelines (limit state design). American Petroleum Institute Cowin TG, Lanan GA, Young CH, Maguire DH (2015) Ice based construction of offshore arctic pipelines. Offshore technology conference, paper 25522 CSA Z662-15 (2016) Oil and gas pipeline systems. Canadian Standards Association DNVGL Standard F101 (2017) Submarine pipeline systems. DNVGL-ST-F101 ISO 13623 (2017) Petroleum and natural gas industries – pipeline transportation. International Standards Organization ISO 19906 (2010) Petroleum and natural gas industries – arctic offshore structures. International Standards Organization

Atmospheric Diving Suit (ADS) Lanan GA, Cowin TG, Hazen B, Maguire DH, Hall JD, Perry CJ (2008) Oooguruk offshore arctic flowline design and construction. Offshore technology conference, paper 19353, May 2008 Larsen PH, Goldsmith S, Smith O, Wilson ML, Strzepek K, Chinowsky P, Saylor B (2008) Estimating future costs for Alaska public infrastructure at risk from climate change. Elsevier: Global Environment Change, Burlington Liberty Energy Project (2017). http://libertyenergyproject. com/wpcontent/uploads/2017/08/Liberty-Project-FactSheet.pdf Paulin M, Caines J (2016) The evolution of design tools for arctic subsea pipelines. Arctic technology conference, paper no. OTC 27374 Paulin MJ, Nixon D, Lanan GA, McShane B (2001) Environmental loadings & geotechnical considerations for the northstar offshore pipelines. In: Proceedings, POAC 2001, Ottawa RMRS 2-020301-005 (2017) Rules for the classification and construction of subsea pipelines. Russian Maritime Register of Shipping Yong Bai, Qiang Bai (2014) Subsea Pipeline Integrity and Risk Management. Gulf Professional Publishing

Areas Beyond National Jurisdiction (ABNJ) ▶ Marine Protected Areas in Areas Beyond National Jurisdiction

Armor Layer ▶ Umbilical Cable

Artificial Air Flow ▶ Wind Tunnel Test

Assistant Icebreaking Systems ▶ Auxiliary Icebreaking Methods

75

Atmospheric Diving Suit (ADS) Tao Liu and Shuai Wang China Ship Scientific Research Center, Wuxi, China

Synonyms Atmospheric diving system (ADS); Human occupied vehicle (HOV); Manned submersible (MS)

Definition An Atmospheric Diving Suit (ADS), also known as Atmospheric Diving System, is a humanoid type deep-sea manned operation system, which can maintain atmospheric pressure when diving. The diver equipped with the suit can directly reach the operation site for observation, navigating by the underwater thruster, or landing and shifting by its own strength. At the same time, with the help of rotary joints, divers can control the gripper of both hands and special tools under underwater operations. The suit is connected to the Tether Management System (TMS) through the neutral cable to obtain energy and communicate. The video image of the operation process is also transmitted to the surface ship for the personnel to make a decision for reference (Jiang et al. 2013c).

Scientific Fundamentals Historical Development As a common underwater operation equipment, ADS has been progressed with the development of human technology. Since the simple “diving tub” developed by John Lethbridge in 1715 for the salvage of underwater wreck, to the Hardsuit2000 equipment for submarine rescue, it has experienced 300 years of history (Thornton 2000). In recent years, with the development of offshore oil industry, the ADS in various countries is developing rapidly. Its submergence ability can descend to depth steadily from more than 10 m

A

76

Atmospheric Diving Suit (ADS)

to 600 m; from single observation ability to complicated operational ability with professional tools; ADS provide a guarantee in wide application fields in deep-sea oil and gas resources and salvaging of sunken ships. Early Development of ADS The birth of the first kind of diving suit 1715 to 1882 Carmagnolle can be thought of as the early development of ADS. At this stage, the development was mainly driven by salvaging sunken wreck treasure, while technical level at a very low level. Shallow operation depth, no life support systems, or just through the air pipe connecting to the surface, no communication system, no propulsion system, small size and flat glass-viewing window are the typical characters. However, it was during this period, the concept of atmospheric diving for underwater operations, and gradually from the initial bucket structure development to the humanoid type structure, from the development of wooden materials to metal materials, emerged from without limbs joint to the primary of the joints. In this period, Lethbridge, Taylor, Plillips, Carmagnolle (Yang 2015) successively appeared. In 1715, John Lethbridge sought a way to acquire wealth by building a device to recover some of the treasures from the sunken ships (Aylmer 1996). The Lethbridge, which he calls “a submersible that is not connected to air,” is widely considered to be the early embryo of ADS. In fact, it is only a wooden bucket that is suspended into the water, through the wall of the bucket with both hands and set up sealing measures to carry out the normal pressure diving. In 1838, the first diving suit equipped with joints, Taylor, was designed. See Fig. 1. Divers in Taylor connected with the water supply through a hose, and the joint is similar to the steel structure of accordion type, leather material helping watertight (Harris 1985). These types of joints have only limited ability in a small range of activities and shallow water depth. Plillips, designed in 1856, was the first fully enclosed diving suit (Davis 1951) and ball-hole joint was first used. There is a buoyancy chamber on the back, a single-hole viewing window,

Atmospheric Diving Suit (ADS), Fig. 1 Taylor atmospheric diving suit design, 1838 (Harris 1985)

a manhole on the top, and a simple clamping device on the upper extremity, all of which are standard modern fixtures. There is no record of the Plillips being built, but many of its features have been applied to successful installations over the next century. Carmagnolle is the most famous ADS of this stage. In 1882, the Carmagnolle brothers applied for the patent of armored diving equipment in France. The joint of the device is tightly assembled from several concentric hemispheres and is attached to each other by a water-tight cloth with a certain folding so that it can slide (Davis 1951). This is the first truly constructed humanoid assembly, and it is the first time to introduce the Ergonomics consideration in the design. Mid-Term Development of ADS After the development of the previous stage, ADS is already applied in wider fields, such as underwater operation of marine oil and gas industry, and aid to the navy submarine rescue. The ADS system also tends to be improved gradually, equipped with independent life support system, communication system, propulsion system, and

Atmospheric Diving Suit (ADS)

operational tools. In this period, there were two important types of joints – oil filled spherical joint and oil filled cylindrical joint, bringing leapforward development. With materials of steel, magnesium alloy, aluminum alloy, and glass fiber reinforced plastic applied, the operation depth of ADS has been developed from several meters to hundreds of meters. With the enhancement of the underwater working ability of the suits, it is gradually recognized by the industry. Some types have also developed from a single prototype in the early stage to an industrial production status. During this period, many different types emerged, such as Bowdoin, Neufeldt & Kuhnke, Galeazzi, Campos, Peress, and JIM (Yang 2015). In 1915, American Bowdin obtained a patent for a new type of oil-filled rotary joint. The joint is cylindrical and has a small catheter that equates the internal and external pressure. However, without lasting lubrication, the joints can easily get stuck (Harris 1985). Although this device was not manufactured, it introduced a very important concept of oil filled pressure balance and played an important role in the development of the joint. Then in 1922, Victor Campos applied for a patent for a similar type of oiled joint and made Campos. The suit was reported to dive to depth of 600 m. Despite diving 600 m, there is no perceptible movement of the joints. It is worth noting that the Campos joint set fail-safe design for the first time. If the joint failure happens, it can automatically seal and not let water into the suit, which has a great significance for the future design of ADS. In 1917, German company Neufeldt & Kuhnke built two models of ADS based on the patent of ball-hole joint and used the ball to bear and transfer water pressure. In 1924, the German navy tested its second generation, diving to a depth of 161 m, which was very difficult to move the upper limbs and the joints had no fail-safe design (Scott 1931a). In 1931, with the help of this type of equipment, a total of 10 tons of silver COINS and 5 tons of gold COINS were recovered from a sinking ship in Egypt. Through this successful salvage, the suit gained a good reputation (Scott 1931b). In 1930, the suit was licensed to be built and sell. A developed type of Galeazzi with many

77

improvements to the original Neufeldt & Kuhnke was manufactured and sold more than 50 sets (Harris 1985). In 1922, the British inventor Joseph Salim Peress applied for a spherical joint of oil filled and tried to make a type of ADS in 1925 but did not succeed. Then he developed the second type of ADS in 1932, named “Tritonia,” which is now often referred to as “JIM I.” There were only 8 ball joints, and equipped with simple tools (Barton 1973). JIM I was successfully used in Lusitania’s wreck salvage, with a maximum depth of 313 m. In 1937, it successfully completed the royal navy sea trial (Loftas 1973). The ball joint of this kind of ADS used hydraulic compensation for the first time, which laid a good foundation for the JIM used widely later. Early 1960s, a new type of JIM was designed, using the material of cast magnesium, which has high specific strength. See Fig. 2. The front of JIM is equipped with ballast, which allows the diver release in an emergency, then the JIM can rise to the surface at a speed of about 30 m per min. In 1971, the first set of JIM was carried

Atmospheric Diving Suit (ADS), Fig. 2 A JIM suit used by NOAA is recovered from the water. (Wikipedia, photo from NOAA)

A

78

out sea trials by the British naval ship Reclaim, and two divers arrived to the depth of 120 m. In 1981, the number of JIM has reached 19 sets (Earls et al. 1979), which is widely used in all kinds of underwater operations. JIM also became the basis of later developed ADSs. The WASP was completed and put into use in 1978. It follows JIM’s design in many aspects but is designed as a GRP column below the waist to replace the lower body. The technology of propeller is adopted for the first time. It is equipped with a small multi-directional propeller, which is controlled by the pedal control board inside the cylinder, thus improving the maneuverability. A new generation of WASP-III put into production in 2001, to be able to descend to 760 m depth. The new WASP has a stronger vector propulsion system, lateral propulsion capability, and two camera systems. Modern ADS Phil Nuytten, developed the NEWTSUIT based on the 1984 patent for rotating joints (Nuytten 1985), which is a truly somatological ADS. It has a wide range of activity allowing it to enter areas previously accessible only to divers. NEWSUIT is equipped with 16 patented hydraulic compensated rotary column joints that allow divers to drive the upper and lower limbs by themselves. The innovative joint greatly improves the working depth and flexibility of ADS and is a milestone in the history. The NEWTSUIT life support system can guarantee 6–8 h of normal operation and 48 h of support in case of emergency. In order to meet the needs of the army, the US navy cooperated with OceanWorks Company developed a series of HARDSUIT1000 (305 m), HARDSUIT1200 (365 m), and HARDSUIT2000 (610 m) on the basis of NEWTSUIT. See Fig. 3. The first two types adopt cast aluminum manufacturing, the other aluminum forging manufacturing. Meanwhile, HARDSUITs have become the standard equipment for French and Italian naval submarine rescue projects. In addition, the commercial model HARDSUIT 2500 of HARDSUIT 2000 will be applied in the industrial field, with a diving depth of 760 m.

Atmospheric Diving Suit (ADS)

Atmospheric Diving Suit (ADS), Fig. 3 U.S. Navy’s ADS 2000 At the Ready. (Photo from OceanWorks Company)

Atmospheric Diving Suit (ADS), Fig. 4 QSZ-I atmospheric diving suit. (Photo from CSSRC)

China Ship Scientific Research Center (CSSRC) started research of ADS since 1980, and the first set of QSZ-I was developed in 1986. See Fig. 4. QSZ-I adopts spherical joints to connect limbs, and the maximum diving depth is 300 m. Sea trials with and without diver were carried out in the South China Sea. On the basis of QSZ-I, QSZ-II was improved in the 1990s. Four propellers were increased for depth control, height

Atmospheric Diving Suit (ADS)

control, and cruise control. The computer control system is improved to make divers’ underwater activities more convenient and faster. Its biggest characteristic is that underwater movement has dual functions – it can choose to walk on the ground on the knuckles of the legs, and it can also rely on the power of the propeller to propel and cruise in the water. It can be controlled by the diver as well as the deck remote control. It is not only a manned submersible but also an unmanned observation submersible with remote control. Since 2011, CSSRC began to develop a new type of ADS with the depth of 500 m, purposed to support marine oil and gas production safety maintenance and guarantee. The ADS has completed sea trials in 2015. The TMS, Launch and Recovery System (LARS), independent life support system, high-definition cameras, imaging sonar, two LED lights, emergency ballast, neutral line cutting, stroboscopic lamp, emergency pinger lamp, etc. equipped with the ADS forming a complete set. After 2000, Phil Nuytten designed the latest EXOSUIT, which will work 305 m deep and reach 610 m in the future. The two salient features of the EXOSUIT are its lightweight and cable-free nature, allowing divers to swim within the EXOSUIT by swinging their lower limbs to drive their flippers, indicating that their joints are already highly flexible. It has 22 highly flexible rotary joints, and the foot swimming fins, the air (excluding divers) weighs only 72 kg. EXOSUIT has the ability of 48 h life support and is equipped with the latest underwater communications. It can be decomposed and loaded into a cylindrical vessel with a diameter of 0.4 m and a height of 0.6 m, which is convenient for storage in the submarine cabin. Traditional underwater operations, from compressed air to communication, rely on umbilical cables, so the effect of uncabled underwater operations needs to be further verified. Principles of Modern Atmospheric Diving Suit The arms and legs of modern ADS are connected by joints. The limbs are human-powered. Propulsion devices are equipped to maintain mobility in the water.

79

Joint is one of the key components of ADS. Hydraulic support column joint based on the patent of Phil Nuytten in 1984 is widely used now (Nuytten 1990). This type of joint has light weight, small rotation torque, large rotation angle, and reliable sealing. At present, the joint technical difficulties include: (1) underwater sealing technology – the research of sealing form and interior design parameters with high reliable seal and low rotating friction under deep water pressure; (2) rotary positioning technology – the research of rotary positioning between cylinder and piston with reliable radial and axial accuracy but not additional joint rotation torque and no appearance of stuck under high pressure; (3) hydraulic support technology – reliable design of hydraulic support to resist water pressure and reduce the rotational resistance under deep water pressure, also make sure that the joints can automatically compensate the amount of oil loss in the process of using; (4) pressure-resistant structure design – design of joints with lightest weight, most reasonable deformation control and uniform stress distribution meeting the requirements of working depth, and deformation under high pressure will not affect the sealing mechanism at the same time; (5) safety self-locking technique – when complete oil loss or sealing failure appears, the joints can lock themselves so as not to allow seawater to enter the cavity (Jiang et.al 2013a). It is a worldwide technical problem to develop high depth ADS that can meet the urgent requirements of high depth atmospheric diving suit. The torso of ADS is somatological and the specific size is usually referred to ergonomic standards. Wrought aluminum milling forming is the popular process using at the time to ensure the density and intensity of the material. In addition, machining precision can be controlled strictly, make the thickness of the shell more reasonable, and the overall ADS weight lighter. There are four large openings in the upper body of the torso, including window opening, left and right upper limb opening, and waist opening, respectively. See Fig. 5. The same three openings in the lower body, respectively in the waist and the left and right lower limbs. It is necessary to carry out relevant theoretical analysis and experimental

A

80

Atmospheric Diving Suit (ADS), Fig. 5 The upper body of ADS torso with hemispherical viewing window. (Photo from CSSRC)

research on such non-regular, multi-channel, and large-opening structures. At present, the waist opening is usually adopted, which make divers in and out of ADS convenient. A bonus is the torso height can be adjusted by adding or removing torso sections to adapt to the needs of different height of the divers (Jiang et.al 2013b). Hemispherical viewing window technology is also important. The JIM was originally designed with four viewing windows on the top. Later it was improved to a fully transparent Plexiglas helmet, providing a wider view for the operator. However, under the action of high pressure seawater, organic glass will undergo continuous creep deformation. This puts forward new requirements for design strength and safety. In addition, the manufacturing process of hemispherical viewing window is rather complicated. It is important to pay attention to the installation form of a hemispherical viewing window with torso connection. The study found that big bearing stress will occur during the progress of hemispherical glass shell inlaiding into metal shell (Taylor and Lawson 2009). Propellers are equipped on various types of ADS after the development of JIM, which are controlled by the pedal control board inside the ADS. Thus, the movement capability is

Atmospheric Diving Suit (ADS)

greatly improved. Two 2.25 hp constant speed adjustable pitch propellers are used on most existing ADS to help divers “fly” underwater or stay in the same site when they flow slightly down (Shen et al. 2015). The developing electronic ring propeller (ERP) is expected to reduce wear and maintenance and is the development direction of future propellers. Neutral cable connects the ADS and TMS, transmitting the underwater power source, image information, status information and communication link between the diver and the deck commander (Liu 2009). When ADS is close to zero underwater buoyancy or a suspended state, the tensile force inside the neutral cable is very small, leading to several circle of cable looseness appears at the same time under fast cable releasing rapid. Therefore, the synchronous transmission mechanism consists of a set of counter-rotating active wheels and passive wheels will be necessary for cable smooth and orderly arrangement. The wheels provide the same direction traction to help send neutral cable out of TMS, while appropriate inverse hysteresis force to keep neutral cable tightly aligned back on the winch (Zhao et al. 2014).

Advantages ADS is able to send divers directly to the underwater site, carrying out more effective operation. Smaller and lighter weight make it easier get into some limited space, engaging complex diving that only wet divers can do before. ADS eliminates or alleviates the physiological risks brought by ordinary wet diving. Divers do not need to decompress or pressurize for a long time, thus extending the underwater residence time and improving the operating efficiency. ADS can be equipped with various operation tools and adjust operation depth above rated work depth by propeller. When hovering over the water, ADS also has the ability of resistance to the current at the same time. With these advantages, ADS has a good military and civilian generality, increasingly wide application in all kinds of underwater operation, and it is gradually forming industry market. The advantages of low economic cost, high efficiency, and sufficient security also gradually revealed.

Atmospheric Diving Suit (ADS)

Key Applications Application range of Atmospheric Diving Suit ADS has become an effective way of underwater operation. In ocean engineering, ADS is currently used in deep-sea oil and gas resources development, realizing many functions such as offshore platform jacket installation, pipeline and cable laying, oil facilities and structure inspection support, underwater platform cleaning, rope hanging, life support POD delivering, and so on. It can also be used in offshore industries, such as underwater industrial operations. In the aspect of submarine rescue, ADS has successfully participated in the Deep Submergence Rescue Program of various countries and carried out the task of underwater rapid assessment and rescue. ADS can be widely used in the exploitation, operation, and application of deep-sea resources. Important Events of Atmospheric Diving Suit In 1975, the JIM won the privilege of petroleum engineering maintenance, carrying out oil well operations for 5 h 59 min at a depth of 300 m under water. JIM created the longest diving record in 150 m+depth work at the time (Curley and Bachrach 1982). The WASP completed the repair of an oil pipeline 20 cm in diameter at a depth of 650 m under water in conjunction with a Remote Operated Vehicle (ROV), setting a record for the depth of the submarine pipeline maintenance work at that time (McCabe et al. 2000). At the beginning of 1988, the QSZ-I conducted a 2500 square meters census of Yingxiu bay reservoir in Aba Tibetan autonomous prefecture, Sichuan province, inspecting concrete erosion and damage. In less than 10 days, the position of more than 2000 m2 of underwater scouring, grinding, and silting was basically found out, which provided a technical basis for the reinforcement of the bottom plate of the dam gate of Yingxiu bay reservoir (Lin et al. 1990). In the summer of 1988, the QSZ - I conducted dam crack detection for Beijing Zhuwo reservoir, scanning and recording five dam sections. According to the accurately specified position, underwater repair was successfully carried out.

81

The NEWTSUIT first participated in the rescue of the wrecked ship SS Edmund Fitzgerald in 1995 (Jiang et al. 2013a). In September 1998, the OceanWorks Company (OWC) completed a 2000-feet-deep manned submersible test for ADS2000 system in NEDU, Panama City. After several times of function demonstration experiments, ADS2000 system was officially delivered to the US navy (Gibson and English 2000).

Cross-References ▶ Human Occupied Vehicle (HOV) ▶ Submarine

References Aylmer AR (1996) John Lethbridge:the first inventor of a diving engine, without communication of air. Hist Diver 8:13–17 Barton R (1973) Armoured suit has 1000ft capability. Offshore Serv 6:18–21 Curley MD, Bachrach AJ (1982) Operator performance in the one-atmosphere diving system Jim in water at 20 degrees c and 30 degrees c. Undersea Biomed Res 9(3):203–212 Davis RH (1951) Deep diving and submarine operations: a manual for deep sea divers and compressed air workers. Siebe, Gorman & Company, Cwmbran Earls T, Fridge D, Balch J (1979) Operational experience with atmospheric diving suits. In: 11th annual offshore technology conference proceedings, pp 1527–1531 Harris GL (1985) Iron suit: the history of the atmospheric diving suit. Best Publishing Company, Arizona Jiang XY, Liu T, Wang X (2013a) Current status of atmospheric diving suit and its key techniques. Ship Sci Technol 35(9):1–8 Jiang XY, Liu T, Wang X, An HR (2013b) Multi-objective optimization analysis of pressure hull in atmospheric diving suit. J Ship Mech 17(8):944–951 Jiang XY, Liu T, Zhang MR, Wang X (2013c) Plastic correction of pressure hull’s limit load considering material properties. J Ship Mech 17(11):1278–1291 Jim Gibson, Jim English (2000) THE U.S. NAVY ADS2000. Ocean Works International, Inc Lin BY, Zhu GX, Wang XH (1990) Underwater detection and reinforce technique for the Ying-xiu bay power plant’s concrete sandbank. Saf Dam 4:60–70 Liu H (2009) The research of underwater vehicle design and control technique. The electronical and mechanical institution of Shanghai University, Shanghai Loftas T (1973) JIM: homo aquatic-metallicum. New Scientist, 621–623

A

82 McCabe, Chuck, John.(2000) Deepwater spool piece repair. Underwater Magazine, 11–12 Nuytten RT (1985) Rotary joint. US, US4549753 Nuytten RT (1990) Pressure equalizing rotary joint. US, US4903941 Scott D (1931a) Seventy fathoms deep. Faber, London Scott D (1931b) The Egypt’s gold. Faber& Faber, London Shen D, Zhao JH, Wang L, Wang Y, Ma L (2015) Application of control technology in atmospheric diving system. Shipbuilding China 4:78–89 Taylor L, Lawson T (2009) Project deepsearch: an innovative solution for accessing the oceans. Mar Technol Soc J 43(5):169–177 Thornton MA (2000) A survey and engineering design of atmospheric. Texas A&M University, Monterey, California USA Yang QS, Hu Y, Cui WC (2015) Development and application of domestic and international atmospheric diving suits. Shipbuilding of China (3):183–191 Zhao JH, Zhang MR, Wang S, Shen D, Yin H, Liu T (2014) Application and development trend of tether management system (TMS) for ROV. Shipbuilding China 3:222–232

Atmospheric Diving System (ADS)

Automatic Identification System ▶ Impact of Maritime Transport ▶ Ship Propulsion System

Autonomous and Remotely Operated Vehicle (ARV) ▶ Hybrid Remotely Operated Vehicle (HROV)/ Autonomous and Remotely Operated Vehicle (ARV) ▶ Submersible

Autonomous Lagrangian Circulation Explorer (ALACE) Atmospheric Diving System (ADS)

▶ Profiling Float

▶ Atmospheric Diving Suit (ADS)

Autonomous Underwater Glider (AUG) ATOT, Arctic Tandem Offloading Terminal

▶ Glider

▶ Moored Ship in Ice

Autonomous Underwater Vehicle (AUV) Automatic Control ▶ Intelligent Control Algorithms in Underwater Vehicles

Zhengping Feng School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China

Synonyms

Automatic Control System ▶ AUV/ROV/HOV Control Systems

Doppler velocity log (DVL); Long baseline (LBL); Ultrashort baseline (USBL); Unmanned underwater vehicle (UUV)

Autonomous Underwater Vehicle (AUV)

Definition Autonomous underwater vehicles (AUVs) are unmanned underwater vehicles (UUVs) without tethers that are powered by onboard energy sources. They are intended to accomplish predefined tasks with little or no human supervision. They can be fully or largely autonomous, communicating intermittently with operators using acoustic or radio links. Gliders form a distinct subclass of AUVs. They move through the water column, translating the vertical forces of positive or negative buoyancy into a horizontal motion using wings. Whereas propeller-driven AUVs have endurance measured in hours or days (tens or hundreds of miles), glider endurance is measured in weeks or months (thousands of miles).

Brief History of AUV Development AUV development began in the late 1950s (Blidberg 2001; Von Alt 2003). A few AUVs were built mostly to focus on data gathering. SPURV I (Widditsch 1973), the first “true” AUV developed by the Applied Physics Laboratory (APL) of the University of Washington in the early 1960s, displaced 480 kg and could operate at 2.2 m/s for 5.5 hours at depths to 3000 m. It was acoustically controlled from the surface and could autonomously run at a constant depth, seesaw between two depths, or climb and dive at up to 50 . During the 1970s, a number of test beds were developed. The University of Washington (APL) developed the Unmanned Arctic Research Submersible (UARS) (Francois and Nodland 1972) and SPURV II (Nodland et al. 1981) (modified from SPURV I) to gather data from the Arctic regions. IFREMER’s Epulard was designed in 1976, assembled by 1978, and fully operational by 1980. Epulard was capable of diving to 6,000 m water depth and was operated remotely by an acoustic link. Also at this time, the development of the SKAT vehicles started under the AUV program of Institute of Marine Technology Problems, Russian Academy of Sciences.

83

In the 1980s a number of technological advances greatly affected AUV development. Small, low-power computers and memory offered the potential of implementing complex navigation and control algorithms on autonomous platforms. Advances in software systems and engineering made it possible to develop complex software systems. The Advanced Unmanned Search System (AUSS), developed by the Naval Oceans System Center (now SPAWAR) of the United States, was launched in 1983. AUSS displaced 907 kg, carried 20 kw hours of energy in silverzinc batteries, and was rated to 6000 m. It had an acoustic communication system that transmitted video images through the water. During 1990–2000, AUVs grew from proofof-concept test beds into operational systems able to accomplish specified tasks. A number of organizations around the world undertook development efforts focused on various operational tasks. Examples include Odyssey of MIT Sea Grant AUV Lab, Autonomous Benthic Explorer (ABE) and REMUS of Woods Hole Oceanographic Institution (WHOI) (Yoerger et al. 1991; Allen et al. 1997), Autosub of Southampton Oceanographic Centre (Brierley et al. 2002), Theseus of International Submarine Engineering (Butler and den Hertog 1993), and Hugin of Kongsberg Simrad of Norway (Storkersen et al. 1998). Since 2000, AUV technology extended from the academic and research environment into the commercial mainstream of the ocean industry. Examples include Nereus (Bowen et al. 2008; Bowen et al. 2009) and Sentry (Yoerger et al. 2006) of WHOI, Bluefin of (Panish et al. 2011), r2D4 of the University of Tokyo (Ura et al. 2004), Tethys long-range AUV of Monterey Bay Aquarium Research Institute (MBARI) (Hobson et al. 2012).

AUV Subsystems and Technologies Pressure and Hydrodynamic Hulls By providing enclosed chambers for the onboard equipment that needs to work in dry, atmospheric environment, pressure hulls withstand the

A

84

ambient pressure. As the depth rating increases, the proportion of vehicle weight allocated to pressure hull increases, thus reducing the proportion of weight allocated to the other systems including energy source. Depending on depth ratings, pressure hulls can have either cylindrical or spherical shapes. The most common materials for pressure hulls are aluminum or titanium. However, the use of ceramics as a pressure hull material appears promising and has been verified in WHOI Nereus (Bowen et al. 2008). Hydrodynamic hulls are intended to reduce flow drag as AUVs move through water to maximize speed and endurance. Streamlined hulls are preferable as they generate less turbulent flows around vehicle body. However, the hydrodynamic performance of the laminar flow body degrades significantly when the hull shape is changed due to mission configuration. Therefore, torpedo body that has a nose cap followed by a parallel midsection and a tapered tail section is applied as an alternative and thus leads to an additional drag of approximately 30%. Ballast Although traditional AUVs are designed to have slightly positive buoyancy and passive stability (the ability to return to the upright position), it is still desirable to adopt ballast to aid ascent and descent. Emergency drop weights, also part of ballast systems, are released in the event of hardware failure so that the vehicle returns to the surface. Energy and Power Management Most power systems for AUVs rely on batteries that supply limited energy. Lead-acid batteries became common AUV power sources in the 1980s. However, such batteries provide relatively little energy given their weight. Silver-zinc batteries replaced lead-acid batteries but proved expensive and vulnerable to failure after relatively few cycles. Alternatively, vehicles have used lithium primary batteries, which are not rechargeable. With advance in the development of more efficient and safer batteries for electric cars, the rechargeable lithium-ion battery has been widely used as energy source for current AUVs.

Autonomous Underwater Vehicle (AUV)

A number of battery cells are connected in series to form battery banks which are then connected in parallel to provide sufficient current draw by onboard electrical devices. To ensure uniform battery drain and to handle ground faults, power management system is needed. Power management system monitors the main bus voltage and the current drawn from each battery bank. Based on this data, the energy used is calculated and the energy remaining can be estimated. Propulsion and Maneuvering Systems Propulsion for torpedolike AUVs is generally provided by electric motors that drive propellers. As the amount of energy AUVs that can carry onboard is limited, the efficiency of the propulsion system is critical to minimize the amount of electrical power consumed. Due to their advantages over brushed motors in efficiency, reliability, and power density, brushless direct-current (DC) motors are applied increasingly for AUV propulsion systems. For a propulsion system to achieve high efficiency, it may be necessary to match the optimal rotational speeds of motors and propellers by reduction gears. Transmission loss needs to be considered as well. Most AUVs maneuver by deflecting control surfaces or vectored propulsors. In missions that require hovering, vehicles can maneuver to face against currents. Alternatively, multiple thrusters can be applied to allow vehicles to hover with demanded heading. Gliders can maneuver by shifting weights along longitudinal axes for pitching and rotating weight (such as batteries) around longitudinal axes for rolling and yawing. To achieve desirable sawtooth pattern, changing buoyancy and shifting internal weights have to be coordinated. Navigation and Positioning Systems Navigation and positioning systems, on their own, reckon AUVs’ positions from various types of motion sensors by fusion algorithms, e.g., Kalman filter or particle filters (Stutters et al. 2008). Positional information is the indispensable part of the survey data collected by AUVs. By working together with control systems, navigation and positioning systems enable AUVs to move along

Autonomous Underwater Vehicle (AUV)

pre-defined tracks which are specified by path/ trajectory (motion) planners. For low-cost AUVs, primary onboard motion sensors include global positioning system (GPS) receiver (valid only when AUVs are on surface), strap-down microelectromechanical systems (MEMS), inertial navigation system (INS), depth sensor, and magnetic compass. INS integrates acceleration and angular rate from inertial measurement unit (IMU) to estimate motion states, which include translational and rotational speeds, position, attitude, and heading. Magnetic compass determines vehicle’s heading relative to the north direction. Depth sensor measures vehicle’s depth in terms of the ambient hydrostatic pressure. To reduce the growing rate of error in position estimate, MEMS-based INS is replaced by fiber optic gyro (FOG)- or ring laser gyro (RLG)-based INS. Moreover, Doppler velocity log (DVL) that transmits four separate beams downward from the vehicle to measure the speed relative to the bottom is required (Kinsey and Whitcomb 2004). Even equipped with FOG
/RLG-based INS and DVL, the positional error involved in navigation and positioning system grows with time. For some missions, external position fixes are usually needed to assist navigation and positioning system. Underwater position fixes are often provided by acoustic positioning systems, e.g., ultrashort baseline (USBL) system and long baseline (LBL) systems. With only one transducer installed on the ship hull, USBL is portable and consequently preferred when a variety of surface ships may be used. However, careful shipboard calibration is required to provide adequate positional accuracy. Traditional LBL requires both the deployment of equipment on the seafloor and careful calibration. Inverted LBL, where GPS receivers are used on the ocean surface, is promising as shipboard calibration is not required. Control Systems Generally, control systems can be divided into motion and equipment control systems. While the latter mainly deals with control of onboard devices, e.g., switching of power for equipment and payload sensors, the former enables the

85

vehicle to move with demanded pattern that matches the pre-defined tasks. From the viewpoint of implementation, equipment control is not difficult as simple logic-based algorithms are sufficient. However, motion control is a challenge as both complex vehicle dynamics and various disturbances have to be dealt with (Yuh 2000). As roll and pitch modes are often left uncontrolled due to their passive stability, primary motion control system enables AUVs to move with demanded forward speed, heading, and depth. Advanced motion control system requires AUVs to move along pre-defined tracks with specified forward speed, heading, and depth. With motion controller as its “brain,” motion control system generates maneuvering commands for propulsion and maneuvering system, which in turn drive thrusters and/or control surfaces, in terms of the deviation between the set and feedback values of interested motion states, e.g., forward speed, heading, and depth. It is the motion controller that needs to deal with the complex vehicle dynamics and various disturbances. Dynamics of underwater vehicles, including hydrodynamic parameter uncertainties, are highly nonlinear, coupled, and time varying. Disturbances come from ocean currents, varying buoyance due to the density variation of seawater at different depths and near-surface wave-suction forces. Typical control schemes include sliding mode control (Yoerger and Slotine 1985; Healey and Lienard 1993), nonlinear control (Nakamura and Savant 1992), and adaptive control (Zhao et al. 2004). Communications Bidirectional acoustic, radio-frequency, and satellite-based communications systems enable human operators to supervise and redirect AUV missions from a ship or from land. However, the duty cycle of the telemetry system can have a significant impact on AUV energy requirements or endurance. Compared to radio-frequency communications, high-speed communications in the underwater acoustic channel has been more challenging because of limited bandwidth, extended

A

86

multipath, severe fading, rapid time variation and Doppler shifts (Chitre et al. 2008). While robust low-complexity incoherent techniques for low data rate acoustic communications have been employed widely, coherent techniques are promising. Motion Planning To a great extent, the autonomy of AUVs is equivalent to their ability of motion planning, that is, generating collision-free, dynamically feasible, and low-cost trajectories which enable AUVs to accomplish their missions. Path planner is the essential part of a motion planner. Traditional path planner often imposes a discretization over the operational area and searches an optimal path over the discretization. The discretization is obtained by imposing a regular grid represent the collision-free areas. Since vehicle dynamics is not taken into account, the planned paths are not necessarily dynamically feasible (Button et al. 2009). Therefore, it is desirable for AUVs to plan their trajectories online in response to vehicle motion states while deliberating on how best to follow the paths planned in advance. In addition, motion planners will have to reason about the high-level aspects that are related to the dynamic interaction between AUVs and their surroundings. There is a growing need to reason about both the high-level and low-level aspects simultaneously (McMahon and Plaku 2016). Payloads Payloads on-board AUVs mainly include acoustic, magnetic, electromagnetic, optical, and CTD (conductivity, temperature, and depth) sensors. Mounted on AUVs that move near the bottom with constant altitudes, the data connected by these payload sensors have higher and more consistent spatial resolution than their shipboard compartments. Acoustic Sensor

Typical acoustic sensors include multi-beam sonar, side-scan sonar, and sub-bottom profiler. Multi-beam sonars consist of a Mills Cross transducer array that produces multiple across-

Autonomous Underwater Vehicle (AUV)

track beams as the intersection of one transmit beam (fan shaped across the survey track) with numerous receive beams (each fan shaped along the track). This allows the sounder to provide continuous swath bathymetry over a 120–150 sector. Side-scan sonars are one of the most accurate sensors for imaging large areas of the ocean floor by transmitting beams of acoustic energy from the sides of the vehicle (across the track). Unlike a ship, the sonar transducers of side-scan sonar are mounted on the vehicle hull rather than towed. Sub-bottom profilers are a shallow geophysical sonar designed to provide higher-resolution profiles below the seabed but with less penetration than lower-frequency seismic equipment such as air guns and sparkers. Sub-bottom profiler images are made up of backscatter from the seafloor strata. The first boundary is at the seabed, between the water and the seafloor itself. As layers of clay, sand, and various other sediments succeed each other, they reflect sound at their interfaces. It is this reflected energy that the system uses to build the image. A recent trend in active sonars is synthetic aperture sonar (SAS). Whereas simple active sonars emit individual pings and process them individually, SAS systems on moving AUVs assemble images from multiple pings and thus give sonar designers the means to increase sonar aperture and improve resolution by an order of magnitude. Magnetic Sensor

Magnetic sensors include magnetic compass and magnetometer. While the former is used for AUV navigation (heading), the latter is applicable to inspect pipelines/cables and to locate ferrous objects on the seabed. Optical Sensor

Imaging optical sensors include still and video cameras augmented by lighting systems. The performance of imaging optical sensors for missions such as inspection can also be enhanced using simple dual-laser scaling devices that emit parallel beams of light separated by a known distance.

Autonomous Underwater Vehicle (AUV)

Pairs of dots projected by these devices provide a scale helpful in visually identifying objects. Non-imaging optical sensors are used for basic tasks, such as measuring water turbidity. CTD Sensor

CTD sensors are used to collect oceanographic data and predict and improve the performance of onboard sonars. The conductivity of seawater is closely linked to its salinity. Salinity, temperature, and depth are, in turn, the predominant factors used to predict undersea sound velocity. Therefore, CTD sensors can be thought of as calibrating tools for the active sonars.

Key Applications With advances in AUV technologies, e.g., highdensity energy source, underwater navigation and communication, and sensing, AUVs have been increasingly applied in ocean exploration and exploitation. Most AUVs have been developed to accomplish science, commercial, and military missions. Science Mission Typical science missions include: • Locating, mapping, and photographing hydrothermal vents by WHOI ABE (German et al. 2008. • High-quality acoustic imaging of seabed by the University of Tokyo r2D4 (Ura et al. 2004. • Conducting swath sonar measurements under sea ice by the University of Southampton Autosub II (Wadhams et al. 2006. • Tracking a coastal upwelling front by MBARI’s Tethys long-range AUV (Zhang et al. 2012. • Capturing water samples at chlorophyll fluorescence peaks in a thin phytoplankton layer by MBARI dorado (Zhang et al. 2010. • Assessing the Deepwater horizon oil spill with WHOI’s sentry (Kinsey et al. 2011) • Oceanographic research with commercial gliders Seaglider (Eriksen et al. 2001), Slocum (Webb et al. 2001), and spray (Sherman et al. 2001.

87

Commercial Mission Typical commercial missions include: • Survey of gas transport pipeline route with Kongsberg Hugin 1000 (Marthiniussen et al. 2004) • Offshore surveying with Kongsberg Hugin 3000 (Marthiniussen et al. 2004) • Undersea-cable deployment and inspection with ISE Theseus (Butler and den Hertog 1993) • Searching wreckages of missing airplanes, e.g., REMUS 6000 for Air France Flight 447 and Bluefin-21 for Malaysia Airlines Flight 370 Military Mission Typical military mission includes autonomous mine reconnaissance survey with Kongsberg Hugin (Marthiniussen et al. 2004).

Cross-References ▶ AUV/ROV/HOV Propulsion System ▶ AUV/ROV/HOV Resistance ▶ AUV/ROV/HOV Stability ▶ Doppler Velocity Log for Navigation System in Underwater Vehicle ▶ Glider ▶ Remotely Operated Vehicle (ROV) in Subsea Engineering ▶ Structural Design ▶ Submersible ▶ Underwater Information Sensing Technology

References Allen B, Stokey R, Austin T, Forrester N, Goldsborough R, Purcell M, von Alt C (1997) REMUS: a small, low cost AUV; system description, field trials and performance results. In: MTS/IEEE Oceans’97, pp 994–1000 Blidberg DR (2001) The Development of autonomous underwater vehicles (AUV); a brief summary. In: IEEE international conference on robotics and automation ’01, Seoul Bowen AD, Yoerger DR, Taylor C, et al. (2008) The Nereus hybrid underwater robotic vehicle for global ocean science operations to 11,000 m depth. In: IEEE Oceans 2008, pp 1–10

A

88 Bowen AD, Yoerger DR, Taylor C, McCabe R, Howland J, Gomez-Ibanez D, Kinsey JC, Heintz M, McDonald G, Peters DB, Bailey J, Bors E, Shank T, Whitcomb LL, Martin SC, Webster SE, Jakuba MV, Fletcher B, Young C, Buescher J, Fryer P, Hulme S (2009) Field trials of the Nereus hybrid underwater robotic vehicle in the challenger deep of the Mariana trench. Oceans 10 Brierley AS, Fernandes PG, Brandon MA, Armstromg F, Millard NW, McPhail SD, Stevenson P, Pebody M, Perrett J, Squires M, Bone DG, Griffiths G (2002) Antarctic krill under sea ice: elevated abundance in a narrow band just south of ice edge. Science 295(5561):1890–1892 Butler B, den Hertog V (1993) Theseus: a cable-laying AUV. In: Proceedings of IEEE Oceans’93, pp I210– I213 Button RW, Kamp J, Curtin TB, Dryden J (2009) A survey of missions for unmanned undersea vehicles. Rand National Defense Research Inst Santa Monica Ca, Ft. Belvoir Chitre M, Shahabudeen S, Stojanovic M (2008) Underwater acoustic communications and networking: recent advances and future challenges. Mar Technol Soc J 42(1):103–116 Eriksen CC, Osse TJ, Light RD, Wen T, Lehman TW, Sabin PL, Ballard JW, Chiodi AM (2001) Seaglider: a long-range autonomous underwater vehicle for oceanographic research. IEEE J Ocean Eng 26(4):424–436 Francois R, Nodland W (1972) Unmanned Arctic Research Submersible (UARS) system development and test report. Applied Physics Laboratory, University of Washington, Seattle German CR, Yoerger DR, Jakuba M, Shank TM, Langmuir CH, Nakamura K (2008) Hydrothermal exploration with the autonomous benthic explorer. Deep-Sea Res I Oceanogr Res Pap 55(2):203–219 Healey AJ, Lienard D (1993) Multivariable sliding mode control for autonomous diving and steering of unmanned underwater vehicles. IEEE J Ocean Eng 18(3):327–339 Hobson BW, Bellingham JG, Kieft B, McEwen R, Godin M, Zhang Y (2012) Tethys-class long range AUVsextending the endurance of propeller-driven cruising AUVs from days to weeks. In: 2012 IEEE/OES autonomous underwater vehicles (AUV), pp 1–8 Kinsey JC, Whitcomb LL (2004) Preliminary field experience with the DVLNAV integrated navigation system for oceanographic submersibles. Control Eng Pract 12(12):1541–1549 Kinsey JC, Yoerger DR, Jakuba MV, Camilli R, Fisher CR, German CR (2011) Assessing the deepwater horizon oil spill with the sentry autonomous underwater vehicle. In: 2011 IEEE/RSJ international conference on intelligent robots and systems, pp 261–267 Marthiniussen R, Vestgard K, Klepaker RA, Storkersen N (2004) HUGIN-AUV concept and operational experiences to date. In: Oceans’ 04 MTS/IEEE TechnoOcean’04, vol 2, pp 846–850 McMahon J, Plaku E (2016) Mission and motion planning for autonomous underwater vehicles operating in

Autonomous Underwater Vehicle (AUV) spatially and temporally complex environments. IEEE J Ocean Eng 41(4):893–912 Nakamura Y, Savant S (1992) Nonlinear tracking control of autonomous underwater vehicles. In: Proceedings 1992 IEEE international conference on robotics and automation (Cat. No.92CH3140-1), vol 3, pp A4–A9 Nodland W, Ewart T, Bendiner W, Miller J, Aagaard E (1981) Spurv II-an unmanned, free-swimming submersible developed for oceanographic research. In: IEEE Oceans 81, pp 92–98 Panish R, Taylor M, IEEE (2011) Achieving high navigation accuracy using inertial navigation Systems in Autonomous Underwater Vehicles. In: 2011 IEEE – Oceans Spain, Oceans-IEEE. IEEE, New York Sherman J, Davis RE, Owens W, Valdes J (2001) The autonomous underwater glider “Spray”. IEEE J Ocean Eng 26(4):437–446 Storkersen N, Kristensen J, Indreeide A, Seim J, Glancy T (1998) Hugin – UUV for seabed surveying. Sea Technol 39(2):99–104 Stutters L, Liu HH, Tillman C, Brown DJ (2008) Navigation technologies for autonomous underwater vehicles. IEEE Trans Syst Man Cybern Part C Appl Rev 38(4):581–589 Ura T, Obara T, Nagahashi K, Kim K, Oyabu Y, Sakamaki T, Asada A, Koyama H, IEEE (2004) Introduction to an AUV “r2D4” and its Kuroshima Knoll survey mission. IEEE, New York Von Alt C (2003) Autonomous underwater vehicles. In: autonomous underwater Lagrangian platforms and sensors workshop, vol 3 Wadhams P, Wilkinson JP, McPhail S (2006) A new view of the underside of Arctic Sea ice. Geophys Res Lett 33(4):L04501 Webb DC, Simonetti PJ, Jones CP (2001) SLOCUM: An underwater glider propelled by environmental energy. IEEE J Ocean Eng 26(4):447–452 Widditsch HR (1973) SPURV-the first decade, Washington Univ Seattle Applied Physics Lab, No. APL-UW-7215 Yoerger DR, Slotine JE (1985) Robust trajectory control of underwater vehicles. IEEE J Ocean Eng OE-10(4):462–470 Yoerger DR, Bradley AM, Walden BB (1991) The autonomous benthic explorer (ABE): an AUV optimized for deep seafloor studies. In: Proceedings of the seventh international symposium on unmanned untethered submersible technology (UUST91), pp 60–70 Yoerger DR, Bradley AM, Martin SC, Whitcomb LL (2006) The sentry autonomous underwater vehicle: field trial results and future capabilities. In: AGU fall meeting abstracts Yuh J (2000) Design and control of autonomous underwater robots: a survey. Auton Robot 8(1):7–24 Zhang Y, McEwen RS, Ryan JP, Bellingham JG (2010) Design and tests of an adaptive triggering method for capturing peak samples in a thin phytoplankton layer by an autonomous underwater vehicle. IEEE J Ocean Eng 35(4):785–796 Zhang Y, Godin MA, Bellingham JG, Ryan JP (2012) Using an autonomous underwater vehicle to

AUV/ROV/HOV Control Systems track a coastal upwelling front. IEEE J Ocean Eng 37(3):338–347 Zhao S, Yuh J, Choi SK, IEEE (2004) Adaptive DOB conltrol for AUVs. In: 2004 IEEE international conference on robotics and automation, vols 1–5, Proceedings, IEEE international conference on robotics and automation ICRA. IEEE, New York, pp 4899–4904

89

model nonlinearity. It works underactuated in complex underwater environment, and the body must maintain autonomous stability in the process of operation. Therefore, the design of appropriate control system to ensure the stability of the underwater platform during the operational process is of great significance to the successful and accurate completion of the underwater mission of AUV/ROV/HOV.

Autonomous Underwater Vehicles (AUVs) Scientific Fundamentals ▶ Environmental Perception for Underwater Vehicles ▶ Hydrodynamics for Subsea Systems

Autopilot Control System ▶ Semisubmersible Vehicle Autopilot Control System

AUV/ROV/HOV Control Systems Changhui Song School of Engineering, Westlake University, Hangzhou, China

Synonyms Automatic control system; Control approach; Control device; Control module; Control unit; Controller; Motion control system

Definition Control system is a kind of active regulation system designed to improve or optimize specific performance or indictors for economic, social, or physical systems. AUV/ROV/HOV belongs to a multi-degree-of-freedom underwater platform system with high redundancy, coupling, and

Difficulties in the Design of Control System Underwater vehicles have a large variety of types, and they are widely involved in undersea surveillance, inspection, and survey missions. Typically, gliders are common with a torpedo shape for long range missions, and human-occupied vehicles (HOVs) as well as remote operating vehicles (ROVs) are generally of a cubic shape used for hovering tasks. For some specific applications, undersea pipeline inspection, offshore infrastructure surveillance, and large vessel maintenance, AUV is preferred. Regardless of modeling issues, the value of a model-based control approach depends on how robust and efficient the control scheme can adopt the hydrodynamic model. Potential trends of current methods focus on faster controllers to assist the pilot or the autopilot with better accuracy. Optimal controllers can reduce propelling actions to save the battery power as well as to increase the propeller lifespan. Moreover, numerous uncertainties should be considered, including parameter variations, nonlinear hydrodynamic damping effects, sensor transmit delays, and ocean current disturbances (Clement et al. 2016). Each underwater vehicle is designed to perform specific functions. Even for the same type of underwater vehicle, their shapes may be very different. Therefore, the mathematical models of underwater vehicles will be much different. Each underwater vehicle pursues unique performance indicators. This makes it difficult to solve all control system design problems with a single theory or model system.

A

90

A decade of operational experience by numerous research groups has demonstrated ROVs to be ideal platforms for “rapid prototyping” and “rapid field deployment” of UUV subsystems. Recent examples include sonar imaging and survey, optical imaging and survey, navigation, control, oceanographic sampling, and subsea manipulation. Numerous research results first pioneered with ROVs, and towed vehicles are now commonly employed for autonomous underwater vehicles (AUV, HOV) and seafloor observatories (Smallwood et al. 1999). Structure of Underwater Vehicle System In the following chapters, the typical structure of the underwater vehicle system will be given. These components are the integral part for underwater vehicle to complete basal motion. The submersible control system has two components, surface ship control system and underwater vehicle control system. The surface ship control system includes system GMT clock, ship dynamic positioning system, ship LBL navigation system, GPS satellite navigation system, real-time data logging system, science pay load interface, instruments, video distribution, and recording subsystem. The underwater vehicle control system includes vehicle control computer system, surface telemetry, pilot’s user interface (such as joystick, keyboard instruction), engineer user interface, manipulator user interface, work package interface, and pilot video display. Vehicle control computer system includes control process, positioning navigation process, LBL-Doppler navigation process, and power management and hotel process, shown in Fig. 1. Surface Systems

The surface control system is the central “brain” of the ROV control system. It is comprised of a “core” system of safety-critical systems that are essential for safety and control of the ROV and an “extended” system providing non-safety-critical systems such as data logging and video recording. The safety-critical core system is comprised of the vehicle control computer and user interfaces for the vehicle pilot and engineer. The pilot station provides real-time video and navigation

AUV/ROV/HOV Control Systems

instruments, has joystick controls for closed-loop control of the vehicle reference trajectories and navigation waypoints, and has controls for the vehicle’s manipulator arms. The engineer station has a more comprehensive set of real-time vehicle status indicators and enables the engineer to control all vehicle subsystems. The modules are depicted in Fig. 1. Concentrating the vehicle intelligence in the ship-board control computer dramatically simplifies and accelerates development – reprogramming an on-ship computer is significantly easier than reprogramming an embedded vehicle control computer. Vehicle on-Board Core Control System The on-board vehicle control system controls and monitors all vehicle sensors and actuators in response to real-time commands from a surface control system. We will adopt a “data concentrator” (DCON) type of architecture. Each data concentrator (DCON) module will independently control the power and data telemetry for an entire vehicle subsystem or scientific payload. The DCONs will receive commands from the surface control computer, monitor the status, and report data from on-board vehicle subsystems and instruments. Each data concentrator operates asynchronously and will communicate to the surface control computer via a high bandwidth fiber-optic telemetry link. The data concentrator vehicle control system architecture employs relatively simple on-vehicle computer systems. We anticipate employing commercial off-the-shelf (COTS) embedded computers for the data concentrators. The simplicity of the data concentrator design will render them both highly reliable and easily reconfigurable (Smallwood et al. 1999).

Realization of Vehicle Control System Generally, the underwater vehicle is equipped with scanning sonars and a color CCD camera, together with depth sensors and a fiber-optic gyroscope. This device is intended primarily as a research platform upon which to test novel

AUV/ROV/HOV Control Systems

91

Surface Systems A

System GMT Clock

Ship Dynamic Positioning System

Surface Core Control System

Ship LBL Acosutic Navigation System

Pilot’s user Interface, joy stick, Instruments

Vehicle Control Computer GPS Statellite Nev Sy stem Real-Time Data Logging System

LBL-Doppler Navigation Process

Navigation Process

Engineer user Interface

Power Management and Hotel Process

Control Process

Manipulator user interface, instruments

Science Payload Interface, instruments

Work package interface, instruments

Video Distribution and Recording Subsystem

Surface Telemetry

Pilot Video Display

Data/Video Telemetry from Vehicle to Surface

Sonar DCON

Manipulator DCON

LBL Navigation DCON

Vehicle Telemetry

Work Package DCON

Doppler Navigation DCON

Thruster DCON

Science Payload DCON

Navigation DCON

Video DCON

Power Mgmt and Hotel DCON

Vehicle On-Board Core Control System AUV/ROV/HOV Control Systems, Fig. 1 Underwater vehicle system structure (Smallwood et al. 1999)

sensing strategies and control methods. Autonomous navigation using the information provided by the vehicle’s on-board sensors represents one of the ultimate goals of the project (Williams et al. 2006). Embedded Controller At the heart of the robot control system is an embedded controller. Figure 2 shows a schematic

diagram of the vehicle sensors and their connections. The vehicle uses a CompactPCI system running Windows CE that interfaces directly to the hardware and is used to control the motion of the robot and to acquire sensor data. While the Windows operating system doesn’t support hard real-time performance, it is suitable for soft realtime applications, and the wide range of development and debugging tools make it an ideal

92

AUV/ROV/HOV Control Systems

AUV/ROV/HOV Control Systems, Fig. 2 Vehicle control system diagram system (Williams et al. 2006)

environment in which to test new navigation algorithms. Time-critical operations, such as sampling of the analog to digital converters, are performed on the hardware devices themselves and use manufacturer-supplied device drivers to transfer the data to the appropriate processes. The sensor data is collated and sent to the surface using an Ethernet connection where a network of computers are used for further data processing and data logging and to provide the user with feedback about the state of the sub. Communications between the computers at the surface and the sub are via a tether. This tether also provides power to the robot, a coaxial cable for transmitting video data, and a leak detection circuit designed to shut off power to the vehicle in case of a leak. While some effort might have been spent on eliminating the tether, it was felt that the development of the navigational techniques was of more immediate interest. Sonar Sonar is the primary sensor of interest on the vehicle. There are currently two sonars on the robot. A sonar unit has been mounted at the front of the vehicle. It is positioned such that its scanning head can be used as a forward and downward looking beam. This enables the altitude above the seafloor as well as the proximity of

obstacles to be determined using the wide of the angle beam of the sonar. The second sonar is an imaging sonar and has a dual frequency narrow beam sonar head that is mounted on top of the sub and is used to scan the environment in which the sub is operating. It can achieve 360 scan rates on the order of 0.25 Hz. The information returned from this sonar is used to build and maintain a feature map of the environment. Internal Sensors A laser Gyro has been included in the robot to allow the robot’s orientation to be determined. This sensor provides yaw rate information and is used to control the heading of the sub. We currently estimate the bias in the gyroscope reading prior to a mission. The bias compensated yaw rate is then integrated to provide an estimate of vehicle heading. Because the yaw rate signal will inevitably be noisy, the integration of this signal will cause the estimated heading to drift with time. At present, missions do not typically run for longer than 30 minutes, and yaw drift does not pose a significant problem on this time frame. In the future, a compass will be added to the system to allow us to periodically reset the heading for longer missions. This will also allow us to detect changes in the yaw rate bias that typically

AUV/ROV/HOV Control Systems

occur as a result of changes in the internal temperature of the unit. A pressure sensor measures the external pressure experienced by the vehicle. This sensor provides a voltage signal proportional to the pressure and is sampled by an analogue to digital converter on the embedded controller. The pressure can then be converted to a depth below the surface of the ocean. Feedback from this sensor is used to control the depth of the sub. Camera A Panasonic camera in an underwater housing is mounted externally on the vehicle. It is used to provide video feedback of the underwater scenes in which the robot operates. This is a color camera and sends the video signal to the surface via the tether. A video acquisition card is then used to acquire the video signal for further image processing. Thrusters There are currently six thrusters on the vehicle. Four of these are oriented in the vertical direction, while the remaining two are directed horizontally. This gives the vehicle the ability to move itself up and down, control its yaw, pitch and roll and move forward and backward, and move lateral motion.

Vehicle Control Method Control system of a mobile robot in sixdimensional space in an unstructured, dynamic environment that is found underwater can be a daunting and computationally intensive endeavor. Navigation and control both present difficult challenges in the subsea domain. We have developed a distributed, decoupled control architecture to help simplify the controller design. The vehicle control architecture currently running on the sub is based on the Distributed Architecture for Mobile Navigation (DAMN) as proposed in Rosenblatt (1997). This behaviorbased control architecture uses a centralized arbiter to combine votes from various behaviors running in the system in order to determine the optimal course of action to pursue. A behavior

93

encapsulates the perception, planning, and task execution capabilities necessary to achieve one specific aspect of robot control and receives only that data specifically required for that task (Brooks 1986). Decoupled Control By decoupling the control problem, individual controller design is greatly simplified. In the case of the typical vehicle, vertical motion is controlled independently of its lateral motion using two separate PID controllers. These controllers are then tuned to provide the required performance in each case. This division of control has been selected as it fits in with many of the anticipated missions to be undertaken by the vehicle. A typical mission might see the vehicle performing a survey of an area of the Great Barrier Reef while maintaining a fixed height above the seafloor (Williams et al. 1999). The task of performing the survey can then be made independent of maintaining the vehicle altitude. This also allows us to optimize the performance of the depth controller prior to deploying the navigation algorithms used for mapping of the environment to ensure that the vehicle has little risk of hitting the sea floor. The behaviors that run on the vehicle are also divided into horizontal and vertical behaviors, and there are consequently two arbiters currently present. One is responsible for setting the desired depth of the vehicle, while the other sets the desired yaw and forward offset to achieve horizontal motion. For a survey mission, the vertical behaviors would typically be responsible for keeping the sub from colliding with the seafloor. The vertical behaviors that run on the vehicle include maintain minimum depth, maintain minimum altitude, maintain depth, and maintain altitude. The combination of the outputs of these behaviors determines the depth at which the vehicle will operate. A large negative vote by the maintain minimum altitude behavior will keep the vehicle at a minimum distance from the seafloor. The horizontal behaviors that would run on a survey mission include follow line (sonar and/or vision), avoid

A

94

obstacles, move to location, and perform survey. The combination of the outputs of these behaviors determines the orientation maintained by the vehicle as well as the forward offset applied to the two horizontal thrusters. This allows the vehicle to move forward while maintaining its heading. Low- and High-Level Control The control of the sub is further decoupled into low level- and high-level control processes. The low-level processes run on the embedded controller and are used to interface directly with the hardware (see Fig. 3). In addition, the PID controllers have been implemented at this level. This allows the PID controllers to respond quickly to changes in the state of the sub without being affected by the data processing and high-level control algorithms running at the surface.

AUV/ROV/HOV Control Systems, Fig. 3 The low-level control processes that run on the vehicle controller. These processes include processes for sampling the internal

AUV/ROV/HOV Control Systems

The high-level processes run on a pair of Pentium machines at the surface control station. Information from the sub’s sensors is fed to a series of processes running on these machines. These processes use the data supplied by the sensors to determine the desired set points for the low-level control processes. The raw sensor data is preprocessed to produce virtual sensor information – information that is of interest to multiple behaviors in the system. The behaviors register their interest in the data being generated by the virtual sensors and send votes to the arbiters to specify their desired course of action. A task-level mission planner is used to enable and disable behaviors in the system depending on the current state of the mission and its desired objectives. The arbiter combines the votes from the behaviors and selects the optimal action to satisfy the goals of the

sensor readings, computing the PID control outputs, and driving the thrusters (Williams et al. 2006)

AUV/ROV/HOV Control Systems

system. A schematic representation of the data flow within the system is shown in Fig. 4. This control strategy relies on the ability of the sub to gather information about its environment and reason about its desired actions. By continuously monitoring the state of the environment, the sub is able to respond to changes as they occur. Distributed Control A number of processes have been developed to accomplish the tasks of gathering data from the robot’s sensors, processing this data, and reasoning about the course of action to be taken by the robot. These processes are distributed across a network of computers and communicate asynchronously via a TCP/IP socket-based interface using a message passing protocol developed at the center. A central communications hub is responsible for routing messages between the distributed processes running on the vehicle and on the command station. Processes register their interest in messages being sent by other processes in the system, and the hub routes the messages when they arrive. While this communications structure has some drawbacks, such as potential communications bottlenecks and reliance on the performance of the central hub, it does provide some interesting possibilities for flexible configuration, especially during the development cycle of the system. The above introduction mostly comes from Smallwood et al. 1999 and Williams (2006). More technical details or design method can be found in their related literature.

Key Applications Over the past 20 years, with the widespread development of large-scale integrated circuit in the world, which plays an important role in the field of marine technology, many new submarine vehicles have been created to solve a wide range of problems. These devices have already demonstrated their effectiveness in performing emergency rescue, ocean survey, environment monitoring, inspections and operation, research, and other types of work.

95

Because the marine environment is unstructured and hazardous, the development of underwater vehicles will face many challenging scientific and engineering problems, and researchers have made great efforts to overcome these problems so far (Paull et al. 2014). The progress in new materials, sensor technology, computer technology, and advanced algorithms has greatly contributed to research and development activities in the underwater vehicle community. With technological advances, underwater vehicles have the advanced control technology and intelligent control system that can efficiently perform scheduled tasks with its own decisionmaking and control capabilities. Advanced Control Technology The AUV control methodologies that have been proposed in the literature include linear control (see Yildiz et al. (2009)), sliding mode control (see Yang et al. (2013) and Kim et al. (2015)), and fuzzy and neural network control (see Khodayari and Balochian (2015) and Lakhekar et al. (2015)). One simple and effective nonlinear control design approach that has been implemented in marine applications is dynamic inversion (DI), in which the control law is formulated to eliminate system nonlinearities by means of feedback. The DI control technique in turn allows to incorporate well-established linear control techniques. In spite of its flexibility and simplicity, standard DI lacks robustness to model uncertainties. Several modifications were added to the basic DI control structure to improve its robustness characteristics; see Steinicke and Michalka (2002) and Wang et al. (2012). Regardless of these attributes, DI has several shortcomings and limitations, including blind nonlinearity cancellation, large control effort, and numerical singularity configurations of square matrix inversion. A new inversion-based control design methodology is Generalized Dynamic Inversion (GDI); see and Bajodah (2009). The methodology is of the left inversion type, and hence it does not involve deriving inverse equations of motion for the plant. In GDI, dynamic constraints are prescribed in the form of differential equation that encapsulates the control objective and is

A

AUV/ROV/HOV Control Systems, Fig. 4 The high-level process and behaviors that run the vehicle. The sensor data is preprocessed to produce virtual sensor information available to the behaviors. The behaviors receive the virtual sensor information and

send votes to the arbiters who send control signals to the low-level controllers (Williams et al. 2006)

96 AUV/ROV/HOV Control Systems

AUV/ROV/HOV Control Systems

generalized inverted using the Moore-Penrose Generalized Inverse (MPGI)-based Greville formula. The GDI control technique has been an effective tool for several engineering problems; see Bajodah (2009), Bajodah (2010), Hameduddin and Bajodah (2012), and Gui et al. (2013). The Robust Generalized Dynamic Inversion (RGDI) control system is obtained by Ansari and Bajodah (2017). Location and Navigation Technology Navigation is one of the key AUV technologies because the localization, path tracking, and control of the vehicle are all based on precise navigation parameters. Some navigation methods commonly used for land and air are not suitable for underwater because of the attenuation effect of water on electromagnetic signals, and underwater navigation has become a challenging issue in AUV research (Paull et al. 2014). Among the many underwater navigation systems available, the inertial navigation system (INS) using inertial sensors typically acts as the central navigation system of AUVs because of its autonomy (Stutters et al. 2008). Generally, the INS contains an inertial measurement unit (IMU), which consists of accelerometers measuring linear acceleration and gyroscopes measuring angular velocity; the

97

accelerometers and the gyroscopes are usually made up of three mutually perpendicular accelerometers and three mutually perpendicular gyroscopes, respectively. For inertial navigation, the instantaneous speed and position of the vehicle are obtained by integrating the measured values of the accelerometers and gyroscopes. The errors of the IMU increase with increasing elapsed time due to the drift of accelerometers and gyroscopes. Theoretically, the velocity and heading errors accumulate linearly over time, and the position error accumulates exponentially over time (Ali and Mirza 2010). Therefore, the INS can provide relatively accurate navigation information within a short time, but it is physically impossible for a pure inertial navigation system to maintain the high-precision level throughout a mission. Aiding the INS with external information or measurements is an effective means of improving navigation accuracy and has been widely used. In AUV navigation, auxiliary sensors or other navigation systems, such as a Doppler Velocity Log (DVL), compass, pressure sensor, Global Positioning System (GPS), acoustic positioning system (APS), or geophysical navigation system, are usually combined with the INS to form an integrated navigation system (Kussat et al. 2005 and Vasilijevic et al. 2012) (Figs. 5 and 6).

AUV/ROV/HOV Control Systems, Fig. 5 SINS/DVL integrated navigation structure (Bao et al. 2019)

A

98

AUV/ROV/HOV Control Systems

a

c Geophysical sensors

Measured geophysical data Matching algorithm

Geophysical reference map

Estimated Geophysical data

Optimal matching position

b d Estimated position INS

Data fusion

AUV/ROV/HOV Control Systems, Fig. 6 Principle diagram of geophysical navigation-assisted inertial navigation (Bao et al. 2019)

AUVs typically use the INS as their main navigation system; however, due to inherent error accumulation of inertial sensors over time, the pure INS has difficulty obtaining long-range precision navigation. Therefore, INS is often combined with other navigation systems or devices such as GPS, DVL, acoustic positioning systems, or geophysical navigation systems to improve the AUV navigation accuracy (Bao et al. 2019).

Cross-References ▶ Automatic Control System ▶ Control Approach ▶ Control Device ▶ Control Module ▶ Control Unit ▶ Controller ▶ Motion Control System

References Ali J, Mirza MRUB (2010) Performance comparison among some nonlinear filters for a low cost SINS/GPS integrated solution. Nonlinear Dyn 61(3):491–502 Ansari U, Bajodah AH (2017) Robust generalized dynamic inversion control of autonomous underwater vehicles. IFAC-PapersOnLine 50(1):10658–10665

Bajodah A (2009) Generalised dynamic inversion spacecraft control design methodologies. IET Control Theory Appl 3(2):239–251 Bajodah A (2010) Asymptotic generalised dynamic inversion attitude control. IET Control Theory Appl 4(5):827–840 Bao J, Li D, Qiao X, Rauschenbach T (2019) Integrated navigation for autonomous underwater vehicles in aquaculture: a review. Inf Proces Agric. https://doi. org/10.1016/j.inpa.2019.04.003. Accepted Manuscript Clement B, Rui Y, Mansour A, Ming L (2016) A modeling and control approach for a cubic AUV. IFACPapersOnLine 49(23):279–284 Gui H, Jin L, Xu S (2013) Attitude maneuver control of a two-wheeled spacecraft with bounded wheel speeds. Acta Astronaut 88:98–107 Hameduddin I, Bajodah AH (2012) Nonlinear generalised dynamic inversion for aircraft manoeuvring control. Int J Control 85(4):437–450 Khodayari M, Balochian S (2015) Modeling and control of autonomous underwater vehicle (AUV) in heading and depth attitude via self-adaptive fuzzy PID controller. J Mar Sci Technol, 20(3):559–578 Kim M, Joe H, Kim J, Yu SC (2015) Integral sliding mode controller for precise manoeuvring of autonomous underwater vehicle in the presence of unknown environmental disturbances. Int J Control, 88(10):2055– 2065 Kussat NH, Chadwell CD, Zimmerman R (2005) Absolute positioning of an autonomous underwater vehicle using GPS and acoustic measurements. IEEE J Ocean Eng 30(1):153–164 Lakhekar GV, Waghmare LM, Londhe PS (2015) Enhanced dynamic fuzzy sliding mode controller for autonomous underwater vehicles. In 2015 IEEE Underwater Technology (UT) (pp. 1–7). IEEE

AUV/ROV/HOV Hydrostatics Liu X, Xu X, Liu Y, Wang L (2014) Kalman filter for crossnoise in the integration of SINS and DVL. Math Probl Eng 2014:1–8 Paull L, Saeedi S, Seto M, Li H (2014) AUV navigation and localization: a review. IEEE J Ocean Eng 39(1):131–149 Smallwood D, Bachmayer H, Whitcomb L (1999) A new remotely operated underwater vehicle for dynamics and control research. In: Proceedings of the 11th international symposium on unmanned untethered submersible technology, Durham, pp 370–377 Steinicke A, Michalka G (2002) Improving transient performance of dynamic inversion missile autopilot by use of backstepping. In: AIAA guidance, navigation, and control conference and exhibit, Monterey Stutters L, Liu H, Tillman C, Brown DJ (2008) Navigation technologies for autonomous underwater vehicles. IEEE T Syst Man Cy C 38(4):581–589 Vasilijevic A, Borovic B, Vukic Z (2012) Underwater vehicle localization with complementary filter: performance analysis in the shallow water environment. J Intell Robot Syst 68(3–4):373–386 Wang Z, Liu L, Wang, Y, Wang Z. (2012) Dynamic integral sliding mode for launch vehicle attitude control system. In 2012 24th Chinese Control and Decision Conference (CCDC). Chengdu, China. IEEE. 1713–1718 Williams S, Newman P, Majumder S, Rosenblatt J, Durrant-Whyte H (1999) Autonomous transect surveying of the great barrier reef. In Proc. Australian Conf. on Robotics and Automation, 16–20 Williams SB, Newman P, Dissanayake G, Rosenblatt J, Durrant-Whyte H (2006) A decoupled, distributed AUV control architecture. In: International symposium on robotics, vol 31, pp 246–251 Yang I, Byun S, Seo B, Lee D, Han DS (2013) Robust dynamic inversion based on sliding mode control for autonomous underwater vehicles. Intell Auton Veh 8:79–84

99

Definition Hydrostatics is a kind of ability to enable an AUV/ ROV/HOVafloat in the certain diving depths. The relationship between buoyancy and weight results in two primary flotation conditions: surfaced and submerged. Variation in weight must be supported by the corresponding buoyancy for each condition. Many configurations, such as the suitable location of the main ballast tanks (MBTs), solid droppable ballast, and buoyancy material, may be adopted to control hydrostatics of submersibles for different purposes.

Scientific Fundamentals

Synonyms

As with any object in a fluid, a submerged AUV/ROV/HOV must conform to Archimedes Principle, which is applied on by two opposite direction forces: upward buoyancy (due to the displacement of water by its hull) and downward weight (Renilson 2015). The AUV/ROV/HOV is sensitive to variation in both buoyancy and weight. An exact equality of these two forces is termed “neutral” buoyancy, which is a hover condition (to keep a given depth while stationary); if weight exceeds buoyancy, known as “negative” buoyancy, the submersible will drop and deeply submerge to the seabed. Conversely, if buoyancy exceeds weight, known as “positive” buoyancy, the submersible will rise to float on the water surface (Burcher and Rydill 1994). An AUV/ROV/HOV on the surface has to satisfy the same hydrostatic principles. However, it has a smaller watertight volume above water and relatively lower water-plane characteristics than that of a surface ship. With the flooding water into the ballast tanks, the weight of AUV/ROV/ HOV increases and the submersible transitions from floating on the surface to being fully submerged. Correspondingly, the immersed volume, termed “displacement,” is also enlarged until the integral structure volume (maximization).

Buoyancy; Density; Displacement volume; Fixed weight; Hydrostatics pressure; Salinity; Submerged depth; Temperature; Variable weight; Weight

Buoyancy Force The buoyancy force of submersible is given by the immersed volume, partly or fully, multiplied by the water density and gravity acceleration, i.e.,

AUV/ROV/HOV Hydrostatics Jinfei Zhang Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China

A

100

F ¼ rgV, where r is the density of seawater, g is the acceleration due to gravity, and V is the immersed volume of the submersible. Hydrostatic Pressure The force acting on the submerged AUV/ROV/ HOV is the weight of the seawater column above it. Since seawater can be considered incompressible and the variation of g can be neglected (the height h of fluid column is much smaller than the radius of Earth), hydrostatic pressure can be calculated according to the following formula: p
p0 ¼ rgH, where p is the hydrostatic pressure, p0 is the atmospheric pressure on sea surface, and H is the height from the surface to the submerged depth. Displacement Volume The changes in the geometry of the AUV/ROV/ HOV will be caused by hydrostatic pressure loading with depth. The hydrostatic pressure is increased with the greater submerged depth, which results in a reduction in displacement volume. Therefore, the buoyancy will be reduced due to the compression as diving depth increases, especially for the deep submersible. On the other hand, as submerging, the temperature around the AUV/ROV/HOV is different, which has also an effect on the immersed volume, especially for the volume of solid buoyancy material. That is to say, the displacement volume is the function of hydrostatic pressure and the temperature (Tie dong 2010). The changes in displacement volume due to the variation in these two parameters result in different buoyancy subsequently. Density Buoyancy is not only dependent on the volume but also on the density of the water. And the density is varied if the AUV/ROV/HOV is operated in different areas. Seawater specific gravity (SG) can range from 1.00 near the mouths of rivers or in fjords where the water is virtually fresh due to melting glaciers, to about 1.03 where there is high salinity. A standard value of 1.0275 toward the higher end of the density range is averagely encountered in a submersible operation. When the AUV/ROV/

AUV/ROV/HOV Hydrostatics

HOV approaches a coast or where there are substantial changes with depth (layers) of temperature and salinity, a quite large change may occur rapidly, and a variation of 3% in buoyancy due to seawater density variation would be adopted in the design (Burcher and Rydill 1994). As well as salinity effecting to the density of displacing seawater around submersible, the hydrostatic pressure due to the submerged depth from the sea surface and the temperature also affect the density. With the increase of the submerged depth, hydrostatic pressure will be larger and the temperature will be lower. For the same salinity, the lower temperature results in a higher density of water; while for the same temperature, the higher salinity leads to higher density. Therefore, the density is determined by the salinity, the temperature, and the hydrostatic pressure. Then any changes of density will result in the variation of buoyancy. Weight The determination of the weight of an AUV/ROV/HOV is more complicated than that of buoyancy. Whereas buoyancy is primarily related to gross volumes of geometrically simple forms and the density of displacing water; weight is the summation of every element (fixed weight and variable weight) that goes into a submersible. The fixed weight consists of large components, such as pressure hull structure, main propulsion plant, batteries, etc., and some minor structures and systems, which are permanently installed components. The variable weight associates with crew, their effects, stores, and the fluid contents of many tanks. TRIM The mass and longitudinal center of gravity of a submersible will change during the operations. In addition, changes in seawater density and hull compressibility will all result in small changes to buoyancy and position of the center of buoyancy. Therefore, it cannot be kept in upright position any more, maybe in longitudinal inclination equilibrium because of these changes.

AUV/ROV/HOV Hydrostatics

Key Applications Unlike for a surface ship, in the case of a deeply submerged AUV/ROV/HOV, the immersed volume cannot be increased by increasing the vessel’s draught. Thus, for equilibrium in the vertical plane, the mass must be balanced exactly by the buoyancy force. The state of equilibrium in a given submergence depth tends to be unstable. A slight upward or downward movement from this position will result in the boat moving away from this initial position. Further, variation in buoyancy will occur continuously due to small changes in seawater density in the vertical and horizontal planes, while variation in weight will mainly be due to the consumption of stores, ballast, or collection samples. These will also have a significant influence on the ability to control the submersible in the vertical plane. Most submersibles have an operational requirement to stop or move at very low speed (hover condition). It can be contrived to keep weight and buoyancy as nearly equal as possible, and means or special control devices for doing so are provided. Another reason for neural buoyancy is related to safety. If the submersible is in power failure and not in neutral buoyancy, it will lose depth control. If lighter than buoyancy, it will rise uncontrolled to the surface. It must, however, be a safety design criterion for HOV. The opposite situation, i.e., heavier than buoyancy, is potential disaster when the submarine will plunge beyond its collapse depth or hit the sea bed. Main Ballast Tanks (MBTs) To keep the depth control, the main ballast tanks (MBTs) are fitted in a suitable location for the submersible where it is flooded or discharged with seawater, either wholly or partially. When it submerges, the submersible must either increase its weight or reduce its buoyancy. Conversely, an increase in buoyancy or a reduction in weight leads it to rise from submerged to surface. Solid Droppable Ballast For deep submersible, which is likely to be for exploration, some solid droppable ballast will be

101

added. The initial weight is larger than buoyancy, which leads the submersible to sink quickly. When the given depth arrives, part of the solid ballast will be abandoned. Then the submersible will be in the hover condition. After cruising is finished, the rest of the solid ballast will be thrown away. The weight is much less than the buoyancy, and the submersible will be back to the surface quickly. Buoyancy Material Adjustment of the relationship of weight and buoyancy is operated by flooding or discharging the seawater in MBTs. They can be readily enough flooded from the sea through the tanks valves, but discharging water from the tanks is not so easy. The water can be blown out to sea using high-pressure air, but that is noisy and subsequent venting of the tanks raises atmospheric pressure inside the boat. Alternatively, a pumping system can also be used to discharge to sea, and all the piping is required to withstand diving pressure. It may be useless for the deep submersible. Some solid buoyancy material will be adopted for the deep submersible. The MBTs are fully flooded, and most of the buoyancy will be provided by this material when it is submerged in deep sea. The MBTs are only discharged when the submersible is almost back to surface, which help to float on the surface better. Compensating Tanks Compensating tanks are used for correcting the trim of a submerged AUV/ROV/HOV, which usually is composed of two tanks, one forward and another afterward. To correct the longitudinal balance, one tank will be emptied and another filled. The amount of correcting depends on the current situation of the submerged submersible.

References Burcher R, Rydill L (1994) Concepts in Submarine Design. Cambridge University Press, United Kingdom Renilson M (2015) Submarine Hydrodynamics. Spring Briefs in Applied Sciences and Technology, United Kingdom Tie dong Z (ed) (2010) Design principle of submersible. Harbin Engineering University Press, China

A

102

AUV/ROV/HOV Propulsion System Yunsai Chen and Kun Liu Department of Technology, National Deep Sea Center of China, Qingdao, Shandong, China

Synonyms Autonomous underwater vehicle (AUV); Brushless DC motor (BLDCM); Humanoccupied vehicle (HOV); Magnetohydrodynamics (MHD); Remote operated vehicle (ROV); Tandem propulsion system (TPS)

AUV/ROV/HOV Propulsion System

unbounded inflow; an actuator disk with no thickness and the water is accelerated only in the axial direction when passing through the disk; velocity and pressure distributions over the disk are uniform. As shown in Fig. 1, when passing through the ideal thruster, the velocity and pressure of the control volume will change. Thrust and induction velocity of ideal thruster: 1. Fluid quality flowing through the agitating plate per unit time: m ¼ rA0 ðV A þ ma1 Þ A0 – disk area, A0 ¼ πD2/4 r – density of water VA – around the fluid velocity of disk 2. The momentum of inflow:

Definition mV A The AUV/ROV/HOV propulsion system is an underwater energy conversion device that converts other forms of energy into kinetic energy of AUV/ROV/HOV. It consists of several thrusters that work together to propel the AUV/ROV/HOV to complete various complex movements underwater, such as cruise, search, hover, and other complex sports. Due to different missions, different underwater vehicles have different requirements for their own propulsion systems. In general, the propulsion system of an underwater vehicle should have good maneuverability, efficient propulsion efficiency, and low weight.

Scientific Fundamentals Fundamentals of Propulsion System Theory of Ideal Thruster

A disk surface of diameter D having no thickness has the function of absorbing external power and pushing water to obtain an axial induction speed so that the ideal disk surface is called ideal thruster, also called agitating plate. The ideal thruster makes the following simplifying assumption: an ideal and incompressible fluid; thruster operating in an

The momentum of outflow: mðV A þ ma Þ The momentum of increment: mðV A þ ma Þ
mV A ¼ mma ¼ rA0 ðV A þ ma1 Þma 3. According to the momentum theorem: the force acting on the fluid is equal to the increment of momentum per unit time (ideal thrust): T i ¼ rA0 ðV A þ ma1 Þma

ð1Þ

4. Application of Bernoulli’s equation Far upstream to the front side of the disk: 1 1 P0 þ rV 2A ¼ P1 þ rðV A þ ma1 Þ2 2 2

ð2Þ

The rear side of the disk to far downstream: 1 P01 þ rðV A þ ma1 Þ2 ¼ P0 2

1 þ rðV A þ ma Þ2 2

Subtracting one equation from another:

ð3Þ

AUV/ROV/HOV Propulsion System

103

$ 3UHVVXUH

&

%

3

3Ą

3 %

$ )ORZ 3DWWHUQ &RQWURO 9ROXPH

&

9$

%

& %

$

9HORFLW\

9 $­D

9 $­D

$

&

9 $­D

9$

A

3

9 $­D

AUV/ROV/HOV Propulsion System, Fig. 1 Pressure and velocity of ideal thruster

Pi ¼ P01
P1 The disk thrust is equal to the pressure difference:     1 T i ¼ A0 P01
P1 ¼ rA0 V A þ ma ma 2

ð4Þ

5. By comparing Eqs. (1) and (4), the induction velocity at the disk surface can be obtained: 1 ma1 ¼ ma 2

ð5Þ

ma1 – axial induction velocity of the disk ma – axial induction velocity of far downstream Propeller Propulsion Theory

The movement of underwater vehicles is usually achieved by propellers, which are simple and widely used thrusters. The function of a propeller is to convert the torque to thrust. Thrust is another name for force, and a basic axiom of

mechanics tells us that force (thrust) is equal to mass multiplied by acceleration. In other words, if we apply acceleration to a large amount of water, we will generate thrust or push that will accelerate the underwater vehicle forward when a large amount of water moves in the opposite direction. As shown in Fig. 2, the blades of the propeller and the shaft are supported on the propeller hub at a certain angle, and the propeller hub is driven by the propeller shaft. When the propeller rotates one revolution, the forward distance in the axial direction is called the process, and the difference between the pitch and the process is called slippage, and the ratio of slippage to pitch becomes the slip ratio, which can be expressed as: Sa ¼

H
v=n H

Sa – slip ratio H – slip, m n – propeller rotate speed, rps v – the speed of underwater vehicles, m/So

ð6Þ

104

AUV/ROV/HOV Propulsion System

AUV/ROV/HOV Propulsion System, Fig. 2 Propeller

In order to generate thrust, the propeller must accelerate or move a large amount of water astern. Now, when the propeller rotates, it looks like a screw and slides over the water without moving any water. If this happened, the propeller would advance an amount equal to the propeller pitch, which is called zero slip. But in order to produce thrust, we must accelerate or move water, and therefore, it is apparent that the propeller will not advance the full amount of pitch in each revolution. In order to generate thrust, we must have slip, and the amount of slip will be proportional to the thrust required by the vehicle. The propeller thrust T can be expressed as: T ¼ rn2 D4 K T

ð7Þ

r – the density of water, kg/m3 n – propeller rotation speed, rps D – propeller diameter, m KT – thrust coefficient In order to generate this thrust, a torque must be applied to the propeller to rotate the propeller and the water is pushed out by the blades. The torque Q can be expressed as: Q ¼ rn2 D4 K Q

ð8Þ

KQ – torque coefficient Thrust coefficient and torque coefficient are both functions of propeller geometric parameters. Thruster Type The core component of the propulsion system is the thruster. Different types of thrusters have been

AUV/ROV/HOV Propulsion System, Fig. 3 Electric thruster

developed according to the type of underwater vehicle and the environment in which it is used. At present, the thrusters commonly used in AUV/ROV/HOV propulsion systems mainly include electric thrusters, hydraulic thrusters, water-jet thrusters, hubless rim-driven thrusters, tandem thruster system, magnetohydrodynamic drive thruster, bionic thrusters, etc. Electric Thruster

Most battery-powered underwater vehicles use motors to directly drive the propeller. DC motors and AC motors can be used. The DC motor has low cost, the speed control and the control system are simple, and the AC motor needs the inverter to convert the DC into AC, which has high cost and complicated system. In particular, underwater vehicles that use battery packs as a power source use DC motors. Brushless DC motor is a new type of DC motor developed with the rapid development of electronic technology in recent years. Its most prominent feature is that there is no complicated commutation mechanism. Usually, permanent magnet is used as rotor and has no excitation loss, no commutation spark, no radio interference, easy operation, and maintenance (Fig. 3). Hydraulic Thruster

Some large and medium-sized underwater vehicles use hydraulic motors as propulsion power. Compared with the underwater motor, the thruster with hydraulic motor has the following advantages: the hydraulic propulsion system controlled

AUV/ROV/HOV Propulsion System

105

A

AUV/ROV/HOV Propulsion System, Fig. 4 Hydraulic thruster of sub-Atlantic

AUV/ROV/HOV Propulsion System, Fig. 5 Hubless rim-driven thruster

by the flow has good speed regulation performance, and it is easy to realize stepless speed regulation in a wide range; the hydraulic propulsion system usually has hydraulic compensation, and it is easier to realize the sealing of the system; the safety is good, the reliability is high, the installation position is flexible, and the cost is low. As shown in Fig. 4, the hydraulic thrusters manufactured by Sub-Atlantic are used in many ROVs.

thruster (Yan et al. 2017). As shown in Fig. 5, the hubless rim-driven thruster is mainly composed of ducts, propeller blades, armature, rareearth magnetic steel, front and rear sliding bearings, bearing supports, and other components. The hubless rim-driven thruster integrates the rotor of the motor with the propeller blades of the thruster. The stator of the motor is integrated into the duct of the thruster. When the motor is running, the rotor of the motor drives the propeller blades to rotate, generating thrust and driving the vehicle to sail. The propeller blades without hub are supported by two sliding bearings that are fixed to the front and rear ducts. Without the rear guide vanes, the space occupied by the propeller hub can be fully utilized, and the blades can be protected from external impurities damage. Due to its compact structure, high efficiency, low vibration and noise, good cooling conditions, no need for dynamic sealing, modular design and disassembly, it has become a hot research topic in the field of underwater vehicles (Song et al. 2015).

Water-Jet Thruster

The water-jet thruster is a propulsion device that uses the reaction of the high-speed water jet ejected from the jet pipe to provide thrust. It is similar to the aviation jet thruster, except that water instead of air combustion mixed gas is used as the working medium. After the water is obtained at a high speed by a large-flow highpressure water pump installed on the underwater vehicle, the jet is ejected to generate thrust. The advantage of the water-jet propulsion device is that almost all accessories on the underwater vehicle are eliminated; the loss of the shafting and transmission and the loss of the thruster’s cavitation are eliminated; the underwater vehicle can be easily manipulated. Hubless Rim-Driven Thruster

In recent years, a propulsion device integrating the structure of a powerful motor and a propeller has appeared, which is called hubless rim-driven

Tandem Propulsion System (TPS)

In 1961, American engineer F. R. Haselton proposed the concept of tandem propulsion system (TPS) (Nanba and Shimizu 1988). After more than 20 years of efforts, in 1985, the engineers of Ametek designed and manufactured an underwater vehicle with TPS. The TPS requires two propellers that are oriented in the longitudinal

106

AUV/ROV/HOV Propulsion System

Magnetohydrodynamic Drive Thruster

AUV/ROV/HOV Propulsion System, Fig. 6 Tandem thruster system

direction of the underwater vehicle (usually mounted on the bow and stern respectively), allowing for flexible control of the underwater vehicle in 6 degrees of freedom, as shown in Fig. 6. This type of propulsion system actually places the stator of the electric machine in the underwater vehicle and supports the rotor on the outer casing of the underwater vehicle, and the blade is directly mounted on the rotor. It differs from a conventional underwater vehicle propeller in that the pitch of the blade of a conventional propeller is usually unchanged, while the blade of the omnidirectional propeller changes at every moment, and the pitch variation of each blade is not according to the same law. Compared with other thrusters, TPS is simple in construction, easy to manufacture, and maintain, especially, when the diameter of the vehicle is limited, TPS has higher efficiency than conventional thrusters, thus saving energy and reducing ROV cable diameter and cable resistance. For HOV and AUV, the weight and volume of the power supply can be reduced. TPS can better absorb external load changes and reduce the impact on underwater vehicles, and because its power and thrust are borne by two sets of blades, TPS has better tail vibration performance than conventional thrusters. In addition, the tail shaft of the TPS system is long, the weight is large, the price is high, the seal is easy to leak, and the control system is complicated and requires computer-aided control. Therefore, the TPS system has not been put into practical use yet, but it represents one of the developments of the underwater vehicle propulsion system, and it will be widely used in future.

A magnetohydrodynamic drive thruster or MHD accelerator is a method for propelling underwater vehicles using only electric and magnetic fields with no moving parts, accelerating an electrically conductive propellant (liquid or gas) with magnetohydrodynamics (Takeda et al. 2005). The fluid is directed to the rear and as a reaction, the underwater vehicle accelerates forward. The working principle involves the acceleration of an electrically conductive fluid by the Lorentz force, resulting from the cross product of an electric current (motion of charge carriers accelerated by an electric field applied between two electrodes) with a perpendicular magnetic field. The Lorentz force accelerates all charged particles (positive and negative species) in the same direction whatever their sign, and the whole fluid is dragged through collisions. As a reaction, the vehicle is put in motion in the opposite direction. This is the same working principle as an electric motor (more exactly a linear motor) except that in an MHD drive thruster, the solid moving rotor is replaced by the fluid acting directly as the propellant (Bui et al. 2010). MHD thrusters are classified into two categories according to the way the electromagnetic fields operate: Conduction devices and induction devices. Conduction devices when direct current flows in the fluid due to an applied voltage between pairs of electrodes, the magnetic field being steady. Inductive devices when the alternating current is caused by a rapidly changing magnetic field, such as eddy currents. In this case, no electrode is required. MHD is attractive for underwater vehicle applications because it has no moving parts, which means that a good design might be silent, stealthy, reliable, and efficient. Additionally, the MHD design eliminates many of the wear and friction pieces of the drivetrain with a directly driven propeller by an engine. The major problem with MHD is that with current technologies, it is more expensive, and much slower than a propeller driven by an engine. In 1991, the world’s first fullsize prototype Yamato 1 was completed in Japan after 6 years of R&D by the Ship & Ocean Foundation (Fig. 7). The ship successfully carried a

AUV/ROV/HOV Propulsion System

107

A

AUV/ROV/HOV Propulsion System, Fig. 7 MHD Thruster of Yamato 1

crew of 10 plus passengers at speeds of up to 15 km/h in Kobe Harbor in June 1992. Bionic Thruster

The traditional underwater propulsion system is propeller propulsion, but the efficiency is relatively low. Modern bionic technology provides new ideas for the development of new water propulsion systems. Fish and other marine life have evolved in the ocean for millions of years, and their perfection is beyond imagination. The data shows that fish in the ocean by the fins and body twist to provide forward momentum, jellyfish through the squeeze and shrink umbrella to provide forward momentum, its advancement is almost perfect, and the efficiency is as high as 98% (Naomi 2000). At present, many countries are actively developing bionic underwater vehicles, such as Charlie I and RoboTuna II of Massachusetts Institute of Technology, as shown in Fig. 8, UPF-2001 and PF-700 of Japan’s National Marine Research Center, Bionic Robotic Eel, and SPC of Beijing University of Aeronautics and Astronautics. Because the performance of materials is far from the advanced level of marine biological muscles, the biomimetic vehicle test platform or prototype developed by scientists in various countries at present is a simple mechanical transmission to simulate the promotion of marine organism.

AUV/ROV/HOV Propulsion System, Fig. 8 RoboTuna II

However, the test results of various countries show that the propulsion efficiency of these bionic thrusters is higher than that of ordinary propeller propulsion. Therefore, with the deepening of research and breakthroughs in key technologies, the bionic thruster will be more widely used. Control Allocation of Thrust Control allocation of thrust is the core of the control system of underwater vehicles (Liu et al. 2018). By properly arranging the number and position of the thrusters on the surface and inside of the vehicle, and properly setting the thrust of each thruster, the complex underwater movement of the submersible is completed (Sordalen 1997), as shown in Fig. 9. The underwater vehicle is a highly nonlinear coupled system with high nonlinearity. It is difficult to obtain accurate hydrodynamic coefficients, so it is difficult to establish accurate maneuvering motion models (Johansen et al. 2004). At the same time, environmental disturbances, such as ocean currents, are difficult to predict (Lindegaard and Fossen 2003). Therefore, most propulsion system power distribution does not depend on precise mathematical models. Intelligent control combines the artificial intelligence method with the feedback control theory and has obvious advantages in dealing with

108

AUV/ROV/HOV Propulsion System

AUV/ROV/HOV Propulsion System, Fig. 9 Thrusters distribution of “Jiaolong” HOV

complexity and uncertainty. Therefore, when the system thrust distribution is promoted, the intelligent control method can obtain sound control effects. At present, the intelligent control methods commonly used in underwater vehicle propulsion systems mainly include classical PID control, fuzzy control, neural network control, synovial variable structure control, and S-plane control method (Cao et al. 2013). Motor of Thruster The brushless DC motor (BLDCM) has the advantages of simple structure, high efficiency, reliable operation, low mechanical noise, good speed regulation, etc., and is widely used in underwater thrusters. Conventional brushless DC motors cannot be used directly in seawater highpressure environments, and motors for underwater thrusters require unique design. First, in order to prevent the brushless DC motor from being damaged by high pressure, the motor housing must be filled with insulated aviation hydraulic oil and connected to a compensator installed inside or outside the thruster to ensure that the oil pressure in the motor housing is always slightly higher than the external seawater, to prevent external seawater from entering the motor housing. Secondly, the waterproof and pressureresistant design of the motor drive circuit, the housing of motor drive circuit is mainly divided into waterproof electronics housing and wet electronics housing. The waterproof electronics housing is protected against seawater pressure by adding a pressure-proof sealed casing to isolate

AUV/ROV/HOV Propulsion System, Fig. 10 Waterproof electronics housing

seawater and ensure the drive circuit is at operating pressure. Working in the environment, the drive circuit does not need special design, as shown in Fig. 10. In the wet electronics housing, the drive circuit is directly immersed in the oil to isolate the seawater by oil, but the drive circuit components need to withstand the pressure of the surrounding oil, so components that cannot

AUV/ROV/HOV Propulsion System

withstand pressure need to be designed with special protection packages. Rotary Dynamic Seal of Underwater Thruster When rotating, there is a gap between the shaft and the motor housing. In order to transfer the torque of the motor to the propeller, the problem of the rotary dynamic seal of the shaft must be solved. If an O-ring is added between the shaft and the motor housing, the O-ring will wear, heat, and deform when the shaft rotates at high speeds, and is liable to leak under high seawater pressure. Current practice has proved that the method of adding O-ring seal is not reliable. For this reason, engineers and technicians have developed a variety of advanced dynamic sealing devices, including mechanical dynamic seals, underwater rotary oil seals, and magnetic coupling isolation seals and so on. Mechanical Dynamic Seal

The essence of the mechanical dynamic seal is to convert the clearance between the shaft and the housing into the clearance between the static ring and the moving ring. The static ring is connected with the motor housing and remains stationary. The moving ring is connected with the motor shaft and rotates following with the motor shaft. Therefore, only the contact surface of the moving ring and the static ring has clearance, as shown in Fig. 11. However, the static ring is made of tungsten carbide, known as hard ring, the moving ring is made of impregnated resin graphite, known as

AUV/ROV/HOV Propulsion System, Fig. 11 Structure of mechanical dynamic seal

109

soft ring, and the two mutual contact surfaces are processed into a mirror, moving ring, and static ring tightly contact together by spring pressure. The moving ring, bushing, spring seat, and the tightening hoop are fixed into one. When the tightening hoop and the motor shaft are tightened, the moving ring can rotate with the motor in the same axis. Because the moving ring is soft ring easy to wear, when following the motor shaft rotation, there will form oil film between the moving ring and the soft ring, and the oil film fills the gap between the contact surface of the moving ring and the stationary ring, so as to prevent seawater from flowing through the contact surface. The thrusters of the 300 m underwater vehicle RECON-IV of Shenyang Institute of Automation used mechanical dynamic seal and achieved good application effect. At present, because of the complex structure, such structures cannot guarantee zero leakage, mechanical dynamic seal has been rarely used in underwater environments. Underwater Rotating Oil Seal

The underwater rotating oil seal can be used for the sealing of pressure compensated thrusters (Li 2005). The oil-filled pressure compensator always maintains motor housing pressure higher than the external seawater pressure of 0.2–0.7 bar, so the inside pressure of the oil seal is slightly higher than the outer side, thus achieving a good sealing effect, as shown in Fig. 12. This sealing method is simple and reliable but does not guarantee zero leakage. The 4500-m “Deep-Sea Warrior” HOV

A

110

AUV/ROV/HOV Propulsion System

developed in China uses this sealing method and has completed more than 100 diving missions with good performance (Liu et al. 2016). Magnetic Coupling Isolation Seal

AUV/ROV/HOV Propulsion System, Fig. 12 Oil seal of underwater thruster

AUV/ROV/HOV Propulsion System, Fig. 13 Cylindrical magnetic coupling isolation seal

The magnetic coupling isolation seal of underwater thruster converts the mechanical energy of the motor into magnetic energy, which is then converted into the mechanical energy of the propeller. According to the structural characteristics, it can be divided into cylindrical structure and planar structure. As shown in Fig. 13, the cylindrical magnetic coupling isolation seal is mainly composed of inner ring, outer ring, and isolating sleeve. The inner and outer rings are filled with high-remanence permanent magnets by U-shaped groove soft iron. The isolation sleeve is made of stainless steel or titanium alloy, and the magnetic permeability is good. The “Jiaolong” HOV thrusters use this sealing method. As shown in Fig. 14, the planar magnetic coupling isolation seal mainly consists of the original moving surface, isolation sleeve, and follow-up surface. Both the original moving surface and follow-up surface are inlaid with high remanence permanent magnets. Under the suction of the magnet, the followup surface rotates following the original moving surface and transmits torque. This seal has a large

AUV/ROV/HOV Propulsion System, Fig. 14 Surface magnetic coupling dynamic seal

AUV/ROV/HOV Propulsion System

axial force and is therefore only suitable for lowpower thrusters.

Key Applications Propulsion System of “Qian Long-III” AUV As one of the representatives of the AUV, the propulsion system of “Qian Long-III” consist of five thrusters, including four Kort-nozzle main thrusters and one horizontal channel thruster, as shown in Fig. 15. These thrusters are designed as oil-filled compensation. The special pressureresistant package design of the circuit components ensures that the drive circuit can work in a highpressure environment, while the oil seal ensures that the motor extends out of the shaft and is reliably sealed. Under the control allocation system of thrust, “Qian Long-III” can get the maximum speed of 2.5 kN, and sail more than 30 h at the speed of 2.0 kN. In April 2018, in the South China Sea, the “Qian Long-III” sailed 156.82 km

AUV/ROV/HOV Propulsion System, Fig. 15 The “Qian Long-III” AUV/ROV/HOV Propulsion System, Fig. 16 Structure of “Hai Long-III”

111

and 42.8 h in a single dive and created a new record for China’s deep-sea AUV (Li et al. 2018). Propulsion System of “Hai Long-III” ROV As one of the representative of ROV, the propulsion system of the “Hai Long-III” HOV is composed of seven thrusters, including four horizontal thrusters and three vertical ones, as shown in Fig. 16. These thrusters are driven by hydraulic motors, and the hydraulic source of the hydraulic motors is provided by a main hydraulic pump station via a seven-way servo hydraulic control valve box. The hydraulic pump station can provide a flow rate of 232 l pm and pressure of 285 bar, the servo hydraulic control valve can adjust the flow rate of pipelines and then adjust the speed of the thrusters. Under the control allocation system of the seven-way servo hydraulic valve, the “Hai Long-III” can get maximum forward and backward speed of 3.2 kN, maximum lateral moving speed of 2.4 kN, and maximum vertical moving speed of 2.0 kN. At present, “Hai Long-III” has carried out several sea tests, and its hydraulic propulsion system works well. Propulsion System of “Jiaolong” HOV As one of the representatives of HOV, the propulsion system of “Jiaolong” HOV is composed of seven thrusters, including four Kort-nozzle main thrusters in the tail, one horizontal channel thruster at the bow, and two rotary Kort-nozzle thrusters at the middle, as shown in Fig. 17. These thrusters use dry housing and wet housing isolation design, integrated built-in oil-filled compensator, magnetic coupling isolation seal drive, etc., to ensure reliable functioning for long time in the

A

112

AUV/ROV/HOV Propulsion System, Fig. 17 “Jiaolong” HOV

high-pressure seawater environment (Cui 2013). Under the control allocation system of thrust, the “Jiaolong” HOV can get maximum forward speed of 2.5 kN, cruise speed of 1.0 kN, maximum transverse velocity of 0.7 kN, and maximum dynamic vertical transfer velocity of 0.7 kN. So far, “Jiaolong” HOV has made more than 150 dives, and its propulsion system is working well.

AUV/ROV/HOV Resistance Li S, Liu J, Xu HX et al (2018) Research status of autonomous underwater vehicles in China (in Chinese). Sci Sin Inform 48:1152–1164. https://doi.org/10.1360/ N112017-00264 Lindegaard KP, Fossen TI (2003) Fuel-efficient rudder and propeller control allocation for marine craft: experiments with a model ship. IEEE Trans Control Syst Technol 11(6):850–862 Liu H, Hu Z, Ma L et al (2016) Research on a rolling diaphragm pressure compensator used for deep-sea manned submersibles. J Harbin Eng Univ 37(10):1313–1317 Liu K, Chen Y, Yang L, Zhiyuan D (2018) Thruster arrangement and fault-tolerant control of deep sea human occupied vehicle. Ship Eng 8(40):82–86 Nanba N, Shimizu T (1988) Development of variable vector propeller. J Kansai Soc Nav Archit Jpn 21:1–8 Naomi K (2000) Control performance in the horizontal plane of a fish robot with mechanical pectoral fins. Ocean Eng 25:121–129 Song BW, Wang YJ, Tian WL (2015) Open water performance comparison between hub-type and hubless rim driven thrusters based on CFD method. Ocean Eng 103:55–63 Sordalen OJ (1997) Optimal thrust allocation for marine vessels. Control Eng Pract 5(9):1223–1231 Takeda M, Okuji Y, Ajazawam T et al (2005) Fundamental studies of helical-type seawater MHD generation system. IEEE Trans Appl Supercond 15(2):2170–2173 Yan XP, Liang XX, Ouyang W et al (2017) A review of progress and applications of ship shaft-less rim-driven thrusters. Ocean Eng 144:142–156

Cross-References ▶ Autonomous Underwater Vehicle (AUV) ▶ Human Occupied Vehicle (HOV) ▶ Remote Operated Vehicle (ROV)

References Bui AK, Takeda M, Kiyoshi T (2010) Measurements of flow loss in helical-type seawater MHD power generation. J Cryog Soc Jpn 45(12):506–513 Cao J, Yin H, Liu C et al (2013) A fuzzy controller based on incomplete differential ahead PID algorithm for a remotely operated vehicle. Ocean Syst Eng 3(3):237–255 Cui WC (2013) Development of the Jiaolong deep manned submersible. Mar Technol Soc J 47(3):37–54 Johansen TA, Fossen TI, Berge SP (2004) Constrained nonlinear control allocation with singularity avoidance using sequential quadratic programming. IEEE Trans Control Syst Technol 12(1):211–216 Li Y (2005) Research on the pressure compensation for external hydraulic systems of submersible vehicles. Zhejiang University, Hangzhou

AUV/ROV/HOV Resistance Zhe Jiang and Pengfei Sun Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China

Synonyms Appendage resistance; Form resistance; Frictional resistance; Hull resistance; Resistance; Viscous resistance

Definition When the underwater vehicles such as AUVs/ ROVs/HOVs or submersibles navigate in the

AUV/ROV/HOV Resistance

sea, they will inevitably suffer the resistance of the water as they move in the water fluid medium. Therefore, the reaction force of the water on the hull is called the resistance. The resistance of the submersible is usually divided into the resistance of the bare hull and the resistance of appendage (Renilson 2015). Appendage resistance refers to the increase in the resistance value of the appendage structure, such as rudders, stabilizers, manipulators, thrusters, etc., which overhung on the naked hull. From the mechanical point of view, the resistance of the submersible consists of the frictional resistance because of the tangential force along the surface of the hull and the pressure resistance because of normal force which is exerted on the surface of the hull. Unlike the ship hull, since the submersible does not have a free surface, the pressure resistance exists only in the composition of the viscous pressure resistance, and there is no wave-making resistance.

Scientific Fundamentals Method for Studying the Submersible Resistance Methods for studying the resistance of submersibles include theoretical analysis, experimental research, and numerical calculation (Sheng 2003). Theoretical analysis can only be applied to simple problems and qualitative analysis because of the simplification of the object. Experimental method has the characteristics of strong authenticity and high reliability relative to theoretical research; but due to the cost, project duration, and other constraints, experimental method is generally only used to validate the results of numerical methods. The towing tank test and wind tunnel test are the mostly used experimental methods currently. In recent years, with the rapid development of computer technology, computational fluid of dynamics (CFD) method in the hydrodynamic performance of submersibles are applied in more and more applications. Compared to traditional theoretical and experimental methods, CFD methods have the advantages of short time consumption and low cost.

113

Classification of Submersible Resistance There are many appendage structures on the surface of the submersible, including the rudder, manipulator, thruster, underwater camera, underwater lighting, sampling basket, etc., so the submersible resistance can usually be divided into the resistance of the bare hull and the resistance of appendage according to the structure of the submersible. From mechanical point of view, the main source of resistance of the submersible under water is the tangential force along the surface of the hull and the normal force which is perpendicular to the surface of the submersible, which are the frictional resistance and the viscous pressure resistance respectively. According to the boundary layer theory, a boundary layer is formed on the surface when the viscous water flows through the submersible, and the rate of change of the fluid velocity in the boundary layer is prominent. According to the Newton internal friction law, the frictional shear stress on the surface of the submersible is great, so the resultant force of these frictional shear forces is the frictional resistance of the submersible. In scientific research, the frictional resistance can be thought of as the sum of the smooth plate frictional resistance with the same wetted surface, the same length and speed, and the additional frictional resistance after considering the tortuosity and roughness. In the theoretical study, scholars often use the formula to estimate the frictional resistance. After comparing with the experimental data, it can be proved that these formulas have appropriate precision within limits. The viscous pressure resistance is another component of the resistance of the submersible, in essence, due to the viscosity of the fluid. It is known from the theory of fluid mechanics that a lot of vortices appear in the rear part of the hull when boundary-layer separation occurs, causing a difference in fore and aft pressure, which causes resistance. This resistance is called viscosity pressure resistance. Sometimes, it is also referred as vortex resistance. There are various methods for measuring the viscosity pressure resistance, and the most commonly used method is the wake pressure measurement method. In the actual

A

114

AUV/ROV/HOV Resistance

research, in order to avoid the tediousness of the experiments and to obtain the value of the viscosity pressure resistance, the Froude two-dimension method and the three-dimensional method which is proposed in the 1950s can be used. Factors Affecting the Resistance of the Submersible The hull form is the most important factor which is affecting the resistance performance of the submersible. The following two parameters are the most sensitive parts of the resistance performance of the submersible (Renilson 2015). 1. L/D: Aspect ratio. Where L is the submarine length, D is the diameter. 2. CP ¼ AM∇ L : Prismatic coefficient. Where ▽ is the volume of the submarine and AM is midships cross-sectional area. In addition, the fore body form, the parallel middle body length and shape, and the aft body form all affect the resistance performance of the submersible.

In the formula, “Rt” is the total resistance. “Rf” is the frictional resistance. “Rpv” is the viscous pressure resistance. “Rap” is the appendage resistance. “r” is the fluid density. “V” is the submersible speed. “Cf” is the frictional resistance coefficient. “ΔCf” is the roughness coefficient. “Cpv” is the viscous pressure resistance coefficient. “Cap” is appendage resistance coefficient. (1) Empirical formula for calculating frictional resistance The following three formulas can be used to calculate the friction resistance of submersible. 1. Schoenherr formula   0:242 pffiffiffiffiffiffi ¼ lg Re C f Cf

ð2Þ

When Re > 106–109, the formula is equal to: 0:4631 ðlgRe Þ2:6

ð3Þ

0:075 ðlgRe
2Þ2

ð4Þ

Cf ¼

Key Applications 2. ITTC formula Studying the resistance performance of the submersible is of great significance for improving the cruising speed for AUV/ROV/HOV. Methods on Measuring Submersible Resistance There are generally three methods to measure the drag of submersible: empirical equation estimation, model test method, and computational fluid dynamics (CFD) method. In different design phases of submersible, different methods are used. Empirical Equation Estimation (Cui et al. 2018)

For submersibles moving underwater, if the depth exceeds one coxswain, the total resistance can be expressed as: Rt ¼ R f þ Rpv þ Rap   1 ¼ rV 2 C f þ DC f þ Cpv þ Cap 2

ð1Þ

Cf ¼

3. Prandtl-Schlichting formula Cf ¼

0:455 ðlgRe Þ2:58

ð5Þ

(2) Empirical formula for calculating viscous pressure resistance Cpv ¼ Cf • K •

A S

ð6Þ

In the formula, K ¼ f(B/H). “S” is the wetted surface area. “Cf” can be expressed as follow:   1 Cf ¼ f LA =A2 , f

ð7Þ

AUV/ROV/HOV Resistance

115

“LA” is the length of outlet section; “f” is the longitudinal prismatic coefficient, f ¼ ▽/L  A. “A” is the midship section area. (3) Empirical formula for calculating appendage resistance The appendage resistance can be expressed as follows: Cap ¼

X

S Cscf • SC þ K SC • Cpv S

ð8Þ

In the formula, “Cscf” is frictional resistance coefficient on control surface. “SSC” is the wetted surface area on control surfaces. “KSC” is the empirical coefficient. “Cpv” is viscous pressure resistance coefficient on naked bodies. The Towing Tank Test

The towing tank test is one of the most used experimental methods to obtain the resistance of underwater vehicles, ships, etc. Due to the limitation of facilities of any towing tanks, scaled-sized models are generally used instead of real size models. In the towing test, the scaled model is usually mounted on the trailer through the support rod, and the resistance of the model is measured in all directions through the movement of the trailer, which simulates the movement of AUV/ROV/HOV Resistance, Fig. 1 Resistance model tests

the submersible. The real body resistance can be converted by the model resistance through the similarity laws. Froude similarity theory is often used for resistance conversion in engineering experiments. A towing tank test of a full ocean depth submersible is shown in Fig. 1 (Jiang 2016). Resistance Analysis Using Computational Fluid Dynamics (CFD) Method

Empirical equation estimation has poor adaptability varying with different shapes and characteristics of different types of submersibles. Towing tank model test is costly and time consuming. Compared to experimental method, using CFD analysis in the resistance analysis will be much faster and require relatively low cost. In addition, in principle it is possible to use CFD to obtain results at full-scale Reynolds numbers, something which is not possible using model experiments. On the other hand, the analysis object can be modeled according to the shape or molded lines of it, and even appendages or local contour can be simulated in a CFD analysis; the results obtained through CFD analysis will be more accurate and reliable compared to using empirical equation estimation. Therefore, the CFD method is usually adopted to conduct flow field simulation, especially in the early stage of submersibles’ design, and numerical calculation model is built in CFD software to obtain submersibles’ resistance.

A

116

Cross-References ▶ AUV/ROV/HOV Propulsion System ▶ Towing Tank Test

AUV/ROV/HOV Stability

center of gravity (G) should be sufficiently below that of the center of buoyancy (B) or metacenter (M).

Scientific Fundamentals References Cui W, Guo W, Wang F, Jiang Z, Luo G, Pan B (2018) Submersible technology and application. Shanghai Scientific and Technical Publishers, Shanghai Jiang Z (2016) Hydrodynamic performance test analysis report of the 11000-meter manned submersible [R]. Technical report. Hadal Science and Technology Center, Shanghai Ocean University, Shanghai Renilson M (2015) Submarine hydrodynamics. Springer Briefs in applied sciences and technology, Switzerland Sheng Z (2003) Principles of ship. Shanghai Jiao Tong University Press, Shanghai

For the submerged AUV/ROV/HOV, only intact stability needs to be considered because there is no reserve of buoyancy. Hydrostatic stability, both transverse and longitudinal, i.e., in heel and pitch, is described by the position relationship between the center of gravity (G) and the center of buoyancy (B). The distance, BG, governs the stability characteristics of the submersible, which determines the restoring moment when it experiences an angle of heel or an angle of pitch. The criteria for the magnitude of BG are in relation to several circumstances: (Burcher and Rydill 1994).

AUV/ROV/HOV Stability Jinfei Zhang Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China

Synonyms Intact stability; Longitudinal stability; Metacentric height; Restoring moment; Stability at large angles; Stable equilibrium; Transverse stability

Definition Stability is a kind of ability to enable an AUV/ROV/HOV to restore the original position after deviating from the equilibrium position under disturbing force. The distance, BG, between the center of gravity (G) and the center of buoyancy (B), governs the stability characteristics of the submerged submersible. For a surfaced boat, the measure of the stability is given by the distance GM (metacentric height). Thus, to be in stable equilibrium when the surfaced boat upright, the vertical position of the

(a) Static: It has sufficient BG that moving weights or men on board athwartships or fore and aft does not cause a large change of attitude. (b) Dynamic: The value of BG affects the behavior of the submersible when proceeding at speed submerged. If it changes course at speed, there is a tendency to cause a heeling moment and to result in a very large heel angle. During a turn, BG provides a hydrostatic moment to the hull resisting heeling and pitching motion. At very slow speeds, the hydrostatic moment results in the depth control surfaces no longer cause the boat to dive, but instead cause it to angle down by the bow while experiencing an upward rising motion. (c) Transition: The transverse metacenter moves from the center of buoyancy to the position of metacenter appropriate to the surface waterline in the transition from the submerged to the surfaced condition. The center of gravity also moves owing to the removal of water from the MBTs, which gives a free surface effect. It is necessary to ensure that during transition the migrating center of gravity is not above the metacenter.

AUV/ROV/HOV Stability

117

Transverse Stability For a submerged AUV/ROV/HOV to be stable in roll, known as transverse stability, the center of buoyancy (B) must be above the center of gravity (G), termed as positive BG value, as shown in Fig. 1a. In this case, if the boat is heeled to a small angle, as shown in Fig. 1b, the hydrostatic moment on it will cause it to return to the upright. On the other hand, if G is above B, at a small angel heeling under an external moment, the hydrostatic moment will cause it to continue to heel, as shown in Fig. 1c. (Martin Renilson 2015). When the submersible is floating on the surface, the situation is different. In this case, the center of buoyancy (B) moves transversely as a function of heel angle. For small angles, the upward force, through the center of buoyancy (B), always acts through the metacenter, designated as “M” in (d). Thus, for a surfaced boat to be in stable equilibrium when upright, the position of metacenter (M) has to be above the center of gravity (G), and measure of the stability is given by the distance GM (metacentric height). The formula of the vertical distance between the center of buoyancy (B) and the metacenter (M) is given as follows: BM ¼ I/ ∇ , where I is the second moment of area of the waterplane around the longitudinal axis and ∇ is the immersed volume. When the submarine is submerged, I will be equal to zero, and hence the position of metacenter (M) will be the same as the position of the buoyancy center (B).

Longitudinal Stability Similar as transverse stability, the same principles apply to a submerged AUV/ROV/HOV as to a floating surface ship. However, the lack of a waterplane results in a very small restoring moment in the longitudinal direction if the submersible is in the pitch motion. Thus, it is essential to have the longitudinal position of the center of gravity (G) lined up with the longitudinal position of the center of buoyancy (B). As the longitudinal position of the center of gravity moves during a voyage due to use of consumables, sample collection, etc., it is necessary to be able to adjust this by use of ballast tanks or other suitable methods.

AUV/ROV/HOV Stability, Fig. 1 When the submersible is floating on the surface, the situation is different. In this case, the center of buoyancy (B) moves transversely as a function of heel angle. For small angles, the upward force, through the center of buoyancy (B), always acts through

the metacenter, designated as “M” in (d). Thus, for a surfaced boat to be in stable equilibrium when upright, the position of metacenter (M) has to be above the center of gravity (G), and measure of the stability is given by the distance GM (metacentric height)

Stability at Large Angles As well as designing an AUV/ROV/HOV to have positive surface flotation at a reasonably level trim, there is also the need to satisfy the heel stability criterion by having a positive GM (metacentric height). A submersible on the surface has very small reserves of buoyancy compared with surface ships. On the other hand, with its small profile, the surfaced submersible does not face as much in the way of rolling excitation from wind and waves as most surface ships. The configuration of a submersible makes it difficult to provide the boat with large heel stability. Motion on the surface is usually characterized by slow large angle rolling, sometimes to alarming angles, whereas, fully submerged, little motion occurs.

A

118

Hence, the surface is not the place for a submarine in heavy weather.

Auxiliary Icebreaking Methods Renilson M (2015) Submarine hydrodynamics. Spring Briefs in Applied Sciences and Technology, United Kingdom

Key Applications The stability characteristics of an AUV/ROV/ HOV are governed by the distance of BG and GM for the submerged and surfaced condition, respectively. Therefore, enough attention must be paid to keep the vertical position of the center of gravity (G) sufficiently below that of the center of buoyancy (B) or metacenter (M), which leads to an adequate separation for the purposes of transverse and longitudinal hydrostatic stability.

Auxiliary Icebreaking Methods

Main Ballast Tanks (MBTs) The purpose of the MBTs is to allow major adjustment of the submersible mass to enable it to operate submerged as well as on the water surface. Water and air enter and leave the MBTs through flooding holes at the bottom and vents at the top of the tanks. The size of the vents and the flooding holes will have a direct effect on how long it will take for the MBTs to fill, and small flooding holes may cause problems with overpressure and stability issues on the surface. To improve the initial stability, the waterline areas should be as large as possible. The MBTs may be located at sides in transverse and at bow and stern in longitudinal, which gains the higher metacenter characteristic on the surface.

Assistant icebreaking icebreaking technologies

Compensating Tanks Compensating tanks is usually composed of two tanks, one forward and another afterward. When the submersible submerged, adjustment ability of MSTs is lost, because it is fully flooded; compensating tanks can be used to correct the longitudinal balance by flooding or discharging of these two tanks separately, which hence effect on the stability of submersible.

References Burcher R, Rydill L (1994) Concepts in submarine design. Cambridge University Press, United Kingdom

Baoyu Ni and Qigang Wu College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China

Synonyms systems;

Auxiliary

Definition Auxiliary icebreaking methods collectively refer to the application of auxiliary systems and/or technologies on the icebreaker to improve its icebreaking ability. They are usually used for the high-level icebreaker which works in high ice conditions. In contrast, conventional icebreaking method usually refers to that an icebreaker breaks ice by its own momentum and/or gravity, in either continuous or crash icebreaking ways (Ettema et al. 1987).

Scientific Fundamentals As mentioned above, there are usually two traditional ways to break ice for an icebreaker: continuous or crash icebreaking ways. The former is to crush the ice by icebreaker’s gravity, and the latter is to crash the ice by icebreaker’s power mainly. As the thickness of ice increases, both methods become difficult, and the capacity of icebreaker will be limited. Under extreme conditions, when the ice thickness exceeds the icebreaking capacity of the icebreaker, the ship is possible to be blocked or trapped and even broken. At this time, auxiliary

Auxiliary Icebreaking Methods

icebreaking methods to improve the icebreaking capacity of the icebreaker become important, which will help the icebreaker get rid of trapped. Beyond that, fast and effective auxiliary icebreaking methods are also proposed to improve the performance of the ice breaker in normal working conditions. One can see various auxiliary icebreaking methods booming. To make it simple, we broadly classify auxiliary icebreaking methods into the following categories according to the working principles: • Mechanical methods, which crush ice by accessory mechanical devices, such as mechanical ice cutting, Alex bow barge, mechanical saws, Archimedes screw vehicle, stem knives, bow ramp, mechanical impact devices, etc. • Auxiliary ship movement methods, such as high-speed heeling system and pitching systems • Auxiliary medium methods, which help to reduce ice resistance by adding auxiliary medium on the ship, such as water hull lubrication systems, bubbler systems, water jets, and low friction hull coatings • Additional floating-body methods, which help to break ice by introducing additional floating bodies whose icebreaking principles can be various, such as explosive icebreaking barge, air cushion vehicles, upper Mississippi icebreaker, etc.

Mechanical Methods Just as its name implies, mechanical methods enhances the icebreaking capability of the icebreaker by installing additional mechanical devices. These accessory mechanical devices could help to break ice directly, but they need to be installed on the ship rather than work independently. As shown in Fig. 1, these devices can be various. Based on the installation positions, they can be further classified into three types roughly. One is devices installed around the bow, including saws, planning tools, plow-form devices, etc. as shown in Fig. 1a and b. This kind

119

is most common, as bow is the principal part during icebreaking. The second one is devices suspended from the hull to the ice surface by suspenders, such as pneumatic actuators and pile hammers, as shown in Fig. 1c. Others are placed in the middle of the hull, such as two large counterrotating screws, as shown in Fig. 1d. Under suitable conditions, mechanical devices can improve the efficiency of icebreaking and increase the safety of navigation in ice-covered areas. However, most of them are limited to research fields rather than actual engineering applications, because they change the shapes of the hull severely and induce a lot of problems when the ship moves in open water. Here we choose mechanical saws as the example to introduce its working principle and development process. The mechanical saw is usually installed on the bow and has corresponding control devices to adjust its installation angle. Cut by the mechanical saw, the ice can be weakened in advance and even broken directly. The weakened ice or crushed ice will be further broken and pushed away by the hull. As a result, the channel is opened up. Various toothed blades, which can cut through the ice layer, can be adopted, such as direct saw, slitting saw, cross cut saw, chain saw, electric bow saw, etc. Stephens designed a semisubmersible oil tanker icebreaker with three steel ice saws mounted on its narrow superstructure, which could undercut the ice (Stephens 1973). In addition, some mechanical saws are equipped with thermal installations. The hot water discharged along the saw tooth reduces the blockage of the ice during icebreaking effectively. The Russians have extensively studied mechanical saws and report that model tests show devices using saws on channel clearing devices requiring 17–28% of the force to move a model of a typical icebreaker. However, there is no literature on full-scale devices in operation (Smith et al. 1981). Americans have also conducted extensive researches on mechanical saws and analyzed the application of such devices to meet the requirements for Coast Guard support in various domestic waterways (Lecourt and Voelker 1974). However, just mentioned above, this technology

A

120

Auxiliary Icebreaking Methods

Auxiliary Icebreaking Methods, Fig. 1 Sketches of some typical mechanical auxiliary icebreaking methods (Smith et al. 1981)

has been limited to the research field, and no use in actual engineering has been found until now.

Auxiliary Ship Movement Methods Auxiliary ship movement methods aim to enhance the motion of the icebreaker in one or two degrees of freedom, usually the roll and pitch motions, in order to get rid of trapped rapidly. Correspondingly the high-speed rolling and pitching systems are developed. Sometimes

the former is also known as high-speed heeling systems. Both could also collectively be named as tilting technology (Harbron 1983). Most common methods to achieve this goal are to adjust the ballast water. The method by adjusting ballast water to achieve pitch motion is widely used for the continuous icebreaking mode of icebreaker. The bow of the icebreaker is designed into a special shape, and ballast tanks are equipped at the stem and stern, respectively. Ballast water is firstly adjusted to stern so that the icebreaker trims by

Auxiliary Icebreaking Methods

121

stern and the bow rides on the ice. Usually the weight of ship bow can crush ice. If not, ballast water is adjusted to stem to add the weight of ship on the ice until the ice is crushed. High-speed heeling system has similar working principle to pitching system. The only different thing may be that the former is usually adopted to prevent the hull from being trapped or frozen, while the latter for continuous icebreaking mode. The working principle of high-speed heeling system is plotted in Fig. 2, where two water tanks are arranged on both sides of the hull. Ballast water loads are continuously transferred between both sides of the tanks, so the hull swings back and forth continuously as a result. In this way, the ship can get rid of the frictional obstacles of the ice on both sides of the hull, thus getting out of trouble. The high-speed heeling system, also known as the active shake system, can be seen as a kind of special antiheeling system. Different from the general ballast water transfer system, the purpose of this system is to be unbalanced in a faster speed. Therefore, compared to the general system, the pump flow is much larger and the piping and valves are bigger. There are many ballast water transfer technologies, including gravity type, water pump-driven type, and pneumatic type. Each has its own advantages and disadvantages, and they are often used in combination. In the design stage, one needs to consider comprehensively and selects one or several combinations according to the actual demand, thus to achieve the best effect of ballast water adjustment. Auxiliary Icebreaking Methods, Fig. 2 The principle of the high-speed heeling system (Yang and Ma 2010)

Auxiliary Medium Methods The auxiliary medium icebreaking method is to decrease the resistance between the hull and the ice by adding extra substances between them. In this way the icebreaker can break ice more efficiently. The media can be low friction coatings, which reduces the friction between the hull and the ice directly. The most successful low friction coatings until now may be unsolvated polyurethane and epoxy (Calabrses et al. 1976; Alliston 1985). On the other hand, the media can also be high-pressure water flow, bubbles, and/or steam water mixture, which is the auxiliary medium method we usually refer to. High-pressure compressed water, gas, or water vapor mixture is injected through a number of nozzles arranged on the hull below the waterline. In this way, a low-resistant film is formed between the hull and the ice, which reduces the friction force on the hull. Although the medium differs, the principles are similar. Here we take bubbler system as the example. Because of the low density of air, bubble drag reduction on ships in open water has been proposed and studied for a long time (Madavan 1985). Similarly, this idea is also used and extended for icebreaker. One of the most representative systems was invented by Wartsila in 1967 and was widely applied to icebreakers in the 1970s, which was called Wartsila Air Bubbling System (WABS) (Parksvangen et al. 1971; Segercrantz 1989), as

1 2

Left water tank

7

8

4

Right water tank

3 6 a

b 5

c

d

8

7

A

122

Auxiliary Icebreaking Methods

AIR COMPRESSOR

SNOW

SHIP

ICE

SPRAY

COMPRESSED AIR NOZZLES WATER ON TOP OF THE ICE

AIR BUBBLES

Auxiliary Icebreaking Methods, Fig. 3 The principle of the air bubble system (Segercrantz 1989)

shown in Fig. 3. The main principle of the system is that the compressed air is ejected from the hole on the lower part of the hull. The rising air bubbles push the broken ice away, thus reducing the friction between the hull and the ice and improving the icebreaking performance of the ship. The icebreaking performance of the ship equipped with the bubble-assisted icebreaking system was studied by using both the scale model and the prototype icebreaker. The results showed that the bubble-assisted icebreaking system could save the power of the icebreaker in the ice-covered zone efficiently and the maximum energy-saving efficiency could reach about 30% (Major 1977; Goodwin 1980; Vance 1980). This technology was also applied to the nuclearpowered heavy icebreaker 50 Let Pobedy, as shown in Fig. 4, which was commissioned in Russia in 2007. The bottom of the ship was equipped with a bubble-assisted icebreaking system that produced 24 m3/s of air bubbles in a region of 9 m deep underwater to assist in icebreaking operations (Zhang et al. 2017).

Additional Floating-Body Methods Compared with the methods above, additional floating-body technologies can be quite complex. It usually has two distinct characteristics: one is that an auxiliary equipment needs to be installed on a floating body outside the hull and the other is the additional floating body has independent function relative to the main hull. For example, the explosive icebreaking method requires a barge to be equipped with an explosive tank with a mixture of compressed air and hydrocarbon fuel. The barge will be placed under the ice. When the mixture explodes, the open-cell structure on the box will instantaneously release the high-pressure gas and destroy the ice above, thus improving the icebreaking efficiency. Another typical example is air cushion icebreaking platform or vehicle, which is not limited by draft and can break ice in both deep and shallow waters. At present, countries such as the United States, Canada, Russia, and Finland have

Auxiliary Icebreaking Methods

123

A

Auxiliary Icebreaking Methods, Fig. 4 Nuclear-powered icebreaker: 50 Let Pobedy (from https://en.wikipedia.org/ wiki/50_Let_Pobedy#/media/File:50letPob_pole.JPG)

Auxiliary Icebreaking Methods, Fig. 5 Icebreaking ship of the Canadian Coast Guard: CCGS Sipu Muin (from https://inter-j01.dfo-mpo.gc.ca/fdat/vessels/98)

used air cushion platforms and hovercrafts in icebreaking engineering applications, and the icebreaking effect is satisfactory (Hinchey and Colbourne 1995; Whitten et al. 1986). Figure 5 provides the picture of an air cushion icebreaking

vehicle CCGS Sipu Muin of Canada. The icebreaking principles of hovercraft can be divided into low-speed mode and high-speed mode. In low-speed operation conditions, the air cushion pressure causes the water surface below

124

Auxiliary Icebreaking Methods

Auxiliary Icebreaking Methods, Fig. 6 Sketch of air cushion vehicle icebreaking

the ice layer to depress, as shown in Fig. 6. The simplified force model of the ice layer can be seen as a cantilever beam model as a result. When the stress of the ice layer is larger than its allowable stress, the ice will be fractured (Muller 1979; Mellor 1980). In the case of high speed, the hovercraft relies on the wave making on the ice surface to break ice. When the hovercraft moves at a critical speed, the energy of the air cushion vessel exerted to the ice cannot be radiated out. Therefore, under the continuous action of the air cushion vessel, the energy accumulates incessantly, and the amplitude of the fluctuating deformation of the ice layer increases, which eventually leads to the fracture of the ice layer due to the internal bending stress over its yield limit (Buck and Pritchett 1978; Buck et al. 1978). In conclusion, auxiliary icebreaking methods or technologies have been reviewed and classified roughly. Here we need to clarify that auxiliary icebreaking technology is developing rapidly, so the classification will be advanced with time.

Cross-References ▶ Ice Breaking Vessel ▶ Ice Management in Offshore Operations ▶ Special Marine Vehicle

References Alliston GR (1985) Low friction and adfreeze coatings. Civil Engineering in the Arctic Offshore ARCTIC’85, San Francisco. ASCE, New York Buck J, Pritchett CW (1978) Air cushion icebreaker test and evaluation program. Volume I: Executive summary. U.S. Coast Guard, Office of Research and Development, Washington, DC

Buck J, Pritchett CW, Dennis B (1978) Air cushion vehicle icebreaker test and evaluation program. U.S. Coast Guard Office of Research and Development, Washington, DC Calabrese SJ, Peterson MB, Ling, FF (1976) Low Friction Hull Coatings for Icebreakers. Phase II, Parts I and II. Laboratory and Field Tests. Rensselaer Polytechnic Inst Troy NY Ettema R, Stern F, Lazaro J (1987) Dynamics of continuous-mode icebreaking by a polar-class icebreaker hull (No. IIHR-REPORT-314). Iowa Institute of Hydraulic Research, University of Iowa Goodwin MJ (1980) Icebreaking and open water tests performed on the USCG Cutter Katmai Bay (WTGB101) (No. CGR/DC-6/80). Coast Guard Research and Development Center Groton CT Harbron JD (1983) Modern Icebreakers. Sci Am 249(6):49–55 Hinchey M, Colbourne B (1995) Research on low and high speed hovercraft icebreaking. Revue Canadienne De Génie Civil 22(1):32–42 Lecourt EJ, Voelker RP (1974) Evaluation of mechanical ice cutter concept for use in domestic icebreaking service. Arctec Inc Columbia MD Madavan N (1985) Numerical investigations into the mechanisms of microbubble drag reduction. Trans ASME J Fluids Eng 107(3):370–377 Major RA (1977) Model tests in ice to confirm effectiveness of the 140-foot WYTM air bubbler system (No. 354C-2). Arctec Inc Columbia MD Mellor M (1980) Icebreaking Concepts (No. CRREL-SR80-2). Cold Regions Research and Engineering Lab Hanover NH Muller ER (1979) Ice breaking with an air cushion vehicle. SIAM Rev 21(1):129–135 Parksvangen FB, Enkvist E et al (1971) Arrangement in ships. United States Patent: 3580204, 05, 25 Segercrantz H (1989) Icebreakers their historical and technical development. Interdiscip Sci Rev 14(1):77–85 Smith JA, Goodwin MJ, McBride MS (1981) Comparative analysis of potential auxiliary icebreaking devices/systems for great lakes. Volume I (No. CGR/DC-14/81). Coast Guard Research and Development Center Groton CT Stephens R (1973) Icebreaker oil tankers: US Patent 3,768,427 Vance GP (1980) Analysis of the performance of a 140foot Great Lakes icebreaker USCGC Katmai Bay (No.

Awareness CRREL-80-8). Cold Regions Research and Engineering lab Hanover NH Whitten J, Hinchey MJ, Hill B, Jones SJ (1986) Some tests at the Institute for Marine Dynamics on high speed hovercraft icebreaking. In: 20th International Conference on Air Cushion Technology, Toronto, Ontario Yang Y, Ma J (2010) Research and design of ballast system for a science icebreaker. In: ASME 2010: 29th international conference on ocean, offshore and arctic engineering. American Society of Mechanical Engineers, pp 759–763 Zhang Y, Li YY, Wang M (2017) Overview and trend of the icebreakers. Ship Science & Technology 39 (12):188–193

Auxiliary Icebreaking Technologies ▶ Auxiliary Icebreaking Methods

125

Auxiliary Navigation ▶ Integrated Navigation

Auxiliary Propulsions ▶ New Technologies in Auxiliary Propulsions

Awareness ▶ Human Factors in the Role of Energy Efficiency

A

B

Bare Wire ▶ Cable

emptied of cargo and ballast, then driven to coast on a high magnitude tide, and stranded on the beach. The workers access the vessel at low tide and start scrapping for recycling materials.

Barges

Scientific Fundamentals

▶ Jack-Up Platforms

Definition

History Until the 1960s, shipbreaking activities mainly took place in industrialized countries and were conducted off the beach (FIDH 2002). The origin of the beaching can be traced to a Greek ship stranded accidentally on the beach of Sitakunda, Chittagong, during a cyclone in 1960. The vessel could not be refloated and so remained there for several years. In 1965, in East Pakistan, the then Chittagong Steel House bought the ship and had it scrapped on beach. From the early 1980s, the global shipbreaking activities started migrating to South Asian to increase profit (FIDH 2002). The industry developed rapidly in India, Bangladesh, and Pakistan where dismantling was exclusively accomplished on beaches (Yujuico 2014). In the recent years, beaching has become the most commonly used method for shipbreaking worldwide. About two-thirds of the end-of-life ships around the globe are dismantled by beaching each year.

Beaching, as a shipbreaking method, generally refers to dismantling ships at grounded condition in intertidal zones. In this method, a ship is

The Layout of the Yards Taking the beach of Chittagong shipbreaking yard as an example, the beach is generally divided up into

BATS (Broadband Acoustic Tracking System) ▶ Ultra-short Baseline Underwater Acoustic Location Technology

Beaching Haiming Zhu and Zunfeng Du Department of Naval Architecture and Ocean Engineering, School of Civil Engineering, Tianjin University, Tianjin, China

© Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

128

several plots about 60 m wide and up to 90 to 160 m deep. Infrastructure is minimal. It may consist of office building, few heavy-duty winches, vehiclemounted cranes, and some walls between plots if preferred. Some temporary storage facilities and areas on concrete or steel bases usually exist. More sophisticated operations may have extensive offices, storage areas, and concrete areas within the facility. And even large separate secondary operations areas are on the shore behind the facility, which might include asbestos treatment areas, materials handling areas, medical facilities, shower room, labor shelter, and messing. Moreover, they have their own fire service and hospitals as well as a large and useful training facility on the hill overlooking the beach. The surroundings are typically made up of worker’s houses as well as shops reselling the items that come from the ship. The Process of Beaching The following passages explain the typical process of beaching in Bangladesh (Hossain and Islam 2006). The process in India and Pakistan is about the same (Deshpande et al. 2013; Ahmed and Siddiqui 2013). 1. Firstly, the ship is anchored in international waters off the coast. The ship will then be inspected, checked, and made gas-free. After the administrative formalities are completed, the ship will obtain a permission to enter territorial waters for beaching. The ship has to wait until the tide condition is ideal for performing beaching. Usually no pre-cleaning of the ships is required for entering the shipbreaking area. 2. When the tide is high, the ship will be driven to the beach by own propulsion power. Usually workers would set up a big colored flag for guidance. After the tide drops, the ship will be lying stable on its flat bottom. The ship must be placed in this exact position and come to ground as high up on the beach as possible to facilitate dismantling operations. If the ships don’t make it to the beach and are stranded on the mudflats, they are pulled higher with chains or heavy steel wire hawsers at the next suitable tide after being made

Beaching

3.

4.

5.

6.

lighter. Beaching has a crucial impact on the final cost. The time needed for dismantling can be doubled, if the beaching operation is not successful. After the ship is grounded, the workers start removing items and cutting the vessel into large parts using blowtorches. The parts will drop down to the mudflats and be progressively dragged to the dry part of the shore by winches. Though the machinery does the main job, a large number of workers are engaged to help dragging the parts. Another group of cutters, helpers, and workers start cutting the dragged parts of the ship into trackable parts as per order of the purchasers. The steel is often cut up into around 2
4 m pieces (usual practice) and then sold for cold rolling. Although it may also be cut into inch thick square bars using hydraulic shears and used directly for reenforcing concrete or similar materials, those plates, frames, bars, girder, stiffener, longitudinal, etc. are also used in local ship building or repair industry. The unskilled workers carry metal plates, metal bars, or pipes on their heads or shoulders, then pile up metal plates in stack yards, or load them on trucks. The supervisors control the group of workers; the onlooker guides them and helps them in pilling up the heavy metal plates in stacks. Heavy equipment like boilers, motors, capstan stocking, etc. are carried to stack yards by moving crane. The valuable components (e.g., small motors and pumps, generator, navigation equipment, life-saving equipment, furniture, electrical cables, utensils, etc.) are dismantled and sold to secondhand market. It needs 5–6 months to dismantle a typical cargo ship.

Hazards of Beaching End-of-life ships contain a great amount of hazardous materials. Depending on the size and function of the ship, crapped ships have an unladen weight of between 5000 and 40,000 tons (the average being 13,000+), 95% of which is steel, coated with between 10 and 100 tons of paint

Beaching

containing lead, cadmium, organotins, arsenic, zinc, and chromium. Ships also contain a wide range of other hazardous wastes, sealants containing PCBs, up to 7.5 tons of various types of asbestos, and thousands of liters of oil (engine oil, bilge oil, hydraulic and lubricant oils, and grease). Tankers additionally hold up to 1000 cubic meters of residual oil. Most of these materials have been defined as hazardous waste under the Basel Convention (Hossain and Islam 2006). The breaking process would release those materials, threating the health of the workers and the ambient environment. The problem is more serious when the ships are dismantled on beach other than in the dock, because hardly any protection measures will be taken. Impact on Intertidal Sediments and Soils

In shipbreaking areas, various refuse and disposable materials are dropped or stacked haphazardly on the seashore. The hazardous materials are accumulated and get mixed in the soil. Those materials are mainly metal fragments and rust (particularly iron). It accelerates the amount of shore erosion and increases the turbidity of seawater and sediments in the area (Hossain and Islam 2006). Trace metals can be found in the sediments. Accumulation levels of Cr, Zn, As, Pd, and Cd are higher than recommended values of unpolluted sediments (Hasan et al. 2013a). There are on average 81 mg of small plastic fragments per kg of sediment. They do not degrade easily and hence pose a threat to the environment and marine ecosystems (Reddy et al. 2006). Impact on Seawater

Ship scrapping activities pollute the seawater environment in the coastal area. Seawater is strongly polluted by Fe, Pd, and Hg, moderately by Mn and Al, and slightly by Pb and Cd. Groundwater is also polluted, strongly by Fe, Pb, and Hg, moderately by Mn and Al, and slightly by As (Hasan et al. 2013b). Toxic concentration of ammonia and marine organisms found in seawater had an increase in PH levels. Critical concentration of dissolved oxygen (DO) and higher biochemical oxygen demand

129

(BOD) were found with an abundance of floatable materials (grease balls and oil films) in the seawater (Hossain and Islam 2006). Impact on Biodiversity

Shipbreaking activities contaminate the coastal soil and seawater environment mainly through the discharge of ammonia, burned oil spillage, floatable grease balls, metal rust (iron), and various other disposable refuse materials together with high turbidity of seawater. The high PH of the seawater and soil observed may be due to the addition of ammonia, oils, and lubricants. High turbidity of water can cause a decrease in the concentration of DO and substantially increase the BOD. Furthermore, oil spilling may cause serious damage by reduction of light intensity, inhibiting the exchange of oxygen and carbon dioxide across the air-seawater interface, and by acute toxicity. As a result, the growth and abundance of marine organisms especially plankton and fishes may seriously be affected. Indiscriminate expansion of shipbreaking activities poses a real threat to the coastal intertidal zone and its habitat (Hossain and Islam 2006). Worker Rights Violation In the majority of the shipyards in developing countries, workers are being deprived of their rights. They work under risky conditions but have no access to safety equipment, job security, or a living wage. Shipbreaking carries a very real risk to life. By any standards, the demolition of ships is a dirty and dangerous occupation. The hazards linked to shipbreaking broadly fall into two categories: intoxication by dangerous substances and accidents on the plots. Explosions of leftover gas and fumes in the tanks are the prime cause of accidents in the yards. Another major cause of accidents is workers falling from the ships (which are up to 70 m high) as they are working with no safety harness. Other sources of accidents include workers being crushed by falling steel beams and plates and electric shocks. Workers are not aware of hazards to which they are exposed. The overwhelming majority of

B

130

workers wear no protective gear, and many of them work barefoot. There is hardly any testing system for the use of cranes, lifting machinery, or a motorized pulley. The yards reuse ropes and chains recovered from the broken ships without testing and examining their strength. There is no marking system of loading capacity of the chains of cranes and other lifting machineries. Gas cutters and their helpers cut steel plates almost around the clock without eye protection. This leaves their eyes vulnerable to effects of welding. They do not wear a uniform and most don’t have access to gloves and boots. Those that are “unskilled” carry truckable pieces of iron sheets on their shoulders, and there are no weight limits to the sheets they carry. Usually, these workers carry weights far above the limit prescribed in the Factories Act and Factories Rules. Besides, the beaches are strewn with chemicals and toxic substances, small pieces of pointed and sharp iron splinters causing injuries. Workers enter into the areas without wearing or using any protective equipment. When there is an injury, some immediate treatment may be given, but there is no longterm treatment for those who have a long-term or permanent injury. In terms of compensation, only a nominal amount of compensation given and often only when there is public pressure. When a worker becomes disabled by a major accident, he gets a maximum of 10 to 15 thousand taka (1 USD ¼ 71 taka) and forced back to his home district. In most cases a worker will only get transportation costs to go back to their home district. When a worker killed in an accident, the contractor, who is responsible for the workers, will only pay the costs of sending the body back to the victim’s family and arranging for their burial. So far, the treatment and compensation problems of workers have not been well resolved.

Beaching Beaching, Table 1 The number of ships dismantled by beaching in 2015–2017 Country India Bangladesh Pakistan Ships dismantled by beaching worldwide Ships dismantled worldwide

2015 194 (25%) 194 (25%) 81 (11%) 469 (61.1%)

2016 305 (35.4%) 222 (25.8%) 141 (16.4%) 668 (77.5%)

2017 239 (28.6%) 197 (23.6%) 107 (12.8%) 543 (65%)

768

862

835

application condition of beaching in 2015–2017 (NGO Shipbreaking Platform 2016, 2017, 2018). The main reasons for the phenomenon including (FIDH 2002):

Applications

1. Shipbreaking industry requires cheap human man power, which is available in developing countries with large population, such as India, Bangladesh, and Pakistan. In these nations, millions of people are in the state of poverty, providing abundant cheap labor. 2. The coastal areas of the shipbreaking yards have wide and gently sloping sand tidal beaches, making it possible to drive ships onshore as far up the beach as possible at spring tides and dismantle the ships at grounded condition. 3. In most countries, beaching had already been prohibited for environmental protection and occupational health and safety concerns. However, regulations and standards are loose in India, Bangladesh (Alam and Faruque 2014), and Pakistan compared to other ship recycling nations. 4. The convenient location of the Indian subcontinent, the suitable climate, and domestic market for scrapped steel are also factors that promote the prosperity.

Beaching activities mainly took place in India, Bangladesh, and Pakistan. Table 1 shows the

The shipbreaking yards that utilize beaching method concentrated in the following regions:

Beaching

1. The Alang-Sosiya beach is in the State of Gujarat on the west coast of India. This region has one of the longest continental shelves and the second highest tide port in the world, making it an ideal site for beaching (Patel et al. 2013). The Alang-Sosiya shipbreaking yard is considered the world’s largest of its kind. According to statistics, in 2012, there were 171 yards in the region (92 in Alang, 79 in Sosiya) with about 60,000 workers, handling around 350 ships yearly (Deshpande et al. 2012). 2. The shipbreaking yards in Chittagong stretch about 20 km along the coast of Sitakunda Thana region (Gregson et al. 2012), a wellknown shipbreaking area which is about 20 km northwest of Chittagong. Chittagong shipbreaking yard was the largest shipbreaking yard in the world from 2004 to 2008. Today, it takes the second place in the industry. 3. Gadani shipbreaking yard located across a 10-km-long beach at Gadani, Pakistan, about 50 km northwest of Karachi. In the 1980s, Gadani was the largest shipbreaking yard in the world with more than 30,000 direct employees. Gadani ranks as the world’s third largest shipbreaking yard after Alang-Sosiya and Chittagong in terms of volume.

Cross-References ▶ Ship Recycling

References Ahmed R, Siddiqui K (2013) Ship breaking industry in Pakistan-problems and prospects. Int J Manag IT Eng 3(9):140 Alam S, Faruque A (2014) Legal regulation of the shipbreaking industry in Bangladesh: the international regulatory framework and domestic implementation challenges. Mar Policy 47:46–56 Deshpande PC, Tilwankar AK, Asolekar SR (2012) A novel approach to estimating potential maximum heavy metal exposure to ship recycling yard workers in Alang, India. Sci Total Environ 438:304–311

131 Deshpande PC, Kalbar PP, Tilwankar AK, Asolekar SR (2013) A novel approach to estimating resource consumption rates and emission factors for ship recycling yards in Alang, India. J Clean Prod 59:251–259 FIDH (2002) Where do the “floating dustbins” end up? Labour Rights in Shipbreaking Yards in South Asia – the cases of Chittagong (Bangladesh) and Alang (India). International Federation for Human Rights. No. 348/2, Dec 2002, Paris Gregson N, Crang M, Ahamed FU, Akter N, Ferdous R, Foisal S, Hudson R (2012) Territorial agglomeration and industrial symbiosis: Sitakunda-Bhatiary, Bangladesh, as a secondary processing complex. Econ Geogr 88(1):37–58 Hasan AB, Kabir S, Reza AS, Zaman MN, Ahsan A, Rashid M (2013a) Enrichment factor and geoaccumulation index of trace metals in sediments of the ship breaking area of Sitakund Upazilla (Bhatiary–Kumira), Chittagong, Bangladesh. J Geochem Explor 125:130–137 Hasan AB, Kabir S, Reza AS, Zaman MN, Ahsan MA, Akbor MA, Rashid MM (2013b) Trace metals pollution in seawater and groundwater in the ship breaking area of Sitakund Upazilla, Chittagong, Bangladesh. Mar Pollut Bull 71(1–2):317–324 Hossain MMM, Islam MM (2006) Ship breaking activities and its impact on the coastal zone of Chittagong, Bangladesh: towards sustainable management. Advocacy & Publication Unit, Young Power in Social Action (YPSA), Chittagong NGO Shipbreaking Platform (2016) 2015 list of all ships scrapped worldwide – facts and figures. http://www. shipbreakingplatform.org/shipbrea_wp2011/wp-content/ uploads/2016/02/Stats-Graphs_2015-List_FINAL.pdf. Accessed 9 Jan 2019 NGO Shipbreaking Platform (2017) 2016 list of all ships scrapped worldwide – facts and figures. http://www. shipbreakingplatform.org/shipbrea_wp2011/wp-content/ uploads/2017/02/Stats-Graphs_2016-List_FINAL1.pdf. Accessed 9 Jan 2019 NGO Shipbreaking Platform (2018) 2017 list of all ships scrapped worldwide – facts and figures. http://www. shipbreakingplatform.org/shipbrea_wp2011/wp-content/ uploads/2018/02/NGO-Shipbreaking-Platform-StatsGraphs-2017-List.pdf. Accessed 9 Jan 2019 Patel V, Patel J, Madamwar D (2013) Biodegradation of phenanthrene in bioaugmented microcosm by consortium ASP developed from coastal sediment of AlangSosiya ship breaking yard. Mar Pollut Bull 74(1):199–207 Reddy MS, Basha S, Adimurthy S, Ramachandraiah G (2006) Description of the small plastics fragments in marine sediments along the Alang-Sosiya shipbreaking yard, India. Estuar Coast Shelf Sci 68(3–4):656–660 Yujuico E (2014) Demandeur pays: the EU and funding improvements in South Asian ship recycling practices. Transp Res A Policy Pract 67:340–351

B

132

Bearing Capacity of Spudcans Long Yu and Heyue Zhang Dalian University of Technology, Dalian, China

Bearing Capacity of Spudcans

Jack-up units are self-elevating mobile platforms which are used extensively in offshore oil and gas industry. Bearing capacity is the ability of soil to safely carry the pressure placed on the soil from any engineered structure without undergoing a shear failure with accompanying large settlements (Lambe and Whitman 2008).

Synonyms Footing; Foundation

Definition Spudcan is the term used for the base cones on mobile-drilling jack-up platform. The spudcans are the inverted cones mounted at the base of the jack-up which provide support for the stability of jack-up rig when deployed into ocean-bed systems. Bearing Capacity of Spudcans, Fig. 1 A typical jack-up unit (https:// cn.bing.com/images/ search?q¼jack-up& FORM¼HDRSC2)

Scientific Fundamentals Jack-Up Unit A typical jack-up unit (as shown in Fig. 1) consists of a floatable platform (hull) and three independent retractable truss-work legs each resting on a spudcan footing. Figure 2 shows the operation sequence of a jack-up unit. Once a jack-up unit is towed to site, its installation begins by lowering the legs to the seabed and pushing the spudcans into the

Bearing Capacity of Spudcans

133

B

Bearing Capacity of Spudcans, Fig. 2 The operation sequence of a jack-up unit (Kong 2011) (a) Towing to site (b) Installation and preloading (c) Operating (d) Removal

soil and then rising the hull over the water. Then preloading can be achieved by pumping water into the hull. The preloading makes the spudcan penetrate deeper to provide more resistances. After preloading, the water is pumped out and the spudcan bearing capacity has some reservation. After all the work of the jack-up has finished, it is removed from the site by retracting the legs from the seabed (Kong 2011). The Typical Geometry of Spudcans The spudcans are of inverted cone shape commonly in polygonal or circular shape in plane. In the early days, the diameter of spudcans was within 5–10 m (Young et al. 1984). The shape and size of spudcans evolved for the operation of jack-up unit in deeper waters, and modern spudcans are typically between 10 and 20 m in diameter. Along with the increasing demands of operating on very soft soils, the footings become larger and flatter at base, such as HYSY944 (Hai-bo 2016) (as shown in Fig. 3c). Typical spudcan designs are illustrated in Fig. 3. Alternative Foundations In some complex environment conditions, such as penetrating on layered soil, especially on the sand overlying clay soil, the use of fusiform spudcan is

limited for its high risk of punch-through failure. To mitigate the punch-through failure potential of spudcan foundations for jack-up rigs on layered soils, skirted footings (Fig. 4a) are increasingly being considered (Yu et al. 2010). The skirted foundation is a flat spudcan foundation fitted with a thin skirt at the circumference. It appears like an upturned bucket. The whole drilling processes of installation and extraction of the spudcan will leave a permanent seabed depression at each footing site, which is referred to as a footprint. With the extensive and more frequent use of jack-up units, the existence of footprints is common. Now jack-up units often have to be installed near or into existing footprints in order to drill, and it can lead to significant loss of time, cost implications, risks to adjacent structures, and potential injury to personnel. Jun et al. (2016) present a novel spudcan with six evenly spaced holes at the base to ease spudcan-footprint interaction issues as shown in Fig. 4b. The Bearing Capacity of Shallow Footing When a load is applied on a limited portion of the surface of a soil, the surface settles. The relation between the settlement and the average load per unit of area may be represented by a settlement curve (Fig. 5). If the soil is fairly dense or stiff, the

134

Bearing Capacity of Spudcans 18m

18m

6m

4m

(a) Mod V “A”

1.7m 17.7m

(b) 116C jack-ups

(c) HYSY 944

Bearing Capacity of Spudcans, Fig. 3 Three typical spudcans (a) Mod V “A” (b) 116C jack-ups (c) HYSY 944

Bearing Capacity of Spudcans, Fig. 4 Alternative foundations. (a) Skirted footing model (Yu et al. 2010) (b) A novel spudcan (Jun et al. 2016; Yu et al. 2010)

Load per Unit of Area [qu]2 [qu]1

Settlement

0.2B

0.4B

C1 C2

0.6B 0.8B B=Width of the Footing

Bearing Capacity of Spudcans, Fig. 5 Relation between intensity of load and settlement of a footing on C1 dense or stiff and C2 loose or soft soil (Terzaghi et al. 1995)

settlement curve is similar to curve C1. The abscissa of the vertical tangent to the curve represents the bearing capacity of the soil. If the soil is loose or fairly soft, the settlement curve may be similar to C2, and the bearing capacity is not always well defined. The bearing capacity of

such soils is commonly assumed to be equal to the abscissa of the point at which the settlement curve becomes steep and straight. In practice, loads are transmitted to the soil by means of footings, as shown in Fig. 6. The footings may be continuous, having a long rectangular shape, or they may be spread footings, which are usually square or circular. The distance from the level of the ground surface to the base of the footing is known as the depth of foundation D. A footing that has a width B equal to or greater than D is considered a shallow footing. For purpose of analysis, the actual situation shown in Fig. 6a is usually replaced by the situation shown in Fig. 6b: the soil above the base of the footing is replaced by a uniform surcharge of intensity q ¼ γD, where γ is the unit weight of the soil and D is the depth of the base of the footing below ground surface. The effect of the weight of the soil above the footing base is thus taken into consideration, and the shear resistance of the soil is neglected. The approximate value of the bearing capacity can be written as the sum of the three terms: the

Bearing Capacity of Spudcans

135

Qv

Qv

D

B

q= gD

B (a)Actual situation

(b)Assumed situation

Bearing Capacity of Spudcans, Fig. 6 Shallow footing under a vertical load (Terzaghi et al. 1995) (a) Actual situation (b) Assumed situation

unit weight of the soil, the surcharge, and the cohesion of soil (only for clay soil) (Terzaghi et al. 1995): 1 qu ¼ cN c sc dc þ qN q sq dq þ gBN g sg dg 2 In which Nc and Nq are the bearing capacity factors with respect to cohesion and surcharge, respectively. The surcharge is represented by the weight per unit area γD of the soil surrounding the footing. The bearing capacity factor Nγ accounts for the influence of the weight of the soil. All the bearing capacity factors are dimensionless quantities depending only on f0. sc,sq,sγ are the correction factors corresponding to the footing shape. dc, dq,dγ are the correction factors corresponding to the embedment depth of footing. B is the diameter of a circular footing or the width of a strip footing. The Analysis Model of the Bearing Capacity of a Spudcan For conventional bearing capacity analyses, the spudcan is often modeled as a flat circular footing. The equivalent diameter is determined from the area of the actual spudcan cross section in contact with the seabed surface, or where the spudcan is fully embedded, from the largest cross-sectional area. Bearing capacity analyses are then performed for this circular foundation at the depth (D) of the maximum cross-sectional area in contact with the soil (Fig. 7). The depth of simplified spudcan penetration is usually defined as the distance from the spudcan bottom to the mudline (SNAME 2008).

The Soil Parameters Where geotechnical analyses are performed, they should be based on geotechnical data obtained from a site investigation incorporating soil sampling and/or in situ testing. Uncertainties regarding the geotechnical data should be properly reflected in the interpretation and reporting of analyses for which the data are used.

Key Applications In determining whether a jack-up unit may be safely used at a particular site, two separate analyses of foundation bearing capacity must generally be undertaken: • Prediction of footing penetration during preloading (vertical load only) • Assessing of footing stability under design storm conditions (combined vertical, horizontal, and moment loading)

Prediction of Footing Penetration During Preloading The Influence of Soil Backflow

During penetration, the possibility of soil backflow over the footing should be considered when computing bearing capacity. In very soft clays, complete backflow may occur, whereas in firm to stiff clays and granular materials, where limited footing penetration may be expected, the

136

Bearing Capacity of Spudcans

=

B

Area A



Area A

Simplify Qv

Area A

4A

Qv

Simplify

B=

4A

Qv

Volume V



Area A

Qv

D

Bearing Capacity of Spudcans, Fig. 7 Spudcan foundation model (SNAME 2008)

significance of backflow diminishes. Backflow in clay may be assumed not to occur if: D

Ncs g0

In this case, cs is taken as the average undrained cohesive shear strength over the depth of the excavation, N is a stability factor, and γ0 is the submerged unit weight of the soil. Conservative stability factors in uniform clays, as a function of excavation depth and diameter, are summarized in Fig. 8. For spudcan penetration analyses, it is recommended that conservative criteria are used and the excavation depth be considered as the depth to the maximum spudcan bearing area. For the conservative evaluation of the hole backflow, the stability factors of Meyerhof (1972) are used. However, for normally

consolidated clay profiles, the Britto and Kusakabe (1983) curve may be more appropriate. It should be noted that the expression above is based on static hole stability. In reality, during penetration of the spudcan, the soil will probably flow along the spudcan upward onto the top of the spudcan. Hence, the hole stability derived from the expression may be too optimistic. Penetration in Clays The ultimate vertical bearing capacity of a foundation in clay (undrained failure in clay,f ¼ 0) at a specific depth can be expressed by: FV ¼ ðcN c sc d c þ q0 ÞA In which c is the undrained cohesive shear strength at D + B/4 below mudline, and B is the effective spudcan diameter at uppermost part of

Bearing Capacity of Spudcans

137

Bearing Capacity of Spudcans, Fig. 8 Stability factors for cylindrical excavations (SNAME 2008)

bearing area in contact with the soil. q0 is the effective overburden pressure at depth D of maximum bearing area (q0 ¼ γ0D). For circular footing, the value of Nc is taken as 5.14. The maximum preload is equal to the ultimate vertical bearing capacity, FV, taking into account the effect of backflow, F00 A, and the effective weight of the soil replaced by the spudcan, γ0V, i.e.: VL0 ¼ FV  F00 A þ g0 V In which F00 is the effective overburden pressure due to backflow at depth of uppermost part of the bearing area. The terms F00 A þ g0 V should always be considered together. Because when the soil flows back during penetration, the backflow soil covers on the top of the footing, which reduces the maximum preload VL0. At the same time, the footing is fully buried in soil and the footing subjected to an up-floating force γ0V, which increases the maximum preload VL0. The bearing capacity formula given above has been empirically derived for surface foundations and does not account for foundation roughness, shape (conical for most spudcans), or the effects of increased shear strength with depth. Penetration in Silica Sands The ultimate vertical bearing capacity of a circular footing resting in silica sand or other granular

B

material (c ¼ 0, f 6¼ 0) can be computed by the following equation: FV ¼


 0:5g0 BN g sg d g þ q0 N q sq dq A

The maximum preload is equal to the ultimate vertical bearing capacity, FV, taking into account the effect of backflow, F00 A, and the effective weight of the soil replaced by the spudcan, γ0V, i.e.: VL0 ¼ FV  F00 A þ g0 V Footing penetrations in a thick layer of clean silica sand are usually minimal with the maximum diameter of the spudcan rarely coming into contact with the soil. It is therefore not usual to consider the effects of soil backflow in this situation. Typically observed load-penetration data for large-diameter spudcans suggest that reduced friction angles may be applicable for this analysis method. To account for this, it is recommended that laboratory triaxial f test values should be reduced by 5∘ for the prediction of large-diameter footing penetrations in silica sands, i.e., fdesign ¼ ftriaxial  5∘. For spudcans on sand, the effects of cyclic loading may be to either increase or decrease the pore water pressure. Positive excess pore water pressure will weaken the soil and in severe cases

138

may cause partial fluidization. Negative excess pore water pressures may temporarily strengthen the soil. Approximate methods are available for the assessment of excess pore water pressure development and associated foundation settlement. Penetration in Silts For silts, it is recommended that upper and lower bound analyses for drained and undrained conditions are performed to determine the range of penetrations. The upper bound solution is modeled as a loose sand and the lower bound solution as a soft clay. Cyclic loading may significantly affect the bearing capacity of silts. Cyclic loads imposed in silty fine sands/silt foundations may cause liquefaction due to the generation of excess pore water pressures. In this situation foundation settlements would be anticipated. Conservative assessments of reduced bearing capacities and increased settlements should be conducted as appropriate. Penetration in Carbonate Sands Penetrations in carbonate sands are highly unpredictable and may be minimal in strongly cemented materials or large, in uncemented materials. Extreme care should be exercised when operating in these materials. Relatively large footing penetrations have been reported for uncemented carbonate materials despite high laboratory friction angles (Dutt and Ingram 1988). This may be attributed to either the high compressibility of these materials or low shear strengths due to high voids ratio and a collapsible structure. The leg penetration is governed by both strength and deformation characteristics of foundation soils. The compressibility of carbonate sands is relatively higher than for silica sands. Hence, greater penetrations should be expected for carbonate sands relative to silica sands despite the similar or even higher laboratory friction angles. The predictions of footing penetrations in carbonate sands are likely to be performed to a lower degree of accuracy compared with those for silica sands. The conventional method is to use the plasticity-based formulation for bearing capacity of shallow foundations in sand. However, friction angles to be used in the formulae should be

Bearing Capacity of Spudcans

considerably smaller than laboratory values to account (in an artificial manner) for the soil behavior. Penetration in Layered Soils Three basically different foundation failure mechanisms are considered in spudcan predictions in layered soils: 1. General shear 2. Squeezing 3. Punch-through The first failure mechanism occurs if soil strengths of subsequent layers do not vary significantly. Thus an average soil strength (either c or f) can be determined below the footing. The footing penetration versus foundation capacity relationship is then generated using criteria from the formulae mentioned above. The punch-through condition concerns a potentially dangerous situation where a strong layer overlies a weak layer and hence a small additional spudcan penetration may be associated with a significant reduction in bearing capacity (Liu et al. 2005; Yu et al. 2012). But it is complicated and no good solution has been proposed. In this section, criteria for squeezing are given below. On a soft clay subject to squeezing overlaying a significantly stronger layer (Fig. 9), the ultimate vertical bearing capacity of a footing given by Meyerhof (1972) is: For no backflow conditions: FV ¼ A

   bB 1:2D aþ þ c þ q0 T B

 AfcN c sc dc þ q0 g and for full backflow conditions:  FV ¼ A

aþ

  bB 1:2D þ c þ g0 V T B

 AfcN c sc dc g þ g0 V where the following squeezing factors are recommended: a ¼ 5.00, b ¼ 0.33, and c refers to the undrained shear strength of the soft clay

Bearing Capacity of Spudcans

139

Bearing Capacity of Spudcans, Fig. 9 The failure mechanism of squeezing

B

layer. T is the thickness of the soft clay beneath the bottom of footing. It is noted that the lower bound foundation capacity is given by general failure in the clay layer and that squeezing occurs when B  3.45T (1 + 1.1D/B). The upper bound capacity (for T 1000 m from seafloor) (Yesson et al. 2011). There are more than 150,000 seamounts and Biodiversity Conservation, Fig. 2 A chemosynthetic community (Bathymodiolus platifrons– Shinkaia crosnieri community) found in Jiaolong Cold Seep I at about 1120 m depth in northeastern South China Sea (Li 2017)

Biodiversity Conservation

knolls and more than 25 million seamounts with summit depths at least 100 m (Wessel et al. 2010; Yesson et al. 2011). Seamounts are hotspots of pelagic biodiversity in the ocean. The biomass, abundance, and diversity of plankton, swimming organisms, and benthos of seamounts are often higher than those of other deep-sea ecosystems (Rogers 2018). Suspension feeders (e.g., sponges, corals) usually dominate the communities of the megabenthos on seamounts, and they can provide important habitat for mobile invertebrates such as molluscs, crustaceans, and echinoderms (Rogers et al. 2008). Some fish can form aggregations around seamounts and pelagic marine predators (e.g., shark, tuna) are attracted to improve opportunities for foraging. Very few data of invertebrates living at seamount are available and over 100,000 seamounts were estimated worldwide, only 200 of seamounts have been biologically sampled (Samadi et al. 2008). The reported number of seamount species may be seriously underestimated of the total number due to very few surveys have confirmed the complete specimens collected into an accurate species as the lacking of taxonomical expertise globally (Samadi et al. 2008). The limited habitat, apparently limited recruitment between seamounts, extreme longevity, and highly localized distribution of many species make seamount communities highly vulnerable to the impacts of fishing

Biodiversity Conservation

(Samadi et al. 2008). Temporary fishing closures and the establishment and enforcement of permanent protection zones are required to achieve efficient and long-term protection of seamounts (Samadi et al. 2008).

References Appeltans W, Ahyong ST, Anderson G et al (2012) The magnitude of global marine species diversity. Curr Biol 22:2189–2202 Ausubel JH, Crist DT, Eds PW (2010) First Census of Marine Life 2010: highlights of a decade of discovery. A Publication of the Census of Marine Life, New York Ayyam V, Swarnam P, Sivaperuman C (2019) Coastal ecosystems of the tropics Butchart SH, Walpole M, Collen B et al (2010) Global biodiversity: indicators of recent declines. Science 328(5982):1164–1168 Convention on Biological Diversity (2000) Sustaining life on Earth. Secretariat of the Convention on Biological Diversity, New York Cooper DH, Mooney NK (2013) Convention on biological diversity. In: Encyclopedia of biodiversity. Elsevier, Amsterdam, pp 306–319 Dong D, Li X, Yang M et al (2020) Report of epibenthic macrofauna found from Haima cold seeps and adjacent deep-sea habitats, South China Sea. Mar Life Sci Technol 3:1–12 Dyke FV, Lamb RL (2020) Conservation biology: foundations, concepts, applications, 3rd edn. Springer, Cham Edgar GJ, Stuart-Smith RD, Willis TJ et al (2014) Global conservation outcomes depend on marine protected areas with five key features. Nature 506:216–220 Gallardo VA (1977) Large benthic microbial communities in sulfide biota under Peru-Chile subsurface countercurrent. Nature 268:331–332 German CR, Ramirez-Llodra E, Baker MC et al (2011) Deep-water chemosynthetic ecosystem research during the census of marine life decade and beyond: a proposed deep-ocean road map. PLoS One 6:e23259 Glover AG, Higgs N, Horton T (2020) World Register of Deep-Sea species (WoRDSS). http://www. marinespecies.org/deepsea. Accessed 20 Aug 2020 Imtiyaz BB, Sweta PD, Prakash KK (2011) Threats to marine biodiversity. In: Santhanam P, Perumal P (eds) Marine biodiversity: present status and prospects. Narendra Publishing House, Delhi Jefferson T, Costello MJ (2019) Hotspots of marine biodiversity. In: Goldstein MI, Della Sala DA (eds) Encyclopedia of the world’s biomes. Elsevier, Dordrecht, pp 586–596 Li XZ (2017) Taxonomic research on deep-sea macrofauna in the South China Sea using the Chinese deep-sea submersible Jiaolong. Integr Zool 12:270–282 Luypaert T, Hagan JG, McCarthy ML et al (2020) Status of marine biodiversity in the Anthropocene. In: Jungblut S, Liebich V, Bode-Dalby M (eds) YOUMARES 9 – the oceans: our research, our future. Springer, Cham

155 Marine Conservation Institute (2021) MPAtlas [online]. Marine Conservation Institute, Seattle. Available at: www.mpatlas.org. Accessed 9 May 2021 Mayr E (1969) The biological meaning of species. Biol J Linn Soc 1:311–320 McNeely JA, Miller KR, Reid WV et al (1990) Conserving the world’s biological diversity. World Conservation Union, World Resources Institute, Conservation International, World Wildlife Fund–US, and the World Bank, Washington, DC Millennium Ecosystem Assessment (2005) Ecosystems and human well-being: synthesis. World Resources Institute, Washington, DC Mutia TM (2009) Biodiversity conservation. Short course IV on exploration for geothermal resources. KenGen and GDC, Nairobi O’Dor RK, Yarincik K (2003) The census of marine life: understanding marine biodiversity past, present and future. Gayana 67(2):145–152 Oliver G, Rodrigues C, Cunha M (2011) Chemosymbiotic bivalves from the mud volcanoes of the Gulf of Cadiz, NE Atlantic, with descriptions of new species of Solemyidae, Lucinidae and Vesicomyidae. Zookeys 113:1–38 Parson EA, Haas PM, Levy MA (1992) A summary of the major documents signed at the Earth Summit and the Global Forum. Environment 34(8):12–36 Paull CK, Hecker B, Commeau R et al (1984) Biological communities at the Florida Escarpment resemble hydrothermal vent taxa. Science 226:965–967 Pearce D, Moran D, IUCN Biodiversity Programme (1994) The economic value of biodiversity. Earthscan, London Rawat US, Agarwal NK (2015) Biodiversity: concept, threats and conservation. Environ Conserv J 16(3):19–28 Rogers AD (2018) The biology of seamounts: 25 years on. Adv Mar Biol 30(79):137–224 Rogers AD, Baco A, Griffiths H et al (2008) Corals on seamounts. In: Pitcher TJ, Morato T, Hart PJB et al (eds) Seamounts: ecology, fisheries & conservation. Wiley-Blackwell, Oxford, UK, pp 141–169 Rossi S (2013) The destruction of the “animal forests” in the oceans: towards an over-simplification of the benthic ecosystems. Ocean Coast Manag 84:77–85 Samadi S, Schlacher T, Forges BRD (2008) Seamount benthos. In: Pitcher TJ, Morato T, Hart PJB et al (eds) Seamounts: ecology, fisheries & conservation. WileyBlackwell, Oxford, UK, pp 117–140 Schemske DW, Husband BC, Ruckelshaus MH et al (1994) Evaluating approaches to the conservation of rare and endangered plants. Ecology 75:584–606 Sibuet M, Olu K (1998) Biogeography, biodiversity and fluid dependence of deep-sea cold-seep communities at active and passive margins. Deep-Sea Res II Top Stud Oceanogr 45(1–3):517–567 Soulé ME (1985) What is conservation biology. Bioscience 35:727–734 Tunnicliffe V, Fowler CMR (1996) Influence of sea-floor spreading on the global hydrothermal vent fauna. Nature 379(6565):531–533 Wessel P, Sandwell DT, Kim SS (2010) The global seamount census. Oceanography 23:24–33

B

156 WoRMS Editorial Board (2020) World Register of Marine Species. Available from http://www.marinespecies.org. Accessed 20 Aug 2020 Yesson C, Clark MR, Taylor M et al (2011) The global distribution of seamounts based on 30-second bathymetry data. Deep-Sea Res I Oceanogr Res Pap 58: 442–453 Young HS, McCauley DJ, Galetti M et al (2016) Patterns, causes, and consequences of Anthropocene defaunation. Annu Rev Ecol Evol Syst 47:333–358

Biofouling ▶ New Technologies in Auxiliary Propulsions

Block Assembly Line Yong Hu1,2 and Chong Wang2 1 Shanghai Jiaotong University, ShangHai, China 2 School of Transportation, Wuhan University of Technology, Wuhan, China

Synonyms Flux copper backing (FCB); TRYGGHET TILLIT SERVICE (TTS)

Definition Block assembly is a technological process of subassemblies and parts into ship block, also known as block manufacturing. According to the characteristics of block production, it can be divided into flat section, curved section, and superstructure section. According to statistics, in modern shipbuilding, hull assembly and welding account for 12–18% of the total labor in shipyard construction. Therefore, improving the mechanization and automation level of assembly and welding work can not only reduce the labor intensity of workers but also effectively shorten the shipbuilding cycle and improve the product quality. Due to the adoption of new technologies such as digital amplification and numerical control, the accuracy of parts processing is continuously improved and the

Biofouling

mechanization of assembly work is implemented (Liu and Wang 2011).

Introduction Subassembly Line There are usually four types of subassemblies: composite members of T iron, internal members of flat section, internal members of curved section, and iron outfits. Foreign large and mediumsized shipyards generally use T iron production lines (some of which are automatic production lines), equipped with automatic transfer rollers, gantry type cutting machines, robot welding machines, and corresponding sorting devices, which have higher production efficiency. Some steel mills roll different specifications of T iron for shipyards, and even there are specialized factories that specially assemble various T iron. For the subassemblies of the flat and curved sections, several technological processes are generally adopted as followed: parts positioning, assembly welding, turning, and assembly. According to the size of the batch, manual welding is generally used on the platform, or mechanized installation and welding equipment is adopted with the auxiliary of transfer roller. In the case of mass production, mechanized frame production lines can be set up or the production lines can be formed as part of a certain sectional production line. For some iron outfits, they are generally assembled on the platform in the specified area of the hull workshop (Xu 2005). For some large batches of splicing plates, reinforced webs and flat grillages, welding stations with higher degree of automation, such as pressure frame splicing plates and reinforced webs with high efficiency, can be used as part of the flat sectional assembly line. For many skeleton frameworks and frames in ship construction, shipyards generally adopt special and efficient welding assembly stations. For example, when Hudong Shipyard was building 70,000 DWT grade bulk carrier, it considered that there were 180 frames in the bottom section, so it adopted a special station and a flow line operation method. Its production process was as follows: steel plate pretreatment, numerical control cutting, partial assembly welding, distortion

Block Assembly Line

correction by frame, frame welding and hoisting into the outfield for block manufacturing. In this way, the speed of block construction is greatly improved (Liu and Wang 2011). Block Assembly Line The structure and shape of the hull are complex and diverse, and it is unrealistic to use a mechanical device (or an assembly line) to complete the manufacture of all blocks. Therefore, when studying the construction of hull block assembly line, it is necessary to divide the sections into several types according to the similarity of the structure and appearance characteristics of various blocks, and formulate standard process regulations according to the section types, so as to form various mechanized intelligent production lines. Flat section and curved section are two basic sections in hull section, and their structures are typical, accounting for a considerable proportion of the workload, of which flat section has more workload. Therefore, at present, the research and test work of mechanized, automatic, and intelligent production lines are all carried out with these two sections as the objects (Ryu et al. 2020). Flat Section Line

Generally speaking, the percentage of flat section must be at least 20%, and the establishment of flat section line is of practical value (Li and Wei 2006). With the large scale of ships, shipbuilding industry attaches great importance to block manufacturing, especially flat sectional manufacturing. Major shipyards generally adopt flat section assembly lines, and the technical level and production efficiency are continuously improving. 1. Coverage of Flat Section Assembly Line Process Under normal circumstances, the flat section assembly line can include: waiting station (plate, longitudinal, floor, preoutfitting item), splicing plate assembly station, splicing plate welding station, inspection and repair station, marking and cutting transposition, longitudinal assembly station, longitudinal welding station, transverse movement station, floor assembly station, floor welding station, turning station, preoutfitting station, and delivery station.

157

The number of work stations in the assembly lines varies from factory to factory. According to the specific situation, there are usually 8–10 work stations. The main work station consists of steel material preparation, panel tailor-welding, marking and cutting, skeleton framework assembly welding, and transportation. The transportation of blocks between stations usually adopts transfer roller. 2. Typical Process Flow of Flat Section Production Line Flat section is a unit structure formed by welding two or more than two steel plates into a panel, and then welding with various skeleton frameworks such as longitudinal trusses and frames. It is mainly composed of flat panel and flat frame. Therefore, its manufacture can be divided into two parts: tailorwelded panel and welding frame. According to the welding methods adopted, the automatic welding of the flat panel can be divided into double-side automatic submerged arc welding and one-side submerged arc welding with flux copper backing (FCB). In the former, the panel turning station should be added to the splicing plate assembly line so as to carry out panel turning and back sealing welding. The latter can save the plate turning station. Typical process of plane sectional production line includes: the whole line assembly and welding method (Fig. 1) and the frame assembly and welding method (Fig. 2). In the whole line assembly and welding method, one component or a group of components is positioned one by one, installed and welded to the strake, and another component is installed and welded after the one component is installed and welded to form a flat section. The frame assembly and welding method is to assemble and weld the longitudinal and transverse components into box frame of well shape, and then assemble and weld it to the strake. At present, large shipyards in our country generally have flat section assembly lines. Most shipyards have introduced advanced flat section assembly lines from abroad, and some shipyards have built their own flat section production lines (Huang 2013).

B

158

Block Assembly Line

Block Assembly Line, Fig. 1 The process flow of the whole line assembly and welding method

Block Assembly Line, Fig. 2 The process flow of frame assembly and welding method

Curved Section Line

The shape and member configuration of curved section vary with the sections. The assembly and welding positions of members are very rechecked, and their assembly and welding datum planes are all spatial curved surfaces. Therefore, it is much more difficult to realize the assembly line operation of curved sections than flat sections (Xu 2005; Zhou Hong 2012). Up to now, it is still in the research and test stage, and few shipyards have application cases. However, due to the large proportion of curved section in ship block manufacturing, it is of great practical significance to realize curved section line operation. In Japan’s test, a simulation test device for automatic

assembly and welding of curved shell plates was adopted, which can carry out tests such as numerical control adjustment of curved surface of the molding bed and automatic welding of shell plates to joints. Japan has also developed a selfpropelled curved assembly machine and a device suitable for assembly tests of curved section frames (Lee et al. 2014). In addition, it is reported that the first TTS curved section production lines successfully developed by Norway’s TTS Company has been installed in Denmark’s Odense Steel Shipyard, as shown in Fig. 3. The one-side welding workstation of the system can be tilted in all directions so that it can carry out one-side submerged arc welding at a horizontal position.

Block Erection Technology

159

B

Block Assembly Line, Fig. 3 TTS curved panel production lines

References Huang H (2013) Technology handbook of hull construction. China National Defense Industry Press, Beijing, China Lee DM, Kim SY, Moon BY (2014) Development of shipbuilding assembly system for ship’s blocks using 3D measurements system [J]. Appl Mech Mater 635/637(Part 1):621, 3485 Li ZL, Wei JL (2006) Technology of ship production. Harbin Engineering University Press, Harbin, China Liu YJ, Wang J (2011) Technology of ship production. Dalian University of Technology Press, Dalian, China Ryu H, Kang S, Lee K (2020) Numerical analysis and experiments of butt-welding deformations for panel block assembly [J]. Appl Sci 10(5):1–6 Xu ZK (2005) Technology of ship production. China Communications Press, Beijing, China Zhou Hong (2012) Advanced shipbuilding technology. China Communications Press. Beijing, China

Block Erection Technology Yujun Liu School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China

Definition Block erection, also known as ship assembly, is the technological stage of completing the overall assembly, welding, outfitting, and painting of the ship on the shipbuilding berth (dock) on the basis of pieces assembly and welding, block and block assembly and welding, pre-outfitting, and pre-

painting. Ship assembly is commonly known as ship general closure. As ship assembly generally needs to be carried out in the berth or the dock which are very limited and important resources of the shipyards, the quality and speed of ship assembly have a great impact on ensuring the quality of ship construction and shortening the period of ship construction (Liu et al. 2011).

Introduction Ship Assembly Facilities for Ships: Berth and Dock The shipbuilding berth (dock) is the working place where the block is assembled into the whole hull. It should have a solid foundation and be generally set up near the hull assembly and welding workshop and close to the launching water area of the ship, so as to shorten the transportation route of the block and facilitate the ship launching. Shipbuilding Berth

The shipbuilding berth is a place where ships are built on land. It can be moved to the water area by launching device. Generally, it can be divided into inclined berth, horizontal berth, and semi-dock berth. The shipbuilding berth also includes a longitudinal inclined berth and a transverse inclined berth, which determine the direction of the ship’s gravity launching. The inclined berth plane and the horizontal plane have a certain inclination (called berth slope), which is generally taken as 1/14 ~ 1/24.

160

Taking the longitudinal inclined berth as an example, the foundation of the longitudinally inclined berth is composed of reinforced concrete (Xu 2011). Parallel crane tracks are laid along both sides of the berth, and cranes with large lifting capacity are equipped. According to the inclination angle of the berth and the requirements of ship closure, the lifting height is required to be higher. The advantage of this kind of berth is that the ship is built and launched at the same position, and the construction site is relatively compact. Generally, there is no need to move the ship. The ship can slide into the water under the action of its own gravity, so there is no need for a special ship moving device. Inclined berth is usually used in combination with oiling and steel ball slideway, which is the most widely used at present (Fig. 1). The Dock

A dock is a hydraulic structure that is lower than the horizontal level and has a gate at its end. After the gate is closed, the water can be drained to be used for shipbuilding. It has some advantages of horizontal berth, and the ship is also built in a horizontal state (Li et al. 2006). Moreover, the dock bottom of the building ship is lower than the ground level, the lifting height of the block is reduced, and gantry cranes with large span and large lifting mass can be configured across the dock and the pre-installed welding area on the dock side, which greatly improves the mechanization degree of ship construction. Dock launching can greatly simplify the process of ship launching and is suitable for building large

Block Erection Technology, Fig. 1 Shipbuilding berth

Block Erection Technology

ships. In addition, the dock is not only used for shipbuilding but also convenient for ship repair. However, the investment in the dock is large, and the scale of ships built in the dock is strictly limited (Fig. 2).

General Assembly Method of Ship Due to the different product objects and shipyard production conditions, the ship assembly methods (called construction methods) are also various. These methods are all determined according to the structural characteristics of the ship and the production conditions of the shipyard and are conducive to balancing the production load, improving the efficiency, shortening the shipbuilding cycle, and improving the working conditions. The most commonly used methods are the block method of hull construction, tower method of hull construction, island method of hull construction, and series method of hull construction (Tokola et al. 2013). Block Method of Hull Construction The construction method of taking block as the hull assembly unit can reduce the berth workload and welding deformation, improve the integrity of pre-outfitting and pre-painting operations, move the workload forward, and shorten the berth construction period due to the large size, good rigidity, and relatively complete space. However, the size and weight of the block are generally limited

Block Erection Technology

161

B

Block Erection Technology, Fig. 2 The dock

Block Erection Technology, Fig. 3 Block method of hull construction

by the lifting capacity of the berth. In the block method of hull construction, the block in the middle of the ship (or close to the middle of the ship) is hoisted to the berth for positioning and fixing, and then the adjacent blocks before and after are hoisted in turn. When the butt joint welding of the two blocks is completed, the outfitting work can be carried out (Fig. 3). Island Method of Hull Construction The method of hull construction has only one construction area, the berth area cannot be fully utilized at the initial stage of assembly, the berth building period is long, and the stem and stern of the completed ship are tilted greatly. Therefore, if the hull is divided into 2–3 construction areas (hereinafter referred to as “islands”), each island selects a benchmark block and is constructed simultaneously according to the tower method of hull construction. The islands are connected with each other by embedded blocks, which can make full use of the berth area, expand the construction surface, and shorten the berth building period. Moreover, the length of its construction area is shorter than that of the tower method of hull construction and the hull rigidity is larger, so its

total welding deformation is smaller than that of the tower method of hull construction. This construction method is called the island method of hull construction. The hull is divided into two construction areas, which is called the two-island method of hull construction. The method of dividing into three construction areas is called the three-island method of hull construction. However, the assembly and positioning operation of its embedded blocks are relatively complicated. As shown in Fig. 4, it is a two-island method of hull construction, in which the blocks are embedded and complementary blocks (Bao et al. 2009). Series Method of Hull Construction When some shipyards use larger berths to build ships with smaller tonnage ships, they often use the series method of hull construction to organize production and improve the utilization rate of the berths. The series method of hull construction is to build the stern of the second ship at the stem of the berth (dock), while the first ship is built at the stern of the berth (dock). After the first ship is launched, the stern of the second ship is moved to the stern of the berth (dock), and other blocks are continuously hoisted to form the whole hull. At the same time, the stern of the third ship is built at the stem of the berth, and so on. This form can greatly improve the utilization rate of berths, shorten the construction period of berths (docks), and carry out outfitting operations in advance. It has many advantages in improving production management and balancing

162

Block Erection Technology

Block Erection Technology, Fig. 4 Twoisland method of hull construction

Block Erection Technology, Fig. 5 Series method of hull construction

production rhythm. However, it can only be used when the length of the berth is greater than the length of the building ship (approximately 1.5 times the length of the ship), and when this method is used on the inclined berth, ship moving equipment must also be equipped. Similarly, if a large dock is used to build a small tonnage ship, and if the dock can accommodate more than one ship, many ships will be built simultaneously in the dock. When a ship needs to be launched after the final assembly, the dock door shall be opened for water inflow. Other ships that have not been completed shall be limited in position by ballast and other technical means. The launched ships shall float upward by buoyancy and be towed outside the dock. After the dock door is closed and the water is drained, other ships shall continue to be built. In actual production, there are also various construction methods. At present, on the basis of vigorously promoting pre-outfitting shipbuilding, the domestic shipbuilding method is changing toward the modern shipbuilding mode, which is guided by the theory of overall planning and optimization, applies the principle of group technology, takes intermediate products as the guidance, organizes production according to

regions, separates the hull, outfitting and painting operations in space and orders in time, realizes the integration of design, production, and management, and realizes the balanced and continuous assembly shipbuilding (Kim et al. 2012). It is worth mentioning that no matter what kind of modern shipbuilding mode, in the shipbuilding process, it is based on several common methods of sectional construction that have been described, and optimizes the combination in time and space respectively, so as to achieve the purposes of expanding the production scale, improving the production efficiency and reducing the manufacturing cost (Fig. 5). Tower Method of Hull Construction During construction, the bottom block at the back of the middle part is taken as the reference block (for medium-sized ships, the engine room block can also be taken). The reference block is positioned and fixed on the berth, and then each block is hoisted from bottom to top to the stern and stern and both sides. Since the installation area formed during the construction process is in the shape of a pagoda with wide bottom and narrow top, it is called the tower method of hull construction, as

Block Erection Technology

163

Block Erection Technology, Fig. 6 Tower method of hull construction

B shown in Fig. 6. The sectional installation of this construction method is relatively simple, but the berth building period is relatively long, and due to the large number of welded closing joints, the welding deformation is not easy to control, and the stern and stern of the ship are seriously tilted after completion.

General Assembly Technology of the Berth (Dock) Tower method of hull construction and island method of hull construction are commonly used for ship assembly. Although the construction methods are different, the sequence of sectional hoisting and the fixing method of sectional positioning in a construction area are the same. At the same time, through the discussion and analysis of the block assembly technology, the block assembly technology of the block construction method can also be obtained. Therefore, taking the tower method of hull construction as an example, the relevant issues of berth assembly and welding sequence and welding process of berth assembly are discussed. Sequence of Berth Assembly and Berth Welding In general, the sequence of berth assembly and berth welding for the tower method of hull construction is as follows: 1. Hoisting reference block. The hoisting reference block is the starting point for berth closure, and its selection should enable berth outfitting and hull construction to be completed at the same time. Due to the heavy outfitting workload of the engine room, the starting point is often selected in and

2. 3.

4.

5.

6.

7.

around the engine room, so as to complete the hull of the engine room as soon as possible and carry out outfitting operations as soon as possible. Bulkhead block and front and rear bottom block on the hoisting reference block. Hoist broadside block. Continue to hoist the bottom block and bulkhead block in the stern and the stem directions. Hoist the deck block. Continue to hoist the bottom block, bulkhead block, and broadside block, and sectional seam welding is carried out at the part where the mega-block of the ship hull has been formed. Continue to hoist the bottom block, bulkhead block, broadside block, and deck block in the stern and stem directions, weld the assembled block large joints, and carry out outfitting operation on the cabins where the block large joints have been welded. Hoist the stern and stem block, and continue to complete the welding of large seams in blocks and outfitting in the cabin. Hoist and weld superstructure, and continue outfitting operation.

When the island method of hull construction is adopted, the assembly and welding sequence of each construction area are the same as that of the tower method of hull construction, except that the work of hoisting, embedding, and repairing blocks is added at the end to connect each construction area. In actual production, sometimes due to the influence of sectional supply, reasonable utilization of hoisting equipment, and other temporary factors, it is required to adjust the sequence of hoisting in certain blocks. In this regard, it is necessary to proceed from reality. As long as it does not cause difficulties in berth assembly and welding, appropriate adjustments can be allowed (Huang 2013).

164

Ship Berth Assembly and Welding Technology Sectional positioning, allowance drawing and cutting, large joint fixing requirements, and large joint welding are common technical problems in berth assembly and welding, which are discussed and analyzed respectively. Positioning of Blocks on the Berth

1. Primary Positioning. The correct position of the blocks in the hull is determined directly by the four factors of the length, width, height direction, and horizontal inspection line of the blocks in the hull. Take the positioning of double bottom blocks as an example, the frame inspection lines on the blocks are aligned with the corresponding frame lines on the berth to determine the position of the blocks along the length direction; align the block centerline with the berth channel centerline to determine the position in the width direction; determine the position of the sectional height direction based on the height benchmark; measure the block left-right level inspection line to determine the block left-right level. After the positioning is completed, the blocks will be fixed. 2. Secondary Positioning. If the blocks are assembled on the berth with the allowance, a secondary positioning is often required. Take the bulwark block with allowance on the berth as an example. First of all, the blocks are hoisted onto the berth. And align the horizontal inspection line of the block with the same horizontal inspection line on the previous side block that has been assembled. Draw the allowance line in the height direction, remove the broadside block and cut off the allowance, then hoist the block onto the berth, align the frame inspection line of the block with the same frame inspection line on the bottom block, draw the allowance line in the length direction, and remove and cut off the allowance. At last, hoist the block onto the berth, complete the block according to the frame inspection line and the horizontal inspection line, and finally complete the secondary positioning.

Block Erection Technology

Determine the Allowance, Draw the Allowance Line, and Cut the Allowance

In the shipyards where precision control is implemented, the assembly is carried out on the berth without any allowance in blocks. The allowance of the large joints in blocks is cut off on the sectional mold bed and then hoisted on the berth. This can cancel the operations of drawing lines, cutting and secondary positioning of the block, reduce the amount and difficulty of berth assembly operations, and shorten the assembly period of the berth. However, due to the limitation of technical conditions, some shipyards have not yet implemented the precision control of berth assembly, so the sectional large joints need to have an allowance, and the allowance drawing and cutting will be carried out when the ship is closed. Sectional Drawing, Butt and Positioning Welding After cutting the block allowance, the groove shall be correctly processed, then the block shall be drawn in, and the block installation position and joint clearance shall be checked. After meeting the requirements of positioning welding, the block positioning welding shall be carried out, and the internal framework near the large joint shall be installed. First, the internal framework of the block is positioned and welded, and then the external plate is positioned and welded. In the method of sectional drawing and matching, the bottom block and the block are generally supported by a hydraulic jack and are drawn and positioned by elastic screw buckle (also known as flower basket screw). The other blocks are drawn and matched with elastic spiral buckles. When positioning welding is carried out for sectional joints, the phenomenon that two frameworks are not aligned often occurs. At this time, the positioning welding between one framework and the plate can be removed by about one gear frame distance, or the positioning welding between the two butted frameworks and the plate can be removed to make them straight or aligned (Fig. 7).

Blowout Preventer (BOP)

165

B

Block Erection Technology, Fig. 7 Cutting the block allowance

Welding Work in Berth Assembly In order to prevent welding deformation, a strong back should be added after positioning welding of the outer plate, and welding should be carried out symmetrically left and right. Before welding, several blocks should be assembled to increase the rigidity of the hull and make it difficult to generate welding deformation. During welding, the inner surface shall be welded first, and the outer back sealing shall be welded. The welding operation of sectional large joints is carried out in parallel with the sectional hoisting operation. This is not only conducive to reasonably organizing the production process of berth assembly and welding but also can reduce the warping deformation of the hull when the length of the construction area is short. In order to reduce the total welding deformation of the hull, the welding operation should be carried out in the area where the mega-block has been formed, so that it has strong structural rigidity of the hull and is convenient to meet the requirements of symmetrical welding. In recent years, with the continuous improvement of shipbuilding equipment automation, some shipyards have begun to use vertical welding robots in the welding of large hull joints, greatly improving the speed and quality of berth closure seam welding.

References Huang H (2013) Technology handbook of hull construction. China National Defense Industry Press, Beijing, p 110 Ji ZS (2005) Mechanics in ship fabrication. China National Defense Industry Press, Beijing, pp 201–203 Jinsong B, Xiaofeng H, Ye J (2009) A genetic algorithm for minimizing makespan of block erection in shipbuilding. J Manuf Technol Manag 20(4):500–512 Kim DE, Chen TH (2012) A virtual erection simulation system for a steel structure based on 3-D measurement data. J Mar Sci Appl 11(1):52–58 Lee H-W, Roh M-I, Ham S-H (2020) Block erection simulation considering frictional contact with wire ropes. Ocean Eng 217 Li ZL, Wei JL (2006) Technology of ship production. Harbin Engineering University Press, Harbin, pp 399–404 Liu YJ, Wang J (2011) Technology of ship production. Dalian University of Technology Press, Dalian, pp 134–159 Tokola H, Niemi E, Remes H (2013) Block erection sequencing in shipbuilding with general lifting and joining times. J Ship Prod Des 29(2):49–56 Tokola HA, Niemi E, Remes H (2016) Block erection in the event of delays in shipbuilding: a scenario-based approach. J Ship Prod Des 32(1):37–49 Xu ZK (2011) Technology of ship production. The People’s Communication Publishing Company, Beijing, p 92

Blowout Preventer (BOP) ▶ Christmas Tree ▶ Hydrodynamics for Subsea Systems ▶ Steel Pipelines and Risers

166

Bridge System ▶ Ship Navigation System

Brilliance of the Seas ▶ Luxury Cruises

Broaching ▶ Surf-Riding and Broaching

Broaching Stability ▶ Surf-Riding and Broaching

Brushless DC Motor (BLDCM) ▶ AUV/ROV/HOV Propulsion System

Bucket Foundations Mi Zhou College of Civil Engineering and Transportation, South China University of Technology, Guangzhou, China

Conception of Bucket Foundations The world’s escalating demands for energy, combined with the continued depletion of oil and gas reserves in shallow waters, has resulted in offshore developments moving into deeper waters and untested environments. In the Gulf of Mexico, West Africa, offshore Brazil, and, more recently, off Australia, developments have proceeded into water depths in excess of 1000 m. These deep

Bridge System

water developments usually consist of moored floating facilities, which are tethered to the seabed via an anchoring system. Bucket foundations (also named as suction caissons or skirted foundation) have been proven as a cost-effective alternative to more traditional anchoring solutions such as piles and drag anchors, because of their ability to confine surface soil and transfer loads to stronger soils at skirt tip level. Bucket foundations are a type of shore shallow foundations, which consist of a plate resting on the seabed and a peripheral skirt (often supplemented by internal skirts) penetrating into the seabed and confining a soil plug. Bucket foundations are best described as upturned foundations that are installed into foundations to anchor floating structures or to support superstructures. The skirts also assist in foundation installation by constraining the lateral movement as the foundation approaches the seabed, compensating for seabed irregularities and reducing scour around the foundation periphery. Bucket foundations (also called buckets, skirted foundations, or suction anchor piles) can be used to sustain high axial and lateral loads. These foundations may be broadly divided into two types; relatively short buckets, often referred to as bucket foundations, which support jacket structures, and relatively long buckets, which are used as foundations for moored structures, which typically have higher aspect ratio than bucket foundations. The typical shapes of bucket foundations are circular and square. For square buckets, the width of edges usually ranges from 3 m to 10 m (Hossain et al. 2012). For buckets with circular shape, it comprise large diameter cylinders, typically in the range of 3–8 m (shown in Fig. 1), open at the bottom and closed at the top, and generally with a length to diameter ratio L/D in the range three to six, considerably less than offshore piles, which have slenderness ratios up to 60. Bucket foundations are a comparatively new foundation system, which have however found relatively widespread use. Bucket foundations have proven to be a costeffective, excellent performing, deep foundation system, that is utilized in offshore engineering worldwide. Typically, they are used for bridges, offshore wind power, cofferdam, and large structures, where large loads and lateral resistance are

Bucket Foundations

major factors. The first bucket foundaiton employing the system as permanent foundations in clay or sand were built in the early 1990s (Tjelta et al. 1990). The foundation keeps water out of the construction area while its open bottom allows workers to place foundations and piers in the seabed or riverbed. In shallow water, an open bucket is used; its open top allows light and air to enter from above the water line. For deep-water construction, a pneumatic bucket has a closed top; pressurized air is pumped in, and personnel enter and leave through an airlock. Either type has a sharply inclined lower edge, allowing the structure to be deeply embedded in the ground so water cannot seep in. A bucket must be firmly mounted on a stable foundation for maximum security and efficiency.

Bucket Foundations, Fig. 1 Bucket foundation used in offshore engineering. (After Dendani and Colliat 2002)

167

Engineers prefer to choose a layer of stiff soil to construct on it. If bedrock is too far beneath the ground, they will sometimes rely on impacted mud or earth, or create an artificial foundation. Bucket foundations are similar in form to pile foundations, but are installed using a different method. It is used when soil of adequate bearing strength is found below surface layers of weak materials such as fill or peat. It is a form of deep foundation, which are constructed above ground level, then sunk to the required level by excavating or dredging material from within the foundation.

Functions of Bucket Foundation The application of bucket foundation and loading condition in various offshore structure are shown in Fig. 2, which includes (a) & (b) gravity-based structures; (c) jacket/template structure; (d) tension leg platform; (e) storage tank Support Vertical Loads Bucket foundations have proven to be competitive alternatives to more traditional foundation solutions like piles in various types of soils and for a wide range of fixed offshore platforms. Bucket foundations have been used for gravity platform jackets, jack-ups, subsea systems, and seabed protection structures. Even more critical than settlement is differential settlement. This occurs when parts of the offshore structures settle at different rates,

Bucket Foundations, Fig. 2 Application of bucket foundations and loading conditions in various offshore structures. (After Acosta-Martinez 2010)

B

168

Bucket Foundations

resulting in cracks, some of which may affect the structural integrity of the offshore structure.

Mechanical Principle of Bucket Foundation

Support Horizontal Loads Bucket foundations are used to anchor floating production vessels using catenary or taut wire mooring chains; in these cases, the foundation is under quasi-horizontal or angled load. In shallow water, a length of the bucket foundation chain will rest on the seabed during calm conditions, with the small mooring loads being resisted by friction against the seabed. The chain may be connected to the foundation at the soil surface, or it may be connected via an embedded pay-eye, which provides a more efficient arrangement.

Application of Bucket Foundation

Types of Bucket Foundations Box Bucket Foundation Box bucket foundations are watertight boxes that are constructed of heavy timbers and open at the top. They are generally floated to the appropriate location and then sunk into place with a masonry pier within it.

Foundation for Offshore Wind Turbines

Bucket foundations have been widely used in offshore wind turbines in recent decades. The foundation of a wind turbine must be strong enough to withstand the maximum force acting on it and not fail during its operation. Furthermore, it must be stiff enough so that the displacements and rotations during its lifespan fall within the serviceability design criteria of the wind turbine manufactures. Bucket foundations, with high vertical and horizontal bearing capacities, have been used as the foundation for offshore wind turbines (Ibsen and Brincker 2004). A foundation concept that is gaining acceptance for the support of bottom-fixed offshore wind turbines is the suction bucket foundation. This may support the turbine superstructure either as an individual bucket foundation or as a group of three or four bucket foundations below a jacket substructure, as shown in Fig. 3 Bucket Foundations Construction Process

Excavated Bucket Foundation Excavated bucket foundations are, just as the name suggests, foundations that are placed within an excavated site. These are usually cylindrical in shape and then back filled with concrete. Floating Bucket Foundation Floating bucket foundations are also known as floating docks and are prefabricated boxes that have cylindrical cavities. Open Bucket Foundation Open bucket foundations are small cofferdams that are placed and then pumped dry and filled with concrete. These are generally used in the formation of a pier. Pneumatic Bucket Foundation Pneumatic bucket foundations are large watertight boxes or cylinders that are mainly used for under water construction.

Suction

A suction bucket foundation is installed pumping the water inside of the foundation to install it by the differential pressure inside and outside as shown in Fig. 4. Initially, bucket foundation was installed to a certain depth by the weight of itself. And then, penetration into the seabed is achieved by suction, via a pump connected to a valve in the top cap of the foundation. Water is pumped out from inside the foundation causing the pressure inside the foundation to fall below that outside. This causes a net downward pressure on the top of the foundation forcing it into the seabed. Jacking

Offshore developments moving beyond the immediate continental shelf into deeper waters (now approaching 3000 m depths) has been driven by the vibrant oil and gas industry and the world’s ever-increasing demands for energy.

Bucket Foundations

169

Bucket Foundations, Fig. 3 Offshore wind turbine with jacket substructure supported by suction bucket foundations. (After Bienen et al. 2018)

These deep water developments rely on floating facilities (e.g., floating production storage and offloading vessels, tension leg platforms, SPAR platforms, and emerging concepts such as floating liquefied natural gas (FLNG) facilities) moored to the seabed through mooring chains and anchoring systems, with suction bucket foundations being identified as the most viable option. Bucket foundations are also used as foundations to support pipeline manifolds and end terminations, subsea structures, and riser towers. In the renewable energy industry, they are increasingly being considered for anchoring floating turbines. Suction bucket foundations are installed by pumping water from inside the foundation after it is allowed to penetrate under its self-weight.

B

Analyses are sometimes carried out using jacking installation process to simplify the problem, especially for bucket foundations in clay, where a foundation is pushed in soil up to the full penetration depth (similar to driven pile). To comply with the increasing size of the floating facilities to be anchored (e.g., the Prelude FLNG is 488 m long and 75 m wide), suction bucket foundations are designed as longer and wider – currently up to 30 m long, with a length to diameter (aspect) ratio L/D in the range 2–7 (Andersen et al. 2005). As the thickness of the skirt (t) is restricted to less than 50 mm to ensure installation viability, the longer bucket foundations are required to include horizontal ring stiffeners at intervals along the inner wall of the thin skirt with local thickening of the wall in the

170

Bucket Foundations

Bucket Foundations, Fig. 4 Bucket foundation installation by suction pressure. (After Andersen and Jostad 1999)

vicinity of the padeye, with or without transverse struts, for structural integrity. Suction bucket foundations are thin-walled (thickness, t  50 mm) and thus prone to buckling during installation or distortion under the horizontal or moment loading. In order to deal with the buckling problems, horizontal ring stiffeners at intervals along the inner wall of the thin skirt are employed with local thickening of the wall in the vicinity of the padeye, with or without transverse struts. As such, horizontal ring stiffeners at intervals along the inner side of the thin skirt, and occasionally vertical stiffeners around the internal periphery, are employed with local thickening of the wall in the vicinity of the padeye, with or without transverse struts, as shown in Fig. 5. Recent designs of rectangular steel foundations for skirted gravity-based platforms have required combined vertical and horizontal stiffening (after Watson and Humpheson 2007). Consequently, Engineers are faced with the challenge of designing foundations with sufficient structural integrity to allow longer skirt lengths while ensuring their installation feasibility. These stiffeners may increase the required installation pressure by as

much as 50–100% and can have a significant influence on the drained tension capacity (House and Randolph 2001; Westgate et al. 2009). The addition of these stiffeners has created significant uncertainties regarding the soil flow mechanisms, in particular the inner soil heave with the risk of potential penetration refusal prior to reaching the designed installation depth (or achieving the designed capacity to sustain operational loadings). The pattern of soil flow at the foundation tip, and the proportion of the bucket foundation wall that is accommodated by inward or outward displacement of the soil, has important consequences for quantifying (i) the external radial stress and excess pore pressure, and ultimately long-term external shaft friction following consolidation; (ii) the internal side friction and stiffener end bearing. The behavior of the clay plug can also affect the maximum penetration depth of the foundation. This is more critical for stiffened bucket foundation. If the plug remains fully or partially self-supporting above the horizontal stiffeners, the gaps formed between the stiffeners result in greater heave volume, and hence higher inner seabed elevation. This entry

Bucket Foundations

171

Bucket Foundations, Fig. 5 Bucket foundation with stiffeners. (After Westgate et al. 2009)

B

has specifically focused on the quantification of inner soil heave during installation of stiffened bucket foundations. Andersen et al. (2005) discussed predictions for four different hypothetical installation cases and six case histories carried out by four predictors using their normal design method. For the hypothetical cases, the predictors calculated different soil heave height inside bucket foundation due to different assumptions in terms of the proportion of soil flow inside bucket foundation, soil plug heave standing ability, and soil infilling in the gaps between the embedded stiffeners. For the case histories presented, comparison between the calculated and observed soil heave showed that soil infilling in the gaps between the embedded stiffeners dictated the soil heave height, with the assumption of no soil infilling in the gaps and fully filled gaps providing over and under predictions, respectively. The stiffeners have a significant effect on the soil flow mechanism of stiffened bucket foundation installation (Zhou et al. 2016). They found that the soft soil will be trapped between stiffeners and move vertically with the same velocity as foundation installation, and the stiffeners have effect on the soil movement around skirt tip and stiffeners. Consequently, it also has effect on the inside heave as reported by Zhao et al. 2017.

Advantages and Disadvantages of Bucket Foundation Advantages of Bucket Foundations Economics Reduced weight Increased installation speeds Ease of decommissioning

Suitable for deep waters and large turbines Slightly less noise and reduced vibrations Easily adaptable to varying site conditions High axial and lateral loading capacity Disadvantages of Bucket Foundations Extremely sensitive to construction procedures Not good for contaminated sites Lack of construction expertise Lack of Qualified Inspectors

References Acosta-Martinez H (2010) Physical modelling of shallow skirted foundations under transient and sustained uplift [D]. The University of Western Australia Andersen KH, Jostad HP (1999) Foundation design of skirted foundations and anchors in clay. In: Proceedings of the Offshore Technology Conference, Houston, Paper 10824 Andersen K, Murff J, Randolph MF, Clukey E, Erbrich CT, Jostad H, Hansen B, Aubeny C, Sharma P, Supachawarote C (2005) Suction anchors for deepwater applications. In: Proceedings of the 1st international symposium on frontiers in offshore geotechnics (ISFOG), Perth, pp 3–30 Bienen B, Klinkvort RT, O’Loughlin C, Zhu F, Byrne BW (2018) Suction caissons in dense sand, part I: installation, limiting capacity and drainage. Géotechnique 68(11):1–47 Dendani H, Colliat J-L (2002) Girassol: design analysis and installation of suction anchors. In: Proceedings of the offshore technology conference, Houston, OTC 14209 Hossain S, Lehaneb M, Hu Y, Gao Y (2012) Soil flow mechanisms around and between stiffeners of caissons during. Revue Canadienne De Géotechnique 49(4): 442–459 House AR, Randolph MF (2001) Installation and pullout capacity of stiffened suction caissons in cohesive sediments. In: Proceedings of the 11th international symposium on offshore and polar engineering, Stavangar

172 Ibsen LB, Brincker R (2004) Design of a new foundation for offshore wind turbines. In: International modal analsyis conference, Dearborn Tjelta TL, Hermstad J, Andenaes E (1990) The skirt piled gullfaks c platform installtion. In: Proceedings of Offshore Technology Conference, Houston, OTC6473, pp 453–462 Watson PG, Humpheson C (2007) Foundation design and installation of the Yolla-A platform. In: Proceedings of the 6th international offshore siteinvestigation and geotechnics conference, society for underwater technology, London, UK, 11–13 September 2007, pp 399–412 Westgate ZJ, Tapper L, Lehane BM, Gaudin C (2009) Modelling the installation of stiffened caissons in oversonsolidated clay. In: Proceedings of the 28th international conference offshore mechanics and Arctic engineering, OMAE2009-79125 Zhao Z, Zhou M, Hu Y, Hossain MS (2017) Behavior of soil heave inside of stiffened caissons installing in clay. Can Geotech J 55(5):698–709 Zhou M, Hossain M, Hu Y, Liu H (2016) Installation of stiffened caissons in nonhomogeneous clays. J Geotech Geoenviron Eng 142(2):04015079

Buffer Station Xinguang Du1 and Yang Cao2 1 Intelligent Equipment Engineering Technology Center, China Ship Scientific Research Center (CSSRC), Shanghai, China 2 China Ship Scientific Research Center, Shanghai, China

Buffer Station

Buffer Station, Fig. 1 The ocean mining system. (1) The surface ship; (2) The lifting riser; (3) The buffer station; (4) The flexible riser; (5) The miner robot

system and the surface supporting system. It is the channel to transfer the polymetallic nodules from the seafloor to the surface ship. Besides, it also acts as the carrier of power and signal cables and the heart of the ocean mining system (Fig. 1). The buffer station is located in the middle of the lifting system. The upper end of the buffer station is connected to the deep-sea mining ship through the rigid riser, and the lower end is connected to the mining vehicle through the flexible riser.

Synonyms Research Process DCOR – dynamic characteristics of the riser; EIP – equipment installation platform

Introduction The basic function of the ocean mining system is to collect the mineral resources of the seafloor, lift them to the sea surface, and transfer them to the port. It is generally composed of four subsystems such as the undersea mining system, the lifting system, the control and power system, and the surface supporting system. The lifting system is the intermediate link between the seafloor mining

For deep-sea mining, many research institutions have done a lot of work in recent decades. In March 1979, several international mining consortia countries, led by the United States, including Canada, the United Kingdom, West Germany, Belgium, the Netherlands, Italy, and Japan, etc., first adopted a deep-sea mining system with a buffer station to collect nodules from 5000 m seabed. Russia began to develop the deep-sea mining system with a buffer station in 1980. In 1991, the system design was completed and a 1/10 prototype test was carried out in 100–1000 m water depth of the Black

Buffer Station

Sea (Wang 2015). Korea has been engaged in the development and research of deep-sea mineral resources since the 1990s. The conceptual design of the riser lifting system of the subsea collector with a buffer station and the structural design of the hydraulic mechanical composite ore collecting system with the lifting system were completed (Yoon 2011). In 2013, the system was tested in 1370 m deep-sea area, 130 km southeast of Puxiang in Qingshang North Road. Canada used a diaphragm positive displacement pump system as the underwater mineral lift pump, which plays a buffer role in the whole deep-sea mining lifting system (Smith 2011). The pump system consists of two pump modules, and each module includes five diaphragm pumps driven by the return water of mineral dehydration from mining vessels. In 2012, the underwater mineral lift pump was put into operation factory test evaluation, and some components were tested in 2500 m of water. Chinese research institutions carried out basic research on deep-sea mining during “the 8th Five-Year Plan” period and proposed a hydraulic lifting deep-sea mining system with buffer function (Tang et al. 2013). An elastic blade wheel feeder was added to the buffer station during the “9th Five-Year Plan” period, which solved the problems of feeding jam, ore bin arching, and emergency discharging. In the “13th Five-Year Plan,” the buffer station of the deep-sea mining mineral lifting system was planned to complete the 1000 m sea trial in 2021 (Yang et al. 2020).

Buffer Station Component Overview The buffer station mainly includes an external frame, an internal equipment system, and a riser system. The external frame includes a swing connecting device, top frame, upper frame body, and the lower frame body. The internal equipment includes a storage bunker, hose pump, constant feeder, hydraulic pressure station, electronic cabin, and power distribution box, etc. (Fig. 2).

173

1 2

3 4 5 6 7 8 9 10 11 12

Buffer Station, Fig. 2 Buffer station component system. (1) Swing connecting device; (2) top frame; (3) swing hose; (4) storage bunker; (5) power distribution box; (6) upper storage bunker; (7) constant feeder; (8) mixer; (9) hydraulic pressure station; (10) hose pump; (11) counterweigh; (12) lower frame

Storage Bunker The volume of the storage bunker is generally determined by the principle that it can continuously feed ores by the bunker if there are no nodules in the collection path in 15 min. The top of the bin is open and the lower part is conical, which is conducive to ores discharge and prevents ores from piling up. The Constant Feeder The constant feeder adopts an elastic blade feeder, which is composed of a shell, a rotor, a rotor support end cover, a hydraulic pressure motor, and a speed measuring device. The shell is processed by connecting the flange, the side plate, and the cylinder body. Its feed inlet is asymmetric and biased to one side of the feed port, to reduce the resistance moment of feeding. An arc-shaped baffle plate is fixed at the outlet to make the feed out. The feed port has a parallelogram shape so

B

174

Buoyancy

that the material falls uniformly and continuously. The constant feeder can solve the blocking problem and achieve uniform feeding. The feeding fluctuation of ores is less than 5%. Swing Connection Device It is located at the top of the buffer station and connects the buffer station body to the rigid riser. It adopts the movable hinged form, which releases the swing of the buffer station body. It can optimize the stress condition of the riser system and improve the stability of the whole system. The flexible riser passes through the middle of the swing connection device and connects the buffer station to the upper rigid riser. External Frame The unsealed frame structure is adopted to protect the internal equipment and prevent the impact when placing and recycling. To facilitate the installation and maintenance, the external frame is modularly designed. It includes a top frame, an upper frame, and a bottom frame. The Hose Pump The ores are pumped from the deep-sea mining vehicle to the storage bunker of the buffer station through the flexible riser. The hose pump should have a robust characteristic.

The Function The main functions are as follows. The ores pretreatment function. The deep-sea ores collected by the mining machine are delivered to the buffer station’s storage bunker. Then the ores are continuously and quantitatively feeds to the lifting pipe by a constant feeder. This will avoid the influence of ore concentration caused by the change of nodule abundance on the operation of the underwater transportation system. That will ensure the stability of the ore lifting process parameters and high lifting efficiency. Providing EIP for mining underwater systems. For example, it can be used as a reference settlement unit of the acoustic positioning system.

Buffer Station, Fig. 3 Mining ore transportation procedure

The hydrodynamic optimization function. The buffer station helps to keep the riser vertical and improves the DCOP. If the weight and shape are designed reasonably, the vertical displacement and axial stress of the riser system caused by ship heave may be reduced by 50% and 17%, respectively, according to the model test (Fig. 3).

References Cao Y, Du X, Song H (2020) Overall strength analysis and assessment of underwater buffer station in deep sea mining. Ship Ocean Eng 49(3):136–139 Smith G (2011) Deepwater seafloor resource production – the Bismarck Sea development project. In: Offshore technology conference, Houston, 2–5 May 2011 Tang DS, Yang N, Jin X (2013) Vertical pipeline hydraulic lifting technology for deep sea coarse grained ore. Min Metall Eng 33(5):1–8 Wang MH (2015) Exploitation of deep sea solid mineral resources. Central South University Press, Changsha Yoon CH (2011) Shallow lifting test for the development of deep ocean mineral resources in Korea. In: Proceedings of the ninth ISOPE ocean mining symposium, Maui

Buoyancy ▶ AUV/ROV/HOV Hydrostatics

Burry Depth ▶ Iceberg Scouring

C

Cable Jun Yan1, Haitao Hu2, Huan Gao3, Xipeng Ying2 and Zhixun Yang4 1 State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian, China 2 Department of Engineering Mechanics, Dalian University of Technology, Dalian, China 3 Shanghai Electric Cable Research Institute, Shanghai, China 4 College of Mechanical and Electrical, Harbin Engineering University, Harbin, China

Synonyms

for transmission of power, control of electricity, and signal transmission (Limei 2016). Insulation is used to provide dielectric strength and electric insulation. There are sheathes in all cables which can protect the cables, making the cables round and adjusting the size and weight. Shield is mainly used for the function of shielding magnetic field. And armor plays an important role in strengthening (Hammons 2003). Besides electric cable, polyester rope has been put into usage as part of mooring lines for two decades and more frequently used in deeper water globally (Mukoyama et al. 2006). Polyester cable is widely used in the mooring system of deep water due to its high strength, light weight, and good anti-fatigue performance, which is mainly consist of polyester, polypropylene, nylon, manila hemp, Dyneema, etc (Honjo 2001).

Bare wire; Conductor; Insulation layer; Polyester rope; Power cable; Winding wire

Scientific Fundamentals Definition An electric cable is usually made up of several or sets of wires twisted together. There is insulation between wires, with a layer of highly insulated cover enclosed outside. There are also shield and armor in some cables. Electric cables can be classified into the power cable and the communication cable. The former one is mainly used to provide electric power, and the latter one is mainly used © Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

Structure Composition of Electric Cable This entry takes a typical structure of cable as an example, which contains conductor, insulation, sheath, and armor (Schmidt 2012). The effects they make in the cable are as follows (Fig. 1). Conductor

Conductor is a component of conducting electric current, which is a vitally important core component in the structure of the electric cable and

176

Cable

Cable, Fig. 1 The structure of electric cable (http://www.orientcable.com/v_pros.asp?/5.html)

which determines the basic performance (Zuijderduin 2012). The specifications of the wires and cables are up to the cross section of the conductors, which are mainly made of high conductivity materials (copper or aluminum). According to the operating conditions of the required flexibility, each core may be twisted by a single wire or multiple wires of the electric cables (Zhong 2015). In general, bare copper wire, tin-plated copper wire, silver-plated copper wire, tin-copper alloy, enameled wire, copper wire, copper clad steel, and so on are the common conductors in the market (Xuyang 2017). Insulation Layer

Insulation layer is used as the insulation material for electric cables. According to different requirements of the withstand voltage conditions, insulation materials are covered outside the conductors with different degree of thicknesses (Ouatah et al. 2013). Insulation layer usually has excellent insulation performance and heat resistance. Generally, the higher the voltage is, the thicker the insulation layer is, but it is not proportional. Usually, the insulation materials used in cables are oilimmersed paper, polyvinyl chloride, polyethylene, cross-linked polyethylene, rubber, and so on (Zhang 2015). Cables are often classified by insulation materials, namely, the oil-immersed paperinsulated cables, the PVC cables, and the crosslinked polyethylene cables.

Seal Sheath

Seal sheath can protect the wire core from damage caused by general external factors or other environmental factors, including machinery, water, moisture, chemicals, and light. Due to the insulation which is susceptible to moisture, the lead or aluminum extrusion seal sheath is generally used (Ohsaki et al. 2012). Armor Layer

As a part of protecting electric cables, armor layer is used to protect seal sheath from mechanical damage. In general, galvanized steel tapes, steel wires, or copper belts and copper wires are used as armor wrapped around the sheath (so it is called armor cable). The armor layer can shield the electric field and can prevent from external electromagnetic interference (Dvorsky et al. 2011). In order to avoid the corrosion of steel tape and steel wire by the surrounding media, they are usually coated with asphalt or wrapped around a jute-immersed layer or extrusion polyethylene and PVC sheath. Classification Wires and cables can be generally classified into the following five categories according to different actual engineering uses. Bare Wire

There are only conductors in bare wires, which have no insulation. Bare wire can be classified

Cable

into copper, aluminum and other metals, composite metal round-single wire and stranded wire, soft wiring, and transmission lines of various structures (Courty and Garo 2017). Power Cable

Power cable is a wire product used in transmission and distribution of high power energy in the main line of power system, which includes power cables that have various kinds of voltage from 1 to 500 or above and various kinds of insulation, such as overhead bare wires, power cables (plastic power cables, oiled paper power cables which are almost replaced by the plastic power cables, rubber sheathed cables, overhead insulated cables), branch cables, electromagnetic wires, electrical equipment cables for electric power equipments, and so on (Grayson et al. 2001). Wires and Cables for Electrical Equipments

There are various power cables whose wires and cables are for electrical equipments and which can transmit power directly from the distribution point of the power system to different electrical equipments. These cables are also applied in the electrical installation lines and control signal for kinds of industry and agriculture (Chen et al. 2012). The structures and performances should be determined in combination with the characteristics of the equipment and the environmental conditions, due to the extensive uses and different types of these cables. Communication Cable and Optical Fiber Cable

Communication cable is used to transmit data and other telecommunication information in telephone, telegraph, television, radio, and fax. There are many kinds of wires and cables which are used in the information transmission system, such as telephone cables, television cables, electronic cables, radio-frequency cables, optical fiber cables, data cables, electromagnetic wires, power communication, and other composite cables. Winding Wire

Winding wire is a conductive metallic wire with an insulation layer, which is used to produce coil or winding used for electrical products. Its

177

function is to generate a magnetic field by electric current or generate an inductive electric current by cutting the magnetic force line, which realizes the mutual conversion of electric and magnetic energy. That is why it is also called an electromagnetic wire (Bicen 2017). Basic Property As is known to all, breakdown often occurs during the electric cable operation. The so-called cable breakdown is the short circuit between the core wire of the inner conductor layer and the metal net on the ground under the high-voltage field after the insulation layer of the cable is punctured. And the short circuit of high-voltage secondary coil is formed on the circuit, which increases the secondary current. Cable breakdown is quite harmful, which will burn the cable directly, leading to serious economic loss and threatening production seriously. Many reasons contribute to the breakdown of cables in operation, and the main reasons are the reduction of cable performance and the damage caused by external forces. Therefore, the basic property indicators of cable are summarized as follows. Shielding Property

In the process of signal transmission, unshielded cable has antenna effect, which not only radiates signals outward but also receives external signals. It is likely to form electromagnetic interference to the signal, which leads to the communication failure, increasing noise, signal error, and other influences. Therefore, cable itself has a certain shielding performance, which is very important in the process of cable operation. Shielding attenuation and transfer impedance are two important indexes to measure the shielding performance of cables. Shielding attenuation is based on electromagnetic field theory which reflects the shielding performances of cables directly. Transfer impedance is based on circuit theory which reflects the shielding performance of cables indirectly. Besides, the structure of conductor has a certain influence on the shielding performance of the cable, which can be enhanced by wearing the outer conductor or the smooth aluminum pipe outer conductor (Chen et al. 2017).

C

178

Cable

Voltage

Since electric cables can be used in power systems and signal transmission systems, the voltage of electric cables usually includes the voltage of power and signal cable. Apparently, the voltage of power cable is the source of power for the cable, and the voltage of signal cable can be used to transmit signals. There are three important indexes which can be used to measure the voltage of power cable and signal cable. The first one is the nominal power frequency voltage(U0), which is between conductor and the ground or metal shield for cable design. Another one is the nominal power frequency voltage(U), which is between conductors for cable design. And the third one is the maximum of the maximum system voltage (Um)in which the device can withstand. According to the ISO 13628-5/API Spec 17E, the voltages of electric cables are as follows: For power cable, the selection of power cable voltage level ranges from 0 V to the nominal power frequency voltage. U0 ¼ 3:6=6ð7:2ÞkV ðrmsÞ U ðU m Þ

ð1Þ

For signal cable voltage, the selection of signal cable voltage level ranges from 0 V to the nominal power frequency voltage. U0 ¼ 0:6=1:0ð1:2ÞkV ðrmsÞ U ðU m Þ

ð2Þ

Electric Current

Electric current is the electricity flow that a cable line can be up to when transmitting power. Electric current must flow through the cable line in order to transmit electricity. The more currents flow through the line, the more power it transmits. The cable load flow can be called the cable longterm allowable load flow when the temperature of conductor reaches the long-term allowable working temperature under thermal stability conditions. As for the working conditions, the maximum load current which is required by the load must be less than the long-term allowable load flow of the conductor in the air. In accordance

with the relevant specific provisions, the maximum allowable load flow for each type of wire can be obtained. The property of conductor is the internal factor that affects the cable load flow, which can be increased by extending the area of the wire cores; using high conductive materials, insulation materials with good high-temperature resistance, and thermal conductivity; and reducing contact resistance. The environment is the external factor that affects the cable load flow, which can be increased by the reasonable increase of the wire spacing and the choosing of the appropriate place for laying. Attenuation

Attenuation refers to the signal attenuation along the length of the cable. When signals pass through the cable, some of the signals can be converted to heat, and some of the signals will leak out of the cable through the external conductor. In most applications, there is the purpose of minimizing the attenuation or keeping it within budget. In general, the larger the diameter of the cable is, the less attenuation of the cable is. In another word, by increasing the size of cable, the attenuation can be reduced. In addition, the higher the temperature is, the more the attenuation is. Direct Current Resistance

Direct current resistance is an important parameter in cable and all aspects of testing, which determines the quality level of the cable. To make it specific, it is possible to judge whether the crosssectional area of conductor is consistent with the manufacturing specifications, whether the total conductivity of cable is qualified, and whether the conductor is broken. Insulation Resistance

Insulation resistance is the most basic insulation index for electrical equipments and circuits. The greater the insulation value is, the less the current is, and the higher the insulation performance index is. General electric conductor has a small resistance value of only a few omega. However, the value of insulation resistance is relatively greater, at least dozens MΩ or above. The value

Cable

of the insulation resistance varies due to the changes of the temperature and the length of cable. Therefore, it is calculated with the electric resistance converted to 20 C per unit length generally for comparison (Dian 2016). Mechanical Property

In general, the properties, such as tensile strength, elongation, bending, flexibility, softness, shock resistance, wear resistance, and mechanical impact resistance, are the main mechanical properties. If the mechanical property cannot meet the actual working strength, the electric cable will be damaged. Polyester Rope Generally, there are three layers in a polyester rope with the outer layer as a braided protective layer, which is wear-resistant and protects the core rope. The secondary outer layer is a filter layer, which prevents particles of 3–5 mm or larger from entering the cable to cause wear and tear. The inner layer is a polyester core rope, which is subjected to tensile force. In addition, there can be two protective layers in the outer layer and two filter layers in the secondary outer layer according to the requirements of customers (Kim et al. 2013). There are some advantages of polyester rope as follows: light weight, which can reduce the weight of the mooring system and increase the efficiency of the mooring level; low cost, much lower than steel cable; excellent in seawater corrosion resistance and no corrosion in seawater; and its fatigue performance which is much better than steel cable from experimental results. It also provides high strength and strength/quality ratio. Disadvantages of polyester rope are concluded as short application history, non-wear resistance, easy damage, and significant nonlinearity of stiffness.

Key Applications An electric cable is made up of conductor, insulation, sheath, and so on, which can be used for

179

communication, power, and other related transmission and which are installed in the air, underground, or subsea. In fact, the distinction between cables and wires is not very strict. Usually the diameter and core of the wires are small, and the structure is simple. The wires without insulation and sheath are called naked wires. And the others are called electric cables (Calmet et al. 2002). In 1879, it was an American inventor named Thomas Edison who wrapped jute around a copper rod, put it into an iron pipe, and filled in an asphalt mixture to form an electric cable. It was this man who laid this cable in New York, which pioneered the underground transmission of electricity. The next year, Cattender from Britain invented a power cable of insulation with bituminous impregnated paper. In 1908, a 20-KV cable network was built in Britain, which made the application of power cable more and more extensive. Three years later, a high-voltage cable with 60 KV was laid in Germany, indicating the scientific revolution of high-voltage cables. Since 1979, ultra-high-voltage cables of cross-link have been put into trial operation in Japan, Finland, Sweden, and Norway. Electric cables have been used for more than 100 years, which have been playing an important role in communication up to now with the development of the information technology. In addition to transmitting electricity, electric cables are also indispensable in communication. In 1839, Cook and Wheatstone built the first 21-kilometer-length telegraph line in London. The first subsea cable in the world was laid across the English Channel between England and France by John Watkins Brett in 1850. But a fisherman mistakenly thought that he had found a big fish and pulled the cable out of the subsea. The following year, Brett laid the cable again and succeeded finally, meaning the UK and the European continent were connected with each other successfully (Fig. 2). The world’s first transoceanic subsea cable was laid successfully by an American rich businessman named Cyrus West Field in 1866. He began this project since 1854, and it lasted more than 10 years, which experienced four failures. In

C

180

1876, thanks to the invention of telephone by Bell, it began to accelerate the laying of subsea cables on a large scale around the world. Until 1902, the global submarine communication cable system was completed basically. Ever

Cable, Fig. 2 John Watkins Brett (https://nl.wikipedia. org/wiki/John_Watkins_Brett) Cable, Fig. 3 Cyrus West Field (http://atlantic-cable. com/Field/)

Cable

since, communication cables have developed rapidly in western countries and spread among big cities, which reached a climax after the 1920s, and many countries have realized connections with communication cables between each other (Fig. 3). Polyester rope mooring systems have been widely used around the world, especially in the waters of Brazil and the Gulf of Mexico. Brazilian State Oil Company began to use experimental polyester rope in 1995 for the first time and replaced within 2-year period. The first practical application was an external mooring buoy by Brazilian State Oil Company in 1997. As mentioned above, electric cables have been used for more than 100 years, which were used to transmit electricity originally. Electric cables played an important role in communication up to now with the development of the information technology. Power system used in wire and cable products mainly includes overhead bare wires, power cables (plastic cables, rubber sets of cables, overhead insulated cables), electromagnetic wires, and power equipments with electrical wire and cable equipment, etc. In addition, the main wires and cables used in the information transmission system are municipal telephone cables, TV cables, electronic cables, radio-frequency cables, optical fiber cables, data cables, electromagnetic cables, power communication cables, and other composite cables.

Capacity of Suction Anchor

Cross-References ▶ Bare Wire ▶ Conductor ▶ Insulation Layer ▶ Polyester Rope ▶ Power Cable ▶ Winding Wire

References Bicen Y (2017) Trend adjusted lifetime monitoring of underground power cable. Electr Power Syst Res 143:189–196 Calmet JF, Carlin F, Nguyen TM, Bousquet S, Quinot P (2002) Irradiation ageing of CSPE/EPR control command electric cables. Correlation between mechanical properties and oxidation. Radiat Phys Chem 63(3– 6):235–239 Chen M-Y, Jin-qian Z, Lang ZQ, Sun F, Hu G (2012) A nonlinear frequency analysis based approach for power cable insulation fault detection. COMPEL 31(2):369–386 Chen J, Li C, Hu L, Cao J, Tian X (2017) Online loss parameters diagnosis device development of power cable insulation. In: APPEEC Courty L, Garo JP (2017) External heating of electrical cables and auto-ignition investigation. J Hazard Mater 321:528–536 Dian L (2016) Monitoring system design for XLPE power cable faults based on virtual instruments. In: MEITA Dvorsky K, Gwinner J, Liess H-D (2011) A fixed point approach to stationary heat transfer in electric cables. Math Model Anal 286–303 Grayson SJ, Van Hees P, Green AM, Breulet H, Vercellotti U (2001) Assessing the fire performance of electric cables (FIPEC). Fire Mater 49–60 Hammons TJ (2003) Power cables in the twenty-first century. Electr Power Compon Syst 967–994 Honjo S, Matsuo K, Mimura T, Takahashi Y (2001) HighT c superconducting power cable development. Phys C 357–360:1234–1240 http://atlantic-cable.com/Field/ https://nl.wikipedia.org/wiki/John_Watkins_Brett http://www.orientcable.com/v_pros.asp?/5.html Kim J-G, Dinh M-C, Kim S-K, Park M, Yu I-K, Yang B (2013) Transient characteristic analysis of an HTS DC power cable using a multi-terminal based test-bed. Phys C 494:302–306 Limei F (2016) Usage of polyester rope in deepwater mooring system. In: Ocean engineering equipment and technology Mukoyama S, Yagi M, Hirano H, Yamada Y, Izumi T, Shiohara Y (2006) Development of HTS power cable using YBCO coated conductor. Phys C 445–448:1050– 1053

181 Ohsaki H, Lv Z, Sekino M, Tomita M (2012) Application of superconducting power cables to DC Electric Railway Systems. Phys Procedia 36:908–913 Ouatah E, Megherfi S, Haroun K, Zebboudj Y (2013) Characteristics of partial discharge pulses propagation in shielded power cable. Electr Power Syst Res 99:38–44 Schmidt F, Maguire J, Welsh T, Bratt S (2012) Operation experience and further development of a hightemperature superconducting power cable in the Long Island Power Authority Grid. Phys Procedia 36:1137– 1144 Xuyang LI, Yanfang Kang, Hu X, Juan L (2017) Research on investment model of power cable about big data. In: ICMMCCE Zhang X, Li D, Wang Z (2015) Design of high voltage power cable real-time monitoring system function. In: IIICEC Zhong H, Xia Y, Wang J, Huang H, Liang Z (2015) Power cable structure recovery and application based on mould melt joint. In: JIMET Zuijderduin R, Chevtchenko O, Smit JJ, Willén D, Melnik I, Geschiere A (2012) Electrical model of balanced AC HTS power cable. Phys Procedia 36:1145– 1148

CAD (Computer-Aided Design) ▶ Introduction to Shipbuilding (Shipyard)

CAM (Computer-Aided Manufacturing) ▶ Introduction to Shipbuilding (Shipyard)

Capacity of Suction Anchor Dengfeng Fu State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China

Definition The suction anchors are usually cylindrical units with large diameter (D of 3–8 m), open at the

C

182

Capacity of Suction Anchor

bottom and closed at the top, and generally with an aspect ratio (length to diameter, L/D) of two to six. The anchoring line is connected to the padeye attached to the side of the caisson at a depth down the mudline. The capacity of suction anchor is therefore the ability to resist the permanent and environmental loading from the anchor line during the operational conditions.

Failure Mechanism The capacity of suction anchor is highly dependence of soil plasticity flow around the foundation. Many influential factors, especially for the complicated boundary conditions, such as anchor geometry, type of mooring system (loading direction and magnitude), installation performance, soil conditions, time after installation, durations of applied sustained loading, cycles of loading, etc., should be explicitly accounted for to investigate the failure mechanism. In the following subsections, the typical failure mechanisms under uniaxial (including mainly vertical and horizontal) and inclined loading are discussed. Under Vertical Uplift Loading Under conditions of pure uplift loading, three failure mechanisms have been identified by a

number of experimental or numerical analyses: three important components of failure modes including reverse end bearing failure, sliding failure and tensile failure, as illustrated in Fig. 1. Reverse End Bearing Failure

Reverse end bearing failure can be relied upon for a suction anchor if the top cap is sealed and the soil response is undrained, typically when the anchor is subjected to short-term (transient) loading. Passive suction is generated in the anchor, so that the soil plug is pulled out together with the caisson. The failure mode at the bottom during uplift was similar to that during compression and was referred to as “a reverse end bearing mechanism.” Sliding Failure

When suction anchor is subjected to a sustained (drained) loading or the anchor lid is vented, reverse end bearing cannot be generated, and the failure occurs along the internal and external skirt. Tensile Failure

When partially drained condition prevails, such as when the suction anchor is pulled out at intermediate rates, passive suction may be generated partially, so that the caisson and the internal soil plug tends to detach from the soil below the caisson.

mudline

mudline

mudline

Suction anchor

Suction anchor

Suction anchor

(a)

(b)

(c)

Capacity of Suction Anchor, Fig. 1 Failure mechanisms for vertical pullout resistance (a) reverse end bearing, under undrained conditions; (b) caisson pullout, under

drained conditions; (c) caisson and plug pullout, under partially drained conditions

Capacity of Suction Anchor

Under Optimal Horizontal Loading The suction anchors under pure horizontal loading is rarely found offshore, while drag angle at the padeye is typically at a small angle of 10 –20 in the catenary mooring system. Meanwhile, the padeye position is often optimized in design, allowing the anchor to slide horizontally with minimal rotation. As shown in Fig. 2, the corresponding failure mechanism for lateral capacity of the suction anchor is considered to be similar to those for laterally load piles (Murff and Hamilton 1993) that a passive/active conical wedge extending from the edge of the caisson at shallow depth to the seabed dominating the soil mechanism; and a confined flow region is assumed below the wedge with the center of rotation locating below the anchor tip (Martin and Randolph 2006). For caissons loaded above the optimal depth, an external scoop mechanism can replace the flow region, with the center of rotation locating within the anchor. Under Inclined Loading The failure mechanism under inclined loading depends on the position of the centerline intercept for the applied load (varying with padeye position and loading angle), the length of the suction anchor, and the soil properties (Supachawarote 2006). The impact of tensile crack on the failure mechanism is examined by Fu et al. (2020).

183

The maximum holding capacity is obtained if the chain is attached at a depth where the anchor moves largely in horizontal translation with minimal rotation. This is called the “optimal padeye depth.” When the centerline intercept is located above the optimal padeye position, the anchor rotates forward, and combinations of wedge flow around and full circular rotational failure were observed. For the short anchor, the wedge and rotational flow mechanisms were observed, without the flow around region. For the longer anchor, the flow around region increasingly dominates. While when the centerline intercept is located below the optimal padeye position, a backward rotation was observed, and the rotational flow failure extends to the mudline. And with the centerline loading point moves deeper, the full circular rotational failure eventually moves below the soil surface, which is evident for anchor with increasing length. For long anchor, the circular rotational flow failure is only observed below the tip of the anchors; and only combination of the wedge and flow around mechanisms was observed within the anchor length.

Design Method of Evaluating Capacity The load capacity of a suction caisson anchor, assuming a sealed cap, is derived from bearing

Capacity of Suction Anchor, Fig. 2 Soil failure mechanism for suction anchor (a) conical wedge and flow region and (b) external base rotational scoop. (After Randolph and House 2001)

C

184

Capacity of Suction Anchor

resistance between the soil and the projected area of the caisson (on a vertical plane for horizontal resistance and the cross-sectional area for reverse end bearing), aided by frictional resistance along the outside of the caisson shaft. Reverse end bearing relies on passive suctions developed within the soil plug, and so consideration needs to be given to the time over which these can be sustained. Vertical Uplift Capacity Equation

The vertical pullout capacity is equal to one of the following depending on the drainage conditions (essentially whether the passive suction is sustained during loading): (a) For undrained conditions, with a nondimensional diameter Tk (¼ cv/vD, where cv is the consolidation coefficient, v is the loading velocity, D is the diameter of the anchor) recommended to be less than 0.002 (Deng and Carter 2000), the passive suction is thought to be sustained during loading V ult ¼ W 0 þ Ase ae suðtÞ þ N c su Ae

ð1Þ

(b) For drained condition, (Tk > 0.6), the passive suction is not generated during loading V ult ¼ W 0 þ Ase ae suðtÞ þ Asi ai suðtÞ

ð2Þ

(c) For partially drained condition (0.002 < Tk < 0.6), passive suction is partially generated V ult ¼ W 0 þ Ase ae suðtÞ þ W 0plug

ð3Þ

where Ase and Asi are the external and internal shaft surface area, Ae is the external crosssectional area, αe and αi are the coefficient of external and internal shaft friction, Nc is the reverse end bearing factor, su is the undrained shear strength at tip level, suðtÞ is the average

undrained shear strength over penetrated depth at time t after installation, W0 plug is the effective weight of the soil plug, and W0 is the submerged caisson weight. Evaluation of Parameters α and Nc

The soil shear strength around the anchor is thought to be remold due to disturbance during skirt penetration during self-weight penetration. And this strength recovers later with time following installation, due to a combination of thixotropy and consolidation (Andersen et al. 2005), which however remains below the intact undrained shear strength. This process is referred as “setup” and has been expressed conveniently with αsu, with α < 1. A base value of α of 0.65 was proposed for suction caisson design (Anderson and Jostad 2004), subjected to their specific soil properties. The shaft friction depends on the anchor surface roughness, soil type, and overconsolidation ratio. And Chen et al. (2009) suggests method of installation (referring jacking or suction installation) leads to negligible difference in α based on the centrifuge and LDFE numerical studies. And their results also suggest α of 15–20% lower than those recommended by the American Petroleum Institute (API) for driven piles in normally consolidated clays. It should also be noted that lower values of friction coefficient for internal shaft friction compared with external friction were reported in the model tests conducted on double-walled caisson (Jeanjean 2006). The reverse end bearing Nc is a function of soil property and the aspect ratio (L/D) of the anchor. For an anchor with L/D of 2 in the overconsolidated kaolin clay, Fuglsang and SteensenBach (1991) reported the centrifuge and laboratory tests, suggesting the reverse bearing capacity factors varying between 6.5 and 8.5. This is lower than the theoretical lower bound results of 9.2 for the caisson with L/D of 2 (Martin 2001). Other centrifuge tests for the anchor with the same aspect ratio (Clukey and Morrison 1993) suggested that reverse end bearing is around 11. This high magnitude of Nc may be related to the vane shear strength adopted for the interpretation, which leads to an overestimation of 25% (Watson

Capacity of Suction Anchor

185

et al. 2000). Considering the loading mode (monotonic transient loading, cyclic loading, and long-term sustained loading), the reverse end bearing falls in a wider range of 9.1–14.6 (Randolph and House 2001). And a conservative Nc value of 9 is suggested to be taken, due to the strain-softening nature of the response as the caisson is extracted. A bearing capacity factor of Nc ¼ 9 irrespective of the aspect ratio for suction anchor is also suggested by El-Gharbawy and Olson based on the results of the laboratory tests in kaolin clay. And by contrast, an Nc value of 12 is found to be mobilized at large displacements (Jeanjean 2006), although values of around 9 were mobilized at the displacement where peak external shaft friction was achieved. Hence it is rational to take Nc as of 9 is appropriate. Optimal Horizontal Capacity

N 2 ¼ 3:22

ð7Þ

Z ¼ 16:8  2:3lgl  14:5

ð8Þ

l¼

sum kD

N pd ¼ 9:14 þ 2:8a

ð9Þ ð10Þ

In Eq. 8, Z stands for the normalized depth (z/ D) at which the soil failure mechanism transits from the wedge failure to the localized flow around failure for a fully rough soil-pile interface in idealized weightless soil. The value of Z is related to the normalized strength homogeneity parameter l. Npd stands for the limiting bearing capacity factor mobilized in a localized flowaround mechanism, expressed as a function of the interface roughness factor α (0  α  1), according to the plasticity solution.

Equation

Assuming the padeye is positioned at the optimum level and pure translation failure occurs, the maximum horizontal resistance is H max ¼ LDe N p su

ð4Þ

where L is the embedded length of caisson, De is the external diameter of the caisson, Np is the lateral bearing capacity factor, and suis the average undrained shear strength over penetrated depth. Evaluation of Parameters Np

Zhang et al. (2016) recommended the following approach to calculate the lateral bearing capacity factor N p0 ¼ N 1

"




z=D  ðN 1  N 2 Þ 1  Z  ð 1  aÞ  N pd

0:6 #1:35

ð5Þ

where N 1 ¼ 11:94

ð6Þ

Inclined Load Capacity In the presence of both vertical and horizontal loading, a reduction occurs in the pure vertical and horizontal capacities, as the caisson is simultaneously displaced vertically and laterally (or rotated). Clukey et al. (2003) suggested for the loading angles applied by the catenary mooring line system, which are generally less than 20 from the horizontal, the caisson capacity is dominated by the horizontal capacity, and the capacity may be estimated by the capacity under pure translation divided by the cosine of the loading angle at the padeye. Conversely for high loading angles from the horizontal applied by taut and semi-taut mooring systems (generally in excess of 30 ), the caisson capacity is essentially governed by the vertical capacity of the caisson and maybe approximately taken as the vertical capacity divided by the sine of the loading angle. For the more general cases, the interaction between vertical and horizontal loading may be conveniently modelled as a failure envelope in the combined vertical-horizontal load space, which was found to vary with the aspect ratio (L/D), location, and direction of the applied load. The shape of the failure envelopes for suction anchor may be modelled by an elliptical relationship

C

186

Capacity of Suction Anchor




H H ult

a


þ

V V ult

b

¼1

ð11Þ

The Effect of Crack on the Suction Anchor Capacity

where Hult and Vult are the uniaxial horizontal and vertical capacities, respectively, and the exponents a and b vary with caisson aspect ratio L/D according to Supachawarote (2006). a¼

L þ 0:5 D

ð12Þ

L þ 4:5 3D

ð13Þ

b¼

Consideration in Design

The sensitivity of caisson capacity to the changes in padeye position or loading angle was also investigated using the threedimensional finite element analysis, limit equilibrium solutions upper bound limit analyses, profiles of lateral resistance based on Murff and Hamilton (1993), and centrifuge modelling (Clukey et al. 2003). It was found that the variation of centerline intercept for the applied load (varying with padeye position and loading angle) results in the large discrepancy of the capacity. As shown in Fig. 3, the centerline loading depth around 0.7 gives the largest capacity. With the shift of the padeye position and loading angle, the capacity reduces gradually within the depth of 0.15 L from the optimal centerline location and reduces sharply beyond this range.

Capacity of Suction Anchor, Fig. 3 Effect of padeye depth on capacity. (After Andersen et al. 2005)

The inclined load capacity of a suction anchor will also depend on whether a crack develops along the trailing edge of the caisson. A crack is normally formed for suction anchors with a long aspect ratio in over-consolidated soils. The finite element results (Fu et al. 2020) show a reduction of up to 50% for any loading angle (the reduction is mainly found at the optimal padeye depth and maintained for loading angles of up to about 45 for L/D ¼ 1.5, 2, and 3 in homogeneous soil). Considering Site Conditions Some changes in site conditions should be explicitly accounted for in the design of geotechnical capacity of suction anchor. The soil scour around a suction foundation is an important scenario in design, where the soil migration around foundation might occur under the wave and current loading. The volume of soil mobilized by foundation is therefore changed, resulting in a significant decrease in capacity. In some cases, the shallow gas accumulation inside a suction foundation also should be given attention (Gylland and de Vries 2008). Additionally, the trenching is another issue and most likely to occur particularly when using semi-taut to taut mooring configurations with caisson employed in the soft deposits. Considerable motion of ground chain could lead to the remolded softening and erosion of soil particles, forming a curved trench in the vicinity of foundation. O’Neill et al. (2018) presented a method to interpret and estimate the primary mechanism of trenching development. Considering Cyclic Loading Effect Offshore foundations are often cyclically loaded in both calm sea condition and extreme events (i.e., storm or hurricane event). For suction anchor, the cyclic wind, wave, current, and structural loadings are transferred to the foundation by mooring lines. It gives rise to pore pressure accumulation for soil around foundation, which is one of the principle concerns in design of foundation’s capacity. Regarding clay, the strain softening may occur as the pore pressure accumulates, and both

Capacity of Suction Anchor

soil stiffness and strength can significantly reduce. Regarding sands, the earlier densification may occur during cyclic loading, then pore pressure starts accumulating, and finally a state of liquefaction may be present with the effective stress of soil almost being zero. Therefore, the continual buildup of excess pore pressure in soil under cyclic loading potentially results in a significant decrease in capacity of foundation. Based on laboratory cyclic triaxial (TA) and direct simple shear (DSS) tests, Andersen (2015) presented a method to assess the accumulation of pore pressure, which is dependence of cyclic shear ratio tcy/s0 vc. tcy is the cyclic shear stress (kPa), and s0 vc is the vertical consolidation pressure (kPa). The corresponding cyclic shear strength tcy,f at failure was indicated using a strain contour diagram, with the equivalent number of cycles to failure captured at the permanent cyclic shear strain of 15%. Besides, many soil models based on the critical soil mechanics theory were numerically developed in the last three decades, to describe and interpret the cyclic behavior of soil. However, no constitutive model has been developed to date, enabling to represent all the key characteristics of cyclic soil response, as many factors may influence the cyclic performance of soil, i.e., cyclic stress level, loading frequency, over-consolidation ratio, static pre-shearing, etc. In practice, the alternative option available for engineers is choosing a soil material factor (ISO 2016) or considering the uncertainty by a partial factor of capacity (ISO 2016), when the cyclic loading effect is necessary to be considered. Considering Reconsolidation Effect For suction anchor, an allowable duration is often found after its installation, e.g., 3 to 6 months. This gives an opportunity for consolidation under self-weight prior to commencing operations. During consolidation, the excess pore pressures generated by the self-weight preloading dissipate reducing the void ratio of soil and enhancing the soil strength, hence increasing the foundation capacity. It is notable that the dissipation of pore pressure also occurs during the cyclic loading condition, as the pore pressures in fact generated during a cyclic duration and will

187

dissipate in the subsequent cycles. The appropriate consideration of reconsolidation in service design is necessary to develop a reliable and economical method. From some centrifuge model tests (Bienen et al. 2010; Fu et al. 2015), the significant increase in bearing capacity of a preloaded foundation in clay was found, for instance, a gain in bearing capacity of 30% after 10% of consolidation and a doubling after 80% of consolidation under a vertical preload of 50% of the ultimate vertical load.

Notation a Ae Ase Asi b cv D De Hmax Hult L Nc Np su su suðtÞ

Tk W0 W0 plug v Vult zcl α α αe αi β tcy tcy,f s0 vc

Parameter depending on L/D External cross-sectional area External shaft surface area Internal shaft surface area Parameter depending on L/D Consolidation coefficient Diameter of suction anchor External diameter of suction anchor Optimal horizontal capacity Uniaxial horizontal capacity Length of suction anchor Reverse end bearing factor Lateral bearing capacity factor Undrained shear strength at tip level Average undrained shear strength over penetrated depth Average undrained shear strength over penetrated depth at time t after installation Nondimensional diameter Submerged weight of suction anchor Submerged weight of soil plug Loading velocity Vertical pullout capacity Centerline loading depth Coefficient of shaft friction Parameter depending on L/D Coefficient of external shaft friction Coefficient of internal shaft friction Parameter depending on L/D Cyclic shear stress Cyclic shear stress at failure Vertical consolidation pressure

C

188

References Anderson KH, Jostad HP (2004) Shear strength along inside of suction anchors skirt wall in clay. In: Proceedings of. annual offshore technology conference, Houston, OTC 16844 Andersen KH, Murff JD, Randolph MF, Cluckey EC, Erbrich CT, Jostad HJ, Hansen B, Aubeny CP, Sharma P, Supachawarote C (2005) Suction anchors for deepwater applications. Frontiers in offshore geotechnics: ISFOG - Gourvenec & Cassidy. London: Taylor & Francis Group 0 415 39063 X Bienen B, Gaudin C, Cassidy MJ (2010) Centrifuge study of the bearing capacity increase of a shallow footing due to preloading. In: Proceedings of the 7th Internationale Conference on Physical Modelling in Geotechnics (ICPMG). 2:1019–1024 Chen W, Zhou H, Randolph MF (2009) Effect of installation methods on external shaft friction of caissons in soft clay. J Geotech Geoenv Eng ASCE 135(5):605–615 Clukey EC, Morrison J (1993) A centrifuge and analytical study to evaluate suction caissons for TLP applications in the Gulf of Mexico. ASCE Geotechnical Special Publication 38:141–156 Clukey EC, Aubeny CP, Murff JD (2003) Comparison of analytical and centrifuge model tests for suction caissons subjected to combined loads. In: Proceedings of the international conference on offshore mechanics and arctic engineering, OMAE2003–37503 Deng W, Carter JP (2000) A theoretical study of the vertical uplift capacity of suction caissons. In: Proceedings of the 10th international offshore and polar engineering conference, pp 342–349 Fu D, Gaudin C, Tian Y, Bienen B, Cassidy MJ (2015) Effects of preloading with consolidation on undrained bearing capacity of skirted circular footings. Géotechnique 65(3):231–246 Fu D, Zhang Y, Yan Y, Jostad HP (2020) Effects of tension gap on the holding capacity of suction anchors. Mar Struct 69(2020) 102679:1–14. https://doi.org/10.1016/ j.marstruc.2019.102679 Fuglsang LD, Steensen-Bach JO (1991) Breakout resistance of suction piles in clay. In: Proceedings of international conference: Centrifuge 91. A.A. Balkema, Rotterdam, The Netherlands, pp 153–159 Gylland AS, de Vries MH (2008) The effect of gas blowout on shallow offshore foundations. In: Proceedings of the Second British Geotechnical Association International conference on foundations (ICOF 2008), volume 1: Piles, Excavations and Offshore Foundations, pp 885–896 ISO (2016) ISO 19901-4:2016(en). Petroleum and natural gas industries specific requirements for offshore structures – part 4: geotechnical and foundation design considerations. International Standards Organisation, Geneva Jeanjean P (2006) Set-up characteristics of suction anchors for soft Gulf of Mexico clays: experience from field

Capex (Capital Expenditure) installation and retrieval. In: Proceedings of the. Annual Offshore Technical Conference, Houston, Texas, Paper OTC 18005 Martin, C.M., (2001). Vertical bearing capacity of skirted circular foundations on Tresca soil. In: Proceedings of 15th international conference on soil mechanics and geotechnical engineering, 1, pp 743–746 Martin CM, Randolph MF (2006) Upper bound analysis of lateral pile capacity in cohesive soil. Géotechnique 56(2):123–132 Murff JD, Hamilton JM (1993) P-ultimate of undrained analysis of laterally loaded piles. J Geotech Eng ASCE 119(1):91–107 O’Neil M, Erbrich C, McNamara A (2018) Prediction of seabed trench formation induced by anchor chain motions. In: Offshore technology conference, OTC Paper No. OTC-29068-MS Randolph MF, House AR (2001) Analysis of suction caisson capacity in clay. In: Proceedings of the annual offshore technology conference, Houston, OTC 14236 Supachawarote C (2006) Inclined load capacity of suction caisson in clay. PhD thesis. The university of Western Australia Watson PG, Randolph MF, Bransby MF (2000) Combined lateral and vertical loading of caisson foundations. In: Proceedings annual offshore technology conference, Houston, OTC 12195, pp 797–808 Zhang Y, Andersen KH, Tedesco G (2016) Ultimate bearing capacity of laterally loaded piles in clay – some practical considerations. Mar Struct 50(2016): 260–275

Capex (Capital Expenditure) ▶ Tension-Leg platform

Catenary Anchor Leg Mooring Liping Sun College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China

Synonyms Catenary mooring; Mooring system; Single anchor leg mooring; Single point mooring; Taut mooring

Catenary Anchor Leg Mooring

Definition A typical CALM system consists of the mooring buoy, chain and anchor system, mooring assemblies, and floating and submarine hose strings. The buoy body provides the necessary buoyancy to keep the system afloat. A rotating deck or turntable is mounted on top of the buoy body to transmit mooring force from the mooring assemblies through the buoy to the anchor chains. The CALM anchoring system consists of 4–8 anchor chains extending from the buoy body radially out and terminating at firmly embedded anchors or anchor piles (Luo et al. 2015).

Scientific Fundamentals System Composition The CALM system consists of a large buoy, which supports a number of catenary chain legs anchored to the sea floor (Fig. 1). Riser systems or flow lines that emerge from the sea floor are attached to the underside of the CALM buoy. Some of the systems use a hawser, typically a synthetic rope, between the vessel and the buoy. Since the response of the CALM buoy is totally different than that of the vessel under the influence of waves, this system is limited in its ability to withstand environmental conditions. When sea states attain a certain magnitude, it is necessary to cast the vessel off. In order to overcome this limitation, rigid structural yokes with articulations are used in some designs to tie the vessel to the top of the buoy (Vryhof 2005). CALM system can be used both in shallow water and deepwater area and are connected to a shore storage facility (tank farm) or to offshore production platforms by means of a submarine pipeline. For this application, the CALM is used as an offloading system for a deepwater Floating Production Storage and Offloading unit (FPSO). CALM is also a complex nonlinear system for oil tanker or FPSO. In addition to the three degrees of freedom in the horizontal plane (surge, sway and yaw), the entire external transmission

189

system has 12 degrees of freedom (buoys 6, tanker or FPSO 6) of the motion response. If the simultaneous CALM system-FPSO-the coupling motion analysis of the tanker, it will reach 18 degrees of freedom. Because the incident wave period is generally greater than 8 s, the longitudinal oscillation is the main motion form of the buoy. Therefore, it is necessary to take into account the pitching motion characteristics of single point mooring system in the design of pipeline (SBM 2012). The CALM system allows the moored tanker to weathervane. With this principle, the tanker offers to the environment (waves, current, and wind), a direction of least resistance, thus the system can operate in much higher conditions than the other systems. The CALM system reacts against the force created by the environment on the moored tanker by a set of two spring effects: (a) The nylon mooring hawser, (b) The buoy mooring legs, which are installed in a Catenary configuration (GL 2014). CALM-catenary anchor leg mooring can be capable of handling very large crude carriers. This configuration uses six or eight heavy anchor chains placed radially around the buoy, of a tonnage to suit the designed load, and attached to an anchor or pile to provide the required holding power. The anchor chains are pretensioned to ensure that the buoy is held in position above the PLEM. As the load from the tanker is applied, the heavy chains on the far side straighten and lift off the seabed to apply the balancing load. Under full design load, there is still some meters of chain lying on the bottom. The flexible hose riser may be in one of three basic configurations, all designed to accommodate tidal depth variation and lateral displacement due to mooring loads. In all cases, the hose curvature changes to accommodate lateral and vertical movement of the buoy, and the hoses are supported at near neutral buoyancy by floats along the length (Chakrabarti 2005). These are • Chinese lantern, in which two to four mirror symmetrical hoses connect the PLEM with the buoy, with the convexity of the curve facing radially outwards.

C

190

Catenary Anchor Leg Mooring

Catenary Anchor Leg Mooring, Fig. 1 CALM (www.sbmoffshore.com, 2012)

• Lazy-S, in which the riser hose leaves the PLEM at a steep angle, then flattens out before gradually curving upwards to meet the buoy approximately vertically, in a flattened S-curve. • Steep-S, in which the hose first rises roughly vertically to a submerged float, before making a sharp bend downwards followed by a slow curve through horizontal to a vertical attachment to the buoy (API RP 2SK 1993).

Historical Development The history of mooring system started from the development and use of the single point mooring device of catenary buoy by the US navy during World War II, and then developed rapidly. Numerous different mooring systems have been developed over the years (Kent et al. 2007). The world’s earliest single point mooring system is CALM. CALM mooring system is the most widely used single mooring. There are over

Catenary Anchor Leg Mooring

560 single point mooring system over the world. And there are about 500 CALM systems by 2008. In 1997, a polyester rope + anchor chain catenary mooring system is first used for a FPSO in Brazil. Afterwards, more and more fiber mooring systems appeared in the Gulf of Mexico (Winkler and Mckenna 1994). Since early 2000, the CALM design has been used and adapted to deepwater conditions, greater than 1,000 m (ABS 2014). Installed CALM in deepwater are listed as following:Agbami (Nigeria, 1435 m), Kizomba A&B (Angola, 1200 m, 1000 m), Dalia (Angola, 1341 m), Erha (Nigeria, 1190 m), Akpo (Nigeria, 1285 m), Bonga (Nigeria, 1000 m), Girassol (Angola, 1320 m), Greater Plutonio (Angola, 1310 m). Key Technology in the Development of CALM Since the 1970s, the research on the CALM system can be divided into the following two aspects: (1) engineering design – the deploy/ recovery of mooring system, the composition of mooring line, the arrangement of mooring system, and the development of anchor. (2) theoretical research – environmental load, static analysis of anchor mooring line, dynamic response between mooring system and mooring floating body. Haixiao Liu et al. (2014) used a specially designed experimental system to investigate the nonlinear mechanical behavior of synthetic fiber cables, including how stiffness changes, how the main factors affect the hydrodynamic stiffness changes, and the nonlinear tension-elongation relationship. The similarity criterion of the hydrodynamic stiffness of fiber cables derives from scale analysis and experiments verification. The accuracy of empirical expressions for hydrodynamic stiffness currently used is verified by measured data. The results show that the uniform load is an important factor affecting the hydrodynamic stiffness, and the effect of the amplitude of strain change on the stiffness cannot be ignored. The cyclic load is also an important factor affecting the hydrodynamic stiffness. Based on the measured data, an empirical expression considering both uniform load, strain amplitude, and the number of cyclic loads is presented.

191

It is the only expression that can evaluate the change of hydrodynamic stiffness under longterm cyclic loading. Minzhe Li (2013) designed a mooring system for semi-platform by combining the semi-physical simulation and mooring system control method, to control the mooring line retracting and deploying to realize platform positioning and to detect the positioning effect under different sea conditions. Amir G. Salem et al. (2012) studied the method of estimating pitch motion of CALM system in frequency domain and verified it by experiment. The hydrodynamics of CALM system is directly related to the fatigue life of the mooring system under the coupling interaction of the mooring line and the oil pipeline. It is very important to accurately predict the hydrodynamic response of the buoy. H. S. Da Costa Mattos and Chimisso (2011) studied the image model of creep test for lowdensity and high-strength HMPE fibers. In the macroscopic method, besides the traditional variables (pressure, total strain), scalar variables related to damage induced by creep process are introduced, and the evolution law of the damage variable is proposed. The life and elongation of HMPE specimens were predicted by creep tests at different loading levels and room temperature, which were in good agreement with the experimental results. Davies P et al. (2011) studies the effects of uniform load, load range, and stiffness loading frequency on synthetic fiber cable including polyester cable, aramid cable, and HMPE in dry environment experimentally. In subsequent experiments, the bending stiffness of aramid cable and HMPE cable and the operation in deep water were discussed. Meng Yuan (2010) used finite element timedomain method to construct the numerical calculation model of mooring cable for single-point and multi-point mooring system. Given a sinusoidal movement at the top of SPM system, the dynamic response of the whole mooring line was calculated. Taking the multi-point mooring system of Spar platform as an example, the time-history variation of the tension at the end of the mooring

C

192

line was calculated. The theoretical calculation results are consistent with the model test. Francois and Davies (2008) carried out a sampling polyester cable test of cable with breaking strength of 70 tons and a full-scale test with the breaking strength of 800 tons. Viscoelastic response of the cable is considered for the quasistatic stiffness to reduce the change of uniformly distributed load under changing environmental conditions. The upper and lower boundaries of stiffness only considered the effect of uniformly distributed load. Jing He (2007) used single-objective and multi-objective optimization methods to optimize the length, material price, and fracture strength of the two-component catenary mooring line of CALM system. Y. T. Chai et al. (2002) proposed a semianalytical quasi-stationary method based on catenary equation to deal with the interaction between the three-dimensional multi-mooring line partial subsection state and all subsection suspension state and the seabed, which can efficiently analyze the parameters of multi-point mooring system and flexible riser under different states. Casey and Banfield (2002) investigates polyester cables with hydrodynamic axial stiffness ranging from 600 to 1000 tons, and points out that the strain amplitude is indeed a variable affecting the hydrodynamic stiffness. Fernandes et al. (1999) carried out a full-scale polyester cable test with a diameter of 0.127 m. It is found that the dependence of hydrodynamic stiffness on frequency is weak.

Catenary Anchor Leg Mooring

Key Applications The CALM is the most popular and widely used type of offshore loading terminal. CALMs have been deployed worldwide for a variety of applications, water depths, and vessel sizes ranging from small product carriers to Very Large Crude Carriers (VLCC). Because of safe and easy berthing and un-berthing operations, the CALM is equally the preferred offshore terminal of Mooring Masters and Tanker Captains (Luo et al. 2015). CALM type single point is divided into the earliest Wheel CALM type, Turntable CALM type, and the newly developed Turret CALM type. At present, the most commonly used type is Turntable CALM. Compared with Wheel CALM, it uses large diameter rolling bearing at the center of the buoy to replace Bogey Wheel and transfer mooring force. In this way, the liquid rotary joint is completely independent of the turntable and bearing structure and no longer acts as a bearing member. The single point in this form consists of the following parts: buoy body, rotary turntable device, pipeline system and liquid rotary joint, anchor system, pipe manifold baseplate, underwater hose and floating hose, mooring rope device, and auxiliary equipment. The schematic diagram of the three types of buoy structure is shown in Fig. 2 (BV 2006). The CALM system has no restrictions on the size of the tanker, is easy to maneuver, works around the clock, requires the least staff, and has strong adaptability to the environment. The advantages of the CALM system can be summarized as follows:

Catenary Anchor Leg Mooring, Fig. 2 Schematic diagram of the three types of buoy structure (www.sbmoffshore. com, 2012)

Catenary Mooring

1. There is no need for a natural and excellent deep-water port, and there is no need for fixed dock facilities to provide loading and unloading operations. 2. The system is of lower cost. 3. It can be installed in open sea areas that do not require protection. 4. Can work normally all the year round. 5. Easy to install. 6. The mooring system is simple. 7. It can transmit a variety of oil and gas products at the same time. 8. The shuttle tanker has its own mooring propulsion system. 9. The terminal does not require a special tugboat for berthing and offshore, only a smaller vessel is required to serve (Luo et al. 2015).

Cross-References ▶ Catenary Mooring ▶ Mooring System ▶ Single Anchor Leg Mooring ▶ Single Point Mooring ▶ Taut Mooring

References American Bureau of Shipping (2014) Rules for building and classing single point mooring. https://ww2.eagle. org/ API RP 2SK (2005) (APE Recommended Practice 2SK), Design and Analysis of Stationkeeping Systems for Floating Structures. American Petroleum Institute. https://www.api.org/ BV (2006) Rules for the classification of offshore loading and offloading buoys. https://group.bureauveritas.com/ Casey NF, Banfield SJ (2002) Full-scale fiber deepwater mooring ropes: advancing the knowledge of spliced systems. In: Proceedings of the 34th annual offshore technology conference, OTC 14243, Houston Chai YT, Varyani KS, Barltrop NDP (2002) Semianalytical quasi-static formulation for threedimensional partially grounded mooring system problems. Ocean Eng 2002(29):627–649 Chakrabarti S (2005) Handbook of offshore engineering. Offshore Structure Analysis, Inc.Plainfield, Illinois, USA da Costa Mottos HS, Chimisso FEG (2011) Modelling creep tests in HMPE fibres used in ultra-deep-sea mooring ropes. Int J Solids Struct 2011(48):144–152

193 Davies P, Reaud Y, Dussud L, Woerther P (2011) Mechanical behavior of HMPE and aramid fibre ropes for deep sea handling operations. Ocean Eng 2011(38):2208–2214 Fernandes AC, Del Vecchio CJM, Castro GAV (1999) Mechanical properties of polyester mooring cables. Int J Offshore Polar Eng 9:208–213 Francois M, Davies P. (2008) Characterization of polyester mooring lines. In: Proceedings of the 27th international conference on Offshore Mechanics and Arctic Engineering, OMAE2008-57136, Estoril GL Noble Denton (2014) Offshore Engineering Technology Guidelines. https://www.dnvgl.com/ He J (2007) Mooring system design for FPSO CALM system. Master’s thesis, Wuhan University of Technology Kent Ostroot, Sara Shayegi, Derrick Zoontjes, Dalia Oil Offloading Export System,. (2007) OTC18546, Houston, USA Li M (2013) Research on positioning control simulation experiment of mooring system. Master’s thesis, Harbin Engineering University Liu H, Huang W, Lian Y, Li L (2014) An experimental investigation on nonlinear behaviors of synthetic fiber ropes for Deepwater moorings under cyclic loading. Appl Ocean Res 2014(45):22–32 Luo Y, Wang HW, Yan FS, (2015) Design and analysis of station keeping system for floating structures. Harbin Engineering University Salem AG, Ryu S, Duggal AS, Datla RV (2012) Linearization of quadratic drag to estimate CALM buoy pitch motion in frequency-domain and experimental validation. J Offshore Mech Arct Eng 134:011305 SBM (2012) Offshore CALM brochure. www. sbmoffshore.com Vryhof Anchor Manual (2005) www.vryhof.com Winkler MM, Mckenna HA (1994) Polyester taut leg mooring concept design study. Shell Development, Houston Yuan M, Fan J, Miao G, Zhu R (2010) Dynamic analysis of mooring system. Res Dev Hydrodyn 2010(25):285–290

Catenary Mooring Hongwei Wang Harbin Engineering University, Harbin, China

Synonyms Drag embedment anchor; Single-point mooring system; Spread mooring system

C

194

Introduction Mooring systems have been around just as long as man has felt the need for anchoring a floating structure at sea. These systems were used, and are still used, on ships and consisted of one or more lines connected to the bow or stern of the ship. Generally, the ships stay moored for a short duration of time (days). When the exploration and production of oil and gas started offshore, a need for more permanent mooring systems became apparent. Due to the demand for marine resource development, a large number of new floating structures have been designed and constructed, and various mooring systems have been emerged over the years; the catenary mooring system is a common and traditional way of locating floating structures, and several pretension mooring lines are arrayed around the structure to hold it in the desired location (Fig. 1).

Definition It gets its name from the shape of the free hanging line, one end of the mooring line is connected to the floating structure, and the other end is fixed at the anchor point of the seabed; the part that is suspended in the seawater will take a catenary shape, which is similar to the rope that is fixed at both ends and freely placed under the uniform force. The catenary forms can be seen everywhere in nature; when you wake up in the morning to see spider webs covered with water drops, when you

Catenary Mooring, Fig. 1 The catenary mooring system of a semisubmersible platform. (From anchor manual 2005)

Catenary Mooring

see the ropes on the suspension bridge, and when you see the wires between the two poles, you know what kind of shape are they? The answer is the catenary. As early as 1690, Jacobi Bernoulli proposed the famous “catenary problem,” but it was not until Newton and Leibniz invented the calculus to get the correct answer. The catenary is a magical curve that has been used extensively in buildings, bridges, ship, and ocean platform moorings (Wren et al. 1989). In marine engineering, spread catenary mooring systems and single-point catenary mooring systems are two common arrangements (Skop 1988). Mono-hull ship and semisubmersible platforms have traditionally been moored using a spread catenary mooring system, and the points are connected to different positions on the platform so that the platform cannot rotate freely, and the orientation of the platform remains basically unchanged. In some cases, excessive displacement caused by environmental forces may cause large loads on the mooring system. In order to overcome this drawback, a single-point mooring system has been developed which is characterized in that a plurality of mooring lines are connected at a point on the longitudinal centerline of the platform. The platform will have a wind vane effect to reduce the environmental loads caused by wind, current, and waves. Single-point moorings are used primarily for ship-shaped vessels. They allow the vessel to weather vane. This is necessary to minimize environmental loads on the ship-shaped vessel by heading into the prevailing weather (API 2005). As can be seen from the above (Fig. 1), the catenary mooring system occupies a large range on the seabed, that is, the radius of influence of the mooring point will be large. In actual ocean engineering, the collision problem has to be considered with other structures, such as risers, conveyor cables, etc. At the seabed, the catenary mooring line lies horizontally, in general, which has a minimum length of 50 m; thus the mooring line has to be longer than the water depth, and the anchor points in a catenary mooring system only bear horizontal forces and are not subject to vertical forces (Fig. 2); the nonlinear restoring force generated by the catenary mooring system provides

Catenary Mooring

195

Catenary Mooring, Fig. 2 The catenary mooring line

C

the positioning function of the floating platform and balances the environmental load acting on the water platform (Samad 2009). Meanwhile, as the water depth increases, the length and weight of the mooring line also increase rapidly, which not only increases the tension in the chain but also increases the vertical load on the floating structure, further reducing the payload capacity of the floating structure. In that case, synthetic ropes are used because of conventional catenary systems become less and less economical (Banfield and Flory 2009). That is to say, the catenary mooring system is suitable for relatively shallow waters ( 0

Cavity Depth The volume of the soil above the spudcan, Vsoil, can be calculated in a manner similar to singlelayer sand.

ð27Þ In this method, the contribution from the frictional resistance around the plug was neglected.

I

834

Installation of Spudcans

Installation of Spudcans, Fig. 7 Soil failure pattern for load spread factor. (After Hossain 2014)

Installation of Spudcans, Fig. 8 Conceptual model for spudcan at punchthrough in sand-over-clay deposits (ISO method)

For the punching shear ISO method, similar to stiff-over-soft clay, a cylindrical plug of diameter D is assumed between the base of the advancing

spudcan and the underlying layer interface, with the base fixed at the sand-clay layer interface regardless of the spudcan penetration. As a

Installation of Spudcans

835

cylindrical plug is assumed, dilatancy of the sand is therefore neglected (dilation angle, c ¼ 0
). The vertical bearing capacity, Qv, of a foundation in sand over clay at a specific depth d can be expressed as

pressure coefficient (K0) and passive earth pressure coefficient (Kp). The values of Ks suggested by ISO (2015) and Hanna and Meyerhof (1980) are given in Fig. 9, as a function of f0 and Qv,clay/ Qv,sand (ratio of single-layer response for a surface spudcan on the clay layer and that on the sand   tan ’0 layer). þ Nc su2si Qv ¼ A 2tr g01 ðtr þ 2dÞKs Nc should be picked from Eq. 4. For bottom D layer with nonuniform undrained shear strength, þ g01 ðAd þ Vb Þ   an average value over a depth of D/2 can be used.  g01 0:5DNg A þ Vb for d  0 For the bottom clay layer, the penetration resis(28) tance should be calculated using the single-layer   approach discussed previously. tan ’0 Qv ¼ A 2tr g01 ðtr þ 2dÞKs þ Nc su2si Lee et al. and Hu et al. approach: Lee et al. D (2013a, b) and Hu et al. (2015, 2018) proposed a þ g01 ðAd þ Vt  Vsoil Þ mechanism-based design approach based on the    g01 0:5DNg A þ dNq dq A þ Vt  Vsoil soil flow mechanisms observed in model tests and for d > 0 LDFE analyses. The approach simplified the ð29Þ spudcan penetration profile as a combination of the peak resistance and post-peak resistance in the where Ks is the punching shear coefficient and sand layer, qpeak and qpost-peak, and the resistance f0 is the effective angle of internal friction. The- in the clay layer, qclay. qpeak is the sum of the oretically Ks should lie in between at rest earth frictional resistance in the sand, the bearing Installation of Spudcans, Fig. 9 Bearing capacity ratio versus coefficient of punching shear

I

836

Installation of Spudcans

capacity of the underlying clay, and the weight of the sand frustum, and it is expressed as  E   1:76Hs tan c qpeak ¼ Nc0 sumi þ q0 þ 0:12g0s Hs 1 þ D " E #   g0s D 1:76Hs  1:76Hs E tan c 1 þ tan c þ 1 1  D D 2 tan cðE þ 1Þ

ð30Þ where Nc0 is the bearing capacity factor for clay at the base of a circular foundation, which

is obtained from Houlsby and Martin (2003); q0 is the effective overburden pressure; and E* is a parameter to simplify the algebra. The depth of the peak resistance in the sand layer is taken as 0.12Hs, where Hs is the sand layer thickness. For assessing spudcan penetration resistance after the peak failure in the top sand layer and before penetrating into the bottom clay layer, an analytical model was proposed as

8  

9  0  g0s D > > d  0:1Hs 0 0 > > > > 14:8 þ 10:6 sumi þ q0 þ gs Hs þ gc  gs ðd  0:1Hs Þ  D E = g0s D <

ð31Þ q¼ þ E > > EðHs  dÞ > > > > exp ; : D

where γ0 c is the effective unit weight of clay and E is also a parameter to simplify the algebra (Hu et al. 2018). For the resistance in the clay layer, the bearing capacity is expressed as

layer of that clay + limiting squeezing depth) < (thickness of the soft clay layer), soil backflow can occur earlier due to the influence of squeezing (Hossain 2014). This means Hcav in soft-over-strong soils may be lower compared to that on single-layer soft clay.

qclay ¼ Nc su0i þ Hplug g0c ¼ Nc su0i þ 0:9Hs g0c

  H 0:16  s  1:00 D ð32Þ

where su0i is the clay shear strength at the lowest level of the spudcan’s widest crosssectional area and Hplug is the height of the sand plug. The bearing capacity factor Nc was summarized from a sand overlying clay centrifuge testing database and LDFE analyses of the full penetration process, incorporating various footing shapes and soil conditions.

Spudcan Installation in Layered Soils with Potential for Squeezing: Soft ClayOver-Strong Layer Cavity Depth If the thickness of the soft clay layer is relatively thin and hence the (limiting cavity depth in single

Design Methods For assessing spudcan penetration in soft clayover-strong layer, four methods will be discussed including (a) the squeezing ISO method (Meyerhof and Chaplin 1953; Brown and Meyerhof 1969), (b) the Merifield-Nguyen method (Merifield and Nguyen 2006), (c) the Meyerhof and Hanna method (Meyerhof 1974; Meyerhof and Hanna 1978), and (d) the CLAROM method (CLAROM 1993). Squeezing ISO method: This method is applicable only for the overlying soft clay layer. A uniform strength is considered for the top layer, and the underlying layer is assumed to be rigid. The penetration resistance in the soft clay layer can be assessed according to Qv



D ¼ A 0:33 su1i þ ðNc  1Þsu1i tr þ g01 ðAd þ Vb Þ  Nc su1i A þ g01 ðAd þ Vb Þ for d  Hcav

ð33Þ

Installation of Spudcans



Qv

D ¼ A 0:33 su1i þ ðNc  1Þsu1i tr

837



þ g01 ðAHcav þ Vt Þ  Nc su1i A þ g01 ðAHcav þ Vt Þ for d > Hcav

ð34Þ

The values of Nc should be picked from Eq. 4 using actual penetration depth of the spudcan base, i.e., d/D ¼ d/D. For soft layer with a nonuniform undrained shear strength, an average value over a depth of D/2 can be used. However, averaging should be restricted within the soft clay layer; otherwise near the first–second layer interface, a significantly higher shear strength would be picked. Clearly, Eqs. 33 and 34 are not a function of the thickness and properties of the underlying strong layer. This is a limitation of this approach. Merifield and Nguyen method: Recently Merifield and Nguyen (2006) and Meyer et al. (2015) carried out small strain finite element analyses on a perfectly rough-based circular surface (d/D ¼ 0) footing in soft-over-stiff clay. Merifield and Nguyen (2006) presented the values of modified bearing capacity factor both numerically in tables and graphically in figures. Best fit through Merifield and Nguyen’s (2006) data provides N ¼ 0:009

 2 D D  0:018 tr tr

þ Ncs for subi =suti ¼ 1:25

ð35aÞ

 2 D D  0:046 N ¼ 0:033 tr tr þ Ncs ¼ 2:0 N ¼ 0:036

for subi =suti

ð35bÞ

 2 D D  0:061 tr tr

þ Ncs for subi =suti ¼ 2:5

ð35cÞ

where Ncs ¼ 6.05. For an embedded footing (d/D > 0), Eq. 35 can be extended using Nc instead of Ncs.

Meyerhof and Hanna method: The above discussion is for soft-over-stiff clay or a rigid layer. In a thin weak-over-strong layer deposit of any soils, Meyerhof (1974) and Meyerhof and Hanna (1978) suggested that the bearing capacity of a flat-based circular footing can be calculated according to   t =D qu ¼ qut þ ðqub  qut Þ 1  r Hf =D

ð36Þ

where qu,t is the bearing capacity of the footing at the penetration depth in the top layer, qu,b is the bearing capacity of the bottom layer at the interface, and Hf ¼ 1 for circular footing regardless of soil (i.e., either sand or clay). CLAROM method: CLAROM (1993) somewhat blended the methods proposed by Meyerhof (1974) and Meyerhof and Hanna (1978) and Brown and Meyerhof (1969) and accounted for the effect of spudcan bottom profile as qu ¼ qut þ ðqub  qut Þ

  Ab V þ g0t A A

ð37Þ

where Ab is the plan area of the spudcan bottom profile embedded in the bottom layer and V is the volume of the spudcan embedded in soil. Ab ¼ 0 if the spudcan does not penetrate into the bottom layer. For soft-over-stiff clay,   d qut ¼ Nmc 1 þ 0:2 s D uti

ð38aÞ

  t qub ¼ Ncs 1 þ 0:2 subi D

ð38bÞ

where Nmc should be taken from Fig. 10 (Brown and Meyerhof 1969) using subi =suti instead of subi/ suti, Ncs ¼ 6.05, suti is the average undrained shear strength of soft clay over thickness tr, and subi is the average undrained shear strength of stiff clay over thickness of Db/2 (Db is the spudcan diameter embedded in the bottom layer) under the expression of qub and over the thickness of D/2 under the interface for calculating subi =suti for picking Nmc from Fig. 10. This average is necessary to take into account the strength increasing with depth.

I

838

Installation of Spudcans

Installation of Spudcans, Fig. 10 Modified bearing capacity factors. (After Brown and Meyerhof 1969)

s ub / s ut

For the bottom sand layer, qub ¼ 0:3g0t DNg þ s0v Nq

ð39Þ

where s0v is the effective overburden pressure at the interface level. For picking Nmc from Fig. 10, subi =suti should be calculated, and for which an equivalent subi should be calculated from the expression below: 0:3g0t DNg ¼ 6subi

ð40Þ

In terms of limiting squeezing depth, hsq (the depth range from where the spudcan starts to sense the underlying strong layer and consequently the resistance profile deviates from that without the influence of the underlying layer) solving Eq. 37, ISO suggests 

tr  0:33 D

ð41aÞ

ð41bÞ ð41cÞ

Spudcan Installation in Multilayer Soils Cavity Depth Investigation in multilayer soils for developing design chart for limiting cavity depth is sparse. In absence of specific expression, for multilayer clay sediments, the limiting cavity depth can be assessed using Hcav ¼ D

 d D 5:05 þ 1:2 þ 0:33 s þ p0o D tr uti  Nc suti þ p0o

  d D s þ p0o 5:05 þ 1:2 þ 0:33 D tr uti   d s þ p0o  6:05 þ 1:2 D uti



suHi g0 D

0:55



1 suHi 4 g0 D

ð42Þ

where suHi is the intact undrained shear strength at the backflow depth, Hcav. Some iteration is

Installation of Spudcans

needed to establish Hcav and the resulting value of suHi. For multilayer soil with a surface sand layer, the volume of the soil above the spudcan, Vsoil, can be calculated in a manner similar to singlelayer sands or sand over clay, as discussed previously.

Design Methods For assessing spudcan penetration in multilayer soils, three methods will be discussed including (a) the bottom-up ISO approach and (b) the topdown approaches (Zheng et al. 2015, 2017, 2018). Bottom-up ISO approach: The bottom-up design approach can be used combining the squeezing (for weak-over-strong layering) and punch-through (for the reverse) criteria for twolayer systems discussed previously. Firstly the bearing capacity of a spudcan at the top of the lowest two layers is computed. These two layers are then treated as one (lower) layer in a subsequent two-layer system analysis involving the immediate upper layer. The equivalent undrained shear strength at the surface of a layer is updated after the completion of assessment of penetration resistance profile of that layer (based on the calculated penetration resistance at the surface of that layer). Top-down approaches (Zheng et al. 2015, 2017, 2018): Recently, top-down approaches have been proposed by Zheng et al. (2015, 2017, 2018) accounting for the effect of the evolution of a soil plug at the base of the spudcan, its accumulation or diminishing, and corresponding effect on the penetration resistance.

Mitigation of Punch-Through and spudcan-Footprint Interactions For the jack-up industry, two major concerns related to geotechnical/structural failures during installation and preloading process include (a) spudcan punch-through in layered soils (53%) and (b) spudcan lateral sliding interacting

839

with an existing footprint from a previous installation (15%) (Jack et al. 2013).

Spudcan Punch-Through Punch-through incidents occur in stratified soil conditions with a surface or interbedded strong (sand or stiff clay/silt) layer overlying a weak layer. Some examples have been reported by, e.g., Young et al. (1984), Kostelnik et al. (2007), and Menzies and Lopez (2011). The consequent loss may be $5~50 million per incident. The risk of punch-through can be identified from the assessed spudcan load-penetration profiles using the design methods just discussed. Once the risk of punch-through failure is identified at a site, mitigation methods are required for allowing a safer installation of the rig. Conventionally, installation procedures (such as leg-byleg preloading; InSafeJIP 2011) have been used for easing punch-through or controlling leg penetration. Recently, several other mitigation methods have been discussed: (a) application of cyclic loading in the strong soil layer to degrade the strength (Erbrich 2005), (b) perforation drilling through the strong soil layer prior to the installation of a spudcan (Maung and Ahmad 2000; Kostelnik et al. 2007; Hossain et al. 2011; InSafeJIP 2011), and (c) a foundation with a peripheral skirt on its bottom side (Teh et al. 2008; Gan et al. 2011; Hossain et al. 2014b; Li et al. 2018). For stiff-over-soft clay deposits, Hossain et al. (2011) proposed an optimized perforation drilling pattern, as shown in Fig. 11. The experimental centrifuge results confirmed that perforation drilling is indeed effective at mitigating punchthrough and severe leg run during jack-up installation in multilayered clays with interbedded stronger layers. For sand-over-clay deposits, perforation drilling and cyclic degradation are not applicable. Hossain et al. (2014b), Lee et al. (2018), and Li et al. (2018) showed that a skirted spudcan with a skirt length 0.25D can effectively be used to eliminate or ease the punch-through risk. An example result is shown in Fig. 12.

I

840

Installation of Spudcans

Installation of Spudcans, Fig. 11 Perforation drilling: (a) mitigated punch-through failure; (b) perforation drilling pattern. (After Hossain et al. 2011)

Spudcan-Footprint Interactions After completing the initial operation, the legs of a jack-up rig are retracted from the seabed, leaving depressions, referred to as a crater or “footprint.” Jack-ups often return to the previous operation site for more drillings, where the footprints from previous explorations are present. Where one of the jack-up legs is located near an existing footprint slope, there is a tendency for the spudcan to slide toward the center of the footprint, inducing excessive lateral displacements and bending moments or rotations of the rig. These detrimental foundation behaviors can result in an inability to install the jack-up at the required position and even worse the occurrence of leg splay and structural damage to the whole jack-up system. The frequency of offshore incidents during installation near footprints has increased by a factor of 4 from the period 1979~1988 to the period of 1996~2005 (Osborne 2005; Jack et al. 2013). There are several mitigation methods reported, including (a) infilling crater (Jardine et al. 2002),

(b) capping the infilled crater with gravel loading platforms, (c) stomping (Jardine et al. 2002), (d) reaming (Hartono et al. 2014), (e) perforation drilling (Hossain and Stainforth 2016), (f) successive repositioning until the legs had stabilized in the desired plan position (Brenna et al. 2006), (g) use of an identical or very similar spudcan diameter and exactly on the existing footprint (Erbrich 2005), and (h) water jetting along with the spudcan preloading (Handidjaja et al. 2009). In relation to case histories in the North Sea, Jardine et al. (2002) and Grammatikopoulou et al. (2007) examined the potential of using the former two. All the other methods require additional working leading to additional cost and time to be applied in the field. Consequently, Jun et al. (2018a, b) have focused on tweaking spudcan shapes to ease the spudcan-footprint interactions. These studies have led to establish a novel spudcan shape with a flat base and four holes, which has been shown to be effective at easing spudcan-footprint interactions (see Fig. 13).

Installation of Spudcans

841

Installation of Spudcans, Fig. 12 Mitigation of punch-through failure using a skirted foundation. (After Hossain et al. 2014b)

I

Installation of Spudcans, Fig. 13 Mitigation of spudcan-footprint interactions using a novel spudcan. (After Jun et al. 2018a, b): (a) horizontal resistance force; (b) structural stress on leg top; (c) reference points and model spudcans

References Brenna R, Diana H, Stonor RWP, Hoyle MJR, Cheng CP, Martin D, Roper R (2006) Installing jack-ups in punch-through-sensitive clays. In: Proceedings of

the offshore technology conference, Houston, OTC 18268 Brown JD, Meyerhof GG (1969) Experimental study of bearing capacity in layered clays. In: Proceedings of the 7th international conference on soil mechanics and foundation engineering, Mexico, vol 2, pp 45–51

842 Cassidy MJ, Houlsby GT (2002) Vertical bearing capacity factors for conical footings on sand. Géotechnique 52(9):687–692 CLAROM (1993) Design guides for offshore structures, Club des Actions de Recherche sur les Ouvrages en Mer (Eds: Le Tirant P and Pérol C). Paris Erbrich CT (2005) Australian frontiers – spudcans on the edge. In: Proceedings of the international symposium frontiers in offshore geotechnics, Perth, Australia, ISFOG, pp 49–74 Gan CT, The KL, Leung CF, Chow YK, Swee S (2011) Behaviour of skirted footings on sand overlying clay. In: Proceedings of the international symposium frontiers in offshore geotechnics, Perth, Australia, ISFOG, pp 415–420 Grammatikopoulou A, Jardine RJ, Kovacevic N, Potts DM, Hoyle M, Hampson KM (2007) Potential solutions to the problem of the eccentric installation of jackup structures into old footprint craters. In: Proceedings of the 6th international conference on offshore site investigation and geotechnics, London, UK, pp 293–300 Handidjaja P, Gan CT, Leung CF, Chow YK (2009) Jackup foundation performance over spudcan footprints analysis of a case history. In: Proceedings of the 12th international conference on the jack-up platform design, construction and operation, London, UK Hanna AM, Meyerhof GG (1980) Design charts for ultimate bearing capacity of foundations on sand overlying soft clay. Can Geotech J 17:565–572 Hartono H, Tho KK, Leung CF, Chow YK (2014) Centrifuge and numerical modelling of reaming as mitigation measure for spudcan-footprint interaction. In: Proceedings of the 2014 offshore technology conference (OTC) Asia, Kuala Lumpur, Malaysia Hossain MS (2014) Experimental investigation of spudcan penetration in multi-layer clays with interbedded sand layers. Géotechnique 64(4):258–276 Hossain MS, Randolph MF (2009a) New mechanismbased design approach for spudcan foundations on single layer clay. J Geotech Geoenviron Eng ASCE 135(9):1264–1274 Hossain MS, Randolph MF (2009b) Effect of strain rate and strain softening on the penetration resistance of spudcan foundations on clay. Int J Geomech ASCE 9(3):122–132 Hossain MS, Randolph MF (2010a) Deep-penetrating spudcan foundations on layered clays: centrifuge tests. Géotechnique 60(3):157–170 Hossain MS, Randolph MF (2010b) Deep-penetrating spudcan foundations on layered clays: numerical analysis. Géotechnique 60(3):171–184 Hossain MS, Stainforth R (2016) Perforation drilling for easing spudcan-footprint interaction issues. Ocean Eng 113:308–318 Hossain MS, Cassidy MJ, Baker R, Randolph MF (2011) Optimization of perforation drilling for mitigating punch-through in multi-layered clays. Can Geotech J 48:1658–1673

Installation of Spudcans Hossain MS, Zheng J, Menzies D, Meyer L, Randolph MF (2014a) Spudcan penetration analysis for case histories in clay. J Geotech Geoenviron Eng ASCE 140(7):04014034 Hossain MS, Hu Y, Ekaputra D (2014b) Skirted foundation to mitigate spudcan punch-through on sand-over-clay. Géotechnique 64(4):330–340 Houlsby GT, Martin CM (2003) Undrained bearing capacity factors for conical footings on clay. Géotechnique 53(5):513–520 Hu P, Wang D, Stanier SA, Cassidy MJ (2015) Assessing the punch-through hazard of a spudcan on sand overlying clay. Géotechnique 65(11):883–896 Hu P, Cassidy MJ, Randolph MF (2018) Bearing capacity on sand overlying clay: an analytical model for predicting post peak behaviour. Mar Struct 59:94–104 InSafeJIP (2011) Improved guidelines for the prediction of geotechnical performance of spudcan foundations during installation and removal of jack-up units. Joint Industry Funded Project ISO (2015) Petroleum and natural gas industries – site specific assessment of mobile offshore units – part 1: jack-ups, International Organization for Standardization, ISO 19905-1 Jack RL, Hoyle MJR, Smith NP, Hunt RJ (2013) Jack-up accident statistics – a further update. In: Proceedings of the 11th international conference the jack-up platform design, construction and operation, London, UK Jardine RJ, Kovacevic N, Hoyle MJR, Sidhu HK, Letty A (2002) Assessing the effects on jack-up structures of eccentric installation over infilled craters. In: Proceedings of the international conference on offshore site investigation and geotechnics diversity and sustainability, London Jun MJ, Kim YH, Hossain MS, Cassidy MJ, Hu Y, Sim JU (2018a) Numerical investigation of novel spudcan shapes for easing spudcan-footprint interactions. J Geotech Geoenviron Eng ASCE 144(9):04018055 Jun MJ, Kim YH, Hossain MS, Cassidy MJ, Hu Y, Park SG (2018b) Optimising spudcan shape for mitigating spudcan-footprint interaction. Appl Ocean Res 79:62–73 Kostelnik A, Guerra M, Alford J, Vazquez J, Zhong J (2007) Jack-up mobilization in hazardous soils. SPE Drill Completion 22(1):4–15 Le Tirant P (1979) Seabed reconnaissance and offshore soil mechanics for the installation of petroleum structures. Technip, Paris Lee KK, Cassidy MJ, Randolph MF (2013a) Bearing capacity on sand overlying clay soils: experimental and finite-element investigation of potential punchthrough failure. Géotechnique 63(15):1271–1284 Lee KK, Randolph MF, Cassidy MJ (2013b) Bearing capacity on sand overlying clay soils: a simplified conceptual model. Géotechnique 63(15):1285–1297 Lee JM, Hossain MS, Hu P, Kim YH, Cassidy MJ, Hu Y, Park SG (2018) Effect of spudcan shape on mitigating punch-through in sand-over-clay. Int J Phys Modell Geotech. https://doi.org/10.1680/jphmg.18.00072

Intact, Damage, and Dynamic Stability of Floating Structures Li YP, Liu Y, Lee FH (2018) Effect of sleeves and skirts on mitigating spudcan punch-through in sand overlying normally consolidated clay. Géotechnique. https://doi. org/10.1680/jgeot.17.P.085 Martin CM (2003) User guide for ABC – analysis of bearing capacity. Department of Engineering Science, University of Oxford, Report No. OUEL 2261/03. Available from http://www-civil.eng.ox.ac.uk/people/ cmm/software/abc/ Maung UM, Ahmad CKM (2000) Swiss cheesing to bring in a jack-up rig at Anding location. In: Proceedings of the IADC/SPE Asia Pacific Drilling Technology, Kuala Lumpur, IADC/SPE 62755 Menzies D, Lopez CR (2011) Four atypical jack-up rig foundation case histories. In: Proceedings of the 13th international conference the jack-up platform design, construction and operation, London, UK Menzies D, Roper R (2008) Comparison of jack-up rig spudcan penetration methods in clay. In: Proceedings of the offshore technology conference, Houston, OTC 19545 Merifield RS, Nguyen VQ (2006) Two- and threedimensional bearing capacity solutions for footing on two-layered clays. Geomech Geoeng 1(2):151–162 Meyer VM, Zhang Y, Kort DA (2015) Theoretical study of a weak layer on the vertical bearing capacity of spudcans in clay. In: Proceedings of the 15th international conference the jack-up platform design, construction and operation, London, UK Meyerhof GG (1974) Ultimate bearing capacity of footings on sand layer overlying clay. Can Geotech J 11:223–229 Meyerhof GG, Chaplin TK (1953) The compression and bearing capacity of cohesive layers. Br J Appl Phys 4:20–26 Meyerhof GG, Hanna AM (1978) Ultimate bearing capacity of foundations on layered soils under inclined load. Can Geotech J 15(4):565–572 Osborne JJ (2005) Are we good or are we lucky? Presentation slides for OGP/CORE workshop: the jack-up drilling option – ingredients for success, Singapore Skempton AW (1951) The bearing capacity of clays. Build Res Congr Lond 1:180–189 SNAME (2008) Recommended practice for site specific assessment of mobile jack-up units, T and R Bulletin 5-5A, 1st Edition – Rev. 3, Society of Naval Architects and Marine Engineers, New Jersey Teh KL, Cassidy MJ, Leung CF, Chow YK, Randolph MF, Quah CK (2008) Revealing the bearing capacity mechanisms of a penetrating spudcan through sand overlying clay. Géotechnique 58(10):793–804 Vesic AS (1975) Bearing capacity of shallow foundations. In: Winterkorn HF, Fang HY (eds) Foundation engineering handbook. Van Nostrand-Reinhold, New York, pp 121–147 White DJ, Teh KL, Leung CF, Chow YK (2008) A comparison of the bearing capacity of flat and conical circular foundations on sand. Géotechnique 58(10):781–792

843

Young AG, Remmes BD, Meyer BJ (1984) Foundation performance of offshore jack-up drilling rigs. J Geotech Eng ASCE 110(7):841–859 Zheng J, Hossain MS, Wang D (2015) New design approach for spudcan penetration in nonuniform clay with an interbedded stiff layer. J Geotech Geoenviron Eng ASCE 141(4):04015003 Zheng J, Hossain MS, Wang D (2016) Prediction of spudcan penetration resistance profile in stiff-oversoft clays. Can Geotech J 53(12):1978–1990 Zheng J, Hossain MS, Wang D (2017) Numerical investigation of spudcan penetration in multi-layer deposits with an interbedded sand layer. Géotechnique 67(12):1050–1066 Zheng J, Hossain MS, Wang D (2018) Estimating spudcan penetration resistance in stiff-soft-stiff clay. J Geotech Geoenviron Eng ASCE 144(3):04018001

Insulation Layer ▶ Cable

Insulation Work ▶ Thermal Insulation

Intact Stability ▶ AUV/ROV/HOV Stability

Intact, Damage, and Dynamic Stability of Floating Structures Shuqing Wang and Liwei Yu College of Engineering, Ocean University of China, Qingdao, China

Definition The stability is the capability of the floating structure to maintain to its upright floating position

I

844

Intact, Damage, and Dynamic Stability of Floating Structures

both in still water and in waves, whether intact or damaged, and it relates to the interaction among the center of gravity (COG), center of buoyancy (COB), and metacenter of intact or damaged hull under various scenarios.

Scientific Fundamentals Introduction The stability is one of the most essential performances for offshore structures. The stability calculation, also referred as stability check, during the design, construction, and operation stage of the offshore structure is fundamental for the safety of the offshore structure and required by the administrations (e.g. Classification Society, Maritime Office). The relation of the COG, COB, and metacenter of offshore structure can be found in Fig. 1, and the nomenclature adopted in this entry is listed in Table 1. GM and GZ When the offshore structure inclines from its equilibrium floating position, the center of buoyancy changes from COB to COB1 as shown in Fig. 2. The righting moment is generated by gravity (G) and buoyancy (F), because the COG and COB1 of the offshore structure are not vertically inline as shown in Fig. 2. The righting moment provides the stability of the offshore structure to maintain its upright floating position. The intersection point between the straight line through the COG and the original COB and the straight line through the COG and the COB1 Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 1 COG, COB, and metacenter of offshore structure

after inclining is referred as the metacenter. When the angle of inclination is small, the position of metacenter doesn’t change. The distance between the COG and metacenter is named as the metacentric height (GM) under small inclination. The distance between the COB and metacenter is named as the metacentric radius (BM) which is calculated as: BM ¼

I ∇

ð1Þ

where I stands for the moment of inertia of the waterline area. ▽ represents the displacement of the offshore structure. Then, GM is calculated as: GM ¼ KB þ BM  KG

ð2Þ

where KB and KG are the vertical heights of COB and COG from the bottom. The lever of the righting moment, i.e., the horizontal distance between COG and COB, is referred as the righting lever (GZ) as shown in Fig. 1. Thus the restoring moment (M) is represented as: M ¼ F  GZ

ð3Þ

The change of the righting lever (GZ) against the angle of inclination forms the righting lever curve (i.e., GZ curve) as shown in Fig. 3. The righting lever curve is calculated from the hydrostatic curves. The downflooding angle stands for the angle of inclination where the water begins to flood into hull through openings. The angle of

Intact, Damage, and Dynamic Stability of Floating Structures

845

Intact, Damage, and Dynamic Stability of Floating Structures, Table 1 The nomenclature Symbol A Ap BM Cs CH COG COB F G GM GZ ▽

Meaning Attained subdivision index Projected area Metacentric radius Shape coefficient Height coefficient Center of gravity Center of buoyancy Buoyancy force Gravity force Metacentric height Righting lever Displacement

Symbol KB, KG I M P R S V Θ r f ζ o0, o

Meaning Vertical height of COB and COG from the bottom Moment of inertia Restoring moment Probability of flooding of the compartments Required subdivision index Survival probability The wind velocity Inclination angle Air density Motion (the pitch angle for spar platform) The damping coefficient Natural frequency, exciting frequency of wave

Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 2 Righting moment of the offshore structure

I

vanishing stability is the angle where the righting lever, i.e., righting moment, is zero. The vessel capsizes after the angle of vanishing stability and returns back to the equilibrium position before the angle of vanishing stability. At zero angle of inclination, the gradient of the GZ curve is GM. Therefore GM should be larger than zero to guarantee a positive righting lever under small inclination. The fundamental condition for the offshore structure to maintain its upright floating position is: GM > 0

ð4Þ

Requirements for Stability Calculation The stability calculation checks the ability of the offshore structure to hold its upright position and

is vital for the safety of the offshore structure. In order to conduct the stability calculation, the following items are required. General Arrangement, Compartments, and Subdivision

The general arrangement of the offshore structure is defined as the design and separation of spaces both up and under the main deck for all the required functions, machineries, and equipment as shown in Fig. 4. In the general arrangement, the spaces are divided by transversal, longitudinal bulkheads and decks into several smaller spaces called as compartment. The major compartments include machinery and fuel compartment, cargo compartment, ballast water compartment, accommodation

846 Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 3 Righting lever (GZ) curve

Intact, Damage, and Dynamic Stability of Floating Structures Righting Lever (GZ) α

Downflooding Angle

Angle of Vanishing Stability Angle of Inclination Back to equilibrium position

Capsize

Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 4 General arrangement of semisubmersible

compartment, and production equipment compartment. The detail information of each compartment including volume and position are summarized in the Table of Compartments. The watertight transversal, longitudinal bulkheads form the watertight subdivision to prevent water from propagating to other compartments

after breaching on one compartment as shown in Fig. 5. Loading Condition

Loading conditions are the conditions determined by the different loading of cargo, fuel, ballast, and provision in the compartment and on the deck

Intact, Damage, and Dynamic Stability of Floating Structures

847

Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 5 Watertight subdivision

Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 6 Curves of the righting moment and the heeling moment (IMO 2009)

in order to meet various operational demands. Different loading conditions have different GM, GZ curves, and stability performances. Therefore, the stability calculation should be conducted on all the typical loading conditions. The loading condition table contains the load, mass, and filling rate of all the compartments. The typical loading conditions of a mobile drilling unit include towing condition, operation condition (minimum draft and maximum draft), and survival condition under storm. Stability Curves

Stability curves are the curves required for stability calculation. The most important curves for stability calculation are the curves of the righting moment and the heeling moment as shown in Fig. 6. The right moment curve is generated from the righting lever (GZ) curve by multiplying with buoyancy force (F).

I

The heeling moment curve is drawn from for wind forces (Fw) calculated by the following formula (IMO 2009): Fw ¼ 0:5Cs CH rV 2 Ap

ð5Þ

where Cs is the shape coefficient depending on the shape of the structural member exposed to the wind. CH represents the height coefficient depending on the height above sea level of the structural member exposed to wind. r stands for the air density. V is the wind velocity. Ap is the projected area of all exposed surfaces in either the upright or the heeled condition. Then, the wind heeling moments are calculated by multiplying the wind force with its lever. The lever of the wind force is taken vertically from the center of pressure of all surfaces exposed to the wind to the center of lateral resistance of the underwater body of the unit.

848

Intact, Damage, and Dynamic Stability of Floating Structures

Stability Criteria

Stability criteria are the criteria constituted by the administrations (e.g., Classification Society, Maritime Office). It sets limits for heeling angle, freeboard, GM, and stability curves to ensure the stability and safety of the offshore structure under certain wind and wave loads, whether intact or damaged. The stability criteria are designed based on the notion that the offshore structure has enough right moment to withstand the designed and extreme wind heeling moment, whether intact or damaged. Major stability criteria for offshore structures include: (a) IMO, Code for the Construction and Equipment of Mobile Offshore Drilling Units (IMO 2009) (b) DNV, Offshore Standard DNV-OS-C301 Stability and Watertight Integrity (DNV 2014) (c) ABS, Rules for Building and Classing Mobile Offshore Drilling Units, Part 3 Hull Construction and Equipment, 2012 (ABS 2012) (d) CCS, Rules for Construction and Classification of Mobile Offshore Drilling Units, Part 3 Stability, Subdivision and Load lines, 2005 (CCS 2005). Stability Calculation Inclining Test

An inclining test is required for the offshore structure, when it is as near to completion as possible, to measure accurately the light ship data (weight, GM, and position of COG). In the inclining test, certain weights P (1%–2% of the light ship displacement) are displaced by the distance L from the equilibrium position to generate a moment (M ¼ PL) causing an inclination of 2–4
to the offshore structure as presented in Fig. 7. The inclination angle (θ) can be measured by a pendulum or a U-tube. Therefore the metacentric height (GM) is calculated as: GM ¼

M ∇g tan y

where g is the gravitational acceleration.

ð6Þ

Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 7 Demonstration of the inclining test

Intact Stability

Intact stability is the calculation of the stability performance of the offshore structure with an intact hull. Firstly, the calculations require measuring and calculating all the centers of mass of objects on the offshore structure to identify the center of gravity (COG) and the center of buoyancy (COB) of the hull under various loading conditions. Then the intact stability calculations are divided into two categories: initial stability and stability at large angle of inclination. Initial stability is the stability calculation at small angle of inclination (within 10–15
). It involves the calculation of COG, COB, metacenter, BM, and GM. Stability at large angle of inclination is the stability calculation. It involves the calculation of the righting lever and moment curves. After the intact stability calculations, the results such as weight, GM, and righting moment curve are utilized to check whether the stability criteria abovementioned are met. A typical stability criteria can be illustrated as follows (IMO 2009): – For column-stabilized units, the area under the righting moment curve to the angle of downflooding should be not less than 30% in excess of the area under the wind heeling moment curve to the same limiting angle. – The righting moment curve should be positive over the entire range of angles from upright to the second intercept.

Intact, Damage, and Dynamic Stability of Floating Structures

Damage Stability

Damage stability is the calculation of the stability performance of the offshore structure after damage with breached compartments. It requires more complicated and heavy calculation than intact stability. Thus, special numerical software such as NAPA are typically employed to handle the heavy calculation works. In the damage condition, one or more compartments are breached and flooded by water. Its contents are assumed to be lost and replaced by water. If contents are lighter than water (e.g., light oil), then buoyancy is lost, and the offshore structure inclines unless the compartment is on the centerline. The new floating position after flooding is achieved. Under the new floating position, the freeboard, GM, and righting moment curves are calculated (Fig. 8). In the damage stability calculations, many damage scenarios with different compartments breached should be selected. There are two methods for damage stability calculations: deterministic damage stability and probabilistic damage stability Deterministic damage stability is a traditional and widely used method for damage stability calculations. A deterministic extent of damage on hull is decided firstly. Then it assumed that all the compartments within this extent of damage

849

are breach deterministically without considering the breaching probability of these compartments. The results of deterministic stability calculations are the floating position, the freeboard, GM, and righting moment curves after breaching of one or more compartments. Then the results are utilized to check whether the deterministic stability criteria are met. Probabilistic damage stability is a newly developed method especially for passenger vessels. The damage stability calculations are of a probabilistic nature, which are based on the breaching probability on one or more compartments and survival probability after breaching (Fig. 9). The probability of flooding of the compartments in the hull position is calculated as P based on injury statistics (probability of opening). The survival probability S (which is the probability of survival without sinking and capsizing even in the waves) is calculated when the partition is damaged or flooded. If the survival probability S is greater than 0, it means that this ship does not capsize even if some compartment is flooded. If S is 0, it means sinking. The total survival probability A is calculated for the entire ship by integrating the product of P and S over the entire length of the ship. It is required that this value should be larger than the criteria’s required value R. This survival probability A is called

Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 8 Floating position of a barge after breaching on a ballast tank

I

850

Intact, Damage, and Dynamic Stability of Floating Structures

Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 9 Diagram for probabilistic damage stability

“attained subdivision index A,” and the regulation’s required value R is called “required subdivision index R.” After the damage stability calculations, the results such as weight, GM, and righting moment curve are utilized to check whether the stability criteria abovementioned are met. A typical deterministic damage stability criteria can be illustrated as follows (IMO 2009): – Columns and braces should be assumed to be flooded by damage having a vertical extent of 3 m occurring at any level between 5 m above and 3 m below the draughts specified in the operating manual. – The angle of inclination after the damage within the extent should not be greater than 17
. – The righting moment curve after the damage should have, from the first intercept to the lesser of the extent of weather tight integrity and the second intercept, a range of at least 7
. Within this range, the righting moment curve should reach a value of at least twice the wind heeling moment curve, both being measured at the same angle.

Dynamic Stability in Waves The abovementioned stability calculations are all of the static nature, which consider the motions of vessels, wind, and wave loads statically. However, dynamic motions and loads can also cause stability failure event such as parametric resonance and excessive acceleration. Parametric Resonance

Parametric resonance, as a self-resonance phenomenon, occurs with excessive inclining motion and even leads to capsizing. It can bring severe cargo loss and damage (France et al. 2003). It is caused by the time varying GM and weakening of righting moment under certain large waves. The GM and righting moment variations can be caused by either the change of the waterline area in waves (such as containerships as shown in Fig. 10) or the change of the COB in waves (such as Spar and semisubmersible platforms). The fundamental dynamics of parametric resonance caused by the time varying of restoring characteristics can be simplified as the damping Mathieu equation:   f00 þ 2zf0 þ o20 þ ϵ cos ot f ¼ 0

ð7Þ

Intact, Damage, and Dynamic Stability of Floating Structures

851

Intact, Damage, and Dynamic Stability of Floating Structures, Fig. 10 Variation on GZ curves in waves of the KCS containership (Yu et al. 2017)

where f is the motion (the pitch angle for spar platform), ζ is the damping coefficient, and o0 and o stand for the motion natural frequency and the exciting frequency of wave, respectively. Through the analysis on the equation, it is found that the unstable and large motion response exists when the o/o0 equals to 2. Therefore, the parametric resonance occurs when the wave exciting frequency is around twice of the motion natural frequency.

Cross-References ▶ Fishing Ships ▶ High-performance Ship ▶ Jacket Platform ▶ Luxury Cruises ▶ Research Ship ▶ Semi-submersible Platform ▶ Service Ships ▶ Special Marine Vehicle ▶ Surface Warships ▶ Transport Ship

Conclusion Stability is the capability of the offshore structure to maintain its upright floating position both in still water and in waves, whether intact or damaged. It is one of the most essential performances for offshore structures and of prime importance for safety. Stability involves a series of calculation on the COG, COB, GM, hydrostatic curves, and stability curves based on the weight distribution, general arrangement, compartment, loading conditions, etc. Traditional stability calculations include inclining tests, intact stability, damage stability, as well as check based on stability criteria. In recent years, the dynamic stability in waves such as parametric resonance and excessive acceleration are also believed to be important parts of stability.

References ABS (2012) Rules for building and classing mobile offshore drilling units. American Bureau of Shipping, Houston, USA CCS (2005) Rules for construction and classification of mobile offshore drilling units. China Classification Society, Beijing, China DNV (2014) Offshore standard DNV-OS-C301 stability and watertight integrity Det Norske Veritas, Hovik, Norway France WN, Levadou M, Treakle T, Paulling JR, Michel RK, Moore C (2003) An investigation of head-sea parametric rolling and its influence on container lashing systems. Mar Technol 40(1):1–19 IMO (2009) Code for the construction and equipment of mobile offshore drilling units International Maritime Organization, London, United Kingdom Yu LW, Taguchi K, Kenta A, Ma N, Hirakawa Y (2017) Model experiments on the early detection and rudder stabilization of ship parametric roll. J Mar Sci Technol 3:1–23

I

852

Integrated Navigation

Scientific Fundamentals

Integrated Navigation Main Underwater Navigation Technology Qing Zhang College of Automation, Harbin Engineering University, Harbin, China

Synonyms Acoustic positioning system (APS); Auxiliary navigation; Doppler velocity log (DVL); Global navigation satellite system (GNSS); Longbaseline (LBL); Magnetic compass (MCP); Multi-source information fusion navigation; Numerically controlled oscillator (NCO); Short baseline (SBL); Strapdown inertial navigation system (SINS); Time of flight (TOF); Ultra-short baseline (USBL)

Definition Integrated navigation refers to the use of two or more different navigation systems to measure the same information source and extract the errors of each system from the comparative values of these measurements to correct each system. The navigation system using integrated navigation technology is called an integrated navigation system, and the navigation systems involved in the integration are called subsystems. As the inertial navigation system has the advantages of autonomy, concealment, information comprehensiveness, and broadband, it is generally used as the key subsystem of integrated navigation system. Besides the inertial navigation system, the integrated navigation system may be composed of different radio navigation systems, satellite navigation systems, acoustic positioning systems, geophysical navigation, and so on. There are many ways and depths of combination. Integrated navigation can take the advantages of each system, make up for its shortcomings, and improve positioning accuracy and data redundancy. So the integrated navigation system is more reliable and complex than a single navigation technique.

Inertial Navigation

Inertial navigation is fully autonomous navigation that does not receive external signals or transmit signals to the outside. With three orthogonal gyros and three orthogonal accelerometers, the inertial navigation system can continuously measure the three orthogonal linear accelerations and the three orthogonal angular rates in an inertial reference frame. By navigation calculation, the information of position, altitude, and velocity is acquired. Two types of inertial navigation systems are platform and strapdown. Due to the influence of cost, energy, volume, and other factors, the strapdown inertial navigation system (SINS) is usually used for underwater vehicles. With the rapid development of the fiber-optic gyro, SINS will be more accurate, smaller in size, more reliable, cheaper, and lower in energy consumption. However, the system errors of SINS will accumulate over time, which is difficult to meet the long-distance and long-time navigation requirements. Therefore, the external navigation information from other navigation systems is necessary for SINS to correct diffuse navigation errors. Global Navigation Satellite System (GNSS)

GNSS is a global, all-weather, high-precision, continuous and real-time navigation and position system based on radio. GNSS has the advantage of not accumulating errors with time and the obvious disadvantage of no signal underwater. In the long-distance navigation, the underwater vehicles can float onto the surface of water regularly to correct the accumulating velocity or position errors of the other navigation systems. Acoustic Positioning System (APS)

Compared with the electromagnetic signal, the acoustic signal travels farther in water. Therefore, acoustic transmitter can be used as the beacon of underwater vehicles. At present, long-baseline (LBL), short baseline (SBL), and ultra-short baseline (USBL) are the three main APS methods. All three navigation methods need to know the ocean

Integrated Navigation

condition in advance. Transducers or transducer array devices are deployed in the sea area beforehand. One or more acoustic sensors pre-installed on the underwater vehicles receive a pulse signal emitted by the transducer acoustic source. The relative position of the transducer acoustic source and underwater vehicles can be obtained by calculating the received pulse signal according to the pre-set mathematical model. APS has no position error accumulation in underwater vehicle navigation. Accuracy of APS is related to the baseline length and the distance between the APS and the underwater vehicles. LBL positioning principle is triangulation with at least three acoustic transponders, which are deployed in the mission area. For SBL, transponders are installed at both ends of the hull of the mother ship, and triangulation is used, and the baseline is determined by the size of the mother ship. The USBL method can determine the relative position of underwater vehicles to the mother ship, and the relative distance and orientation are solved by the time of flight (TOF) and the phase difference of an acoustic pulse arriving at different receivers on the bottom of the mother ship. Geophysical Navigation

Geophysical navigation needs to be able to establish relatively accurate underwater environmental survey maps of geophysical parameters (such as seabed depth, gravity, magnetic field, etc.) in advance. Because the seabed structure, topography, and depth are different in different sea areas, underwater vehicles can estimate their positions by measuring the geophysical parameters and comparing with the previous underwater environmental survey maps of geophysical parameters. The precondition of geophysical navigation is that the measured parameters vary sufficiently in spatial distribution. Auxiliary Navigation Device Doppler Velocity Log (DVL)

DVL is to calculate the relative velocity of underwater vehicles relative to the seabed or water layer by transmitting sound waves continuously to the bottom or water layer under the carrier and

853

according to the relationship between the returned beam and the emitted beam received by the receiver. DVL can measure the left, right, front, and back traveling velocities of underwater vehicles. DVL can work all-weather without being restricted by various environments. Magnetic Compass (MCP)

MCP measures the direction of the geomagnetic field through the magnetic sensor and then gives the angle between the longitudinal axis of underwater vehicles and the magnetic meridian in the horizontal plane, that is, the so-called magnetic heading angle. MCP is more susceptible to external interference, so its accuracy is low. However, because of its low cost, simple structure, and high reliability, it can be used as auxiliary navigation equipment for underwater vehicles. Work Principle At present, the commonly used underwater navigation positioning methods include inertial navigation, terrain matching, dead reckoning, geophysical navigation, and acoustic navigation. Various single navigation methods have more or less deficiencies in accuracy, reliability, or other aspects, which cannot meet the needs of the development of underwater vehicles. In addition to improving the intrinsic performances of each single navigation device, the low-cost, highperformance integrated navigation has become another development direction of underwater navigation technology. Most of the underwater integrated navigation system is mainly based on the inertial navigation system, supplemented by acoustic navigation, gravity matching, terrain, and geomagnetic matching system. The common working principle of an integrated navigation system is shown in Fig. 1. Each navigation system provides corresponding navigation information, which is fused by the filtering method to obtain more accurate and reliable navigation information. According to different application environments and requirements, one or more other navigation modules are chosen for integrated navigation. The general process of building integrated navigation system can be described as follows: by modeling and analyzing

I

854 Integrated Navigation, Fig. 1 The principle of the integrated navigation system

Integrated Navigation

SINS

Positon Attitude Velocity

Positon Velocity

GNSS Positon Attitude Velocity

Positon APS

Geophysical navigation

Positon

Data Fusion

Velocity

DVL

Heading MCP

the system structure abstractly, the state equation and measurement equation of the system is established, and the state information or state error information of the system is estimated optimally by Kalman filter, and the optimal estimation is used to correct the navigation parameter information of subsystems. Data Fusion Technology The essence of the integrated navigation is a multi-sensor navigation information optimization processing technology, so information fusion technology is the key technology of integrated navigation. Kalman filter method is a recursive least mean square error estimation method in the time domain, which has the characteristics of engineering application and easy realization. Kalman filter is the basic technology of information fusion estimation in an integrated navigation system. Kalman filtering method includes the direct method that directly takes the navigation parameters as the estimation objects and the indirect method that takes navigation system error as the estimation objects. The direct method reflects the dynamic process of navigation parameters, while the indirect method uses error equation, which has some approximation (Yan et al. 2013).

However, the equation obtained by the direct method is non-linear, and the order of magnitude of each navigation parameter varies greatly, which easily affects the estimation accuracy. So the indirect method is generally used in engineering. The indirect method includes output correction and feedback correction, as shown in Fig. 2. (1) Output correction uses filter estimation as the output of the integrated system or as the output of INS to improve the accuracy of output, but it does not modify the internal error state of INS. The accuracy of filter estimation determines the accuracy of correction. Its advantage is that subsystems and filters work independently and are easy to be realized in engineering. The fault of filters will not affect the operation of the system, so it has high reliability. However, system model changes will occur during long-time operation, which will lead to the reduction of filtering accuracy. (2) Feedback correction is to feedback the filter estimation to INS and other navigation systems, whose error state will be corrected. The corrected parameters of INS and other navigation systems enter the next operation. In the feedback correction mode, the corrected attitude matrix is fed back into the system to participate in the solution, so the system error is always small, and there will

Integrated Navigation

855 Xˆ I

XI SINS

Output correction

+ Kalman Filter Other Navigation System

ΔXI Feedback correction

Integrated Navigation, Fig. 2 Output correction and feedback correction

be no model error, so it has higher accuracy. Engineering implementation is more complex, and filter failure will directly affect the system output, thereby reducing reliability. There are three common data fusion structures of centralized structure, distributed structure, and hybrid structure. (1) For the centralized fusion structure, there is a total data processing center to collect the data of the whole system. The data are processed and fused by the processing center according to the corresponding algorithm. Because the original data from all sensors are processed by the fusion center, there is no loss of information, and the performance is better, and the fusion result is optimal theoretically. (2) For the distributed fusion structure, each sensor has its independent data processor. First, they perform some operations and preprocess the data by themselves. Then they directly transmit the current state estimations to the main processor of the fusion center. After fusing all local state estimations, the fusion center outputs the global estimations. Therefore, the distributed fusion is also called sensor-level fusion or autonomous fusion. (3) Hybrid fusion structure is a synthesis structure of centralized structure and distributed structure. The fusion center can obtain either original information or local state estimations.

Typical Applications SINS/GNSS Integrated Navigation At present, the common modes of SINS/GNSS integrated navigation are loose integration, tight

integration, and ultra-tight integration. For these three combinations, there are differences in system structure, the physical quantity used in modeling and filtering algorithm. Loose Integration The GNSS and SINS of the loose integration system are independent of each other in their work, and the navigation data can be solved without changing the internal structure of each subsystem. The differences of position and velocity information obtained by GNSS and SINS are transmitted to Kalman filter as the observation of the integrated navigation system. The optimal estimation of error is used to correct the SINS. If any single system is not available for a short time, the loose integration system can still provide navigation output. The loose integration system has better robustness and accuracy than those of pure SINS. However, because the noise in the system is correlative, the system error may be largen. If there are less than four stars available, the longtime unlocking of the GNSS signal will cause error divergence of the whole system. The structure of the loose integration system is shown in Fig. 3. Tight Integration Tight integration does not directly use the position and velocity information given by all sensors but uses the intermediate quantities of the receiver: pseudo-range and pseudo-range rate. GNSS signal receiver is needed to give the original observation information. Tight integration not only has

I

856

Integrated Navigation GNSS signal receiver

RF Frontend

Integration

Baseband signal processing

Navigation Solution

GPS output Position Velocity

Data Fusion

SINS

IMU

Error compensation

SINS Solution

Position Velocity

SINS output

Integration output

Integrated Navigation, Fig. 3 Structure of loose integration

GNSS signal receiver

RF Frontend

Integration

Baseband signal processing

GPS output

Navigation Solution

pseudo-range pseudo-range rate Data Fusion

SINS

IMU

Error compensation

SINS Solution

pseudo-range pseudo-range rate

SINS output

Integration output

Integrated Navigation, Fig. 4 Structure of tight integration

all the advantages of loose integration but also can effectively improve the dynamic performance, anti-interference performance, and filtering accuracy of the system. The system structure diagram is shown in Fig. 4. Both theory and practice prove that tightly integration navigation has higher precision. Because tightly integrated navigation uses the original information of the receiver, it can still

provide high navigation accuracy even if there are less than four stars available. Because the observation information is irrelevant, the system error convergence speed is accelerated, and the GNSS cycle slip can be effectively suppressed by INS output. However, the structure of a tight integration system is more complex, which needs to change the internal structure of the receiver to

Integrated Navigation

857

achieve, and the computation is also large, and the real-time performance is not good. Ultra-tight Integration The ultra-tight integration navigation system is the most complex and the most precise integration mode. It combines INS with co-directional signal (I) and quadrature phase signal (Q) from the receiver correlator. The function of the GNSS receiver whose internal hardware structure needs to be changed is realized by software. The numerically controlled oscillator (NCO) of code ring and carrier ring are controlled by the output of navigation filter, which improves the ability of the receiver to keep signal tracking under high dynamic and interference conditions. When the receiver is out of the lock, the fast re-acquisition of the signal can also be realized by using accurate navigation parameters of the ultra-tight integration. The structure diagram is shown in Fig. 5. Because the ultra-tight integration system integrates signal tracking and data fusion, it has a complex structure, large computation, and is not easy to realize in engineering. Li et al. (2018) suggest an enhanced tightly coupled navigation approach using pseudo-range, Doppler, and carrier phase measurements, which can increase computation efficiency without iteration calculations.

INS/DVL Integrated Navigation The INS/DVL integrated navigation mainly uses the velocity of DVL to restrain the INS accumulation error. In many applications, the DVL-aided inertial navigation system uses a depth sensor and compass as auxiliary sensors. Figure 6 shows a typical SINS/DVL integrated navigation structure. In Fig. 6, the error state Kalman filter is used to estimate the SINS navigation errors. The navigation solution and the navigation error estimates are independent of each other. The navigation error estimates are transmitted to the SINS to reset the navigation parameters. Subsequently, the corrected navigation parameters are used as recent initial conditions of the navigation equations. DVL measures the velocity of the carrier relative to the sea bottom. Integrated Navigation Combining INS with USBL In the SINS/USBL integrated navigation system, SINS continuously outputs the real-time information of position, attitude, and velocity acquired by navigation calculation from the data measured by three orthogonal gyros and three orthogonal accelerometers. Using the method of phase difference or phase comparison to measure the phase differences of the acoustic unit, the position of the transponder/responder in the coordinate system of the acoustic array is obtained. The relative

GNSS signal receiver

RF Frontend

Integration Signal capture and tracking

Correlator

Q

Data Fusion

SINS

IMU

I

Error compensation

SINS Solution Integration output

Integrated Navigation, Fig. 5 Structure of ultra-tight integration

I

858

Integrated Navigation Velocity in b

DVL

Decompose in n frame

Velocity in n

Accelerometers

Specific force

Angular velocity

Compass Error state Kalman filter

Attitude

Navigation equation

Gyros

Pressure sensor

IMU Depth

SINS

Reset

Integrated Navigation, Fig. 6 SINS/DVL integrated navigation structure (Bao et al. 2019)

Positon Attitude Velocity

SINS PI +

ΔP

Kalman Filter

PU USBL

Integrated Navigation, Fig. 7 Schematic block diagram of SINS/USBL integrated navigation system

distance between the acoustic array and the underwater vehicles is calculated by the time of sound wave propagation in the water. USBL outputs the position information in the geographic coordinate system of underwater vehicles. Using the indirect filtering method, the differences between the position information of SINS and the position information of USBL are taken as the measurement quantities and output into the filter to obtain the optimal estimations of the states of the integrated navigation system. The navigation error of SINS is also corrected with the optimal estimations. The schematic block diagram of the SINS/USBL integrated navigation system is shown in Fig. 7.

Integrated Navigation Combining INS with Geophysical Navigation An integrated navigation system composed of INS and geophysical navigation, which uses inertial navigation as its core, can achieve highprecision navigation by correcting the cumulative error of the INS in real time using the geophysical field within traveling range of the underwater vehicles. The principle diagram of the geophysical navigation assisted INS is shown in Fig. 8. In Fig. 8, the measured geophysical data are obtained using geophysical sensors mounted on the vehicles (see Fig. 8a). Meanwhile, according to the estimated position provided by the INS, the

Intelligent Control Algorithms in Underwater Vehicles

859

Integrated Navigation, Fig. 8 Principle diagram of geophysical navigation assisted inertial navigation (Bao et al. 2019)

I estimated geophysical data are achieved from an existing geophysical reference map (see Fig. 8b). Then the measured geophysical data and the estimated geophysical data are transmitted to the navigation computer. The optimal matching position of the vehicle is determined by the matching algorithm (see Fig. 8c). Through fusing the INS position and the optimal matching position, cumulative errors of the INS can be effectively corrected and the navigation performance of the INS is improved (see Fig. 8d). Geophysical navigation mainly consists of terrain matching navigation, geomagnetic matching navigation, and gravity matching navigation.

Li Z, Wang D, Dong Y, Wu J (2018) An enhanced tightlycoupled integrated navigation approach using phasederived position increment (PDPI) measurement. Optik 156:135–147 Yan X, Ouyang Y, Sun F, Fan H (2013) Kalman filter applied in underwater integrated navigation system. Geodesy Geodynamics 4(1):46–50

Intelligent Algorithm Based ▶ Underwater Acoustic Sensor Network

Cross-References ▶ Auxiliary Navigation ▶ Doppler Velocity Log for Navigation System in Underwater Vehicle ▶ Long Baseline Underwater Acoustic Location Technology ▶ Multi-source Information Fusion Navigation

Intelligent Control Algorithms in Underwater Vehicles Changhui Song School of Engineering, Westlake University, Hangzhou, China

References

Synonyms

Bao J, Li D, Qiao X, Rauschenbach T (2019) Integrated navigation for autonomous underwater vehicles in aquaculture: a review. Inf Process Agric. https://doi. org/10.1016/j.inpa.2019.04.003

Advanced control; Automatic control; Fuzzy control; Neural network control; Optimal control; Robust control

860

Definition Intelligent Control Algorithm is a kind of control method, which could efficiently perform scheduled tasks with its own decision-making and optimization capabilities, derived from classical control theory and optimization algorithm. Underwater vehicles have become an important tool for various underwater tasks because they have endurance, stationarity, speed, and depth capability, as well as a higher factor of safety, than human divers. However, the marine environment is unstructured and hazardous, and the development of underwater vehicles will face many challenging scientific and engineering problems. In the last three decades, researchers have made great efforts to overcome these problems by using intelligent control algorithm in underwater vehicles.

Intelligent Control Algorithms in Underwater Vehicles

operating conditions of the system vary, it is necessary to retune the gains or parameters to obtain the desired performance, resulting in time consumption. Mathematical Model for Underwater Vehicle The nonlinear model of a 6 DOF to build the mathematical model that represents the underwater vehicle dynamics two reference frames were used; one referenced to earth (called the Earth-fixed frame) and another referenced to the vehicle (called the body-fixed frame), Fig. 1 (Hernández-Alvarado et al. 2016; Fossen 2002). Kinematic Model

The general velocity vector is represented as: v ¼ ½v1 v2 T ¼ ½u n w p q r T

Scientific Fundamentals Underwater vehicles have been widely used in many subsea tasks, and seven critical areas in ocean system engineering are identified as follows: system for characterization of the sea bottom resources; systems for characterization of the water column resources; waste management systems; transport, power, and communication systems; reliability of ocean systems; materials in the ocean environment; and analysis and application of ocean data to develop ocean resources (Asokan and Singaperumal 2008). Very often, according to the task, the underwater vehicle is required to continuously change its operating tool and/or to pick up and release loads causing a change in behavior. That results as an inherent change in its weight, buoyancy, and hydrodynamic forces and as a consequence, a decrease in the position tracking performance. In addition, underwater vehicles have to deal with the highly dynamical underwater environment represented in the form of ocean currents and waves in shallow water (Xu et al. 2006; Xu and Xiao 2007). With this in mind, when the dynamic characteristics of the system are time dependent or the

ð1Þ

where u, n, and w are components of the linear velocity in surge, sway and heave directions, respectively, and p, q, and r are components of the angular velocity in roll, pitch, and yaw, respectively. The position vector 1  R3 and orientation vector 2  R3 coordinates expressed in the Earth-fixed frame are:  ¼ ½1 2 T ¼ ½x y z f y c T

ð2Þ

where x, y, and z represent the Cartesian position in the Earth-fixed frame and f represents the roll angle, θ the pitch angle, and c the yaw angle. The relationship between velocities in the Earth-fixed and body-fixed frames is

_ 1 _ 2

¼

J 1 ð 2 Þ

O33

O33

J 2 ð 2 Þ



v1 v2

ð3Þ

where J1(2)  R3  3 is the rotation matrix which expresses the transformation from body-fixed to Earth-fixed frame, and J2(2)  R3  3 is another transformation matrix that relates the angular velocity v2  R3 with the time derivative of 2  R3.

Intelligent Control Algorithms in Underwater Vehicles

861

I Intelligent Control Algorithms in Underwater Vehicles, Fig. 1 Frame coordinates of an underwater vehicle (Hernández-Alvarado et al. 2016)

Hydrodynamic Model

Equations of motion are expressed by the following equation, Mv_ þ CðvÞv þ DðvÞv þ GðÞ ¼ t _ ¼ J ðÞv

represented in terms of relative velocity of the vehicle and the currents, vr ¼ v  vCI

ð4Þ

where v  Rn and   Rn were previously defined, M  Rn  n denotes the inertial matrix (including the added mass), C  Rn  n is the Coriolis matrix and centripetal forces (including the effects of added mass), D  Rn  n refers to the damping matrix, G  Rn  n represents the vector of gravitational forces, and t  Rn is the input control vector.

ð5Þ

where vCI ¼ [uC vC wC 0 0 0]T is a nonrotational vector of the current velocity according to Eq. (3). Note that the linear velocity on the fixed frame can be transformed to linear velocity in the equation by applying the elemental rotation matrices. Suppose the current velocity in the equation as constant or at least with a minimum variation, so that: v_CI ¼ 0 ! v_r ¼ v_

Ocean Currents

Ocean current is generated by wind, tide, variation of densities, and re-circulation of water, among others. The detailed information about ocean currents can be obtained from the model of induced ocean currents proposed by Fossen (2002). In the mentioned work, the equations of motion are

Then, the relative equations of motion become: Mv_ þ Cðvr Þvr þ Dðvr Þvr þ GðÞ ¼ t

ð6Þ

If the reader is interested in the derivation of the above formula, you can refer to the

862

literature: Marine Control Systems: Guidance (Fossen 2002). Traditional PID Control Methods and Its Limitations For decades, PID (Proportional + Integral + Derivative) controllers have been successfully used in academia and industry for many kinds of plants. This is thanks to its simplicity and suitable performance in linear or linearized plants, and under certain conditions, in nonlinear ones. A number of PID controller gains tuning approaches have been proposed in the literature in the last decades, most of them off-line techniques. However, in those cases wherein plants are subject to continuous parametric changes or external disturbances, online gains tuning is a desirable choice. This is the case of modular underwater vehicles where parameters (weight, buoyancy, added mass, among others) change according to the tool it is fitted with. In practice, some amount of time is dedicated to tune the PID gains of an underwater vehicle. Once the best set of gains has been achieved the underwater vehicle is ready to work. However, when the underwater vehicle changes its tool or it is subject to ocean currents, its performance deteriorates since the fixed set of gains is no longer valid for the new conditions (Hernández-Alvarado et al. 2016).

Intelligent Control Algorithms The control issue of underwater vehicles is very challenging due to the nonlinearity, time-variance, unpredictable external disturbances, such as the environmental force generated by the sea current, and the difficulty in accurately modeling the hydrodynamic effect. The well-developed linear controllers may fail in satisfying performance requirements especially when changes in the system and environment occur during the AUV operation since it is almost impossible to manually retune the control parameters in water. Therefore, it is highly desirable to have an AUV controller capable of self-adjusting control parameters when the overall performance degrades. Various advanced control schemes for underwater robots

Intelligent Control Algorithms in Underwater Vehicles

have been proposed in the literature as some of them are summarized below. Fuzzy logic control: The theoretical basis of fuzzy logic control is that any real continuous function over a compact set can be approximated to any degree of accuracy by the fuzzy inference system. For control engineering applications, researchers use fuzzy logic to form a smooth approximation of a nonlinear mapping from system input space to system output space. This makes it suitable for nonlinear system control. However, determining the linguistic rules and the membership functions requires experimental data and, therefore, very time-consuming, and the rule-based structure of fuzzy logic control makes it difficult to characterize the behavior of the closed-loop system in order to determine response time and stability. Neural network (NN) control: Neural networks attracted many researchers because they can achieve nonlinear mapping. Using NN in constructing controllers has the advantage that the dynamics of the controlled system need not be completely known (Yuh 1994). This makes NN suitable for underwater vehicle control. However, NN-based controllers have the disadvantage that no formal mathematical characterization exists for the closed-loop system behavior. The validation of the final design can only be demonstrated experimentally. There are mainly two approaches to use NN for control purpose: learning with a forward model and direct learning. In the former approach, generally, the forward model is trained by the output error or state error and then used for gain derivation (Shi et al. 2006), while in the latter approach, the state or output error is used directly to map the desired control input. Sliding mode control (SMC): SMC restricts the system states inside a certain subspace of the whole state space and makes them asymptotically converge to their equilibrium point. It requires a raw estimation of the system parameters and an estimation of the system uncertainty for the switching surface design and variable-structure control law design. Even though SMC has been well known for its robustness to parameter variations, it has the inherent problem of chattering phenomenon.

Intelligent Control Algorithms in Underwater Vehicles

Optimal/robust control: The principles of the optimal/robust control are calculus of variations, Pontryagin maximum principle, and Bellman dynamic programming. However, due to the difficulty of deriving an accurate model of AUV system, it is difficult to apply optimal control directly. Therefore, generally optimal control combined with system identification or robust control is used in AUV control (Zhao and Yuh 2005 and Yuh 1990). Fuzzy Control Algorithms Classical control theory is based on mathematical models that describe the behavior of the plant or system under consideration. Fuzzy systems are known for their capabilities to approximate any nonlinear dynamic system (Wang 1992). The main idea of fuzzy control is to build a model of a human control expert who is capable of controlling the plant without thinking in mathematical model terms. AUV’s fuzzy modeling is constructed based upon the input-output data that have been characterized from the open loop system results of the AUV’s mathematical model. The input data is considered as the force generated by thruster or pump which moves the AUV in a certain direction, and the output data is considered as the

863

resulted linear or angular velocity of the vehicle taking into account the coupling effect of the other degree of freedom in that direction. Figure 2 shows the configuration of a fuzzy model system, which it consists of three fuzzy logic modules that represent surge, pitch, and yaw motions. A Mamdani fuzzy controller was used in this section. Fuzzy Modeling AUV Surge

For surge motion fuzzy model, the input for the fuzzy logic control is the force required for the thruster, X, to produce the desired motion of the AUV in forward motion corresponding to desired pose. The output of the fuzzy control is the linear velocity in x-direction, u. Fuzzy Modeling AUV Pitch

For pitch motion fuzzy model, the input for the fuzzy logic control is the force required for the pumps (one pump for up direction and the other one for down) to produce the desired rotation of the AUV in pitch motion corresponding to desired pose. There are three outputs for this fuzzy model. The first output of the fuzzy control is the linear velocity in x-direction, u, and this output represents the coupling effect on the forward direction, which means the effect of the pitch motion on the

Intelligent Control Algorithms in Underwater Vehicles, Fig. 2 The configuration of fuzzy modeling for the underwater vehicle (Hassanein et al. 2011)

I

864

Intelligent Control Algorithms in Underwater Vehicles

Fuzzy Controller Design

For surge motion, the inputs to the fuzzy controller are “x” potion error and its error difference. The output of the fuzzy controller is the force required by the thruster. The membership function for this controller is shown in Fig. 4. The total number of rules used for the fuzzy controller is 9. For pitch motion, the inputs to the fuzzy controller are pitch angle error and its error difference. The output of the fuzzy controller is the time required to operate the pump to rotate the AUV in the required direction. The membership functions are the same for surge fuzzy control with different values. For yaw motion, the inputs to the fuzzy controller are yaw angle error and its error difference. The output of the fuzzy controller is the time required to operate the pump to rotate the AUV in the required direction. The membership functions are the same for surge fuzzy control with different values (Hassanein et al. 2011).

The fuzzy controller is shown in Fig. 3, where the inputs to the fuzzy controller are the error and error difference. Generally the depth of AUV can be maintained by controlling the pitch and forward motion. Moving right and left of AUV can be achieved by controlling the yaw angle. The pitch and yaw angles are controlled by controlling the operating time of the pump that is responsible for moving the AUV in that direction.

Neural Networks (NN) Control Algorithms PID control is widely used underwater vehicle control systems. In the absence of accurate mathematical model for underwater vehicle systems, a PID controller may be the best controller, because it is model-free, and its parameters can be adjusted easily and separately. Tuning of PID controllers depends on adjusting its parameters

forward motion. The second output represents the coupling effect on heave direction. The third output is the angular velocity about y-axis, q. Fuzzy Modeling AUV Yaw

For pitch motion fuzzy mode, the input for the fuzzy logic control is the force required for the pumps (one pump for right direction and the other one for left) to produce the desired rotation of the AUV in yaw motion corresponding to desired pose. There are three outputs for this fuzzy model. The first output of the fuzzy control is the linear velocity in x-direction, u, and this output represents the coupling effect on the forward direction, which means the effect of the yaw motion on the forward motion. The second output represents the coupling effect on sway direction. The third output is the angular velocity about z-axis, r.

Intelligent Control Algorithms in Underwater Vehicles, Fig. 3 The structure of the fuzzy control system for underwater vehicle (Hassanein et al. 2011)

Intelligent Control Algorithms in Underwater Vehicles

865

I

Intelligent Control Algorithms in Underwater Vehicles, Fig. 4 Membership functions for the error and the derivative of the error (Hassanein et al. 2011)

(i.e., Kp, Ki, Kd), so that the performance of the system under control becomes robust and accurate according to the established performance criteria. The proposed auto-tuning algorithm is based on NN which exhibit the following characteristics: 1. Parallelism and generalization. A NN is able to produce useful outputs for inputs not provided under the learning phase. 2. Non-linearity. A NN can be linear or not allowing it to represent systems generated by nonlinear guidelines. 3. Adaptability. NN is capable of re-adjusting weights and adapting to new environmental situations. This is especially useful when the system offers non-stationary data, that is, the properties involved by the system vary over time.

4. Fault tolerance. When an operational failure occurs on a local part of the network, it lightly affects the global performance. A block diagram of the auto-tuning control for underwater vehicle with an artificial neural network (NN) is shown in Fig. 5. In the discrete time domain, the digital PID algorithm can be expressed as follows: tðnÞ ¼ tðn  1Þ þ K p ðeðnÞ  eðn  1ÞÞ þ K i eðnÞ þ K d ðeðnÞ  2eðn  1Þ þ eðn  2ÞÞ where t(n) is the original control signal, e(n) ¼ d   represents the position tracking error, d denotes the desired trajectory, Kp is the proportional gain, Ki is the integral gain, Kd is the derivative gain, and n the sample time.

866

Intelligent Control Algorithms in Underwater Vehicles

Intelligent Control Algorithms in Underwater Vehicles, Fig. 5 Block diagram of an auto-tuned PID with artificial NN control (Hernández-Alvarado et al. 2016)

Intelligent Control Algorithms in Underwater Vehicles, Fig. 6 Block diagram of the implemented backpropagation NN (Hernández-Alvarado et al. 2016)

The algorithm used as auto-tuning is the backpropagation method, chosen for its ability to adapt to changing environments. Operation begins applying the inputs to the network (see Fig. 6), and this is propagated from the first layer to the hidden layers, up to produce output (Kp, Ki, and Kd). The output signal is compared to the desired output and an error signal is calculated for each of the outputs; this is shown in Fig. 5. The error outputs backpropagate, starting from the output layer, to all neurons in the hidden layer that contribute directly to the output; however, the hidden layer neurons receive only a fraction of the total error signal. This process repeats iteratively, layer by layer, until all neurons in the network have received an error signal describing its relative contribution to the total error.

Figure 6 presents the topology of the NN used to auto-tune the PID controller gains implemented on the ROV. u(n) and u(n1) are reference inputs (desired trajectory), y(n) and y(n1) are reference outputs (real trajectory), C(n) and C(n1) correspond to the control signals, wji are the weights of the hidden layer, and vji are the weights of the output layer. The criteria used to minimize the error:

Eð n Þ ¼

t 1X ðy ðkÞ  yðkÞÞ2 2 k¼1 r

The adjustments of weighting coefficients wji and vji can be made by means of the expressions:

Intelligent Control Algorithms in Underwater Vehicles

  @ey 2 wji ðn þ 1Þ ¼ wji ðnÞ þ a dx @eu j j   @ey 1 vji ðn þ 1Þ ¼ vji ðnÞ þ a d hj @eu

867

where the unknown nonlinear function of AUV dynamic is given by f ðxÞ ¼ MðqÞðq€d þ Le_ Þ þ Cðq_ Þðq_ d þ LeÞ þ Dðq_ Þq_ þ G

where a is the learning coefficient, wji(n + 1) is a vector of weights for the hidden layer, vji(n + 1) is the vector of weights of the output layer and @e equivalent gain @euy is unknown.

 T One may define  eT , e_ T , q_ Td , q€Td . A general sliding mode controller structure is based on t ¼ fb þ K v r  uðtÞ

Sliding Mode Control Algorithms Because of the nonlinearity and the unpredictable operating environment of the AUVs, many design parameters must be considered during the design of AUVs control system. Indeed, the high frequency oscillating movement can seriously affect the performance of sensors, especially optical and acoustical sensors. In brief, the main factors that make the control of AUVs difficulty are: (1) the highly nonlinear, time-varying dynamic behavior of the AUVs; (2) uncertainties in hydrodynamic coefficients; and (3) disturbances by ocean currents. To remedy these aforementioned problems and enhance the AUVs performance along with strengthen robustness, adaptability, and autonomy, it is necessary that the motion control system has the ability of learning and self-adaptation. The AUV dynamic in (4) can be rewritten as M€ q þ Cðq_ Þq þ Dðq_ Þq þ G þ td ¼ t

ð7Þ

Moreover, q is the configuration and td represents environmental forces and/or disturbances. To make the AUV follow a prescribed desired trajectory qd(t), we define the tracking error e(t) and filtered tracking error r(t) by e ¼ qd  q, r ¼ e_  Le with Λ > 0 a positive definite design parameter matrices. The AUV dynamics are expressed in terms of the filtered error as Mr_ ¼ Cr þ f ðxÞ þ td  t

with fb an estimate of f(x), K v r ¼ K v e_ þ K v Le an outer PD tracking loop, an u(t) an auxiliary signal as uðtÞ ¼ ðFðxÞ þ Þ sgn ðr Þ where sgn(.) is the sign function and F(x) is a known function which can be computed using the boundedness property of AUV’s dynamics. This term is used to maintain the robustness in the face of external forces, disturbances, and modeling error.  is a design parameter and can be selected as a small value. Employing this controller, the closed-loop error dynamics are Mr_ ¼ Cr  K v r þ fe þ td þ uðtÞ where the function approximation error is defined as fe ¼ f  fb     so that fe  FðxÞ and k.k is Frosenius norm. The stability and numerical simulation of the introduced sliding mode control system can be obtained in the work of Tabar et al. (2015). Optimal Control Algorithms To achieve better robustness and handling coupling in the system dynamics, MIMO-based techniques such as LQR method has been reported. The literature revealed that LQR provides better performance over classical control scheme such as

I

868

Intelligent Control Algorithms in Underwater Vehicles

PID though with higher design and implementation complexity. On the other hand, it represents the simplest model-based MIMO controller in terms of design and implementation when compared to others such as H-infinity, m-synthesis, and nonlinear controllers. However, LQR control is a well-known optimal control method, and the optimality of the resulting compensator is a subject of appropriate design parameters’ (Q and R) selection. However, one of the common challenges associated with LQR and generally with the majority of modern control techniques is their dependency on selection of appropriate design parameters. The selection is usually based on technical guess followed by several iterative tunings which are mostly based on trial and error for a given question. Considering the complexity and dimension of the underwater vehicle, this conventional trial and error design approach would be time consuming in proportionate with experience of the designer, and often limits the achievable control performance objectives which are usual conflicting. In order to overcome this, the control problem is formulated as a multiobjectives optimization task, and a proposed multi-objectives differential Evolution algorithm is applied to achieve an optimal/suboptimal compromise between the performance objectives (Alvis et al. 2007; Castillo-Effen et al. 2007; Tijani 2012). Optimization Problem Formulation

The optimization problem is to determine the set of decision vectors F, which in this context is the weighting matrices Q and R’s parameters: F  F≔ F1



F_n þm



that minimizes the cost function: Jb ¼

1 ð



xbT Qxb þ dT Rd

subject to Q  0 and R  0 with 0 < Fj < Hj where Hj is the upper bound on the decision parameter Fj. The problem is casted as nonconstraint optimization problem, meanwhile, depends on design goal and application requirements; it is possible to introduce additional constraints such as frequency response parameters or actuator limitation. Figure 7 shows the proposed design method. As shown in the Fig. 1, the performance objective function is given by the response of the fullstate feedback system formed for a given decision parameter set. In this study, five control objective functions are defined for the pitch angle tracking control as follows: h

f i ðFÞ≔

ðu,w,qÞ

tys , OS y , max ts

,

max bðu,w,qÞ , max d

i

where tys and OSθ are the settling time and percentage overshoot of the pitch angle θ, respectively, max β(u, w, q) is the maximum off-axis (other states, {u, v, w}) settling time, max β(u, w, q) is the maximum peak of the off-axis response, and max δ is the maximum control signal expended. Application to the UUV System

In tracking and regulation control problem as shown in the Fig. 7, the system states are first augmented with two extra integral states vector to improve the tracking performance. The new state vector xi is given as: 2 xi ≔4u, q, w, y,

1 ð

3 ydt 5

0



0

And set of performance objectives of size Ω: min f i ðFÞ, i ¼ 1, 2, , O

The augmented state space model is then expressed as: x_ i ≔Ai xi þ Bi d and the control law becomes:

Intelligent Control Algorithms in Underwater Vehicles

869

MODE-LQR ALGORITH

Σ

∫

-Klqr

d

_

qref

x

PLANT

[u,q,w] qout Intelligent Control Algorithms in Underwater Vehicles, Fig. 7 Block diagram of the proposed MODE-Based LQR controller synthesis (Tijani and Budiyono 2016)

di ¼ Kxi As indicated in Fig. 7, the design procedure involves placing the MODE in the LQR conventional design loop for optimal tuning of the Q and R matrices, and can be summarized step-wise as follows: Step 1: Specify the optimization parameters: population size, NP, decision vector size, Z, DE cross-over constant, CR, and generation size, GEN. Step 2: Specify the dimension of the Q and R matrices and initialize population P of size NP for the Q and R matrices’ parameters. Step 3: Test for the positive definiteness of the initialized matrices, and remove any unfit parameters set(s); repeat step 2 to complete the size of population. Step 4: Compute the objective function and extract the objectives vector for the population. Step 5: Start the optimization process: while the stopping criteria are untrue, e.g., repeat steps 6 to 9 else go to step 10 GEN k while. Step 6: Generate new child vector from randomly selected three vectors from the old population using the DE operation of mutation and crossover processes. Test the positive definiteness of the child vector and compute its objective function.

Step 7: Compete the child vector with the parent vector for Pareto dominance. That is, determined if the child vector dominates the parent vector. If not, repeat step 6 to 7, else proceed to step 8. Step 8: Update the new population with the dominant child vector. Step 9: Compute the stopping criteria and update the generation count: k ¼ k + 1. Step 10: Stop the optimization and report the Pareto-dominance candidates. The numerical simulation of the introduced optimal control system can be obtained in the work of Tijani and Budiyono (2016).

Key Applications In the work of Hernández-Alvarado et al. (2016), the intelligent control was implemented on an underactuated mini-ROV. This vehicle is a ROV developed in CIDESI named Nu’ukul Ja (which in the Mayan language means “water instrument”). Its dimensions are: 50 cm long, 30 cm wide, and 30 cm height; as shown in Fig. 8. It has a cylindrical pressure chamber of 15 cm diameter where the major part of the electronic architecture is placed. The total weight of the ROV is 10 kg. According to the experimental environment, it was placed in a pool of 2.5 m where both PID

I

870

Intelligent Control Algorithms in Underwater Vehicles

Intelligent Control Algorithms in Underwater Vehicles, Fig. 8 Underactuated mini-ROV under water (HernándezAlvarado et al. 2016)

controllers (auto-tuned and conventional) were implemented. The gains of the conventional PID control were obtained by means of the NN. The ROV was requested to get the set point of 1 m depth by using the Auto-tuned PID controller. Once the ROV reached the stability and the PID gains, computed by the NN, became stationary, these gains were programmed into the conventional PID as Kp, Kd, and Ki. This way the conventional PID gains were tuned. It is important to remark that once the conventional PID was tuned, the gains remained constant along the experiment, even when the disturbances took place, unlike the auto-tuned PID controller wherein gains were dynamically changing to attain better performance along the experiment. The controls were evaluated by performing a data capture of 3 m, once the ROV was placed 1 m underwater. In the first minute, nondisturbance took place. After this time, the weight was increased by 400 g as disturbance until 2 min mark. Finally, in the last minute of data capture, the weight was removed. Figure 9 shows the desired trajectory (solid line) versus the real path (dotted line) and the control signals for thrusters (Hernández-Alvarado et al. 2016). Apparently, the control signal given by the auto-tuned PID (shown in Fig. 9), seems to be more active than the conventional PID’s signal; though, the root mean square (RMS) value of each

one (the complete experiment) shows that the RMS of the conventional PID is 6.8874 whereas in the auto-tuned PID is 6.6781. The auto-tuned PID has a 3.038% of energy saving against the conventional PID. The experimental work (Zhao and Yuh 2005) of the proposed controller was carried out on ODIN III, which is shown in Fig. 10. It is a six-DOF autonomous underwater robot developed by the Autonomous Systems Laboratory of the University of Hawaii. It is a close-framed sphere-shaped vehicle that makes its dynamics in each direction nearly identical. It has eight thrusters: four horizontal and four vertical, which make ODIN III capable of six-DOF maneuvering and also have thrust redundancy for fault tolerance purpose. It also has various navigation sensors including eight sonar sensors, a pressure sensor, and an Inertial Measurement Unit (IMU). The eight sonar sensors are used to measure the displacements in the horizontal plane, the pressure sensor is used to measure the depth of the vehicle, and the IMU is used to measure the angular displacements. A Kalman filter is used to suppress the sensor noise and to estimate the translational and angular velocities. All the tests were done in the diving pool of Kahanamoku Pool at the University of Hawaii. The effectiveness of the control system was experimentally investigated by implementing three controllers: PID, PID plus DOB, and

Intelligent Control Algorithms in Underwater Vehicles

871

Intelligent Control Algorithms in Underwater Vehicles, Fig. 9 (a) Conventional PID controller, (b) auto-tuned PID (Hernández-Alvarado et al. 2016)

Intelligent Control Algorithms in Underwater Vehicles, Fig. 10 Omni-Directional intelligent navigator (ODIN III), (a) View in water, (b) Inside view (Zhao and Yuh 2005)

ADOB on the autonomous underwater vehicle, ODINIII. Figure 11 shows tracking performance in x, y, and z. The ADOB consists of the regressor-free adaptive control and DOB, taking advantages of DOB robustness with respect to external disturbances and modeling errors, and the regressorfree adaptive controller’s robustness with respect to uncertainties in the system model. The ADOB controller has the capability of self-tuning control gains and adapting to changes in the system and

environment while PID requires a lengthy pretuning process for satisfactory performance. The PID would need retuning control gains when the performance degrades due to changes in the system and environment. However, it is almost impossible to retune control gains of underwater robots until they are brought up to the surface where hydrodynamics would change again. Therefore, as shown in the experimental result (Fig. 11), the ADOB controller is promising for underwater vehicles, especially when the

I

872

Intelligent Control Algorithms in Underwater Vehicles

Intelligent Control Algorithms in Underwater Vehicles, Fig. 11 (a) PID control with external disturbance, (b) PID plus DOB control with external disturbance, (c) ADOB control with external disturbance (Zhao and Yuh 2005)

performance degrades or fails by PID type controllers (Zhao and Yuh 2005).

Cross-References ▶ Advanced Control ▶ Automatic Control ▶ Fuzzy Control ▶ Optimal Control ▶ Robust Control

References Alvis W, Castillo C, Castillo-Effen M, Moreno W, Valavanis KP (2007) A tutorial approach to small unmanned helicopter controller design for nonaggressive flights. In: Advances in unmanned aerial vehicles. Springer, Dordrecht. 119–170 Asokan T, Singaperumal M (2008) Autonomous underwater robotic vehicle (AUV) project. Indian Institute of technology, Madras Castillo-Effen M, Castillo C, Moreno W, Valavanis KP (2007) Control fundamentals of small/miniature helicopters-a survey. In: Advances in unmanned aerial vehicles. Springer, Dordrecht. 73–118

Internal Turret Single-Point Mooring (SPM) System Fossen TI (2002) Marine control systems: guidance, navigation and control of ships, rigs and underwater vehicles. Marine Cybernetics, Trondheim Hassanein O, Anavatti SG, Ray T (2011) Fuzzy modeling and control for autonomous underwater vehicle. In: The 5th international conference on automation, robotics and applications, pp 169–174 Hernández-Alvarado R, García-Valdovinos LG, SalgadoJiménez T, Gómez-Espinosa A, Fonseca-Navarro F (2016) Neural network-based self-tuning PID control for underwater vehicles. Sensors 16:1429 Shi Y, Qian W, Yan W, Li J (2006) Adaptive depth control for autonomous underwater vehicles based on feedforward neural networks. In: Intelligent control and automation. Springer, Berlin, Heidelberg. 207–218 Tabar AF, Azadi M, Alesaadi A (2015) Sliding mode control of autonomous underwater vehicles. World Academy of Science, Engineering and Technology. Int J Comput Electr Autom Control Inf Eng 8(3): 546–549 Tijani IB (2012) Flight control system with MODE based H-infinity for small scale autonomous helicopter. PhD thesis submitted to Mechatronics Engineering Department, IIUM, Malaysia Tijani IB, Budiyono A (2016) Control of an unmanned underwater vehicles using an optimized LQR method. Mar Underw Sci Technol, ISIUS 1(1):41–48 Wang LX (1992) Fuzzy system are universal approximators. In: IEEE proceeding of international conference on fuzzy systems, pp 1163–1170 Xu YR, Xiao K (2007) Technology development of autonomous ocean vehicle. Acta Automat Sin 33(5):518–521 Xu YR, Pang YJ, Gan Y, Sun YS (2006) AUV-state-of-theart and prospect. CAAI Tran Intell Syst 1(1):9–16 Yuh J (1990) Modeling and control of underwater robotic vehicles. IEEE Trans Syst Man Cybern 20:1475–1483, https://ieeexplore.ieee.org/ Yuh J (1994) Learning control for underwater robotic vehicles. IEEE Control Syst Mag 14:39–46, https:// ieeexplore.ieee.org/ Zhao S, Yuh J (2005) Experimental study on advanced underwater robot control. IEEE Trans Robot 21(4):695–703

Intensified Silicon Intensifier Target (ISIT)

873

Internal Tieback Connector (ITBC) ▶ Steel Pipelines and Risers

Internal Turret Single-Point Mooring (SPM) System Yougang Tang Tianjin University, Tianjin, China

Synonyms Mooring system; Positioning system; Singlepoint mooring system

Definition Internal turret single-point mooring system is a type of single-point mooring device and belongs to the turret type single-point mooring device. This type of single-point mooring is moored to the seabed through uniform or grouped anchor chains on a turret inside the hull. The FPSO hull rotates 360
around the internal turret under wind, wave, and flow environmental loads. It has a “weathervane effect,” which makes the hull adjust to the direction with smallest load. Because the SPM pontoon and turret are installed inside the hull, it is called the internal turret SPM system. The crude oil enters the oil storage tank through a subsea pipeline into a rotary sealed joint in the internal turret.

▶ Underwater Lander

Development History

Internal Rate of Return (IRR)

The world’s first SPM pontoon was designed by IMODCO in the United States in 1959 and put into production in the port of Detio (Yifeng 2012), Sweden. It is used as a deep water transport dock. The pontoon is connected to the sea floor by

▶ Christmas Tree

I

874

Internal Turret Single-Point Mooring (SPM) System

Internal Turret Single-Point Mooring (SPM) System, Fig. 1 The world’s first SPM pontoon (Yifeng 2012)

mooring lines, and the oil tanker is connected to the SPM device by steel cables (Fig. 1). In the early 1980s, SBM Company first proposed a turret concept based on the principle of “weathervane effect” (Yifeng 2012). In 1985, an external turret was installed on the bow of a 140,000-ton floating storage tanker, which makes the concept formally applied to reality (Yifeng 2012). The advantage of the outer turret SPM is that the tanker’s weathervane effect is significant, which makes the rotation to the position with the smallest environmental load become easy, and does not occupy the hull storage space, so the oil tanker has high oil storage efficiency; the shortcoming is that the bow movement is the most responsive, especially in deep water mooring, and the riser and turret of the outer turret device are all within the range of wave slamming, which easily causes damage of the riser and the turret. Therefore, the outer turret SPM is only suitable for medium-deep waters with better marine environment. In the early 1990s, the internal turret SPM system was proposed, in order to overcome the shortage of out turret SPM and meet the development demand of deep water oil and gas fields which are over 100m. (Zhigang and Yanping 2006), the internal turret SPM system was proposed. The early internal turret SPM system2 is generally the permanent type. In order to adapt the FPSO mooring demand under the harsh sea

conditions, the development trend is the internal turret SPM system of detachable type.

Operational Principle and Component The Internal Turret SPM System of Permanent Type The early internal turret mooring system was not detachable. Generally the SPM is designed under the sea condition once in 100 years, to provide sufficient weathervane effect and mooring force under severe sea conditions and ensure the FPSO has mooring and transmission capabilities under most sea conditions. Some internal turret mooring systems of permanent type are equipped with locking devices that are tightened as necessary to limit the sudden movements of the hull. The internal turret mooring system installed in the Marlim Leste field in Camps Bay (Zhigang and Yanping 2006), Brazil, in 2007 would be the world’s largest internal turret mooring system of permanent type. It can accommodate up to 75 hoses and is moored with 8 mooring legs in combination of polyester ropes and anchor chains. The Internal Turret SPM System of Detachable Type The detachable type is the development trend of SPM system. The detachable internal turret mooring system can be quickly disengaged and return

Internal Turret Single-Point Mooring (SPM) System

according to the working sea conditions, and can be quickly released under extreme sea conditions to avoid dangerous sea conditions that may cause personal injury and damage to floating structures. It is more suitable for offshore oil fields in harsh environments and complex sea conditions. The detachable internal turret mooring system is mostly in the form of internal turret pontoon. This single-point mooring system can be installed at sea at an early stage, which shortens the time for FPSO return operations. In recent years, the detachable internal turret SPM system is gradually designed under the conditions that FPSO is not released under the sea conditions of 100 years, making the mooring system to have the function that does not have to be released when faced with typhoon, further ensuring the personal and platform’s safety and normal production. Common detachable internal turret mooring system includes: pontoon turret mooring system, submerged turret handling system, and submerged turret production system (Shan et al. 2008). The internal turret mooring system consists of a pontoon and an internal turret which is inside the bow and connected by structural connectors. The pontoon can provide sufficient buoyancy to

Internal Turret SinglePoint Mooring (SPM) System, Fig. 2 The internal turret SPM system of detachable type (Shan et al. 2008)

875

withstand the weight of the mooring legs and risers. The pontoon turret mooring system is capable of repairing critical components such as manifolds under severe sea conditions. The installation of turret can be carried out in dock, reducing the amount of on-site installation work at sea. The submerged turret handling system consists of an underwater buoy and a complete turret system. The inside of the conical buoy moored to the sea floor is a turntable that connects the mooring chain and the riser system. The outer structure of the pontoon can be rotated around the turret with the hull. The submerged turret handling system can be released in any climatic conditions, and it also has a function of simple quick release and return for high safety. The submerged turret production system is a production of a submerged turret handling system and mooring technology combined with a multifunction rotary joint. It is a new generation of internal turret SPM system that integrates mooring system, turret device, and rotary joint. Figure 2 shows the detachable internal turret SPM system (http://image.baidu.com/search/index? tn¼baiduimage&ps¼1&ct¼201326592&lm¼-1& cl¼2&nc¼1&ie¼utf-8&word¼FPSO; Zhao 2009). The submerged internal turret SPM mainly includes: the slip ring stack, the pontoon, the

I

876

locking device, the mooring system, and so on. The details are as follows: (1) The Slip Ring Stack The slip ring stack, also known as the rotary joint assembly, is one of the key equipments for the mooring system. It consists of a well-flow rotary joint, an electric rotary joint (electric slip ring), a common rotary joint (common slip ring), and a supporting hydraulic control system. The rotary joint assembly is composed as shown in Figs. 3 and 4. 1. The well-flow rotary joint: The inlet end is connected to the underwater flexible hose, and the outlet end is connected to the FPSO production processing module inlet line to form a crude oil output passage. A hydraulic oil seal system is arranged on the well-flow rotary joint to ensure normal operation without leakage. 2. The electric rotary joint: Power is supplied to the platform through the electric rotary joint

Internal Turret Single-Point Mooring (SPM) System

and power cables for use on equipment and facilities. 3. The hydraulic rotary joint: The hydraulic rotary joint provides hydraulic power to control the emergency shutoff valve. 4. The emergency shutoff valve: It is used to shut off the oil passage in an emergency state.

(2) The Pontoon The pontoon is conical, and its schematic diagram is shown in Fig. 5. The upper part of the pontoon is provided with a bearing assembly, and the lower part is connected to the mooring line through the lifting-eye to transmit the mooring tension. The upper part is fixed to the FPSO by a special hydraulic locking device. The FPSO rotates or drifts around the mooring center under the action of environmental loads such as wind, wave, and current through the bearing assembly on the pontoon. (3) The Locking Device The locking device is located in the singlepoint compartment, clamping and locking the pontoon, so that the FPSO is integrated with the SPM to achieve safe production. The locking device is the most critical device of a SPM system. In actual production operations, the locking device must maintain sufficient preload. (4) The Mooring System

Internal Turret Single-Point Mooring (SPM) System, Fig. 3 The slip ring stack

Most of the mooring systems adopt asymmetrical arrangement of 3  3 and 3  4. This mooring arrangement has better adaptability to sea areas with bad conditions. In the design of the mooring system, the weighting block is generally added to the mooring line which section is laid on the seabed in order to increase the recovery stiffness and improve the resilience of the mooring system. According to this design, the length of anchor chain laid on the seabed could be reduced and the construction and installation could be more facilitated.

Internal Turret Single-Point Mooring (SPM) System

877

Internal Turret SinglePoint Mooring (SPM) System, Fig. 4 The components of slip ring stack

I

Application The internal turret SPM is widely used, and most of the FPSOs worldwide use the internal turret SPM. The internal turret SPM device is located in the bow opening of the hull. The advantage is that the diameter of the turret can be designed to be large, which can provide sufficient space for the arrangement of equipment and manifolds. In addition, the turret is located inside the hull, which reduces the environment loads and effectively protects the SPM structure. The disadvantage is that the turret is installed inside the hull, affecting the arrangement of hull structures and the strength, as well as reducing the effective storage capacity (http://image.baidu.com/search/index?

tn¼baiduimage&ps¼1&ct¼201326592&lm¼1&cl¼2&nc¼1&ie¼utf-8&word¼FPSO). In addition, the effect of the weathervane of mooring tanker is restricted by the turret. When the wind wave is large, the azimuth speed at which the tanker turns to the least force direction is slow. The internal turret SPM system is suitable in moderate sea conditions or in harsh conditions of deep sea operations. At present, the world’s largest internal turret single-point mooring device is built by Dubai DryDocks World (Zhao 2009; Shengfa 2012). This SPM unit is 100 m high, weighs 4300 tons, and is connected to the sea floor by 16 mooring lines. This mooring system positions the 600,000ton Prelude FLNG in a gas field of approximately

878

International Maritime Organization (IMO)

International Maritime Organization (IMO) ▶ Decommissioning of Offshore Oil and Gas Installations ▶ Net Structures: Biofouling and Antifouling

International Organization for Standardization ▶ Shallow Foundations

Internal Turret Single-Point Mooring (SPM) System, Fig. 5 The pontoon schematic diagram

200 km away from the northwest coast of Australia for 25 years.

International Standards Organization (ISO) ▶ Decommissioning of Offshore Oil and Gas Installations

Cross-References ▶ External Turret Single Point Mooring System ▶ Mooring System ▶ Positioning System ▶ Single-Point Mooring System ▶ Soft YOKE Single Point Mooring System

International Towing Tank Conference (ITTC) ▶ Ice Tank Test

References Shan L-z, Dong B-j, Liu M et al (2008) Study of technical state and development tendency for FPSO [J]. Oil Field Equip 37(21):26–30. (In Chinese) Shengfa L (2012) The critical technology of single point Mooring system [J]. Offshore Platform 27(1):39–43. (In Chinese) Yifeng D (2012) The development and application of single point mooring technology. https://wenku.baidu. baidu.com/view (In Chinese) Zhao G-x (2009) Technical development of floating production storage offloading units in China [J]. Shang Hai Shipbuild 78(2):48–52. (in Chinese) Zhigang L, Yanping H (2006) The technical characteristics and development trend of FPSO turret mooring systems [J]. Chin Offshore Platform 21(5):1–6. (In Chinese)

Interpolation Technique by Small Strain (RITSS) ▶ Suction Piles

Intersymbol Interference (ISI) ▶ Underwater Acoustic Communication

Introduction to Shipbuilding (Shipyard)

Introduction to Shipbuilding (Shipyard) Yujun Liu School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China

Synonyms CAD (Computer-aided design); CAM (Computer-aided manufacturing); CIMS (Computer integrated manufacture system); CNC (Computer numerical control); NC (Numerical control cutting)

Definition Shipbuilding technology is generally divided into hull construction process, outfitting process, and painting process. The hull construction process is the process of manufacturing hull components, then assembling and welding them into intermediate products (blocks) and then hoisting them to the berth for assembly into the hull. Its operations generally include ship hull lofting, ship hull marking, hull processing, hull assembly, berth assembly, and ship launching. The shipbuilding industry generally refers to the mechanical and electrical installations, operating equipment, living facilities, various attachments, and cabin decorations other than the main hull and superstructure, collectively referred to as outfitting projects. It uses not only steel, but also nonferrous metals such as aluminum and copper and their alloys, and a wide range of nonmetallic materials such as wood, engineering plastics, cement, ceramics, rubber, and glass. Outfitting operations involve as many as dozens of work types such as assemblers, welders, carpenters, copper workers, fitters, and electricians. Therefore, ship outfitting can be divided into mechanical outfitting, electrical outfitting, piping outfitting, hull iron outfitting, and woodwork

879

according to the professional content; if according to the stage of outfitting work, it can be divided into outfitting parts manufacturing (purchasing), outfitting palletizing, block outfitting, block outfitting, and interior outfitting, etc.; according to the regional outfitting method, it can be divided into engine room outfitting, deck outfitting, cabin outfitting, and electrical outfitting. The painting operation is to remove rust and apply various paintings on the inner and outer surfaces of the hull and the outfitting parts according to the technical requirements to separate the metal surface from the corrosive medium and achieve the purpose of anti-corrosion treatment. It generally includes manufacturing-level production operation systems such as steel pretreatment, block painting, block painting, berth painting, and dock painting. The modern shipbuilding method is based on the region, so that the three different types of hull construction, outfitting, and painting are coordinated and organically combined to form an integrated construction technology of hull, outfitting, and painting, that is, the regional shipbuilding method, and to establish the production process flow shipbuilding.

Introduction The Content and Process Flow of Shipbuilding Technology Hull Lofting

Lofting is the first process in the shipbuilding production process. Although the workload is very small compared with the entire shipbuilding, it is a very complicated and precise work, otherwise it will directly affect the quality of subsequent processes and even the final product. Manual lofting started in the mid-1940s. The main work contents are: hull line smoothing, drawing frame line drawing, hull component expansion, drawing construction drawing and making prototypes and sample boxes for construction, and determining additional processing and assembly allowance. Full-scale lofting is performed at the lofting table at a ratio of 1:1,

I

880

while proportional lofting is performed at a certain reduced proportion on the lofting table. These two methods are traditional lofting methods which are manual operations, labor intensive, and poor accuracy. In addition, a large area of prototypes and a large amount of materials are needed to manufacture prototypes and prototype boxes. The methods are high cost and low efficiency, which is not conducive to the development of shipbuilding in the direction of mechanization and automation. With the development of electronic computer technology and shipbuilding technology, lofting has developed from manual lofting to mathematical lofting. It is now possible to implement computer smoothing and lofting of the whole ship’s line type and structure. It can also modify the line type and structural arrangement by man-machine dialogue to realize graphic display and automatic drawing and can automatically store the obtained data in the database for the next process such as numerical control drawing, numerical control marking, numerical control cutting, thus fundamentally eliminating manual lofting (Liu et al. 2011).

Hull Marking

Marking is the subsequent process of lofting. It is to copy the shape of the hull components after lofting to the steel plate or block steel according to the sketch, sample bar, template, sample box, sample diagram or projection diagram, CNC paper tape, etc., and mark the processing and assembly symbols, construction information for use in subsequent processes (Huang 2013). At present, most shipyards have generally adopted CNC marking. In addition, the marking device attached to the CNC cutting machine has become commonplace. The most commonly used is to install a marking mechanism or a line drawing nozzle on the CNC cutting machine, which can simultaneously mark material at the same time of cutting. Moreover, nesting also belongs to the category of marking materials (Liu et al. 2011). At present, it is generally used for interactive and automatic graphics nesting with the help of large computers.

Introduction to Shipbuilding (Shipyard)

Hull Steel Processing

The hull steel processing is to process the pretreated steel into the specifications and shapes required by the design with machinery and tools after marking. Generally speaking, the processing of ship hull steel can be divided into two categories: cold processing and hot processing according to the processing characteristics: it can be divided into edge processing (including planning, cutting, shearing, blanking, etc.) and forming processing (including rolling, pressing, bending, orthopedics, etc.) according to the shape of the component (Li et al. 2006). Steel Pretreatment The surface of steel generally has defects such as oxide scale, rust, local unevenness, warping, or distortion, and it is necessary to perform operations such as leveling, rust removal, applying protective primer, and drying on the steel. These operations are collectively referred to as steel pretreatment. Steel Cutting In modern shipyards, the cutting of ship steel plates has shifted from manual cutting and photoelectric tracking cutting to CNC cutting. In addition to adopting new methods, the development of cutting technology has also turned to automation and even unmanned development through numerical control, computers, and robots. In terms of cutting technology, there are mechanical cutting, gas flame cutting, plasma cutting, laser cutting, and water jet cutting. Edge Processing of Hull Components The edge processing of hull components generally includes three processing operations: firstly, mechanical shearing or chemical or physical cutting method is used to cut the hull components from the raw materials according to the construction information; secondly, according to the technical requirements of welding and assembly welding, groove processing is carried out on the components; and thirdly, according to the design requirements, the free edges and manholes of some components are polished with grinding wheels, thus obtaining hull components meeting different technical requirements (Ji 2005).

Introduction to Shipbuilding (Shipyard)

881

Forming and Processing of Hull Components After edge processing of hull components, for some components with spatial shapes such as bending, angle folding or edge folding, bending processing methods should be used to bend or bend them into the required spatial shapes. The forming process of hull components is to process the parts (flat panels, profiles, etc.) after edge processing into the actual shapes required by the components. Generally speaking, the bending operation accounts for about 10% ~ 18% of the hull steel processing work, while the bending restriction of profiles accounts for 9% ~ 16%. ①Sheet forming processing: marine sheet metal has complex line types, and its processing has always been the most difficult work in shipbuilding industry. Usually, conventional cold working equipment (plate bending machine, hydraulic press, etc.) is used for plate parts with general single curvature or small curvature, while for complex linear outer plates (hyperbolic plates), it still needs to be solved by hot working or water-fire plate bending process, etc. Mechanization and automation technology of plate processing has always been an important research content in hull construction. ②Profile forming and processing: generally, shipyards mostly use hydraulic profile bending machines to bend and form profiles. In recent years, CNC frame control cold bending technology and equipment have been continuously developed and are developing towards artificial intelligence and microcomputer control.

automation of assembly and welding operations can not only reduce labor intensity, but also effectively shorten the cycle and improve quality (Suwasono et al. 2011). Hull assembly generally includes component assembly (such as various welded T-beams, frame frames, stern posts, and rudders), block assembly (such as flat section, curved section, semidimensional unit, three-dimensional unit, and mega block), and berth assembly (blocks assembly, large three-dimensional blocks, and blocks into the entire hull on the berth or in the dock).

Hull Assembly

Ship Test

Hull assembly is the process of assembling qualified hull parts into sub-assembling, block, mega block and up to the entire hull. Due to the use of mathematical lofting and various numerical control processing technologies and equipment, the processing accuracy of hull components has been continuously improved, which has made the mechanization and automation of the hull assembly operation continuously improved. According to statistics, assembly and welding account for 12–18% of the total labor in ship construction. Therefore, improving the mechanization and

The ship test includes mooring test, tilt test, and sailing test, which are divided into two test stages. The mooring test is a test that the ship is moored on the dock after the ship is basically completed and the shipyard obtains the consent of the ship owner and the survey agency. Its task is to test the ship’s main engine, auxiliary machinery, and various equipment systems according to the design drawings and test procedures to check the ship’s integrity and reliability. Then the ship is placed in a still water area and a tilt test is performed to determine the center of gravity of

Ship Launching

When the ship is built on the berth (or in the dock) to the predetermined amount of work, it needs to rely on special equipment and operation methods to move the ship into the water. This operation is called ship launching. There are many ways to launch a ship, which can be roughly divided into three types: On the inclined slipway, the ship uses the component force generated by its own weight to overcome the friction between the slipway and the ship, so that the ship slides into the water by itself, which is called gravity launching. Using the towing slide to cooperate with the launching vehicle (ship lift, etc.) to tow the ship into the water is called towed launching. Water is drained into the dock to float the ship itself, and then the dock door is opened and the ship is towed out, which is called floating launch.

I

882

the completed ship. These two tests constitute the first stage of the ship test. The sailing test is a comprehensive assessment of a newly built ship, including two types of lightload test and full-load test. It belongs to the second stage of the ship test and is carried out by the shipyard together with the shipowner and the survey agency. Before the test, the sea trial should be carried out at sea or in the river according to the type of ship. Before the ship sails, fuel, life-saving, daily necessities, test instruments, meters, and special test equipment should be prepared. During the sea trial, various technical indicators of the main engine, auxiliary engines, various equipment systems, and communication and navigation instruments should be measured, and various navigation performance indicators of the ship should be measured to check whether they meet the design requirements. Delivery and Acceptance

After the ship test, the shipyard should immediately organize and implement various operations to eliminate the defects found in the test. At the same time, the ship and all equipment on board should be submitted to the shipowner for inspection one by one in accordance with the drawings, instructions, and technical documents, for example, the handover of cabins, the inventory handover of spare parts, the handover of main engines, auxiliary engines, various equipment systems, and communication and navigation equipment. After the above work is completed, the delivery and acceptance documents can be signed, and the survey agency will issue a certificate of conformity, and the shipowner can arrange for the ship to participate in operation. Shipbuilding Mode Connotation of Shipbuilding Mode

Pattern is the standard form or standard style of things and the description of the basic characteristics of things. For complex shipbuilding projects, because different shipyards have different technical levels and production conditions, even if their basic shipbuilding characteristics are the

Introduction to Shipbuilding (Shipyard)

same, the specific shipbuilding methods adopted are also different. For example, it is also a shipyard that adopts the sectional construction method, but its berth assembly method and sectional manufacturing method will vary according to the conditions of the shipyard. Therefore, the shipbuilding mode does not reflect the specific shipbuilding method (Koenig 2001). Shipbuilding mode is the general term of shipbuilding system and technology. It expresses the existence form and activity mode of shipbuilding industry as a whole and dynamically. Analyze the past and present of shipbuilding industry and explore its future and the shipbuilding mode have shown an orderly development. The Orderly Development of Five Shipbuilding Modes

With the advancement of science and technology and the growth of ship demand, the shipbuilding mode is constantly developing and changing, but it is relatively stable and unchanging for a period of time. The traditional shipbuilding industry is a laborintensive industry. A large shipyard has tens of thousands of employees and produces tens of thousands of tons of ships per year. The worldclass modern shipyard has an annual production capacity of more than one million tons of ships, and the total number of employees is only about 1000. The fundamental reason for such a disparity in production efficiency is the timely introduction of advanced manufacturing technology at that time. Before the 1950s, riveting technology was mainly used to develop the ancient wooden ship construction into modern shipbuilding with steel ship construction as the main body. In the 1960s, welding technology generally replaced riveting technology, transforming the ancient shipbuilding method oriented by “system” into “region” orientation, extending the assembly, outfitting, and painting operations originally concentrated on berths and docks to larger working surfaces of workshops and platforms. Since the 1970s, with the large scale of ships, in the construction of new shipyards and the modernization of old shipyards, the “group technology” has been introduced and studied comprehensively and deeply. Through the

Introduction to Shipbuilding (Shipyard)

similarity analysis of different types of construction processes, the classification of ship areas, operation types, and construction stages has been realized, and the shipbuilding flow water and virtual flow water production have been organized according to the concept of “intermediate products.” As a result, a large number of mechanized equipment have replaced heavy manual labor, and the original labor-intensive shipbuilding industry has undergone a qualitative change, becoming a modern “equipment-intensive” industry, and the total number of employees has been reduced by orders of magnitude. The “decentralized” specialization mechanism of social technology (organizational technology) in shipbuilding has been actually brought into play, and productivity has been significantly improved. Since the 1980s, the application of electronic computer technology in shipbuilding CAD (computer-aided design) and CAM (computer-aided manufacturing) has continued to expand and deepen, and shipbuilding precision control technology and ship engineering management technology are improving day by day, which has enabled the “integration” of shipbuilding social technology. The mechanism is fully functioning, and it is moving towards the integration of “space separation and orderly time,” namely the development of CIMS (Computer Integrated Manufacture System) of the shipbuilding industry, and then becoming an “information-intensive” industry, that is, an advanced state of modern shipbuilding mode (Podder et al. 2015). Currently, countries with advanced shipbuilding technology in Europe, America, and Asia are developing shipbuilding technology with two different technical routes. The first is the “simulation technology” route, which uses computer technology, robotics, and artificial intelligence technology on the basis of intensive shipbuilding equipment. The second is the “innovative technology” route, through the concept of digitization, simplifying the design, manufacturing and operation of ships, characterized by precision and agility, and strive to study a new generation of shipbuilding mode. For half a century, riveting technology, welding technology, group technology, and

883

information technology have promoted and dominated the development of shipbuilding mode one by one and successively formed the ship’s “integrated manufacturing mode,” “segmented manufacturing mode,” and “separated manufacturing mode,” and “integrated manufacturing mode.” This deductive process is an innovative process in which technology and economy are closely combined. The formation of each mode is due to the introduction of a new leading technology and the establishment of a new production function, which introduces a new combination of production factors and production conditions into the production system. Its development, like the whole manufacturing industry, is based on “technology as the center.” The development of shipbuilding industry is closely related to the improvement of the scientific and technological level of the whole industry. It is essentially a comprehensive effect produced by the organic combination of soft technology research and development and hard technology equipment and facilities investment. The transformation of the global shipbuilding mode fully reflects the convergence of technologies, that is, it does not tend to be the same with regional influence, showing the development law of shipbuilding technology (Tokola et al. 2016). Development Trend of Shipbuilding At present, the development trends of shipbuilding technology mainly include: low-consumption and high-efficiency ship production technology, green shipbuilding technology, digital shipbuilding technology, and intelligent shipbuilding technology. High Production Efficiency of Shipbuilding

High production efficiency shipbuilding: giant block, large-scale unit, outfitting unit assembly line, laser or electric induction heating outer plate forming, curved surface block assembly line, robot group welding of hull structure, and efficient welding technology, etc (Xu 2005). Low resource consumption shipbuilding: shipyard production processes without intermediate storage yard, shipbuilding activities moving forward and parallel, flange welding before bending pipe processing technology, etc.

I

884

Greening of Shipbuilding

Greening of shipbuilding is a shipbuilding technology with the highest utilization rate of production resources and the smallest impact on the environment. Therefore, the shipyard is responsible for environmental protection during shipbuilding; the pollution to the ocean must be reduced during ship operation; after the ship is scrapped, most of the materials can be reused. Therefore, greening of shipbuilding includes two aspects: “greening of ships” and “greening of shipyards.” “Greening of ships” can be called 3R Ship: environmentally friendly design, harmless materials, efficient technology, and antipollution equipment are adopted in shipbuilding and using ships to reduce the consumption of materials and energy and the pollution to the land and sea environment. When repairing the ship, the spare parts can be conveniently classified and recycled. When the ship is decommissioned, most of the materials can be reused. Research and development of greening of shipbuilding cases: the automation of hull processing and assembly and welding can be fully realized, and the utilization rate of steel can be improved; single-pass welding should be replaced by multiple-pass welding to reduce environmental pollution caused by welding smoke arc; nonemission steel pretreatment and coating technology should be adopted; shipbuilding sites should be sealed; and the air in the cabin should be filtered. Digitization of Shipbuilding

The goal of digital shipbuilding: the entire shipbuilding process is accurately defined by the computer system and all shell outfitting operations and system test tasks are specified in the form of electronic process charts, as well as production resources and operating methods to perform the tasks. Then, the integrated process chart is released to all construction departments including subcontractors. For this reason, the database of the manufacturing part of the digital shipbuilding must be stored, and the historical data of the solution, the logical data of the relationship, and

Introduction to Shipbuilding (Shipyard)

the capability data of all parties must be updated in real time. Digital shipbuilding requires threedimensional modeling of “ships” and “shipyards” in order to use the shipyard’s 3D environment to make process, operation plans, robot operations, NC (Numerical Control Cutting) simulations, and logistics simulations. Before the production process, the operations of each cutting seam, assembly seam, and welding seam of the ship must be simulated in the computer to obtain relevant technical data and management data (Stott et al. 2018). Intelligent Shipbuilding

With the development of shipbuilding technology, a large number of intelligent software and hardware suitable for it will surely appear. Globalization of Shipbuilding

Global economic integration refers to the adjustment of industrial structure in the world and the flow of production factors in the global scope. Production resources are allocated beyond national borders, so a unified development trend, process, and result are formed. Its main feature is “parallel and seamless integration in different places.” “Parallel in different places” aims to maximize the assembly efficiency (using giant blocks and giant outfitting units) and minimize shipbuilding costs (ship component processing park and transnational ship production block. According to the comprehensive modularization and digitization of manufacturing, the “seamless integration” of the whole process of ship construction in terms of technology and time is realized.

References Huang H (2013) Technology handbook of hull construction. China National Defense Industry Press:16–22, Beijing Ji ZS (2005) Mechanics in ship fabrication. China National Defense Industry Press 1–27, Beijing Li ZL, Wei JL (2006) Technology of ship production. Harbin Engineering University Press:54–59, Harbin Liu YJ, Wang J (2011) Technology of ship production. Dalian University of Technology Press:1–11, 227– 259, Dalian

Inventory of Hazardous Materials Koenig PC (2001) An introduction to the office of naval research and its activities in manufacturing and shipbuilding. Bull Soc Naval Archit Korea 38(3):1–8 Podder D, Kenno S, Das S, Ranjan Mandal N (2015) Numerical investigation on interruption in the welding process used in shipbuilding. J Ship Prod Des 31(04):1–4 Stott PW (2018) Shipbuilding innovation: enabling technologies and economic imperatives. J Ship Prod Des 34(02):10–13 Suwasono B, Widjaja S, Zubaydi A, Yuliadi Z, Budiantara IN (2011) Development of technology parameter towards shipbuilding productivity predictor using cubic spline approach. Makara J Technol 14(2):4–5 Tokola HA, Niemi E, Remes H (2016) Block erection in the event of delays in shipbuilding: a scenario-based approach. J Ship Prod Des 32(01):1–5 Xu ZK (2005) Technology of ship production. The People’s Communication Publishing Company:12, Beijing

Inventory of Hazardous Materials Xifeng Gao, Enhao Wang and Wanhai Xu State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China

Definition An Inventory of Hazardous Materials (IHM) is a document in which all potentially hazardous materials onboard a vessel that can pose a risk to the health and safety of people or to the environment is located, identified, and quantified.

Scientific Fundamentals IHM is an inventory that details the type, amount, and location of hazardous materials in the constructions, systems, and equipment of a vessel. It is increasingly recognized as a means to enhance onboard safety and environmental awareness throughout the whole life until the ship is being recycled.

885

An IHM on board primarily concerns a limited number of hazardous materials, such as asbestos, ODS, PCBs, PFOS, and antifouling that need to be assessed. If technically feasible, heavy metals, radioactive components, and some other substances should also be assessed. The main objectives of IHM are: 1. To gain insight into and have at hand specific information about the presence of hazardous materials on board ships 2. To safeguard the health and safety of workers and crew throughout the ship’s life cycle and beyond, thus also during dismantling 3. To prevent environmental pollution in and around shipyards, docks, shipbreaking yards, and ship recycling companies Background Ship scrapping industry used to be virtually unregulated and even was one of the worst safety record industries, which caused massive environmental pollution. People had little awareness or acknowledgment of the appalling working conditions and environmental pollution until environmental groups brought widespread awareness of ship scrapping practices (Naruse et al. 2010). In order to address the issues in shipbreaking, industry working groups developed the Industry Code of Practice on Ship Recycling. This guidlines subsequently fed into discussions at the International Maritime Organization (IMO), which resulted in the IMO Guidelines on Ship Recycling, adopted by member states in December 2003. These voluntary guidelines introduced the concept of a “Green Passport,” which is the predecessor of IHM, for the first time (Lloyd’s Register 2014). In 2009, the Hong Kong International Convention for the Safe and Environmentally Sound Recycling of Ships (the Hong Kong Convention, or the HKC, for short) was formally adopted at a Diplomatic Conference in Hong Kong. The HKC requires that each ship shall have on board an IHM. The Inventory is detailed in accordance with the actual conditions of each ship and shall specify at least the hazardous materials listed in

I

886

Appendices 1 and 2 of the Regulations for Safe and Environmentally Sound Recycling of Ships and the hazardous materials contained in hull structures and ship’s equipment. The location and approximate number of them should be noted clearly. The IHM consists of three parts (van Hooren 2015): Part I: Materials contained in ship structures or equipment. Part I of the IHM shall be developed for new and existing ships. Part II and Part III: Operationally generated wastes and stores. These parts do not need to be completed until the ship is being prepared for recycling. Materials that shall be listed in Part I of the IHM are divided in two categories: Table A: Comprises materials listed in Appendix 1 of the HKC. All Table A materials, if present on board, shall be included in the IHM. Table B: Comprises materials listed in Appendix 2 of the HKC. Table B materials, if present onboard, shall be included in the IHM of new ships if above the threshold values. For existing ships Table B materials shall be listed as far as practicable. The time window between the adoption of the HKC and its entry into force led to the appearance of a parallel convention, the EU Ship Recycling Regulation (the EU Regulation), which entered into force on 30 December 2013. The Regulation is mostly aligned with the Hong Kong Convention but differs in some aspects. The EU Regulation requires the establishment of a list of approved ship recycling facilities (the “EU List”) which meet the design, construction, and operation requirements of the EU but may be anywhere in the world (European Parliament 2013). The requirements for an EU IHM are expected to be more onerous than for the HKC IHM, especially in terms of the accuracy and comprehensiveness. Guidance is expected to be produced by the European Commission (EC) on implementation.

Inventory of Hazardous Materials

It should be noted that the EU Regulation, in addition to the Hong Kong Convention requirements, does not permit the presence of the following hazardous materials: perfluorooctane sulfonic acid (PFOS) and brominated flame retardant (HBCDD). Since the EU Regulation is at present incomplete in its requirements in so far as the permitted threshold values are concerned and is in the process of being amended, for implementation of the requirements of this Regulation, consideration should be given to the guidelines developed by the IMO to support the Hong Kong Convention. Hazardous Materials The Hong Kong Convention

The tables below show the category of hazardous materials and the minimum list of items for the IHM that should be listed in the Hong Kong Convention (International Maritime Organization 2009). The EU Regulation

Hazardous materials in the EU Regulation are mostly covered by the Hong Kong Convention, but there are still some differences. For ozone-depleting substances, except those in the Hong Kong Convention, HCFC-22 chlorodifluoromethane is prohibited in the EU Regulation. However, hydrochlorofluorocarbons (HCFCs) contained in new installations are permitted until 1 January 2020 in the Hong Kong Convention. The EU Regulation also involves perfluorooctane sulfonic acid (PFOS) in the category of hazardous materials. Perfluorooctane sulfonic acid (PFOS) means perfluorooctane sulfonic acid and its derivatives. In accordance with Regulation (EC) No 850/2004 of the European Parliament and of the Council, new installations which contain perfluorooctane sulfonic acid (PFOS) and its derivatives shall be prohibited. As for the list of items for the Inventory of Hazardous Materials, the EU Regulation adds brominated flame retardant (HBCDD) to the Hong Kong Convention.

Inventory of Hazardous Materials

Key Applications Development of Part I of the IHM for New Ships Part I of the IHM for new ships should be developed at the design and construction stages (Yan and Liu 2011). Checking of Materials Listed in Table 1

During the development of the Inventory (Part I), the presence of materials listed in Table 1 should be checked and confirmed; the quantity and location of Table 1 materials should be listed in Part I of the Inventory. If such materials are used in

887

compliance with the Convention, they should be listed in Part I of the Inventory. Any spare parts containing materials listed in Table 1 are required to be listed in Part III of the Inventory.

Checking of Materials Listed in Table 2

If materials listed in Table 2 are present in products above the threshold values, the quantity and location of the products and the contents of the materials present in them should be listed in Part I of the Inventory. Any spare parts containing materials listed in Table 2 are required to be listed in Part III of the Inventory.

Inventory of Hazardous Materials, Table 1 Hazardous materials and control measures Hazardous materials Asbestos Ozonedepleting substances

Polychlorinated biphenyls (PCB)

Antifouling compounds and systems

Definitions Materials containing asbestos Ozone-depleting substances means controlled substances defined in paragraph 4 of article 1 of the Montreal Protocol on Substances that Deplete the Ozone Layer, 1987, listed in Annexes A, B, C, or E to the said Protocol in force at the time of application or interpretation of this Annex Ozone-depleting substances that may be found on board ship include but are not limited to: Halon 1211 Bromochlorodifluoromethane Halon 1301 Bromotrifluoromethane Halon 2402 1,2-Dibromo-1,1,2,2tetrafluoroethane (also known as Halon 114B2) CFC-11 Trichlorofluoromethane CFC-12 Dichlorodifluoromethane CFC-113 1,1,2-Trichloro-1,2,2-trifluoroethane CFC-114 1,2-Dichloro-1,1,2,2tetrafluoroethane CFC-115 Chloropentafluoroethane “Polychlorinated biphenyls” means aromatic compounds formed in such a manner that the hydrogen atoms on the biphenyl molecule (two benzene rings bonded together by a single carbon-carbon bond) may be replaced by up to ten chlorine atoms Antifouling compounds and systems regulated under Annex I to the International Convention on the Control of Harmful Antifouling Systems on Ships, 2001 (AFS Convention), in force at the time of application or interpretation of this Annex

Control measures For all ships, new installation of materials which contain asbestos shall be prohibited New installations which contain ozonedepleting substances shall be prohibited on all ships, except that new installations containing hydrochlorofluorocarbons (HCFCs) are permitted until 1 January 2020

For all ships, new installation of materials which contain polychlorinated biphenyls shall be prohibited

1. No ship may apply antifouling systems containing organotin compounds as a biocide or any other antifouling system whose application or use is prohibited by the AFS Convention 2. No new ships or new installations on ships shall apply or employ antifouling compounds or systems in a manner inconsistent with the AFS Convention

I

888 Inventory of Hazardous Materials, Table 2 Minimum list of items for the IHM Any hazardous materials listed in Table 1 Cadmium and cadmium compounds Hexavalent chromium and hexavalent chromium compounds Lead and lead compounds Mercury and mercury compounds Polybrominated biphenyl (PBBs) Polybrominated diphenyl ethers (PBDEs) Polychlorinated naphthalenes (more than three chlorine atoms) Radioactive substances Certain short-chain chlorinated paraffins (alkanes, C10– C13, chloro)

Process for Checking of Materials

The checking of materials should be based on the Material Declaration furnished by the suppliers in the shipbuilding supply chain (e.g., equipment suppliers, parts suppliers, material suppliers). To preclude the introduction of non-compliant components into a vessel’s structure or equipment after the Inventory for the vessel has been prepared, Material Declarations are also to be obtained for purchases of spare parts that would be included in the vessel’s spares at delivery. If any of the Material Declarations for spare parts contain materials listed in Tables 1 or 2 above the respective threshold values, these spare parts are to be documented in an appendix to Part I of the IHM. When these spare parts are used, Part I of the IHM is to be updated accordingly. Development of Part I of the IHM for Existing Ships When compiling the Part I of the IHM for existing ships, reference can be got from the IMO “Guidelines for the Development of the Inventory of Hazardous Materials” or guidelines from other classification societies. Many of the items referred to or requested can be found in the ship’s onboard documentation and plans. Machinery specifications should show details of items such as gaskets, synthetic bearings, heat insulation, oils, plastics, asbestos, and

Inventory of Hazardous Materials

transformer cooling media. Insulation and accommodation plans should show many of the common materials in the ship. Electrical drawings and specifications should show details of wiring and wiring coverings. The items themselves may well be labeled, for example, lighting ballasts (for PCB content) and HVAC and refrigeration systems (for refrigerant type). The process of preparing an Inventory of Hazardous Materials is shown in Fig. 1, which is simplified from the IMO guidelines (International Maritime Organization 2011): 1. 2. 3. 4. 5.

Collection of necessary information Assessment of collected information Preparation of visual/sampling check plan Onboard visual check and sampling check Preparation of Part I of the Inventory and related documentation

Collection of Necessary Information

The shipowner should identify research, request, and procure all reasonably available documentation regarding the ship. Information that will be useful includes maintenance, conversion, and repair documents; certificates, manuals, ship’s plans, drawings, and technical specifications; product information data sheets (such as Material Declarations); and hazardous material inventories or recycling information from sister ships. Potential sources of information could include previous shipowners, the ship builder, historical societies, classification society records, and ship recycling facilities with experience working with similar ships. Assessment of Collected Information

The information collected in Step 1 above should be assessed. If one or more materials listed in Table 1 are found to be present in concentrations above the specified threshold value, the products which contain these materials shall not be installed on a ship. However, if the materials are used in a product in accordance with an exemption specified by the Convention (e.g., new installations containing hydrochlorofluorocarbons (HCFCs) before 1 January 2020), the product should be listed in the Inventory. If one or more

Inventory of Hazardous Materials

889

Collection of necessary information

Analysis and Definition of scope of assessment

Can you recognize what it contains by document analysis?

No

Is it clearly labelled on board ship?

Yes

Yes No

No

Can you exempt sampling analysis according to a criterion?

Yes Visual check plan

List of equipment system and/ or area potentially containing Hazardous Material

Sampling check plan

Preparation of visual/ sampling check plan

Onboard visual check, sampling check

No

Was visual checking/ sampling actually possible?

Yes

Does it contain Hazardous Material?

No

Listing not necessary

Yes Equipment, system and/ or area classed as containing Hazardous Material

Equipment, system and/ or area classed as potentially containing Hazardous Material

Preparation of Inventory Part 1

Inventory of Hazardous Materials, Fig. 1 Flow diagram for developing Part I of the Inventory

I

890

materials listed in Table 2 are found to be present in concentrations above the specified threshold value, the products should be listed in the Inventory. The results of the assessment should be reflected in the visual/sampling check plan. Preparation of Visual/Sampling Check Plan

While the original IMO Guidelines on Ship Recycling did not require sampling to be carried out, the Hong Kong Convention does require it, for existing ships. This new requirement is in Regulation 5.2, as follows: Existing ships shall comply as far as practicable with paragraph 1. . .The Hazardous Materials listed in Appendix 1, at least, shall be identified when the Inventory is developed. For existing ships, a plan shall be prepared describing the visual/sampling check by which the Inventory of Hazardous Materials is developed, taking into account the guidelines developed by the Organization.

The requirement for sampling is further amplified in the IMO guidlines: To specify the materials listed in Appendix 1 of these guidelines, a visual/sampling check plan should be prepared taking into account the collated information and any appropriate expertise. The visual/sampling check plan is based on the following three lists: 1. List of equipment, system, and/or area for visual check. Any equipment, system, and/or area specified regarding the presence of the materials listed in Appendix 1 by document analysis should be entered in the list of equipment, system, and/or area for visual check. 2. List of equipment, system, and/or area for sampling check. Any equipment, system, and/or area which cannot be specified regarding the presence of the materials listed in Appendix 1 by document or visual analysis should be entered in the list of equipment, system, and/or area as requiring sampling check. A sampling check is the taking of samples to identify the presence or absence of hazardous material contained in the equipment, systems, and/or areas, by suitable and generally accepted methods such as laboratory analysis.

Inventory of Hazardous Materials

3. List of equipment, system, and/or area classed as “potentially containing hazardous materials.” Any equipment, system, and/or area which cannot be specified regarding the presence of the materials listed in Appendix 1 by document analysis may be entered in the list of equipment, system, and/or area classed as “potentially containing hazardous materials” without the sampling check. The prerequisite for this classification is a comprehensible justification as to the impossibility of conducting sampling without compromising the safety of the ship and its operational efficiency. Visual/sampling checkpoints should be all points where: 1. The presence of materials to be considered for the Inventory (Part I) as listed in Appendix 1 is likely 2. The documentation is not specific 3. Materials of uncertain composition were used Onboard Visual/Sampling Check

The onboard visual/sampling check should be carried out in accordance with the visual/sampling check plan. When a sampling check is carried out, samples should be taken, and the sample points should be clearly marked on the ship plan with the sample results referenced. Materials of the same kind may be sampled in a representative manner. Such materials are to be checked to ensure that they are of the same kind. The sampling check should be carried out drawing upon expert assistance. Any uncertainty regarding the presence of hazardous materials should be clarified by a visual/ sampling check. Checkpoints should be documented in the ship’s plan and may be supported by photographs. If the equipment, system, and/or area of the ship is not accessible for a visual check or sampling check, they should be classified as “potentially containing hazardous materials.” The prerequisite for such classification should be the same prerequisite as in Step 3. Any equipment, system, and/or area classed as “potentially

Inventory of Hazardous Materials

containing hazardous materials” may be investigated or subject to a sampling check at the request of the shipowner during a later survey (e.g., during repair, refit, or conversion). For example, if you have a room with many diverse items, all of which have a high likelihood of being asbestos, it may be economically more viable to declare them all as asbestos and treat them accordingly. Alternatively, if the ship has a space with a large amount of concrete in it which is highly homogeneous, has a low likelihood of containing asbestos, and would be very expensive to remove as an asbestos waste, then a practical set of tests to provide the required confidence that the material does not contain asbestos would be sensible. Most importantly, the approach should be transparent and demonstrate the required duty of care. The first step to achieving this is to assume the worst possible hazard, to take all precautions, and then to design the sampling regime on this basis. Shipowners can further enhance the Inventory and better discharge their liability by carrying out a limited amount of testing of known materials, in order to satisfy themselves that the available information is accurate and reliable. Lastly, it is expected that an authorized recycling facility could be capable of checking the principal hazards itself or for the ship to have been pre-cleaned by a yard authorized for that hazard. Each facility should have its own sampling procedures independent of anything which is in the IHM, since the Inventory is only based on “estimates” and the facility is expected to discharge its responsibility to its own workers in a sensible manner. This is essential when one considers the inaccuracies inherent in any Inventory and the lack of knowledge of what is behind, under, or around anything which may have been sampled. The knowledge that a facility will “double check” and the fact that an owner can ask the facility to test materials he has been unable to test (due to time, access, cost, or other factors) can also impact on the economic balance of the sampling plan.

891

Only when the ship is being dismantled can actual, accurate checks of all material be made. Thus, sampling for the Inventory only adds confidence; it can never provide a factual record of all materials on board the ship, and it cannot do the job of checking during dismantling, which must be done by an authorized recycling facility. Preparation of Part I of the Inventory and Related Documentation

If any equipment, system, and/or area is classed as either “containing hazardous materials” or “potentially containing hazardous materials,” their approximate quantity and location are to be listed in Part I of the Inventory. These two categories are to be indicated separately in the remarks column of IHM. The results of the onboard visual/ sampling check are to be recorded on the checklist. Part I of the Inventory is to be developed with reference to the checklist. After the development of IHM, the shipowner is to determine the identification/verification number for Part I of IHM of the ship according to its own management system documents. The information received for the Inventory, as contained in Tables 1 and 2, ought to be structured and utilized according to the following categorization for Part I of the Inventory: (1) paints and coating systems, (2) equipment and machinery, and (3) structure and hull. The following tables show the standard format (Tables 3, 4, and 5). “Name of Column

Equipment

and

Machinery”

Equipment and Machinery The name of each item of equipment or machinery should be entered in this column. If more than one hazardous material is present in the equipment or machinery, the row relating to that equipment or machinery should be appropriately divided such that all of the hazardous materials contained in the piece of equipment or machinery are entered. If more than one item of equipment or machinery is situated in one location, both name and quantity of the equipment or machinery should be entered in the column (American Bureau of Shipping 2016).

I

892

Inventory of Hazardous Materials

Inventory of Hazardous Materials, Table 3 Paints and coating systems containing materials

No. 1 2

Application of paint Anti-drumming compound Antifouling

Name of paint Primer, xx Co., xx primer #300 xx Co., xx coat #100

Location Hull part Underwater part

Materials (classification in Table 1) Lead

Approximate quantity 35.00 kg

TBT

120.00

Remarks

kg

Inventory of Hazardous Materials, Table 4 Equipment and machinery containing materials

No. 1

2

3

4

Name of equipment and machinery Switch board

Diesel engine, xx Co., xx #200 Diesel generator (x 3) Radioactive level gauge

Location Engine control room Engine room

Materials (classification in Table 1) Cadmium Mercury Lead

Engine room

Lead

No. 1 cargo tank

Radioactive substances

Parts where used Housing coating Heat gauge Starter for blower Ingredient of copper compounds Gauge

Approximate quantity 0.02 kg 60 years) and deferred transportation of used fuel at operating and decommissioned nuclear power plant sites (Chopra et al. 2014). An investigation on polyether ether ketone (PEEK) composite for longterm storage of nuclear waste highlights the effect of radiation and chemical and thermal environments on mechanical and thermal properties of PEEK and presents which of these materials could be an alternative material for long term storage of nuclear (Ajeesh et al. 2015). The results they have obtained are shown as follows: (1) the dispersion of carbon short fiber in the PEEK Composites is significantly uniform from the study under optical microscopy; (2) there are no significant changes in thermal properties of PEEK composite when exposed to aggressive environments from differential scanning calorimeter (DSC) and thermo gravimetric analysis (TGA). As a result, to determine the storage period and material could be the key problem of long-term storage of nuclear waste with offshore structure. Fatigue Problem During Long-Term Storage Long-term fatigue assessment of an offshore structure is a challenging practical problem, no matter during its working or storage periods. Various efficient strategies have been proposed in the literature; however, they generally suffer from one or more shortcomings. Low (2016) proposed a new analysis approach, based on using the

945

classical control variates technique to improve the efficiency of Monte Carlo simulation (MCS). According to his case study, the results show that substantial reduction in the sampling variability of MCS are provided. Time domain simulation is another common method to predict the longterm fatigue damage in offshore engineering. Taking the high-pressure hydraulic power take-off (PTO) machinery in a heaving-buoy wave energy converter (WEC) as example, Yang and Moan (2013) presented the fatigue analysis with time domain simulation. They obtained long-term pressure loads by combining the short-term time simulation results and the occurrence probability of each sea state. Two models (Weibull and generalized Gamma distributions) were applied to fit the long-term rain flow-counted pressure cycles. Corrosion Problem During Long-Term Storage Corrosion problem is one of the significant issues during the offshore structure operation, due to the wet and salty ocean environment. During its lifespan, there are some approaches, such as sacrificial anode, polymer anticorrosive material, duty paint, etc., to solve or relieve this slow chemical reaction. However, during the long-term storage, the corrosion protection should be paid attention to, as most of the protection terms are out of work. If severe corrosion occurs on the storage structures, it will clearly affect the following reuse. Moreover, there is a potential way to store the decommissioned offshore structures in some underground area, if it is not against local law. Subsurface developments have many potential uses ranging from defense installations to transport and retail outlets. Besides, it has great potential ability for the storage. If this storage is adopted, the corrosion issue will be more critical to the structures. Gschwandtner and Galler (2018) assessed the stability of underground structures during a long-time behavior. According to their investigation, geotechnical engineering and geology, hydrogeology in particular, show great influences on the behavior of structure and surface area. They conducted a four-year-length survey, as well as a numerical simulation, to perform the

L

946

study. Their results show that the influence of underground and surface waters, especially for those areas that are sensitive to water, cannot be neglected in the consideration of long-term stability.

Loss of Stability Yang L, Moan T (2013) Prediction of long-term fatigue damage of a hydraulic cylinder of a wave energy converter subjected to internal fluid pressure induced by wave loads. Int J Mar Energy 2:43–60 Yano KH, Mao KS, Wharry JP, Porterfield DM (2018) Investing in a permanent and sustainable nuclear waste disposal solution. Prog Nucl Energy 108:474–479

References Ajeesh G, Bhowmik S, Sivakumar V, Varshney L, Kumar V, Abraham M (2015) Investigation on polyetheretherketone composite for long term storage of nuclear waste. J Nucl Mater 467:855–862 Chopra OK, Diercks DR, Fabian RR, Han ZH, Liu YY (2014) Managing aging effects on dry cask storage systems for extended long-term storage and transportation of used fuel (REV. 2) (no. ANL-13/15). Argonne National lab.(ANL), Argonne (United States) Correa R, Russel M (2017) Decommissioning opportunities in Brazil’s oil and gas horizon. Export. Gov. published in 06/08/2017. Available at. https://www.export.gov/Des commissioning-Opportunities-in-Brazil-s-Oil-and-GasHorizon Dexter C, Ghorashi J (2016) What do you do with an obsolete oil ring? Chem Eng 903:38–39 Gerold S (2018) Dry storage of spent nuclear fuel and high active waste in Germany current situation and technical aspects on inventories integrity for a prolonged storage time. Nucl Eng Technol 50:313–317 Gschwandtner GG, Galler R (2018) Long-term behaviour of complex underground structures in evaporitic rock mass–experiences gained from calculations and geotechnical observations. Tunn Undergr Space Technol 78:159–167 Junior Alves SL, Souza R (2017) Best practices for decommissioning of floating production systems FPS. In: offshore technology conference, Rio de Janeiro, Brasil, Oct 2017, pp 24–26 Liu Z, Sun L, Guo Y, Kang J (2015) Fuzzy FMEA of floating wind turbine based on related weights and TOPSIS theory. In: 2015 fifth international conference on instrumentation and measurement, computer, communication and control (IMCCC) (pp 1120–1125). IEEE Low YM (2016) A variance reduction technique for longterm fatigue analysis of offshore structures using Monte Carlo simulation. Eng Struct 128:283–295 Rouse S, Hayes P, Davies IM, Wilding TA (2018) Offshore pipeline decommissioning: scale and context. Mar Pollut Bull 129(1):241–244 Sudaia DP, Bastos MB, Fernandes EB, Nascimento CR, Pacheco EB, da Silva ALN (2018) Sustainable recycling of mooring ropes from decommissioned offshore platforms. Mar Pollut Bull 135:357–360 Suh YA, Hornibrook C, Yim MS (2018) Decisions on nuclear decommissioning strategies: historical review. Prog Nucl Energy 106:34–43

Loss of Stability ▶ Pure Loss of Stability

Low Cycle Resonance ▶ Parametric Rolling

Low Earth Orbiting (LEO) ▶ Underwater Acoustic Communication

Low-Density Parity Check (LDPC) ▶ Underwater Acoustic Communication

LS – Limit States ▶ Design of Renewable Energy Devices

Luxurious Cruise Ship ▶ Luxury Cruises

Luxury Cruises

Luxury Cruises Fu-Zhen Pang1 and Hai-Chao Li2 1 College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China 2 College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, China

Synonyms Brilliance of the Seas; Luxurious cruise ship; Luxury passenger liner

Definition Luxury cruise is regarded as the “mobile palace in the sea” (Yin 2012), which is the high-valued equipment for the tourism industry. It provides tourists with unforgettable sailing experiences and incredible enjoyment through its different types of facilities.

Scientific Fundamentals Development History In the late nineteenth century and the early twentieth century, people traveled across the sea only by cruise ships, which just provided passengers with limited rooms and food services. With the increasing maturity of aircraft technology, in order to save time and money, many passengers choose to travel by airplane. Therefore, in the middle of the twentieth century, the cruise ship industry declined. In order to survive, cruise companies developed the concept of cruise vacation (Duman and Mattila 2005), which transformed the transport-oriented cruise ship into a marine holiday village and built the cruise ship with more luxurious facilities, more programs, and larger displacement. Therefore, luxury cruise has been gradually more and more flourishing since the 1980s (Shan et al. 2017) and has become an independent part of the world tourism industry.

947

Structural Features As a typical representative of the high-end product of manufacturing industry, the luxury cruise has integrated the features of advanced manufacturing with the concept of modern services, sightseeing, tourism, and entertainments. The luxury cruise is totally different from mainstream ships in design concept, construction technology, operation, management, and other aspects, which directly reflect the scientific and technological level and comprehensive industrial ability of a country. Compared with the conventional ships, luxury cruise has the following characteristics (Luo and Gan 2017): 1. The molded breadth is relatively large, while the molded depth, relatively small. 2. Double bottom, double hull, long superstructure, square stern, curved nose bow, and underwater bulb. 3. There are many water-tight compartments in the main ship, all of which are plane bulkheads. The deck, board side, and bottom are longitudinal structures. The framework is mostly constructed by flat bulb steel. 4. The superstructure is divided according to its functions, and the public entertainment place is spacious with few pillars. 5. The visible structure focuses on coordination and beauty. The upper and lower structures are designed to be aligned. 6. The high requirements of vibration control and noise elimination. 7. The type of rooms in the luxury cruise involves standard room, sea-view room, superior royal suite, and so on. For the specialty in comfort and function, the structural type and layout in rooms are also different (Fig. 1).

Difficulties in the Structural Design of Luxury Cruise The structural design of luxury cruise should not only meet the intensity requirements of classification regulations but also comply with its mission of providing high-end services to tourists. The design difficulties can be summarized as follows:

L

948

Luxury Cruises

Luxury Cruises, Fig. 1 Basic structure of luxury cruise (http://image.baidu.com/)

Plate Welding Distortion Control High-strength steel has been widely used in shipbuilding. Its beneficial effect is to reduce the weight of the structure and improve the navigation performance and energy efficiency of ships. However, it also brought some negative effects, one of which was that as the thickness of the plate decreased, the welding deformation increased. The thickness of the hull structure of a luxury cruise should be relatively small, especially for superstructures and deck compartments. Most of the plate thicknesses can be among 5–6 mm. Large welding distortions above the waterline seriously affect the aesthetics of the hull, while larger welding distortions below the waterline will not only affect the navigation performance of the vessel but also reduce the ability of the vessel’s external plating to withstand the effects of water pressure. The exterior appearance of the luxury cruise ship needs to be aesthetically pleasing. Therefore, the exterior surface of the ship must not exhibit any aesthetic welding distortion.

Vibration and Noise Control Tourists take a luxury cruise tour to have the relaxing and enjoyable life. However, ship noise can not only influence the normal navigation of the ship but also reduce the comfort of passengers and sailors, causing complaints and dissatisfaction. Therefore, luxury cruises must control the vibration of the ship and the resulting noise (Braghin et al. 2011). At present, almost all classification societies have clear requirements for the vibration and noise of cruises. As the regulation goes, the noise level of all passenger compartments and public spaces shall comply with the requirements of IMO MSC 337 (91): Ship Noise Level Rules and ISO 6954 (2000): Mechanical Vibration Guidelines. For luxury cruises, the control of vibration and noise needs to be far stricter than normal ships in order to pursue higher comfort. Structural Strength and Workload of Calculation As an advanced passenger ship, a large luxury cruise requires high structural strength. The

Luxury Cruises

requirements of the various specifications for cruise ship structures, given by some of the major western classification societies, namely, LR, RINA, BV, and DNV, are mainly concentrated on the calculation of structural strength, which involves the calculation of the longitudinal strength, the ultimate and remaining strength of the hull girder, the fatigue strength, and the strength of the entire ship. For the main supporting parts of the decks, the strength shall be directly calculated to check the tenacity. As for the ultimate and residual strength of the hull girders, besides the standard method, it can also be calculated by the nonlinear finite element method. In addition, the nonlinear finite element method can also be used to eliminate the noise of the ship (Fig. 2). Structural Details The luxury cruise should strive for excellence and each part requires exquisite work. Ship design workers in Japan and the West have attached great importance to the design and research of structural details. As a “mobile palace in the sea,” a large luxury cruise boasts a variety of sport, entertainment, dining, and leisure facilities. Every place and facility needs to be dedicated in design and manufacturing. Therefore, detailed design can also be a complex point for cruise design.

949

main functions of luxury cruise determine that the requirement is stricter than commercial ships in terms of safety, energy saving, and environmental protection. Safe Accidents of luxury cruises are generally caused by collision and cruise fire. Therefore, cruise ships must meet the requirements of the International Convention for the Safety of Life at Sea (SOLAS) and the requirements of the Safe Return to Port (SRtP). As SRtP notes, when a fire or flooding accident occurs, the ship should safely return to the port on its own power. During the process, passengers can safely stay within the “safety zone” and meet basic living needs. Even when the accident exceeds the safety zone, the ship should operate for at least 3 h to ensure orderly evacuation of passengers. Eco-friendly In order to create an eco-friendly marine environment, the International Maritime Organization (IMO) launched Energy Efficiency Design Index (EEDI) for controlling CO2, sulfur oxide, and nitrogen oxide (SOX, NOX) emissions (Li et al. 2014). These rules will greatly affect the design of large luxury cruise. Other Rules International Labour Convention

Design Specifications The luxury cruise is not only a transportation vehicle but also a place for amusement. The

Luxury Cruises, Fig. 2 Overall of vibration characteristics (http:// image.so.com/)

The latest Maritime Labour Convention, 2006 issued by the International Maritime Organization puts forward higher requirements for sailor’s living conditions. For example, the room area for

L

950

Luxury Cruises

four sailors should be larger than 14.5 m2. However, many of the cruises built in recent years cannot meet this requirement.

second giant indoor dock was built, with a specification of 504 m in length, 125 m in width, and 75 m in depth. The shipyard can build three luxury cruises per year.

Other Regulations

Among the cruise associations, Cruise Lines International Association (CLIA) is one of the most influential in the industry. The association has established the self-regulation rules widely followed by its members in the area of waste disposal, restricted access to the driving cab, extra life jackets, heavy weight fastening on ships, and passenger prototype exercises (Fig. 3).

Fincantieri Shipyard, Italy Fincantieri shipbuilding corporation in Italy has a long history of designing and building warships for nearly 200 years. The main products are passenger liners, ferries, and submarines, representing Italy’s advanced industrial technology and export around the world. In particular, its passenger ships and luxury cruises reign at the world’s No.1, accounting for 40% of the international market.

The World’s Major Cruise Shipyards Aker Shipyard, Finland Aker Shipyard was established in 1738, which has a history of more than 270 years. Remarkably, decades ago, Aker Shipyard used to spend 2 years building the famous luxury cruise Marine Independence, which made a stir in the whole cruise community and replaced its sister ship Marine Liberation, becoming “the largest luxury cruise” in the world at that time (Wang et al. 2005).

Key Applications The World’s Leading Luxury Cruise Company (Group) Carnival Corporation & plc

Meyer Shipyard, Germany Meyer Shipyard is one of Germany’s largest and most modern shipyards. It was founded in 1795 and mainly built of wooden boat at first and started the construction of iron ships in 1874. Its first indoor dock was completed in 1987, 470 m long, 101.5 m wide, and 60 m deep. In 2000, the

Carnival Corporation & plc (Zhou et al. 2010) is the world’s largest cruise company and has a total of 11 cruise brands, including Carnival, Aida, Costa, Princess, Holland, Crown, Ibolo, P&O, P&O Australian, Saab, and Ocean Village Classes. The fleet operates in Europe, the Caribbean, the Mediterranean, Mexico, and the Bahamas throughout the year. Seasonal routes include Alaska, Hawaii, the Panama Canal, the Canadian shipping lines, etc. Its fleet advantage lies in its various leisure facilities and innovative and spacious compartments.

Luxury Cruises, Fig. 3 Design specifications (http://www. baidu.com/)

Location

Passenger ships, Passenger Accommodation Frequency weighted r.m.s values in mm/s from 1 Hz to 80 Hz.

Comfort rating number (crn) 1 2 3

Passenger, top grade cabins

1.5

1.5

2.0

Passenger cabins, standard

1.5 1.5 2.0

2.0 2.0 2.7

3.0 3.0 3.5

Public spaces Open deck recreation

For passenger ships with comfort rating, no single frequency component within the frequency range 6.3 Hz to 12.5 Hz shall exceed 1 mm/s r.m.s (weight).

Luxury Cruises

Royal Caribbean Cruises Ltd

Royal Caribbean Cruises Ltd. is the second largest cruise company in the world and owns six major brands (Royal Caribbean International (RCI), Fine Diamond Cruises, Freedom Cruises, Pullmantur Cruises, CDF Cruises, and TUI Cruises), 41 luxury cruises, and 460 diverse sailing lines. It can visit nearly 300 tourist destinations, covering more than 70 countries and regions including the Caribbean, Alaska, Canada, Europe, the Middle East, Asia, Australia, and New Zealand. Genting Group

Genting Group is a leading cruise corporation in Malaysia, which is composed of five major subsidiary companies: Genting Malaysia Berhad, Genting Plantations Berhad, Genting Singapore PLC, Genting Hong Kong Limited, and Kien Huat Realty. Established in September 1993, Genting Hong Kong runs the cruise travel business in Asia under the brand of Star Cruises. It is considered to be a pioneer in the Asian cruise industry and is committed to develop the Asia Pacific region as an important international cruise destination.

951

Caribbean, Alaska, Europe, the Mediterranean, and Bermuda. The company’s major shareholders are Genting Hong Kong, Apollo Global Management, and TPG Capital. Famous Luxury Cruises in the World Queen Mary 2

Queen Mary 2 (shown in Fig. 4) is an ultra-luxury ocean liner affiliated to British Canada Cruise Line Company. The liner costs more than 800 million US dollars and has a displacement of about 150,000 t. QM2 can be regarded as a star in the world’s cruise and is currently the largest ocean liner, with more than 1250 sailors at service. What is truly impressive is the ship size. She is 345 m long and 72 m tall, which is taller than the Statue of Liberty and larger than the largest aircraft carrier in the United States. Queen Mary 2 is honored for many advanced technologies. A powerful marine mechanical propulsion system enables the sculpting of the giant hull, and advanced navigation and communication equipment can make sailing safer. MS Voyager of the Seas

MSC Cruises

MSC Cruises is the leader of the cruise market around the Mediterranean Sea with ships throughout the region all year round. At the same time MSC Cruises offers seasonal cruise journey around the world including destinations such as the Nordic Atlantic Caribbean North America South America South Africa and other places. Possessing one of the world’s most modern fleets which consists of 11 cruise ships the corporation has achieved the number of 1.3 million tourists annually. Norwegian Cruise Line

Founded in 1966, Norwegian Cruise Line is headquartered in Miami-Dade County, Florida, and has become one of the most well-known brands in the North American cruise industry. Together with the newly joined fleets Ocean Class and Regent Seven Seas Class, the corporation has a total of 23 cruise ships operating throughout North America, Hawaii, the

MS Voyager of the Seas (shown in Fig. 5) is the lead ship of the voyager-class cruises operated by Royal Caribbean International (RCI), with a displacement of 137,000 t, able to carry 3840 passengers. She was the largest five-star luxury cruise in Asia, 311 m in length and 39 m above the waterline. What is worth mentioning, the ship possesses a royal ballroom, which is larger than the size of two football field, and a huge theater, with a capacity of 1350 people. The most famous facility on MS Voyager of the Seas is the 120-m-wide deck. It is connected to two 11-story halls at each end side of the deck. Under the Royal Avenue, there are special facilities such as skating rinks, basketball courts, mini golf courses, and sea climbing walls. MS Explorer of the Seas

MS Explorer of the Seas (shown in Fig. 6) is a voyager-class cruise ship owned and operated by Royal Caribbean International. With a displacement of 138,000 t and 1138 sailors at

L

952

Luxury Cruises

Luxury Cruises, Fig. 4 Queen Mary 2 (https://en.wikipedia.org/wiki/Ocean_liner)

Luxury Cruises, Fig. 5 MS Voyager of the Seas (https://en.wikipedia.org/wiki/Ocean_liner)

service, she can accommodate over 3100 guests. The ship is fitted with six powerful Wartsila engines and three podded propulsors. The hull is 311 m in length, 38 m in width, and 47 m above the waterline, providing enough activity space for passengers. Passengers can enjoy

skating, board walking, and cliff climbing on the ship. Sea Adventurer

Sea Adventurer (shown in Fig. 7) is a luxury cruise managed by the Royal Caribbean “Voyager Class,”

Luxury Cruises

953

Luxury Cruises, Fig. 6 MS Explorer of the Seas (https://en.wikipedia.org/wiki/Ocean_liner)

L

Luxury Cruises, Fig. 7 Sea Adventurer (https://en.wikipedia.org/wiki/Ocean_liner)

with a displacement of 138,000 t and 1180 sailors at service. She has a length of 311 m, a width of 38 m, and a height of 47.5 m above the waterline, which owns 667 standard compartments. Adventure of the Seas is best known for her spectacular three-story themed restaurant, under which there is a huge stadium that can

accommodate 1350 spectators. Besides a skating rink, climbing walls, and golf courses, the stadium also features a large gymnasium including basketball, bowling, and volleyball venues. In addition, Adventure of the Seas also boasts a wedding chapel, a hallmark of luxury cruise ships.

954

Navigator of the Seas

Navigator of the Seas (shown in Fig. 8) is one of the cruise liners of Royal Caribbean International. She measures about 138,000 GT and carries 3807 passengers plus 1180 sailors. Her length amounts to 311 m with a width of 38 m, and the height above the waterline is about 49 m. Navigator of the Seas has a learning room equipped with 19 personal computers, the famous “Navigator’s Library” with a collection of thousands of books, a world-renowned caravan piano bar coupled with a nightclub, two swimming pools, as well as a cosmopolitan theater that can accommodate 1359 seats. Other service facilities include the Cloud Nine cocktail lounge, a jazz club, and a golf bar. The most considerate design is the large game room outside the library. Here, the popular games and game facilities make young passengers immersed in joy.

Chinese Market Distribution and Future Development Trend While the ship market continues to be in the doldrums, the large cruise market is still active (Duman and Mattila 2005). Cruise tourism is currently on a large scale in Europe and America. There are 300–400 cruises a day with a large

Luxury Cruises

number of tourists sailing in Alaska, Canada, the Caribbean, Mexico, Bahamas, Hawaii, Bermuda, South America, Panama Canal, Northern Europe and Russia, the Mediterranean, Greece, United Kingdom, and more than 100 countries and regions in Asia and Australia. The voyage spreads over 7 continents and travels more than 260 ports around the world. With the rapid growth of the cruise economy, the market potential of luxury cruise ships in emerging countries such as China has attracted the attention of global cruise giants. According to the analysis of 2016 China Cruise Industry Development Status and Prospects, the demand of the cruise market in China is growing rapidly, for its rapid economic growth and large population (Sun et al. 2014). The market scale continues to expand, and the number of cruise ship visitors has experienced an explosive annual growth of over 40% in 2016 (Wang et al. 2018). Considering that the penetration rate of China’s luxury cruise tourism is still less than 0.2%, and the impact of future consumption upgrades and policy promotions, the huge development potential of China’s cruise industry can be optimistic in the future. It is expected that the Chinese cruise market will maintain a growth rate of over 30% in the next 5 years and will have more than nine million cruise visitors by 2020. It can be said that a cruise feast that

Luxury Cruises, Fig. 8 Navigator of the Seas (https://en.wikipedia.org/wiki/Ocean_liner)

Luxury Passenger Liner

focuses on Chinese market will kick off in the near future.

References Braghin F, Cinquemani S, Resta F (2011) Vibrations Control in Cruise Ships Using Magnetostrictive Actuators. Structural Dynamics Vol 3. Springer, New York. Duman T, Mattila AS (2005) The role of affective factors on perceived cruise vacation value. Tour Manag 26(3):311–323. Li F, Huang M, Chen M (2014) Initial Analysis of Building Characteristic on Cruise Ship. Mar Technol Luo L X, Gan S Y (2017) Difficulties and Counter Measure Analysis of Structure Design of Large-size Luxury Cruise. Ship Eng 39(8):1–4+83 Sun X, Feng X, Gauri D K (2014) The cruise industry in china: efforts, progress and challenges. International J Hosp Manage 42:71–84

955 Shan Y, Li S F, Xue Q (2017) Review and Prospect of Internal and International Cruise Tourism Research. Journal of Chongqing Jiaotong University (social science edition) 17(6):65–72+77 Wang H, Shi J, Ye X, Wang Y, Mei J (2018) China’s cruise industry in 2016–2017: transformation, upgrading and steady development Wang JW (2005) The Re-organized Stream of European Large Shipyards. Technology and Economy Information of Ship Building Industry Yin Y (2012) Previous and Present Life of “Sea Palace”. China Ship Survey Zhou Y (2010) Carnival corporation & plc. Aida

Luxury Passenger Liner ▶ Luxury Cruises

L

M

Machine Learning ▶ Big Data-Based Decision Support Systems

Machinery Maintenance ▶ New Technologies in Auxiliary Propulsions

Maneuverability of Polar Vessel Qiaosheng Zhao1 and Baoshan Wu2 1 Department of Hydrodynamic Research, China Ship Science Research Center, Wuxi, China 2 China Ship Scientific Research Center (CSSRC), Wuxi, China

Synonyms

Mach-Zehnder Interferometer (MZI)

Discrete element method (DEM); Dynamic positioning (DP); National Maritime Research Institute (NMRI); Planar Motion Mechanism (PMM); The Institute for Ocean Technology (IOT)

▶ Fiber Optic Hydrophone

Definition

Magnetic Compass (MCP) ▶ Integrated Navigation

Maneuverability of polar vessel refers to the performance that the polar vessel can keep or change its motion state according to the intention of the pilot. It mainly involves the ability of polar ships to maintain or change speed, course, and position.

Introduction

Magnetohydrodynamics (MHD) ▶ AUV/ROV/HOV Propulsion System © Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

The key principle for ships’ successful ice navigation is to keep freedom of maneuver. Once a

Baoshan Wu: deceased.

958

Maneuverability of Polar Vessel

ship is trapped, the ship goes wherever the ice goes. Ship maneuvering in ice-covered waters is far more complex than that in open water, given the reason that the ice-hull interaction is stochastic in nature, resulting in irregular icebreaking pattern with high uncertainty. To better understand polar ships’ maneuverability, the maneuvering tests, maneuvering equations, maneuvering performance, and DP in ice are presented and further discussed.

Nv Y v_ N v_ Yδ Nδ Yr

Nomenclature

Nr

L B m Cb Iz Rb sf Hi lcr D R R/L V v v_ R r r_ t xG Y0 K N X Y T x y f β δ l Yv

Y r_

Ship’s waterline length (LWL) [m] Ship’s beam [m] Mass [kg] Block coefficient Yaw moment of inertia [kg-m2] Icebreaking resistance [N] Ice flexure strength [Pa] Ice thickness [m] Crack length [m] Turning diameter [m] turning radius [m] Non-dimensional turning radius Forward speed [m/s] Lateral speed [m/s] Lateral acceleration [m/s2] Turning radius [m] Yaw rate [rad/s] Yaw acceleration [rad/s2] Time [s] Position of center of gravity [m] Sway amplitude [m] Roll moment [N-m] Yaw moment [N-m] Surge Force [N] Sway Force [N] Draft [m] Forward position from global origin [m] Lateral position from global origin [m] Yaw angle [degrees] Drift angle [degrees] Rudder angle [degrees] Scale factor Derivative of sway force due to sway velocity [kg/s]

N r_

Derivative of yaw moment due to sway velocity [kg-m/s] Derivative of sway force due to sway acceleration [kg] Derivative of yaw moment due to sway acceleration [kg-m] Derivative of sway force due to rudder angle [kg-m/s2] Derivative of yaw moment due to rudder angle [kg-m2/s2] Derivative of sway force due to yaw rate [kg-m/s] Derivative of yaw moment due to yaw rate [kg-m2/s] Derivative of sway force due to yaw acceleration [kg-m] Derivative of yaw moment due to yaw acceleration [kg-m2]

Maneuvering in Ice The extreme environment in Polar Regions poses great challenges to ships’ navigation, and ice is the primary factor that affects ship’s maneuvering performance, especially to icebreakers. The typical circumstances ships would encounter in icecovered waters are listed as follows. When the average ice thickness exceeds 50 cm, icebreakers cannot go forward with full speed due to high resistance from ice, and the channel behind icebreakers freezes quickly afterwards, in which case the ship is likely to be trapped. Besides, the shoulder of ship is easily wrecked either in turning or advancing owing to the inhomogeneity of ice. And if a ship encounters a crack, the bow is forced to slide along the edge of crack. This may lead to rudder out of control. When ice-ship interaction is acute, the shipborne equipment would likely to be damaged, and the motion of rudder is encumbered by ice, leading to difficulty of bow turning. Poor maneuverability is one of the most important reasons. Therefore, successful ice navigation calls for good maneuvering performance. A ship’s capability to maneuver in ice-covered waters depends on its available steering forces and its transverse/rotational resistance. Sufficient steering force and propulsive power are key

Maneuverability of Polar Vessel

factors to overcome the increased turning moment generated by the ice force along the broadside during inception of a turn and to reach a steady turning rate. Steering forces are realized through lift generated by water flow over the rudder(s), differential propeller shaft thrust, directional thrust capability (such as podded-propellers and adjustable propeller nozzle direction), bow thrusters, and lift generated from ship heel angle. A ship’s transverse and rotational resistances are directly influenced by its L/B ratio, block coefficient, shape of the icebreaking waterline, and slope of the hull (or “icebreaking angle”) along the icebreaking waterline, shape of its underwater hull, and its pivot point. According to size, age, thickness, and concentration, ice can be classified into four primary types: broken ice, sheet ice, ridged ice, and icebergs (Aboulazm and Muggeridge 1989). Sheet ice, also called level uniform homogenous ice, is the most common and severe ice condition that ships (icebreakers and ice going ships) navigating in polar regions would encounter. Majority of fullscale maneuvering tests were carried out in sheet ice. Events associated with a ship maneuvering in level uniform homogenous ice can be categorized by ice thickness. For very thin ice, a ship’s turning radius will normally be very near that of its open water turning radius. This is largely attributed to the icebreaking action of the bow wave. As ice thickness increases, the effect of the bow wave diminishes and the ice sheet begins to interact with the ship’s hull. Ice breaking occurs mostly at the bow. The broken channel is wider than the ship’s beam so that the stern can move out and point the bow into the turn. The sides and aft of ship also break ice. As ice thickness increases, the ship’s ability to clear away broken ice from between its sides and the ice channel edges diminishes. A limiting ice thickness is approached where turning resistance is too high and the ship is no longer able to making turns at all. Quantitative values for ice thicknesses were not provided in the description because thickness alone does not dominate the ship-ice interactions. Ice strength, both in flexural and crushing, and hullice friction are also major influential factors. Besides, the authors also take into account the changes of broken channel edges to research the

959

phenomenon of icebreaking in aft shoulder of ships in level ice (a simplified model of sheet ice in model test and numerical simulation). For other conditions, ice distribution (pack or rubble ice, ridges, etc.), ice pressure (e.g., due to wind), snow cover, surface current, and water depth also directly impact a ship’s maneuvering performance. Pack or rubble ice is usually a common condition for ice going ships and icestrengthened ships (Riska 2010). Turning and zigzag are two main maneuvers in pack ice according to the real navigation. And this was simulated by Zhan et al. adopting DEM method (Zhan and Molyneux 2012).

Equation of Motion in Ice Coordinate Systems In ship maneuvering simulations, the ship can be regarded as a rigid body. The co-ordinate systems (Fig. 1) and equations of motion of ship maneuvering in ice are the same as that in open water. And the surge force, sway force, and yaw moment are the three major global forces to determine the ship’s maneuvering motions (Zhou et al. 2016). 8 > < mðu_
rvÞ ¼ X mðv_ þ ruÞ ¼ Y ð1Þ > : I z r_ ¼ N

Maneuverability of Polar Vessel, Fig. 1 Coordinate systems

M

960

Maneuverability of Polar Vessel

External Forces The external forces include forces from the hull, the thruster, the rudder, and other appendages. During ship’s ice navigation, forces on the hull mainly consist of ice forces, hydrodynamic forces, current forces, and wind forces. See Fig. 2. The forces from appendages and other environmental factors like wind are usually ignored. Until now, most researchers divide external forces into several parts, which is (Lubbad and Løset 2011): 8 > < X ¼ XH þ XP þ XR þ XIce Y ¼ Y H þ Y p þ Y R þ Y Ice > : N ¼ N H þ N P þ N R þ N Ice

ð2Þ

H, P, R, and ice represent forces and moment generated from hydrodynamic force, propeller force, rudder force, and ice load, respectively. Ice Force The basic premise to get ice force is to understand the mechanics of ice-ship interaction. Two categories, analytical approach and numerical approach, are used to classify the existing models of ice-ship interaction process. In terms of analytical approach, the methodology in which the total

ice force is divided into several independent force components that represent the corresponding physical processes during the continuous ship maneuvering in level ice has been widely used. The global ice force is equal to the linear sum of the three force components, that is, the breaking, buoyancy, and clearing force components. It can be written as: 8 > < Xice ¼ Xbr þ Xcl þ Xbouy Y ice ¼ Y br þ Y cl þ Y bouy > : N ice ¼ N br þ N cl þ N bouy

The ice breaking force component represents the contributions from the ice breaking process which is stochastic in nature resulting in irregular icebreaking pattern with high degree of uncertainty in predictability during ship maneuvers. To get ice force by numerical approach is mainly depends on its numerical model.

Overview of Ship Maneuvering Prediction in Ice To predict ship maneuvering performance in ice, a model applying the analytical approach with

Ship motion responses (displacement, velocity,acceleration)

External loads on the ship (surge, sway forces and yaw moment)

Hull

Ice force

Hydrodynamic force

Current force

ð3Þ

Thruster

Wind force

Rudder

Others

Maneuverability of Polar Vessel, Fig. 2 Ice-ship interaction in maneuvering (Liu et al. 2007)

Appendages

Maneuverability of Polar Vessel

numerical implementation for simulating various ship maneuvers in level ice is established. The model is used to simulate real-time maneuvering and support maneuvering simulator for its efficiency. Also, numerical methods have witnessed great advancement with the development of the computer technology. They can be used to solve analytical equations or to simulate the continuous ship-ice interaction process in various ice conditions (Liu et al. 2007). Analytical Approach The analytical approach is subdivided into empirical, semi-empirical models. With a large number of ship model tests and full scale ship trials having been carried out, experimental data (e.g., coefficients) can be obtained through sorting and fitting test results. Majid and Menon et al. (1983) built a time domain model for ship maneuvers in ice based on conventional maneuvering equations. The Taylor’s series expressions with coefficients obtained from model tests were adopted to estimate the ice forces on the hull due to the ship motion in the level ice. Williams et al. (1996) proposed an ice-hull force model for ship maneuvers in level ice from a series of PMM model tests. Robert et al. (2002) conducted a series of resistance and maneuvering tests using the R-class icebreaker model (scale ratio 1:40) and MV Arctic Bulk Carrier model (scale ratio 1:80), in which the damping coefficient and the acceleration control coefficient of the roll were calculated. Lau et al. (2004) discussed the effect of breaking channel width on ship maneuverability from PMM tests. And the effect of external moment on ship-ice interaction was also studied. Li et al. (2013) conducted a series of model tests on icebreaker in ice basin. The change of model speed and heading angle in different ice thickness were analyzed. Phenomena such as bending broken on ice and ice crushing on hull surface were observed. The analytical models applying semi-empirical approaches take into account more details of the pertinent ship-ice interaction processes. Tue-Fee et al. (1987) proposed a semi-empirical model for predicting ship’s steady turning maneuvers in level, unbroken, homogeneous ice fields. The

961

formulas for calculating sway force and yaw moments caused by pure ice forces are theoretically derived from basic assumptions. Aboulazm (1993) theoretically analyzed the turning performance of the ship in the block ice condition, and the external force of the ship in steady turning was calculated. Numerical Approach Discrete element method (DEM), which divides the continuous ice materials into many small elements, is widely applied in ice mechanics issues. Based on DEM, Lau (2006) simulated advancing and turning motion of TERRY FOX numerically using commercial discrete element code software. The ship was regarded as rigid body, and both level ice and ship model were established in discrete elements. The numerical results were compared with PMM model test results, which agreed very well. The shortcoming is that ice model was greatly simplified, and the failure of old discrete elements and the generation of new discrete units were not considered. Sawamura (2010) also calculated ship maneuvering in level ice using DEM model. The level ice in waterline surface was divided into a number of small circles, and the disappearance of circles indicated the breaking of the ice. This method is a good way to observe the maneuvering trajectory, yet it only paid attention on the ice force near the waterline, ignoring the friction of the broken ice along the hull. Many other researchers have also contributed greatly to this problem, such as Zhan et al. (2010), Zhan and Molyneux 2012, Derradji (2003), Valanto (2001). Another common numerical model was polygon model. This method is a 2D numerical solution, in which the broken channel edges and the ice breaking in ships’ aft shoulder during turning are observed in detail. This method can be found in Martio (2007), Su et al. (2010), and Zhou (2016).

Maneuvering Tests in Ice Maneuvering test is a collective name for all those tests in which the rudder is turned or the turning forces and moments are obtained by other means,

M

962

for example, azimuthing thrusters, tunnel thrusters in bow, different rpms at twin propellers. The primary purpose of maneuvering tests is to investigate the effectiveness of the hull in making turns. The other considerable purpose is to investigate the effectiveness of the turning devices like rudders, thrusters, or azimuthing propulsors. Maneuvering tests are also applied to investigate the flow of ice floes around the hull in various maneuvers. The design of aft shoulders down to baseline is especially important for turning capability. Quinton et al. (2005) had collected test data of all publicly available full-scale and model-scale ship-ice maneuvering data before 2005. Full-Scale Ice Maneuvering In terms of full-scale ice maneuvering, common maneuvers conducted by icebreaking ships are: (1) ahead progress, (2) channel breakout, (3) turning circle, (4) captain’s turn, (5) modified captain’s turn, (6) Kempf maneuver (or zig-zag), (7) breaking out a beset ship, (8) close coupled escort, and (9) ridge ramming. The turning circle and the Kempf maneuver are the most common of all in a “maneuvering in ice” performance evaluation. The purpose of the turning circle test is to find out how much area is needed to turn the ship. In practice, the circle may not be a perfect circle, but

Maneuverability of Polar Vessel

a spiral. The progress of this test is just like that in open water (Fig. 3), which involves four phases. However, the detail of external force acting on the hull is different because of the ice. In open water, steady turning radius R is the simplest measure of a ship’s maneuverability, while the situation is different in ice condition. Because variations in ice thickness and strength also affect the ship’s maneuverability, R/L is not as reliable a representative of “maneuvering performance in ice” as it is for open water. Yet, most researchers consider this parameter as a standard. Generally, the smaller the R/L values for a ship, the greater its ability to maneuver while keeping continuous motion. Some modern icebreaker designs are able to turn the ship in level ice so effectively, that the diameter of the broken area in ice is almost the same as the waterline length of the ship. The turning ability is not the only measure for the maneuvering performance of an ice-going ship. It is important to perform different maneuvers (e.g., zigzag and star maneuvers) in shortest time possible. A good maneuvering performance can be achieved by a proper hull form design, having a large turning rate of the rudder(s) or azimuthing thruster(s) and providing a large transverse force. Breaking out of channel test is mainly conducted by merchant ships. Those ships

Maneuverability of Polar Vessel, Fig. 3 Turning circle schematic (ITTC Dictionary of Hydromechanics)

Maneuverability of Polar Vessel

navigate mostly in channels made by icebreakers. Therefore, the turning circle is not a relevant description of the agility of the ship but the ability of the ship to turn out from a channel. The test can be performed from zero speed or some other specified speed. The channel width and local pattern of ice floes and shapes of the channel edges (before the test) have big influence on the results. If this test is performed from zero speed in the channel made by the test in presawn ice, the result may differ from that in naturally broken channel. A lot of full-scale maneuvers in ice were conducted, for example, Max Waldec, Coast Guard 140 Foot Icebreaker, Canmar Kigoriak, Robert LeMeur, USCGC Polar Star、USCGC Healy, AHTS/IB Tor Viking II. The database of tests can be found in Quinton et al. (2005).

963

or a combination of devices that cause the same motion control (e.g., a rotating arm in combination with other devices). The purpose of PMM test is to obtain a series of hydrodynamic and derivatives which govern the maneuvering performance of a ship. Six standard PMM tests, including static rudder, yaw sweep, pure sway, pure yaw, and pure yaw with drift, are carried out to get forces and moment of the model. Ship maneuvering characteristics can be predicted afterwards. The Institute for Ocean Technology (IOT) in Canada has performed a series of model tests using its PMM. A PMM test (Lau 2007) was conducted by the institute in manifold conditions, and the process of PMM test was described in detail.

DP in Ice Model-Scale Ice Maneuvering Ice maneuver tests in model scale can be grouped into two categories, that is, free running model test and captive model test. The free maneuver tests involve the use of a remotely operated model that is unrestricted and capable of self-propulsion and steering. An operator directs the model via remote control and a model tracking system recording its motions. Two maneuvers in particular are used to test the maneuvering performance of free running models in ice: turning circles and Kempf maneuvers. The general process is to place the model on one side of the ice sheet, and then setting the power. The rudder angle will be given until the ship model runs straightly and steadily, and the turning diameter can be measured by running out of the 1/4 turn path. The self-propelled model test can directly observe the maneuverability of the ship model in different ice condition, but the scale of ship model is usually limited by the scale of the ice tank. And it costs a lot. A free maneuver test conducted by NMRI (National Maritime Research Institute) in japan (Izumiyama et al. 2005) found the difference of ice load distributions in the turning-going. In the turning mode, significant ice loading occurs in the aft-body in the outside of the turn, while the inside hull receives very little load. Captive maneuver tests involve the use of some form of Planar Motion Mechanism (PMM)

With an increasing interest of operations in Arctic and subarctic areas, the station-keeping capabilities in ice have attracted wide attention. Vessels operating in various ice conditions require suitable dynamic positioning (DP) systems to help course-keeping or position-keeping. DP is widely used in ice-free waters and open seas where the impacts from wind, waves, and currents are involved in the force balance algorithms. DP in ice conditions infers additional parameters such as the local and global ice loads on hull and the performance variations of propulsion systems. To understand and predict the ice forces acting on a DP ship, a wide range of numerical simulation studies and development projects have been initiated throughout the years. The numerical simulations focus on a wide range of applications from hull and propulsion designs, DP capability limits, ice management, and oil spill response capabilities evaluation to operational training for navigational officers.

References Aboulazm AF (1993) Ice forces involved in steady ship turning in pack ice. In: International conference on Marine Simulation and Ship ManeuverabilityMARSlM’93, Newfoundland Aboulazm AF, Muggeridge DB (1989) Analytical investigation of ship resistance in broken or pack ice. In:

M

964 Proceedings of the 8th conference on Offshore Mechanics and Arctic Engineering, The Hague Derradji-Aount A (2003) Multi-surface failure criterion for saline ice in the brittle regime. Cold Reg Sci Technol 36:47–70 Izumiyama K, Wako D, Shimada H, Uto S (2005) Ice load measurement on a model ship Hull. In: Proceedings of the 16th international conference on Port and Ocean Engineering under Arctic Conditions (POA C ‘02), vol 2. Potsdam, pp 635–646 Jorma K (2006) Theoretical investigation on the effect of fluid flow between the hull of a ship and ice floes on ice resistance in level ice. Helsinki University of Technology Department of Mechanical Engineering Laboratory for Mechanics of Materials Lau M (2006) Discrete element modeling of ship manoeuvring in ice. NRC Institute for Ocean Technology Lau M (2007) Preliminary modelling of ship manoeuvring in ice using a PMM. Institute for Ocean Technology (NRC/JOT) Report, TR-2006-02 Lau M, Jiancheng L, Ahmed D-A, Mary Williams F (2004) Preliminary results of ship maneuvering in ice experiments using a planar motion mechanism. In: 17th international symposium on Ice Saint Petersburg Li Z, Kaj R, Torgein M (2013) Numerical modeling of ice loads on an icebreaking tanker: comparing simulations with model tests. Cold Regions Sci Technol 87:33–46 Liu J, Lau M, Williams FM (2007) Mathematical modeling ice-hull interaction for real time simulations of ship manoeuvring in level ice. Institute for Ocean Technology (JOT) Report, LM-2007-06 Liu JC, Lua M, Williams FM (2006) Mathematical modeling of ice-hull interaction for ship maneuvering in ice simulations. Institute for Ocean Technology Lubbad R, Løset S (2011) A numerical model for real-time simulation of ship–ice interaction. Cold Regions Sci Technol 65(2):111–127 Majid I, Menon B (1983) Investigative study of simulation techniques and navigation problems for the Arctic marine environment. Prepared for Transportation Development Centre, TP 4339, Transport Canada, Montreal by Arctec Canada, Ottawa, report no FR964C Martio J (2007) Numerical simulation of vessel’s maneuvering performance in uniform ice. Report no M-301. Ship Laboratory, Helsinki University of Technology Riska K (2010) Ship-ice interaction in ship design: theory and practice. Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford, UK Robert C, Brown B, Eng (2002) An experimental investigation of ship maneuverability in pack ice. Faculty of Engineering and Applied Science Memorial University of Newfoundland Sawamura J, Tsuchiya H, Tachibana T, Osawa N (2010) Numerical modeling for ship maneuvering in level ice. In: Proceedings of 20th international symposium on ice (IAHR), Lahti, Finland Su B, Riska K, Moan T (2010) Numerical simulation of ship turning in level ice. Am Soc Mech Eng 4:751–758

Maneuvering Tests Tue-Fee K, Keinonen AJ (1986) Full scale maneuvering tests in level ice of CANMAR KIGORIAK and ROBERT LEMEUR. Mar Technol 23:131–138 Tue-Fee K et al (1987) Model for predicting the steady turning performance of conventional icebreakers in level unbroken ice. In: Proceedings of the international conference on ship maneuvrability, paper no 12 Valanto P (2001) On the cause and distribution of resistance forces on the ship hulls moving in level ice. In: Proceedings of the 16th international conference on Port and Ocean Engineering under Arctic Conditions (POAC’01), Ottawa, Ontario, Canada, pp 803–813 Williams FM, Waclawek P, Hyunsoo K (1996) Simulation of maneuvering in ice; IMD-SAMSUNG collaborative project status report. Institute for Ocean Technology, St. John’s, Canada (Protected), TR-1996-28 Yu S (2002) Model test data analysis of ship maneuverability in ice. Masters Abst Int 41(3):0845 Zhan D, Molyneux D (2012) 3-Dimensional numerical simulation of ship motion in Pack Ice. In: ASME 2012, international conference on Ocean, Offshore and Arctic Engineering, pp 407–414 Zhan D, Agar D, He M et al (2010) Numerical simulation of ship Maneuvering in pack ice. In: ASME, international conference on Ocean, Offshore and Arctic Engineering, pp 855–862 Zhou Q, Peng H (2013) A numerical simulation for operating a dynamic positioned vessel in level ice. In: Proceedings of the international offshore and polar engineering conference, pp 1300–1307 Zhou Q, Peng H, Qiu W (2016) Numerical investigations of ship–ice interaction and maneuvering performance in level ice. Cold Regions Sci Technol 122:36–49

Maneuvering Tests ▶ Towing Tank Test

Manned Submersible (MS) ▶ Atmospheric Diving Suit (ADS) ▶ Human Occupied Vehicle (HOV) ▶ Submersible

Marine Controlled-Source Electromagnetic Method (MCSEM) ▶ Deep Tow System

Marine Ecological Red Line

Marine Ecological Red Line Wei Huang1, Guanqiong Ye2, Quanzhen Chen1 and Jiangning Zeng1,2 1 Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China 2 Ocean College, Zhejiang University, Zhoushan, China

Synonyms Ecological sensitive areas; Ecological vulnerable areas

Definition The marine ecological red line is a marine spatial planning tool, referring to the institutional arrangement of important marine ecological functional areas, ecological sensitive areas, and ecological vulnerable areas as key control areas which implement strict classified management and control measures in order to maintain marine ecological health and security.

965

as a spatial planning tool was first used in China by a Chinese scholar Dr. Gao Jixi when he was doing ecological planning in Anji County, Zhejiang Province, in 2000 (Gao 2014). In 2006, the State Council formulated the cultivated land red line of 1.8 billion mu (1 mu ¼ 666.6666667 square meters), which was the first management policy officially named as “red line” in China. Subsequently, the concept of red line was gradually introduced into the field of resources and environment, and related concepts such as water resources red line and forestry red line were derived. The connotation of red line also expanded from spatial constraints to quantitative constraints (Rao et al. 2012). By the end of 2020, China completed the national ecological protection red line delineation; by 2030, China’s ecological protection red line layout will be further optimized (Fig. 1). So far, the ecological red line system has risen to the height of national strategy and has become a new system to guide China’s social and economic development. It is also an innovative measure in regional ecological protection and management in China.

Scientific Fundamentals

Principles of Marine Ecological Red Line Zoning There are five key principles in marine ecological red line zoning.

The Origin and Development of the Red Line System The red line was originally defined as a red sign warning the maximum safe flight speed or a red line marking other hazardous bases. “Red line”

1. Regional conjugation. Any marine ecological red line area must be a relatively complete, scarce (unique) natural geographical unit, and its scope should include the key areas to maintain the integrity and connectivity of the

Marine Ecological Red Line, Fig. 1 Timeline of red line policy development in China

M

966

2.

3.

4.

5.

ecosystem, so as to ensure the flow and transmission of ecosystem material, energy, and information. Ecological orientation. The scientific knowledge of ecosystem and its dynamics should be used to guide the division of marine ecological red line, with emphasis on the specific ecosystem and the influence range of various activities. Integration of land and sea development. It is necessary to fully consider the internal relationships between ocean and land resources, natural environment and ecology, correctly handling the links between ocean and land ecological protection, as well as formulating strategic thinking of the integrated development of sea and land. Coordination principle. Marine ecological red line zoning should be connected with land ecological red line zoning as far as possible, coordinating with the boundaries of various marine ecological protection areas, adapting to the needs of economic and social development as well as the local regulation ability, and reserving appropriate future development space and environmental capacity space. Dynamic principle. Marine ecological red line zoning should be forward-looking, and the area should only be increased but not be decreased. Whenever the boundary and threshold of the ecological red line zone has changed due to the disturbances from the external environment, it should be adjusted in time to ensure the continuity of its basic ecological process and function.

Theoretical Basis of Marine Ecological Red Line Ecological succession (Wikipedia 2021a) is the process of change in the species structure of an ecological community over time. The time scale can be decades (e.g., after a wildfire), or even millions of years after a mass extinction (Sahney and Benton Michael 2008). It is a phenomenon or process by which an ecological community undergoes more or less orderly and predictable changes following a disturbance or the initial colonization of a new habitat. Succession may be

Marine Ecological Red Line

initiated either by formation of new, unoccupied habitat, such as from a lava flow or a severe landslide, or by some form of disturbance of a community, such as from a fire, severe windthrow, or logging. Succession that begins in new habitats, uninfluenced by preexisting communities, is called primary succession, whereas succession that follows disruption of a preexisting community is called secondary succession. Succession is among the first theories advanced in ecology, and the study of succession remains at the core of ecological science. A coupled human-environment system (Wikipedia 2021b) (known also as a coupled human and natural system, or CHANS) is an integrated scientific framework for studying the interface and reciprocal interactions that link human (e.g., economic, social) to natural (e.g., hydrologic, atmospheric, biological) sub-systems of the planet (NSF, Marina et al. 2011). The phrase “coupled human-environment systems” appears in the earlier literature (dating back to 1999) noting that social and natural systems are inseparable (Sheppard and McMaster 2004, NRC 1999). Research into CHANS builds on the disciplines of human ecology, ecological anthropology, environmental geography, economics, and other eco-bio-geo-physical fields. Moving beyond some of the traditional research methods in social and natural sciences, CHANS tackles broader investigations into the complex nature of reciprocating interactions and feedbacks between humans on the environment and the effect of the environment on humans. The theory of human-sea relations. In a narrow sense, it means that human society, in order to survive and develop, constantly expands and deepens the transformation and utilization of the marine environment (Kappel et al. 2012), enhances the ability to adapt to the marine environment, and changes the appearance of the marine environment; in turn, the marine environment also affects human activities, resulting in sea area differences. There is a unity-contradiction between them. Sustainable development (Wikipedia 2021c). Economic development ensures that environmental depletion and degradation do not occur. In the

Marine Ecological Red Line

late 1980s, the term came to have a wider application as concern with environmental issues grew. Criteria of sustainable development came to be applied to all forms of economic development. Hitherto those economic developments had ignored environmental effects that could undermine those developments. So sustainable development would be seen as economic and social development that could avoid pollution, conserve nonrenewable energy forms, and in general would not cause future problems for which there were no easily available solutions. The carrying capacity (Wikipedia 2021d) of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment. In population biology, carrying capacity is defined as the environmental maximal load (Hui 2006), which is different from the concept of population equilibrium. The carrying capacity is the number of individuals an environment can support without significant negative impacts to the given organism and its environment. Below carrying capacity, populations typically increase, while above, they typically decrease. A factor that keeps population size at equilibrium is known as a regulating factor. Population size decreases above carrying capacity due to a range of factors depending on the species concerned but can include insufficient space, food supply, or sunlight. The carrying capacity of an environment may vary for different species may change over time due to a variety of factors, including food availability, water supply, environmental conditions, and living space. The balance of nature (Wikipedia 2021e) is a theory that proposes that ecological systems are usually in a stable equilibrium (homeostasis), meaning that a small change in some particular parameter (e.g., the size of a particular population) will be corrected by some negative feedback that will bring the parameter back to its original “point of balance” with the rest of the system. It may apply where populations depend on each other, for example, in predator/prey systems or relationships between herbivores and

967

their food source. It is also sometimes applied to the relationship between the Earth’s ecosystem, the composition of the atmosphere, and the world’s weather. Theoretical paradigm of delimitation of marine ecological red line. The delimitation of marine ecological red line should be based on the ecological integrity of marine resources and environment, and natural interference and human interference should be regarded as external interference. The delimitation of marine ecological red line should be based on finding the threshold between disturbance pressure and ecological integrity in the process of system development and formulate the threshold value of spatial resources, environmental elements, and ecological protection.

Key Applications National Marine Red Line Policy in China Review and Comparison of National Policies

In recent years, the state has paid more and more attention to the delimitation, management, and supervision of marine ecological red line and promulgated many important policies. In 2018, the State Oceanic Administration (SOA) promulgated the “measures for supervision and administration of the red line of marine ecological protection (Draft for comments),” pointing out that the implementation of the national marine ecological protection red line should be uniformly guided, coordinated, and supervised by the State Oceanic Administration. The provincial marine administrative departments shall, in accordance with the law, organize and implement the management and control of marine ecological protection red line areas, marine ecological environment monitoring, and ecological protection and remediation. This method mainly makes detailed requirements for sea-related review, assessment and supervision, regular evaluation, monitoring, and so on. In 2019, the Ministry of Ecological Environment issued the “measures for the management of ecological protection red line (Trial)” (Draft for comments). It pointed out that local governments at all

M

968

levels are responsible for delimiting and strictly abiding by the ecological protection red line, and the department in charge of ecological environment under the State Council, together with relevant departments, shall formulate policies and standards for delimiting and strictly observing the ecological protection red line. The departments in charge of ecological environment at all levels shall exercise unified supervision over the red line of ecological protection in their respective administrative areas and carry out unified monitoring and evaluation, supervision and law enforcement, and supervision and accountability. Relevant departments in charge of development and reform, finance, natural resources, water conservancy, agriculture and rural areas, forestry, and grassland at all levels shall, in accordance with their respective responsibilities, do a good job in protecting and managing the red line of ecological protection. The measures mainly regulate and restrict the delimitation and adjustment of red line, human activity control, protection and restoration, and ecological compensation. In 2020, the Ministry of Natural Resources issued the “ecological protection red line management measures (Trial)” (Draft for comments). The measures pointed out that the department in charge of natural resources under the State Council, together with relevant departments, should formulate and improve policies for delimiting and managing ecological protection red lines, establish and improve relevant technical standards and regulatory systems, and guide the delimitation and management of ecological protection red lines in all provinces (regions and cities). According to the land and space planning, the local natural resources departments at all levels shall establish a red line coordination mechanism for ecological protection and uniformly carry out the work of use control, monitoring and evaluation, supervision and law enforcement, and assessment and evaluation. The measures have detailed regulations on the red line delineation and adjustment, limited human activity control, supervision, and implementation, covering the main aspects of the two measures issued in 18 and 19 years, with relatively complete and comprehensive contents.

Marine Ecological Red Line

Detailed Introduction of National Policies

Measures for Supervision and Administration of the Red Line of Marine Ecological Protection (Draft for comments) in 2018. The “red line of marine ecological protection” determined the boundary line of geographical area and the control line of relevant management indicators of important marine ecological functional areas, marine ecological sensitive areas, and marine ecological vulnerable areas. The red line of marine ecological protection is the bottom line of maintaining marine ecological function and marine environmental quality, which cannot be adjusted in principle. After the delimitation of the red line of marine ecological protection, the red line area, the retention rate of the natural coastline of the mainland, the retention rate of the natural shoreline of the island, the sandy coastline of the island, and the quality of the sea water can only be increased, but not reduced. In terms of monitoring and inspection, it is stipulated that the implementation of the red line of marine ecological protection should be included in the content of national marine supervision. The provincial marine administrative department shall establish a dynamic monitoring platform for the marine ecological protection red line in the administrative area to monitor the development and utilization activities and ecological environment status of the islands in the marine ecological protection red line area and the surrounding sea areas and report the annual monitoring results to the marine regional Branch Bureau before the end of December of each year. The State Oceanic Administration carries out assessment on the implementation of marine ecological protection red line of coastal provincial government. The assessment contents mainly include the implementation of marine ecological protection red line control indicators, implementation of control measures, and protection and restoration of marine ecological protection red line areas. In terms of public supervision, any unit or individual has the right to report to the marine administrative departments at all levels any behavior that violates the red line system of marine ecological protection, and the marine administrative department receiving the report shall deal with it according to law and regulations.

Marine Ecological Red Line

Measures for the management of ecological protection red line (Trial) in 2019 (Draft for comments). It is stated that areas with special important ecological functions within the scope of ecological space must be strictly protected. It is the bottom line and lifeline to ensure and maintain national ecological security. It usually includes important ecological function areas with important water conservation, biodiversity maintenance, soil and water conservation, wind prevention and sand fixation, coastal ecological stability, soil erosion, land desertification, rocky desertification, salinization, and other sensitive and fragile areas of ecological environment. In order to delimit and strictly observe the ecological protection red line, we need to establish the ecological protection red line system, ensure the national ecological security, and build a beautiful China, and these measures are formulated in accordance with the requirements of several opinions on delimiting and strictly observing the ecological protection red line and relevant laws and regulations. In principle, the ecological protection red line shall be managed according to the requirements of prohibited development areas. This method follows the principles of ecological priority, strict control, and equal emphasis on rewards and punishments. All kinds of development activities that do not conform to the main function orientation are strictly prohibited. According to the orientation of dominant ecological function, differential management should be implemented to ensure that the ecological function, area, and nature of ecological protection red line will not be reduced. In terms of human activity control, urbanization and industrialization activities are prohibited within the ecological protection red line, and all kinds of development activities that do not conform to the main function orientation are strictly prohibited. The measures list specific items of prohibited activities and permitted activities and formulate approval rules for human activities or construction projects within the ecological protection red line. The management of existing human activities and construction projects within the red line of ecological protection should follow the principles of respecting history, seeking truth from facts, handling according to

969

law, and gradually solving problems and strictly investigate and deal with illegal construction projects. In addition, the measures also require all localities to formulate ecological protection red line protection and restoration plans, give priority to the protection of good ecosystems and important species habitats, repair damaged ecosystems, build ecological corridors and important ecological nodes, and improve the integrity and connectivity of the ecosystem. In accordance with the principle of overall planning and comprehensive management of land and sea, it shall carry out ecological renovation and restoration of the ecological protection red line of marine land and space and focus on strengthening the comprehensive renovation of estuaries, coastal zones, islands, and polluted sea areas within the ecological protection red line. Ecological protection red line management measures (Trial) in 2020 (Draft for comments). They are the areas with special important ecological functions in the land and marine ecological space which must be strictly protected under compulsion. These areas include water conservation, biodiversity maintenance, soil and water conservation, windbreak and sand fixation, coastal protection and other ecological functions of extremely important areas, soil erosion, land desertification, rocky desertification, coastal erosion and sand source loss and other ecologically vulnerable areas, as well as other areas with potential important ecological value which cannot be determined at present. In order to formulate and strictly observe the ecological protection red line, establish the ecological protection red line system, ensure the national ecological security, and build a beautiful China, these measures are formulated in accordance with the requirements of “several opinions on delimiting and strictly observing the ecological protection red line” and relevant regulations. According to the national and regional ecological security pattern and on the basis of scientific assessment, all provinces (districts and cities) shall identify areas with extremely important ecological functions and extremely fragile ecology, and other areas with potential important ecological value that cannot be determined by assessment at present, and shall be included in

M

970

the red line of ecological protection, so as to make sure that they should be fully delineated and protected. The demarcation of ecological protection red line should coordinate the contradictions and conflicts with permanent basic farmland, urban development boundary, and existing land space development and utilization activities, so as to ensure that the three control lines do not cross and overlap. In order to maintain the continuity and integrity of the ecosystem, scattered cultivated land, garden land, artificial commercial forest, artificial grassland, improved grassland, transportation, communication, energy pipeline, power transmission and other linear infrastructure, wind power, photovoltaic, marine energy and other facilities, and military, cultural relics, religious, funeral, and other special land in areas with extremely important ecological functions and extremely fragile ecology can be designated to enter the red line of ecological protection. Within the red line of ecological protection, in principle, human activities are prohibited in the core natural reserves, and development and productive construction activities are strictly prohibited in other areas. Once the red line of ecological protection is delimited, it shall not be adjusted without legal procedures. All localities are not allowed to adjust the ecological protection red line by modifying the land spatial planning at the city, county, and township level without

Marine Ecological Red Line

authorization. The regulations and requirements for transfer in and adjustments of nature reserves and transfer out (major national projects involving land/Sea Island) in the adjustment of red line are introduced in detail. At the end of the “measures,” social supervision, performance appraisal, and accountability are emphasized. The whole management method provides a good system guarantee for ecological protection red line. Due to the institutional adjustment and the state’s attention to the red line, it is believed that the state and local governments will issue further regulations on delimitation, management, and supervision in the next few years. Red Line Delineation Methods: “Double Evaluation”

“Double evaluation,” the abbreviation of the evaluation of resource and environmental carrying capacity and territorial development suitability, is the important basis and prerequisite for the implementation of spatial planning (Fig. 2). The evaluation of resources and environment carrying capacity is a comprehensive evaluation of natural resources endowment and ecological environment background. The evaluation of territorial development suitability, on the premise of maintaining ecosystem health, comprehensively considers the suitability of human activities such as agricultural production, urban construction, and so on, by

Marine Ecological Red Line, Fig. 2 Technological system evolution in the field of “double evaluation” in China (Tian and Liu 2020)

Marine Ecological Red Line

comprehensively considering the resources and environment elements, location conditions, and specific land space. Based on the integrated evaluation results of “double evaluation,” ecological protection red line could be delineated. According to the “requirements of several opinions on the establishment of land space planning system” and supervision of implementation issued by the CPC Central Committee and the State Council as well as the “notice on comprehensively developing land and space planning” issued by the Ministry of Natural Resources, the “double evaluation” has become the basis for optimizing the spatial pattern of land and the prerequisite for the compilation of land and space planning. As an important basis of land and space planning, “double evaluation” plays an important role in finding out the basic background of land space, ensuring the scientificity and rationality of land space planning, supporting ecological restoration and land space policymaking. “Double evaluation” is the reference basis for delimiting marine ecological protection red line and determining land and sea use planning indicators. Due to the richness of the connotation of ecological red line, the demarcation methods of ecological red line are diverse, and there is no unified standard for dividing ecological red line. Based on the importance of ecological function and ecological vulnerability, the existing method for dividing ecological red line is to use geographic information system (GIS) for spatial analysis and processing. Relationship and Difference Between Marine Ecological Red Line Zoning and Existing Marine Zoning

Marine ecological red line zoning is closely related to marine main function zoning, marine reserve, and marine functional zoning, but there are some differences (Table 1). As the basic and restrictive planning of marine space development in China, marine main function zoning has a wider scope of action and stronger effectiveness than other plans. Marine main function zoning plays an important role in guiding other marine-related planning and is an important carrier and way to

971

ensure the implementation of marine ecological red line zoning, and marine ecological red line zoning and marine function zoning are the important basis of marine main function zoning. Marine protected areas (MPAs) refer to the areas designated in accordance with the law for special protection and management of coasts, estuaries, islands, wetlands, or sea areas, including the protected objects, for the purpose of marine natural environment and natural resources protection. The core factor of the value of marine reserves is the inherent scarcity and typicality of the protected objects, which is also applicable to the marine ecological red line areas. Marine functional zoning (MFZ) is a type of marine spatial planning implemented widely in China and one of the three major systems defined in the Law of the PRC on the Administration of Sea Area Use. China adopts “top-down management” for MFZ, in which upper management levels impose clear constraints and restrictions on lower levels. The sea area is divided based on its geographical location, natural resources, natural environmental conditions, and social needs. It is used to guide and restrict the practical activities of marine development and utilization and ensure the economic, environmental, and social benefits of marine development. Marine functional zoning refers to all kinds of functions based on human needs. It emphasizes the economic attribute that the ocean can be used by human beings to produce use value, and it is a man-made overall arrangement of sea area use positioning. Therefore, marine functional zoning is essentially a management method to implement protection in development.

Case of Study Currently, coastal regions in China are carrying out marine ecological red line zoning. Most of the regions have carried out extensive scientific research for zoning. The people’s Government of Guangdong Province promulgated and implemented “the outline of the environmental protection plan for the Pearl

M

972

Marine Ecological Red Line

Marine Ecological Red Line, Table 1 Differences and relations of several current marine zoning in China Zoning type Resource development and protection

Zoning basis

Purpose

Marine principle function zoning The optimized and key development zones focus on development, while the restricted and prohibited development zones focus on ecological protection Environmental carrying capacity, current development density, and development potential of marine resources

Marine functional zoning Develop and protect according to function plan

Marine ecological red line zoning Strict protection

Sea area location, natural resources, environmental conditions, and requirements for development and utilization

Marine natural attributes, resources and environmental characteristics, regional ecological sensitivity and vulnerability, ecological importance

Establish a rational development order, optimize the allocation and utilization of marine resources, protect the environment, and promote sustainable development

Guide the use of sea areas, protect and improve the marine ecological environment, and promote the sustainable utilization of resources

Maintain the integrity and connectivity of regional marine ecosystem

River Delta” (2005), which put forward a complete ecological red line for the first time in the field of environmental planning. In 2014, Tianjin divided the red line area into six categories, mountains, rivers, lakes, wetlands, parks, and forest belts, and determined the proportion of different zones, and then strictly controlled the corresponding ecological regions. So far, the urban ecological red line system has basically formed. Based on the analysis of the system structure of ecological, water, atmosphere, and other environmental elements, the environmental protection intensity level of each region is determined based on the sensitivity and vulnerability of the areas affected by pollution formation and transmission process, and the important difference of the protection area, and the management is carried out with hierarchical management and control measures. In February 2014, the Ministry of Environmental Protection issued “the national ecological protection red line - Technical Guide for

Marine protected area Restrict human activity

Intertidal zone and subtidal zone protected by law or other effective means, including the plants, animals, historical sites, and cultural characteristics inside the area For a conservation purpose, typically to protect natural or cultural resources (MPA 2016)

delimiting ecological function baseline (Trial),” and in June 2016, the Oceanic Administration issued “the technical guide for delimiting marine ecological red line.” These guidelines have a good guiding role for the development and practice of ecological red line theory and delimitation technology in China.

References Environmental Resource and Education Funding Opportunities, National Science Foundation. Gao J (2014) Ecological Protection Red Line: The 'lifeline' of Maintaining national ecological security – the construction idea of national ecological protection Red line system. Ring Environ Protect 42(2):17–21 Hui C (2006) Carrying capacity, population equilibrcaquita deliciosavironment's maximal load. Ecol Modell 192: 317–320 Kappel CV, Halpem BS, Napoli N (2012) Mapping cumulative impacts of human activities on marine ecosystems. Sea Plan, Boston

Marine Operations Marina A, Asbjornsen H, Baker LA, Brozovic N, Drinkwater LE, Drzyzga SA et al (2011) Research on Coupled Human and Natural Systems (CHANS): Approach, challenges, and strategies. Bull Ecol Soc Am 92:218–228 “Marine Protected Areas”. National Ocean Service. National Oceanic and Atmospheric Administration. Retrieved 2016-09-02 National Research Council Policy Division Board on Sustainable Development (1999) Our common journey: a transition toward sustainability. National Academic Press, Washington, DC Rao S, Qiang Z, Xuejie M (2012) Delimiting ecological red line and innovating ecosystem management. Environ Econ 6:57–60 Sahney S, Benton Michael J (2008) Recovery from the most profound mass extinction of all time. Proc R Soc B 275:759–765 Sheppard E, McMaster RB (eds) (2004) Scale and geographic inquiry: nature, society, and method. Wiley, New York Tian C, Liu G (2020) Practice and thinking of “Double Evaluation” under the land and space planning system. Retrieved from https://www.163.com/dy/article/ FJQJJ3OI0521C7DD.html Wikipedia (2021a) Ecological succession. Retrieved from https://encyclopedia.thefreedictionary.com/ Ecological+succession Wikipedia (2021b) Coupled human environment system. Retrieved from https://encyclopedia.thefreedictionary. com/Coupled+human-environment+system Wikipedia (2021c) Sustainable development. Retrieved from https://encyclopedia.thefreedictionary.com/ sustainable+development Wikipedia (2021d) Carrying capacity. Retrieved from h t t p s : / / e n c y c l o p e d i a . t h e f r e e d i c t i o n a r y. c o m / carrying+capacity Wikipedia (2021e) Balance of nature. Retrieved from https://encyclopedia.thefreedictionary.com/balance+ of+nature. Wiley-Blackwell. p 288. ISBN 0-63123070-X

Marine Operations Lin Li Department of Mechanical and Structural Engineering and Materials Science, University of Stavanger, Stavanger, Norway

973

object(s) and/or vessel(s) in the marine environment during temporary phases (DNVGL 2017). A marine operation is a process involving interactions between dynamic systems, operational procedures, environmental actions, and human intervention. A marine operation shall be designed to bring an object from one defined safe condition to another. Examples of Marine Operations Marine operations include a large variety of activities. The definitions of the following commonly used operations are provided (DNVGL 2016). • Towing: The transfer at sea from one location to another location of a self-floating structure or a structure resting on a barge by pushing/ pulling by tugs. • Launching: The activities comprising cutting of sea fastening of a structure resting on a launch barge, the structure’s slide-down on the launch rails on the barge and diving into the water until the structure is free floating. • Lifting: The activities necessary to lift or assist a structure by a crane. • Load transfer operation: The operation to transfer the load (i.e., an object) from/to vessel(s) without using cranes, that is, by using (de-)ballasting. Typical load transfer operations are load-out, lift-off, mating, and floatover. • Pipelay: The operation of assembling and laying the pipeline on the seabed, from start-up point to lay-down point. General Terms Related to Marine Operations The relevant terms on marine operations are defined as follows (DNVGL 2016): Operation Reference Period

Duration of marine operations shall be defined as an operation reference period, TR. T R ¼ T POP þ T C

ð1Þ

Definitions Marine operations are nonroutine operation of a limited defined duration related to handling of

where TPOP is the planned operation period, and TC is estimated maximum contingency time. TPOP shall be based on a detailed schedule for the

M

974

operation. In early planning phase, where a detailed schedule is not available, TPOP can be based on experience with similar operations. TC should cover the general uncertainty in TPOP, the unproductive time during the operation, and possible contingency situations that will require additional time to complete the operation. Weather Restricted and Weather Unrestricted Operations

An operation shall be defined as weather restricted or weather unrestricted based on its reference period. Marine operations with a reference period (TR) less than 96 h and a planned operation time (TPOP) less than 72 h may normally be defined as weather restricted. However, in areas and/or seasons where the duration of the reliable weather forecast is less than 96 h, the maximum allowable TR is the duration of the reliable forecast. A weather restricted operation shall be planned to be executed within a reliable weather window. If the weather restricted design environmental condition is too low, severe waiting on weather delays can occur. Marine operations that cannot be defined as weather restricted shall be defined as weather unrestricted operations. Environmental criteria for these operations should be based on longterm statistics. If found beneficial, operations of shorter duration may also be defined as weather unrestricted. Operational Limiting Criteria

Operational limiting environmental criteria (OPLim) shall be established and clearly described in the marine operation manual. OPLim shall not be taken greater than the minimum of: (a) the environmental design criteria, (b) maximum wind and waves for safe working and object handling or transfer conditions for personnel, and (c) weather restrictions for equipment. Forecasted and Monitored Operational Limits, Alpha Factor

Uncertainty in both the monitoring and the forecasting of the environmental conditions shall be considered. This should be done by defining a

Marine Operations

forecasted (and, if applicable, monitored at the operation start) operational criteria, OPWF: OPWF ¼ a  OPLim

ð2Þ

where the alpha factor, α, depends on the planed operation period, TPOP, the operational limiting OPLim significant wave height, the forecast levels and whether or not meteorologists or measurement equipment are available on site (DNVGL 2016).

Assessment of Operational Limits Operational limits need to be assessed during planning of marine operations. The limits can be expressed in terms of environmental conditions (sea states, wind, and current conditions) or motions that could be monitored on-board the installation vessels before executing the operation. The operational limits depend on the type of operation and the property of the dynamic system. The operational limits can be used to improve the system performance in the planning phase, that is, to select vessels and equipment, to optimize the procedure, and to propose contingency or mitigation actions. They can also be used together with the weather forecasts to support on-board decision making in the execution phase. Traditionally, operational limits have relied mostly on practical marine operation experiences. However, it is important to quantify the responses (forces, motions) and corresponding operational limits for complicated operations with strict requirements. A systematic method to establish the operational limits is required. Li (2016) and Guachamin-Acero (2016b) established a general methodology to establish the operational limits (Li 2016; GuachaminAcero 2016). It includes six main steps, see Fig. 1. 1. Identification of potentially critical events. Based on the operational procedure, a preliminary selection of activities which could lead to critical events is required. The preliminary selection requires qualitative risk assessment

Marine Operations

975

Marine Operations, Fig. 1 General methodology to establish the operational limits. (Li 2016)

2.

3.

4.

5.

based on experience, guidelines, and by reviewing of relevant operations. Numerical modeling of operational activities. Numerical modeling and analysis of the potential critical events are required to evaluate the dynamic responses of the installation systems. A quantitative assessment of the dynamic responses under reasonable environmental conditions will indicate which response parameters may reach high levels and thus limit the operation. Identification of critical events and limiting parameters. By assessment of the dynamic responses, the events governing each offshore activity and leading to failure events are identified. They are identified as critical events, and the governing dynamic responses are defined as limiting parameters. Calculation of characteristic dynamic responses. Once the limiting parameter is identified, a characteristic value of its dynamic response needs to be calculated. The dynamic responses should be treated in a probabilistic way to take into account the stochastic nature of the environmental conditions (e.g., wind, wave, and current conditions). Evaluation of the allowable limits. The allowable limits are the maximum values that the limiting parameters may reach to remain within acceptable safety margin. It needs to be specified based on safety criteria to avoid structural failure and the exceeding of specified

installation requirements. For events related to structural failure, structural analysis or finite element modeling to determine the strength or the capacity of the structure is normally required to provide the allowable limits. 6. Assessment of the operational limits. By comparing the characteristic dynamic responses and their allowable limits for all possible sea states, the allowable sea states at which the responses are less than the allowable limits can be found. These sea states can be transformed into allowable motion responses. In general, both the allowable sea states and responses can be used as operational limits. This general methodology uses responsebased criteria to determine the allowable limits of sea states and to assess the safety of the operation. The operation is considered to be safe if the characteristic value of the governing response is less than the capacity. Often, safety factors need to be considered to take into account the uncertainties associated with the analyses or the data in the assessment of both the load effect and the resistance. Uncertainties on the weather forecasts need to be included by implementing alpha factor. Other uncertainties related to the wave spectra should also be implemented (Guachamin-Acero and Li 2018). This general methodology has been applied in analyses of various marine operations (Li et al. 2016a; Gao et al. 2016; Guachamin-Acero et al. 2017).

M

976

Installation Methods for Offshore Wind Turbines The installation of an offshore wind farm includes the transportation and installation of foundations, turbine components (tower, rotor, and nacelle assembly, RNA), substations, and cables. The most commonly used method for foundation installation is heavy lifting operation using either floating cranes or jack-ups. Turbine components are normally lifted and installed using jack-up vessels in shallow water depths. A review of the current installation methods for bottom-fixed offshore wind turbine (OWT) foundations, turbine components, as well as floating wind turbines is presented here. Recently developed installation concepts are also discussed. Installation Methods for Bottom-Fixed Foundations Methods for installing foundations depend on the foundation type. The most commonly used bottom-fixed foundations include monopiles, gravity-based foundations, jackets, and tripods. Monopiles

Monopiles are transported either on-board of a barge or an installation vessel or capped and wet towed (Herman 2002). The wet tow of a single floating monopile has been applied during installation of two wind farms (Npower Renewable 2006; Ballast Nedam 2011). The transportation of more than one monopile per trip can be achieved using proper connection between the monopiles. Installation of monopiles using crane vessels in general includes three main steps: upending, lowering, and hammering operations. A combined wet-tow and upending in water can be performed by lower capacity cranes than those required for transporting and upending on board. However, the upending of long monopiles in water is more weather sensitive than upending on board. Moreover, the verticality of the monopile during hammering operation should also be carefully controlled. Figure 2a shows a monopile lifting operation by the heavy lift vessel (HLV) “Svane.” Li (2016) studied extensively the

Marine Operations

monopile lowering operation by considering the nonstationary features of the installation process (Li et al. 2014, 2015, 2016b). The dynamic responses during the hammering process were also investigated (Li et al. 2016a). The allowable sea states in terms of significant wave height (Hs) and wave spectral period (Tp) and the operability at one reference site for the whole monopile installation have been derived (Guachamin-Acero et al. 2016b). Gravity-Based Foundations

Gravity-based structures (GBS) for wind turbines weigh over 2500 tons. They can either be wettowed or dry-transported on a barge or an installation vessel. Most of the existing GBS in very shallow waters are dry-transported to the offshore site. Wet-tow can reduce the installation costs by chartering lower capacity lifting vessels. Although the wet-tow method is widely used for transporting gravity-based platforms, it has not been applied for installing GBS of OWTs because their weight is still within the crane capacity of available HLVs. However, if larger GBS are applied for offshore farms in deeper waters, the wet-tow method may be more cost-efficient. Figure 2b displays a lifting operation of a GBS by a HLV. A novel installation concept was proposed to transport and install a fully assembled gravitybased foundation OWT using double-barge supports and standard tugboats (Wasjø et al. 2013). The concept aimed to reduce the costs by avoiding the use of heavy lift crane vessels. Model tests and numerical studies have been conducted to assess the feasibility of this concept (Bense 2014). Jackets and Tripods

Jackets and tripods for OWTs can range from 400 to 1000 tons and with a height of 30–90 m in water depth of around 20–70 m. Figure 2c and d shows typical installation activities for jacket and tripod. The jackets can be transported in either an upright or horizontal position depending on the size of the foundations and the available transport barges. The installation of piles could be carried out either after positioning the jackets (post-piling) or before jackets installation (pre-piling) (LORC 2013).

Marine Operations

977

M Marine Operations, Fig. 2 Installation of bottom-fixed OWT foundations. (a) Monopile lifting operation. (Source: https://www.offshorewind.biz/), (b) GBS installation.

(Peire et al. 2009), (c) Jacket upending operation. (Source: http://www.rechargenews.com), (d) Tripod lifting operation. (Source: http://www.4coffshore.com/)

Post-piling is traditionally used in the oil and gas industry and was applied for the jackets in Beatrice wind farm. Experience with pre-piling is limited, but it was first used for the jackets at Alpha Ventus wind farm (Østvik 2010). Pre-piling is considered to be a faster method than post-piling. With pre-piling, smaller vessels can be employed for the piling operation and the HLVs are only required to lift the jackets into the preinstalled piles. With post-piling, the expensive HLVs are used to install both the jacket and the piles. In addition, a considerable amount of steel can be saved using pre-piling because the sleeves for the piles are unnecessary.

on-board an installation vessel or a feeding barge. The turbine, particularly the nacelle and the rotor, have sensitive components which only tolerate very limited accelerations during transportation and installation. Moreover, lifting operations are weather-sensitive especially at large lifting heights, and the mating between the components is challenging. There are many alternatives for turbine installation. Figure 3 shows the commonly used installation strategies. The weight of each component for the NREL 5 MW reference turbine (Jonkman et al. 2009) is included in the figure. The choice of method is related to the vessel size, distance from port to site, size of the wind turbines, and the lifting capacity of the crane. By increasing the amount of onshore assembly, the offshore construction work can be reduced. However, the assembled components reduce the efficiency in

Installation Methods for Turbine Components Transportation and installation methods for turbine components are very different from those for foundations. They must be dry-transported

978

Marine Operations

Marine Operations, Fig. 3 Installation alternatives for turbine components including number of lifts and lift weights. (Kaiser and Snyder 2011)

using the deck space and increase the number of trips for transportation when installing a large wind farm. In addition, the weight of the fully assembled turbine with the large lift height requires very large and expensive crane vessels (Ku and Roh 2014). Among the methods for blade installation, single blade installation is most frequently used for offshore installation in recent years, due to small deck space requirement and flexible blade orientations during installation (Ahn et al. 2017).

During the installation process, the blade is lifted and installed in a feathered position, which is kept during the whole installation operation (Kuijken 2015). Recently, extensive studies on a single blade installation have been carried out. (Zhao et al. 2018a, b) developed an integrated aerohydro-soil-elastic-mechanical tool for simulating installation of a single blade for wind turbines. (Jiang et al. 2018a) studied the final blade installation phase onto a monopile wind turbine. The effects of mean wind speed, wind turbulence,

Marine Operations

significant wave height, wave spectrum peak period, wind-wave misalignment, and water depth on the blade installation were evaluated. Moreover, some studies have been focusing on developing active control schemes to control the tugger lines used for blade installation, with the purpose to increase the weather window for the final mating phase between the blade root and the hub (Ren et al. 2018a, b). In addition to the methods shown in Fig. 3, a few innovative concepts to install fully assembled tower and RNA have been proposed. Sarkar and Gudmestad (2013) designed a floating substructure to transport the fully assembled structure, but the concept was only applicable for telescopic tower (Sarkar and Gudmestad 2013). Guachamin Acero et al. (2016a) proposed a new concept based on the principle of the inverted pendulum (Guachamin Acero et al. 2016a). The feasibility of this installation concept was assessed by numerical analyses. Installation Methods for Floating Wind Turbines Installation methods for floating wind turbines are quite different from those for bottom-fixed wind turbines due to larger water depth of the installation site. For turbine installation in shallow water, jack-up vessels are normally used to provide stable platform for lifting and offshore bolting, which could hardly be carried out by a floating vessel with motions in six degrees of freedom. However, for deep waters, if onshore assemble is chosen, the installation can only be performed by floating vessels, and it was proven to be difficult and costly. The installation method differs with different floating structures. The Hywind Scotland, which was the first offshore floating wind farm, applies a spar-type floating wind turbine. The spar buoy was dry-towed in a horizontal configuration using a transportation vessel and upended to a vertical position by ballasting the spar. The tower, nacelle, and blades were preassembled onshore and installed by a single lift using a large heavy lift vessel. Both the upending of the spar and the mating between the tower and the spar buoy are critical operations. In order to

979

increase the operability, the installations were done at a well-sheltered location in deep water. Then, the fully assembled floating unit was towed to the site and hooked up to the mooring system (Lien 2016). The installation of Windfloat, on the other hand, was the first offshore wind turbine to be deployed without the use of any offshore heavy lift vessel. Due to the shallow draft of the semisubmersible foundation, the turbine could be fully assembled onshore prior to the unit being towed offshore (Roddier et al. 2010). In this way, all the weather-sensitive lifting operations can be carried out onshore, which could reduce the installation costly significantly when installing a large number of wind turbines with this type of foundations. Once at shore, the floating structure was hooked up to the preinstalled mooring system. In order to reduce the installation cost to make floating wind turbine more cost-effective, innovative installation strategies are required. In the Hywind installation challenge campaign (Equinor 2018), and among the proposed innovative installation concepts, there is a tendency to favor novel installation vessels and facilities to reduce offshore lifts and operation time. A novel wind turbine installation concept was proposed to use a catamaran installation vessel for installations of fully assembled OWTs (Jiang et al. 2018b, c). This concept avoids extremely weather-sensitive high lifts from a floating vessel by carrying the wind turbine on the catamaran and a gripper device. This installation method was deemed to be suitable for both offshore bottomfixed or floating foundations.

References Ahn D, Shin S-c, Kim S-y, Kharoufi H, Kim H-c (2017) Comparative evaluation of different offshore wind turbine installation vessels for korean west– south wind farm. Int J Nav Archit Ocean Eng 9(1):45–54 Ballast Nedam (2011) Supporting offshore wind – alternative foundation installation. Technical report, Ballast Nedam Offshore B.V. Available from http://flowoffshore.nl/images/flow-openbaar/alternative-founda tion-installation.pdf

M

980 Bense MP (2014). Comparison of numerical simulation and model test for integrated installation of GBS wind turbine. Master’s thesis, Department of Marine Technology, Norwegian University of Science and Technology, Trondheim DNVGL (2016) Standard DNVGL-ST-N001, Marine operations and marine warranty. DNV GL AS, Oslo, Norway. DNVGL (2017) Recommended practice DNVGL-RPN101, Risk management in marine and subsea operations. DNV GL AS, Oslo, Norway. Equinor (2018). Hywind installation. Available at https:// www.equinor.com/en/how-and-why/innovate/the-hyw ind-challenge.html. Accessed 7 May 2018 Gao Z, Wilson Guachamin Acero LL, Zhao Y, Li C, Moan T (2016) Numerical simulation of marine operations and prediction of operability using response-based criteria with an application to installation of offshore wind turbine support structures. In Marine operations specialty symposium (MOSS 2016) Guachamin-Acero W (2016) Assessment of marine operations for offshore wind turbine installation with emphasis on response-based operational limits. PhD thesis, Department of Marine Technology, Norwegian University of Science and Technology Guachamin-Acero W, Li L (2018) Methodology for assessment of operational limits including uncertainties in wave spectral energy distribution for safe execution of marine operations. Ocean Eng 165:184–193 Guachamin-Acero W, Moan T, Gao Z (2016a) Assessment of the dynamic responses and allowable sea states for a novel offshore wind turbine installation concept based on the inverted pendulum principle. Energy Procedia 94:61–71 Guachamin-Acero W, Li L, Gao Z, Moan T (2016b) Methodology for assessment of the operational limits and operability of marine operations. Ocean Eng 125:308–327 Guachamin-Acero W, Gao Z, Moan T (2017) Methodology for assessment of the allowable sea states during installation of an offshore wind turbine transition piece structure onto a monopile foundation. J Offshore Mech Arct Eng 139(6):061901 Herman SA (2002) Offshore wind farms – analysis of transport and installation costs, report no. ECN-I-02002. Technical report, Energy research centre of the Netherlands Jiang Z, Gao Z, Ren Z, Li Y, Duan L (2018a) A parametric study on the final blade installation process for monopile wind turbines under rough environmental conditions. Eng Struct 172:1042–1056 Jiang Z, Li L, Gao Z, Halse KH, Sandvik PC (2018b) Dynamic response analysis of a catamaran installation vessel during the positioning of a wind turbine assembly onto a spar foundation. Mar Struct 61:1–24 Jiang Z, Ren Z, Gao Z, Sandvik PC, Halse KH, Skjetne R, et al (2018c) Mating control of a wind turbine towernacelle-rotor assembly for a catamaran installation vessel. In The 28th international ocean and polar

Marine Operations engineering conference, international society of offshore and polar engineers, Sapporo, Japan Jonkman J, Butterfield S, Musial W, Scott G (2009) Definition of a 5-MW reference wind turbine for offshore system development. Technical report, NREL/TP-50038060, National Renewable Energy Laboratory (NREL) Kaiser MJ, Snyder B (2011) Offshore wind energy installation and decommisioning cost estimation in the US outer continental shelf. Technical report, US department of the interior, bureau of ocean energy management, regulation and enforcement, Herndon, TA & R study 648, 340 pp Ku N, Roh M-I (2014) Dynamic response simulation of an offshore wind turbine suspended by a floating crane. Ships Offshore Struct 10(6):1–14 Kuijken L (2015) Single blade installation for large wind turbines in extreme wind conditions. Master’s thesis, Master of science thesis, Technical University of Denmark & TU Delft Li L (2016) Dynamic analysis of the installation of monopiles for offshore wind turbines. PhD thesis, Department of Marine Technology, Norwegian University of Science and Technology, 1–70 Li L, Gao Z, Moan T, Ormberg H (2014) Analysis of lifting operation of a monopile for an offshore wind turbine considering vessel shielding effects. Mar Struct 39:287–314 Li L, Gao Z, Moan T (2015) Response analysis of a nonstationary lowering operation for an offshore wind turbine monopile substructure. J Offshore Mech Arct Eng 137(5) Li L, Acero WG, Gao Z, Moan T (2016a) Assessment of allowable sea states during installation of offshore wind turbine monopiles with shallow penetration in the seabed. J Offshore Mech Arct Eng 138(4):041902 Li L, Gao Z, Moan T (2016b) Operability analysis of monopile lowering operation using different numerical approaches. Int J Offshore Polar Eng 26:88 Lien KH (2016) Hywind scotland – marine operations. In Science meets industry Stavanger, Norway LORC (2013) The jacket – a path to deeper waters. Available at http://www.lorc.dk/offshore-wind/foundations/ jackets. Accessed 11 May 2017 Npower Renewable (2006) Capital grant scheme for the North Hoyle offshore wind farm annual report: July 2005-june 2006. Technical report, Npower Renewables Limited, Essen Østvik I (2010) Lessons learned from the first German offshore wind farm –Alpha Ventus. Presented in SPE conference, 14 Apr, Bergen Peire K, Nonneman H, Bosschem E (2009) Gravity base foundations for the Thornton bank offshore wind farm. Terra et Aqua 115:19–29 Ren Z, Jiang Z, Gao Z, Skjetne R (2018a) Active tugger line force control for single blade installation. Wind Energy 21:1344 Ren Z, Jiang Z, Skjetne R, Gao Z, et al (2018b) Single blade installation using active control of three tugger

Marine Protected Areas in Areas Beyond National Jurisdiction lines. In The 28th international ocean and polar engineering conference, international society of offshore and polar engineers Roddier D, Cermelli C, Aubault A, Weinstein A (2010) Windfloat: a floating foundation for offshore wind turbines. J Renewable Sustainable Energy 2(3):033104 Sarkar A, Gudmestad OT (2013) Study on a new method for installing a monopile and a fully integrated offshore wind turbine structure. Mar Struct 33:160–187 Wasjø K, Bermúdez J, Bjerkas M, Søreide T (2013) A novel concept for self installing offshore wind turbines. In Proceedings of the 32nd International Conference on Ocean, Offshore and Arctic Engineering, Nantes, 9–14 June 2013 Zhao Y, Cheng Z, Sandvik PC, Gao Z, Moan T (2018a) An integrated dynamic analysis method for simulating installation of single blades for wind turbines. Ocean Eng 152:72–88 Zhao Y, Cheng Z, Sandvik PC, Gao Z, Moan T, Van Buren E (2018b) Numerical modeling and analysis of the dynamic motion response of an offshore wind turbine blade during installation by a jack-up crane vessel. Ocean Eng 165:353–364

Marine Protected Area (MPA) ▶ Marine Protected Areas in Areas Beyond National Jurisdiction

Marine Protected Areas in Areas Beyond National Jurisdiction Dong Sun1 and Miaozhuang Zheng2 1 Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China 2 China Institute for Marine Affairs, Ministry of Natural Resources, Beijing, China

Synonyms Areas beyond national jurisdiction (ABNJ); Marine protected area (MPA); Marine protected areas in areas beyond national jurisdiction (MPA in ABNJ)

981

Definition A marine protected area (MPA) is “a clearly defined geographical space, recognized, dedicated and managed, through legal or other effective means, to achieve the long-term conservation of nature with associated ecosystem services and cultural values” (Muraki Gottlieb et al. 2018). If a part of or whole MPA is located on the ABNJ, then we call it “marine protected areas in areas beyond national jurisdiction (MPA in ABNJ).” MPAs do not mean absolutely no fishing or other human activities; in fact, most MPAs in the world are multipurpose areas. The no-fishing MPAs are often referred to as “no-take areas.”

Scientific Fundamentals Areas beyond the national jurisdiction (ABNJ) amount to approximately 61% of the oceans, 44% of the surface of the Earth, and 65% of the volume of the biosphere but remain the least protected space on the planet (Gjerde et al. 2016). However, these areas are increasingly under threat from anthropogenic activities such as pollution, overfishing, mining, and geoengineering. At the UN Conference on Sustainable Development in Rio de Janeiro in June 2012, the world’s political leaders committed to the conservation and sustainable use of marine biological diversity in areas beyond national jurisdiction (ABNJ) (UN 2012). After that, the General Assembly decided to convene an Intergovernmental Conference to elaborate the text of an international legally binding instrument under the United Nations Convention on the Law of the Sea (UNCLOS) on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction. The Conference will meet for four sessions. The first three sessions were conducted in 2018 to 2019. By decision 74/543 of March 11, 2020, the General Assembly decided to postpone the fourth session of the conference to the earliest possible available date to be decided by the General Assembly (UN 2020) (https://www.un.org/bbnj/). After

M

982

Marine Protected Areas in Areas Beyond National Jurisdiction

Marine Protected Areas in Areas Beyond National Jurisdiction, Fig. 1 Diagram of maritime zones by UNCLOS

this, a new regime about the marine protected areas in ABNJ will be expected. ABNJ legally comprise the “high seas,” which indicated the waters beyond the exclusive economic zones (EEZ) of national jurisdiction, and the “international seabed area” (“the Area”), which indicated the seabed, the ocean floor, and subsoil thereof beyond national jurisdiction (UNCLOS Articles 1 and 86) (Fig. 1). If a part of or whole MPA is located on the ABNJ, then we call it “MPA in ABNJ.”

Objectives of Establishing MPAs in ABNJ For the past few decade years, the ABNJ were under increasing and intensive threats from human activities, such as overfishing, pollution, maritime shipping, and climate change. Besides, it will also be strongly threatened by potential deepsea resource exploitation, including oil, gas, and metallic ores, in the future (Sharma 2015; Gjerde et al. 2016). These issues not only threaten the biodiversity in ABNJ (Oleary et al. 2020) but also depress the ecosystem function and service in

these areas (Worm et al. 2006; Rogers et al. 2014) (Table 1). MPAs are widely considered as an important tool for the conservation of biological diversity and marine ecosystems in the past several decade years (Lester et al. 2009). By the end of August 2020, 17,237 MPAs were established in the world, and they covered near 27 million square kilometers in area, about 7.45% area of world’s oceans. However, only less than one in a thousand MPAs were established in ABNJ (Smith and Jabour 2018). It meant that the ABNJ were largely under absolutely unprotected conditions (Gjerde et al. 2016).

The Potential Cost of MPAs in ABNJ The establishment of MPAs in ABNJ, especially the “no-take” MPAs, could be also with some cost, at least in short term. First, fisheries data show that 6% of global fish catch is obtained in ABNJ (www. seaaroundus.org/data/#/global). Thus, if the current and potential fishing areas in ABNJ are protected and all forms of fishing are strictly prohibited in these areas, the global supply of fish will be

Marine Protected Areas in Areas Beyond National Jurisdiction

983

Marine Protected Areas in Areas Beyond National Jurisdiction, Table 1 The current and potential threats to biodiversity and ecosystems in ABNJ, from human activities and climate change Activity Fishing

Maritime shipping

Climate change and associated effects

Land-based pollution

Deep-sea mining

Oil and gas exploration and exploitation

Bioprospecting for marine genetic resources and scientific research Aquaculture

Renewable energy

Military

Submarine cables and pipelines

Impacts or threats to biodiversity and ecosystems in ABNJ Fishing is the most significant direct threat to biodiversity in ABNJ now and also with high and widespread environmental impacts to habitats and ecosystems (Pauly et al. 2005) Given the large spatial extent of shipping activities, environmental impacts are likely to be high. For example, anthropogenic noise from ship was considered to be with great impacts on marine life (Nowacek et al. 2010; Williams et al. 2015) Ocean ecosystems are already experiencing significant change mainly because of ocean acidification, hypoxia, and warming, and changes will continue to extend across ABNJ in the future (Doney et al. 2012) Environmental impacts from land-based pollution are high and affect all aspects of marine life, even in deep seafloor (Van Cauwenberghe et al. 2013) Environmental impacts are likely to be high and broadly distributed and impact the entire seabed to surface ecosystem. Although deep-sea mining is not a current threat in “the area,” it is widely considered as a reality in the near future (Durden et al. 2018) The local and regional impacts are experienced which can have high negative environmental impacts to the entire seabed to surface ecosystem (Gray et al. 1999). No offshore oil and gas drilling operations currently take place in ABNJ, but it could happen accompanied by shortage of energy and technological advancement in the future Bioprospecting and scientific research have a small scope and temporal and spatial footprint. Thus, the environmental impacts to biodiversity and ecosystems are considered to be weak Currently, aquaculture activities are mainly concentrated near to shore in EEZs, and the expansion of aquaculture offshore is likely to be contained within areas of national jurisdiction in the future. But, some ecological and environmental impacts of aquaculture activities are still largely unknown, such non-native species escapes from aquaculture (Ju et al. 2020) Currently, engineering construction of renewable energy in marine remains in EEZs, and the expansion is likely to be contained within areas of national jurisdiction in the future Because of its secrecy, less data are able to be used to evaluate the environmental impacts on marine biodiversity and ecosystems. However, a limited amount of evidence showed the potential impact from military, especially the underwater noise, could not be ignored (Tyack et al. 2011; Morell 2015) The submarine cables only cover 0.00002% of seabed in ABNJ, and no significant and widespread environmental impacts were found (Taormina et al. 2018). The oil and gas pipelines are considered to be with great potential environmental impacts in offshore and continental shelf (Dey et al. 2004), and it was unlikely given the lack of oil and gas exploration and exploitation in deep sea of ABNJ

Adapted from Oleary et al. (2020)

reduced, especially the tunas and squids (Sala et al. 2018). Second, a large proportion of maritime shipping routes are located on the ABNJ. Environmental protection terms of MPAs in ABNJ, such as

control of air pollution emissions and underwater noise levels of ships in the protected area, will inevitably increase the costs of maritime shipping (Gallucci 2018). Third, some underwater

M

984

Marine Protected Areas in Areas Beyond National Jurisdiction

engineering, such as laying or maintaining of submarine cables, pipelines, and other facilities, may face stricter environmental impact assessment.

Key Applications

ABNJ is viewed as an important measure to protect marine biodiversity and widely accepted (Smith and Jabour 2018). To date, 13 MPAs have been established in ABNJ: 2 in the Southern Ocean, 10 in the North-East Atlantic region, and 1 in the Mediterranean Sea (Table 2).

The Current Status of MPAs in ABNJ

The Future Harder Task MPAs in ABNJ: Lessons from Two High Seas Regimes

Although there is still much debate about the details, establishing a network of MPAs in

The world’s ocean represents the largest ecosystem on Earth comprising 1.3 billion km3 of water. Considering the strong and widespread

Marine Protected Areas in Areas Beyond National Jurisdiction, Table 2 Thirteen MPAs in ABNJ (including wholly or partly) have been established to date 1.

Name of MPAs South Orkney Islands southern shelf MPA

Location Southern Ocean

2.

Ross Sea region MPA

Antarctica and Southern Ocean

3.

Pelagos Sanctuary

Mediterranean Sea

4. 5.

Charlie-Gibbs South MPA Milne Seamount Complex MPA Mid-Atlantic Ridge north of the Azores High Seas MPA Altair Seamount High Seas MPA Antialtair High Seas MPA Josephine Seamount High Seas MPA Charlie-Gibbs North High Seas MPA

North-East Atlantic Ocean

6. 7. 8. 9. 10.

11. 12. 13.

Rainbow Hydrothermal Vent Field SAC Hatton Bank Hatton-Rockall Basin

Remarks It is the world’s first wholly high-seas MPA (in 2009). And it is also the first no-take marine reserve in the CCAMLR’s network of Southern Ocean MPAs The world’s largest MPAs in ABNJ (It covers 1.55 million square kilometers, of which 72% is “no-take” area.). It is also in the CCAMLR’s network of Southern Ocean MPAs Maybe, it is the first MPAs in ABNJ (in 2002), because it currently is located in part on the high seas. The Sanctuary has been designated and is jointly managed by France, Italy, and Monaco Entirely within ABNJ. The seabed, the subsoil, and the water column are protected by all OSPAR CPs These four MPAs are located within an area subject to a submission by Portugal to the UN CLCS for an ECS. Portugal has expressed the intention to assume the responsibility to take measures for the protection of the seabed and the subsoil within these areas. Upon invitation by Portugal, the OSPAR Commission agreed to collectively protect the water column of these MPAs This MPA is partly situated within an area subject to a submission by Iceland to the UN CLCS for an ECS. The water column is protected collectively by all CPs. The seabed and the subsoil remain unprotected These MPAs are situated within areas subject to a submission by a CP to the UN CLCS for an ECS. The seabed and subsoil of these sites are protected by the respective CP, while the water column remains unprotected

CCAMLR: the 1980 Commission for the Conservation of Antarctic Marine Living Resource OSPAR: the 1992 Convention for the Protection of the Marine Environment of the North-East Atlantic (also referred to as the OSPAR Convention) UN CLCS: Commission on the Limits of the Continental Shelf, United Nations ECS: Extended Continental Shelf CP: Contracting Party of OSPAR

Marine Protected Areas in Areas Beyond National Jurisdiction

connectivity of marine ecosystem and the multiple threats on marine biodiversity, more MPAs in ABNJ are absolutely necessary in the future. However, there are still some barriers about more MPAs in ABNJ. First, recent study showed that 54% of the present fishing grounds in ABNJ would be unprofitable at current fishing rates, if the subsidies from governments disappear. The first five countries which provide largest subsidies are Japan, Spain, China, South Korea, and the United States. All of these countries also organize the largest high-seas fishing fleet in the world (Sala et al. 2018). Thus, we must more rationally regulate high-seas fishery subsidies and management, along with the process of establishing more MPAs in ABNJ. Second, several independent frameworks to manage and protect the marine ecosystems in ABNJ have already existed. For example, fishing is managed regionally by some regional fishery management organizations (RFMOs), shipping is managed by various conventions under the International Maritime Organization (IMO), and deep-sea mining in “the areas” is managed by the International Seabed Authority (ISA) (Altvater et al. 2019). Nonetheless, cooperation and coordination among these different frameworks are largely limited, which challenges the protection of marine ecosystems in ABNJ. Third, our understanding of deep-sea biodiversity and deep-sea ecosystem functions is far from enough until now (Appeltans et al. 2012, Thurber et al. 2013). This gap in knowledge is a great barrier in establishing of MPAs in ABNJ. To overcome it, more new methods, such as data-driven planning tools (Visalli et al. 2020), are needed to instructing the planning model for MPAs.

References Altvater S, Fletcher R, Passarello C (2019) The need for marine spatial planning in areas beyond National Jurisdiction. In: Zaucha J, Gee K (eds) Maritime spatial planning. Springer, pp 397–415 Appeltans W, Ahyong ST, Anderson G, Angel MV, Artois T, Bailly N, Bamber R, Barber A, Bartsch I, Berta A, Błażewicz-Paszkowycz M, Bock P, Boxshall G, Boyko CB, Brandão SN, Bray RA, Bruce

985

NL, Cairns SD, Chan T-Y, Cheng L, Collins AG, Cribb T, Curini-Galletti M, Dahdouh-Guebas F, Davie PJF, Dawson MN, De Clerck O, Decock W, De Grave S, de Voogd NJ, Domning DP, Emig CC, Erséus C, Eschmeyer W, Fauchald K, Fautin DG, Feist SW, Fransen CHJM, Furuya H, Garcia-Alvarez O, Gerken S, Gibson D, Gittenberger A, Gofas S, GómezDaglio L, Gordon DP, Guiry MD, Hernandez F, Hoeksema BW, Hopcroft RR, Jaume D, Kirk P, Koedam N, Koenemann S, Kolb JB, Kristensen RM, Kroh A, Lambert G, Lazarus DB, Lemaitre R, Longshaw M, Lowry J, Macpherson E, Madin LP, Mah C, Mapstone G, McLaughlin PA, Mees J, Meland K, Messing CG, Mills CE, Molodtsova TN, Mooi R, Neuhaus B, Ng PKL, Nielsen C, Norenburg J, Opresko DM, Osawa M, Paulay G, Perrin W, Pilger JF, Poore GCB, Pugh P, Read GB, Reimer JD, Rius M, Rocha RM, Saiz-Salinas JI, Scarabino V, Schierwater B, Schmidt-Rhaesa A, Schnabel KE, Schotte M, Schuchert P, Schwabe E, Segers H, SelfSullivan C, Shenkar N, Siegel V, Sterrer W, Stöhr S, Swalla B, Tasker ML, Thuesen EV, Timm T, Todaro MA, Turon X, Tyler S, Uetz P, van der Land J, Vanhoorne B, van Ofwegen LP, van Soest RWM, Vanaverbeke J, Walker-Smith G, Walter TC, Warren A, Williams GC, Wilson SP, Costello MJ (2012) The magnitude of global marine species diversity. Curr Biol 22:2189–2202 Dey PK, Ogunlana SO, Naksuksakul S (2004) Risk-based maintenance model for offshore oil and gas pipelines: a case study. J Qual Maint Eng 10:169–183 Doney SC, Ruckelshaus M, Duffy JE, Barry JP, Chan F, English CA, Galindo HM, Grebmeier JM, Hollowed AB, Knowlton N, Polovina J, Rabalais NN, Sydeman WJ, Talley LD (2012) Climate change impacts on marine ecosystems. Annu Rev Mar Sci 4:11 Durden JM, Lallier LE, Murphy K, Jaeckel A, Gjerde KM, Jones DOB (2018) Environmental impact assessment process for deep-sea mining in ‘the area’. Mar Policy 87:194–202 Gallucci M (2018) At last, the shipping industry begins cleaning up its dirty fuels. https://e360.yale.edu/ features/at-last-the-shipping-industry-begins-cleaningup-its-dirty-fuels. Accessed 30 Aug 2020 Gjerde KM, Reeve LLN, Harden-Davies H, Ardron J, Dolan R, Durussel C, Earle S, Jimenez JA, Kalas P, Laffoley D (2016) Protecting Earth’s last conservation frontier: scientific, management and legal priorities for MPAs beyond national boundaries. Aquat Conserv Mar Freshwat Ecosyst 26:45–60 Gray JS, Bakke T, Beck HJ, Nilssen I (1999) Managing the environmental effects of the Norwegian oil and gas industry: from conflict to consensus. Mar Pollut Bull 38:525–530 Ju RT, Li X, Jiang JJ, Wu J, Liu J, Strong DR, Li B (2020) Emerging risks of non-native species escapes from aquaculture: call for policy improvements in China and other developing countries. J Appl Ecol 57:85–90

M

986

Marine Protected Areas in Areas Beyond National Jurisdiction (MPA in ABNJ)

Lester SE, Halpern BS, Grorudcolvert K, Lubchenco J, Ruttenberg BI, Gaines SD, Airame S, Warner RR (2009) Biological effects within no-take marine reserves: a global synthesis. Mar Ecol Progr Ser 384: 33–46 Morell V (2015) U.S. Navy to limit sonar testing to protect whales. https://www.sciencemag.org/news/2015/09/ us-navy-limit-sonar-testing-protect-whales. Accessed Aug 2020 Muraki Gottlieb H, Laffoley D, Gjerde K, Spadone A (2018) Report of the workshop on marine protected areas in areas beyond national jurisdiction, 9–11 October, IUCN Headquarters, Gland, Switzerland. IUCN, Gland Nowacek DP, Thorne LH, Johnston DW, Tyack PL (2010) Responses of cetaceans to anthropogenic noise. Mammal Rev 37:81–115 Oleary BC, Hoppit G, Townley A, Allen HL, Mcintyre CJ, Roberts CM (2020) Options for managing human threats to high seas biodiversity. Ocean Coast Manag 187:105110 Pauly D, Watson R, Alder J (2005) Global trends in world fisheries: impacts on marine ecosystems and food security. Philos Trans Roy Soc B: Biol Sci 360:5–12 Rogers AD, Sumaila UR, Hussain SS, Baulcomb C (2014) The high seas and us: understanding the value of high-seas ecosystems. Global Ocean Commission, Oxford, UK Sala E, Mayorga J, Costello C, Kroodsma D, Palomares MLD, Pauly D, Sumaila UR, Zeller D (2018) The economics of fishing the high seas. Sci Adv 4:eaat2504 Sharma R (2015) Environmental issues of deep-sea mining. Procedia Earth Planet Sci 11:204–211 Smith D, Jabour J (2018) MPAs in ABNJ: lessons from two high seas regimes. ICES J Mar Sci 75:417–425 Taormina B, Bald J, Want A, Thouzeau G, Lejart M, Desroy N, Carlier A (2018) A review of potential impacts of submarine power cables on the marine environment: knowledge gaps, recommendations and future directions. Renew Sustain Energy Rev 96: 380–391 Thurber AR, Sweetman AK, Narayanaswamy B, Jones DOB, Ingels J, Hansman RL (2013) Ecosystem function and services provided by the deep sea. Biogeosciences 11:3941–3963 Tyack PL, Zimmer WMX, Moretti D, Southall BL, Claridge D, Durban JW, Clark CW, Damico A, Dimarzio N, Jarvis S (2011) Beaked whales respond to simulated and actual navy sonar. PLoS One 6: e17009 UN (2012) The future we want. United Nations, Rio de Janeiro UN (2020) Intergovernmental conference on marine biodiversity of areas beyond national jurisdiction. https:// www.un.org/bbnj/. Accessed 29 Aug 2020 Van Cauwenberghe L, Vanreusel A, Mees J, Janssen CR (2013) Microplastic pollution in deep-sea sediments. Environ Pollut 182:495–499 Visalli ME, Best BD, Cabral RB, Cheung WWL, Clark NA, Garilao C, Kaschner K, Kesner-Reyes K, Lam

VWY, Maxwell SM, Mayorga J, Moeller HV, Morgan L, Crespo GO, Pinsky ML, White TD, McCauley DJ (2020) Data-driven approach for highlighting priority areas for protection in marine areas beyond national jurisdiction. Mar Policy 2020: 103927 Williams R, Wright JA, Ashe E, Blight LK, Bruintjes R, Canessa R (2015) Impacts of anthropogenic noise on marine life: publication patterns, new discoveries, and future directions in research and management. Ocean Coast Manag 115:17–24 Worm B, Barbier EB, Beaumont N, Duffy JE, Folke C, Halpern BS, Jackson JB, Lotze HK, Micheli F, Palumbi SR (2006) Impacts of biodiversity loss on ocean ecosystem services. Science 314:787–790

Marine Protected Areas in Areas Beyond National Jurisdiction (MPA in ABNJ) ▶ Marine Protected Areas in Areas Beyond National Jurisdiction

Maritime Ocean Engineering Research Institute (KRISO) ▶ Ice Tank Test

Material Takeoff (MTO) ▶ Steel Pipelines and Risers

Maximum Likelihood Sequence Detection (MLSD) ▶ Underwater Acoustic Communication

Maximum Likelihood Sequence Estimation (MLSE) ▶ Underwater Acoustic Communication

Mega-Float

MBS – Multibody Simulation ▶ Analysis of Renewable Energy Devices

MDO Method ▶ Multidisciplinary Design Optimization (MDO)

MDO-Computing Framework ▶ Multidisciplinary Design Optimization (MDO)

ME – Morison’s Equation ▶ Analysis of Renewable Energy Devices

Medium Access Control Layer ▶ Underwater Acoustic Sensor Network

Mega-Float Kazuhiro Iijima Department of Naval Architecture and Ocean Engineering, Osaka University, Osaka, Japan

987

originates from a coined word meaning “Mega” (huge) þ “Float” (floating structure). It is sometimes referred to as “Mega-Float.” Technological Research Association of Mega-Float (TRAM) in Japan initiated the project with the same name “Mega-Float” in the 1990s. Mega-Float also denotes such a pontoon type very large floating structures (VLFS) for ocean space utilization as studied and developed by TRAM. The objective of Mega-Float is ocean space utilization, being deployed for long years in a sheltered sea area, which is contrary to Mobile Offshore Base (MOB) deployed in rather offshore sea area for sometimes tentative use. The Mega-Float project by TRAM started in 1995 and continued for 6 years. The focus of Phase I project (1995–1996) was on the development of fundamental technologies such as design and construction of VLFS while it was on the demonstration as an airport in Phase II (1997–2001). A VLFS with the length 1000 m was designed, constructed, and tested to demonstrate its function as a floating runway in Phase II project. This VLFS was regarded as the largest man-made floating island and certified in 1999 by the Guinness World Records. A semi-submersible type MegaFloat (SSMF) for offshore deep waters was also studied by TRAM. However, the investigations into SSMF were limited. This article mainly overviews the Mega-Float concept and the technologies developed in Mega-Float projects that were carried out in Japan between 1995 and 2001. Reference may also be made to the literatures such as Suzuki (2005) and Fujikubo and Suzuki (2015).

Scientific Fundamentals Synonyms Mobile offshore base (MOB); Very large floating structures (VLFS)

Definition Mega-Float is a type of VLFS whose concept was developed, particularly in Japan. Mega-Float

Mega-Float Concept The concept of Mega-Float developed by TRAM is illustrated in Fig. 1. Mega-Float is installed in a sheltered sea area (such as bay), and it consists of a large floating structure and a mooring system. An access from land can be a part of it. The breakwater to protect Mega-Float from severe waves is also constructed around it if necessary. The structure is constructed by the at-sea joining

M

988

Mega-Float

Mega-Float, Fig. 1 Conceptual sketch of Mega-Float system (Taken and reproduced from SRCJ web page)

and welding of the steel structural units that have been pre-constructed in shipyards. It can create artificial ocean space on the sea, of an arbitrary shape fitting for its function. The advantages of Mega-Float over the land reclamation may be summarized below. • Mega-Float can be installed in the sea area with soft ground and/or deep waters. • Mega-Float can comply with high tidal variation • Mega-Float is extensible, movable, and removal. Design has a high flexibility. • Mega-Float gives less impact to marine environments. • Mega-Float construction costs lower and is made in a shorter period. • Mega-Float is stronger against ground motions in earthquakes. Design Technology of Mega-Float Numerical simulation methods had to be developed for the design since Mega-Float was an unprecedented structure and the design need to be proceeded together with the numerical analysis (Design-by-Analysis). The key issue is hydroelasticity. Several hydroelasticity codes for VLFS have been developed and cross-validated in the Mega-Float project since the design of VLFS must be carried out together with the numerical simulation tool which takes account of the hydroelasticity of Mega-Float. Most of the codes are based on the diffraction theory in frequency domain. Structural modeling is different among the codes; some used beam elements, while the other plate theory, shell FEM, etc.

Other technological issues have also been investigated. They include the optimum arrangement of mooring system, and safety evaluation in the extreme event and catastrophic event (drop object, collision, earthquakes, damaged condition). Hydraulic tests using scaled models are also performed to validate the numerical simulations. Environmental impact has also been investigated in terms of flow blockage, salinity change, and temperature distribution. The impact on ecosystem around and below MegaFloat is clarified by the numerical simulations and field measurement in Mega-Float project. The results indicate only little effect, except for a small reduction in dissolved oxygen adjacent to Mega-Float. Construction Technology of Mega-Float Mega-Float is finally assembled and constructed at sea. The construction process is as follows (Yamashita et al. 2007; see Fig. 2): • Unit structures (modules) are pre-fabricated/ built in shipyards. The maximum size of the unit structure depends on the size of the dock, however, typically ranging from 100 m to 300 m in length. The ship-building technologies can be applied. • The units are towed out from the dock to the site by using towing boats. The relative motion among the units are restrained and stiffened gradually by using mechanical joints and finally welded together. When joining two structures, at least, one of the two is moored to the “dolphin.”

Mega-Float

Stage 1

989

Mega- float under construction

Floating unit

Tug- boat

Turnbuckle Stage 2

Mega- float under construction

Floating unit

Mega- float under construction

Floating unit

Restrain by Mechanical device

Strong backs Stage 3

Restrain by Strong backs

Welding Drained chamber

Mega-Float, Fig. 2 Construction process of Mega-Float

• At the beginning of the restraining process, mechanical devices such as jacks, turnbuckles and wooden wedges are used to reduce the relative motion. In the later stage, the degree of restraints is strengthened. Steel strong-backs and fitting pieces are welded to the units, in order to conduct the welding works with good quality between the two units. • For the underwater welding, a specially designed chamber attached to the bottom of a hold compartment is drained of the water by using blowers to pump in the compressed air. • The above process is repeated until Mega-Float is formed at sea. • Mega-Float is moored to the mooring facility in and after the construction process. • The thermal deformation to the sunlight and welding deformation are to be considered in the fabrication and construction. Mooring Technology of Mega-Float The mooring system of Maga-Float may be selected and designed from various options depending on the water depth and environmental conditions. For deep waters, conventional catenary mooring system may be adopted. For shallow to mid-water depth (20–40 m), the mooring system consisting of steel pile/jacket structure and fender is typically adopted. The marine jacket for mooring is sometimes called “dolphin.” The dolphin is piled to sea floor. Mega-Float is equipped with steel “arms” to hold the dolphin. Between the arms and dolphin, the fenders are inserted for shock-absorbing the contact loads between the

dolphin and Mega-Float. The fender is a rubbermade structure, with the diameter 1–2 m, which can bear the large drift force on Mega-Float due to waves, wind, and current. It is attached either to the dolphin or the floating structure side. Figure 3 shows a sample of dolphin-fender system used for Mega-Float (left) and the nonlinear reaction force characteristics of the mooring system (right). Normally, there is a gap between the fender and Mega-Float, of few tens of centimeters as the excess play. Within the excess play, Mega-Float moves freely. No reaction force is supplied in this region. When the contact starts between the fender and the float, or the fender or the dolphin, the fender gives the reaction force to the structure in proportion to the contact displacement. When the reaction force reaches a certain level to the increased displacement, the fender undergoes buckling of the rubber. Then, the reaction force becomes almost constant to the further increase of displacement. This reaction force characteristics are beneficial; the mooring system allows large displacement and dissipate the energy, while the constant load does not damage the dolphin structure due to the further increase of the reaction force. Historical/Societal Background of Mega-Float Japan is an island country surrounded by seas. About 80% of the land is mountainous, while the rest of 20% is used as the industrial or city areas, and they are concentrated near the shorelines. Ocean space utilization has been considered necessary, particularly in the metropolitan areas.

M

990

Mega-Float

Load

Buckling-type Fender

Displacement

Mega-Float, Fig. 3 Mooring system for Mega-Float and its mechanical characteristics. (Reproduction from Iijima et al. 2002)

However, the seas around the metropolitan areas that had good conditions for reclamation in terms of water depth and soil condition was already reclaimed. In the 1970s, the feasibility of a floating airport was investigated for the phase 1 construction of Kansai airport using a semisubmersible type VLFS, as a gateway to Osaka (Takarada 1982). Even though the proposal of building the floating runway for Kansai airport was not accepted, then the ship-builders of Japan and academia started to pursue the technologies for VLFS. With these backgrounds, TRAM was founded in 1995 and started their investigations (Okamura 2004).

Key Applications Mega-Float Phase I Project TRAM was comprised of 17 leading shipbuilding companies and steel companies in Japan and was founded in April, 1995, on the initiative of Japanese government. The research activities were carried out in Phase I and Phase II projects. Phase I project focused on the development of the fundamental technologies of design and construction. Phase II project focused on the demonstration (Technical Research Association of Mega-Float 1999, 2000, 2001; Sato and Inoue 2003; Yoshida 2003). The main aims of Phase I were (1) establishment of technologies for design, (2) establishment of technologies for the construction, (3) evaluation

of impact on the upper structures, (4) establishment of long-term durability, and (5) establishment of evaluation method for environmental impact. In Phase I project, the application of Mega-Float was not specified to the airport. The construction technology as explained in the “Construction Method of Mega-Float” section was pursued. For establishing the joining technology, a small prototype Mega-Float structure with the length 300 m, the width 60 m, and the depth 2 m was constructed as sea off Yokosuka, Japan. The MegaFloat consisted of nine units, each of which had the size 100 m  20 m. For the welding technique development, the welding shrinkage and deformation were measured in the at-sea test. The dry welding using the drainage system was found to be effective in securing the welding quality rather than wet welding. The small prototype Mega-Float in Phase I was later reinforced and extended to the Mega-Float with the length 1000 m. Mega-Float Phase II Project The application as an airport, whether or not airplanes can land and take-off, was questioned for Phase II project. TRAM designed and constructed a floating runway (see Fig. 4) using Mega-Float technologies off Yokosuka (the same site as Phase I). The size of the structure was 1000 m in length, 60 m in breadth (121 m partially), and 1 m in draft. The structural depth was 3 m. The size was equivalent to the existing small commuter airport. The frequency domain simulation was extended to

Mega-Float

991

Mega-Float, Fig. 4 1000 m class Mega-Float off Yokosuka, Mega-Float Phase II project (By the courtesy of Shipbuilding Research Centre of Japan)

1000 m airport case and used for checking its function. Time domain simulation was developed, and the taking-off and landing of an airplane was simulated for safety. For functionality check as an airport, several considerations on the facilities were further necessary. They include the following: • The dolphin top must be below the line extending at a predetermined angle from the end of the runway known as “Obstacle Limitation Surface.” Low-headed dolphin for mooring system was developed. • Approach lights arranged on fixed piles and Mega-Float must be in line within a certain allowance to guide the airplane landing. • The surface of the steel Mega-Float structure which has dynamic deformation to waves need to be paved with asphalts. Pavement method was investigated, and durability test was performed.

• Navigation equipment such as “Instrumental Landing System (ILS),” “Precision Approach Pass Indicator (PAPI),” and “Future Air Navigation System (SAS)” must function on Mega-Float. After the completion of the at-sea tests, the Mega-Float structure in Phase II was dismantled (actually, dismantling works were part of the research activities) and removed from the test site. Some parts were reused as “Data Backup Base” in case of disaster, “World Cup Megapark,” and marine fishery parks. TRAM was dissolved in 2001, and the activities were succeeded by the Shipbuilding Research Centre of Japan (SRC). Haneda Airport Extension Bid Haneda airport located in Tokyo Bay is famous as a gateway to Tokyo and one of the world largest and busiest airports. The Japanese Government

M

992

decided to construct the fourth runway to Haneda airport which was planned to be in operation in 2009. The fourth runway was to be constructed near the river mouth of Tama River. There were three concepts proposed for the runway: Mega-Float, pile-supported wharf, and a hybrid of reclamation and pile-supported wharf. The Shipbuilders’ Association of Japan bid for the construction and proposed the Mega-Float with the length 4000 m (Sato and Inoue 2003; Yoshida 2003). The design service life was 100 years. The design wave height at the site was 2.3 m in significant wave height and the significant wave period 5 s for operation condition. Even for the storm condition, the significant wave height was 3.7 m considering a storm with 200 years of return period. The technical committee to the fourth runway of Haneda airport concluded that all of the three construction proposals have the possibility of being adopted with not serious technical defects. Finally, the consortium for the hybrid of reclamation and pile-supported wharf made a successful bid. Other Applications Mega-Float may be used as airport, container terminal, recreation spot, emergency rescue base, storage facility, marine renewable energy platform, solar energy platform, etc. There are various application proposals for these applications. However, no Mega-Floats have been realized so far, except the ones in the Mega-Float projects. Recently, Mega-Float seems to be re-gaining attentions by the engineers. The development of autonomous ship, hydrogen-driven ships, etc. may imply a need for the offshore base, or an ocean space in deeper waters. Mega-Float may also be utilized in such a context.

Melt Inert Gas Welding (MIG)

References Fujikubo M, Suzuki M (2015) Mega-float. In: Wang CM, Wang BT (eds) Large floating structures, technological advances. Springer Iijima K, Shiraishi S, Satoh H (2002) Motion characteristics of floating structure moored by hybrid type fender – a report on information backup center by Megafloat. Report PARI 41(4):39–94 Okamura H (2004) The history of development of Megafloat in Japan. Sci Ships Sea 2004(summer issue):30–35, in Japanese Sato C, Inoue K (2003) Results of 6 years research project of mega-float. Proceedings of international symposium on ocean space utilization technology. Jan. 28–31 2003, Tokyo, Japan, pp 436–442 SRCJ, Introduction to Mega-Float. http://www.srcj.or.jp/ html/megafloat_en/index.html. Accessed on 6 May 2021 Suzuki H (2005) Overview of Megafloat: concept, design criteria, analysis and design. Mar Struct 18:111–132 Takarada N (1982) Technology assessment of VLFS for floating airport. Bull Soc Nav Archit Jpn 642:702–719, in Japanese Technical Research Association of Megafloat (1999) Summary of practical research on Megafloat airport in 1998. TRAM, in Japanese Technical Research Association of Megafloat (2000) Summary of practical research on Megafloat airport in 1999. TRAM, in Japanese Technical Research Association of Megafloat (2001) Summary of practical research on Megafloat airport in 2000. TRAM, in Japanese Yamashita Y, Okada S, Shimamune S, Yonezawa M (2007) Joining technology of very large floating structures considering thermal distortion and thermal stress caused by sunshine. Q J Jpn Weld Soc 25(1):114–121 Yoshida K (2003) A Brief review of recent activities on VLFS in Japan. Proceedings of international symposium on ocean space utilization technology. Jan. 28–31, Tokyo, pp 21–28

Melt Inert Gas Welding (MIG) ▶ Welding Technology

Cross-References ▶ Connectors of VLFS ▶ Station-Keeping System for VLFS ▶ Structural analysis and design of VLFS ▶ Very Large Floating Structures (VLFS): Overview

Metacentric Height ▶ AUV/ROV/HOV Stability

Meteorological Monitoring and Measurement Buoy

Metal Net ▶ Net Structures: Design

Metallic Tubes ▶ Umbilical Cable

Meteorological Monitoring and Measurement Buoy Wanan Sheng SW MARE Marine Technology and Consultation, Cork, Ireland

Definition Meteorological monitoring and measurement buoys (aka weather buoys) are the buoys to measure parameters for monitoring and weather forecasting. The measurements include air temperature above the ocean surface; wind speed and direction; barometric pressure; sea water temperature and salinity; wave height, period and direction; and current etc. The weather buoys can be an important part of the global weather monitoring and prediction system (see the ocean data buoy in Fig. 1). Generally, raw data can be processed and logged on board of the buoy and then transmitted via radio, cellular, or satellite communications to meteorological centers for use in weather forecasting and climate study.

Scientific Fundamentals Meteorological buoys are instruments which collect weather and ocean data within the world’s oceans, as well as aid during emergency response to chemical spills, legal proceedings, and engineering design. Moored buoys have been in use since 1951, while drifting buoys have been used

993

since 1979. Moored buoys are connected with the ocean bottom using either chains, nylon, or buoyant polypropylene. Different types of weather buoys are used by different organizations (see Figs. 2 and 3). The first known proposal for surface weather observations at sea occurred in connection with aviation in August 1927, and starting in 1939, United States Coast Guard vessels were being used as weather ships to protect transatlantic air commerce. During World War II The German Navy deployed weather buoys (Wetterfunkgerät See – WFS) at fifteen fixed positions in the North Atlantic and Barents Sea. They were launched from U-boats into a maximum depth of ocean of 1000 fathoms (1,800 m), limited by the length of the anchor cable. Overall height of the body was 10.5 m (of which most was submerged), surmounted by a mast and extendible aerial of 9 m. Data (air and water temperature, atmospheric pressure and relative humidity) were encoded and transmitted four times a day. When the batteries (high voltage dry-cells for the valves, and nickel-iron for other power and to raise and lower the aerial mast) were exhausted, after about 8–10 weeks, the unit self-destructed. The Navy Oceanographic Meteorological Automatic Device (NOMAD) buoy’s 6-m (Fig. 4) hull was originally designed in the 1940s for the United States Navy’s offshore data collection program. The United States Navy tested marine automatic weather stations for hurricane conditions between 1956 and 1958, though radio transmission range and battery life was limited. Between 1951 and 1970, a total of 21 NOMAD buoys were built and deployed at sea. Since the 1970s, weather buoy use has superseded the role of weather ships, as they are cheaper to operate and maintain. The earliest reported use of drifting buoys was to study the behaviour of ocean currents within the Sargasso Sea in 1972 and 1973. Drifting buoys have been used increasingly since 1979, and as of 2005, 1250 drifting buoys roamed the Earth’s oceans. Between 1985 and 1994, an extensive array of moored and drifting buoys was deployed across the equatorial Pacific Ocean to monitor and help

M

994

Meteorological Monitoring and Measurement Buoy

Meteorological Monitoring and Measurement Buoy, Fig. 1 WMO global observing system (http://www.wmo.int/ pages/prog/www/TEM/WMO_RFC/index_en.html)

Meteorological Monitoring and Measurement Buoy, Fig. 2 Oceanographic buoy operated by the marine data service

Meteorological Monitoring and Measurement Buoy, Fig. 3 Weather buoy operated by the National Data Buoy Center

Meteorological Monitoring and Measurement Buoy

995

and unlike the conventional land weather stations, they measure more oceanographic parameters, including: – Measure sea water temperature – Sea water salinity density – Wave height, and dominant wave period and wave direction – Ocean/tidal current Raw data is processed and can be logged on board the buoy and then transmitted via radio, cellular, or satellite communications to meteorological centers for use in weather forecasting and climate study. Types of Buoys Moored Buoys

Meteorological Monitoring and Measurement Buoy, Fig. 4 A 6-m NOMAD

predict the El Niño phenomenon. Hurricane Katrina capsized a 10 m buoy for the first time in the history of the National Data Buoy Center (NDBC) on August 28, 2005. On June 13, 2006, drifting buoy 26,028 ended its long-term data collection of sea surface temperature after transmitting for 10 years, 4 months, and 16 days, which is the longest known data collection time for any drifting buoy. The first weather buoy in the Southern Ocean was deployed by the Integrated Marine Observing System (IMOS) on March 17, 2010.

Key Applications Measurements Weather buoys, like other types of weather stations, measure the parameters that the conventional weather station measures, including: – – – –

Air temperature above the ocean surface Wind speed (steady and gusting) Wind direction Barometric pressure

Weather buoys range in diameter from 1.5–12 m (Fig. 5). Those that are placed in shallow waters are smaller in size and moored using only chains, while those in deeper waters use a combination of chains, nylon, and buoyant polypropylene. Since they do not have direct navigational significance, moored weather buoys are classed as special marks under the IALA scheme, are coloured yellow, and display a yellow flashing light at night. Discus buoys are large round and moored in deep ocean locations, with a diameter of 10–12 m. The aluminum 3-m (10 ft) buoy is a very rugged meteorological ocean platform that has long-term survivability. The expected service life of the 3-m (10 ft) platform is in excess of 20 years and properly maintained; these buoys have not been retired due to corrosion. The NOMAD is a unique moored aluminum environmental monitoring buoy designed for deployments in extreme conditions near the coast and across the Great Lakes. NOMADs moored off the Atlantic Canadian coast commonly experience winter storms with maximum wave heights approaching 20 m (66 ft) into the Gulf of Maine. Drifting Buoys

Drifting buoys are smaller than their moored counterparts, measuring 30–40 cm in diameter.

M

996

Meteorological Monitoring and Measurement Buoy

12-METER DISCUS

3-METER DISCUS

3-METER VE DISCUS

10-METER DISCUS

2.4-METER COASTAL

2.4-METER VE COASTAL

6-METER NOMAD

1.8-METER COLOS

1.5-METER COLOS

Meteorological Monitoring and Measurement Buoy, Fig. 5 Weather buoy operated by the National Data Buoy Center (NDBC)

They are made of plastic or fiberglass and tend to be either bicolored, with white on one half and another color on the other half of the float, or solidly black or blue (Fig. 6). It measures a smaller subset of meteorological variables when compared to its moored counterpart, with a barometer measuring pressure in a tube on its top. They have a thermistor (metallic thermometer) on its base, and an underwater drogue, or sea anchor, located 15 m below the ocean surface connected with the buoy by a long, thin tether. Many different drifting buoys exist around the world that vary in design and the location of reliable temperature sensors varies. These measurements are beamed to satellites for automated and immediate data distribution. Other than their use as a source of meteorological data, their data is used within research programs, emergency response to chemical spills, legal proceedings, and engineering design. Moored weather buoys can also act as a navigational aid, like other types of buoys.

Meteorological Monitoring and Measurement Buoy, Fig. 6 Drifting buoy

TAO Buoy/Global Tropical Moored Buoy Array

The TAO/TRITON Array was designed to better understand and predict climate variations related to El Niño and the Southern Oscillation

Meteorological Monitoring and Measurement Buoy

(ENSO). ENSO, the warm phase of which we refer to as El Niño and the cold phase La Niña, represents the strongest year-to-year climate fluctuation on the planet. ENSO events significantly disrupt normal patterns of weather

Meteorological Monitoring and Measurement Buoy, Fig. 7 A TAO buoy

997

variability, affecting agriculture, transportation, resource management, energy production, and the lives of millions of people around the globe. ENSO also affects Pacific marine ecosystems and commercially valuable fish stocks such as tuna and anchovy. The project was motivated by the 1982–1983 El Niño event, and it took over the 10 year period 1985–1994 to deploy the buoys (Fig. 7), and the full TAO/TRITON system was built (Fig. 8) and is presently supported by the USA (NOAA/National Weather Service/ National Data Buoy Center) and Japan (Japan Agency for Marine-Earth Science and Technology). The TAO/TRITON array was extended to the Global Tropical Moored Buoy Array (GTMBA, see Fig. 9) after mid-1990, with the additions of the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA), and the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) in the Indian Ocean (McPhaden et al. 2009). Now the GTMBA is a global system with its interest spanning intraseasonal-to-decadal and longer timescales on global basis, including: • El Niño/Southern Oscillation and its decadal modulation in the Pacific • The meridional gradient mode and equatorial warm events in the Atlantic

30°N

TAO/TRITON Array

20°N 10°N 0° 10°S 20°S 30°S 120°E

ATLAS 140°E

160°E

180°

TRITON 160°W

Subsurface ADCP 140°W

120°W

100°W

80°W

Meteorological Monitoring and Measurement Buoy, Fig. 8 The TAO/Triton array (https://www.pmel.noaa.gov/ gtmba/)

M

998

Methanol

Meteorological Monitoring and Measurement Buoy, Fig. 9 Global Tropical moored buoy array (https://www. pmel.noaa.gov/gtmba/)

• The Indian Ocean Dipole • The mean seasonal cycle, including the Asian, African, Australian, and American monsoons • The intraseasonal Madden-Julian Oscillation, which originates in the Indian Ocean but affects all three ocean basins • Trends that may be related to global warming.

References McPhaden MJ et al (2009) The global tropical moored buoy array. In: OceanObs09. 21–25th Sep 2009. Venice, Italy Website: http://www.wmo.int/pages/prog/www/ TEM/WMO_RFC/index_en.html. Cited on 10 Sep 2018 Website: https://www.pmel.noaa.gov/gtmba/. Cited on 10 Sep 2018

Microplastics Chunfang Zhang and Dongdong Zhang Ocean College, Zhejiang University, Zhoushan, China

Synonyms Microplastic particle; Micro-polymer particle; Micro-synthetic organic particle

Definition Plastics are polymers, which are chains of molecules derived from small monomer molecules that are extracted from fossil origin (crude oil, gas, etc.), renewable (sugarcane, starch, vegetable oils, etc.) or even mineral base (salt). Microplastics are usually defined as plastic fragments with sizes less than 5 mm.

Methanol ▶ Alternative Fuel for Ship Propulsion

Microplastic Particle ▶ Microplastics

Scientific Fundamentals Plastic materials have been widely used in many applications since 1970. The common types of plastics include polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinylchloride (PVC), and polyethylene terephthalate (PET) (Table 1). The global production of plastics has increased rapidly over the past 60 years, reaching almost

Microplastics

999

Microplastics, Table 1 Plastic types and examples of items commonly found in marine debris Type of polymer Polyethylene (PE) Polyethylene terephthalate (PET) Polyvinyl chloride (PVC) Polypropylene (PP) Polystyrene (PS) Expansible polystyrene (EPS) Acrylonitrile butadiene styrene (ABS) Polymethyl methacrylate (PMMA) Polyamide or nylon (PA) Polyurethanes (PU)

High density polyethylene (HDPE) Low density polyethylene (LDPE)

Common examples of marine debris Plastic bags, bottles, gear, cages, and pipes for fish farming Bottles, strapping, gear Film, pipe, plumbing pieces, containers, buoys Rope, bottle caps, gear, strapping, drinking straws Disposable cutlery, utensils, containers, packaging Bait boxes, floats, cups, expanded packaging Electronics and electrics, car interior Architecture, instrument and meter parts, automobile lamp, optical lens, transparent pipe Gear, fish farming nets, rope, toothbrushes Packing of fragile goods, aviation, aerospace, automobile manufacturing, liquefied natural gas transport vehicle (ship) manufacturing Cleaning product Preservative film

Specific density 0.91–0.94 1.34–1.39 1.16–1.30 0.90–0.92 1.04–1.09 0.01–1.05 1.03–1.11 1.15–1.19 1.13–1.15 1.2–1.25

0.91–0.94 0.94–0.98

M

Microplastics, Fig. 1 Overview of relevant size ranges for plastic particles

360 million tons in 2018 (PlasticsEurope 2019). However, due to improper plastic disposal across the world, the majority of the plastic litter ends up in marine ecosystems transported via wind, river flow, and effluent discharge from sewage treatment plants. This results in global plastic pollution, particularly in estuarine and marine environments. Plastics in the sea are exposed to ultraviolet (UV) radiation, heat, oxidation, biodegradation, and mechanical disruption and eventually disintegrate into small debris (Shim et al. 2017). Microplastics are widely defined as synthetic organic polymers with an upper size limit of 5 mm (Fig. 1) (Lusher et al. 2013; Zhang et al. 2020), which are derived from the polymerization of monomers extracted from oil or gas (Thompson et al. 2009). These microplastics can be divided

into two categories according to their sources: secondary microplastics, as described above, and primary microplastics. The latter are produced intentionally as microbeads, microfibers, and in other forms (Fig. 2) (Dris et al. 2016) for specific domestic and industrial applications. Since the 1940s, when plastics were massproduced, the volume of plastics has increased rapidly. Consequently, the amount of plastic debris entering the marine environment rose in parallel with rates of production. Microplastics have been detected in aquatic systems almost all over the world, including freshwaters, oceans, polar environments, and even pristine mountain lakes or beaches of remote and unpopulated islands (Kettner et al. 2017). When one looks at vertical distribution, microplastics exist in bottom

1000

Microplastics

Microplastics, Fig. 2 Microplastic particles with different shapes

sediments (including abyssal and hadal deep-sea sediment), benthic zone of water mass, water columns, surface waters, and beaches. Numerous investigations have shown that microplastics have the highest abundance in sediment sample, and the values of abundances range from 1.3 to more than 3300 items kg
1 dry sediment. However, the abundances of microplastics in surface waters are some orders of magnitude smaller, and the values of abundances range from 10
5 to 105 item/m3. Meanwhile, the distribution shows distinct geographical variations. The factors affecting the transportation and distribution include large-scale forces currents driven by wind, ocean currents, geostrophic circulation, and oceanographic effect. As pivotal factors, the inherent properties of microplastics (such as density, size, and shape) can also affect transportation and distribution modes (Fig. 3). During long-distance transportation via wind and turbulence, microplastics may serve as substrates for microflora in the ill-nourished open seas (Miao et al. 2019; Zettler et al. 2013). The microplastic surfaces are considered as novel habitats for microbial communities and termed as “plastispheres” (Zettler et al. 2013). Microbial life may facilitate the degradation of plastic waste (Yang et al. 2014) and

affect plastic debris density, buoyancy forces, and the sinking rate (Rummel et al. 2017). They may also influence the toxicity of microplastics (Imran et al. 2019). Microplastics are small in size and may be mistakenly ingested by marine organisms, potentially resulting in physical or toxicological effects (Waller et al. 2017), and have a serial negative effect on the organisms throughout the food web (Lusher et al. 2013). Some studies have reported the existence of indigestible microplastics in deep-sea organisms in Western Pacific Ocean (Zhang et al. 2020) as well as in tiny shrimp living in the six deepest ocean trenches in the world (Peng et al. 2018). This suggests that the pollution by microplastics has already touched the deepest part of the world’s ocean.

Categories of Microplastics Microplastics in the marine environment are composed of particles that are different in polymer type, size, shape, and specific density. They are widely divided into two categories: primary microplastics and secondary microplastics.

Microplastics

1001

Microplastics, Fig. 3 Migration pathways of microplastics in the ocean

Primary Microplastics Primary microplastics are plastics produced for specific domestic or industrial applications with microscopic dimensions, including personal care consumer products (Fig. 4) and industrial or pharmaceutical products. As for domestic utilization, microplastics are typically used in toothpaste, resin pellets, facial cleansers, and cosmetics like eye shadow (Zitko and Hanlon 1991). They were also applied to medicine as vectors for drugs (Patel et al. 2009). Virgin plastic production pellets, usually with diameter about 2–5 mm, can also be considered as primary microplastics, although their inclusion within this category has been criticized (Andrady 2011; Cole et al. 2011). Since microplastics have been approved for use in cosmetics in the 1980s, the use of exfoliating hand cleansers and facial scrubs containing microplastics has risen remarkably, and microplastic scrubbers have replaced customarily used natural ingredients (i.e., ground almonds, oatmeal, and pumice) (Derraik 2002; Fendall and Sewell 2009). The majority of facial cleansers now

contain polyethylene microplastics which are not captured by wastewater plants and will enter the oceans. With regard to industrial applications of microplastic, the use of primary microplastics in consumer products constitutes millions of small sources, and the commercial or industrial use of similar products can be expected to constitute significant point sources of microplastics. From the microplastics-related reports, very few commercial-use products with primary microplastics are documented: abrasive blasting media for cleaning metal surfaces, abrasive hand cleaner soaps (Gregory 1996), and brief mentions of some unspecified use in petroleum industry. Secondary Microplastics Secondary microplastics, as the name suggests, are tiny particles of plastic derived from the breakdown of large pieces of plastics. The combined action of physical, chemical, and biological processes can weaken the structural completeness of plastic debris, leading to fragmentation

M

1002

Microplastics

Microplastics, Fig. 4 The personal care consumer products containing microplastics

(Cole et al. 2011). Both the environmental factors (such as temperature, pH, salinity, and sunlight) and the properties of the microplastic (such as size, shape, and specific gravity) will act on the disintegration of large plastics. Macroplastics exposed to sunlight may suffer from light degradation, and ultraviolet (UV) radiation from the sunlight causes oxidation of the polymer matrix, resulting in bond cleavage (Andrady 2011; Moore 2008). Plastic debris on beaches is exposed to both high oxygen and sunlight, which will lead to rapid degradation. When the plastics losing the structural integrity were washed out to estuary and sea, they are cumulatively susceptible to fragmentation resulting from mechanical disruption (i.e., wave action, turbulence, and abrasion) (Barnes et al. 2009). In addition, the microbial activities and animal activities will also affect the fragmentation of macroplastics to microparticles.

Sources of Microplastics The ocean-based sources of marine microplastics, resulting from commercial fishing, vessels, and other activities in marine environment, only contribute 20% of total plastic debris in marine environment (Andrady 2011). The discarded fishing net floating at sea may lead to

the continued trapping and killing of marine life, which is called “ghost fishing.” Products (such as clam netting, oyster bags, cages, and floats) applied in shellfish aquaculture can become marine debris when they are discarded or washed out during storms. The microplastics from land sources contribute the remaining 80%. Land sources contain different origins that mainly are personal care products, air-blasting process, incorrectly disposed plastics, or leachates from landfill (Cole et al. 2011). A mass of marine microplastics are derived from land-based sources, such as floating garbage cans, litter tossed along roadsides, cigarette butts, food, agricultural plastic mulch, domestic sewage, beverage containers, and plastic straws; improper disposal; or illegal dumping. Once land microplastics are released into the natural water systems, most of them would be eventually transported to oceans by rivers, while the remaining would reside in freshwater environment, even including such isolated water systems as remote mountain lakes (Free et al. 2014). Light items, such as styrofoam, plastic grocery bags, and helium-filled balloons, can blow for miles in the air before landing in waterways. At the land-water boundary, degenerating coastline structures (i.e., wharves, old piers, and bulkheads) will breakdown and finally become marine debris.

Microplastics

Sample Extraction The small size ( Cd > Cu > Hg > Zn > Co > Mn > Ni > As. The lead adsorption rate in wastewater is 90% ~99% at pH 1.4~2.0, and the saturated adsorption capacity of lead can reach 200 mg/g ore. At pH more than 2.0, the adsorption rate of lead, zinc, cadmium, cobalt, copper, nickel, and manganese in wastewater can reach more than 99%, and the saturated adsorption capacity of zinc, cadmium, cobalt, copper, nickel, and manganese are all more than 40 mg/g ore (Tan et al. 2003). Power Material As a battery material, the iron-manganese polymetallic ores have good load characteristics, high discharge capacity, and good cycle stability characteristics. When the lithium-ion battery cathode material is prepared with iron-manganese polymetallic ore, the insertion potential of lithium ions is 2.6~3 V, and the actual reversible capacity of electrode reaches 110 mAh/g ore. There is still 70 mAhg ore after 250 time cycle of charge and discharge (Yu et al. 2001).

1017 In: Proceedings of the third international conference on hydrometallurgy, Kunming, China Jiang K, Jiang X, Wang S et al (2005) Reductive ammonia leaching of ocean polymetallic nodules[J]. Nonferrous Met 57(4):54–59 Meyer-Galow E, Sehwara KH, Boin U (1973) Metal extraction from manganese nodules by sulphating treatment[J]. Interocean 1:458–468 Richard Tinsley C (1976) Processing-no longer a problem [J]. Min Eng 27(4):32–37 Sridhar R, Jones WE, Warner JS (1976) Extraction of copper, nickel and cobalt from sea nodules [J]. J Met 4:32–37 Tan X, Xiuying Z, Wang F (2003) Study on adsorption of heavy metal cation on ocean cobalt-rich crusts [J]. Miner Ore Dress 40(12):33–35 Tan Z, Mei G, Li W et al (2004) Manganese metallurgy [M]. Central South University Press, Changsha, China pp 728–732 Yin C, Jiang X et al (1998) Treatment of solution from atmospheric acid leaching of ocean polymetallic nodules[C]. In: Proceedings of the third international conference on hydrometallurgy Yu J-C, Chu W, Liu D-Z et al (2001) A new lithium ion battery cathode material- Lithium insertion behavior of manganese nodules [J]. Power Technol 25(2):1–5

MIZ, Marginal Ice Zone ▶ Numerical Simulation of Ice-Going Ships

Mobile Offshore Base (MOB)

References Agarwal JC et al (1979) The Cuprion process for ocean nodules. Chem Eng Process 75(1):59–61 Cardwell PH (1973) Extractive metallurgy of manganese nodules[J]. Min Congr J November:38–43 Cheng J-p, Zhang X-b, Liu F et al (2002) In-situ composite carbon nanotubes with natural nano-mineral and their hydrogen-absorbing properties[J]. Acta Acad Sinica 23(6):743–747 Han KN, Hoover MP, Fuerstenau DW (1974) Int J Miner Process 1:215 Hoover M, Han KN, Fuerstenau DW (1975) Segregation roasting of nickel, copper and cobalt from deep-sea manganese nodules[J]. Int J Miner Process 2:173–185 Jiang X, Yin C et al (1998) Separation of nickel and cobalt from sulfuric acid leaching solution of ocean polymetallic nodules under atmospheric pressure[C].

▶ Mega-Float ▶ Station-Keeping System for VLFS

Mobile Offshore Drilling Unit (MODU) ▶ Polar Offshore Engineering

Mobile Offshore Drilling Units (MODU) ▶ Jack-Up Platforms

M

1018

Modal Superposition Method ▶ Aquaculture Structures: Numerical Methods

Mode Fibers ▶ Fiber-Optic Cable

Model Test ▶ Experimental Investigation of Offshore Renewable Energy

Modern Aquaculture Structures Zhen Wang DNV AS, Høvik, Norway

Synonyms Closed-containment systems; Semi-closed containment system; Submersible aquaculture structures

Definition Aquaculture production is growing and contributing in increasing volumes to global demand for marine foods. It is natural that fish farmers wish to expand and diversify their operations. Globally, the suitable land, fresh or coastal water, for fish farming has become more limited. Thus, fish farmers in many countries are considering expanding aquaculture production into locations that are further from the coast and where the conditions are harsher for fish, structures, and personnel. Currently, the conventional gravity net cage is widely used for aquaculture production. The

Modal Superposition Method

gravity net cage system normally consists of four components: the float collar system, the net cage system, the sinker system, and the mooring system. The float collar provides buoyancy and the sinker system provides weight, maintaining a stable shape of the whole cage system. The net cage can significantly deform when subjected to ocean waves and currents. In moving the fish farm to exposed/offshore areas, environmental loads from wave, current and wind increase rapidly. Increased current loads will cause excess deformation of the net cage and might cause injury to the fish. Larger waves may cause fish to escape and challenges for operation and daily duties. In order to overcome these constraints on conventional fish farm, it is necessary to develop an offshore fish farm, which can be sited in highenergy environments. Moreover, there are many problems with traditional fish farming including: accumulation of waste and feces on the seabed, disease, and fish escapes. Moving fish farms from the sheltered coastal areas to exposed sites leads to more space, stronger currents, and deeper waters. These can help to solve a number of these problems. Stronger ocean currents are particularly effective to dilute and disperse the fish waste and reduce the build-up wastes below fish cages. Sea lice settlement on fish is less successful under stronger currents and the impact of sea lice is therefore reduced. Greater distance to the shore also minimizes interactions with wild fish and results in negative impacts such as compromised reproductive health. Given the legal and environmental restraints present in the aquaculture industry today, sea farmers have to look for new, innovative ways to increase volumes. The future will most likely be diversified – changing from one way of producing fish as seen today, to an industry approaching sea farming with several solutions.

Global Development of Aquaculture The aquaculture industry has large regional differences. Regional variations are important in both the amount of fish farming activity and in

Modern Aquaculture Structures

the diversity of farmed species. Norway, Chile, and Canada are leaders in the world for farming salmon, whereas China is the largest producer of farmed fish by volume. Some of the recent developments of offshore fish farm are listed in Tables 1 and 2. Norway is a hub for offshore farming innovation due to its high value of its salmon farming. The Norwegian government has desired to have a significant growth in aquaculture. In 2015, Norwegian Ministry of Fisheries and Coastal Affairs introduced a free development concession for up to 15 years to promote new technologies that can solve environmental challenges and area issues facing the aquaculture sector. The aim is to support larger and more specific technology-oriented projects including prototypes, industrial designs, equipment in installations, and full-scale trial production. By the closing date 17 November 2017, the scheme had attracted 104 applications. Many applications are seeking to explore locations in more open waters than those presently used for salmon farming. The first project was accepted in 2016 and, as of today (May 2021), 22 projects have been granted for concessions. Two of these projects are described in greater detail below. China is the largest player in the aquaculture industry. It is developing offshore salmon farms on an unprecedented scale with projects in the Yellow Sea, while the country’s growing domestic appetite for other fish species will continue to drive nontraditional aquaculture practices. In 2016, the Ministry of Agriculture announced a “National Construction Plan for Marine Ranch Demonstration Zone (2017–2025),” which will build 178 pilot farms and increase China’s aquaculture production by 30% by 2025. China’s provincial governments are increasingly partnering with both privately owned and state-owned companies to build offshore finfish aquaculture farms.

New Technology in the Modern Aquaculture Fish Health and Welfare Farm-raised fish are susceptible to illness and disease. The welfare of fish is affected when

1019

they are held in captivity as opposed to their natural habitat. Fish welfare is related to physical conditions at the aquaculture, such as fish density, temperature, water quality, disease, etc. Welfare issues may also be linked to other health problems that include dysfunctions related to poor feed or side effects of vaccines. Good fish health is a precondition for fish welfare. In 2016 alone, 53 million salmon died in their pens in Norwegian fish farms, mostly due to sea lice (Veterinærinstituttet 2017). Improvement of the health status and welfare situation is crucial for future expansion of aquaculture industry. The aggregation of fish in cages increases the risk of infections and diseases. Aquaculture installations in open waters may help mitigate some risk factors. For example, greater distances between cages will reduce the risk of diseases spreading. However, fish farming under exposed conditions requires fish to cope with stronger waves and currents. Weather conditions should be monitored to ensure that they are within acceptable limits for the fish. The stress from handling of fish for counting and delousing treatments of lice compromises fish welfare and increases mortality. Sound digital sea lice monitoring method, efficient delousing methods, and robust regulations will pave the way for fish farming under good welfare and sustainable conditions.

Going to Offshore Within the fish farming community, a siteclassification system is generally accepted. The site-classification system is based on wave energy of local wave climates, which is linked to distance from shore. In a report “Farming the deep blue” published at 2005 (Ryan 2004), four site classes were conceived: Class 1 sheltered inshore site, Class 2 Semi-Exposed inshore site, Class 3 Exposed offshore site and Class 4 Open ocean offshore site. Traditional surface-based aquacultures are mostly suitable for Class 1 and Class 2. Further development of aquaculture system suitable for Class 3 and Class 4 requires novel technology (Fig. 1).

M

1020

Modern Aquaculture Structures

Modern Aquaculture Structures, Table 1 Offshore development licenses awarded by the Norwegian Directorate of Fisheries as of 23/04/2021 (https://www.fiskeridir. No. 1

Company Ocean Farming AS

Project Name Ocean Farm 1

2

Nordlaks Oppdrett AS

3

no/Akvakultur/Tildeling-og-tillatelser/Saertillatelser/ Utviklingstillatelser/Kunnskap-fra-utviklingsprosjektene)

Concept Independent unit Rigid steel structure Semi-submersible Permeable expanded nets Exposed locations

Status In operation at location 33757 Håbranden

Havfarm 1&3

Independent unit Ship-like open frame structure in steel Permeable nets Exposed locations #1: Permanently anchored #3: Dynamic positioning

Havfarm 1: In operation at Hadseløya

MNH Produksjon AS

Aquatraz

Rigid steel structure Semi-closed facility Permeable bottom net Active power setting Existing locations

Cage #1–#3 in operation at Kyrøyene; Cage # 4 in operation at Kipholmen

4

AkvaDesign AS

Semiclosed facility at sea

Floating collar in concrete Flexible closed net bag Semi-closed facility Sheltered sites Sludge collection

The concept is operated on the premises: 35,737 Seterrosen, 38,037 Andalsvågen, and 38,057 Hamnsundet

5

Mowi Norway AS, Hauge Aqua

Egg

Composite material Closed facility Existing locations Sludge collection

Detail engineering in progress

6

Atlantis Subsea Farming AS

Atlantis

Floating collar in plastic Continuously submerged production Permeable nets Partially exposed localities Underwater aeration

The first cycle at Gjerdinga and others at Skrubbholmen

(continued)

Modern Aquaculture Structures

1021

Modern Aquaculture Structures, Table 1 (continued) No. 7

Company Norway Royal Salmon ASA

8

Hydra Salmon Company AS, SalMar ASA

9

10

Project Name Arctic Offshore Farming

Concept Rigid steel structure Semi-submersible construction Continuously submerged operation Permeable nets Exposed locations Continuously submerged production Underwater aeration

Status Under construction

Production tank

Rigid steel construction, Semi-closed facility Permeable bottom nets Existing locations Passive power supply Existing locations

Detail engineering in progress

Cermaq Norway AS

iFarm

Technology for increased resource utilization, fish welfare and lice control

Detail engineering in progress

Måsøval Fiskeoppdrett AS

Aqua Semi

Semi-submersible semi-enclosed fish farm

Detail engineering in progress

11

Mowi Norway AS

Marine Donut

Solid closed unit

Detail engineering in progress

12

Mariculture AS

Smart fish farm

Comprehensive solution for the open sea

Detail engineering in progress

13

Nova Sea AS

Spider cage

14

Stadion Laks AS

Stadium pool

M

Detail engineering in progress

Closed floating pool

Detail engineering in progress

(continued)

1022

Modern Aquaculture Structures

Modern Aquaculture Structures, Table 1 (continued) No. 15

Company Nekst AS

Project Name Havliljen

16

Salaks AS

17

Concept “Sea platform” – submersible system

Status Within purpose

Fjordmax

Semi-closed integrated farming platform

Within purpose

Fishglobe AS

Fish globe

Closed cage technology

Detail engineering in progress

18

Lerøy Seafood AS

Pipe farm

Closed floating longitudinal current plant

Within purpose

19

Reset

Reset

RAS facility at sea

Within purpose

20

Salmon Zero

RAS facility on land and production concrete tanks at sea

Within purpose

21

Blue Farm

Floating concrete cage collar with tension anchoring to the seabed

Within purpose

22

AquaBarge

A closed containment system based on RAS technology

Within purpose

Moving offshore aquaculture to more exposed water is an ongoing process, and the destination is to establish complete offshore installations in open rough waters. Farming in exposed areas requires new technical solutions

combined with operational concepts for maintaining security and ensuring production reliability. Knowledge and experience will be essential in the progression to full offshore aquaculture.

Modern Aquaculture Structures

1023

Modern Aquaculture Structures, Table 2 Recent development of offshore fish farm in China No. 1

Company Rizhao Wanzefeng Fishery

2

De Maas SMC

3

Project Name Deep Blue 1

Concept Submersible floating truss fish farm (perimeter of 180 m and height of 35 m, culture volume 50,000 m3)

Status In operation at 130 nautical miles to the Yellow Sea

Hai Xia 1

Central column semi-submersible deep-sea fish farm (139 m in diameter and 12 m deep, culture volume 150,000 m3)

In operation at East China Sea

Guangzhou Institute of Energy Conversion

Peng Hu

Semi-submersible wave power fish farm (68 m long, 28 m wide and 16 m deep, culture volume 1000 m3)

In operation at Zhuhai Wanshan

4

Zhuhai De-sail Marine Fishery Technology Co., Ltd.

De Sail 1

Semi-submersible floating truss fish farm (91.3 m long, 30 m wide, and 7.5 m deep, culture volume 30,000 m3)

In operation at Zhuhai Wanshan

5

Changdao HongXiang

Chang Jing 1

Gravity-based fish farm (66 m in width and length, culture volume 60,000 m3)

In operation at Daqin island of Bo Hai

6

Shandong Ocean Group

Geng Hai No.1

Gravity-based marine ranch complex platform (3 net cages with diameter of 40 m, culture volume 27,000 m3)

Installed at 1 km away from the coastline of fisherman’s wharf in Laishan district of Yantai

(continued)

M

1024

Modern Aquaculture Structures

Modern Aquaculture Structures, Table 2 (continued) No. 7

Company Shanghai Zhenhua Heavy Industries

Project Name Zhen Yu No. 1

Concept Deep-sea automatic rotating marine fish farming platform with rugby shape (60 m long, 30 m wide and draft 1.2–1.5 m, culture volume 13,000 m3)

Status In operation at Ding Hai Wan, Lianjiang, Fuzhou city

Modern Aquaculture Structures, Fig. 1 Four site classes (Ryan 2004)

Submersible (Semi-Submersible) System A submersible cage is a cage that can be lowered below sea level for a certain period, usually during storms. Some types are always partly under surface, where maintenance and normal operation are carried out at surface. There are many advantages by lowering the facilities and keeping the fish further below sea

level. Wave forces on facilities are much smaller when below the sea level and risk from boat traffic and floating objects is reduced. A new design for submersible cages was emerged in 2004, such as 40,000 m3 Ocean Globe (Fig. 2) from Byks of Norway (Fish Farming International 2004), but few of them have been built and tested in field at full scale. AKVA

Modern Aquaculture Structures

1025

Modern Aquaculture Structures, Fig. 2 Ocean Globe designed by Byks of Norway. (Source: https://www.byks.no/)

Group and Egersund Net have developed a concept for submersible cages called “Atlantis Subsea Farming.” The submersible cage must be submerged in the sea as far as possible and as little as possible in surface so that salmon lice will not become a problem. Salmon farmers in Norway are also looking to the knowledge transfer from Norway’s offshore oil and gas industry to develop semisubmersible fish farm, which can move operations further offshore where environmental conditions are best suited for the growth of fish stocks. Semi-submersible structures are designed to have small water-plan area, which is less affected by wave loadings. Larger buoyant tanks (pontoons) below the ocean surface can be ballasted/de-ballasted to match payload and freeboard needs, as well as raise platforms from a deep to shallow draft. Salmar’s Ocean Farm 1 has now been operating for several years and utilizes such a concept to enclose a pen environment within its vertical “columns.” There are also a couple of projects that are under development, for example, “Havfarm 1,” “Aqua Semi,” “Arctic fish farm,” and “Smart fish farm”.

Closed and Semi-Closed System Closed-containment systems (CCS) and semiclosed containment system (S-CCS) tackle some of the challenges with offshore farming. Placing closed or semi-closed system will enable to prevent escapes and sea lice as physical barriers. As the facilities are closed, the feed will not be picked up and transferred out of facility by currents. Hence, the feed conversion ratio is decreased. Closed facilities need to process the water moving in and out of the facility. Water will be pumped up from 20–30 m below the sea level, where sea lice are not able to live. Moreover, closed facilities enable collection of sludge further reducing sea farming’s environmental footprint. Many players such as Lerøy, Stadion Laks, and Mowi have chosen to focus on completely closed system, and the most famous of these projects is the “Egg” of Mowi. An egg-shaped farm is used to avoid lice and escape of fish, at the same time waste is collected at the bottom of the “Egg.” Mowi has also developed another closed concept, “Marine Donut,” which is a closed facility shaped like a donut.

M

1026

Several companies such as Midt-Norsk Havbruk, Måvasøl Fiskeoppdrett, Nova Sea, AkvaDesign, and Hydra Salmon Company focus on partially closed facilities.

Recirculating Aquaculture Systems (RAS) The use of recirculating aquaculture systems (RAS) will play an important role in the future aquaculture industry. Anadramous fish like salmon and trout are typically raised in fresh water until they are mature enough to migrate to salt water, where they are farmed in sea cages. With RAS technology these fish might spend their entire life on land by alternating fresh and saltwater environments through controlling the water chemistry. Currently, sea farmers are looking into producing post-smolt of up to 500–1000 g or some even larger in land-based farming in order to decrease mortality and increase the number of production cycle (Ernst & Young 2019). RAS system can help to produce post-smolt with a good condition for better survival in sea when transferred to the open sea cage. RAS technology can reduce water consumption and use lower energy for heated water during winter and spring seasons. Recirculation systems use 100 times less water per kilo of fish than traditional land-based systems. In addition, the water quality can be monitored continuously, which lessens the risk of disease and the need for antibiotics. Denmark is a leader in recirculation system aquaculture. Hallundbæk Dambrug is using RAS technology to produce rainbow trout with recirculating over 96% of water (https://state ofgreen.com/en/partners/akva-group-denmark/ solutions/fish-farm-hallundbaek-dambrug/). The discharged water is filtered, and the sludge is used for biogas or fertilizer. The discarded water is treated for removal of nitrate. The carbon footprint is predicted to increase as fish farms move offshore due to increased energy use for transportation of materials, feed, and cultured fish. Facilities with RAS technology can be placed closed to the end market, reducing the transportation costs and carbon footprint.

Modern Aquaculture Structures

Digitalization Digitalization has the potential to simplify offshore operations and aquaculture is focusing extensively on digitally based technologies and solutions. In Norway, a hub for offshore farming innovation, Fishtalk (AKVA Group) and Mercatus (ScaleAQ) are the main registration and reporting tools for production data. The aim of digital solutions is to reduce mortality rates, increase efficiency of farm inputs such as feed and vaccines, prevent disease and lice infection, and optimize farm management. Even more interactive tools based on cloud services are anticipated for the future operation of large-scale offshore farm, providing real-time structural monitoring, complex analyses, and early warning system based on real-time processing of measurements. Cloud services can help to easily access relevant data and exchange the knowledge output and response process. Digitalization has been promoted in application to a free development concession from Norwegian Ministry of Fisheries and Coastal Affairs. Some examples of different projects focusing on digital solutions are: Salmar’s Ocean Farm 1 and Cermaq’s iFarm. Ocean Farm 1 is the first in the world to combine marine engineering, marine cybernetics, and marine biology via a “big data” approach fusing all the available underwater sensors and in this way offer decision support systems for the operators controlling and monitoring the feeding of the salmon and the overall physical environment of the sea (Fig. 3). iFarm is a technology focusing on farmed fish health and welfare and recognizing fish as individuals – it thus has the potential to revolutionize fish farming. This allows us to monitor factors including growth, sea lice, disease, lesions, and other aspects that affect the health and welfare of the individual fish (Fig. 4). Automation Automation will be a strong contributor to efficient fish farming in the future. Automation can minimize the requirement for people in high-risk operations and can enable remote control.

Modern Aquaculture Structures

1027

Modern Aquaculture Structures, Fig. 3 Kongsberg digital farm. (Source: https://www.kongsberg.com)

M

Modern Aquaculture Structures, Fig. 4 iFarm from Cermaq. (Source: https://www.cermaq.com)

Based on technology development, new innovations and individual business goals, it is likely that the intensification of technology used in aquaculture will further strengthen the safety of the employees. One application is the shift from on-site to a more off-site feeding control regime, where the

employee is located on a nearby safe feed barge or onshore. The feeding is carried out using a central feeding system involving video cameras and computers. This approach reduces the potential for incidents, during harsher weather conditions. The other application is autonomous Remote Operated Vehicle (ROV). The equipment is being

1028

developed with the intention of carrying out net integrity (check for holes) and net cleaning. Development and implementation of future autonomous vehicles for carrying out various operational aspects at cage site, is likely to lower the requirement for physical constraint and thereby enhance the safety of the employees. Salmar’s Ocean Farm 1 is one example of operation focusing highly on applying advanced technology for farming purposes. Ocean fram1 is fully automated and equipped with an integrated high-tech sensor and measuring system. The entire facility can be run by a crew of 2–4 people only and heavier manual operations are avoided. Therefore, all farming operations can be managed either onboard or remotely, minimizing the use of service vessels and outside equipment, making the entire facility more environmentally friendly.

Pioneer Projects for Offshore Fish Farm Offshore fish farms operate in the open ocean far from the coast. The offshore fish farm should be

Modern Aquaculture Structures

robust enough to resist heavier environmental condition, especially during storm events. Offshore fish farms in Norway have been designed with experiences from offshore oil rig technology. Fully enclosed cage is normally used for offshore fish farm, which can be tethered or moored to the seabed. The offshore fish farm can be either partly or fully submerged in the sea in order to reduce the loadings from waves. Several designs have been developed in the world today, which is either for commercial production or experimental pilot unit with a small scale. Some recent pioneer projects in commercial production in Norway and China are introduced in the following sections (Fig. 5). Sea Station InnovaSea has developed a semi-rigid submerged net pen, “Sea Station (Fig. 6).” The system has a double cone form and includes a single central steel tube vertical spar inside a circular tube rim. These two elements are joined by radiating frame lines and the netting is fitted around this framework.

Modern Aquaculture Structures, Fig. 5 Offshore Aquaculture Cages (O’Shea et al. 2019)

Modern Aquaculture Structures

1029

Modern Aquaculture Structures, Fig. 6 Sketch for concept of Sea Station (Ryan 2004)

The central spar is used to provide buoyancy. The steel rim is to maintain net’s shape and has ballasting capacities. In harsh weather, the cage can be fully submerged by varying the buoyancy in the central spar. A small platform on top of the central spar allows for feeding, access, and monitoring. The system is moored at the central spar, allowing either for single point or fixed configurations. The standard production model of Sea Station has a volume of 3000 m3 and the volume could be increased to 6000 m3 for larger version. 20 Sea Stations have been installed at Open Blue Farm, which is 11–12 km (7 miles) off the North coast of Panama. Currently 2000–3000 mt of cobia (Rachycentron canadum) can be produced each year (Fig. 7). Aquapod Marine biologists at Ocean Farm Technologies (Now InnovaSea) have developed a spherical fish cage, “Aquapod,” (Fig. 8) which can be carried on the high seas. The system can be fixed on deep sites or drift according to currents. The cages consist of a large number of triangular galvanized steel frames. Their assembly makes it possible to obtain spheres measuring 8–28 m in diameter (capacity of 115– 11,000 m3). Each triangle consists of a frame containing a polyethylene net, made of 80% from recycled products, covered with a

geometallic coating (https://en.how10.com/1529 763-the-aquapod-an-amazing-concept-of-marinefarms-on-the-high-seas). The cages can be used on the surface or at depth, both on the coast and offshore. The triangles weigh between 40 and 50 kg in the air, but their weight vanishes once in the water. These spheres can be immersed with ease, allowing them to escape the action of waves, for example, in case of storm, or to protect them from any risk of collision with floating devices such as ships. The Aquapod is firstly being trialed in Hawaii in a research project called Velella. Now 34 Aquapods are currently deployed in Puerto Rico, Indonesia, Panama, Florida, and Hawaii. They are mainly anchored, using long cables, in deep water with water depth between 200 and 300 m. In the future, Aquapods could potentially be equipped with propellers and a GPS system, and used to transport fish to arrive at their destination with the fish ready to harvest (Fig. 9). Ocean Farm 1 and Smart Fish Farm The world’s first offshore fish farm with a semisubmersible design is already operating off Frohavet in Norway since September 2017. Ocean Farm 1 (Fig. 10) is owned by Norwegian owner, SalMar and was built in the China Shipbuilding Industry Corporation (CSIC) in Qingdao, China.

M

1030

Modern Aquaculture Structures

Modern Aquaculture Structures, Fig. 7 InnovaSea’s Sea Station at Open Blue Farm. (Source: https://www. openblue.com)

SalMar has developed the world’s first offshore fish farm from 2012 to 2015. In 28 February 2016, the Norwegian Ministry of Fisheries and Coastal affairs awarded first development licenses for aquaculture purposes to Ocean Farm 1 (Ocean Farming 2019). SalMar has invested approximately NOK 1 billion to design and develop Ocean Farm 1. Ocean Farm 1 is an anchor fixed structure (diameter 110 m, height 68 m, and volume 250,000 m3) floating steadily in the ocean at water depths of between 100 and 300 m. It has a cylindrical net cage including two closable fixed bulkheads and a sliding bulkhead rotatable about the central column. The facility can be divided into three separate compartments if needed, enabling various fish operations. A bottom that can be elevated is provided between the two closable fixed bulkheads. The net is fixed to the structure and has an incredible strength in order to prevent fish from

escaping. In addition, there is an extra net in the surface zone to protect against drifting matters. Ocean farm1 is fully automated and equipped with an integrated high-tech sensor and measuring system. The entire facility can be run by a crew of 2–4 people only and heavier manual operations are avoided. Therefore, all farming operations can be managed either onboard or remotely, minimizing the use of service vessels and outside equipment, making the entire facility more environmentally friendly. This means that the fish can stay inside the net from stocking to harvestable fish. After the facility was successfully installed, the company initiated a pilot phase with around one million 270–280 g salmon smolt in the cage. After 15 months of production in the sea, the fish has shown very good growth and that the quality is smooth and good. Few salmon lice have been observed and it has not been necessary to carry out a single lice treatment (Ocean Farming 2019).

Modern Aquaculture Structures

1031

Modern Aquaculture Structures, Fig. 8 Aquapod from InnvoaSea. (Source: https://www.innovasea.com/)

M

Modern Aquaculture Structures, Fig. 9 Aquapod fish farm. (Source: https://atlasofthefuture.org/project/aquapodfish-farm/)

1032

Modern Aquaculture Structures

Modern Aquaculture Structures, Fig. 10 Ocean Farm 1. (Source: https://salmar.no/)

A second production cycle started in August 2019 and so far in the cycle good biological status has been observed, with good growth, low lice, and low mortality. Salmar is eying farming in deeper, more exposed locations after the Norwegian Ministry of Fisheries and Coastal affairs awarded permission to “the Smart Fish Farm” concept Fig. 11. The Smart Fish Farm will have twice the capacity of Ocean Farm 1 and the total aquaculture volume of the chambers is 510,000 m3 when the operating depth is 45 m. The Smart Fish Farm concept is based on a semi-submersible steel structure consisting of a wide center column and a surrounding framework mainly with circular cross-sections. The framework stretches supports netting panels that provide eight separate chambers. The Smart Fish Farm has an estimated price tag of NOK 1.5 billion. Although the Smart Fish Farm looks similar to Ocean Farm 1, it differs significantly in some areas. It will withstand substantially more exposed areas and have twice the capacity. But the main difference is that the central closed column will be equipped for processing fish, control

and management of the unit, as well as an advanced system for transporting fish related to the eight surrounding production chambers. Havfarm 1 & 2 The Havfarm concept was developed by Nordlaks along with veteran ship creators at NSK Design in 2015 and awarded 21 licenses for a stationary Havfarm (Havfarm 1) (Figs. 12 and 13) and a dynamic Havfarm (Havfarm 2) (Fig. 14). Havfarm 1 is a moored, long, and slender shiplike fish farm, 385 m long and 60 m wide. The unit consists of a bow section to reduce the wave and current loads in the cage system, a central open frame construction that holds six pyramid-shaped net pens, and a stern section with superstructure. The construction weight is around 33,000 tonnes and can hold up to 2 million salmon. The Havfarm 1 is moored through a turret in the bow, and a total of 11 mooring lines and 11 anchors weighing 22 tonnes each. The unit will weathervane around this, thus making it capable of absorbing the feces and eventual feed spill without negative effects on the environment. This has resolved some of the challenges in the

Modern Aquaculture Structures

1033

Modern Aquaculture Structures, Fig. 11 Smart fish farm. (Source: https://mariculture.no/)

M

Modern Aquaculture Structures, Fig. 12 3D model of Havfarm 1. (Source: https://www.tu.no/artikler/det-forstelakseskipet-har-12-ganger-sa-mye-stal-som-en-vanlig-bronnbat/450811)

aquaculture industry, where environmental footprint in small geographical areas is often a consequence if the natural current does not transport any feed spill and feces away.

Havfarm 1 was built at CIMC Raffles Shipyard in China and has been anchored at the site at Ytre Hadseløya, Norway in July 2020. The smolt will be released in traditional facilities for growth up to

1034

Modern Aquaculture Structures

Modern Aquaculture Structures, Fig. 13 Havfarm 1 on site. (Source: https://www.nordlaks.no/pressekt-havfarm)

Modern Aquaculture Structures, Fig. 14 Concept of Havfarm 2. (Source: http://www.nskshipdesign.com)

1–1.5 kg before the fish is transferred to Havfarm 1. The first stock of fish is scheduled to be released into the farm in September 2020. Havfarm 2 will not be permanently moored but will use a dynamic positioning (DP) system to maintain position. The dynamic positioning

system allows vessels to automatically change their position and heading using thrusters and propellers. The unit can move to a sheltered location in the event of a storm by its own propulsion. Havfarm 2 is planned to operate in two different zones: an exposed zone, which can be divided into

Modern Aquaculture Structures

several anchor points, and a safe zone. Havfarm 2 shall be located in an exposed location when the weather conditions allow and shall shelter in a location less exposed to waves in harsh weather by its own propulsion. This design allows the unit to operate in larger and more exposed areas.

1035

Deep Blue 1 In 2018 China’s first deep-sea fish farm, “Deep Blue 1,” (Fig. 15) was successfully launched by Wuchang Shipbuilding Industry Group and towed to Cold Water Mass area in Yellow Sea, China.

Modern Aquaculture Structures, Fig. 15 Deep Blue 1 in dry dock. (Source: http://www.wanzefeng.com)

Modern Aquaculture Structures, Fig. 16 Deep Blue 1 with new retrofitted tower. (Source: http://m.rzw.com.cn/ pcarticle/485837)

M

1036

Modern Aquaculture Structures

Modern Aquaculture Structures, Fig. 17 Hai Xia 1 in dry dock. (Source: http://www.sasac.gov.cn/n2588025/ n2588129/c14167773/content.html)

The unit has a perimeter of 180 m and height of 35 m. The volume is 50,000 m3 and can produce about 1500 tonnes fish per season. In 2019 the “Deep Blue 1” was retrofitted with a tower of 35-m height (https://ilaks.no/den-kinesiskehavfarmen-deep-blue-no-1-tilbake-i-drift-detteer-nytt/). The central tower (spar) houses machinery spaces, feed storage, and provides accommodation for operators (Fig. 16). Its position underwater can be adjusted between 4 and 50 m to secure the best temperature for the salmon. By submerging under water, the pen will be able to withstand typhoon. Hai Xia 1 The Dutch company De Maas SMC, a firm operating in the offshore oil and gas industry, has partnered with the local government in Fujian province to develop central column semi-submersible deep-sea fish farm, “Hai Xia 1 (Fig. 17).” “Hai Xia 1” is 139-m in diameter and 12-m high, which is composed of a central cylinder

structure and the outer frame structure. The unit has a floater, which is below the surface and fused to the central spar. Water can be pumped in and out to sink/rise the unit. The spar houses the control room for the unit (https://www.under currentnews.com/2018/10/01/expert-qa-design ing-building-offshore-aquaculture-pens/). “Hai Xia 1” was constructed in a shipyard in the port city Mawei, Fujian and successfully deployed at East China Sea.

Cross-References ▶ Net Structures: Design ▶ Net Structures: Hydrodynamics ▶ Traditional Aquaculture Structures

References Ernst & Young AS (2019) The Norwegian aquaculture analysis. Ernst & Young

Modification for Reuse Fish Farming International (2004) Monthly trade neespaper for food-fish and shellfish farmers worldwide. Heighway/Informa 31(3) O’Shea T, Jones R, Markham A (2019) Towards a blue revolution: catalyzing private investment in sustainable aquaculture production systems. The Nature Conservancy and Encourage Capital, Arlington Ocean Farming (2019) SLUTTRAPPORT Prosjekt Ocean Farm 1 Ryan J (2004) Farming deep blue, Irish Sea Fisheries, Irish Marine Institute Veterinærinstituttet (2017) Fiskhelseraporten

Modification for Reuse Pei Zhang and Yan Li State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University, Tianjin, China

Synonyms Change for reuse; Conversion for reuse

Definition Some decommissioning vessels, offshore structures, or their components are in relative good conditions. After the condition assessment and a series of maintenance and transformation, such as adding some new facilities, deck reinforcement, changing the single-layer tank to double layer, the updated vessels or platforms can continue to work for other projects.

Scientific Fundamentals Background and Introduction Shipowners scrap their ships for various reasons, such as aging, technical obsolescence, low earnings, high scrap prices, and bad market expectations (Stopford 2009). Most shipowners base this decision primarily on the price offered by the ship

1037

recycling yard to buy an end-of-life ship. The recycling yard offering the best price usually wins the contract (Jain et al. 2017). The recycling yards offering “green” recycling services generally quote lower prices than other yards due to the higher cost of dismantling a ship by following international ship recycling regulations and health, safety, and environmental (HSE) management systems, or the ship recycling regulations such as the Hong Kong Convention and EU Ship Recycling Regulation are considered innocuous to environment. According to an estimate by Abdullah et al. (2012), the annual global capacity of recycling was around 780,000 lightweight tonnes (LDT) in 2012. Such yards generally offer a lower price compared to other yards operating in the same region. The ship recycling process recovers steel and other materials in good condition. These materials can be reused and sold to the steel industry. The recycling shipyards in South Asia have been using substandard and standardized methods. The substandard method is the most common and corresponds to the (beaching) modality utilized mainly in India, Bangladesh, and Pakistan. The standardized method uses the landing and dry docking methods in Turkey, China, Europe, and North America (Ocampo and Pereira 2019). Various shipyards have experience in managing repair and conversion projects with different vessels in order to extend their life or have more functions. The modification work includes but does not limit to structural steel renewal and refitting, hull blasting and painting, large machine shop facility, tail shaft and propeller repairs, engine overhaul, turbo charger overhaul, electrical repairs, automation and control systems, tank cleaning and coating, aluminum hull repairs, yacht repairs and refurbishments, deck machinery overhauls, pipeline and valve overhauls/renewals, and so on. During the modification progress, some guidelines or rules proposed by the official societies, such as DNV (2013), ABS (2014), BV (2017), CCS (2016) etc., should be obeyed or referred. Apart from vessels, some of the offshore platforms are approaching the end of their production life and will need a strategy for removal, reuse, and recycling in the following future. For each

M

1038

existing, as well as new, platform, it will be necessary to document the removal and modification procedures in detail. The opportunity to reuse a platform would require a favorable circumstance for old removed, reinstalled, and refurbished structure to be considered in comparison to building an entire new and purpose-built facility (Ole Olsen 2001). It is therefore important that available reusable platforms are advertised well in advance. The operators must be aware of the reuse option when planning for new field developments. Within some years, the operators may have several existing platforms to choose from, when assessing the best option for the actual new field development (FIB 2002).

Key Applications Representative Modifications Oil Tanker Modification for FPSO/FLNG

In recent offshore oil and gas markets, there are two major approaches to build FPSOs (Floating Production, Storage, and Offloading Facilities). One way is to construct a new facility, and the other way is to modify oil tankers. Comparing with the latter approach, building a complete new FPSO is more time-consuming and demands for relative large funds. Hence, more shipyards and shipowners would like to choose modifications, which will save almost 10-month construction periods as well as 20% of the total cost. In some regular sea states, the rental fee of a FPSO

Modification for Reuse

converted by oil tanker is more than the sum of modification fee and rental fee of oil tanker. Hence, it attracts more and more shipowner to modify their aged oil tankers to FPSOs (Zhang 2017). Some converted FPSOs in China are shown in Fig. 1. The base of FPSO modification project is to choose a suitable old oil tanker. First of all, based on the requirement, crude production, deck area, and transportation ability of shuttle tanker in operation offshore oil field, the main dimensions and tonnage of the target oil tanker are determined. Afterward, the next step is to seek the suitable oil tanker according to the information in every way. Based on a set of hull design parameters, different hull configurations are evaluated and the respective advantages and disadvantages assessed in order to identify the best candidates for conversion (Biasotto et al. 2005). Furthermore, based on investigations on the target vessels, the cost of the whole modification project could be predicted, taking all factors into consideration, including the age of vessel, status of vessel and its facilities, etc. During the project demonstration of the conversion, the key factor of the feasibility is the economic performance compared with the new building FPSO. Finally, a structural assessment is necessary to judge whether the oil tanker meets the requirement of the design life. The tanker conversion activities include the following parts: • Hull conversion • Mooring structure conversion • Risers

Modification for Reuse, Fig. 1 Converted FPSOs in China. (Source: CNOOC)

Modification for Reuse

• • • • • •

Deck reinforcement Accommodation – living and safety Helideck and deck cranes Hull corrosion protection Tanker propulsion Tanker services (power and heat plant)

1039

offshore structures, when well designed and built. There are also a lot of other proposed uses for old platforms: bridge piers, coastal defense, wind farms, and artificial reefs in addition to some more exotic examples as prison, casino, and fish farms. However, there are also several issues existing:

Reuse of Offshore Platform

After deciding to totally remove a platform from the seafloor, operators have several options (O’Connor 1998; Van Voorst 1999; Gibbs 2000). • The platform can be taken to shore, where it is disassembled and the components either recycled, sold as scrap, or discarded in landfills or other depositories. • The structure can be reconditioned and reused. As an example, in 1997 a platform was removed from the North Sea, taken to shore and cleaned, refurbished, and shortened by 10 m (33 ft) and installed in another North Sea location. A few small platforms have also been reused in the Gulf of Mexico (Schroeder and Love 2004). • Platform structure can be towed to a site remote from the intact platform (in either shallow or deep water) and reefed. Remote, shallow-water reefing has occurred a number of times in the Gulf of Mexico, with the most extreme example towing structures of two Tenneco platforms over 1480 km (920 mile) from offshore Louisiana to a site 2.4 km (1.5 mile) off Dade County, FL (Wilson et al. 1987). A platform could be either reused in situ or removed, reinstalled, and reused at its new location. The design purpose, to produce oil and gas, could be changed as well. Finding another oil field that will match all the platform properties and production capacity is perhaps impossible but also not necessary. Some modifications and refurbishment must be performed anyway. Successful reuse of offshore platforms is dependent on water depth, seabed conditions, and other environmental loads. An advantage for reused structures could be a shorter timescale from planning to production start. Another advantage is the good durability of

• Skirts and bottom slabs are designed for particular soil conditions. If the conditions at the new location are totally different, this may make relocation impractical. • Estimated life remaining (particularly with regard to fatigue) must be equal or longer than the estimated production life for the new field. Assessment of structure life remaining is important in this process. • Using the platform for new activities requires due consideration of personal safety, transportation issues, and maintenance of the platform. There will always be a day for end use and decommissioning for a platform; thus, the dismantling process will always be applicable. However, it should be noted that steel jackets will have an imaginable thickness loss due to the corrosion after its lifetime service. It is a possible choice to evaluate and certain the high-value elements which will be used in the following projects, in order to judge whether it is fit and economic for reuse. On the other hand, concrete gravity-based structures are usually not removable, and they are commonly modified and reuse in its “former” operation area. Reuse for Subsea Components

It is widely accepted that subsea structures, such as wellheads, production manifolds, etc., are designed as a reusable facility. It will not only reduce the development cost of the offshore oil fields but also be beneficial to protect the offshore environment and maritime safety. As one of the intricate machined hardware sized for the flow rates, well shut-in pressures, installation vessel interfaces, and intra-field connections, it is normally designed to a high specification with corrosion resistance (Gorman and Neilson 2012). For these deepwater subsea structures, they are

M

1040

utilized for production in a short duration. Besides, they hardly experienced external corrosion, so they are pretty suitable for a second-round operation in another oil field. However, it should be noted that there exist many issues or obstacles before to make the decision to reuse this facility in another place. On the one hand, the factors, including valve size, material class, and its remaining useful design life, should be carefully evaluated and examined. On the other hand, the designers should check the tree’s flowloop configuration as well as the valve number. According to the working area water depth, the subsea trees could be categorized into four types, which are mudline, diver assist, diverless, and guidelineless. The different type has its individual features, such as thickness, metal loss protection, and structure complexity. Hereby, this is another factor to be considered during the modification. Moreover, the wellheads, foundations, control systems, and flowline connection techniques may also affect successful reuse (Kawase et al. 1997).

Modification for Reuse

fatigue, and handling, so can the anchor components. However, a careful inspection work on field life, strength, design temperature, and installation equipment should be adopted in order to check the feasibility to the new field requirements. Similarly, the risers are also able to hold the reusable feature, although they are custom-designed for their corresponding area. Specifically, the lazy wave and free hanging catenary risers are easier to re-utilize as the riser forms part of the flowline after touchdown. However, the inspection before the second-time adoption contains much more terms, such as service life and type, design temperatures and pressures, site particulars, riser configuration, and installation equipment. Recertification of the riser by the riser manufacturer or the certifying authority may also be required. Moreover, a detailed examination of the external sheath and the end fittings will be required. Buoyancy modules will need to be removed, refurbished, and replaced during reinstallation (Kawase et al. 1997).

Reuse for Mooring and Riser System

For the moored offshore platforms, there are mainly two mooring types, one is permanent and the other is disconnectable. Taking FPSO as an example, this system usually contains turret, mooring cables, and risers. Based on the evaluation from different aspects, each part of them could be reused in other oil fields. In general, both internal and external turret design standardizations further facilitate reuse in that plans for additional, or future, risers may be well thought out avoiding the complications due to structure or piping interference in a future modification. The turret system piping, manifold, swivels, and safety features must be evaluated for compatibility with the new field requirements following a thorough inspection to determine the existing condition (Kawase et al. 1997). Furthermore, if the modification is adopted, it is best to perform this progress in a shipyard, and in some particular cases, dry-docking may be needed due to the project plan. The mooring cables can also be reused with the proper consideration of corrosion, wear,

Future Technics Combined Offshore Energy Harvesters Renewable energy resources, called sustainable or alternative energy, are energies generated from natural resources such as wind, sunlight, tide, hydro, biomass, and geothermal which are naturally replenished (Díaz-de-Baldasano et al. 2014). The main challenge of replacing legacy systems with more environmentally friendly alternatives is how to capture the maximum energy and deliver the energy at a minimum cost. A combination of two or more types of energy sources might provide a good chance of optimizing power generation system (Da and Khaligh 2009). Hence, a series of novel offshore structures for renewable energy power generations, such as wind/tidal, wind/wave, wind/solar, and so on, are developed. However, most of present offshore energy harvesters only have single function. In order to establish the hybrid power system, a modification is necessary.

Modification for Reuse

CO2 Emissions of Oil and Gas Production Platforms Oil and gas platforms are energy-intensive systems, and each facility uses from a few to several hundred MW of energy, depending on the petroleum properties, export specifications, and field lifetime. For instance, the Norwegian oil and gas offshore sector has contributed for about 20–30% of the total Norwegian CO2 emissions in the last decade, and this number is expected to stay in the same magnitude in the coming years. These emissions are caused in a large share by the combustion of natural gas in gas turbines to produce the power required to drive the compression and pumping operations, and the remaining is associated with gas flaring and diesel combustion. Several technologies for increasing the energy efficiency of these plants are investigated. Among them, it is an effective way to make some modifications or add some new facilities on the old platforms in order to lessen CO2 emissions. They aim at reducing the electrical or thermal energy use, by redesigning some sections of the processing plant (production manifolds), re-dimensioning the compressors (gas recompression and treatment), promoting energy and process integration (heat exchanger network), and implementing expanders and waste heat recovery cycles. The savings potentials differ significantly from one platform to another (Nguyen et al. 2016).

1041

Fish Farms Nowadays, more and more researchers are considering setting up fish cage structures in large offshore structures such as platforms or jackets to create such new structures for offshore ranching. However, there still exit several issues to be taken into account. On the one hand, there will be many difficulties for the cage structure, such as motion response according to the change in draft, lowering and lifting, and so on. On the other hand, storm damage due to snagging and fretting of nets or cages is likely to be frequent and not easily repaired. Furthermore, the development and maintenance cost is likely to exceed the profits of inshore fish farming. Modification for Entertainment, Tourism, or Living Apart from the above solutions, there is an interesting and creative way to reuse the retired offshore platforms. This answer is to modify the platform as a sea-view hotel or a diving resort. The Seaventures (see Fig. 2) is a dive resort made from a converted oil rig offering a perfect location for nonstop diving. Besides, the dive resort also provides accommodation and entertainment facilities. Another similar idea is performed on the abandoned oil platform “Albuskjell 2/4-F” by Norwegian architect Sverre Max Stenersen. The platform is modified to add some living or business features, and it is planned to be located in the port of Trondheim.

Modification for Reuse, Fig. 2 Seaventures dive resort. (Source: sipandan.com)

M

1042

References Abdullah HM, Mahboob MG, Banu MR, Seker DZ (2012) Monitoring the drastic growth of ship breaking yards in Sitakunda: a threat to the coastal environment of Bangladesh. Environ Monit Assess 185:3839–3851 American B. S (2014) Rules for building and classing floating production installations. American Bureau of Shipping, New York Biasotto P, Bonniol V, Cambos P (2005) Selection of trading tankers for FPSO conversion projects. In: Offshore technology conference. Offshore Technology Conference, Jan, 2005 Bureau V (2017) Ship conversion into offshore units – deployment and life extension of offshore units, BV guidance note NI 593 DT R01 E. China C.S (2016) Guidelines for Major Conversions of Ships. China Classification Society, Guidance notes GD10–2016. (2016, in Chinese) Da Y, Khaligh A (2009) Hybrid offshore wind and tidal turbine energy harvesting system with independently controlled rectifiers. In: Industrial Electronics, 2009. IECON’09. 35th Annual Conference of IEEE, pp 4577–4582. IEEE, Nov 2009 Díaz-de-Baldasano MC, Mateos FJ, Núñez-Rivas LR, Leo TJ (2014) Conceptual design of offshore platform supply vessel based on hybrid diesel generator-fuel cell power plant. Appl Energy 116:91–100 FIB Recycling of offshore concrete structures. International Federation for Structural Concrete (2002) Gibbs B (2000) Offshore structure abandonment: solutions for an aging industry Sea Technology 41(4):25–32 Gorman DG, Neilson J (2012) Decommissioning offshore structures. Springer Science & Business Media, London Jain KP, Pruyn JFJ, Hopman JJ (2017) Material flow analysis (MFA) as a tool to improve ship recycling. Ocean Eng 130:674–683 Kawase M, Skeels HB, Stemmler PA (1997) Design and evaluation of Floating production storage offload (FPSO) Systems for Decommissioning and Reuse, deep offshore technology conference (DOT ‘97) Nguyen TV, Voldsund M, Breuhaus P, Elmegaard B (2016) Energy efficiency measures for offshore oil and gas platforms. Energy 117:325–340 O’Connor PE (1998) Case studies of platform re-use in the Gulf of Mexico. In: The re-use of offshore production facilities. Proceedings of an International Conference on the Reuse of Offshore Production Facilities, The Institute of Petroleum and the Netherlands Energy Research Foundation Ocampo ES, Pereira NN (2019) Can ship recycling be a sustainable activity practiced in Brazil? J Clean Prod 224:981–993 Ole Olsen T (2001) Recycling of offshore concrete structures. Struct Concr 2(3):169–173 Schroeder DM, Love MS (2004) Ecological and political issues surrounding decommissioning of offshore oil

Monopile Foundations in Offshore Wind Farm facilities in the Southern California bight. Ocean Coast Manag 47(1–2):21–48 Stopford M (2009) Maritime economics 3e. Routledge, New York Van Voorst O (1999) Offshore facility re-use– a viable option. Pet Rev Lond 53(632):38–39 Veritas D.N (2013) Conversion of Ships. DNV Classification Notes, (No.8) Wilson CA, Van Sickle VR, Pope DL (1987) Louisiana Artificial Reef Plan. Louisiana Department of Wildlife and Fisheries Technical Bulletin No. 41, Louisiana Sea Grant College Program, p 51 Zhang M (2017) Description of Hull Conversions in the typical projects of FPSO modified by oil tanker. Shipbuild Stand Qual 271(4):37–40 (in Chinese, 2017)

Monopile Foundations in Offshore Wind Farm Guoliang Dai School of Civil Engineering, Southeast University, Nanjing, China

Synonyms Single pile foundation

Definition Monopile foundations refer to the commonly used steel pipe piles with large diameter and thick wall, which are usually driven (hammered) into the seabed.

Scientific Fundamentals Scope for Development of Monopile Foundation The energy crisis and air pollution caused by traditional energy resources around the world have led to an urgent need for clean and renewable resources in the twenty-first century. Under this background, offshore wind farms have become an important source of renewable energy in recent years. The first large-scale offshore wind farm was successfully installed in 2002 in Denmark, which is the

Monopile Foundations in Offshore Wind Farm

1043

milestone of offshore wind farm construction. Since then, in Europe, there have been booming developments in offshore wind farm benefitted from strong political and financial support. Moreover, political strategies in Europe, and in the United States, aim to enlarge to the offshore wind energy sector to limit the dependence on oil, gas, and coal (Malhotra 2011). When it comes to China, the first large-scale offshore wind farm (offshore wind farm of Donghai Bridge) is built in Shanghai by 2009, indicating the new epoch of offshore wind energy. By 2015, the capacity of offshore wind farms in China has reached over 1.01 GW, and several projects that made this happen are shown in Table 1. The relative statistical data of several countries of annual offshore wind capacity from 2012 to 2015 and 2017 are shown in Table 2 and Fig. 1, respectively. There are several types of foundations to support offshore wind turbine structures, which include monopile foundations, gravity foundations, tripod foundations, suction foundations, and floating foundations. Each type of foundation has their own structural advantages and limitations. Among these foundations, monopiles are most commonly used foundations in offshore wind farm as they can withstand harsh loading condition transferred from the supported superstructures in deep waters with the advantage of lower cost, more structural simplicity, and smaller foundation settlement. In Europe, the monopiles constitute 81.7% of all installed turbine substructures, which are shown in Fig. 2. The same phenomenon can also be found in China’s offshore wind farms.

Monopile Foundations in Offshore Wind Farm, Table 1 Offshore wind farms in China from 2007 to 2015 (http://www.cwea.org.cn)

Monopile Foundations

monopiles with large diameters and long embedment would allow the supporting of larger wind turbines – from 3–4 to 5–8 MW of power capacity and with the installation possible in deep waters of 30 m. “Offshore wind turbines with 6–8 MW capacity have already existed in the energy market, with superstructure where the height of the hub can reach up to 100 m and blade diameters up to 150 m, e.g., DONG’s Westermost Rough and Burbo Bank Extension wind farms” (Ortolani 2017).

Monopile foundations are usually steel pipe piles with large diameters and thick walls that are driven (hammered) into the seabed. Carlo (Ortolani 2017) and Byrne (2015) reported commonly used monopile foundations with large diameter (D) of 4–7 m (Fig. 3), sometimes even up to 10 m in diameter with their lengths of 40–50 m (while in China, the length of several monopiles is as long as 70 m, i.e., monopiles in Xiangshui offshore wind farm). The

year 2007 2009

2010

2011 2012

2013 2013 2014

2015

Total

location The Bohai Sea, Liaoning Nantong, Jiangsu Yancheng, Jiangsu Weihai, Shandong Shanghai Nantong, Jiangsu Nantong, Jiangsu Yancheng, Jiangsu Nantong, Jiangsu Shanghai Nantong, Jiangsu Nantong, Jiangsu Weifang, Shandong Fuqing, Fujian Nantong, Jiangsu Yancheng, Jiangsu Nantong, Jiangsu Binghai, Tianjing Rudong, Jiangsu Shanghai Rudong, Jiangsu Rudong, Jiangsu Putian, Fujian Putian, Fujian Haimen, Guangdong Dafeng, Jiangsu Rudong, Jiangsu Xiangshui, Jiangsu Binghai, Jiangsu Rudong, Jiangsu Rudong, Jiangsu

Capacity (MW) 1.5 1.5 8.0 16.0 2.0 6.0 102.0 135.5 24.5 2.5 6.5 101.0 109.6 8.6 110.0 127.0 3.0 9.0 5.0 5.0 8.0 3.0 4.0 31.0 27.0 20.0 227.2 102.2 56.0 49.0 12.0 360.5 50.0 1.5 9.0 100.0 32.0 20.0 56.0 80.0 1016.3

M

1044

Monopile Foundations in Offshore Wind Farm

Monopile Foundations in Offshore Wind Farm, Table 2 Capacity of offshore wind farm in several countries (in GW) (https://windeurope.org) 2012 New 854.2 80.0 46.8 127.0 185.0 0.0 0.0 0.1 1293.0 1298.0

Year Country Britain Germany Denmark China Belgium Netherland Sweden Japan Total Global Total

in summary 2948.0 280.0 921.0 389.6 380.0 247.0 164.0 25.3 5355.0 5415.0

2013 new 733.0 240.0 350.0 39.0 192.0 0.0 48.0 24.4 1626.0 1631.0

Net Installation Capacity in MW

Monopile Foundations in Offshore Wind Farm, Fig. 1 Annual offshore wind capacity installations per country in 2017 (MW) (https:// windeurope.org)

in summary 3681.0 520.0 1271.0 428.6 571.5 247.0 212.0 49.7 6981.0 7046.0

1800

2014 new 813.0 529.0 0.0 229.3 140.0 0.0 0.0 0.0 1711.0 1725.0

in summary 4494.0 1049.0 1271.0 658.0 711.0 247.0 212.0 49.7 8692.0 8771.0

2015 new 566.0 2282.0 0.0 3610.0 0.0 180.0 0.0 3.0 3392.0 3392.0

in summary 5060.0 3331.0 1271.0 1091.0 711.0 427.0 212.0 52.7 12084.0 12105.0

165

2

Finland

France

1679 1247

1200

600

0 United Germany Kingdom

315

80

6

1

18

Monopile Gravity Base

283

Jacket Tripod Floating spar buoy 3720

Floating Barge others

Monopile Foundations in Offshore Wind Farm, Fig. 2 Share of substructure types for grid-connected wind turbines (units) (https://windeurope.org)

Components of Monopile-Supported Offshore Wind Turbine As illustrated by Velarde (2016), a typical monopile-supported offshore wind turbine consists of a steel pipe pile with a large diameter which is driven into the seabed by a steam or

hydraulic-powered hammer. The support structure consists of three main parts: foundation pile, transition piece (or without), and tower as shown in Fig. 4. These components of the support structure hold the rotor-nacelle assembly in place. The nacelle houses electronic and mechanical parts of the turbine such as gearbox and generator. The function of monopile is to transmit loads such as wind loads (on the turbine and tower), wave and current loads, lateral load, and overturning moments (due to cantilever structure of turbine) and axial loads (due to the weight of the superstructure) to the underlying soil without any failure over the design period. The monopile is connected to the tower by the transition piece which is grouted. This transition piece can be used for anchoring of boats, as a ladder, as platform, and can also be used for correction of vertical misalignments during pile driving. The

Monopile Foundations in Offshore Wind Farm

1045

Monopile Foundations in Offshore Wind Farm, Fig. 3 A 7.5-m diameter monopile in an offshore wind

M monopile and transition piece assembly are the most important parts to connect the rotor-nacelle assembly to the tower. Installation of Monopile Foundation The installation procedure for monopile includes: (1) Transportation to site by feeder barge, (2) transportation to installation vessel or floating vessel, (3) upending and lifting into position, (4) alignment to position, and (5) driving or drilling into the seabed. The installation of monopoles can mainly be done in three methods (Fig. 5) depending on the subsurface conditions of the seabed: (1) Impact method, (2) vibratory method or grouted into sockets, and (3) drilled into rock. The drilling method is more efficient and less cost-effective of installation than the driving method. Most offshore piles are installed with impact-driven piles, which produce noise, and the noise must be reduced using expensive techniques to limit the damage on sea mammals. Vibratory driven piles are commonly used in sandy soils; the pile is driven at the head by

applying quick sequences of downward and upward motions to the pile in order to reach the required embedded length without noise mitigation system and fatigue induced by impact driving (Matlock 2015). Drilled method is used when the soil is too hard for installation. This installation method has large effect on the bearing capacity of piles. Monopiles used for offshore wind turbines can be considered as low-displacement piles as Pedram (2015). There are many researches focusing on the effect of installation methods on the pile behavior; this has been studied by various methods such as field tests, laboratory study, mechanical modeling, or numerical studies. During design of monopiles, installation methods should be taken into consideration while determining soil strength and stiffness around pile body (Phanikanth et al. 2012). A typical installation physical modeling was proposed by Hokmabadi et al. (2015), a numerical modeling by McCabe and Sheil et al. (2015), and some field testing/observations was done by Zhuang and Cui ((2015); (Kog 2016; Eslami and

1046

Monopile Foundations in Offshore Wind Farm

Monopile Foundations in Offshore Wind Farm, Fig. 4 The monopile support structure

Fellenius 1997; Eslami et al. 2012). Zarrabi and Eslami (2016) has conducted more than 30 axial compressive and tensile load tests which were performed on various monopiles installed with six different installation methods (jacking, drilling and grouting, driving, drilling and placing, screwing, and postgrouting). From the results, Zarrabi and Eslami (2016) found that jacked and precast-in-place piles had the highest and lowest capacities, respectively. Also driven piles had the next highest capacity among other piles.

Field Tests Example on Monopile with Large Diameters In offshore wind projects, field test on monopiles is an essential part in construction; the main purpose of the field test is to make sure of the bearing capacity before construction and to prove that the existing pile is secure under static or dynamic loading conditions.

Depending on the force direction, there are two kinds of loading methods: vertical loading tests under axial-compressive and tensile loads, and lateral load test. Depending on the test methods, the commonly used tests are conventional loading test, bidirectional test (Osterberg cell or O-Cell test), low strain impact integrity test, and high strain impact test. The conventional axial compressive load test is one of the most commonly used methods to determine the vertical bearing capacity of monopile in offshore area. Anchor piles as a load test reaction system and a jack as a force-applied system are used to offer the vertical load on the pile head, which can be seen in Fig. 6; the conventional static load test is a reliable method to determine the bearing capacity of piles (Russo 2013). But for monopile with very large diameter, it is unattainable for this loading test to determine the capacity behavior of these piles (where the load test reaction systems often do not have the capacity to take the pile all the way to plunging).

Monopile Foundations in Offshore Wind Farm

1047

Monopile Foundations in Offshore Wind Farm, Fig. 5 Pile installation by (a) impact method (Yushan Super Bridge project), (b) vibratory method) (De Neef et al. 2013), and (c) drilling method (Mai 2012) Monopile Foundations in Offshore Wind Farm, Fig. 6 Conventional load test of an offshore wind project in China (offshore wind farm of Donghai Bridge)

M

As for the bidirectional test, it can solve the above problem, and this method has been successfully used in some offshore wind projects. In bidirectional load test, a very important equipment is load cell, which is shown in Fig. 7. During the loading process, the top and bottom planes of load cell were apart and pushed their corresponding pile sections to move contrarily until the ultimate resistance of top pile is reached. The displacement versus applied load of top and bottom planes was recorded at each loading step. However, there is a need for several hypotheses in bidirectional test to transform experimental results into those of an equivalent conventional load test. As for the low-strain impact integrity test and high-strain test, the low-strain test can be

Monopile Foundations in Offshore Wind Farm, Fig. 7 (a) Bidirectional test of pipe pile and (b) Load cell of pipe pile

used to find out the integrity of pile body, while high-strain impact test can be used to determine the vertical bearing capacity of pile only if the result can be compared with that of static load test.

1048

Monopile Foundations in Offshore Wind Farm

Sample Field Tests on Monopile

coast area of Jiangsu province; the soil profile here consists of marine clay and sand. The relative parameters of piles (A and B) are shown in Table 3, the corresponding vertical capacity test results are shown in Figs. 8 and 9, and the shaft resistance of each layer of piles A and B is shown in Table 4.

In this part, the field static loading tests results of an offshore wind farms in China are introduced. These loading test methods include axialcompressive and tensile load test, as well as lateral load test. The wind farm project is located at the

Monopile Foundations in Offshore Wind Farm, Table 3 Test pile parameters in field test (Li et al. 2019) Project name: Pile name Pile length (m) Pile diameter (m) L/D Test method

0

10000

20000

30000

40000

0

b 90 80

load(kN)

70 displacement(mm)

20 displacement(mm)

B 77.5 2.0 38.8 Axial compression & tensile load test

40 60 80

60 Pile A

a

Project 1 A 71.5 2.0 35.8 Axial compression & tensile load test, lateral load test

50 40 30 20 10

100

load(kN)

0 0

120

c 0

0

10000

20000

30000

40000

10000

15000

20000

25000

100

d

90 load(kN)

80

20

70

60 80

100

60 Pile B

40

displacement(mm)

displacement(mm)

5000

50 40 30 20 10

load(kN)

0 120

Monopile Foundations in Offshore Wind Farm, Fig. 8 (a & c) are downward load-displacement of pile top from test of pile A and B, respectively; (b & d) are

0

5000

10000

15000

20000

25000

uplift load-displacement of pile top from test pile A and B, respectively. (Source: Li et al. 2019)

Monopile Foundations in Offshore Wind Farm

1049

From Fig. 8a and b, the vertical compressing capacity of A is 32,800 kN, the total shaft resistance is 31,076 kN, and the uplifting capacity of B is 22,800 kN; in Fig. 8c and d, the vertical compressing capacity of A is 34,850 kN, the total shaft resistance is 33,260 kN, and the

uplifting capacity of B is 22,000 kN. From Fig. 9, the displacement of the pile at load-applied point of 500 kN is 0.0779 m. The ultimate shaft friction resistance at different soil layers is shown in Table 4. From these results, we can find that the friction resistance from compressive load test is much larger than that from tensile load test.

600

The Problems with the Use of Monopiles

load (kN)

500 400 300 200 100 0

0

0.02

0.04

0.06

0.08

0.1

displacement (m)

Monopile Foundations in Offshore Wind Farm, Fig. 9 Lateral load-displacement at mud line of A

Monopiles are widely used in offshore wind projects, while large diameter single piles with diameters of 5–10 m (Byrne 2015) are considered for future design purpose in deep offshore areas. The most difficult problem in the use of monopile foundation is the current design methods, originally used for small diameter piles. There are many problems when using the traditional design method on the large diameter monopiles, some of which are mentioned below:

Monopile Foundations in Offshore Wind Farm, Table 4 Shaft resistance of A and B from load tests Pile name ZK01

ZK28

Soil type Mud Silt clay with mud Silt sand Silt sand Silt clay with mud Silt clay Silt clay Silt sand Silt sand Silt clay with mud Silt sand Silt sand Silt clay with mud Silt sand Silt clay Silt sand Silt clay Silt

Thickness of each layer (m) 2.62 7.90

Shaft resistance (kPa) from compression load 23 54

Shaft resistance (kPa) from tensile load 11 20

3.00 8.20 9.80

67 107 105

36 69 81

16.30 1.70 4.08 1.37 7.90

94 95 128 32 40

77 79 101 9 12

3.30 7.00 10.10

63 77 80

31 44 53

12.00 4.60 7.40 1.90 3.53

103 111 135 97 114

66 81 93 64 77

M

1050

(a) The mechanical model of pile-soil interaction of monopiles with large diameter in sand and clay (b) The definition of initial tangent modulus in p-y curves considering embedment conditions (c) The calculation method of natural frequency of monopile considering embedment conditions (d) The influence of installation method on soil response around the large diameter monopiles (e) The cyclic load effect on the lateral capacity of large diameter monopiles

Cross-References ▶ Pile Capacity

References Byrne BW, McAdam R, Burd HJ, Houlsby G, Martin C, Zdravković L, Schroeder FC (2015) New design methods for large diameter piles under lateral loading for offshore wind applications. In: Third international symposium on frontiers in offshore geotechnics (ISFOG 2015). Oslo, Norway, 10–12 De Neef L, Middendorp P, Bakker J (2013) Installation of monopiles by Vibrohammers for the Riffgat. Pfahlsymposium, Braunschweig, pp 1–14 Eslami A, Fellenius BH (1997) Pile capacity by direct CPT and CPTu methods applied to 102 case histories. Can Geotech J 34(6):886–904 Eslami A, Veiskarami M, Eslami MM (2012) Study on optimized piled-raft foundations (PRF) performance with connected and non-connected piles-three case histories. Int J Civil Eng 10(2):100–111 Hokmabadi A, Fatahi B, Samali B (2015) Physical modeling of seismic soil-pile-structure interaction for buildings on soft soils. Int J Geomech 15(2):1–18 Kog YC (2016) Axially loaded piles in consolidating layered soil. Int J Geomech 16(1):1–11 Li X, Dai G, Zhu M, Gong W (2019) Application of static loading tests to steel pipe piles with large diameters in Chinese offshore wind farms. Ocean Eng 186(3):106041 Mai AQ (2012) Design monopile foundation of offshore wind turbines. Doctoral dissertation. Université de Liège, Liège Malhotra S (2011) Selection, design and construction of offshore wind turbine foundations. In: Ibrahim Al-Bahadly (eds) Wind turbines, InTech, Croatia, pp 231–264. ISBN: 978-953-307-221-0 Matlock BGWM (2015) Comparison of the lateral bearing capacities of hammered and vibrated piles. In: Fifth

Moored Ship in Ice international conference Offshore Foundations, Bremen Ortolani C (2017) Laterally loaded monopiles for offshore wind turbines: analysis and improvement of the p-y curves. Thesis Pedram B (2015) A numerical study into the behaviour of monopiled footings in Sand for Offshore Wind Turbines. Doctoral dissertation, University of Western Australia Phanikanth VS, Choudhury D, Reddy GR (2012) Behavior of single pile in liquefied deposits during earthquakes. Int J Geomech 13(4):454–462 Russo G (2013) Experimental investigations and analysis on different pile load testing procedures. Acta Geotech 8(1):17–31 Sheil BB, McCabe BA, Hunt CE, Pestana JM (2015) A practical approach for the consideration of single pile and pile group installation effects in clay: numerical modelling. J Geo Eng Sci 2(3):4 Velarde J (2016) Design of monopile foundations to support the DTU 10 MW offshore wind turbine. Master’s thesis, NTNU Zarrabi M, Eslami A (2016) Behavior of piles under different installation effects by physical modeling. Int J Geomech 16(5):04016014 Zhuang Y, Cui X (2015) Case studies of reinforced piled high-speed railway embankment over soft soils. Int J Geomech 16(2):1–7

Moored Ship in Ice Li Zhou Jiangsu University of Science and Technology, Zhenjiang, China

Synonyms ATOT, Arctic Tandem Offloading Terminal; FPSO, Floating Production, Storage and Offloading Unit; FPU, Floating Production Unit; HSVA, Hamburg Ship Model Basin; RMRS, Russian Maritime Register of Shipping; SPS, Subsea Production System; STL, Submerged Turret Loading Concept; UFR, Umbilical, flow line, and riser

Definition Moored ship means a ship to be secured or fixed to some bodies by using cables, lines, or anchors.

Moored Ship in Ice

The ship is often used to assist underwater activities such as diving, seeking, and retrieval. It could also be used to perform oil and gas exploration or exploitation at seas.

1051

numerical simulation, model tests, and fullscale measurements.

Moored Vessel Types Introduction Interests in the Arctic and sub-Arctic waters have been growing since several large big hydrocarbon fields in the Barents and Kara Seas were discovered. However, it is still challenging to perform hydrocarbon exploration and exploitation in these locations, which always involves risks from low temperature, sea ice, wind, waves, currents, darkness, icing, etc. One of the biggest challenges in the Arctic and sub-Arctic areas is the sea ice. It exists in many features, such as level ice, broken ice, ice ridge, iceberg, and so on. Resulting ice loads are dominant to open water load, wind load, current load, and wave load on most occasions for polar ships as well as offshore structures. To resist ice action and keep the station, different marine structures are used for drilling, production, and offloading operations in ice-covered waters. Fixed structure is a good solution to shallow water operation, such as gravity-based structure, jacket platform, artificial island, etc. As water depth increases, moored floating vessels are shown to be attractive. This chapter will mainly focus on the types of Arctic moored ship, industrial operations, Moored Ship in Ice, Fig. 1 Moored ship ice in ice

Generally speaking, there are three kinds of marine structures. The first is bottom-fixed. The second is moored with mooring lines. And the third is the dynamic-positioned. Mooring systems are often used for polar ship station keeping in severe ice with medium waters. As we know, ice crushing against vertical structure often leads to large ice force which may exceed capability of the mooring system. Thus, moored vessel is required to be designed with downward slope which could bend pack ice easily. Two typical concepts are included herein. One is traditional ship-shaped structure and the other one is the conical structure. Ship-Shaped Structure A ship-shaped structure includes relative long parallel mid-body and icebreaking bow. Some have also icebreaking capability with stern. In ice-covered waters, ice drift direction often changes from time to time. This makes ice vanning capability of moored ship very important. The moored ship (as shown in Fig. 1) should have a quick response to change heading under ice action and keep heading toward the ice drift. In general, a ship-shaped structure preforms well in surge, pitch, and heave but may experience large

M

1052

sway and roll motion when ice intrudes from sideways. Relevant experience with moored structures in ice is obtained from drilling operations in the Beaufort Sea. Starting in the mid-1970s to the late 1980s, Dome Petroleum deployed floating drillships named Canmar during the summer months. These were moored on site during the summer (open water) months, where relatively light ice conditions were encountered (Wright 1999). With the support of icebreakers, these drillships developed the capability of station keeping in a variety of ice conditions. This extended their open water operating season, although they did not work extensively in heavy ice. Unfortunately, although Canmar gained a great deal of experience with their Beaufort Sea drillships, there is very little documentation about their operations, particularly with regard to the load levels experienced by these moored vessels in ice. For the development of the Grand Banks oil fields, the Terra Nova scheme was implemented (Wright 1998). It involves a floating ship-shape production vessel with integrated storage and offloading systems (FPSO), which is designed to continue operations in most environmental conditions. The FPSO could disconnect with the mooring lines and risers system and move off the site when avoiding severe ice actions. This approach is attractive for operations. The vessel has been operating year-around with light ice conditions encountered. The advantage is that capital cost is low and response to the ice conditions is quick, but the disadvantage is the potential for much downtime due to ice and the associated production delays. This experience has shown that moored vessels, with adequate levels of ice strengthening and ice management support, can be very effective in a wide range of moving pack ice conditions. It is expected that the gas-condensate field Shtokmanovskoye, located in the central part of the Barents, will be developed in the near future. The water depth is 340 m. At this field, both occurrences of sea ice and icebergs have to be expected during operations. The general offshore facilities development scheme that has been

Moored Ship in Ice

selected is based on the Subsea Production System (SPS) tied-back through a system of umbilical, flow line, and riser (UFR) to the ice-resistant ship-shaped Floating Production Unit (FPU) hosting gas processing, gas compression, living quarter, power generation, and all other utilities required to operate. Some concept studies for different kinds of marine structures have been tried in model scale with level ice, broken ice, and ice ridge. Løset et al. (1998) performed a series of model-scale tests with the Submerged Turret Loading Concept (STL) for loading oil offshore in the Hamburg Ship Model Basin (HSVA) ice tank in Hamburg. The modelled ship had a conventional icebreaking bow at a scale of 1:36. The purpose of the tests was to study the feasibility of the STL concept in level ice, broken ice, and pressure ridges. It was found that pressure ridges produced for the model tests may cause forces over the capacity of the STL system. Later, a number of model tests with another concept were conducted in the HSVA ice tank (Løset et al. 2003). The concept comprises a single anchored moored ship located in the wake behind a moored buoy floating freely on the surface. The buoy with smooth surface was expected to break the ice in upward bending and also ridges. However, the results show that it is probably not practically feasible to apply a buoy with enough buoyancy to break the design ridges since ridges may exceed the breaking capacity of the buoy unless disconnection of the ship can be done. Ettema and Nixon (2005) reported model test data regarding ice-rubble loads acted on a moored conical platform. How ice-rubble loads were influenced by horizontal stiffness of the platform’s mooring system were investigated with great interest. Aksnes (2009) used a simplified moored ship to perform model test in level ice. The ship model was fixed except surge degree of freedom with a linear spring. Different dynamic properties of the ship model as well as drifting ice were studied and analyzed. Bonnemaire et al. (2008) proposed a new concept for offshore offloading operations in ice. The concept named Arctic Tandem Offloading Terminal (ATOT) is composed of a turret moored offloading icebreaker and an

Moored Ship in Ice

offloading tanker in tandem. It was tested in the HSVA ice tank with focus on the measurement of mooring loads during interactions with ice ridges in head on drift. Aker Solutions and Aker Arctic proposed an Arctic drillship concept which enables to extend operation season in waters with sea ice (Bruun et al. 2015). The concept was developed to perform drilling, coil tubing, wireline operations, and running and pulling x-mas tree through a forward turret for low air temperature. The design work was performed regarding sizing of the hull, drilling, turret, and station keeping system. General arrangement drawings were developed for each deck level, and the technical work was well documented through development of an outline specification. The drillship was designed to operate in late ice season, summer season, and early ice season. The corresponding mooring system could resist a maximum load equivalent to interaction with level ice cover of 1.5 m thickness during ice drift change. This includes design of hull lines for effective ice breaking, a forward turret position to reduce the ice load during change of ice drift direction, and station keeping system (mooring system) with a high restoring capacity. A dual-class design complying with both RMRS (Russian Maritime Register of Shipping) ARC 6 and PC 5 (Polar Class) was performed. The thrusters can be used for both transit and station keeping. There are three open podded thrusters at stern and two nozzle retractable thrusters at bow used for both transit and station keeping. For drilling in open water, the five thrusters provide DP3 capability, while for drilling in ice, the turret mooring system will be used for station keeping assisted by aft thrusters during rotation in ice (forward thrusters will always be retracted when operating in ice). Conical Structure Considering the limited ice vanning capability of ship-shaped structure, conical structure with an axis symmetrical hull was developed. The waterline is circular. The structure does not need to change heading. Therefore, ice vanning is no longer required. The cost is that it may result in weak performance in surge, heave, and pitch.

1053

A typical conical drilling unit, the Kulluk platform, was designed with a variety of special features to improve the performance under ice conditions in the shallow water (Wright 1999). It was deployed in water depths ranging from 20 m to 60 m. The system has a downward sloping circular hull near the waterline that breaks the oncoming ice mainly in flexure and an outward flare near the bottom that clears the broken ice cusps away from the moon pool and mooring lines. The strong mooring system could resist ice forces up to 450 t. It worked successfully with the downtime in operations less than 10%, but at a cost of extensive ice management by three icebreakers. Considering the possible change in ice drift direction which may lead to a significant increase in ice load on the hull, some buoy-shaped structures based on prototype of the Kulluk were tested. The structure of this sort is attractive in that the need to keep heading toward the ice drift is no longer required. The conical structure FPUIce (by SEVAN Marine) was tested in the spring 2008 at HSVA (Løset and Aarsnes 2009). The purpose was to study the ice load level on the structure and its response in extreme first-year ice including the interaction with unmanaged ice ridges exceeding 20 m draft. A Joint Industry Project was reported by Bruun et al. (2011) on development of conical floaters in ice, where a typical SPAR platform was developed during the project. Two large ice model test campaigns were performed in the period 2007–2010. The objectives were to investigate different floater geometries and ice model test setups (model fixed to a carriage and pushed through the ice vs. ice pushed toward a floating model moored to the basin bottom) and their influence on the ice failure mode and structure responses in the various tested ice conditions.

Main Considerations of Moored Ship Design Three key elements should be well considered when designing a moored ship operating icecovered waters. The hull lines of the vessel should

M

1054

be optimized to reduce ice impact as much as possible and minimize the response of hull. The mooring and riser system are required to resist global ice action and keep natural position within an allowable watch circle. To estimate ice-moored ship interaction, some analytical methods and ice model tests are applied to calculate ice loads, mooring loads, and the responses of the ship, based on which both hull lines and mooring systems could be designed safely. Vessel Systems The specific hull lines of a moored vessel are important in that they have a strong influence on the vessel’s ability of icebreaking and ice clearing process and the resultant ice loads that it is exposed to. In particular, the ice forces are significantly affected by the width of the vessel. The ice forces increase with beam size. The icebreaking load level at the waterline is often affected by the shape of bow to a large extent. How to optimize the bow shape to reduce ice load is a key consideration for moored vessels as well. The overall hull form and draft are key factors with respect to the vessel’s ability to clear ice and the potential for ice interference with its mooring and riser systems. Clearly, well-designed thruster systems are helpful to enhance ice clearance around a moored FPSO vessel or tanker. Especially for an azimuth thruster, it could assist both vessel’s vanning response and ability to resist ice and other environmental forces. The configuration of the thrusters needs to be taken into consideration, which is expected to reduce ice resistance and ice impact on propellers. Good configuration will improve overall thrust efficiency of the vessel and save power. Moreover, any FPSO vessel or tanker that is used for ice operations should be structurally capable of sustaining the relatively high local ice pressures that may be experienced, particularly in heave ice, mixed ice and wave conditions, and small glacial ice. Mooring and Riser Systems Generally speaking, a vessel’s mooring system should be strong enough to withstand relatively large ice forces, making sure that the vessel could maintain its position within an acceptable offset.

Moored Ship in Ice

The overall mooring loads and individual mooring line tensions are of obvious importance and should not be exceeded. In the Arctic area, the drifting ice is changing direction frequently. Therefore, the mooring system is required to afford sound vanning capability to the vessel, which makes the vessel head toward to the new ice drift direction smoothly. During this process, the ability for riser system to track vessel motions with allowable offsets and stress levels is also important and should be taken into consideration. When ice attacks the vessel from sideways, it is possible that ice floes move down the hull and become entangled with its turret, mooring, and riser systems. To avoid this potential risk, increasing the draft of the vessel preferably with some protection skirt around their submerged mooring and riser system is a reasonable solution. Ice ridge is often embedded into a level ice field. When it interacts with the moored ship, mooring lines are possible to be impacted by the keel part of the ice features. The resulting ice load and effect on the overall response of the system are also important, which endanger the safety of the mooring system. Under the condition of large ice features, the vessel has to disconnect from riser and mooring systems quickly and safely and move off location. This is one of the major challenges for most station keeping operations in pack ice. Ice Loads and Vessel Responses When designing a moored vessel in ice-covered waters, the ice conditions have to be determined as a basis. The ice loads and related ice-vessel interaction cases together with vessel responses to the ice loads are primary considerations. The ice management support should also be included to reduce ice load level if the ice condition is severe. Researchers have carried out a considerable amount of model testing and analytic work to give estimation on ice loads, responses, and capabilities of moored vessels in drift level or pack ice. Ice forces, vessel’s responses, and the resulting mooring forces that occur during ice interaction process with moored vessels are three key factors to be studied. Toyama and Yashima (1985) applied a numerical model and a model test to conclude that the surge response was greater at

Moored Ship in Ice

low ice drift speeds. Sayed and Barker (2011) applied the particle-in-cell method based on a hybrid Lagrangian-Eulerian formulation to simulate the interaction between broken pack ice and a moored Kulluk platform. Aksnes (2010) presented a semi-empirical method incorporating probabilistic models based on the model test results. However, this model is limited to onedimensional simulations in the surge direction only. Moored structures in ice conditions may be subjected to ice drift from different directions depending on variations in currents and wind. The contact geometry and thus ice failure are influenced by the different incident angles between the hull and ice motion. However, this model is limited to one-dimensional simulations in the surge direction only. Zhou et al. (2011, 2012) presented a 2D method in the horizontal plane for simulating level ice-hull interaction process, where the ice load during submersion, sliding, and accumulation were simplified based on empirical and analytical methods. The simplified numerical model was validated through full-scale measurements of a conical platform called the Kulluk. Some researchers are interested in model tests in ice basins. A number of model tests were conducted by Comfort et al. (1982), Evers et al. (1983), and Nixon and Ettema (1988). Comfort et al. (1999) assembled an extensive set of ice model test data for floating and moored structures and presented the data in a common format to identify overall trends, and the Kulluk is also included as a typical structure. Recently, Aksnes et al. (2008) and Bonnemaire et al. (2008) carried out ice model tests of an Arctic Tandem Offloading Terminal with a focus on mooring forces in level and ridged ice. Later, Aksnes et al. (2010) and Bonnemaire et al. (2010) conducted ice basin tests on a moored offloading icebreaker in variable ice drifting directions. Zhou et al. (2013a) performed a series of ice model tests to investigate the ice load experienced by an icebreaking tanker. The tanker was towed through the unbroken ice sheet to simulate the interaction process. Then the ice loads were measured. Zhou et al. (2013b) applied a numerical model to simulate the dynamic ice loads acting on the

1055

icebreaking tanker Uikku in level ice, considering the action of ice in the vicinity of the waterline caused by breaking of intact ice and the effect of submersion of broken ice floes. The numerical simulations were also compared with the measured data as given in Zhou et al. (2013a). Good agreement was achieved though there are some deviations between predicted and measured results for some cases due to uncertainties from input factors.

Conclusion To sum up, moored ships have been widely used in ice-infested waters for many kinds of polar activities. The interaction between moored structures and ice is a complex process which is difficult to predict theoretically. Due to severe ice conditions, the structures may experience much downtime which is not desirable. How to ensure the overall safety and extend ice operation season for moored ship remains a challenge to industrial and academic worlds of polar engineering. Some main aspects for designing a moored vessel operating in icy waters could be taken as a reference in this chapter.

Cross-References ▶ Design of Mooring System ▶ Numerical Simulation of Ice-Going Ships ▶ Offshore Structure Design Under Ice Loads

References Aksnes V (2009) Model tests of the interaction between a moored vessel and level ice. In: The 20th IAHR international symposium on ice. Lahti, June 14–18, 2010 Aksnes V (2010) A panel method for modeling Level Ice Actions on Moored Ships. Part1: local Ice Force Formulation. Cold Reg Sci Technol 63:29–39 Aksnes V, Bonnemaire B, Løset S, Lonoy C (2008) Model testing of the Arctic Tandem offloading terminal – tandem mooring forces and Relative Motions between vessels. In: Proceedings of the 19th IAHR international symposium on ice, vol 2. Vancouver, pp 687–698

M

1056 Aksnes V, Bonnemaire B, Koch R, Lonoy C, Løset S (2010) Investigation of response of moored ships in level ice. In: Proceedings of the HYDRALAB III joint user meeting. Hannover Bonnemaire B, Lundamo T, Evers KU, Løset S, Jensen A (2008) Model testing of the arctic tandem offloading terminal–mooring ice ridge loads. In: Proceedings of the 19th IAHR international symposium on ice, vol 2. Vancouver, pp 639–650 Bonnemaire B, Aksnes V, Lundamo T, Evers KU, Løset S, Ravndal O (2010) Ice basin testing of a moored offloading icebreaker in variable ice drift: innovations and new findings. In: Proceedings of the HYDRALAB III joint user meeting. Hannover Bruun PK, Løset S, Gürtner A, Kuiper G, Kokkinis T, Sigurdsen A, Hannus H (2011) Ice model testing of structures with a downward breaking cone at the water line JIP; presentation, set-up & objectives. In: Proceedings of the 30th international conference on ocean, Offshore and Arctic Engineering (OMAE). Rotterdam Bruun PK, Ågedal B, Matala R (2015) Arctic drillship design for severe ice conditions. In: Proceedings of the 23rd international conference on port and ocean engineering under arctic conditions, June 14–18, 2015. Trondheim Comfort G et al (1982) Experimental studies of ice performance of conical drilling unit, ARCTEC Canada Ltd. report 897 submitted to Gulf Canada Resources Ltd. Comfort G, Singh S, Spencer D (1999) Evaluation of ice model test data for moored structures. PERD/CHC report 26–195 Ettema R, Nixon WA (2005) Ice tank tests on ice rubble loads against a cable-moored conical platform. J Cold Reg Eng 19:103–116 Evers K et al (1983) Conical drilling unit – model tests in ice ridges, HSVA report E 126/83 submitted to Gulf Canada Resources Ltd. Løset S, Aarsnes JV (2009) Icebreaking buoy in arctic waters. In: The 9th international conference and exhibition for oil and gas resources development of the Russian arctic and CIS Continental Shelf RAO/CIS Offshore 2009, vol 1. St. Petersburg, pp 138–143 Løset S, Kanestrøm Ø, Pytte T (1998) Model tests of a submerged turret loading concept in level ice, broken ice and pressure ridges. Cold Reg Sci Technol 27: 57–73 Løset S, Grøsland R, Jensen A (2003) Model testing of a single anchor moored ship in the wake of a buoy in level ice and pressure ridges. In: Proceedings of the 17th international conference on port and Ocean Engineering under Arctic Conditions (POAC), vol 1. Trondheim, pp 393–405 Nixon WA, Ettema R (1988) Ice sheet interaction with a cable-moored platform, University of Iowa IIHR report 148 Sayed M, Barker A (2011) Numerical simulations of ice interaction with a moored structure. The offshore technology conference. Houston, OTC22101

Mooring Toyama Y, Yashima N (1985) Dynamic response of moored conical structures to a moving ice sheet. In: Proceedings of the 8th international conference on port and ocean engineering under arctic conditions, vol 2. Narssarssuaq, pp 677–688 Wright B (1999) Evaluation of full scale data for moored vessel stationkeeping in pack ice. PERD/CHC report 26-200. Ottawa Wright B, Associates Ltd. Canatec Consultants Ltd. AKAC Inc (1998) Moored vessel stationkeeping in Grand Banks Pack ice conditions, PERD/CHC report 26-189, submitted to The National Research Council of Canada Zhou L, Su B, Riska K, Moan T (2011) Numerical simulation of moored ship in level ice. In: Proceeding of the 30th international conference on Offshore Mechanics and Arctic Engineering. The Netherlands, Rotterdam Zhou L, Su B, Riska K, Moan T (2012) Numerical simulation of moored structure station keeping in level ice. Cold Reg Sci Technol 71:54–66 Zhou L, Riska K, Moan T, Su B (2013a) Numerical modeling of ice load on an icebreaking tanker: comparing simulations with model tests. Cold Reg Sci Technol 87:33–46 Zhou L, Riska K, von Bock und Polach R, Moan T, Su B (2013b) Experiments on level ice loading on an icebreaking tanker with different ice drift angles. Cold Reg Sci Technol 85:79–93

Mooring ▶ Thruster-Assisted Mooring

Mooring Anchor Yong Luo Shanghai Jiao Tong University, Shanghai, China

Synonyms Drag anchor, Offshore mooring system, Pile anchor, Station keeping system, Suction anchor

Definition The passive mooring is the most commonly adapted station keeping method for offshore

Mooring Anchor

floating facilities. An offshore mooring system usually consists of one or multiple mooring lines that connect the floater to the seabed to retain floater’s position and limit offset to enable designated operations in various environments and water depths. A mooring system is made up of mooring lines, anchors, and connectors, and the mooring line connects the floater to the seabed with its lower end terminate at the anchor at sea floor. The anchor is a physical device that is connected with the mooring line and penetrates into the seabed soil to hold the mooring line into position (Ma et al. 2019). The mooring system is designed to withstand the environmental loads and operation loads in an offshore environment. Thus, the anchor holding power is a critical link of mooring system strength.

Historical Development The history of the anchor dates back millennia. The most ancient anchors were probably made of rocks to hold ship at sea. However, using pure mass to resist the forces of a storm only works well in certain situations. Originated from anchor of rocks, advances in craftship and metallurgy encouraged development of improved shapes for more compact, durable, and efficient anchors. The modern navigation uses metal device with efficiently designed shape to connect a vessel to the seabed to prevent ship from drifting due to wind, waves, and current. Over the years, the anchor technology has been continuously developed. The anchor design takes into account the soil resistance data and the requirements of horizontal and vertical holding capacities for safe mooring application. For certain marine application, continuous deploying and retrieving anchors is an operation requirement, and anchors that were designed for such function have been developed. Nowadays there are the following main types of mooring anchors (Vryhof 2015): 1. Drag embedment anchor 2. Vertical Loaded Anchor

1057

3. 4. 5. 6.

Gravity installed deep penetration anchor Pile anchor Suction anchor Gravity anchor

Working Principles of Anchors The working principle of anchor is through its own weight or penetration into the seabed to interact with the soil to generate holding capacity. Therefore, there are two primary factors for anchor design. 1. Structural factor that is the material and shape of the anchor should have adequate strength and life expectancy 2. Geotechnical factor that is the soil characteristics, anchor size and depth of penetration should generate sufficient holding capacity Drag Anchor A drag embedment anchor (DEA) is the most utilized anchor for mooring floating MODUs. The drag anchor is dragged along the seabed until it penetrates the required depth. As it penetrates the seabed, it uses soil resistance to hold the anchor in place. The drag embedment anchor is mainly used for catenary moorings, where the mooring line arrives on the seabed horizontally. It does not perform well under vertical forces (Ozmutlu 2012) (Figs. 1 and 2). The main advantage of the drag embedment anchor is it is highly mobile and can be deployed and retrieved without using heavy marine equipment. The main drawback is that the anchor’s final position is less predictable which would be a problem for permanent mooring systems. Additional features of drag anchors include: • • • • • •

Standard off the shelf equipment Wide range of anchor types and sizes High capacity (greater than 100,000 lb) Performs poorly in rock seafloors Lower resistance to uplift loading Holding power highly directional

M

1058

Mooring Anchor

Mooring Anchor, Fig. 1 Drag embedment anchor (Courtesy of Vryhof)

Mooring Anchor, Fig. 2 Drag anchor during installation. (Courtesy of Vryhof)

There are many designs and brands of drag embedment anchors. Following is a brief summary on a few well-known anchor types and their specific uses. • The Stevpris New Generation accommodates the widest range of soils possible and its holding power is more than 30% higher than any other existing drag anchor. • Stevpris Mk 5 is easy to handle, install, and retrieve and is used to secure semi-submersible rigs and permanent installations. • The Stevshark Mk 5 does well in hard soils such as limestone, calcarenite, very dense sands, and coral. • The Stevin Mk 3 was the original anchor design for Vryhof and outperformed all existing anchors at the time of its inception. • The Bruce Mk 4 Twin Shank offers a choice of fluke angles for superior holding power in all

types of seabeds. It also has self-righting ability, even when it lands upside down. • The Flipper Delta has an open construction for smooth penetration in different kinds of soil and no rotation, which means no decrease of holding capacity and no dragging of the anchor. • Danforth is used for boats up to 27 ft. The I-beam fluke construction provides exceptional holding power. The anchor holding capacity of drag embedment anchor is function of soil conditions, anchor type, anchor size, and fluke/shank angle setting. Designers often reply upon anchor capacity chart to select the suitable anchor (Fig. 3). Vertical Loaded Anchor The conventional drag embedment anchor does not perform well with vertical mooring load.

Mooring Anchor

1059

Mooring Anchor, Fig. 3 Anchor holding capacity. (Courtesy of Vryhof)

However, development has been made of Vertical Loaded Anchor (VLA) which would allow certain amount of mooring vertical toad. Vertical load anchors are similar to drag anchors as they are installed in the same way. However, the vertical load anchor can withstand both horizontal and vertical mooring forces. It is used primarily in taut leg mooring systems, where the mooring line arrives at an angle the seabed. For example, the Stevmanta Vertical Loaded Anchor (VLA) allows uplift at the anchor point, which is a requirement in semi-taut and taut leg mooring systems. Its main features include: deep penetrating anchor in soft soils, suitable for supporting large vertical and horizontal loads, easy installation like a conventional drag embedment anchor and loading in all directions possible (Fig. 4). SEPLA Anchors The patented SEPLA was introduced in 1997. It was a revolutionary concept for deepwater moorings that combines two proven anchoring concepts (i.e., suction installed piles and plate anchors capable of resisting vertical loads) to increase the accuracy of anchor positioning and burial depth for preset moorings. It gave the

M

Mooring Anchor, Fig. 4 Stevmanta vertical loaded anchor. (Courtesy of Vryhof Anchor)

industry a way of realizing the holding capacity of a suction installed anchor pile without the higher cost. SEPLA anchors are believed to be more geotechnical efficient than the suction piles that are commonly used to withstand vertical loads. The SEPLA plate anchor is fully embedded in deeper, higher strength soil layers with all components

1060

Mooring Anchor

Mooring Anchor, Fig. 5 SEPLA anchor. (Courtesy of OnePetro)

actively resisting the mooring loads. On the other hand, a large part of a suction pile’s structure is in shallower, weaker soils and does not contribute much to the holding capacity (Fig. 5). Torpedo Anchors Torpedo piles, essentially gravity-embedded cylindrically shaped projectiles, are used to anchor deepwater flowlines and facilities offshore. Torpedo piles typically range in size from 24 to 98 tons, and the largest torpedo pile can provide an anchor-holding capacity of up to 1000 tons (Fig. 6). Pile Anchor For mooring situations that the accurate positioning of the anchor is important, there is presence of vertical mooring load, the seabed surface soil consists of soft soil, and the drag embedment anchor becomes unsuitable. One possible alternative is to use pile anchor made of tubular steel pipe which is driven by underwater hammer to the desired penetration below the seabed surface. The mooring line is connected to the pile anchor through a bracket prewelded before pile installation (Fig. 7). The behavior of a pile under lateral and axial loading interacting with the seabed soil is analyzed to determine the optimal length and diameter of the anchor pile, the position of the bracket along the pile, and the depth below the mudline to which the pile should be driven. Anchor piles generate lateral capacity through passive resistance of the soil bed and axial

Mooring Anchor, Fig. 6 Torpedo anchor. (Courtesy Deep Sea Anchors)

capacity by friction or adhesion along the pile shaft. In most cases, the mooring line connection is located below the top of the pile and it can vary from ½ to 1/3 of pile penetration. The most common piles are long slender tubular piles (L/D ratio > ~10), which are typically fabricated from rolled steel sections. Diameters are in the range of 2 – 8 feet for the large mooring systems. During installation, the pile is first lowered on the seafloor using a crane and gradually penetrates under the self-weight through a guide frame. The driving head is installed on top of the pile and underwater hammer is used to drive the pile to its design depth. When the seafloor is rock or composed of thin sediment over rock then piles cannot

Mooring Anchor

1061

Mooring Anchor, Fig. 7 Pile anchor deployment. (Courtesy of InterMoor)

be installed by driving. In this case, an oversize socket must be predrilled for a pile to be inserted and grouted in place. The key features of pile anchor include: • • • •

High lateral capacity achievable Resists high uplift load Performs well on substantial slopes Suitable hard seafloors (rock and coral) by drilling and grouting • Need quality site soil data • Installation cost high Suction Anchor The suction pile is a relatively new type of anchor system. It is made of tubular steel pipe with sealed top and is driven into the seabed using pump to suck out the water from the top of the tubular, which creates negative pressure inside the pipe. The application has been growing steadily in the offshore industry particularly for soft soil in deep water. Suction piles can be installed from a single workboat making installation quick, relatively inexpensive, and less weather dependent than for driven or drilled piles. Suction piles can be more expensive to fabricate since they are welded construction but they are easier and cheaper to transport. Suction piles

employ a lower slenderness ratio (length/diameter) than tubular piles. They are shorter and with larger diameter, ranging up to 10 m for soft soil. There are a number of suction pumps available including some that are operable by a remotely operated vehicle (ROV) a capability that provides flexibility in installation. An important feature of suction piles is their ability to be extracted and recovered by reversing the pump to apply pressure inside the pile (Fig. 8). Suction piles are the predominant mooring and foundation system used for deepwater development projects worldwide. Suction piles can be used in sand, clay, and mud soils, but not gravel, as water can flow through the ground during installation, making suction difficult. They are also effective in normal sand seafloors but are not appropriate for hard bottom conditions. Once the pile is in position, the friction between the pile and the soil holds it in place. It can resist both vertical and horizontal forces. The key features of suction pile anchors include: • Requires less specialized installation equipment • High lateral and vertical capacity • Needs extensive and better quality soil data

M

1062

Mooring Anchor

Mooring Anchor, Fig. 8 Suction pile anchor. (Courtesy of Drill Formulas)

Mooring Anchor, Fig. 9 Gravity anchor. (Courtesy of Subcon)

• Removable by reversing installation pump • Cost competitive installation Gravity Anchor A gravity anchor is made of heavy object placed on the seafloor to resist vertical and/or lateral loading. It is typically fabricated from concrete and steel and configured to enhance lateral capacity. Gravity anchors are often used because they are inexpensive and readily sized for most seafloor and loading conditions. Especially there is less requirement of anchor position accuracy and lack of specialized installation equipment. In general, they are not very efficient (ratio of holding capacity to weight) compared to the other anchor types. They may require heavy lift capabilities for installation and they are a poor choice on sloping seafloors. However, on very hard bottoms they

might provide the only reasonable anchoring option (Fig. 9). The main features of gravity anchors include: • • • • • • • •

Resist large vertical load Reliable holding capacity Simple on-site construction Material readily available and economical Reliable on thin sediment over rock Not suitable in seafloor slope Size limited by load handling equipment Lateral load to weight ratio is low

Key Applications Since the anchor connects the mooring line to the seabed, it is a critical component for the integrity of mooring system. The various anchor types find

Mooring Connector

their applications in different types of mooring systems. For permanently mooring systems, the suction pile and driven pile are most commonly used for its reliability and location accuracy. The highefficiency drag anchor and VLA have also been used for small floating units under mild environment. For drilling operations with MODUs, the drag anchors are most commonly used for easy deployment and retrieval without specialized facilities. However, they have limited capability to withstand vertical loads. VLAs are the alternative where high vertical loads at anchor are present. Driven pile or suction pile are only used under special conditions such as very high vertical load or anchor movement strictly prohibited. Because of the temporary nature of the operation, a thorough soil investigation is normally not conducted, which makes the anchor design more challenging. Torpedo pile and gravity-installed anchor are relatively new anchor concepts, which have been used in MODU and permanent moorings. The anchor design requires the full range of geotechnical analysis. In situations where penetration into the seabed is not possible, for example, rock seabed, dead weight anchors made of reinforced concrete or scrap steel may be used. Vertical capacity is simply the submerged weight of the anchor.

1063

Mooring Connector Yong Luo Shanghai Jiao Tong University, Shanghai, China

Synonyms Anchor shackle; Chain connector; D-shackle; Offshore mooring system; Station keeping system

Definition The passive mooring is the most commonly adapted station keeping method for offshore floating facilities. An offshore mooring system usually consists of one or multiple mooring lines that connect the floater to the seabed to retain floater’s position and limit offset to enable designated operations in various environments and water depths. A mooring line consists of line segments of different materials, such as chain, wire rope, and polyester. The connector is a physical device that connects different line segments and anchors. The mooring system is designed to withstand the environmental loads and operation loads in an offshore environment. As part of the strengthcarrying element, the connectors shall have compatible breaking load as other mooring components (API 1981).

Cross-References

Historical Development

▶ Drag anchor ▶ Mooring system ▶ Suction anchor

The traditional mooring line for station keeping of ships in harbor was typically made with chain of uniform size. As the offshore moorings evolved, mooring systems become more complex with mooring lines made of different segments to achieve the desired performance characteristics. As such, a mooring line usually consists of a number of segments with different materials such as chain, wire rope, polyester, etc. Even if a mooring line is made of a single type of material, the line may be segmented for the purpose of transportation and installation. Therefore,

References Ma K-T, Luo Y, Kwan T, Wu Y (2019) Mooring system engineering for offshore structures. Elsevier Inc Ozmutlu S (2012) The use of drag embedment anchors in offshore applications Vryhof Anchors (2015) Vryhof manual, the guide to anchoring. Vryhof Anchors B.V.

M

1064

Mooring Connector

connectors are used to connect the various mooring line segments. There are many types of connectors for connecting different types of mooring components. The commonly used ones include D-shackles for connecting the chain segments, D-shackle in association of wire rope termination for connecting the chain to wire rope, H-link for connecting the chain to polyester segment, etc. (Ma et al. 2019).

types for connection among the chain, wire rope, and polyester. Because inspection and replacement of connecters in a permanent mooring are difficult and costly, their designs need to be robust with adequate fracture toughness, fatigue life, and corrosion resistance. Manufacturing of connectors should be subject to an appropriate level of quality assurance corresponding to the same level as those of mooring chain.

Working Principle

Applications

Since the connector is a load-carrying link within a mooring line, the strength and design life of the link must be compatible with those of mooring line segments to maintain the basic integrity and reliability of the complete mooring line. The design of the mooring link should take the following factors into consideration:

D-Shackle The D-shackle is most commonly used for joining the adjacent chain segments. It consists of a bow,

• • • •

Adequate strength Adequate fatigue life Physically compatible with segment terminations Ease of connection and disconnection

For permanent mooring systems, D-shackle and H-link are the two most commonly used

Mooring Connector, Fig. 2 Common D-shackle measurement. (Courtesy of Sotra Marine)

Mooring Connector, Fig. 1 Common D-shackle. (Courtesy of Zhengmao)

Mooring Connector, Fig. 3 Wire rope termination. (Courtesy of Lebeon)

Mooring Connector

which is closed by a pin with single or double locking nut. The pin can be of rounded shape or oval shape depending on the purpose of application (Fig. 1). The shackle is made by forging and with corresponding grade as per chain links. D-shackle can be used in both temporary and

1065

permanent moorings. The dimensions of the D-shackle are standardized as illustrated by the sketches below (Fig. 2). D-shackle can also be used to connect chain segment to wire rope in association of the closed or open socket termination of the wire rope (Fig. 3).

Mooring Connector, Fig. 4 Anchor shackle measurement. (Courtesy of Sotra Marine)

M

Mooring Connector, Fig. 5 H-link. (Courtesy of Vicinay)

Mooring Connector, Fig. 6 H-link in polyester connection. (Courtesy of Oceanside Equipment)

1066

Anchor Shackle Anchor shackle is another type of D-shackle that connects the chain segment to the mooring anchor. Like a common D-shackle, it consists of a bow, which is closed by a pin with single or double locking nut. The pin is of rounded shape for free rotation. This type of D-shackle is made by forging and with corresponding grade as per chain links. It can be used in both temporary and permanent moorings. The dimensions of the anchor shackle Mooring Connector, Fig. 7 Kenter link and application. (Courtesy of Sotra)

Mooring Connector

are also standardized as illustrated below (Fig. 4). H-Link The H-link is commonly used in mooring lines for connecting segments of the line. This type of connector has been traditionally used for connecting chain segments. Lately the H-link is introduced to connect polyester rope with chain segment. The main feature is to avoid timeconsuming handling of bulky thimbles for the

Mooring Connector

eyes of polyester ropes. They can also be used to connect two lengths of polyester ropes in deepwater mooring lines (Figs. 5 and 6). Kenter Link The connecting kenter-type link is most commonly used for the connection of two pieces of chain mooring line, where the terminations of the two pieces have the same dimensions. It has the same outside dimension as a chain link of the same diameter. It therefore allows the connected chain piece going through mooring devices such as fairlead, chainstopper, windlass, etc. The kenter link is commonly used to connect chain of mobile offshore drilling units which require frequent handling of mooring lines. Generally speaking, the kenter link is not used in permanent mooring systems, first because the frequent line handling is not a requirement and second, the kenter link has a shorter fatigue life than the chain of compatible strength. The kenter-type joining link contains three parts along with taper pin and lead plug. The two main halves have numbers to be matched and arrows to be lined up for ease of assembly with the third piece (stud). The two main parts are attached to the ends of the chain in a vertical position and then fitted together, and the stud is then slid into place, which locks the link. The stud is secured by hammering a tapered pin into the hole drilled diagonally through all three parts of the joining link (Fig. 7). Pear Link The pear-shaped connecting link is, in essence, similar to kenter link and C-link, except that it is used for the connection of two pieces of mooring chain with different dimensions. Like kenter link and C-link, the pear-shaped connecting links are not used in permanent mooring systems. Note there is a product called trident link that combines the features of kenter and pear links. Trident link is mainly used to connect an anchor shackle directly to a chain, thus reducing the amount of required connections. In this way, it is very similar to a pear Link with the only notable differences being the method of assembly. This type of shackle can also be used in a variety of

1067

other applications where the crossover from one size to another is required. The pear link is often used during offshore installation, for example, where a smaller piece of line is connected to pull in the pre-laid mooring lines (Fig. 8). C-Link Like the kenter link, the connecting link C-type is used for the connection of two pieces of mooring chain with terminations that have the same dimensions. The major difference between the kenter type and the C-type is the way that the connector is opened and closed (Fig. 9).

M

Mooring Connector, Fig. 8 Pear link. (Courtesy of Vryhof)

Mooring Connector, Fig. 9 C-Link. (Courtesy of Vryhof)

1068

Mooring Lines

twist and torque that builds up in the mooring line (Fig. 10). The swivel can be placed at various locations along the mooring line. There are many different types of swivels available. One of the main design concerns is that when loaded, the swivel link may lock up due to the high friction inside the turning mechanism. Some newly designed swivels are fitted with bearing to enable swiveling under load. Triplate Mooring triplate can also be used in association with D-shackles to connect the mooring line segment. It is often used for handling during mooring installation (Fig. 11).

Cross-References ▶ Anchor Shackle ▶ D-Shackle ▶ Mooring System Mooring Connector, Fig. 10 Swivel link. (Courtesy of Zhengmao)

References API Spec 2F (1981) Specification for mooring chain, 3rd edn. American Petroleum Institute (1st Ed issued 1974), January 1981 Ma K-T, Luo Y, Kwan T, Wu Y (2019) Mooring system engineering for offshore structures. Elsevier

Mooring Lines Yinghui Tian and Wenlong Liu Department of Infrastructure Engineering, The University of Melbourne, Melbourne, VIC, Australia

Mooring Connector, (Courtesy of Le Beon)

Fig.

11 Mooring

triplate.

Swivel Shackle A swivel shackle can be used in a mooring line, generally of a temporary nature, to relieve the

Introduction Mooring lines provide the connections between floating facilities and anchoring foundations embedded in the seabed and are used for station keeping of floating facilities. Mooring line is

Mooring Lines

normally made up of steel chain links, wire ropes, and synthetic fiber ropes or a combination of the three. In shallow water zone including rivers and lakes, mooring lines are used for limiting the shift of boats and barges, as shown in Fig. 1a. The most common choice for mooring line component is usually chain. In most practices, single line mooring is the most popular mooring pattern, where two-line mooring is also widely used. In offshore oil and gas industry, mooring lines are used for limiting the movement of offshore vessels and platforms to control the offset of risers and drill pipes connected to these floating facilities. The mooring patterns in deep water are usually using groups of mooring lines (see Fig. 1b), which can adopt a spread mooring, single point mooring, or turret mooring. Steel wire rope is a better choice in water depths between 300 and 2000 m due to its lighter weight and higher elasticity than chain. In ultra-deep water greater than 2000 m, multicomponent mooring line is

(a)

(b)

Mooring Lines, Fig. 1 Mooring lines in shallow and deep water. (a) Mooring line for boat, (b) mooring lines for semisubmersible

1069

generally used, which is a combination of chain, wire rope, and synthetic fiber rope. Mooring lines, functioning as a stationkeeping component of an anchoring system, play the crucial role in safe operation of the moored floating facilities. The floating facilities would be out of control in case of failure of the mooring lines, which may cause serious casualties, property losses, and damage to marine environment. It is significant to understand the behaviors and failure mechanisms of mooring lines. This entry is to provide readers with a general introduction of mooring lines, especially for offshore practice. The content includes historical development of mooring lines, materials, configurations and layouts in industry practice, and analytical solutions of mooring line behaviors.

Performance of Mooring Lines Historical Development of Mooring Lines Natural fiber rope was probably human’s first invention used for mooring boats and ships. Tales of early anchor chain usage come from China. Around 2200 B.C., the Emperor Yu is reported to have used “iron chains, two fore and aft, which were thrown overboard to steady and stop the vessel.” However, the iron chain was hardly used to moor vessels before the seventeenth century. Natural fiber rope was still used for mooring until the nineteenth century before steel chain and wire rope eventually replaced it. Steel chain was successfully produced by electric welding after World War I, which contributed to the rapid and wide spreading of chains. Synthetic fiber materials, including nylon, polypropylene, polyester, aramid, and polyethylene, were introduced into marine mooring around the mid-twentieth century (Flory et al. 2015). Nowadays, synthetic fiber ropes are becoming a promising alternative to wire ropes in many mooring applications, especially for oil production platforms in deep water. As the offshore oil and gas industry is moving toward deep water, mooring patterns including spread moorings and single point moorings were used to withstand ocean environmental load.

M

1070

Mooring Lines

Spread moorings are mainly used for semisubmersibles and spars, while single point moorings tend to be used more for ship-shaped vessels (API 2005). Mooring Lines Components A mooring system comprises mooring lines, connectors, anchors, and winches or windlasses. The mooring line is usually made up of chains, wire ropes, synthetic fiber ropes, or their combination. Chain is the most common product type used for mooring lines. There are mainly two different designs of chain, studlink and studless chain, as shown in Fig. 2a. The studlink chain is commonly used for mobile moorings where the mooring line can be reset numerous times during their lifetime, such as semisubmersibles and mobile offshore drilling units (MODUs). The studless chain is often used for permanent moorings (such as a floating production storage and offloading (FPSO)) with design lives over 10 years. The studless chain has lower weight per unit of strength and less manufacture expense than the studlink chain. Wire rope is made up of individual wires wound in a helical pattern to form a “strand” (Brown 2005). The types of wire rope used as mooring line include multistrand and singlestrand rope. Multistrand wire rope, also called stranded rope, consists of a number of strands wound in the same rotational direction around a center core to form the wire rope (DNV 2013). The center core may be either a fiber or a metallic core to support the outer wires. As shown in Fig. 2b, six-strand rope is the most common type of multistrand rope and often used for temporary mooring. Single-strand rope, also called spiral rope, uses bundles of wires wound in opposing

(a)

directions to obtain the torque-balanced characteristics. Single-strand rope has longer fatigue life than the multistrand rope and thus is more commonly used in permanent mooring. Typical materials of synthetic fiber rope that are currently used for mooring are polyester and high modulus polyethylene (HMPE), as shown in Fig. 2c. High-performance fiber rope materials, including aramid, HMPE, liquid crystal aromatic polyester (LCAP) fiber, and so on, have been introduced into the mooring since the mid-1960s. The major advantages of synthetic fiber ropes are their light weight and elasticity of the material (Vryhof Anchors 2015). The synthetic fiber ropes are usually employed with combination of chain and wire rope in deep water. During deployment, it is normally not permissible for fiber rope to contact with the seabed unless specifically qualified, because the ingress of foreign particles such as sand will affect the rope’s yarn-on-yarn abrasion resistance and hence will adversely affect the rope’s fatigue life (DNV 2008). Connectors Connectors are the components to be used to connect two different segments of a mooring line or a mooring line to vessels or to padeyes on anchors. Typical connectors include Kenter shackle, D-shackle, C-link, pear link, and swivel, as shown in Fig. 3. Mooring Configurations in Water Column Mooring configurations can be catenary, taut, or semi-taut line or vertical moorings, as shown in Fig. 4. A catenary mooring configuration presents a mathematical catenary curve between the

(b) Studless chain

Studlink chain

Six strand

(c)

Spiral strand

Mooring Lines, Fig. 2 Mooring lines components. (a) Chain, (b) wire rope, (c) HMPE rope

Mooring Lines

1071

(a)

(b)

(c)

(d)

(e)

Mooring Lines, Fig. 3 Typical connectors. (a) Kenter shackle, (b) D-shackle, (c) C-link, (d) pear link, (e) swivel

θ

(a)

(b)

(c)

(d)

Mooring Lines, Fig. 4 Mooring configurations. (a) Catenary mooring, (b) taut line mooring, (c) semi-taut line mooring, (d) vertical mooring

floating facility and the seabed. The mooring line is suspended from the floating facility and touches down on the seabed. Therefore, an obvious characteristic of catenary mooring line is part of the mooring line lays on the seabed. During operation, most of the restoring forces to the floating facility are generated by the weight of the mooring line (Randolph and Gourvenec 2011). Compared with the catenary mooring that arrives at the seabed horizontally, a taut or semi-taut line mooring arrives at the seabed at an angle, resulting in both horizontal force and vertical force to the anchor. The restoring forces of the taut line are mainly generated by the elasticity of the mooring line. Synthetic fiber ropes that mainly include polyester ropes and polyethylene ropes are often used in taut line moorings. An advantage of a taut

line mooring superior to the catenary mooring is its shorter line length and smaller seabed footprint, which means the spread radius of taut line mooring is smaller than that of catenary mooring for a similar application. Semi-taut line moorings provide a greater seabed footprint than taut line moorings but reach similar maximum angles under critical design conditions (Randolph and Gourvenec 2011). Typical horizontal distance from the touch-down point normalized by the water depth ranges from 1 for taut line mooring, to 1.5 for semi-taut line mooring, and to 2 for catenary mooring. Vertical moorings or tendon/tension leg moorings are used to anchor large production units, such as tension-leg platforms, in very deep water. Recently, vertical moorings are also used in small floating units.

M

1072

Mooring Lines

Offshore Mooring Systems Layout Patterns Offshore mooring systems can be classified into spread mooring, single point mooring, and dynamic positioning. A spread mooring system consists of a group of mooring lines symmetrically distributed to the longitudinal center line of the platforms or vessels. The symmetrical arrangement of anchors keeps the heading of floating facilities being essentially fixed and prevent the rotation in the horizontal plane due to wind, waves, or current.

(a)

Figure 5 shows some typical offshore mooring patterns: Fig. 5a, b shows the patterns often used by vessels like drillship and FPSO, Fig. 5c shows the pattern used by the semisubmersible, and Fig. 5d shows the pattern used by a spar platform. Spread mooring is versatile because it can be applied to most vessels in varying water depth. However, large loads can be caused on the mooring line in ocean environment. Single point moorings connect all the mooring lines to a single connection point that can be a

(b)

90⁰

(c)

(d)

Mooring Lines, Fig. 5 Typical spread mooring (plan view). (a) Vessel mooring (ten lines), (b) vessel mooring (eight lines), (c) semisubmersible mooring, (d) spar mooring

Mooring Lines

1073

Mooring Lines, Fig. 6 Single point moorings. (a) Turret mooring, (b) CALM, (c) SALM

buoy body or turret or tower. The vessel can rotate freely (i.e., weathervane) around the single point with the environment loads. There is a wide variety in the design of single point moorings, which typically include turret mooring, catenary anchor leg mooring (CALM), and single anchor leg mooring (SALM), as shown in Fig. 6. A turret mooring system connects a turret assembly of a vessel, generally FPSO or floating storage and offloading (FSO), to the seabed by means of the mooring lines. The turret system that is fully passive contains a bearing system allowing the vessel to rotate around the fixed geostatic part of the turret. The turret mooring system is considered to be more economic and reliable and is widely used today. The turret can be located externally or internally with respect to the vessel hull structure. For the external turret mooring system, the turret is located at the extreme end of an outrigger structure attached to the bow of the vessel. For the internal turret mooring system, the turret is integrated into the hull structure at the bow of the vessel, as shown in Fig. 6a. Disconnectable turret mooring system has also been developed to further reduce the environmental loading on the mooring system in extreme conditions. The disconnectable turret uses a buoy that is located at the lower end of the turret. In a harsh ocean environment, the buoy can break away from the vessel and can still provide support to the risers and mooring. The catenary anchor leg mooring (CALM) (sometimes called a single buoy mooring) consists of a large buoy held in place by a number of catenary mooring lines anchored to sea floor

(Olsen 2007). The vessel is fastened to a turntable or platform on the deck of the buoy through a hawser that is typically synthetic rope, or rigid arm or soft yoke system, so that the vessel can rotate around the buoy. The vessel can be easily evacuated from a harsh environment by unfastening the connections between the vessel and buoy. For the single anchor leg mooring (SALM), a buoy under or on the water surface is anchored to an anchor point or base by a mooring line (taut wire rope or vertical chain), which is tensioned to pull the buoy against its buoyancy. The restoring force of the system comes from the buoyancy force of the buoy and the elasticity of the mooring line. The buoy is connected to the vessel through a hawser or yoke. In Fig. 6c, an underwater hose rises from the fluid swivel at the base or at a point above the base to the sea surface at a point away from the buoy for some distance. Basic Mechanics of Mooring Lines The mooring line of a vertical mooring is attached to the top of an anchoring foundation, and the onedimensional responses of the mooring line in water are relatively easy to be analyzed. For catenary and taut line moorings, the behavior of the mooring line in water can be analyzed by solving the differential equations governing the segment of the line in water column. For catenary and taut line moorings using anchor piles, suction caissons, or drag anchors, the optimal attachment point of the mooring line is below the mudline. Therefore, it is essential to consider the performance of the anchor line in soil, which forms an inverse catenary shape due to soil resistance acting on the line. The behavior of embedded anchor line can be described by

M

1074

Mooring Lines

solving the differential equations governing the segment of the line in soil.

S¼

Behavior of Mooring Line in Water A mooring line element is shown in Fig. 7. The differential equations governing the segment of the line are: ðT þ dT Þ cos ðy þ dyÞ
T cos y ¼ 0

ð1Þ

ðT þ dT Þ sin ðy þ dyÞ
T sin y
wdl ¼ 0 ð2Þ where T is the line tension, θ is the angle between the tension and horizontal direction, w is the submerged line weight per unit length, and l is the distance along the line. Provided that a mooring line is single-component (the submerged line weight per unit length is constant) and the elastic stretch is ignored, as shown in Fig. 8, the equations below can be obtained: T x ¼ T 0 cos y0 ¼ T p cos yp

 

T0 sinh
1 tan yp
sinh
1 ð tan y0 Þ w ð6Þ

l¼



T0 tan yp
tan y0 w

ð7Þ

where the T0 and Tp are the tensions at the touchdown point and top of the mooring line, respectively; Tx is the horizontal component of T0; θ0 and θp are the angles between the horizontal direction and the tension T0 and Tp, respectively; h is the vertical distance from the touch-down point; and S is the horizontal distance from the touchdown point. When θ0 ¼ 0, the mooring state becomes the catenary mooring, and the following equations can be obtained: tan yp ¼

ð3Þ

T p ¼ T 0 þ wh

T p ¼ T 0 þ wh ¼ T 0 þ

ð4Þ

wl T0

ð8Þ

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðwl Þ2 þ T 0 2

ð9Þ

 qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi T0 2 h¼ tan yp þ 1
1 w       T0 wS ¼ cosh
1 T0 w 

  T h¼ 0 w qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi  tan 2 yp þ 1
tan 2 y0 þ 1    T0 1 1 ¼
cos yp cos y0 w



ð10Þ

ð5Þ

Tp

T + dT

θp

θ + dθ

p l

dl

θ T

wdl dx

Mooring Lines, Fig. 7 Force equilibrium of an inelastic mooring line element in water

Tx T0

0 θ0

h

dz

z wl

x S

Mooring Lines, Fig. 8 Forces acting on inelastic mooring line in water

Mooring Lines

1075

S¼





T0 sinh
1 tan yp w

ð11Þ

A typical mooring line is usually multicomponent line made up of connectors, wire rope, polyester rope, and chain. For the multicomponent line, the tangential slopes of two components at the connectors are treated to be equal in order to solve the equations. Behavior of Embedded Anchor Line in Soil As shown in Fig. 9, the anchor line inclination at the attachment point of anchor or pile is critical in the design, because it will determine the mode of failure for anchor pile or suction caisson and the embedment performance of drag anchors. Figure 10 shows the force equilibrium of a segment of anchor line. The differential equations governing the embedded segment of the anchor line are (Randolph and Gourvenec 2011)

T0

za θa Ta Mooring Lines, Fig. 9 General configuration of anchor pile and embedded anchor line

T + dT θ + dθ

dl

F θ

wdl

Q

T Mooring Lines, Fig. 10 Force equilibrium of an embedded anchor line element

T

dT ¼ F þ w sin y dl

ð12Þ

dy ¼
Q þ w cos y dl

ð13Þ

where F is the soil friction (per unit length, parallel to the line) acting on the segment of the line, Q is the soil resistance (per unit length, normal to the line) acting on the segment of the line. The soil friction F and normal soil resistance Q can be expressed as F ¼ As asu

ð14Þ

Q ¼ Ab N c s u

ð15Þ

where As is the effective surface area of the anchor line per unit length, α is the interface friction coefficient (typical values of α in clay range from 0.2 to 0.6 depending on whether wire rope or chain is used), su is the undrained shear strength, Ab is the effective bearing area of the anchor line per unit length, and Nc is bearing capacity factor. For wire rope, Ab is equal to the diameter of the rope d and As ¼ πd. For a standard link chain, Ab ¼ 2.5d and As ¼ 8-11d. Neubecker and Randolph (1995) proposed a simplified analytical solution of an embedded anchor line, in which the self-weight of the anchor line is ignored. The analytical solutions are expressed as

Ta 2 y
y20 ¼ 2 a

ð za 0

Qdz ¼ za Qav

T0 ¼ emðya
y0 Þ Ta

ð16Þ ð17Þ

where Ta is the embedded anchor line tension at the attachment point, θa is the embedded anchor line inclination at the attachment point, za is the depth to the padeye, Qav is the average bearing resistance over the depth range of 0 to za, and m is the friction coefficient and calculated by F/Q.

Cross-References ▶ Catenary Mooring ▶ Diving of Anchors

M

1076

▶ External Turret Single Point Mooring System ▶ Fatigue of Mooring Lines ▶ Internal Turret Single-Point Mooring (SPM) System ▶ Mooring System ▶ Single Point Mooring ▶ Spread Mooring ▶ Taut Mooring

References API (2005) Design and analysis of station-keeping systems for floating structures. API-RP-2SK. American Petroleum Institute, Washington Brown DT (2005) Mooring systems. In: Chakrabarti S (ed) Handbook of offshore engineering. Elsevier, Amsterdam, pp 663–708 DNV (2008) Position mooring. DNV-OS-E301. Det Norske Veritas, Høvik DNV (2013) Offshore mooring steel wire ropes. DNV-OSE304. Det Norske Veritas, Høvik Flory JF, Hearle J, McKenna H, Parsey M (2015) About 75 years of synthetic fiber rope history. In: OCEANS 2015 – MTS/IEEE Washington, 19–22 Oct 2015. IEEE, Washington, DC, pp 1–13 Neubecker SR, Randolph MF (1995) Profile and frictional capacity of embedded anchor chains. J Geotech Eng 121:797–803. https://doi.org/10.1061/(ASCE)0733-94 10(1995)121:11(797) Olsen O (2007) Mooring. In: Tanker jetty safety: management of the ship/shore interface. Witherby, Livingston, pp 84–122 Randolph M, Gourvenec S (2011) Anchoring systems. In: Offshore geotechnical engineering. Spon Press, Perth, pp 308–360 Vryhof Anchors (2015) Anchor manual 2015 – the guide to anchoring. Vryhof Anchors, Schiedam

Mooring System Liping Sun College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China

Synonyms Dynamic positioning system; Single point mooring; Spread mooring

Mooring System

Definition A mooring refers to any permanent structure to which a floating structure may be secured. Examples include quays, wharfs, jetties, piers, anchor buoys, and mooring buoys. A floating platform is secured to a mooring to forestall free movement of the structure on the water. An anchor mooring fixes a floating structure’s position relative to a point on the bottom of a waterway without connecting the structure to shore. The mooring systems are usually composed of anchors, mooring lines, buoy, and connectors.

Scientific Fundamentals Mooring system and dynamic positioning system are the two main methods to keep a floating structure positioning. They can be used with either ship-shaped or offshore floating structures. Since ancient times, mooring system has been a traditional positioning way. Mooring system for ships is generally used to meet the needs of temporary berthing and prevents the ship from drifting freely on the water surface. It is mostly used in storm-free shallow water areas. Mooring system is also the most commonly used passive positioning form for offshore platforms. Considering severe ocean environment and the positioning requirements of deepwater drilling and production platform, the research, design, and manufacture of deepwater structure mooring system is so challenging that once become a technical bottleneck for deep-sea oil and gas exploitation. The research and development of mooring forms and mooring materials have been progressing steadily. Mooring ways change from traditional catenary mooring to tension mooring used in drilling and mining platform, such as SPAR and TLP platforms. Traditional high-quality mooring chains and wires are increasingly unable to meet the needs of the development of deep-sea drilling and mining, and the research and development of new mooring materials have been conducted (Luo 2015).

Mooring System

Usually there are three kinds of mooring systems according to the different positioning time. The mobile mooring system is used for pipe laying ship, lifting ship, and so on. Temporary mooring system is used for drilling ship or drilling platform. Permanent mooring system is used for the production of varity of floating platforms and FPSOs. Mooring system can also be divided into catenary mooring system and tension mooring system according to the shape of mooring line. The former is mostly used for moderate depth and shallow water, and the latter has smaller mooring radius, length, and load than the former. Catenary mooring system is a traditional deployable mooring system. It has a long history and can adapt to harsh marine environment. It still plays an important role in current positioning technology of deepwater offshore oil and gas platforms. Tension mooring system is gradually developed with the application of fiber materials in deep sea. It was first applied to the tension leg platform and Spar platform in the 1980s. According to the arrangement of lines, there are single point and spread mooring system. The former is mostly used for ship-shaped platform. In 1959, the first set of CALM (Catenary Anchor Leg Mooring) system designed by American IMODCO Company was successfully made in Sweden. It unveiled the prelude to the application of single mooring technology in offshore oil exploitation and offloading. From 1976 to 1985, single point mooring for FPSO experienced the initial mooring development phase of offshore oil and gas production. Single mooring technology welcomed its growth stage from 1986 to 1994, and extension stage from 1995 to 1998. Since 1999, the number of FPSO has increased rapidly. Major breakthroughs of mooring technology have been developed, especially for limits of water depth. Spread mooring is a natural extension of traditional ship mooring. It is suitable for Spar, Semi-submersible platforms, FPSO, and ship-shaped structures. And the environment conditions for spread mooring need to be moderate (Flory 2001). In terms of mooring lines’ materials, the typical materials have changed from steel chains and

1077

wires to synthetic fibers. Steel chain is the most traditional mooring material. It has been widely used in single point and multi-point mooring of drilling and production ships and platforms since the early stage (Corbetta and Sloan 2001). Wire mooring line is made of steel wires, and its quality is lighter than steel chains, which is suitable for deeper-water mooring (Costa et al. 2001). With the development of tension mooring, synthetic mooring has become one of the key technologies of system research (Dove et al. 2000). Synthetic fiber line is usually made of polyester fiber (PET), high strength polyethylene (HMPE), aromatic nylon (Aramid), and so on, among which, polyester line is the most popular one. In the 1970s, foreign scholars began to study the traditional polyester fiber and nylon mooring lines as mooring materials. In 1996, a synthetic fiber mooring line consisting of PET, nylon, and HMPE was successfully installed on DeepStar platform. In 1997, a polyester rope + anchor chain catenary mooring system is first used for a FPSO in Brazil. Afterwards, more and more fiber mooring systems appeared in the Gulf of Mexico (Winkler and Mckenna 1994). When oil and gas exploration and production was conducted in shallow to deep water, the most common mooring line configuration was the catenary mooring line consisting of chain or wire rope. For exploration and production in deep to ultra-deep water, the weight of the mooring line starts to become a limiting factor in the design of the floater. To overcome this problem, new solutions were developed consisting of synthetic ropes in the mooring line (less weight) and/or a taut leg mooring system (Vryhof 2005). The major difference between a catenary mooring and a taut leg mooring is that where the catenary mooring arrives at the seabed horizontally, the taut leg mooring arrives at the seabed at an angle. This means that in a taut leg mooring, the anchor point has to be capable of resisting both horizontal and vertical forces, while in a catenary mooring the anchor point is only subjected to horizontal forces. In a catenary mooring, most of the restoring forces are generated by the weight of the mooring line. In a taut leg mooring, the restoring forces are

M

1078

generated by the elasticity of the mooring line (API 2005).

Key Applications The history of mooring system started from the development and use of the single point mooring device of catenary buoy by the US navy during World War II and then developed rapidly. Numerous different mooring systems have been developed over the years. Generally, the mooring systems are divided into single point mooring and spread mooring (DNV 2008). Single Point Mooring A single point mooring system connects all the lines to a single point. It links subsea manifolds connections and weather vaning tankers, which are free to rotate 360 . The single point system includes a buoy, mooring and anchoring elements, product transfer system, and other components. Single point moorings are used primarily for ship-shaped vessels. They allow the vessel to weather vane. This is necessary to minimize environmental loads on the ship-shaped vessel by heading into the prevailing weather. There is wide variety in the design of single point moorings, such as Catenary Anchor Leg Mooring, Single Anchor Leg Mooring, Turret mooring. CALM buoy – Generally the buoy will be moored using four or more mooring lines at equally spaced angles. The mooring lines generally have a catenary shape. The vessel connects to the buoy with a single line and is free to weather vane around the buoy. SALM buoy – These types of buoys have a mooring that consists of a single mooring line attached to an anchor point on the seabed, underneath the buoy. The anchor point may be gravity based or piled. Turret mooring – This type of mooring is generally used on FPSOs and FSOs in much harsh environments. Multiple mooring lines are used, which come together at the turntable built into the FPSO or FSO. The FPSO or FSO is able to rotate around the turret to obtain an optimal orientation relative to the prevailing weather

Mooring System

conditions. The turret can be mounted externally from the vessel bow or stern with appropriate reinforcements or internally within the vessel. The chain table can be above or below the waterline (Fig. 1). Spread Mooring The spread mooring system does not allow the vessel to weather vane, which means to rotate in the horizontal plane due to wind, waves, or current. Spread mooring is versatile as it can be used in any water depth, on any vessel, in an equally spread pattern or a group. In a typical spread mooring system, groups of mooring lines are terminated at the corners of the vessel, holding a stable vessel heading. Since the environmental force on a semi-submersible or a spar is relatively insensitive to direction, a spread mooring system can be designed to hold the vessel on location regardless of the direction of the environment. However, this system can also be applied to ship-shaped vessels, which are more sensitive to environmental directions. The mooring line can be chain, wire rope, fiber rope, or a combination of the three. Either conventional drag anchors or anchor piles can be used to terminate the mooring lines (Baritrop 1998). The catenary mooring system is the most commonly used system in shallow water. It gets its name from the shape of the free hanging line as its configuration changes due to vessel motions. At the seabed, the mooring line lies horizontally; thus, the mooring line has to be longer than the water depth. Increasing the length of the mooring line also increases its weight. As the water depth increases, the weight of the line lessens the working payload of the vessel. In that case, synthetic ropes are used. As water depth increases, conventional, catenary systems become less and less economical (ABS 2014). The taut leg system typically uses polyester rope that is pre-tensioned until taut. The rope comes in at a 30–45 angle on the seabed where it meets the anchor (suction piles or vertically loaded anchors), which is loaded vertically. When the platform drifts horizontally with wind or current, the lines stretch and this sets up an opposing force.

Mooring System

1079

M

Mooring System, Fig. 1 (a) Typical internal turret mooring (b) typical external turret mooring

The semi-taut system combines taut lines and catenary lines in one system. It is ideally used in deepwater (SBM 2012).

Cross-References ▶ Catenary Anchor Leg Mooring ▶ Catenary Mooring ▶ Design of Mooring System ▶ Dynamic Analysis Method ▶ External Turret Single Point Mooring System ▶ Internal Turret Single-Point Mooring (SPM) System

▶ Single Anchor Leg Mooring ▶ Single Point Mooring ▶ Soft YOKE Single Point Mooring System ▶ Spread Mooring ▶ Station-Keeping System for VLFS ▶ Taut Mooring ▶ Turret Mooring

References American Bureau of Shipping (2014) Rules for building and classing single point mooring. https://ww2.eagle. org/

1080 API RP 2SK (APE Recommended Practice 2SK) (2005) Design and analysis of stationkeeping systems for floating structures. American Petroleum Institute. Baritrop NDP (1998) Floating structures: a guide for design and analysis. CMPT, London Corbetta I, Sloan F (2001) HMPE mooring line trial for scarabeo III. OTC 13272 Offshore Technology Conference, Houston Costa LCS, Castro GAV, Goncalves RCF (2001) Polyester mooring systems-petrobras experience. Proceedings of the Deep Offshore Technology Conference. Rio de Janeiro, Brazil. Rio de Janeiro: PennWell Corporation DNV (2008) DNV-OS-E302. Offshore mooring chain. https://www.dnvgl.com/ Dove P, Weisinger D, Abbassian F (2000) The development and testing of polyester moorings for ultra-deep drilling operations, OTC 12172 (Offshore Technology Conference, Houston) Flory JF (2001) Improved potted socket terminations for high-modulus synthetic-fiber rope. OIPEEC Round Table Conference , Bethlehem Luo Y (2015) Design and analysis of station keeping system for floating structures. Harbin Engineering University Press, China GL Noble Denton (2014) Offshore Engineering Technology Guidelines. https://www.dnvgl.com/ SBM (2012) Offshore CALM brochure. www. sbmoffshore.com Vryhof Anchor Manual (2005) www.vryhof.com Winkler MM, Mckenna HA (1994) Polyester taut leg mooring concept design study. Shell Development, Houston

Mooring System of Renewable Energy Devices Zhen Gao Norwegian University of Science and Technology, Trondheim, Norway

Definition A mooring system is a system of several mooring lines which are connected to a floating structure of renewable energy device at one end and fixed to the sea bed at the other end, to restrict the horizontal excursions and orientation of the floating structure.

General Purpose of Mooring System A station-keeping system (ISO 2005) is to restrict the horizontal excursions of the floating structure

Mooring System of Renewable Energy Devices

within prescribed limits, as well as to provide means of active or passive directional control when the structure’s orientation is important for safety or operational considerations. For floating offshore renewable energy devices, including floating wind turbines, floating wave energy converters, and floating tidal turbines, a passive station-keeping system, i.e., a mooring system, is needed to limit the offset of the floater under environmental actions of waves, wind, and current, so that the desired normal operations, i.e., power production, can be maintained, without breaking the power cable. Active station-keeping system, such as dynamic positioning system with propellers and thrusters, is not relevant for offshore renewable energy devices because of the high cost and the high electricity used to keep the floating structure in position. A mooring system typically consists of a group of mooring lines which can be configured as spread mooring or turret (or single point) mooring. Most of the mooring systems for offshore renewable energy devices are based on spread mooring configurations, as shown in Fig. 1 for floating wind turbines. Mooring lines are slender structures of chain links, steel wire, and/or fiber ropes, which are connected to the floater at its fairlead and to the anchor on the sea bed. Mooring systems for offshore oil and gas platforms are designed with redundancy so that failure of one line will not lead to failure of the whole mooring system and will not result into a drift off of the platform. This is because the consequence of such failure might be significant in terms of not only property loss but also fatalities and environmental pollution. However, floating renewable energy devices are usually unmanned, and there are less significant consequences due to mooring failure, which is mainly property loss. Most of the mooring systems used today for floating wind turbines just have three minimum lines with no redundancy. Depending on the way that a mooring system provides the restoring effect on floater motions, we have catenary mooring, taut mooring, and tension legs. For example, catenary moorings are suitable for spar and semisubmersible floating wind turbines, and tension legs are designed for TLP floating wind turbines, as shown in Fig. 1.

Mooring System of Renewable Energy Devices

1081

Mooring System of Renewable Energy Devices, Fig. 1 Floating wind turbines and their mooring systems (From left: spar, semisubmersible, and TLP) (Graphic by Joshua Bauer at NREL)

Catenary line is a series of chain links, and it provides the restoring effect via the change of the catenary shape under large gravity force. It has a large proportion of the line on the sea bed, to avoid a sudden increase in mooring stiffness when the whole mooring line is lifted up from the sea bed. When this happens, the stretching of the chain links will take place and give too large mooring stiffness. Taut lines of steel wire or fiber ropes and tension legs provide the restoring effect through the axial extension of the line. When a clump weight or a buoy is used, a catenary effect can be generated from the relative angles between the two segments that are connected by the clump weight or the buoy. An illustration of the different mooring configurations, typically for floating wave energy converters, is shown in Fig. 2. For floating wind turbines in a farm configuration, it is important to reduce the footprint of each mooring system to limit the range of the offshore wind farm. Normally, catenary mooring systems have a much larger footprint as compared to the taut line or TLP systems. In a TLP platform, the pretension of the tendons is provided by the extra buoyancy force of the floater which is larger than the gravity of the whole system and should be large enough to avoid slack and large transient dynamics

in mooring tendons considering the floater motions under wind, wave, and current loads. Mooring system has a strong influence on the motions of floating structures. It provides a restoring effect on the horizontal motions of the floater, i.e., surge, sway, and yaw, for which there is no hydrostatic restoring effect. This is particularly important for floating wind turbines, which may have significant mean thrust force on the wind turbine under normal operations and may potentially lead to a large offset of the floater. As shown in Fig. 3, the mooring stiffness is normally characterized by the (horizontal) tension-offset curve, which is typically nonlinear when the offset is large. The stiffness of mooring lines is designed so that the natural periods for horizontal rigid-body motions of the floater are in the order of 1–2 mins, which are much larger than the main wave periods, to avoid resonance due to the first-order wave loads. However, low-frequency resonant horizontal motions can be excited by either second-order wave loads or slowly varying wind loads, which are one order of magnitude smaller than the first-order wave loads. Both catenary mooring system and deep water taut mooring system have limited influence on the vertical motion modes of the floater, i.e., heave, roll, and

M

1082

Mooring System of Renewable Energy Devices

Mooring System of Renewable Energy Devices, Fig. 2 Mooring configurations for floating wave energy converters with catenary line, taut line, TLP as well as with clump weights and buoys (EMEC 2015)

Mooring line tension (KN) 18

10000 8000

200

128

MSL

6000 Clump Weight

4000 2000 Anchor

258

0 726 884

0

2

4

6

8

10

12

14

16

Offset (m)

Mooring System of Renewable Energy Devices, Fig. 3 Typical catenary mooring system for a floating wind turbine (left, units in meters) and mooring line characteristic curve (tension-offset relationship) (right) (Xu 2015)

Mooring System of Renewable Energy Devices

pitch. While tension legs in a TLP are designed with high axial stiffness so that the natural periods of the vertical motion modes are in the order of 1– 3 s, which are smaller than the main wave periods. In other words, the wave-frequency motions of the floaters are not constrained in a catenary and taut line system, and the first-order wave loads are compensated by the inertia loads of the floater, while such motions in the vertical modes are constrained by the tendons in a TLP, and the first-order wave loads in these modes are taken directly by the tendons, as the restoring effect.

Mooring Line Components Mooring lines may consist of chain links, steel wire, fiber ropes, and/or a combination of these; see Fig. 4. Chain links are welded and connected steel bars, with or without stud. In deep waters, because the total weight of chain links can be very large and have to be compensated by the additional buoyancy of the floater, they are used in combination with steel wire or fiber ropes with less weight for such conditions. Chain link has a good property against friction and abrasion and are often used at the fairlead and/or at the sea bed. Steel wire might be six-strand or spiral-strand constructions. Synthetic fiber ropes are polyester, aramid, or nylon, which are light materials and suitable for very large water depths. Chain links are normally used in a catenary mooring system. Steel wire can be used in both catenary and taut moorings, while fiber ropes are normally used for taut-line systems. A particular challenge for mooring system in shallow waters is that the mooring stiffness can increase significantly for a small

1083

increase in the horizontal offset of the fairlead, which leads to a significant increase in mooring line tension. Therefore, clump weights or buoys might be placed in between the mooring line segments to increase the catenary effect for such conditions. Anchors are placed at the lower end of mooring line to provide a fixation for the mooring line and also for the floater. Typically anchors are designed to take only horizontal loads, such as fluke anchor and plate anchor, while some anchors, like pile anchor, suction anchor, and gravity anchor, can take in addition vertical loads. For large oil and gas platform, winches are arranged at the platform level which allows the length change of individual lines and therefore the heading change of the platform. However, because of the cost issues, floating wind turbines typically do not have winches for mooring system, and mooring lines are fixed at the fairlead. Moreover, connectors are used when combining chain links with steel wire or fiber ropes. Technical specifications in terms of dimension, weight, ultimate strength, and fatigue strength of mooring line components are provided in DNV (2010). In particular, fatigue design of mooring systems requires in the first step to have a global model for coupled mooring analysis considering both wind and wave conditions. Fatigue S-N (stress-number to failure) curves and very often T-N (tension-number to failure) curves for mooring lines are then used in combination with the global response analysis results for fatigue damage calculation. Fatigue property of chain link and steel wire is well-known, while fatigue tests show a large value and a big scatter of the material slope of the S-N curve for synthetic fiber ropes. Therefore, Parallel Strands Half Right Lay and Half Left Lay

Yarns

SPECIAL L TM D JOINING SHACKLE COMMON LINK

COMMON LINK

Heavy Braided Jacket

Strands

Mooring System of Renewable Energy Devices, Fig. 4 Chain links (left), six-strand steel wire ropes (middle), and parallel-subrope fiber ropes (right) (DNV 2010)

M

1084

fatigue design safety factors are typically chosen very large to reflect the big uncertainties in fatigue property of fiber ropes (DNV 2010).

Mooring System for Floating Wind Turbines, Wave Energy Converters, and Tidal Turbines In this section, examples of mooring systems for floating renewable energy devices will be given. Figure 1 shows the three types of floating wind turbines (spar, semi-submersible and TLP) and their mooring systems. In fact, there exist MWscale floating spar and semi-submersible wind turbine demos, for example, Hywind spar wind turbine (Equinor 2018) and WindFloat semisubmersible wind turbine (PrinciplePower 2018). The third one is a TLP wind turbine with vertical tendons as mooring lines. The mooring system of the Hywind demo is a taut-line mooring system in combination with clump weights. Near the fairlead of the mooring lines, a delta-line configuration of the mooring system is applied in order to increase the mooring stiffness in yaw so that the natural period of yaw motions is around 8 s. A wind turbine rotor in turbulent wind field may experience unbalanced rotor plane loads, which induces a yaw moment. If the yaw stiffness from the mooring system is too low, there will be a large yaw offset, which may strongly influence the power production of the wind turbine. The mooring system for the WindFloat prototype is a four-line spread catenary mooring system. Two lines are attached to the column which supports the wind turbine, and the other two lines are for the two remaining columns. The fairleads of the three mooring lines are located at the columns, which is far enough from the central position of the wind turbine tower, to create a large yaw stiffness from the mooring system. The TLP wind turbine as shown in Fig. 1 has three vertical tendons which are significantly pretensioned due to the excessive buoyancy of the floater as compared to its gravity. As a design requirement, the pretension in each tendon should

Mooring System of Renewable Energy Devices

be large enough so that it will not go below zero under environmental loads due to wind, waves, and current, which will otherwise induce a transient dynamic effect and therefore large loads in the tendon. Single tendon mooring system is also proposed for one of the floating wind turbine concept, SWAY (2012). Mooring system for floating wave energy converters depends strongly on the concept and size of wave energy converters. Catenary and single point mooring system is used for large-sized wave energy converters, such as the Wave Dragon overtopping device (2018). Such weather-vane mooring system allows the floater to rotate towards the favorable wave directions. Similar moorings are used for large platforms hosting multiple wave energy converters, for example, oscillating water columns. Most of the pointer absorber wave energy converters are small, and their mooring systems, as shown in Fig. 2, might have a strong interaction effect on the wave-frequency motions of the pointer absorbers and therefore the power production. For commercial purpose, a big number of wave energy converters should be developed in a farm configuration, similar as those for offshore wind turbines. It has the advantage of smoothing power production based on an appropriate configuration and sharing infrastructures to lower the cost. The simplest way to share the infrastructure is to share the anchors for multiple wave energy converters. In such cases, anchors with vertical capacity are needed. Moreover, the wave energy converters can be interconnected so that the total number of anchors and mooring lines can be minimized to reduce the cost. However, the dynamic behavior of the whole system, including multiple wave energy converters and mooring system, can become quite complicated, and large loads in connecting lines might be induced by adjacent wave energy converters with opposite wavefrequency motions (Gao and Moan 2009). Most of the ocean and tidal current turbines developed today are bottom-fixed. Some floating tidal turbine plants have been proposed, typically with a spread-moored floating platform which supports one or two turbines. Similar to floating

Multidisciplinary Design

wind turbines, large mean thrust from tidal turbines will need to be compensated by the mooring forces. In addition, since the tides change directions every 6 h, the tidal turbines are normally designed to work in both directions. As a result, the floater may experience large offset in both directions, and the mooring system should be designed to consider this.

Cross-References ▶ Design Rules and Standards ▶ Economic Assessment ▶ Offshore Wind Turbines ▶ Tidal and Ocean Current Turbines ▶ Wave Energy Converters

References DNV (2010) Offshore standard – position mooring. DNV OS-E301 EMEC (2015) Moorings and foundations catalogue, deliverable 5.1. Report of the Project: Reliability in a Sea of Risk Equinor (2018) How hywind works? https://www.equinor. com/en/what-we-do/hywind-where-the-wind-takes-us/ hywind-up-close-and-personal.html Gao Z, Moan T (2009) Mooring system analysis of multiple wave energy converters in a farm Configuration. In: Proceedings of the 8th European wave and tidal energy conference (EWTEC), September 7–10, Uppsala, Sweden ISO (2005) Petroleum and natural gas industries – specific requirements for offshore structures – part 7: station keeping systems for floating offshore structures and mobile offshore units. ISO 19901-7 PrinciplePower (2018). http://www.principlepowerinc.com/ en/windfloat SWAY (2012). http://www.sway.no/?page¼166 WaveDragon (2018). http://www.wavedragon.net/ Xu K (2015) Design and analysis of mooring system for semi-submersible floating wind turbines in shallow water. MSc Thesis. Department of Marine Technology, Norwegian University of Science and Technology

1085

MOSES TLP ▶ Tension-Leg platform

Motion Control System ▶ AUV/ROV/HOV Control Systems

Motion Reference Unit (MRU) ▶ Optical Compass ▶ Ultra-short Baseline Underwater Acoustic Location Technology

MSS – Mineral Storage System ▶ Surface Mineral Storage and Dump

MSTS – Mineral Storage and Transport System ▶ Surface Mineral Storage and Dump

MTS – Mineral Transport System ▶ Surface Mineral Storage and Dump

Morison-Force Model

Multidisciplinary Design

▶ Aquaculture Structures: Numerical Methods

▶ Detailed Design

M

1086

Multidisciplinary Design Optimization (MDO) Hao Chen Zhejiang University – Westlake University Joint Training, Zhejiang University, Hangzhou, China

Synonyms Approximate technology; MDO method; MDOcomputing framework; Optimization algorithm; System decomposition; System modeling

Definition Multidisciplinary design optimization (MDO) is a design methodology for complex engineering systems, which aims to explore the mechanism of synergistic action among subsystems and design complex engineering systems. MDO focuses on the use of optimization algorithms for the design of complex engineering systems which involve a number of subsystems or disciplines. In MDO, the engineering system is divided into different subsystems or disciplines, then the mathematical model of each subsystem is established and the appropriate MDO method is applied to reorganize each subsystem model. Finally, the appropriate optimization algorithm is selected for optimization so as to achieve the optimal design of complex engineering system.

Scientific Fundamentals Mathematical Model and Basic Concept of MDO Problems The mathematical model of MDO problems is more complex than that of traditional optimization problems, because the coupling relationship among multiple disciplines or subsystems should be considered in MDO problems. Without loss of generality, for MDO problems that involve a number of disciplines, the mathematical model can be described as follows:

Multidisciplinary Design Optimization (MDO)

Min : f ðxs , x, zÞ    S:t: : gi xs , xi , zi xs , xi , yji  0 ði ¼ 1, 2, . . . , N; i 6¼ jÞ    hi xs , xi , zi xs , xi , yji ¼ 0 ði ¼ 1, 2, . . . , N; i 6¼ jÞ

where f represents optimization objective, gi and hi represent inequality constraints and equality constraints of discipline i, respectively. xs refers to shared design variables, xi and zi refer to local design variables and state variables of discipline i, respectively, and yji is the coupled state variable that discipline j outputs to discipline i. Compared to traditional optimization problems, MDO problems involve more basic concepts. Combined with the MDO problem that involves two disciplines in Fig. 1, some basic concepts involved in MDO problems are introduced as follows: 1. Design variables: Design variables are a group of relatively independent parameters controlled by the designer during the design process. Design variables can be used to represent the basic characteristics of the engineering system. According to the scope of design variables, it can be divided into shared design variables xs and local design variables x1, x2 (see Fig. 1). 2. State variables: State variables are a set of parameters used to represent the response of the engineering system, which can reflect the performance or characteristics of the engineering system. State variables are usually obtained from analysis or calculation models. State variables include system state variables such as the optimization objective, discipline state variables z1, z2, and coupled state variables. The discipline state variables employed as the input to the analysis of another discipline are coupled state variables (i.e., y12, y21 shown in Fig. 1). 3. Disciplines: Disciplines, also known as subsystems, represent the basic modules that maintain their relative independence in engineering systems. Different ways of decomposition lead to different disciplinary divisions. 4. Discipline analysis: Taking the design variables of discipline i and the coupled state variables of other disciplines as input, the process

Multidisciplinary Design Optimization (MDO)

1087

Multidisciplinary Design Optimization (MDO), Fig. 1 The MDO problem that involves two disciplines

of solving the state equation of discipline i to obtain the output state variable of discipline i is called discipline analysis. 5. System analysis: System analysis is also called multidisciplinary analysis. The system performs repeated iterative calculations with given input variables to coordinate the coupled state variables obtained from the analysis of various disciplines; this process is called system analysis. Main Research Contents of MDO Due to the coupling relationship between disciplines, there will be two problems in the multidisciplinary design optimization of complex engineering systems, including organizational complexity and computational cost. A series of technologies and methods on how to solve the two problems of MDO constitutes main research contents of MDO (Sobieszczanski-Sobieski and Haftka 1997), including system decomposition, system modeling, approximate technology, optimization algorithm, MDO method, and MDO computing framework. System Decomposition

The design of complex engineering system involves high-dimensional nonlinear design variable space, and coupling relationship exists between disciplines; it is very difficult to design and optimize the system directly. Therefore, it

is necessary to use system decomposition technology to change the organizational structure of MDO problems. System decomposition refers to the decomposition of a complex system into several relatively independent subsystems (or disciplines), thus reducing the organizational complexity of the system and shortening the system design cycle. According to the different ways of data transfer within the system after decomposition, system decomposition methods can be divided into two categories: 1. Hierarchical decomposition: For a hierarchical decomposition system, as shown in Fig. 2, data transmission occurs between subsystems of the same level as each other, while there is no information exchange between subsystems of the same level, so parallel analysis and calculation can be carried out. This decomposition method is suitable for multidisciplinary design optimization problems with weak coupling, but difficult to deal with problems with strong coupling. 2. Nonhierarchical decomposition: As shown in Fig. 3, there is no hierarchical relationship in the nonhierarchical decomposition, and data is directly transferred between each subsystem. The decomposition method is suitable for multidisciplinary design optimization problems with strong coupling, which is in line with the practice of complex engineering system design.

M

1088

Multidisciplinary Design Optimization (MDO)

Multidisciplinary Design Optimization (MDO), Fig. 2 Hierarchical decomposition

Multidisciplinary Design Optimization Fig. 4 Approximate technology

Multidisciplinary Design Optimization Fig. 3 Nonhierarchical decomposition

(MDO),

After the decomposition of the system, each subsystem can be analyzed and optimized independently, but coordination among subsystems is needed. There are various coordination methods, and consistency constraint (Haftka 1985) is often used to replace the connection between subsystems. System Modeling

System modeling is realized by using mathematical language to establish the optimization model of the MDO problem and the analysis model of various disciplines. In addition, to clarify the way of data transfer between subsystems, the mathematical model of coupling relationship between subsystems is also needed. System modeling is the basis of multidisciplinary design optimization of complex engineering systems. Approximate Technology

The approximation technique is the way to build approximate relationships between data based on existing data sets. As shown in Fig. 4, for a given

(MDO),

inputx, there will be a corresponding outputy, but the functional relationship between x and y is unknown. Given a large number of inputs(x1, x2, . . ., xn), the corresponding output(y1, y2, . . ., yn) can be obtained through analysis and calculation. Then, assuming thatx and y meet a specific functional relationship (i.e., approximation model), the function relationship can be determined through the existing data set of input and output; this method is called approximation technique. By replacing the complex discipline analysis process with simple and efficient approximation models, the computational work can be greatly reduced while ensuring a certain accuracy, and the key of approximation technology is to build an appropriate approximation model to replace the corresponding discipline analysis model. Common approximate models include artificial neural network, response surface model, etc. (Sobieszczanski-Sobieski and Haftka 1997). For the MDO problem of complex engineering system, the calculation amount of a complete multidisciplinary analysis is huge. If the process is coupled into the optimization model for optimization, the calculation amount increases dramatically. In addition, for some subsystems that use

Multidisciplinary Design Optimization (MDO)

high-precision numerical software as the discipline analysis model, it is difficult to imagine the amount of computing tasks since the highprecision discipline analysis model of the subsystem will be repeatedly called during the whole multidisciplinary design optimization process. So, approximation technique is an essential research content in multidisciplinary design optimization. Optimization Algorithm

After establishing the optimization model of MDO problem, it is necessary to search the design variable space to get the optimal design scheme. In this process, the optimization algorithm is needed to find the optimal solution. MDO problem is an optimization problem in essence, and the appropriate optimization algorithm has an important impact on the final solution of the multidisciplinary design optimization problem, so the optimization algorithm is also an important research content of MDO. Optimization algorithms can be divided into two categories: (1) traditional optimization algorithms (Nocedal and Wright 2006), such as conjugate gradient method, trust-region method, newton method, etc.; and (2) intelligent optimization algorithm (Simon 2013), such as particle swarm optimization algorithm, genetic algorithm, ant colony algorithm, etc. MDO Method

Multidisciplinary design optimization method is an optimization solution strategy for complex engineering system design. MDO methods reorganize the system through system decomposition and establish the mathematical model of MDO problem by using system modeling technology. The MDO method starts from the engineering system design problem itself and involves several major research contents of MDO, such as system decomposition, system modeling, approximation technology, optimization algorithm, etc. MDO methods can be divided into single-level method and multilevel method. Single-level method only has an optimizer for optimization at the system level, and there is only analysis within each

1089

subsystem (or discipline) without optimization. The multilevel method has an optimizer at the system layer and subsystem layer for optimization. MDO Computing Framework

The MDO computing framework refers to the computer hardware and software environment that implements the MDO method. The MDO computing framework can integrate and execute the analysis and design of each subsystem, realize the data transfer between systems, and complete the multidisciplinary design optimization of complex engineering systems. As multidisciplinary design optimization is widely used in the engineering field, the market demand for high-performance MDO computing frameworks increases sharply. A variety of commercial MDO computing frameworks are developed (Salas and Townsend 1998), such as iSIGHT (Engineous Software), ModelCenter (Phoenix), Optimus (LMS Technologies), etc. In recent years, some open source high-performance multidisciplinary design optimization platforms, such as pyMDO (Martins et al. 2009) and OpenMDAO (Gray et al. 2019), have been developed for MDO researchers to learn.

Historical Development Multidisciplinary design optimization originates from the aircraft design direction in the field of aerospace research (Sobieszczanski-Sobieski and Haftka 1997). In the 1970s, aircraft design methods mostly adopted the traditional serial design method; this method has many drawbacks, such as ignoring the coupling relationship between disciplines, low efficiency, long design cycle, and high cost. In order to overcome the drawbacks of traditional design methods, multidisciplinary design optimization was proposed as a new design methodology in the 1980s. Sobieszczanski-sobieski (1982) proposed the concept of multidisciplinary design optimization for the first time in a research paper on structural optimization. Since it was

M

1090

proposed, MDO has received great attention from academia and industry. In 1986, AIAA, NASA, OAI, and USAF in the United States jointly organized the first symposium on “Multidisciplinary Analysis and Optimization.” Since then, the conference has been held every 2 years and has become a leading international academic conference in the field of MDO. In order to promote the research and development of MDO, Sobieszczanski-Sobieski (1995) presented a review about MDO; this paper attempts to define the MDO as a new field of research endeavor and as an aid in the design of engineering systems. The Multidisciplinary Design Optimization Branch (MDOB), established by NASA’s Langley Research Center, proposed a test suite in 1996 to measure the performance of MDO methods (Padula et al. 1996). With the promotion of these scientific research institutions, the theoretical research of MDO entered the stage of rapid development in the 1990s, among which the multidisciplinary design optimization method is the core content and frontier of the theoretical research of MDO. In this stage, many classical MDO methods are put forward one after another, including multidisciplinary feasible method (MDF) (Cramer et al. 1994), all-at-once method (AAO) (Cramer et al. 1994), individual disciplinary feasible method (IDF) (Cramer et al. 1994), concurrent subspace optimization method (CSSO) (Sobiesczanski-Sobieski 1988), collaborative optimization method (CO) (Kroo et al. 1994), and bilevel-integrated system synthesis method (BLISS) (Sobiesczanski-Sobieski et al. 2000), in which MDF, AAO, and IDF belong to single-level MDO methods, and CSSO,CO, and BLISS belong to multilevel MDO methods. In the twenty-first century, the theoretical research of MDO focuses on the improvement of the classical MDO method. Sobieszczanskisobieski et al. (2003) reconstructed the system optimization problem on the basis of BLISS and proposed the BLISS-2000 method, in which the information exchange between the system and the subsystem is realized by the approximate model of the subsystem optimization, and the objective function of the subsystem optimization is

Multidisciplinary Design Optimization (MDO)

represented by the weighted sum of the state variables of the subsystem. Based on the MDF method, Chittick and Martins (2009) proposed a new distributed MDF method, which is called Asymmetric Subspace Optimization (ASO). Aiming at the problem that the coupling variables are difficult to be resolved, Li et al. (2016) proposed a standard for determining the coupling variables, combined it with CO method, and proposed an improved collaborative optimization (ICO) method.

Key Applications After nearly 40 years of rapid development, the multidisciplinary design optimization theory is becoming mature and gradually moves from the theoretical research stage to the engineering practical application stage. In addition to the successful application in the aerospace field, such as aircraft design optimization (Braun et al. 1996; Jun et al. 2006; Park et al. 2009; Setayandeh and Babaei 2020), multidisciplinary design optimization technology is also widely applied in the field of ship and ocean engineering. Wang et al. (2007) applied the concurrent subspace design method (CSD) to the shape design of a certain AUV. Luo and Lyu (2015) applied the collaborative optimization method to the hydrodynamic performance optimization of underwater unmanned vehicle (UUV). Liu et al. (2017) carried out the research on the multiple objective multidisciplinary design optimization of heavier-than-water underwater vehicle using CFD and approximation model. Bidoki et al. (2018) proposed the PSO-MDF method, by combining the particle swarm optimization algorithm and MDF method, and applied it to the multidisciplinary design optimization of an autonomous underwater vehicle (AUV). Chen et al. (2018) divided the design of AUV into three subdisciplines, including hydrodynamic discipline, control discipline, and energy and weight distribution discipline, and then applied the MDF method to the overall conceptual design optimization of AUV. Bidoki et al. (2019) presented an improved multidisciplinary design optimization methodology for conceptual design

Multidisciplinary Design Optimization (MDO)

of an autonomous underwater vehicle in both engineering and tactic aspects under uncertainty.

Cross-References ▶ Concept Design ▶ Design of Submersibles ▶ Preliminary Design

References Bidoki M, Mortazavi M, Sabzehparvar M (2018) A new approach in system and tactic design optimization of an autonomous underwater vehicle by using Multidisciplinary Design Optimization. Ocean Eng 147:517–530 Bidoki M, Mortazavi M, Sabzehparvar M (2019) A new multidisciplinary robust design optimization framework for an autonomous underwater vehicle in system and tactic design. Proc Instit Mech Eng Part M J Eng Maritime Environ 233(3):918–936 Braun R, Moore A, Kroo I (1996) Use of the collaborative optimization architecture for launch vehicle design. In: 6th symposium on multidisciplinary analysis and optimization, American Institute of Aeronautics and Astronautics. Bellevue, WA, U.S.A, p 4018 Chen X, Wang P, Zhang D, Dong H (2018) Gradient-based multidisciplinary design optimization of an autonomous underwater vehicle. Appl Ocean Res 80:101–111 Chittick IR, Martins JR (2009) An asymmetric suboptimization approach to aerostructural optimization. Optim Eng 10(1):133 Cramer EJ, Dennis JE Jr, Frank PD, Lewis RM, Shubin GR (1994) Problem formulation for multidisciplinary optimization. SIAM J Optim 4(4):754–776 Gray JS, Hwang JT, Martins JR, Moore KT, Naylor BA (2019) OpenMDAO: an open-source framework for multidisciplinary design, analysis, and optimization. Struct Multidiscip Optim 59(4):1075–1104 Haftka RT (1985) Simultaneous analysis and design. AIAA J 23(7):1099–1103 Jun S, Jeon YH, Rho J, Lee DH (2006) Application of collaborative optimization using genetic algorithm and response surface method to an aircraft wing design. J Mech Sci Technol 20(1):133 Kroo I, Altus S, Braun R, Gage P, Sobieski I (1994) Multidisciplinary optimization methods for aircraft preliminary design. In: 5th symposium on multidisciplinary analysis and optimization, American Institute of Aeronautics and Astronautics, Panama City Beach, FL, U.S. A, p 4325 Li W, Jia YJ, Wen Y, Li LX (2016) An improved collaborative optimization for multidisciplinary problems with coupled design variables. Adv Eng Softw 102:134–141

1091 Liu X, Yuan Q, Zhao M, Cui W, Ge T (2017) Multiple objective multidisciplinary design optimization of heavier-than-water underwater vehicle using CFD and approximation model. J Mar Sci Technol 22(1):135–148 Luo W, Lyu W (2015) An application of multidisciplinary design optimization to the hydrodynamic performances of underwater robots. Ocean Eng 104:686–697 Martins JR, Marriage C, Tedford N (2009) pyMDO: an objectoriented framework for multidisciplinary design optimization. ACM Trans Math Softw (TOMS) 36(4):1–25 Nocedal J, Wright S (2006) Numerical optimization. Springer Science & Business Media, New York Padula S, Alexandrov N, Green L (1996) MDO test suite at NASA Langley Research Center. In: 6th symposium on multidisciplinary analysis and optimization, American Institute of Aeronautics and Astronautics, Bellevue, WA, U.S.A, p 4028 Park C, Joh CY, Kim YS (2009) Multidisciplinary design optimization of a structurally nonlinear aircraft wing via parametric modeling. Int J Precis Eng Manuf 10(2):87–96 Salas A, Townsend J (1998) Framework requirements for MDO application development. In: 7th AIAA/USAF/ NASA/ISSMO symposium on multidisciplinary analysis and optimization, American Institute of Aeronautics and Astronautics, St.Louis, MO, U.S.A, p 4740 Setayandeh MR, Babaei AR (2020) Multidisciplinary design optimization of an aircraft by using knowledge-based systems. Soft Comput 24:1–20 Simon D (2013) Evolutionary optimization algorithms. Wiley, Hoboken Sobieszczanski-Sobieski J (1982) A linear decomposition method for large optimization problems. Technical report, NASA Langley Research Center; Hampton, VA, United States Sobieszczanski-Sobieski J (1988) Optimization by decomposition: a step from hierarchic to non-hierarchic systems. Recent Advances in Multidisciplinary Analysis and Optimization, 51–78 Sobieszczanski-Sobieski J (1995) Multidisciplinary design optimization: an emerging new engineering discipline. In: Advances in structural optimization. Springer, Dordrecht, pp 483–496 Sobieszczanski-Sobieski J, Haftka RT (1997) Multidisciplinary aerospace design optimization: survey of recent developments. Struct Optim 14(1):1–23 Sobieszczanski-Sobieski J, Agte JS, Sandusky RR Jr (2000) Bilevel integrated system synthesis. AIAA J 38(1):164–172 Sobieszczanski-Sobieski J, Altus TD, Phillips M, Sandusky R (2003) Bilevel integrated system synthesis for concurrent and distributed processing. AIAA J 41(10):1996–2003 Wang P, Song B, Wang Y, Zhang L (2007) Application of concurrent subspace design to shape design of autonomous underwater vehicle. In: Eighth ACIS International Conference on Software Engineering, Artificial Intelligence, Networking, and Parallel/Distributed Computing (SNPD 2007), vol 3. IEEE, Qingdao, China, pp 1068–1071

M

1092

Multihop Network ▶ Underwater Acoustic Sensor Network

Multihop Network

Multi-source Information Fusion Navigation ▶ Integrated Navigation

Multiple Input Multiple Output (MIMO)

Multi-user Long Baseline (MULBL)

▶ Underwater Acoustic Communication

▶ Long Baseline Underwater Acoustic Location Technology

Multiple Line Moorings

Mussel Farm

▶ Spread Mooring System

▶ Traditional Aquaculture Structures

N

National Maritime Research Institute (NMRI) ▶ Maneuverability of Polar Vessel

National Maritime Research Institute of Japan (NMRI) ▶ Ice Tank Test

National Research Council Canada-Ocean ▶ Ice Tank Test

Navigation Buoy Wanan Sheng SW MARE Marine Technology and Consultation, Cork, Ireland

Definition A Navigation Buoy is a special floating buoy (or maybe fixed in occasional cases) that are set on waters for enhancing safety of sea activities © Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

by providing lights and/or marks and other relevant information. For instance, it is of vital importance for marine traffic to obtain correct LOPs. It is also called Aids to Navigation buoy (AtoN buoy). Figure 1 shows a typical navigation buoy.

Scientific Fundamentals The International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA, previously known as International Association of Lighthouse Authorities (http:// www.iala-aism.org/)) is an Intergovernmental organization founded in 1957 to collect and provide nautical expertise and advice. Since 1973, the principal work has been implemented as the IALA Maritime Buoyage System. This rationalized system was introduced as a result of two accidents in the Dover Straits in 1971 when the Brandenburg hit the wreck of the Texaco Caribbean off Folkestone; and shortly later the Niki struck the Texaco Caribbean. The combined loss of lives in these two accidents was 51 persons. As a result of the accidents, a new system was essentially established to replace some 30 dissimilar buoyage systems in use throughout the world with two internationally standardized systems. Although the international agreement of 1982 implementing a harmonized buoyage system is a major achievement for the IALA Organization, through its committees carried out a lot of works in other directions resulting in innovating

1094

Navigation Buoy

Navigation Buoy, Fig. 2 Lateral marks

N

E

Navigation Buoy, Fig. 1 Typical navigation buoy with a light and a chart symbol on top. (Adopted from https:// www.ybw.com/features/navigation-essential-buoysmarks-8611)

techniques being adopted all over the work, such as the AIS (Automatic Identification System), DGNSS (Differential Global Navigation System), and many others.

S

W

Key Applications Regardless of which system you use, there are six types of navigational marks: lateral; cardinal; safe water; isolated danger; emergency wreck, and special. Now IALA is known for the IALA Maritime Buoyage Systems or sea mark systems that are used in the pilotage of vessels at sea (following information adopted from https:// www.irishlights.ie/): 1. Lateral Marks Lateral Marks are generally used for welldefined channels (Fig. 2). They indicate the port and starboard sides of the route to be followed. They are positioned in accordance with a Conventional Direction of Buoyage.

Navigation Buoy, Fig. 3 Cardinal marks

Lateral Marks in region A use red to denote port and green to denote starboard when returning from sea. In region B, the reverse applies. 2. Cardinal Marks A Cardinal mark is named after the quadrant in which it is placed. The name of a Cardinal mark indicates that it should be passed to the named side of the mark. The mariner will be safe if they pass north of a North mark (“N”),

Navigation Buoy

1095

Navigation Buoy, Fig. 4 Safe water mark Navigation Buoy, Fig. 6 Emergency wreck marking buoy

N

Navigation Buoy, Fig. 5 Isolated danger marks

south of a South mark (“S”), east of an East mark (“E”) and west of a West mark (“W”) in Fig. 3. A Cardinal mark may be used, for example, to: • Indicate that the deepest water in that area is on the named side of the mark. • Indicate the safe side on which to pass a danger. • Draw attention to a feature in a channel such as a bend, a junction, a bifurcation, or the end of a shoal. Cardinal Marks are also used for permanent wreck marking whereby North, East, South, and West Cardinal buoys are placed around the wreck. In the case of a new wreck, any

Navigation Buoy, Fig. 7 Special marks

one of the Cardinal buoys may be duplicated and fixed with a Radar Beacon (racon). 3. Safe Water Marks Safe water marks serve to indicate that there is navigable water around the mark (Fig. 4). These include centre line marks and mid-channel marks. They may also be used to indicate channel entrance, port or estuary approaches, or landfall. 4. Isolated Danger Marks Isolated danger marks are used to mark small, isolated dangers with navigable water

1096

Navigation of Polar Vessel

Navigation Buoy, Fig. 8 Symbols and abbreviations for light characteristics

around the buoy. Typically used to mark hazards such as an underwater shoal or rock. They are red and black in color (Fig. 5). 5. Emergency Wreck Marking Buoy These buoys mark new wrecks clearly and unambiguously. Used as a temporary response, they are colored in an equal number of blue and yellow vertical stripes and fitted with an alternating blue and yellow flashing light (Fig. 6). 6. Special Marks Special marks are used to indicate a special area or feature whose nature may be apparent from reference to a chart or other nautical publication. Special marks are yellow. They may carry a yellow “X” top-mark and any light used is also yellow (Fig. 7). Uses of special marks include: • Ocean Data Acquisition Systems (ODAS) marks • Traffic separation marks where use of conventional channel marking may cause confusion • Spoil ground marks • Military exercise zone marks • Cable or pipeline marks • Recreation zone marks • Boundaries of anchorage areas • Structures such as offshore renewable energy installations • Aquaculture In addition, each type of mark has a distinctive color, shape, and possibly a characteristic light (see Fig. 8).

References CIL, Commissioner of Irish Lights. https://www. irishlights.ie/. Cited on 15 Aug 2018 IALA, website: http://www.iala-aism.org/. Cited on 15 Aug 2018 Website: https://www.ybw.com/features/navigationessential-buoys-marks-8611. Cited on 15 Aug 2018

Navigation of Polar Vessel Jianhua Cheng and Jing Cai College of Automation, Harbin Engineering University, Harbin, China

Introduction In terms of geodynamics, meteorology, hydrology, and geography, the polar regions are too unique to lead to the normality of the conventional navigation methods commonly used in the lowmedium latitude. Therefore, it is impossible to reach the predetermined destination safely, accurately, and effectively for the carries and the individuals. With the further exploration of polar natural resources, the researches corresponding to the polar navigating methods have already been becoming a critically significant part of safe voyage in polar regions. Firstly, the article defines the polar region and polar navigation. Then, the challenges easily encountered by conventional navigation methods are

Navigation of Polar Vessel

analyzed. Finally, the application status of existing methods is introduced in detail.

Introduction of Polar Navigation Individuals and carriers, such as vessels, aircrafts, spacecrafts, terrestrial vehicles, etc., utilize the electric, magnetic, acoustic, optical, mechanical, and other methods in the polar regions. And, the target is to locate the moving body by measuring the corresponding kinematic parameters and then to guide it from one point to the destination along the predetermined route safely, accurately, and economically, which is called polar navigation. Baidu Baike proposes the definition of the polar navigation: navigation in the Antarctic and the Arctic. However, the definition of polar regions corresponding to navigation differs from it defined by the geographic circle of the Antarctic and the Arctic. Hitherto, these two definitions have not agreed with each other yet. In Advisory Circular (issued on June 13, 2018), Federal Aviation Administration (FFA) defines the polar region for aviation navigation. 78
N and more is the Arctic region; 60
S and more is the Antarctic region. This is the most authoritative definition of polar regions. Nowadays, the ice sheet in the Arctic and the Antarctic is melting rapidly along with global warming. With the background of economic growth and regional integration, polar regions weight heavily on aspects of strategy, economy, science, environmental protection, marine channel, natural resource, etc. With the geospatial advantages in military, resource exploration, and marine transportation, the polar area significantly values in sustainable economic development and national security. Therefore, the polar regions place the pivotal position in marine exploration and probe. However, due to the special geographic location and natural environment in the polar regions, the navigation methods, such as radio, satellite, geomagnetic, inertial, and celestial navigation, cannot work properly, which are commonly used in the low-medium latitude. For example, polar regions are near the South Pole

1097

and the North Pole of the earth. Its unique location causes the convergence of geographic meridians at the geographic poles. Because of the acute convergence of meridian, it is significantly hard to define the heading, relative to the meridian. Moreover, all directions are even toward the south, overhead the North Pole. That, mentioned above, directly restricts the application of the traditional mechanism of the inertial navigation system in the polar regions. The geomagnetic poles are also located in the Arctic and the Antarctic. Its characteristics are the weak horizontal component of the geomagnetic field and the large change of magnetic variation over a large part of the polar regions. Then, it leads to the incapability of the magnetic compass to show reliable directions. Another factor is the abominate and capricious polar natural environment, such as geomagnetic storm, polar day and night, etc., which totally differs from the low-medium latitude. The working characteristic of navigation systems will change and even fail to perform properly. For instance, in polar regions, the ionospheric scintillation frequently occurs. The magnetic storm and solar flare periodically happen, directly triggering the cutoff effect. It is prone to affect the positioning capability of satellite navigation. Radio navigation requires an arrangement of navigation stations on the ground. However, because of polar landforms and climate conditions, its arrangement is restricted. Thereby, applications of radio navigation are limited as well. Besides, wind and low visibility of polar regions, as the major meteorological factors, limit the implementation of landmark navigation technique, visual navigation technique, and celestial navigation technique (Maclure 1949; Qi-Ju et al. 2014). Navigation technology has always been a critical warranty for the safe and economic navigation of civil vehicles, while the development of polar navigation technology strongly supports the feasibility of polar navigation. In August 21, 1914, Y.I.Nagurskiy, the Russian Royal Navy Captain, flew to the high latitude for the first time. In 1945, Aries I completed the mission of aviation toward the North Pole. So far, western developed countries, especially in Europe and

N

1098

America, and Russia already have a much more perfect strategy to aviate in the polar regions and even through at the poles. In 2001, it indicates that the polar navigation technology has already matured in Europe and America, when Boeing opened a polar commercial airline connecting North America and Asia. The latest models of large active commercial aircrafts, belonging to Boeing and Airbus, are able to achieve global flight. IRS (inertial reference system) is equipped as the main navigation system when flying over the polar regions. In addition, attribute to the Russian research about the polar navigation, its polar navigation technology grows more and more maturely. Due to the huge potential of polar routes, 2001 China Eastern Airlines 2350 Airbus A340 aircraft, Boeing 777-21BER B-2055 aircraft of China Southern Airlines was trialed for the polar flight. At present, Chinese scientific research ship “Xue Long” has completed eight times scientific research missions in the Arctic. Obviously, during the polar region navigating, polar navigation technology plays a critically important role. It can not only determine the location of the vehicle itself and its destination but also reduce the frequency of the accident occurrence.

Polar Navigation Methods Along with the improvements and developments of polar navigation until now, the common navigation methods include: Inertial Navigation The earliest application of the polar inertial navigation could date back to 1958. American “Nautilus” nuclear submarine, equipped with N6A inertial navigation system, sailed underwater for 21 days and succeed to cross the North Pole. Its voyage is 8146 nautical miles, while its positioning error is only 20 nautical miles during the whole sailing (Lyon 1984). Compared with traditional navigation methods, like electromagnetic navigation technique, and traditional navigation methods, the polar inertial navigation technology has the advantage of stable

Navigation of Polar Vessel

performances in the harsh polar environment. And it is proved to be an optimal strategy to sail toward and in the polar regions. The inertial navigation systems can be arranged by different mechanisms. The mechanism propagated in the east-north-up frame is easy to understand and clear to physically expressed. However, its shortcomings in the polar regions are to hardly apply torques on azimuth gyro, to overflow in the system computer calculation, and to amplify errors of positioning parameters. To solve its problems, the inertial navigation mechanism proposed in wander angle frame can avoid the overflow caused by convergence of polar meridians. This mechanism was adopted by the early LN-51 aviation navigation system (DelCore and Nascro 1986). However, as for the wander angle introduced purposely, its error is also amplified with the increase of the latitude. Meanwhile, the position extracted from the cosine direction matrix (CDM) is almost singular, when it is very close to or just at the pole. Thus, the system performs badly. For solving problems of the wander angle frame in the polar regions, the mechanism of the earth-centered earth-fixed coordinate system (ECEF), grid coordinate system (Ignagni 1972), and transverse coordinate system (Dyer 1971) can be adopted reasonably. They are all with abilities of global flight, further to achieve polar navigating. In 1958, “Skate” nuclear submarine and “Sargo” just utilized the grid inertial navigation system and completed polar navigating missions. The MAPS inertial navigation device of Honeywell is used by the National Defense Department of Canada for autonomous navigation in the high latitude (84
N). The Russian Vega-M inertial compass system is able to guarantee the medium-precision output of attitude and heading between 85
S and 85
N. The icebreaker, equipped with the Vega-M system, arrived at the area of 89
N in 2003. It is proved that, when the operation exceeds the range of the system, the navigation errors will surge obviously (John et al. 2003). Satellite Navigation At present, four major global satellite navigation systems are GPS of the United States, GLONASS

Navigation of Polar Vessel

of Russia, Galileo of Europe, and BDS of China. In the polar regions, the arrangement of the satellite navigation system constellations directly affects the positioning accuracy. BDS is mainly a high-orbit satellite, mainly above the Asia-Pacific. The average number of satellites over the medium-high latitude is about two, less than GPS, Galileo, and GLONASS. Its geometric arrangement is poor, and then positioning precision descends sharply. The number of visible satellites of GPS changes little with the latitude and longitude, all about 8–10 satellites. So is in the polar regions. The number of visible satellites of Galileo in the polar regions is always more than four. Moreover, with the completion of the full constellation in 2018, the number of its visible satellites in the high latitude will be more than that of GPS. Because Russia is located at the highlatitude area, the GLONASS is designed to place more satellites in the high-latitude region. So the number of visible satellites in the polar regions is the largest. Besides, its satellite inclination is the highest, which results in a better performance of constellation geometry in high latitude. Although more visible satellites are distributed in polar regions with the comparison of the low-medium latitude, most satellite’s elevation angle is relatively low. In addition to constellation distribution, the tropospheric delay is another key factor for satellite positioning. The related research confirms that the tropospheric delay influences more on the observation of satellites of a low elevation angle. The polar ionosphere scintillation occurs frequently, while the daily fluctuation of the total electron content (TEC) is more fierce than lowmedium latitude. Besides, due to the uniqueness of polar regions, it is hard to use satellite-based or ground-based augmentation systems to modify the positioning accuracy. For example, for satellite-based systems like EGNOS and WWAS, the polar regions cannot be covered by the geostationary earth orbit (GEO) satellites, only seen in part of regions and time. For ground-based augmentation systems, there have been a few observation stations in polar regions. Meanwhile, the harsh environment condition makes the establishment of longtime stations difficult, like lack of support of

1099

sustainable energy and chain of real-time communication, etc. (Yuanxi and Junyi 2016). Therefore, the positioning performance of the satellite navigation system in the polar area is at subpar levels. Celestial Navigation Same as the polar inertial navigation technology, the polar celestial navigation technology is also autonomous. The polar celestial navigation technique uses the star sensor to track the relative celestial bodies’ position in space, in which it is an accurate and passive system. Then, the navigation computer can calculate the navigation information through observed parameters. The advantage is that it is not influenced by the magnetic field deception jamming and has a good performance of concealment. Thus, since the development of the star sensor in the1990s, it has been widely used in the military and civil (van Bezooijen 1994) and has increasingly played a key role in polar navigation as well. Even under some specific conditions, it is the only method that can be relied on. However, the special sailing conditions in the polar regions restrict the operation of polar celestial navigation technology to a certain extent. Especially the polar navigators might be caught in the long twilight which may last for several days, when neither sun nor stars are available. Meanwhile, because the update rate of the celestial navigation system is low, it lacks the capability of the provision of real-time navigation information. Thus, it is usually an adding method to correct accumulative errors of the inertial navigation system for autonomous, high-precision, and long-time navigation. It has been confirmed that the careful dead reckoning and hourly celestial bodies’ observations are sufficient for reasonably accurate navigation (Molett 1954). Taking the American air force as an example, it has been contributing to this kind of research since the 1950s, such as the NAS-26 inertial/celestial integrated navigation system in the 1980s and the SAIN strapdown inertial/celestial navigation system in the 1990s. They are all the typical airborne inertial/celestial integrated navigation products (Ming 2019).

N

1100

Underwater Acoustic Navigation Polar underwater acoustic navigation technology helps increase the transparency of underwater space and enhance the survival ability of underwater vehicles. Research in navigation and localization algorithms, along with advances in acoustic positioning and seafloor relative Doppler velocity log (DVL) measurements, has significantly advanced the state of the art over the past two decades. However, operating in the polar regions presents unique challenges – first and foremost that surface roughness interacts with wind and current due to the polar sea ice, which tends to form underwater noise easily. The noise will extremely limit the performance of the sonar. Moreover, polar seafloor conditions are more unpredictable and severe. Under the unknown underwater condition, it is difficult for acoustic signal beacons to be installed and arranged all over the seafloor. By this very existence, vehicle and ship are hard to access to the free surface and, therefore, require fundamental changes in the methods of operation. At the same time, the navigation methodology employed must be modified as well (McFarland et al. 2015). In order to extend the voyage, Russia, America, and other countries are all active to develop innovative underwater acoustic navigation systems to adapt to the special underwater sailing circumstance in the polar regions. For example, Russia actively explores an innovative underwater acoustic navigation system, composed of the GLONASS navigation system, sonar buoy, and unmanned underwater vehicles. And, the system is located on the continental shelf of the Arctic Ocean of Russia. Integrated Navigation In order to further improve the accuracy and reliability of navigation, the vehicle can adopt a combined working mode as the integrated navigation, which means that it takes one of the navigation methods as the dominant with the aid of various navigation systems. Thus, the integrated navigation system can suppress respectively systematic errors contained in each system to achieve accurate positioning and navigating. Considering the mature technology of the integrated navigation of the foreign underwater

Navigation of Polar Vessel

vehicles, the integrated navigation system is mainly the strapdown inertial navigation system plus Doppler sonar. Its positioning accuracy can reach 0.01% of its voyage. For example, with the aid of the same Doppler velocity log (DVL), one underwater vessel of the Bluefin Robotics Company of the United States carries the laser inertial navigation system, while another takes optical fiber inertial navigation system for the sea trial. And its results demonstrate that both two systems have relatively high precision (Tal et al. 2017). Because the performance of celestial navigation will be interrupted by the polar environment, it always collaborates with the inertial navigation system. For instance, the LN-120G inertial/celestial integrated navigation system of the United States can globally navigate. It is with capabilities of fully autonomous, highprecision, and long-time navigation. Its positioning precision even reaches 0.5 nautical miles per 18 h (https://www.northropgrumman.com/Capa bilities/LN120GStellarInertialNavigationSystem/ Pages/default.aspx). Until now, China has been also active to develop the integrated navigation system to adapt to polar navigation. For example, “Yong Sheng” owned by China Ocean Shipping (Group) Company (COSCO) first voyaged successfully through the Arctic in 2013. The GPS compass equipped on the ship is the highprecision integrated navigation system. The system is improved by the fusion of dual antenna azimuth solution technology of GPS and fiber optic gyroscope technology.

Cross-References ▶ Polar Acoustics

References DelCore G, Nascro V (1986) A world-wide mechanization in inertial navigation systems[J]. J Navig 39(3):441–445 Dyer GC (1971) Polar navigation – a new transverse Mercator technique. J Navigation 24(4):484–495 Ignagni MB (1972) An all-earth inertial navigation scheme. Navigation 19(3):209–214

Net Structures: Biofouling and Antifouling John S, Ab C, Eaton G et al (2003) Use of an autonomous underwater vehicle for environmental effects monitoring[C]. In: Proceedings of unmanned untethered submersible technology Lyon W (1984) The navigation of Arctic polar submarines [J]. J Navig 37:155 Maclure KC (1949) Polar navigation. Arctic 2(3):183–194 McFarland CJ, Jakuba MV, Suman S, Kinsey JC, Whitcomb LL (2015) Toward ice-relative navigation of underwater robotic vehicles under moving sea ice: Experimental evaluation in the Arctic sea, 2015 IEEE International Conference on Robotics and Automation (ICRA), Seattle, WA pp 1527–1534 Ming T (2019) Review of polar integrated navigation algorithm. J Phys Conf Ser 1213(3):032017. IOP Publishing Molett WE (1954) Recent developments in polar navigation. Navigation 4(3):118–121 Tal A, Klein I, Katz R (2017) Inertial navigation system/ Doppler velocity log (INS/DVL) fusion with partial DVL measurements[J]. Sensors 17(2):415 van Bezooijen RW (1994) True-sky demonstration of an autonomous star tracker. In: Acquisition, tracking, and pointing VIII, vol 2221. International Society for Optics and Photonics, Orlando, FL, United States pp 156–168 Yuanxi Y, Junyi X (2016) Navigation performance of BeiDou in polar area. Geomatics and Information Science of Wuhan Univers 41(1):15–20 Zhu QJ, Qin YY, Zhou Q (2014) Summary of polar air navigation[J]. Meas Control Technol 33:5–25

Navy Oceanographic Meteorological Automatic Device ▶ Wave Measurement Buoy

NC (Numerical Control Cutting) ▶ Introduction to Shipbuilding (Shipyard)

Neighbor Discovery ▶ Underwater Acoustic Sensor Network

1101

Net Hydrodynamic Characteristics ▶ Net Structures: Hydrodynamics

Net Present Value (NPV) ▶ Christmas Tree

Net Structures: Biofouling and Antifouling Hailong Zhang and Ting Qu National Engineering Research Centre for Marine Aquaculture, Institute of Innovation & Application, Zhejiang Ocean University, Zhoushan, China

Synonyms 2,3,5,6-tetrachlora-4-methylsulfonyl (TCMS); 2thiocyanomethylthiobenzo-thiazole (TCMTB); Dissolved oxygen (DO); International Maritime Organization (IMO); Netpen liver disease (NLD); Tributyltin (TBT)

Definition Biofouling, i.e., marine biological fouling, corresponds to the accumulation of microorganisms, plants, and aquatic animals on artificial surfaces immersed in seawater. Biofouling is an ocean phenomenon and an important scientific and technical term to understand what happens to artificial surfaces in seawater while exploiting ocean resources in terms of the following in aquaculture and mariculture: the biofouling community, fouling community, and foulant communities; the foulant, fouler, and fouling organisms; pens, artificial structures enclosed on all sides with the bottom formed by the sea bed, or cages, artificial

N

1102

structures enclosing all submerged surfaces; the stocking density, the amount of fish in the cage or the total number of fish inside; and the mesh occlusion and mesh plugging abundance of fouling organisms.

Scientific Fundamentals The structure, composition, and large surface areas of netting materials, especially multifilament meshes, are highly suitable for the colonization and development of biofouling (Ashraf et al. 2017). Biofouling often develops rapidly because the seawater surrounding aquaculture operations is enriched by inorganic and organic wastes (food residues, feces, and excretory material) generated by high-density fish populations (Navarro et al. 2008; Sanderson et al. 2008). The increases in carbon, nitrogen and phosphorus in the seawater surrounding mariculture farms facilitate the growth of annual filamentous algae (Ruokolahti 1988). The rapid growth of fouling in eutrophic seawater leads to the complete blockage of the netting mesh within 2–3 months (Neori et al. 2004). The biofouling of fish-cage netting can lead to significant operational problems in aquaculture. Mesh plugging and the resulting restriction on water exchange adversely influence the health of fishes owing to the reduction in dissolved oxygen (DO) and the accumulation of metabolic ammonia. Fouling is an additional concern because it significantly decreases cage flotation, increases structural fatigue and cage deformation, and may act as a reservoir for pathogens (Amaraa et al. 2018). The impacts of fouling vary dramatically depending on the season and location and are also influenced by the farming methods and practices. The fouling of mariculture structures differs from that of many other marine industries, in particular, marine transport, in terms of the surface characteristics; specifically, the surface is rough, and consequently, the surface area is large (Bixler and Bhushan 2015). Moreover, the fouling of mariculture structures is not subject to the high water velocities and shear forces associated with ship hulls or the internal surfaces of pipes. Early

Net Structures: Biofouling and Antifouling

studies on the fouling on mariculture netting showed that the netting material and mesh size significantly affected the fouling rate, mesh occlusion, and density and abundance of fouling species (Rothwell and Nash 1977). According to these data and observations of mesh deterioration, materials were rated for their suitability in the construction and maintenance of fish cages. More recently, the effects of the net angle and microfouling development on multifilament meshes (Corner et al. 2007) were investigated. However, due to the importance of the aquaculture industry in global economic development, the number of studies on the impact of marine biofouling in all forms of aquaculture is limited and often disparate and sparse.

Development of Biofouling in Mariculture In intensive commercial mariculture, multifilament netting bags or cages suspended from a floating frame are usually utilized. In particular, high standards of water quality must be maintained through water exchange, which depends on the speed and direction of water flow, which is affected by the salinity, temperature, and topography of the site (Beveridge 2004). The key nature of water exchange renders the influence of biofouling critical on all forms of aquaculture, especially cagebased aquaculture. The main effect of biofouling on cages is to restrict the water current, the effect of which increases as the biofouling communities develop from a biofilm to a complex threedimensional climax community dominated by sessile invertebrates. The development and composition of fouling communities on fish cages has been investigated for many types of mariculture (Cronin et al. 1999; Greene and Grizzle 2007). Multifilament mesh materials are generally regarded ideal fouling surfaces, and the succession of organisms attached to aquaculture networks has been specifically evaluated (Svane et al. 2006). Even after immersion for a short period of time, for instance, less than a month, macroalgae are usually found to be the most serious type of foulants on cages (Hodson

Net Structures: Biofouling and Antifouling

Net Structures: Biofouling and Antifouling, Fig. 1 Hydroids fouling a testing net in Zhoushan during late summer. Hydroids are common and problematic fouling organisms, which are hard to dislodge and regenerate rapidly. These organisms reduce the flow and oxygen levels within cages, and constant management is required to prevent their impact on the growth and survival of cultured fishes in the cage. (Photograph by Hailong Zhang)

and Burke 1994). In contrast, several other marine organisms, such as bivalves, ascidians, and hydroids (Fig. 1), may be the predominant foulants on cages after immersion for longer periods, although these organisms may also cause serious fouling problems even in a brief period, especially during periods of high larval settlement (Greene and Grizzle 2007). Variation in Biofouling Between Sites: On a large scale, considerable differences exist in the biofouling between sites, for example, between temperate and tropical waters (> 1000 km). However, spatial variation also occurs on a smaller scale (< 100 km). The differences in sites may represent variations in the environmental conditions, such as differences in the seawater quality, salinity and temperature, as well as differences in the abundance of larval stages (Santhanam et al. 1983). For instance, the fouling communities on polyethylene netting differ between cages immersed in brackish and marine waters. Cages in brackish water (24.5–33.8%) are usually colonized by the algal genera Enteromorpha and Ectocarpus. However, the cages in marine conditions (36%) are usually colonized by a more diverse community, including bivalves, sea anemones, solitary and colonial ascidians, algae (Caulerpa spp., Codium

1103

sp., and Gracilaria sp.), amphipods, barnacles, and polychaetes (Santhanam et al. 1983). The Variation in Biofouling Within Sites is mainly driven by the effectiveness and availability of light and water flow, which are related to the depth and orientation of the cage (Cronin et al. 1999). The differences in the photosynthetic biomass between the cage sides are detectable only near the surface where light intensity variation is most pronounced; for instance, the significant fouling changes that occur at a depth of 0.5 m become nonsignificant at a depth of 2.0 m. Overall, the fouling mass decreases significantly with increasing depth. The direction of immersed surfaces affects the development of fouling organisms, and a significant difference exists between vertical and horizontal substrates. This aspect was demonstrated in a comparison of vertical and horizontal net panels. The vertical panels fouled more rapidly, developed a greater fouling biomass, and exhibited an increased abundance of compound ascidians and tubeworms. However, barnacles and oysters were found to be more abundant on the horizontal frame (Cheah and Chua 1983). The increase in biomass on the vertical panel was believed to reflect a greater interception of horizontally moving planktonic larvae, which increased the larval settlement. However, an increase in collisions with suspended material increases the nutrition of filter-feeding organisms. Compared with the vertical surface, communities on the horizontal surface are more prone to siltation and predation, and vertical or stacked species are favored. However, on vertical surfaces, in which critical competition for space occurs and the predation pressure is less, colonial growth is more effective (Harris and Irons 1982). In addition, the relative abundance of individual bivalves was observed at the bottom of a cage, and more individuals were observed to grow on the outer than on the inner surfaces of a cage (Lee et al. 1985).

Netting and Biofouling Because the waters around mariculture sites are rich in organic and inorganic wastes produced by

N

1104

high-density fish populations, biofouling usually occurs extremely rapidly. The fouling of mariculture structures is different from that of structures in many other marine industries, especially marine transportation, because of the rough surface and high surface area. Moreover, such fouling is unaffected by the high flow velocities and shear forces associated with the surface of ship hulls and the inner surface of pipes. Early studies on the surface fouling of mariculture cages showed that cage materials and mesh sizes considerably influence the fouling rate, mesh occlusion, and density and abundance of fouling organisms (Rothwell and Nash 1977). Based on these data and the observed mesh deterioration, materials are evaluated to determine their suitability for the construction and maintenance of fish cages. Recently, the influences of the mesh angle and development of microfouling on multifilament mesh have also been investigated (Corner et al. 2007). Influence of the Mesh Size of a Cage In commercial fish farming, a variety of mesh sizes are adopted, ranging from 12–40 mm, 60–90 mm, and 100–150 mm for salmon cages, bluefin tuna cages, and predator fences, respectively. Larger grids usually have thicker gauges; however, a smaller mesh size corresponds to a larger surface area per square meter. Therefore, smaller grids usually incur more fouling organisms and total biomass. In general, the fouling rate, fouling quality, species diversity, and species richness increase as the grid size decreases (Cheah and Chua 1983). Consequently, to maintain acceptable water exchange, small grid nets must be cleaned more frequently than larger nets. High sediment loading does not require an excellent substrate for the settlement and growth of foulants because the accumulation of silt makes the surface of the multifilament mesh rougher. Thus, the grid size and total surface area are believed to interact and influence the development of biofouling. Influence of the Mesh Structure The distribution and type of the initial fouling process were reported to be influenced by the micromorphology of the multifilament mesh

Net Structures: Biofouling and Antifouling

(Hodson and Burke 1994). The cylindrical shape of the grid strip resulted in different light intensities on the upper and lower surfaces of the horizontal submerged grid strip. Therefore, a community of phototrophic organisms (such as diatoms) formed on the upper surface of the horizontal strip, and a heterotrophic protozoan community developed on the lower surface. The large crevices and many filaments on the surface of netting rope are likely to contribute to the attachment of fouling organisms, either because of the entrapment of suspended matter or because several larvae of fouling invertebrates and spores of common fouling organisms preferentially settle in small depressions. For many organisms, a preferred settlement size exists, which may affect the community composition of micro- (Scardino et al. 2006) and macrofoulants (Scardino et al. 2008). The three-dimensional structure of a net mesh directly affects the development of fouling on netting. The occurrence of biofouling attachment has been noted to be preferential at grid intersections (Tseng and Yuen 1979); for instance, researchers observed the appearance of a large aggregation of mussels at the intersection and the presence of bryophytes, barnacles, and green algae mainly at the intersection. This preferential attachment is presumably due to the larger surface area and turbulence changes in certain sea areas. Influence of the Mesh Material A number of suitable materials have been employed for the construction of fish cages. These materials have different degrees of antifouling capabilities. In this respect, some studies have proven the relative capacity of many types of netting: multifilament polymer nets, extruded polymer meshes, metallic hardware cloths, and extruded metal meshes. After examining ten mesh types, polymer-fiber nets and galvanized meshes were found to be the most and least vulnerable to marine fouling, respectively. After 4 months of immersion, the polymer fiber mesh was completely blocked by the growth of marine organisms (Fig. 2), and the weight of the test panel (0.4 m2) increased from 5.5 kg (clean) to more than 15.5 kg. In contrast, a

Net Structures: Biofouling and Antifouling

1105

same as that immersed for 2 months, although the weight of the former will be doubled (Cheah and Chua 1979). Nevertheless, large amounts of silt are often deposited and associated with those biofouling communities. For example, one study reported that 58% of the total fouling biomass with an area of 4.5 kg/m2 is silt (Lee et al. 1985).

Impact of Biofouling on Mariculture

Net Structures: Biofouling and Antifouling, Fig. 2 Settlement of marine organisms on the small mesh net. As a monospecific group, hydroids usually breed rapidly, increasing the weight of nets, and can easily block the water flow through nets of small mesh sizes. (Photograph by Hailong Zhang)

reasonable flow of water passed through the galvanized material mesh, and the weight of the panel increased from approximately 7 kg to 9 kg. Furthermore, nylon and polyethylene meshes were found to foul at a significantly greater rate than metal meshes. In addition, the polyethylene mesh and galvanized mesh exhibited the greatest and least fouling, respectively, after 5 months (Rothwell and Nash 1977). In addition, the fouling community composition differed among various grid types. First, algae propagated on most nets but became most abundant on nylon nets and nets with ineffective antifouling paints. All the panels were rich in serpulid tubeworms; however, these organisms were not widely observed on extruded polymer mesh- and PVC-coated chain links, on which barnacles were abundant after 5 months (Rothwell and Nash 1977). According to this discussion, the material, mesh structure, and mesh size of cages have important impacts on the biofouling rate, mesh blockage, and fouling biological density and quantity. Fouling communities in cages are usually developed and characterized by a large quantity of biomass. For example, the species composition of a biofouling community immersed in seawater for 4 months is almost the

Factors Limiting Water Exchange The main concerns pertaining to fishnet cage fouling relate to the mesh blockage and change in the water quality due to the limitation on the water flow. The water exchange inside and outside the cage is influenced by the external velocity (Edwards and Edelston 1976) and the angle between the mesh and flow (Gularte and Huguenin 1984). The differences in transmission measurements may be due to the methods used to quantify the flow, the stocking density of the cages, and the circulating flow generated by the fish. The transmission of a clean net is related to the mesh size and usually varies between 50% and 80%. Due to the biofouling of the mesh and the grouping of the cages, the transmission decreases significantly. After 52 days, 80 days, and 120 days in the ocean, the transmission rate (57.5%) of a clean 13 mm mesh decreased to 23.4%, 18.7%, and 13.1%, respectively, with the corresponding fouling biomass weights being 1.85 kg/m2, 2.84 kg/m2, and 4.98 kg/m2 (Wee 1979). When three 9 mm mesh cages were placed parallel to the flow, the flow decreased in a serial manner, and the transmission rate decreased from 70% for the first cage to 35% and 18% for the second and third cages, respectively (Inoue 1972). As the cages were arranged in a series and the netting became fouled by marine organisms, these two effects dramatically reduced the exchange of water (Aarsnes et al. 1990). Hence, grouped cages are suggested to be oriented perpendicular to the current, with no more than two or three cages in a series being placed parallel to the current (Beveridge 2004). In the fish farming industry, a common practice is to increase the size of the net pen and place large

N

1106

nets in the sea throughout the production cycle (Sunde et al. 2003). In this scenario, the effects of biofouling on the water exchange and net deformation are expected to become more severe because larger cages and nets have smaller surface area to volume ratios than smaller nets, resulting in lower water exchange rates (Lader et al. 2008). Factors Limiting Water Quality Water exchange is essential to replenish dissolved oxygen and remove excess feed and waste materials to maintain the water quality. Many studies have demonstrated a decrease in the oxygen concentration from the outside to the inside of cages and clarified the relationship between the oxygen reduction and short-term water exchange (Wee 1979). In addition, an increased stocking density increases the oxygen consumption inside cages (Kadowaki et al. 1978). Therefore, combined with low current flow and significant mesh blockage and a high density of fish, dissolved oxygen may rapidly decrease to critical levels (Edwards and Edelston 1976). Kennedy et al. (1977) reported the mortality of fish due to anoxia in severely fouled cages, in which the dissolved oxygen (DO) concentration was less than 4.0 mg/L. Low water exchange was found to directly cause this low DO concentration in the cages. After installing a clean net, the concentration of DO increased to 8.25 mg/L. For salmon aquaculture, the oxygen concentration is recommended to be greater than 7 mg/L; notably, a concentration less than 5 mg/L will have a negative impact on the growth and respiration of fish, and a concentration less than 2 mg/L will lead to mortality (Boyd 1982). Many factors contribute to the total supply and consumption of DO in the cage (Silvert 1994; Cronin 1995). In particular, oxygen supply occurs primarily through water exchange but also through the photosynthesis of foulant communities and atmospheric diffusion. Although oxygen is mainly consumed by fish, to some extent, it is also consumed by the biochemical oxygen demand of the immediate environment and fouling communities. The maximum stocking density of fish depends almost completely on the exchange of water and can be calculated

Net Structures: Biofouling and Antifouling

according to oxygen consumption and the oxygen supply rate. Although the oxygen levels in cages are mainly controlled by the water exchange, the production or consumption of oxygen by the fouling community can affect the oxygen concentration (Cronin et al. 1999). Reduced water exchange may also affect the fish health, as the ammonia levels in cages may increase compared to those of the surrounding waters. Factors Influencing the Fish Disease Risk Biofouling has been reported to be a risk factor. Fouling communities may pose health risks to cultured fish species because they can act as reservoirs for pathogenic microorganisms that exist within large fouling species or in a wide range of microbial communities on cage netting (Meyers 1984). Marine aquaculture may lead to unusual parasitic infections caused by farming in new geographic areas or in net pen environments (Kent 2000). The occurrence of caged fish diseases is also linked to the consumption of fouling organisms by cultured fish species (Andersen et al. 1993). Fouling communities may directly affect fish by causing physical damage to the cultured species. Moreover, a severely fouled net can also support the existence of the free swimming stage of sea lice (Lepeophtheirus salmonis) (Kent et al. 1995). Nevertheless, biofouling organisms may also reduce the disease risk. The potential for the mussel Mytilus edulis to harbor bacterial kidney disease makes the survival of the bacterium Renibacterium salmoninarum unlikely. These mussels kill the majority of R. salmoninarum during digestion and may reduce the level of pathogenic bacteria in the cage environment (Paclibare et al. 1994). Cage Deformation and Structural Fatigue Exposure to currents causes net cages to change their shape through deflection and deformation (Fredheim 2005). The extent of this shape change depends on the flow velocity, the original shape and construction of the cage, the placement of weights, the type of net, and the degree of biofouling (Lader et al. 2008). An increase in mesh occlusion will significantly increase the drag

Net Structures: Biofouling and Antifouling

forces on mesh netting. Milne (1970) measured the current forces on clean and fouled nets under different current velocities and showed that the forces on a fouled net may be 12.5 times greater than those on a clean net. Consequently, unless the cage is heavily weighed, the shape of the cage may be severely distorted by the current flow (Osawa et al. 1985). Aarsnes et al. (1990) calculated the deformation rate of a 12,000 m3 cage with a bottom weight of 400 kg and found that the cage volume was reduced by 45% (to 6600 m3) and 80% (to 2300 m3) under velocities of 0.5 m/s and 1 m/s, respectively. Wee (1979) observed a 50% reduction in the volume of a heavily fouled cage in use. Reducing the cage volume may affect the fish health, as the oxygen consumption and ammonia production are expected to increase per unit volume and crowding is likely to stress the cultured fishes. Lader et al. (2008) analyzed the influence of incoming currents of varying velocities on the deformations of net cages. They found that a current velocity of 0.35 m/s resulted in a 40% reduction in the cage volume. Highly deformed nets increased the structural stress of the cage. Although increasing the cage weight could reduce the deformation, the structural stress will increase (Anon 1993). Tomi et al. (1979) indicated that the weight added to cage corners caused a two- to sixfold increase in the horizontal forces on the cage. Specifically, with heavy weighting, waves cause the floating frame to move upward, and the weight pulls the net down. The structural loading and fatigue may further increase when predator netting is attached to cages. The biomass of the fouling community usually directly impacts the static load of net cages, which may increase the weight of cages by a factor of 200 (Beveridge 2004). This additional load must be considered in the design of floating and mooring systems. Failure to do so may incur net failures or breakage, which have been devastating for commercial mariculture (Huguenin 1997). In addition, Swift et al. (2006) measured the increase in the fluid resistance in net cages due to biofouling. Biofouling resistance coefficients generally increase with increasing solids (ratio of projected area to defined area) and biomass, and the

1107

resistance of fouled nets may be more than three times that of clean nets. Summary of Biofouling Impacts Biofouling in marine cages can lead to mesh clogging, resulting in decreased productivity and health risks to fishes as well as structural fatigue and cage deformation. Furthermore, biofouling is a critical management issue. If the impact of biofouling is not adequately considered, the costs of operation and maintenance will increase. Surprisingly, there is little information about the effects of fouling, a problem of such high impact, and this aspect is only now beginning to be discussed in detail. Considering the limited products available to control aquaculture fouling, a quantitative study of the spatiotemporal variation of biofouling communities at the species level, as well as the impacts of animal husbandry and farm management on fouling development, can help the mariculture industry to choose the most cost-effective fouling control method. The rapid development of cage aquaculture in tropical and subtropical areas, in which biofouling occurs most rapidly, and the shift to offshore cage mariculture with limited coastal space poses new challenges to understanding the impact of biofouling, especially to implementing successful marine fouling control strategies.

Principles of Controlling Biofouling Physical Approach In view of the serious impact of biofouling in commercial fish farms employing cage culture, protective measures typically involve a variety of methods to control net fouling, usually including the utilization of farm management techniques, namely, frequently changing and cleaning the netting, and the use of antifouling coatings. In the following, these methods are reviewed along with the upcoming options for the nonbiocidal control of biofouling in marine aquaculture. This aspect is particularly important because of the restrictions on the application of traditional metal-based coatings in the aquaculture industry.

N

1108

Net Changing In almost all parts of the world, fouling develops rapidly at a certain stage in use. Frequently replacing and cleaning nets are essential practices to maintain water exchange within cages. The replacement rate of a large mesh cage is relatively low because critical mesh blockage or occlusion occurs only under a considerable amount of biofouling. Although nets are frequently changed in temperate and tropical regions, cages immersed in offshore locations and extremely cold water can be immersed in water for a considerably long period without cleaning. Moreover, the cleaning frequency can be delayed to a certain extent by raising the top several meters of the cage above the water surface (Needham 1988); however, this technique is only applicable to the case in which the fouling is limited to the upper area of the cage. Net changing may incur considerable costs in mariculture, and it is necessary to purchase a large number of nets and support dedicated net replacement and cleaning teams. In addition, frequent net changes may result in the damage or loss of fish in the cages and interrupt or disturb feeding, which may reduce the fish growth rate. However, the economic impacts of fouling and fouling control on the aquaculture industry cannot be quantified at present. Shore-Based Net Cleaning Usually, biofouling communities are removed from netting cages by replacing the fouled nets and transporting them to the shore for manual or semiautomatic cleaning (Lewis 1994a). However, the frequent replacement of nets in standard floating cages is labor- and capital-intensive, and large-scale cages require marine hydraulic cranes. Furthermore, washing procedures and the handling of nets often cause damage to nets and shorten their service life. Underwater Net Cleaning Underwater cleaning is feasible and commercially plausible; however, this approach usually requires diving, and thus, it is more expensive and dangerous than shore-based cleaning. An Australian company tested the efficacy of an underwater net cleaner, which could prevent biofouling for

Net Structures: Biofouling and Antifouling

10 weeks in summer (Hodson et al. 1997). However, due to physical constraints, the fouling organisms in the net grid or crevices were not completely removed, leading to the rapid regrowth and recolonization of the fouling organisms. Many cleaning practices have been adopted in Norway. Three main strategies are employed to address biofouling on fishing nets, including cleaning nets onshore and in situ. Copper-based coatings are also used on cage netting in combination with regular on-site cleaning.

Biological Control Increased profitability and sustainability can be achieved through the smart use of herbivorous fish or invertebrates to control biofouling (Beveridge 2004) and the use of benthic/debris feeders to remove uneaten food (Angel et al. 2002). The concept of biological control is limited by the dramatic changes in the fouling types of algae and invertebrates, which indicates that only herbivores and omnivores with extensive feeding habits are successful control agents. Furthermore, continuous grazing may provide a selective environment for nonfood species, and thus, polyculture may only reduce the frequency of net changes. For example, using sea urchins and resident crabs for biological control has been demonstrated to be effective in controlling the fouling of suspended shellfish systems (Lodeiros and Garcia 2004; Ross et al. 2004). In the case of finfish, biological control of fouling has been successful with the coculture of other finfish (Chua and Teng 1980). In salmon aquaculture, detrivorous animals such as red sea cucumbers, Parastichopus californicus, which feed on broken or rotten food, have been shown to effectively reduce the growth of fouling organisms. However, due to the negative effects of wave-generated undulation, sea cucumbers cannot maintain their position on both sides of the cages suspended with buoys, although they can maintain their position in rigid frame pens (Ahlgren 1998). The advantage of polyculture with the sea cucumber is that sea

Net Structures: Biofouling and Antifouling

cucumbers are a key commercial aquaculture product, and there is a large demand for sea cucumbers in Asian markets (Conand and Sloan 1989). Alternative Cage Designs Another alternative to frequent net changing and underwater cleaning is the utilization of totally enclosed rotating cages (Willinsky et al. 1991). Such cages are either horizontally mounted cylinders rotating on a central axis (Menton and Allen 1991) or rectangular boxes with inflatable buoyancy devices at each corner. The rectangular cage rotates gradually by changing the buoyancy of the corners in turn (by inflation and deflation or by displacement and water filling). When using a rotatable cage, no area of the net needs to be immersed for a long time, and the net can be brought to the surface to air dry, thereby killing the attached biofouling. In addition, the cage can easily remove biofouling and help repair the net; moreover, significant growth of biofouling can be avoided by keeping the net immersed for only a short period of time. Blair et al. (1982) noted that a cage rotation of 90
per week was sufficient to keep cages basically free from biofouling. Geffen (1979) reported that cage rotation every 3 days could help keep cages completely clean. Although completely enclosed and rotating cages have many other benefits, such as preventing birds from predation and avoiding storms and ice by cage submergence, rotating cages are not widely utilized. To hold volumes of fish comparable to conventional floating collars with a circumference >90 m, it would be necessary to construct extremely large rotating cages. Furthermore, commercial rotating cages are more expensive than traditional designs, and continuous exposure to direct sunlight can hasten the degradation of nets (Beveridge 2004). Protective Coatings with Antifoulants In the last 50 years, antifouling coatings have been intensively investigated. Chemical antifouling agents in coatings prevent the formation and establishment of marine biofilms through the leaching of bactericide, which can produce a thin layer of toxic solution around the net. Some of the

1109

earliest published cage antifouling tests indicate that the antifouling agent keeps the net completely clean for 5 months, during which the untreated fishing net is completely blocked (Koops 1971). However, only a few antifouling products have been specially designed for aquaculture cages, and the industry has typically learned from other marine industries, especially the shipping industry. Therefore, several antifouling products that contain chemicals and heavy metals clearly recognized as harmful to the environment have been used in the aquaculture industry. Sufficient public concern has been voiced regarding the use of these chemicals in aquaculture, particularly antibiotics and antifouling agents (Costello et al. 2001). Therefore, the broader aquaculture industry, including producers, regulators and research providers, must conceptually and realistically develop a safe industrial alternative. Toxicity of Heavy Metal Organic Compounds Tributyltin (TBT), one of the most widely used and “successful” (in addressing biofouling) antifouling agents on ship hulls since the 1960s (Yebra et al. 2004), is a broad-spectrum algaecide, fungicide, insecticide, and acaricide. Because of its antifouling effect, TBT is also widely used as a cage coating in mariculture. However, the use of TBT antifouling agents has demonstrated several hazards related to toxic coatings in mariculture (Terlizzi et al. 2001). TBT seeped from an impregnated net was recorded in the water around the treated cage (Balls 1987); in addition, the release of TBT from a newly coated cage was measured, with Sn contents of 1 mg/m3, 0.1 mg/m3, and 0.005 mg/m3 discovered after 1 day, 2 weeks, and 5 months, respectively. The use of TBT-impregnated nets in salmon aquaculture resulted in histopathological effects (Bruno and Ellis 1988) and mortality (Lee et al. 1985). Moreover, salmon raised in treated nets could rapidly bioaccumulate TBT. Short and Thrower (1986) reported bioaccumulation after 3–4 days of exposure to 1.5 pg/L. The authors recorded wet weights of 6.4, 1.9, and 0.3 pg TBT/g for the liver, brain, and muscle, respectively.

N

1110

Moreover, TBT antifouling products pose an unacceptable risk to nontarget species, which cannot be identified when introduced in the market. Furthermore, TBT induces sexual aberrations in gastropods (Gibbs et al. 1991) and has since been found in fish, bivalves, seabirds, and marine mammals (Terlizzi et al. 2001 review). The adverse effects of the widespread use of TBT have led to a ban on its use (Evans 1999). In 1986, the National Farmers’ Union of Scotland voluntarily participated in the prohibition of its use on fish cages, and in 1987, the Scottish government banned its retail sale (Balls 1987). The International Maritime Organization has banned the use of TBT in coatings since 2003 (Julian 1999), and many governments have thus prohibited the use of organotin in antifouling coatings (Costello et al. 2001). The aquaculture industry is facing future developmental challenges. To ensure that similar TBT scenarios are not repeated, the six criteria followed by the aquaculture industry are as follows (Lewis 1994b): (1) must be effective for a wide range of fouling groups, (2) must be harmless to the environment, (3) must exert no negative impact on the cultured species, (4) must leave no residues in cultured species, (5) must be capable of withstanding onshore handling and cleaning, and (6) must be economically feasible. Feasibility of Copper-Containing Coatings After the implementation of the TBT ban, people soon focused on copper- and copper-containing coatings, which have a long history of applications in shipping and mariculture (Lewis 1994b). The main active components in copper-based antifouling agents are cuprous oxide and copper. Copper is leached from the coating of impregnated nets into seawater. To prevent barnacles and diatoms from adhering and growing, leaching rates of 10 and 20 mg/cm2/day should be applied for response treatments and measures, respectively (Callow 1999). However, relatively low concentrations of copper are known to be harmful to fish and many marine organisms, especially invertebrate larvae, and toxicity studies have reported diverse effects (Brooks and Mahnken 2003). Furthermore, in salmon farms, the

Net Structures: Biofouling and Antifouling

intestinal copper content of green sea urchins was noted to be increased (Chou et al. 2003), and copper bioaccumulation was found in the hepatopancreas and oysters of crayfish sampled near the salmon farm (Chou et al. 2000). Fish are likely to be exposed to antifouling agents for long periods, up to several months. Therefore, from a “clean and green” marketing perspective, the use of toxic metal antifouling agents, i.e., simply using copper as an antifouling compound, is relatively undesirable. At present, most countries are committed to reducing the use of copper-based antifouling agents in the short term. Other Biocides Many other biocides are currently used as antifouling agents worldwide; although these products are not necessarily used in mariculture (Konstantinou 2006), they are potential candidates to supplement or replace copper as an antifouling agent. The most commonly used biocides include chlorothalonil, dichlofluanid, diuron, irgarol 1051, sea-nine 211, thiram, TCMS (2,3,5,6-tetrachloro-4-methylsulfonyl), pyridine, pyrithiones, TCMTB (2-thiocyanomethylthioben zo-thiazole), zinc pyrithione, and zineb (Konstantinou 2006). Coatings using isothiazolinones as the sole biocide have been successfully tested in Australia (Svane et al. 2006); however, little peer-reviewed literature exists on the efficacy of other biocides tested in aquaculture environments. The known chemical and physical properties of common biocides vary widely, and their properties, toxicity, environmental fate, and knowledge gaps in the aquatic environment have been extensively reviewed (Konstantinou and Albanis 2004; Konstantinou 2006). A potential danger remains because the listed biocides are largely untested in some cases, and they may be less efficient and/or more harmful to the environment than TBT or copper (Evans 1999). Moreover, the biocides released during the cleaning process persist in the environment when associated with paint particles (Thomas et al. 2003). Considering the gaps in our understanding of the long-term effects of biocides, it is difficult to assess their impacts

Net Structures: Biofouling and Antifouling

1111

Net Structures: Biofouling and Antifouling, Table 1 Key data for a comparative environmental assessment of relevant biocides Chlorothalonil Dichlofluanid Diuron Irgarol 1051 Sea-Nine 211 Zinc pyrithione Zineb Thiram Pyrithiones Pyridine TCMTB TCMS

Persistencea No No Yes Yes No No

Toxicity

Bioaccumulation

Least Least

No Yes No No No

Performanceb Poor Poor Poor Poor Poor Best Best

High Poor Poor Poor

a

persists in the water column highest performance in terms of environmental parameters; TCMS pyridine and TCMTB demonstrate environmental characteristics similar to TBT (Voulvoulis et al. 2002)

b

and risks on the aquatic environment; therefore, effective environmental policies must be formulated according to precautionary principles. Key data are presented in Table 1 regarding a comparative environmental assessment of biocides (Voulvoulis et al. 2002). To date, all developed synergistic biocides affect the water environment, and no ideal substitute exists for TBT or copper. Moreover, the aquatic environment is affected by booster biocides, and no ideal replacement exists for either TBT or copper. The focus of future research and development has shifted to both effective and environmentally friendly antifouling agents in terms of their chemical (nontoxic coatings) and physical properties (fouling release coatings and nonleaching biocides) (Yebra et al. 2004).

absorption capacity for traditional fiber nets but low absorption capacity for synthetic materials, and the effectiveness is usually short term (Lai et al. 1993). However, the potential for the use of natural antifouling agents is limited because they are simply another chemical entity, and considerable commercial development time is required in the regulatory and commercial environment to prepare surface effect coatings. This kind of compound must be synthesized in large quantities at a reasonable cost, added to the coating matrix, and subject to the same regulatory assessment as biocides by environmental agencies before its practical application can be formally adopted. Fusetani and Clare (2006) comprehensively reviewed antifouling compounds from natural sources, including potential effective compounds.

Development of Environmentally Benign Coatings

Fouling Release Coatings In recent years, research has focused on biocidefree low surface energy siloxane elastomers and fluoropolymers, which may provide a nontoxic alternative to control biofouling and facilitate the application of such coating products (Yebra et al. 2004; Chambers et al. 2006). These “fouling release” coatings are designed to reduce or prevent the adhesion of biofouling, and siliconebased coatings are not toxic to any tested

Natural Biocide Products Natural products have had a long history in aquaculture. Before using modern polymer-based netting, farmers in Malaysia soaked cotton nets with tannins extracted from the bark of mangroves (Rhizophora sp.). Tannins are toxic and function as natural biocides. These tannins have a high

N

1112

organism (Karlsson and Eklund 2004). Nevertheless, nets and panels coated with nontoxic silicone effectively reduce the initial stage of fouling development and make it easier to remove the accumulated biofouling (Hodson et al. 2000; Terlizzi et al. 2000). At present, these materials are considered substitutes for toxic coatings on the surface of ship hulls, for which the speed of the vessel produces the hydrodynamic shear force required for loosely attached biofouling to fall off (Yebra et al. 2004). However, the commercial development of these technologies and their application in fixed aquaculture infrastructure are difficult, and research to solve these problems requires additional time. The principle of superhydrophobicity has been further developed in the field of fouling release technology (Genzer and Efimenko 2006; Marmur 2006). This principle can likely be combined with the abovementioned technologies to solve the biofouling problem of relatively static cage nettings. Nonleaching Biocides Coatings: Contact Type Biocides that irreversibly bind (via covalent bond grafting) to the surface of antifouling coatings or antifouling nets are called nonleaching biocides (Clarkson and Evans 1993, 1995). Although this approach can limit environmental contamination, it has not been successfully implemented, possibly due to technical problems and a wide range of fouling organisms, many of which may not respond to bound biocide entities. These technologies have been effectively used to inhibit the biological attachment and growth of bacteria on biomedical devices (Hume et al. 2004; Zhu et al. 2008). Under legislation restricting antifouling technology to a nonrelease mechanism, this aspect may be promising with broad prospects (Silva et al. 2019). Microtexturing of Surfaces Research on the identification of physical defenses against biofouling in specific animals and plants may also have commercial applications in antifouling technologies. Such methods are characterized by topography and microstructure surfaces to prevent the attachment of common

Net Structures: Biofouling and Antifouling

fouling organisms. For instance, natural regular rippled surface features have been visualized on blue mussels (Scardino et al. 2003), and these structures significantly inhibit the settlement and development of biofouling (Scardino and de NYS 2004). Surface microtopographies, many with a bioinspired design, inhibit the attachment and growth of specific fouling organisms and promote their release (Scardino et al. 2006, 2008). In many cases, the efficacy depends on the proportion of morphology, i.e., micro/nanostructures, relative to the size of the settled larvae or propagules, which limits the surface effectiveness to a limited range of fouling organisms. To enhance the effectiveness of prevention or broaden their deterrent impacts, surfaces with multiple scales of topography are now being developed (Schumacher et al. 2007). This nonleaching surface effect technology can be used in combination with fouling release coatings and may be effective in preventing biofouling in aquaculture, in which the dominant single species in the fouling community can be targeted.

Conclusions At present, methods of protecting against fouling on fishing nets and other aquaculture structures are relatively limited, and most of them are based on the release of copper and zinc by adding booster biocides. The use of zinc and copper is restricted by the International Convention on the elimination of zinc, and thus, the use of such products may be limited as well. Consequently, specific biocides with a low environmental impact are the only mechanism for biofouling control. However, new products can be developed with emphasis on antifouling technologies based on low surface energy (foulant-release) coatings, textures, and surface-bound compounds. Unfortunately, the fouling release technology mainly depends on the hydrodynamic force to remove fouling organisms with low adhesion on the fouling-release surface, making such methods less suitable for aquaculture. Moreover, with the continuous improvement of vessel antifouling technology, the transfer of technology to

Net Structures: Biofouling and Antifouling

aquaculture industries is expected to become more feasible, and product development is expected to be targeted at larger aquaculture industries. Another alternative to heavy metal and biocide technologies, biological control, has yet to be proven to have broad-spectrum efficacy in controlling biofouling. Although such methods are industry- and sitespecific and it is difficult to envision their wide application, certain industry sectors may significantly benefit. On the other hand, with the withdrawal of technologies based on metals and biocides from the market, the aquaculture industry is expected to become greener and environmentally friendly. More and better technologies are expected to emerge as solutions for biofouling protection.

Cross-References ▶ Aquaculture Structures: Experimental Techniques ▶ Aquaculture Structures: Numerical Methods ▶ Modern Aquaculture Structures ▶ Net Structures: Design ▶ Net Structures: Hydrodynamics ▶ Traditional Aquaculture Structures

References Aarsnes JV, Rudi H, Loland G (1990) Current forces on cages, net deflection. In: Engineering for offshore fish farming. Thomas Telford, London, pp 137–152 Ahlgren MO (1998) Consumption and assimilation of salmon net pen fouling debris by the red sea cucumber Parastichopus califormicus: implications for polyculture. J World Aquaculture Soc 29:133–139 Amaraa I, Mileda W, Slamab RB, Neji Ladharic N (2018) Antifouling processes and toxicity effects of antifouling paints on marine environment. A review. Environ Toxicol Pharmacol 57:115–130 Andersen RJ, Luu HA, Chen DZX, Homes CFB, Kent ML, Le Blanc F, Taylor FJR, Williams DE (1993) Chemical and biological evidence links microcystins to salmon netpen liver disease. Toxicon 31:1315–1325 Angel DL, Eden N, Breitstein S, Yurman A, Katz T, Spanier E (2002) In situ biofiltration: a means to limit the dispersal of effluents from marine finfish cage aquaculture. Hydrobiologia 469:1–10 Anon. (1993) How ocean spar solves problems of currents. Fish Farm Int 21:20

1113 Ashraf PM, Sasikala KG, Thomas SN, Edwin L (2017) Biofouling resistant polyethylene cage aquaculture nettings: a new approach using polyaniline and nano copper oxide. Arab J Chem. ISSN:1878-5352 Balls PW (1987) Tributyltin (TBT) in the waters of a Scottlish Sea loch arising from the use of antifoulant treated netting by salmon farms. Aquaculture 65:227–237 Beveridge M (2004) Cage aquaculture. Blackwell, Oxford, UK, pp 1–368 Bixler GD, Bhushan B (2015) Rice and butterfly wing effect inspired low drag and antifouling surfaces: a review. Crit Rev Solid State Mater Sci 40:1–37 Blair A, Campbell R, Grant PT (1982) A submersible fish cage that can be rotated on the surface to remove biofouling and for other purposes. Aquaculture 29:177–184 Boyd CE (1982) Water quality management for pond fish culture. Developments in aquaculture and fisheries science, vol 9. Elsevier, Amsterdam, p 318 Brooks KM, Mahnken CVW (2003) Interactions of Atlantic salmon in the Pacific northwest environment. III. Accumulation of zinc and copper. Fish Res 62: 295–305 Bruno DW, Ellis AE (1988) Histopathological effects in Atlantic salmon, Salmo salar L., attributed to the use of tributyltin antifoulant. Aquaculture 72:15–20 Callow ME (1999) The status and future of biocides in marine biofouling prevention. In: Fingerman M, Nagabhushanam R, Thompson M-F (eds) Recent advances in marine biotechnology, vol 3, Biofilms, bioadhesion, corrosion, and biofouling. Science Publishers, Enfield, pp 109–126 Chambers LD, Stokes KR, Walsh FC, Wood RJK (2006) Modern approaches to marine antifouling coatings. Surf Coat Technol 201:3642–3652 Cheah SH, Chua TE (1979) A preliminary study of the tropical marine fouling organisms on floating net cages. Malaysian Nat J 33:39–48 Cheah SH, Chua TE (1983) The rate of encrustation of biofouling organisms on experimental floating netcages in tropical coastal waters. Proc Symp Coast Aquac 6:677–683 Chou CL, Paon LA, Moffat JD, Zwicker B (2000) Copper contamination and cadmium, silver, and zinc concentrations in the digestive glands of American lobster (Homarus americanus) from the Inner Bay of Fundy, Atlantic Canada. Bull Environ Contam Toxicol 65: 470–477 Chou CL, Haya K, Paon LA, Moffat JD (2003) Metals in the green sea urchin (Strongylocentrotus droebachiensis) as an indicator for the near-field effects of chemical wastes from salmon aquaculture sites in New Brunswick, Canada. Bull Environ Contam Toxicol 70:948–956 Chua TE, Teng SK (1980) Economic production of estuary grouper, Epinephelus salmoides Maxwell, reared in flfl oating net cages. Aquaculture 20:187–228 Clarkson N, Evans LV (1993) Evaluation of a potential non-leaching biocide using the marine fouling diatom Amphora coffeaeformis. Biofouling 7:187–195

N

1114 Clarkson N, Evans LV (1995) Further studies investigating a potential non-leaching biocide using the marine fouling diatom Amphora coffeaeformis. Biofouling 9: 17–30 Conand C, Sloan NA (1989) World fisheries for echinoderms. In: Cadey JF (ed) Marine invertebrate fisheries: their assessment and management. Wiley, New York, pp 647–663 Corner RA, Ham D, Bron JE, Telfer TC (2007) Qualitative assessment of initial biofouling on fish nets used in marine cage aquaculture. Aquac Res 38:660–663 Costello MJ, Grant A, Davies IM, Cecchini S, Papoutsoglou S, Quigley D, Saroglia M (2001) The control of chemicals used in aquaculture in Europe. J Appl Ichthyol 17:173–180 Cronin E (1995) An investigation into the effects of net fouling on the oxygen budget of southern bluefin tuna (Thunnus maccoyii) farms. Honours thesis, University of Adelaide, South Australia, p 72 Cronin ER, Cheshire AC, Clarke SM, Melville AJ (1999) An investigation into the composition, biomass and oxygen budget of the fouling community on a tuna aquaculture farm. Biofouling 13:279–299 Edwards A, Edelston DJ (1976) Marine fish cages – the physical environment. Proc R Soc Edinb B 75:207–221 Evans SM (1999) Tributyltin pollution: the catastrophe that never happened. Mar Pollut Bull 38:629–636 Fredheim A (2005) Current forces on net structures. PhD thesis, Department of Marine Technology, Norwegian University of Science and Technology, Trondheim Fusetani N, Clare AS (2006) Antifouling compounds. Mar Mol Biotech 42:225 Geffen A (1979) Rotating fish cage to prevent fouling. Aquaculture 16:83–85 Genzer J, Efimenko K (2006) Recent developments in superhydrophobic surfaces and their relevance to marine fouling: a review. Biofouling 22:339–360 Gibbs PE, Pascoe PL, Bryan GW (1991) Tributyltininduced imposex in stenoglossan gastropods: pathological effects on the female reproductive system. Comp Biochem Physiol 100C:231–235 Greene JK, Grizzle RE (2007) Successional development of fouling communities on open ocean aquaculture fish cages in the western Gulf of Maine, USA. Aquaculture 262:289–301 Gularte RC, Huguenin JE (1984) Mesh hydrodynamic data. Design guide for use of copper alloy expanded metal mesh in marine aquaculture. INCRA Project 268B, Woods Hole Engineering Associates, pp 54–58 Harris LG, Irons KP (1982) Substrate angle and predation as determinants in fouling community succession. In: Cairns J (ed) Artificial substrates. Ann Arbour Science, Michigan, pp 131–174 Hodson SL, Burke C (1994) Microfouling of salmon-cage netting: a preliminary investigation. Biofouling 8: 93–105 Hodson SL, Lewis TE, Burke CM (1997) Biofouling of fish-cage netting: efficacy and problems of in situ cleaning. Aquaculture 152:77–90

Net Structures: Biofouling and Antifouling Hodson SL, Burke CM, Bissett AP (2000) Biofouling of fi sh-cage netting: the efficacy of a silicone coating and the effect of netting colour. Aquaculture 184:277–290 Huguenin JE (1997) The design, operations and economics of cage culture systems. Aquacult Eng 16:167–203 Hume EBH, Baveja J, Muir B, Schubert TL, Kumar N, Kjelleberg S, Griesser HJ, Thissen H, Read R, PooleWarren LA, Schindhelm K, Willcox MDP (2004) The control of Staphylococcus epidermidis biofilm formation and in vivo infection rates by covalently bound furanones. Biomaterials 25:5023–5030 Inoue H (1972) On water exchange in a net cage stocked with the fish, Hamachi. Bull Jap Soc Sci Fish 38: 167–176. (Abstracts and illustrations in English) Julian MH (1999) The roles and responsibilities of the international maritime Organisation’s marine environment protection committee. In: 10th international congress on marine corrosion and fouling, Melbourne Kadowaki S, Kasedo T, Nakazono T (1978) Continuous records of DO contents by cruising in the coastal culture farms. 1. Relation between DO content and fish density in cages. Mem Fac Fish Kagoshima Univ 27: 273–289. (translated manuscript from Can Transl Fish Aquat Sci, 1985, no 5189) Karlsson J, Eklund B (2004) New biocide-free anti-fouling paints are toxic. Mar Pollut Bull 49:456–464 Kennedy WA, Griffifioen W, Solmie A (1977) The 1976 crop of salmon reared on the Pacifific Biological Station experimental fish farm. Mar Fish Serv Tech Rep 726:21 Kent ML (2000) Marine netpen farming leads to infections with some unusual parasites. Int J Parasitol 30:321–326 Kent ML, Whyte JNC, La T, C. (1995) Gill lesions and mortality in seawater penreared Atlantic salmon Salmo salar associated with a dense bloom of Skeletonema costatum and Thalassiosirea species. Dis Aquat Org 22: 77–81 Konstantinou IK (2006) Antifouling biocides, vol 5. Springer, Berlin. 266p. ISBN 10 3-540-31404-0 Konstantinou IK, Albanis TA (2004) Worldwide occurrence and effects of antifouling paint booster biocides in the aquatic environment: a review. Environ Internat 30:235–248 Koops H (1971) Contribution to fouling-prevention of net cages in the Western Baltic Sea. Arch Fisch 22:65–67. (in German) Lader P, Dempster T, Fredheim A, Jensen Ø (2008) Current induced net deformations in full-scale sea-cages for Atlantic salmon (Salmo salar). Aquac Eng 38:52–65 Lai HC, Kessler AO, Khoo LE (1993) Biofouling and its possible modes of control at fish farms in Penang, Malaysia. Asian Fish Sci 6:93–116 Lee HB, Lim LC, Cheong L (1985) Observations on the use of antifouling paint in netcage fish farming in Singapore. Singapore J Primary Ind 13:1–12 Lewis T (1994a) Impact of biofouling on the aquaculture industry. In: Kjelleberg S, Steinberg P (eds) Biofouling:

Net Structures: Biofouling and Antifouling problems and solutions – proceedings of an international workshop. University of New South Wales, Sydney, pp 32–38 Lewis JA (1994b) Biofouling and fouling protection: a defense perspective. In: Kjelleberg S, Steinberg P (eds) Biofouling: problems and solutions – proceedings of an international workshop. University of New South Wales, Sydney, pp 39–43 Lodeiros C, García N (2004) The use of sea urchins to control fouling during suspended culture of bivalves. Aquaculture 231:293–298 Marmur A (2006) Super-hydrophobicity fundamentals: implications to biofouling prevention. Biofouling 22: 107–115 Menton DJ, Allen JH (1991) Spherical (Kiel) and square steel cages: first year of comparative evaluations at St. Andrews, NB. Bull Aquacult Assoc Canada 91:111–113 Meyers TR (1984) Marine bivalve molluscs as reservoirs of viral finfish pathogens: significance to marine and anadromous finfish culture. Mar Fish Rev 46(3):14–17 Milne PH (1970) Fish farming: a guide to the design and construction of net enclosures. Marine research, no. 1. Department of Agriculture and Fisheries for Scotland, HMSO, Edinburgh, p 31 Navarro N, Leakey RJG, Black KD (2008) Effect of salmon cage aquaculture on the pelagic environment of temperate coastal waters: seasonal changes in nutrients and microbial community. Mar Ecol Prog Ser 361: 47–58 Needham T (1988) Sea water cage culture of salmonids. In: Laird L, Needham T (eds) Salmon and trout farming. Ellis Horwood, Chichester, pp 117–154 Neori A, Chopin T, Troell M, Buschmann AH, Kraemer GP, Halling C, Shpigel M, Yarish C (2004) Integrated aquaculture: rationale, evolution and state of the art emphasizing seaweed biofiltration in modern mariculture. Aquaculture 231:361–391 Osawa Y, Tawara Y, Taketomi H (1985) Studies on behaviour of fish cages against flow of water. On relationship between volume of fish cages and current velocity. Bull Nat Res Inst Fish Eng (Japan) 6:297–321. (in Japanese) Paclibare JO, Evelyn TPT, Albright LJ, Prosperi-Porta L (1994) Clearing of the kidney disease bacterium Renibacterium salmoninarum from seawater by the blue mussel Mytilus edulis, and the status of the mussel as a reservoir of the bacterium. Dis Aquat Org 18: 129–133 Ross KA, Thorpe JP, Brand AR (2004) Biological control of fouling in suspended scallop cultivation. Aquaculture 229:99–116 Rothwell GN, Nash CE (1977) Aquaculture in tropical oceans, year 01. The Oceanic Institute, Hawaii, p 82 Ruokolahti C (1988) Effects of fish farming on growth and chlorophyll a content of Cladophora. Mar Pollut Bull 19:166–169 Sanderson JC, Cromey CJ, Dring MJ, Kelly MS (2008) Distribution of nutrients for seaweed cultivation around salmon cages at farm sites in north-west Scotland. Aquaculture 278:60–68

1115 Santhanam R, Srikrishnadhas B, Natarajan P (1983) Fouling problems in cages and pens. In: Proc Natl seminar on cage and pen culture. Fisheries College, Tamil Nadu Agricultural University, Tuticorin, pp 143–147 Scardino AJ, de Nys R (2004) Fouling deterrence on the bivalve shell Mytilus galloprovincialis: a physical phenomenon? Biofouling 20:249–257 Scardino A, de Nys R, Ison O, O’Connor W, Steinberg PD (2003) Microtopography and antifouling properties of cell surface of the bivalve mollusks Mytilus galloprovincialis and Pinctata imbricata. Biofouling 19(Suppl):221–230 Scardino AJ, Harvey E, de Nys R (2006) Testing attachment point theory: diatom attachment on microtextured polyimide biomimics. Biofouling 22:55–60 Scardino AJ, Guenther J, de Nys R (2008) Attachment point theory revisited: the fouling response to a microtextured matrix. Biofouling 24:45–53 Schumacher JF, Aldred N, Callow ME, Finlay JA, Callow JA, Clare AS, Brennan AB (2007) Species-specific engineered antifouling topographies: correlations between the settlement of algal zoospores and barnacle cyprids. Biofouling 23:307–317 Short JW, Thrower FP (1986) Accumulation of butyltin in mussel of Chinook salmon reared in sea pens treated with tri-n-butyltin. Mar Pollut Bull 17:542–545 Silva ER, Ferreira O, Ramalhod PA, Azevedod NF, Bayóne R, Igartuae A, Bordadoc JC, Calhorda MJ (2019) Eco-friendlynon-biocide-release coatings for marine biofouling prevention. Sci Total Environ 650: 2499–2511 Silvert W (1994) Simulation models of finfish farms. J App Ichthyol 10:349–352 Sunde LM, Heide MA, Hagen N, Fredheim A, Forås E, Prestvik Ø (2003) Review on technology in the Norwegian aquaculture industry. SINTEF fisheries and aquaculture report STF 80 A034002. Trondheim, Norway, p 32 Svane I, Cheshire A, Barnett J (2006) Test of an antifouling treatment on tuna fish cages in Boston Bay, Port Lincoln, South Australia. Biofouling 22:209–219 Swift MR, Fredriksson DW, Unrein A, Fullerton B, Patursson O, Baldwin K (2006) Drag force acting on biofouled net panels. Aquac Eng 35:292–299 Terlizzi A, Conte E, Zupo V, Mazzella L (2000) Biological succession on silicone fouling release surfaces: long term exposure tests in the harbour of Ischia, Italy. Biofouling 15:327–342 Terlizzi A, Fraschetti S, Gianguzza P, Faimali M, Boero F (2001) Environmental impact of antifouling technologies: state of the art and perspectives. Aquatic Conserv Mar Freshw Ecosyst 11:311–317 Thomas KV, McHugh M, Hilton M, Waldock M (2003) Increased persistence of antifouling paint biocides when associated with paint particles. Environ Pollut 123:153–161 Tomi W, Naiki K, Yamada Y (1979) Investigations into technical development of mariculture on commercial scale applied to offshore region. Proc Jpn Sov Joint Symp Aquaculture 7:111–120

N

1116 Tseng WY, Yuen KH (1979) Studies on fouling organisms on mariculture nets and cages in Hong Kong. In: Proceedings of the aquatic environment in Pacific region, Taipei, pp 151–159 Voulvoulis N, Scrimshaw MD, Lester JN (2002) Comparative environmental assessment of biocides used in antifouling paints. Chemosphere 47:789–795 Wee KL (1979) Ventilation of floating cages. MSc thesis, University of Stirling, p 42 Willinsky MD, Robson DR, Vangool WJ, Fournier RA, Allen JH (1991) Design of a spherical, submersible, self-cleaning aquaculture system for exposed sites. In: Hirata GN (ed) Proceedings of the National Science Foundation workshop on offshore engineering and Mariculture, Honolulu, pp 317–336 Yebra DM, Kiil S, Dam-Johansen K (2004) Antifouling technology – past present and future steps towards efficient and environmentally friendly antifouling coatings. Prog Organ Coat 50:75–104 Zhu H, Kumar A, Ozkan J, Bandara R, Ding A, Perera I, Steinberg P, Kumar N, Lao W, Griesser SS, Britcher L, Griesser HJ, Willcox MDP (2008) Fimbrolide-coated antimicrobial lenses: their in vitro and in vivo effects. Optometry Vision Sci 85:292–300

Net Structures: Design Fukun Gui National Engineering Research Center for Marine Aquaculture, Zhejiang Ocean University, Zhejiang, China

Synonyms Copper Alloy Net; Metal Net; Polyamide (PA) Net; Polyethylene (PE) Net; Ultrahigh Molecular Weight Polyethylene (UHMWPE) Fiber Net

Introduction A net is a porous structure composed of net twine constructed by twisting and weaving. Nets are commonly applied in fishery production (e.g., fishing industry, cage aquaculture, and net enclosure aquaculture) and engineering construction (e.g., building protection and area isolation). In this chapter, we describe the application design of

Net Structures: Design

a net in cage aquaculture and net enclosure aquaculture (NEA). Net Types In practice, synthetic fibers, metals, and other new types of materials are commonly used for net making. Among these materials, polyethylene nets, polyamide (PA) nets, ultrahigh molecular weight polyethylene (UHMWPE) fiber nets, polyester PET (polyethylene terephthalate) nets, copper alloy nets, and coated metal wire nets have been widely used in cage aquaculture and NEA (see Fig. 1). Polyethylene (PE) Net: Polyethylene monofilaments are twisted to form net twines and later woven to form a net. Polyethylene is flexible and exhibits a high tensile strength, high impact resistance, and low density (less dense than water, approximately 953 kg/m3). The net twine used in PE nets is normally composed of 3 strands, and the number of monofilaments per strand is set according to the mesh size and twine strength. PE netting is one of the most widely used net types in cage aquaculture. Polyamide (PA) Net: Polyamide, commonly known as nylon (nylon), was invented in the early 1930s and rapidly became the leading industrial product of polymer synthetic fibers. Its favorable characteristics include its high strength, high abrasion resistance and good elasticity, and the density (approximately 1140 kg/m3) is slightly higher than that of water. Generally, the single-yarn diameter of PA fibers used as net materials is 0.66–2.22 tex, considerably smaller than that (36 tex) of PE monofilaments. Under the same diameter, the breaking strength of PA fibers is generally slightly higher than that of PE fibers. Ultrahigh Molecular Weight Polyethylene UHMWPE Fiber Net: UHMWPE fiber was successfully developed by the DSM company (Netherlands) in 1979. This net has many advantages, such as a high strength, low density, high fatigue resistance, and low temperature resistance. This material was once used to prepare bulletproof jackets. Research has demonstrated that the strength of a net cable woven from UHMWPE fibers is 3–4 times that of a PE net cable, demonstrating a considerable advantage in strength.

Net Structures: Design

1117

Polyethylene (PE) net

Polyamide (PA) net

UHMWPE fiber net

Polyester (PET) net

Copper alloy net

Metal wire coated by nickel-zinc

Net Structures: Design, Fig. 1 Nets commonly used in the farming industry (by Fukun Gui)

However, the UHMWPE fiber weaving process is more complicated than that of PE netting, and the price of a UHMWPE fiber net is 5–6 times that of a PE net. Therefore, UHMWPE fiber nets are often applied in important aquaculture projects with high manufacturing costs (such as cage aquaculture projects in the open sea and large-scale NEA projects). Polyester (PET) Net: The PET net is a newly developed net that exhibits a hexagonal mesh structure made of a monofilament structure through a special twisting process. The diameter of a PET net monofilament is generally approximately 2.5–4 mm, and the strength is approximately 1–1.5 times higher than that of an ordinary PE net with the same diameter but lower than that of a UHMWPE net. PET nets exhibit an excellent fatigue resistance strength. Owing to the monofilament structure, the surface of the net is smooth and has no voids. Moreover, the biofouling rate is lower than that of other fiber nets, which helps to relieve the impacts on nets from currents and waves. Furthermore, the price of a PET net is close to that of a UHMWPE net, and the comprehensive cost-performance ratio of

PET nets is higher. The PET net has been gradually applied in key farming projects. Metal Net: Metal nets in farming projects are usually made of copper alloy wire or steel wire coated by nickel-zinc. The abovementioned metal nets exhibit excellent antifouling characteristics, and thus, they have been applied in cage aquaculture and NEA projects. However, the application of copper alloy nets is restrained by their high cost compared with other types of nets currently used in farming projects. Key Technologies in Net Design The design of the net system in aquaculture projects generally requires several key procedures, such as the net model design and material selection, net load calculation, net strength design, and net assembly design. Net Model Design and Material Selection

The selection and design of nets are mainly based on the functional requirements of aquaculture. Generally, the following main factors are considered:

N

1118

Net Structures: Design

Mesh Size Generally, the mesh size of the net should be chosen according to the actual size and body characteristics of the farming fishes. For small fish fry, the mesh size of the net can be small. For large fish fry, a larger mesh size should be selected to ensure sufficient water exchange. In the entire farming process, as the body length of the fishes increases, the nets should be replaced over time by nets with larger meshes. Therefore, it is necessary to rationally design nets with several different mesh sizes. Preliminary Selection of the Twine Diameter First, the net load strength must be calculated to determine the diameter of the net twine. The selection of the twine diameter depends on not only the strength requirements but also the weaving process of the mesh. A certain relationship exists between the twine diameter and mesh size of the net. Smaller meshes generally adopt a smaller diameter of twine. Choosing a twine diameter that is excessively large may lead to the failure of net fabrication. Under normal circumstances, the twine diameter is initially determined according to the mesh size and later optimized according to the load strength of the net. In terms of the twine diameter of the polyethylene net, Table 1 (Shi et al. 2016) can be referred to for the preliminary selection. When the mesh size exceeds 40 mm, the number of twine strands varies according to the practical use. The corresponding twine diameter can be estimated according to formula (1): D ¼ 0:022  G þ 1:1865

ð1Þ

where D represents the twine diameter and G represents the number of twine strands.

Selection of the Net Material When choosing the net material, several key factors should be carefully considered, such as the cost of the net, the demanded strength and toughness, and the antifouling capability. Among the nets commonly used in aquaculture projects, copper alloy nets exhibit a favorable antifouling performance. However, they are the most expensive option, and their toughness is insufficient. UHMWPE fiber nets exhibit excellent strength, but the cost is relatively high, and their antifouling function is inadequate. PET nets have a relatively high tensile strength and excellent fatigue strength, and their antifouling performance is higher than that of other fiber nets; however, the cost is also high. For the PE net, the overall strength is lower than that of the abovementioned materials, and the antifouling functionality is lacking; however, PE nets are inexpensive, which contributes to their higher cost-performance ratio. Therefore, PE nets have been widely used in aquaculture projects. In recent years, the development of large-scale deepsea aquaculture equipment and ultra-large NEA equipment has imposed higher requirements on the strength of the net; therefore, UHMWPE fiber nets and PET nets are attracting increasing attention. Calculation of the Net Load

The net load is an important basis for the net design. The selection of the net material and twine diameter is based on the calculated net load. Three methods can be used to calculate the net load: theoretical analysis, physical model testing, and numerical simulation. Regardless of which method is adopted, the design standard of

Net Structures: Design, Table 1 General specifications of the PE net Mesh size (mm) 0.5–1 1–2 3–10 10–13 13–20 20–25 25–30 30–40

Twine specification 0.23/1 0.23/12 0.23/13 0.23/22 0.23/23 0.23/33 0.23/43 0.23/53

Twine diameter (mm) 0.23 0.46 0.53 0.67 0.78 0.96 1.13 1.29

Weight (g/100 m) 4.36 9.33 14.0 17.0 28.0 42.0 56.0 67.0

Breaking strength (kgf) 2.37 3.55 5.32 6.62 9.94 14.9 18.4 23.0

Net Structures: Design

1119

the farming project must be determined first. The selection of the design criterion for a farming project depends on the conditions of the sea area in which the farming facility is located and the importance and influence of the farming project. For general near-shore cage culture, the design criterion is generally set to once every 25 years. For aquaculture projects in offshore waters, a design criterion of once every 50 years is recommended. For large-scale sea cage aquaculture in the outer sea and NEA projects, the design criterion is generally set to once every 100 years due to their significance and influence. Theoretical Analysis Method The core purpose of the net load calculation is to determine the load strength of the key parts in the net system. Necessary simplifications and assumptions to the calculation model are often implemented when carrying out a theoretical analysis of the net load in aquaculture engineering. The flow load acting on the net unit can be calculated by the general hydrodynamics equation (2): 1 FD ¼ r  CD  A  u2 2

ð2Þ

where FD represents the flow force acting on the net; r represents the fluid density; CD represents the drag coefficient of the net; A represents the projected area of the net; and u represents the fluid velocity. The inertial force produced by unsteady flow dynamics can often be ignored due to the smallscale structure of the net, and thus, formula (2) can be applied to a net force analysis under wave conditions with u representing the fluid point velocity. The net load is calculated by the Stokes finite amplitude wave theory and Airy linear wave theory in deep-water sea cage aquaculture engineering. The third- or fifth-order Stokes finite amplitude wave theory can be used to calculate the net load when cage aquaculture or NEA projects are constructed in shallow waters. However, when the water depth is extremely shallow or there is a shore-linking section (such as shorelinked NEA), the theoretical calculation may

induce a large error, and it is generally necessary to carry out a special study. The drag coefficient CD is related to the impact angle of the current, Reynolds number, and solidity of the net and other parameters. According to the existing research literature (Li and Gui 2005), the drag coefficient of the mesh twine can be calculated by the following formula when analyzing the force of the net: CD90 ¼ 3ð Re Þ0:04

ð3Þ


CDy ¼CD90 1  cos2 ycos2 ’þ  pffiffiffiffiffi Sn cos2 ysin’ cos3 ’  3Sn cos3 ysin2 ’ (4) Regarding the drag coefficient of the knot, Fredheim and Faltinsen (2003) suggested that it is reasonable to use a drag coefficient in the range of 1.0–2.0 when modeling the knot part as a sphere. The projected area of the mesh is related to the impact angle of the mesh unit and mesh structure. In general, the net mesh has rhomboidal, rectangular, and hexagonal structures, which can be classified into nodular and nonnodular types. Rhomboidal and hexagonal meshes are the most commonly used. A rhomboidal mesh consists of four wires and four knots, as shown in Fig. 2. A knot is shared by four meshes, and a twine is shared by two meshes; specifically, a mesh consists of a knot and two mesh twines, as shown in Fig. 3. Therefore, this definition is used when calculating the projected area of the mesh. The inclination should be considered to calculate the projection area of a rhomboidal mesh when the mesh is slanted. Assuming that the angle between the mesh and direction of water flow is θ, the projected area of the mesh unit can be calculated as follows (Gui 2006): A¼ad

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi m1 2 þ m2 2  sin 2 y  N

ð5Þ

where A represents the projection area of the net; a and d represent the length and diameter of the twine, respectively; m1 and m2 denote the hanging

N

1120

Net Structures: Design, Fig. 2 Sketch of a diamond mesh (Gui 2006)

Net Structures: Design

Net Structures: Design, Fig. 4 Sketch of a hexagonal mesh (Gui 2006)

Net Structures: Design, Fig. 3 Definition of a single diamond mesh (Gui 2006)

ratio in the horizontal and vertical directions, respectively; and N refers to the total number of meshes in the net unit. For a hexagonal mesh without knots, as shown in Fig. 4, the calculated features mainly include the height H and width L of the mesh, length a1 and diameter d1 of the bevel mesh, and length a2 and diameter d2 of the vertical mesh. In the case of a certain inclination angle, the expressions to calculate the projected area of different mesh segments are different, and these aspects should thus be considered separately in the calculation. Similar to a mesh with knots, one mesh is equivalent to one twine with diameter d1 and length a1 and two twines with diameter d2 and length a2, as shown in Figs. 4 and 5. The calculation of the projected area of a mesh can start from the calculation of the projected area of a single mesh. Assuming that

Net Structures: Design, Fig. 5 Definition of a single hexagonal mesh (Gui 2006)

the impact angle between the plane net and the water flow is θ, the projected area of the plane net at this impact angle can be calculated according to the following formula.  qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi A ¼ a1 d 1 sin y þ d 2  ðL  d 1 Þ2  ðH  2a1 Þ2  sin2 y N

(6) where A is the projected area of the mesh, θ represents the water impulse angle, and N denotes the total number of meshes in the net unit. A general biofouling situation will occur in the fiber net after marine farming for a certain period,

Net Structures: Design

1121

leading to an increase in the projected area of the net. In the actual calculation, the effect of biofouling should be considered. Physical Model Tests Modeling Criteria for Fishing Nets in Experiments Model experiments are highly useful for examining the hydrodynamic characteristics of fishing nets; however, it is challenging to establish reasonable simulation criteria for the model tests of fishing nets. For such model tests, the geometric scale l is usually greater than 20:1. If the model net is designed strictly according to geometric similarity principles, two challenges arise. First, the yarn used for the model net will be extremely thin, which renders the manufacturing process difficult. Second, the Reynolds number (Re) for the model net will change significantly because the mesh is modeled to be extremely small, leading to a large difference in the hydrodynamic behavior between the model and prototype nets. Thus, special simulation methods must be used. Tauti’s criteria (Tauti 1934), which were developed in the 1930s during research into fishing net problems, are used only for conditions where a current is present. Tauti’s Simulation Criteria Tauti’s simulation criteria involve two geometric scales for nets, l and l0, which represent the global and model mesh scales, respectively: l¼

Lp dp ap and l0 ¼ ¼ , Lm d m am

ð7Þ

where d is the filament diameter, a is half the mesh size, and subscripts p and m denote the model and prototype sizes, respectively. Based on the geometric similarity and dynamic similarity, the following expressions can be obtained according to Fig. 6: W p Sp r p Sp T p Lp Fp ¼ ¼ ¼ , W m Sm r m Sm T m Lm Fm

ð8Þ

where W and r denote the gravity and hydrodynamic force per unit area on the net, respectively, and T is the force per unit length on the net edge. When the net material is the same for the model and the prototype, the equation can be replaced by l2 l0 ¼ l2

Tp Fp V 2P ¼l ¼ 2 T m Fm Vm

ð9Þ

In trawl experiments, Tauti’s simulation criteria are suitable and widely used. However, in model tests of net cages, two limitations arise for practical experiments. First, in model tests, the model mesh scale cannot be excessively large, and thus, a greater current velocity is required. Second, Tauti’s simulation criteria cannot be applied to model tests under wave conditions because Eq. (9) is not satisfied if geometric similarity is applied in the presence of waves. Thus, for model tests of net cages under wave and current conditions, the following gravity simulation criteria are recommended.

Net Structures: Design, Fig. 6 Model to calculate forces acting on a micro-segment of a fishing net (Gui 2006)

N

1122

Net Structures: Design

Extended Gravity Simulation Criteria (Gui 2006) The main principles for an extended gravity simulation are as follows: 1. Two geometric scales for the nets are used as in Tauti’s simulation criteria: l and l0 represent the global scale and the model scale for the yarn diameter and net mesh size, respectively. 2. Since the porosity ratio for the model net is the same as that for the prototype, the external forces acting on the net will follow the gravity simulation criteria by a scale of l3. 3. The model net weight simulated by a scale of l3 is modified as follows:  DW ¼

   pd21 1 1 4    10 4a1 m1 m2 l0 l

 ðr  rw Þ  q  S,

ð10Þ

where r is the density of the net material, rw is the water density, q is the packing fraction of the filament, S is the area of the net, and m1 and m2 are the hanging ratios (see Fig. 7) defined in Eqs. (11) and (12), respectively. In the crosswise direction of the net, the hanging ratio is defined as m1 ¼ a=2L

ð11Þ

In the longitudinal direction, the ratio is

m2 ¼ b=2L:

ð12Þ

Based on the gravity simulation criteria, the following equation can be derived: l3 ¼ l 2

V 2p V 2m

¼l

Tp Fp ¼ : T m Fm

ð13Þ

Numerical Simulation Method

It is necessary to establish an appropriate calculation model when using a numerical simulation method to analyze the net load. At present, the most widely used method for flexible fiber nets is the lumped-mass model. The finite element method is generally used for more rigid nets, such as those involving a copper mesh, using mature commercial software such as Ansys. Here, we simply introduce a lumped-mass model for flexible fiber nets. Lumped-Mass Model By applying a lumpedmass model (Li et al. 2006), a fishing net is assumed to be a connected structure with limited masses and springs. The lumped point masses are set at each knot and at the center of each mesh twine (see Fig. 8). Depending on the use of knots, two different types of nets are commonly used: nets with knotted meshes and nets with knotless meshes. In the model, the diameter of the sphere d reflects the physical properties of the net. For a mesh with knots and a knotless mesh, d is considered to be 3.14-fold and 1.5-fold greater than the diameter of the twine, respectively. According to Newton’s second law, the equation of motion for a lumped mass i in waves can be expressed as Mi a ¼

n X ! ! ! ! ! T ij þ F D þ F I þ W þ B ,

ð14Þ

j¼1

where Mi is the lumped mass of point i, a is !

Net Structures: Design, Fig. 7 Definition of mesh properties (Gui 2006)

the acceleration of mass point i, T ij is the vector of the tension in twine ij ( j represents the knots at the other end of twine ij), n is the number!of knots ! adjacent to point i, F is the drag force, F!I is the D ! inertial force, W is the gravity force, and B is the

Net Structures: Design

1123

Net Structures: Design, Fig. 8 Schematic of the mass-spring model (Li et al. 2006)

N

Net Structures: Design, Fig. 9 Sketch of the mesh grouping method (Zhao 2007)

buoyancy!force. According to research, the inertial force F I on a fishing net is rather small under wave conditions compared to other external forces and can thus be omitted. The drag force ! FD

can be calculated using equation (2), with the drag force coefficient CD calculated by equations (3) and (4). Equation (14) can be solved using Runge-Kutta methods. The net shape and force distribution at each time step can be calculated numerically by solving these ordinary differential equations for a given initial condition. Mesh Grouping Method When all the knots in the mesh and at the twine are used as mass points,

more than 10,000 mass points exist for a common plane net, for which the calculation time in a practical simulation is extremely large. To reduce the computational cost, a mesh grouping method can be employed in the calculations. The method consists of modeling a given number of actual meshes as a fictitious equivalent mesh that has the same physical qualities as the actual meshes, such as the projected area of the net, specific mass, and weight. Figure 9 shows an example of a 4  4 mesh with 65 lumped mass points that is approximated to a 2  2 mesh with 21 lumped mass points. According to calculations by Zhao (2007), using 1  1 (G0), 2  2 (G4), and 4  4 (G16) meshes to model the same panel yields

1124

Net Structures: Design

Net Structures: Design, Fig. 10 Comparison of the calculation time for different mesh grouping methods (Zhao 2007)

similar results for the predicted hydrodynamic forces for current-only loading, although with a considerable time reduction, as shown in Fig. 10. Strength Design of the Net The wire with the maximum tension in the net is generally considered to have the basic properties for the net strength design after the net load distribution is obtained. The net strength is determined mainly by the diameter of the mesh but is also affected by the knot form and mesh shape. It is still necessary to consider the attenuation of mesh strength caused by aging and biofouling when considering the service life of the net. Therefore, the safety factor K, which equals 3–4, is recommended for net design; specifically, the strength of the net selected for use should be 3–4 times the calculated load. Stress concentration is strictly forbidden to appear when performing net design. If the situation is unavoidable, special protection or reinforcement should be introduced. Net Assembly Design Net Sewing

First, a certain width of net panel is established during net manufacturing, and net cutting and sewing are performed according to the overall structure of the cage or NEA. The common methods of net suturing in aquaculture engineering include braiding and winding.

Braiding involves connecting two pieces of net panels and can be categorized as longitudinal and transverse braiding according to the direction of the braiding mesh, as shown in Fig. 11. The material and diameter of the net line required for knitting should be the same as that of the net. The size of the mesh formed by knitting and the knotting method must also be the same as those for the original net. The net forms a complete and integral unit after knitting, which involves strict requirements in terms of manual weaving techniques. Winding involves the connection of two net panels. The requirements for winding are relatively approximate, and such methods are generally used for emergency repair or sewing processes, which do not involve high requirements. Winding can be categorized as ordinary winding (see Fig. 12) and cutting winding (see Fig.13). Rope Assembly

After the net is sewn, it needs to be assembled with the rope. The rope is an important structure that transfers the net load to the cage frame or NEA posts. It is necessary to consider the net load and select the rope strength by referring to the design principle of the net strength. After the rope has been selected, it is necessary to sew the net evenly on the rope with an appropriate method and ensure that the net forms the expected shrinkage shape. This process is known as rope assembly.

Net Structures: Design

1125

Net Structures: Design, Fig. 11 Net sewing methods (by Fukun Gui) (a) Longitudinal sewing (b) Transverse sewing

N

Net Structures: Design, Fig. 12 Ordinary winding methods (Shi et al. 2016) (a) Half mesh winding (b) One mesh winding (c) Multimesh winding

The net and rope are generally divided into several parts according to the mesh size and rope length during the course of assembly (see Fig. 14). The parts are marked at equal points and then assembled segment by segment to ensure the uniformity of the mesh distribution. For items with higher overall requirements for the rope assembly, the net is stretched and fixed according to the design size, and then the ropes are sewn onto the net. The ductility of the rope should be considered in the net assembly. The rope should be pre-tensioned before assembly to eliminate the plastic deformation of the rope.

The rope may or may not pass through the mesh during the assembly (see Fig.15a–c). To ensure a more uniform stress distribution, the rope should ideally not pass through the mesh (see Fig. 15d–e). The material and diameter of the wire used for sewing the net and rope are generally required to be the same as those of the original net. Sewing is usually performed mesh by mesh, and a dead knot is introduced every several meshes when assembling and sewing to ensure that the whole rope does not fall off the net in case a sewing line breaks (see Fig. 15f).

1126

Net Structures: Design

Net Structures: Design, Fig. 13 Cutting winding methods (Shi et al. 2016)

Net Structures: Design, Fig. 14 Physical map of the rope assembly (by Fukun Gui)

Final Assembly of the Net

The final assembly design is performed after the net has been assembled with the rope. Generally, the net has the main force direction. For example, in the case of a fiber net, the trend of the net system is generally the main force direction, as shown in Fig. 16. It is necessary to identify the main direction of the net load to ensure that the main direction of the load of the net twine is consistent with the main direction of the net load of the whole system during the design and final assembly. In general cage farming projects, the net is generally suspended from the cage floating frame system with the weights attached at the net

bottom. The main direction of the net load is the vertical direction, and thus, the main direction of the net line stress should be in the vertical direction. Therefore, the net is normally assembled vertically in cage aquaculture systems. For a pile-post NEA project, the stress of the net is generally borne by the pile, and the main direction of the net load is transverse. Therefore, the main direction of the stress of the net is horizontal, and the net panels need to be assembled horizontally. For sea cage aquaculture in the open ocean, the main assembly direction of the net can be determined according to the length-width ratio of the net unit. Generally, both horizontal and vertical assemblies are acceptable.

Net Structures: Design

1127

Net Structures: Design, Fig. 15 Schematic of the rope assembly (Shi et al. 2016) Net Structures: Design, Fig. 16 Main force direction of the net (by Fukun Gui)

N

1128

Net Structures: Design 









Protecting Net L.H.L





H.W.L.

Main Net





Floats





Lower Chain

Net Structures: Design, Fig. 17 Protective design of the net in a pile-post NEA project (by Fukun Gui)

Regardless of what kind of assembly method is adopted for the net, a uniform assembly should be ensured, and the stress concentration phenomenon should be strictly avoided during the net assembly. In assembly situations in which stress concentration cannot be avoided, special design and reinforcement should be implemented.

Protective Design of the Net In addition to dynamic factors such as water flow and waves, the impact of floating objects should also be considered during net design. A protection net is mainly used to prevent the impact of floating objects such as bamboo and wood with the culturing net. Therefore, the strength of the protection net must be relatively high. Generally, PE ropes with a diameter of more than 6 mm are recommended for use, and the mesh size (2a) is expected to be more than 10 cm according to the main type of floating objects in the sea area. For cage aquaculture, a protection net can be generally arranged along the cage periphery at a certain distance from the cage group to achieve effective protection and avoid any influence of normal management operations. For pile-post NEA projects, the protection net can be generally arranged on the peripheral piles, and the layout height of the bottom of the protection net is 1 m below the lowest tide (see Fig. 17).

Cross-References ▶ Aquaculture Structures: Experimental Techniques ▶ Aquaculture Structures: Numerical Methods ▶ Modern Aquaculture Structures ▶ Net Structures: Biofouling and Antifouling ▶ Net Structures: Hydrodynamics ▶ Traditional Aquaculture Structures

References Fredheim A, Faltinsen OM (2003) Hydroelastic anslysis of a fishing net in steady inflow conditions. In: 3rd International conference of the hydroelasticity in marine technology, Oxford, Great Britain, University of Oxford Gui FK (2006) Hydrodynamic behaviors of deep-water gravity cage. Doctoral dissertation, Dalian University of Technology. (in Chinese) Li YC, Gui FK (2005) Experimental study and selection of the drag coefficient of knotted and knotless plane fishing net. China Offshore Platform 20(6):11–17. (in Chinese) Li YC, Zhao YP, Gui FK, Teng B (2006) Numerical simulation of the hydrodynamic behavior of submerged plane nets in current. Ocean Eng 33(17–18): 2352–2368 Shi JG, Sun MC, He B (2016) Wave resistant sea cage engineering and technology. Ocean Press, Peking Tauti M (1934) A relation between experiments on model and on full scale of fishing net. Bull Jpn Soc Sci Fish 3(4):171–177

Net Structures: Hydrodynamics Zhao YP (2007) Numerical investigation on hydrodynamic behavior of deep-water gravity cage. Doctoral dissertation, Dalian University of Technology. (in Chinese)

Net Structures: Hydrodynamics Chunwei Bi and Yunpeng Zhao State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China

Synonyms Fluid dynamics of net structure; Fluid mechanics of net structure; Net hydrodynamic characteristics

Definition Net hydrodynamics

Describes the hydrodynamic forces acting on the associated fluid mechanics around and the deformation of a net structure under external environmental loads, such as currents and waves.

Scientific Fundamentals Historical Development Aquaculture is expanding all over the world, and net cages are becoming increasingly prevalent in the aquaculture industry. A thorough understanding of the hydrodynamic characteristics of a net cage is important for the design of the net cage and the welfare of the fish. An important component of a net cage is the fishing net, where the fish are kept and grown. A fishing net is completely submerged and infinitely flexible. When exposed to a current, a fishing net changes its shape to reduce the hydrodynamic force acting on it, and the deformed net in turn affects the flow field around the fishing net. In this way, the flow field and deformation of the fishing net interact and

1129

mutually influence each other. Therefore, it is necessary to consider the hydrodynamics of the fishing net when designing a net cage. Over the past decade, many researchers have attempted to determine the magnitude of forces caused by the fluid flow through a fishing net (Balash et al. 2009; Bi et al. 2014a; Dong et al. 2008; Fredheim 2005; Patursson 2007; Tsukrov et al. 2011; Zhao et al. 2013a). Some previous studies (Endresen et al. 2013; Lader et al. 2014) investigated the drag characteristics of net structures for fisheries and aquaculture by considering a cylindrical bar as the basic element. However, simply summing the forces acting on all the cylinders/twines of a net structure without representing the geometrical features of the intersections/knots in viscous flow yields unreliable predictions of the total drag (Fredheim 2005). As an alternative approach, a cruciform element that corresponds to one intersection of two cylinders with the length of a mesh bar can be considered as the basic element of the net structure (Bi et al. 2018). Overall, the reduction in the current downstream of the fishing net has been considered in examining the hydrodynamic force and the effective volume of the net cage. However, in most numerical studies, only a reduction factor was estimated to represent the shielding effect of the fishing net. A numerical model that can consider the fluid–structure interaction between the flow and a flexible net has not been established. As an extension of previous works (Zhao et al. 2013a, b), a coupled fluid–structure model is developed by combining the porous-media fluid model and lumped-mass mechanical model. Using an appropriate iterative scheme, the fluid–structure interaction between the flow and fishing nets can be clarified. Porous-Media Fluid Model The porous-media fluid model can simulate the flow field around a plane net. Therefore, the porous-media fluid model is introduced to model a planar fishing net, and the finite volume method is used to solve the governing equations of the numerical model. A brief review of the porousmedia fluid model is presented in this section.

N

1130

Net Structures: Hydrodynamics

The governing equations of the porous-media fluid model are the Navier–Stokes equations: @r @ ðrui Þ þ ¼0 @xi @t


ð1Þ



@ ðrui Þ @ rui uj @P þ ¼ þ rg i @t @xi @xj @ þ ðm þ mt Þ @xj   @ui @uj þ Si þ @xj @xi

(2)

where t is the time; m and r denote the viscosity and density of the fluid, respectively; mt is the eddy viscosity; P ¼ p þ (2/3)rk, where p is the pressure and k is the turbulent kinetic energy; ui and uj are the average velocity components; gi is the acceleration due to gravity; i, j ¼ 1, 2, 3 (x, y, z); and Si is the source term for the momentum equation. The porous-media fluid model is a hypothetical model that produces the same water-blocking effect as the fishing net by setting the coefficients of the hypothetical porous media. For a flow through porous media, a pressure gradient exists: !! ! ∇p ¼ au þ b u  u

ð3Þ !

where a and b are constant coefficients and u is the flow velocity. This expression was proposed by Forchheimer in 1901 based on Darcy’s law. In the case of large porosities (e.g., an array of fixed cylinders), turbulence will occur, and the quadratic term for the frictional force will completely dominate over the viscous term (the linear term). In this case, the linear term is only a fitting term that has no physical meaning and can thus be neglected. Outside the porous media, the source term for the momentum equation is defined as Si ¼ 0. Inside the porous media, Si is calculated by the following equation: 1 !! Si ¼ Cij r u  u 2 where Cij is given by

ð4Þ

0

Cn B Cij ¼ @ 0

0 Ct

0

0

1 0 C 0A Ct

ð5Þ

where Cij represents the material matrices consisting of porous media resistance coefficients and Cn and Ct represent the normal and tangential resistance coefficients, respectively. The drag force (Fd) and lift force (Fl) acting on the flow through the porous media can be expressed as follows: !! ! 1 Fd ¼ Cn rlA u  u 2

ð6Þ

!! ! 1 Fl ¼ Ct rlA u  u 2

ð7Þ

where l and A represent the thickness and area of the porous media, respectively. The porous coefficients in Eqs. (6) and (7) can be calculated from the drag and lift forces. Moreover, the drag and lift forces acting on a fishing net are strongly correlated with the features of the net. Therefore, the connection between the net features and the flow field is established using the porous coefficients in the numerical model. Generally, the drag and lift forces of the plane net can be obtained from laboratory experiments or calculated using the Morison equation: 1 Fd ¼ rCd Au2 2

ð8Þ

1 Fl ¼ rCl Au2 2

ð9Þ

where Cd and Cl are coefficients that can be calculated using empirical formulas (Bi et al. 2014b). The porous coefficient Cn can be calculated from a curve fit between the drag forces acting on a plane net and corresponding current velocities using the least squares method when the plane net is oriented normal to the flow. The other coefficient Ct can be obtained when a plane net is oriented at a certain attack angle (see Fig. 1a). In this case, the coefficient Ct should be transformed to Ctα using Eq. (10) (Bear 1972). Next, Ctα can be

Net Structures: Hydrodynamics

1131

Net Structures: Hydrodynamics, Fig. 1 Definition of the angles α and β: plane nets (a) in the horizontal plane and (b) at an arbitrary position (Bi et al. 2014b)

calculated from a curve fit between the lift forces acting on a plane net and corresponding current velocities using the least squares method. Cta ¼

Cn  Ct sin ð2aÞ 2

ð10Þ

where α is the attack angle, defined as the angle between the flow direction and plane net in the horizontal plane, and Ctα is the tangential inertial resistance coefficient for the plane net at an attack angle α. When a plane net is oriented at an arbitrary position (see Fig. 1b), the porous coefficients should be transformed using Eq. (11): 0

C0n

1

equations can be established mainly based on Newton’s second law. Given an initial net configuration, the motion equations can be solved numerically for each lumped-mass point. Finally, the configuration of the net in current can be simulated. The calculation method for the model has been explained in previous studies (Li et al. 2006; Zhao et al. 2007b), and thus, only a brief outline is provided in this section. Under a uniform current, the motion equations of lumped-mass point i can be expressed as follows: !

ðMi þ DMi Þa ¼

n X ! ! ! ! T ij þ F d þ B þ W ð12Þ j¼1

B 0C BC C ¼ @ tA C0t 1 0 sin 2 a sin 2 b cos 2 a sin 2 a cos 2 b 0 1 C Cn B 1 1 C B1 2 2 CB b  b sin 2a sin sin 2a sin 2a cos CB C t C B 2 2 C@ A B2 A @ 1 1 Ct sin 2b 0  sin 2b 2 2

ð11Þ

where β is the angle between the normal vector of ! the plane net (n en) and z-direction. The cosines of α and β can be calculated between the corresponding two vectors. Lumped-Mass Mechanical Model The lumped-mass mechanical model is introduced to simplify the fishing net, and the motion

where Mi and ΔMi are the mass and added mass ! of lumped-mass point i, ! respectively; a is the acceleration of the point; T ij is the tension force in twine ij ( j is the index for the knot at another end of the bar ij); n is the number of knots ! ! ! adjacent to point i; and F d , W , and B denote the drag force, gravity force, and buoyancy force, respectively. To consider the direction of the hydrodynamic forces acting on mesh bars, local coordinates (t, , x) are defined to simplify the procedure (see Fig. 2). The origin of the local coordinate system is set at the center of a mesh bar, and the -axis lies on the plane, including the t-axis and ! flow velocity u . The drag force on a lumpedmass point in the t-direction can be obtained from the Morison equation as follows:

N

1132

Net Structures: Hydrodynamics

Net Structures: Hydrodynamics, Fig. 3 Schematic of a plane-net element (Bi et al. 2014b)

Net Structures: Hydrodynamics, Fig. 2 Local coordinate system for a mesh twine (Bi et al. 2014a)

FDt

   ! ! ! ! 1 ¼  rCDt At V t  R_ t  V t  R_ t ð13Þ 2

where CDt is the drag coefficient in the t-direction, At is the projected area of the twine ! ! normal to the t-direction, and R_ t and V t are the velocity components of the lumped-mass point and water particle in the t-direction, respectively. Similar expressions can be applied to the other two components of the drag force, FD and FDx. The mesh-grouping method (Tsukrov et al. 2003; Zhao et al. 2007a) is used to reduce the computational effort of the net. Each grouped mesh is defined as a plane-net element (see Fig. 3). The normal vector of the plane-net element ! (n en ) is calculated as follows: !

!

n n n en ¼ !i1 !i2   n i1  n i2 

!

!

ð14Þ

!

where n i1 and n i2 are given by ! ! j1  i1  n i1 ¼ ! ! ,  j1  i1 

!

! ! i2  i1  n i2 ¼ ! !  i2  i1 

!

ð15Þ

Because of the deformation of the net, the area of a plane-net element is not constant, which influences the solidity of the plane-net element. Consequently, the solidity Sn must be corrected

based on the varying area of the plane-net element: S0n ¼

A Sn A0

ð16Þ

where Sn and A denote the solidity and area of the undeformed plane-net element, respectively, and S0n and A0 are the corrected solidity and area of the plane-net element, respectively. To calculate the area of the plane-net element, the four-sided element is divided into four triangles, as shown in Fig. 3. The area of the element can be obtained by the sum of the four triangles. Coupled Fluid–Structure Interaction Model Based on the above work, the interaction between the flow and fishing net can be simulated by dividing the net into many plane-net elements (see Fig. 4). The main concept of the numerical approach is to combine the porous-media fluid model and lumped-mass mechanical model to simulate the interaction between the flow and flexible nets (Bi et al. 2014a, b). Considering the example of a single flexible net, the calculation flow chart of the numerical approach is shown in Fig. 5. The details of the calculation procedure are as follows. The calculation procedure includes four steps. Step 1 involves the simulation of the flow field around a vertical plane net without considering the net deformation using the porous-media fluid model. Step 2 involves the determination of the drag force and the configuration of a flexible net in a current using the lumped-mass mechanical model. The given initial flow velocity is the

Net Structures: Hydrodynamics

1133

Net Structures: Hydrodynamics, Fig. 4 Schematic of the net model

average value exported from the upstream surface of the plane net in the last step. In Step 3, according to the configuration of the net, the orientation and the porous coefficients of each planenet element can be obtained, thereby determining the flow field around the fishing net. In Step 4, the drag force and configuration of the net are calculated again. The flow velocity acting on each lumped-mass point is the average value exported from the upstream surface of the corresponding plane-net element in the last step. The terminal criterion of the calculation procedure is defined as ΔF ¼ (Fi þ 1  Fi)/Fi þ 1, where Fi and Fi þ 1 are the drag forces of two adjacent calculations. If ΔF 0:490:65 Clay > > > = <  ¼ 0:49 Silt > > > > ; : 0:49 Sand qu ¼ 1:3cN c þ g1 DN q þ 0:6gRN r f þ nt g1 ¼ g þ 2 2s ðn  1ÞR

ð9Þ

where  is Dynamic effect coefficients, R is the inner radius of the pile, and γ1 is the equivalent unit weight of soil above the pile tip. γ is the unit weight of the soil above the pile tip, fs is the ultimate raft friction, and t is the shear strength of the soil above the pile tip. By the survey data of CPT method, the calculation method of the bearing capacity of pipe piles with complete and incompletely occlusion was summarized (Lehane et al. 2005) and the calculation of pile tip resistance in the case of complete occlusion is as follows:

Offshore Pile Driving

1209

p Qb ¼ qb0:1 D2 4 qb0:1 ¼ 0:6 qc

ð10Þ

where qc is average CPT end resistance, qb0.1 is the pile end bearing resistance at a pile base movement of 10% of the pile diameter, and D is the pile diameters. Under the condition of partially occlusion, the pile end bearing is calculated as follows: p Qb ¼ qb0:1 D2 4 qb0:1 ¼ 0:15 þ 0:45  Arb qc
2 D  Arb ¼ 1  FFR i2 D (

0:2 ) Di ðmÞ FFR ¼ min 1, 1:5m

ð11Þ

the average IFR measured over the final 20 diameters of penetrations, G is operational shear modulus (assumed equal to the in-situ very small strain value), Δr is interface dilation (assumed ¼ 0.02 mm for the database), and patm is a reference stress ¼ 100 kPa. Velocity-Dependent Penetration Resistance The strength behavior of soils can be significantly affected by the applied rate of loading, which is very important for the design of pile bearing capacity. Some new methods such as Cone Penetration Test (CPT) have been in popular use considering the speed of pile penetration into the ground and the relative velocity of the pile with respect to the surrounding soil. A parameter Rf was adopted to describe the effect of velocity on soil strength (Chow et al. 2015), which can be expressed as: "

Arb is

the effective where Di is Inner Diameter, area ratio, the other parameters as same as 10 equation. And the skin resistance is calculated as follows: ð Qs ¼ pD tf dz

v=d Rf ¼ n ðv=dÞref

#b ð13Þ

(12)

where vref is a reference velocity equal to the penetration rate adopted in the measurement of su(CPT), d is the FFP diameter, n is introduced to account for the greater rate effects reported for shaft resistance compared to tip resistance, and β is a strain rate parameter. The bearing and frictional resistances were scaled by a rate function Rf and assumed that at any given location the operational strain rate may be approximated by the normalized velocity (O’Loughlin et al. 2013). Rf can be expressed as: " # v=d R f ¼ 1 þ l log or Rf ðv=dÞref " #b v=d ¼ ð14Þ ðv=dÞref

where δcv is constant volume interface friction angle, srf is radial effective stress at failure, s0rc is radial effective stress after installation and equalization, Ds0rd is increase in radial stress due to loading stress path (dilation), f/fc is 1 for compression loading and 0.75 in tension, IFRmean is

where l and β are strain-rate parameters and v is velocity of penetration in static penetration tests. The effect of shear rate on measured vane shear strength was studied (Sharifounnasab and Ullrich 1985) and the relevant formula is:

 f  0 src þ Ds0rd tan dcv fc
 0:5 h ,2 s0rc ¼ 0:03  qc ðArs  Þ0:3 max D
2 D i Ars ¼ 1  IFRmean D2 "
 # Di ðmÞ 0:2 IFRmean ¼ max 1, 1:5m tf ¼ s0rf tan dcv ¼

Dr withG ¼ qc  185  qc1N 0:7 and D  0:5 ¼ ðqc =patm Þ= s0vo =patm

Ds0rd ¼ 4G qc1N

O

1210

Offshore Pile Driving


b sv o ¼a sv0 o0

ð15Þ

in which sv is vertical shear strength; svo is vertical shear strength, measured at the standard shear rate; o is shear rate; o0 is standard shear rate; and α and β are coefficients which depend on the properties of the soil. The majority of dynamic pile tests are analyzed using pile–soil interaction models based on Smith (1960), (Randolph 2003b) with the soil resistance expressed as:
 wp b td ¼ Min 1, ð1 þ JvÞts Q

ð16Þ

where wp is the local pile displacement, td and ts are the dynamic and static shaft friction values, Q is the displacement, or “quake,” to mobilize the limiting static resistance, and J is a damping parameter multiplying the local pile velocity, v. American Petroleum Institute (API) does not provide guidelines for the effects of cyclic loading and rate of loading on the axial capacity of piles. (Iskander 2010) There is evidence that cyclic tensile loading, in particular, may significantly reduce pile capacity (Kraftjr 1990). Thus, it can be seen the velocity do have a significant effect on the properties of soil which cannot be ignored and more research needs to be further developed.

Refusal and Pile Running During the Driving Pile is an important part of offshore platform structure. The materials and operations of construction have a significant impact on the cost of offshore projects. It has proved that there are certain risks in the construction of pile and may cause some serious problems during the operation, such as pile driving refusal and pile running. With the development of offshore platforms into deep water and large scale, the impact of such kind of risks is even more prominent. Therefore, it is necessary to have a good understanding of the

causes of these risks from the technical perspective and present the preventive methods and measures in the design and construction. Pile Driving Refusal Super long piles with large diameters usually have to be manufactured by segments before installation because of transportation and hoisting difficulties. The segments of the pile will be assembled by welding to the formerly penetrated one. The assembling work often takes 1 day or even a longer time. In additional, the construction process may pause due to other various problems which will take a long time to restart the driving (Yan et al. 2012). During this period of time, the excess pore pressure in the soil below and around the pile, which is built up during pile driving, will dissipate to some extent, increase the strength of the soil, and make restarting the successive penetration very difficult, sometimes even refusal may take place. This matter has been encountered quite often in many engineering cases and puzzled the designers for years. As for the pile driving refusal, many experts have conducted extensive research and made a series of achievements. Based on the platform WHPE in Bohai Gulf, Yan et al. (2012) proposed several measures to reduce the refusal risk for restarting a segmented pile: 1. Cutting down the pile extension time is the most effective measure to minimize the refusal risk. 2. To keep the pile tip in a clay layer instead of in the sand layer when extending the pile segment. 3. When the stick-up stability was satisfied, increasing the length of the last segment of the pile and assembling the pile segments when the pile tip penetrates into a clay layer could greatly ease the difficulty of driving the pile. The reasons of piling refusal in the restarting process were analyzed and presented a numerical method for judging the risk of refusal by estimating the blow counts after pile extension, in which

Offshore Pile Driving

1211

the regain of soil strength is considered (Yan et al. 2015a). A fatigue factor β, which can be expressed as the following formula, is consistently introduced to cover all reasons and associated with the degree of consolidation. ( b¼

 X 2 Y5 , X

Y5 1, Y  5 < X  Y

ð17Þ

where Y is the designed penetration and X is the specified pile tip penetration. In order to predict if refusal may occur at any restart penetration after pile extension, blow counts needed to penetrate the pile for further 30 cm are estimated. If the estimated blow counts less than an acceptable value, refusal is considered not to take place at this penetration. A case of a practical offshore pile installation which experienced refusal is analyzed (Sa et al. 2013). Empirical equations are provided to predict soil resistance during driving and after setup. According to the research results of Skov and Denver (1988), the empirical relationship to estimate the time effect on the resistance which helps to analyze bearing capacity can be expressed as:


Qt t ¼ 1 þ A log t0 Q0

ð18Þ

where the soil resistance corresponding to finishing one pile section is denoted as Q0 while Qt represents the soil resistance after a suspension of time t. A and t0 are two empirical parameters depending on the soil properties. Characteristics of local soil around the pile are summarized though comparing the resistance changes between local geologic data and pile driving record data (Pu 2012). Result shows that the soil resistance within a period of time after driving is much higher than that in the process of pile driving. Based on the driving records, the back-figured method is applied to estimate the pile bearing capacity after refusal taking place. The required equipment, key technology, and main technological processes in the installation process of the shallow water jacket after pile refusing were described (Hui and Wang 2014).

The researches relevant to the driving refusal mainly focused on the mechanism and some measures based on the practical engineering or simulation software, which can provide the references and analytical analysis to the design and construction of practical project. Some more flexible and economic measures need further study. Pile Running Offshore platforms in deep seas require extremely long large diameter pipe piles (LDPPs) to support the loads generated from the structure itself, wind and waves. If the LDPPs are in two or more segments, in situ pile splicing is required, which requires additional construction time and leads to premature refusal. One solution to this problem is to use a single segment of LDPP and drive it continuously into the seabed. As the LDPP could be very heavy (700 t or more), pile running may occur.(Randolph 2003a; Dover and Davidson 2007; Olson and Flaate 1967) The unexpected pile running may break the steel wire or even cause the hammer to be lost in the sea. The researches relevant to the pile running are mainly engaged in the predicting procedure based on the energy conservation method or critical equilibrium conditions. Yan et al. (2015b) proposed a procedure for predicting the pile-running zones based on the limit equilibrium of pile weight and soil resistance. The total soil resistance can be expressed as: Qd ¼ Q f þ Qp ¼ f As qu A

ð19Þ

where Qd is the total soil resistance, Qf is shaft resistance, Qp is the bearing capacity of the pile sand, fis the average frictional force per unit area, qu is the bearing capacity of the pile end, and A is the area of the annular pile end. Pile-running may occur if the following conditions are satisfied: Qd  W P

or

Qd  W P þ W H

ð20Þ

In which WH is the hammer weight and WP is the weight of the pile. The equilibrium conditions above belong to different states. Yan et al. (2016) also established a predicting procedure based on

O

1212

Offshore Pile Driving

the energy conservation method of the running pile. The key theoretical formula can be expressed as: EG ¼ W r þ Es

Qp is the end bearing resistance, and the Fb is Buoyant weight of the displaced soil. The LDPP driven can be analyzed by this formula.

ð21Þ

Conclusions where EG is the potential energy of pile hammer, Wr is the work done by lateral friction resistance and the tip resistance, and Es is the consume energy. Sun et al. (2016) proposed an analytical method to predict the occurrence of pile running and established the framework for determining the calculation parameters from a laboratory or field test. The process can be separated into two phases: (1) the energy transfers from the hammer to the pilehammer system and (2) the pile and hammer sink together into the soil embedment, which can be, respectively, expressed as the following formulas: b mh ghp ¼

 1 mh þ mp v20 2

  1 mh þ mp v2j  v2j1 2 ¼ ðW  Fs  Ft  Fb ÞDS

ð22Þ

ð23Þ

where mh is the mass of the ram (unit in kg); g is the gravitational constant; hp is the stroke of the hammer; mp is the total mass of the LDPP, anvil, helmet, and follower with units in kg; v0 is the instantaneous velocity of the hammer and pile at the time immediately after the impact; and b is the efficiency of the blow. Sun et al. (2017) also proposed a simplified theoretical method to explain the mechanisms of the pile running and proposed a factor of friction degradation to calculate the dynamic skin friction from the static ultimate skin friction of surrounding soil to predict the pile running condition. Based on the force equilibrium on the vertical direction, the resultant force F could be derived as: F ¼ W  Q f  Qp  Fb

ð24Þ

where W is the effective self-weight of the LDPP and hydraulic hammer, Qf is the side skin friction,

The driveability of the open-ended piles is influenced significantly by the soil resistance during the driving (SRD); SRD consists of the outer skin resistance, inner skin resistance, and bearing resistance. The soil plug has a great influence to the SRD. The soil strength is dependent on the penetration velocity; during the driving, the penetration velocity will also influence the SRD. Based on the influence factor, the calculation method of the penetration resistant is summarized, the judgment approach of the pile running and premature pile refusal are also summarized.

References Brucy F, Meunier J, Nauroy JF (1991) Behaviour of pile plug in sandy soils during and after driving. In: Proceedings of 23rd annual offshore technology conference, vol 1, pp 145–154 Chow SH, O’Loughlin C, Randolph M (2015) Soil strength estimation and pore pressure dissipation for free-fall piezocone in soft clay. Géotechnique 64(10):817–827 Dover AR, Davidson J (2007) Large Diameter steel pipe piles running under self weight in soft clay: predicted vs. observed behavior-Richmond San-Rafael Bridge Seismic Retrofit// Triennial International Conference on Ports, pp 1–10 ENR (1965) Michigan pile test program test results are released. Eng News Rec 26(8):33–34 Fattah MY, Al-Soudani WH, Omar M (2016) Estimation of bearing capacity of open-ended model piles in sand. Saudi Soc Geosci Gates M (1957) Empirical formula for predicting pile bearing capacity. Civ Eng ASCE 1(2):479–482 Guo SC, Shao-Lin WU (2011) Problems of rapid pile sinking during pile driving and solutions. Port Waterway Eng 163–166 Hiley A (1925) A rational pile–driving formula and its application in piling practice explained. Engineering 119(3100): 657–658, and 721 Hui D, Wang J (2014) Installation technology of jacket after pile refusing in shallow water. Ship Standardization Engineer Iskander M (2010) Review of design guidelines for piles in sand//behavior of pipe piles in sand. Springer, Berlin/ Heidelberg, pp 7–23

Offshore Structure Janbu N (1953) An energy analysis of pile driving with the use of dimensionless parameters. Norwegian Geotechnical Institute, Oslo, Publication no 3 Jeong S, Ko J, Won J, Lee K (2015) Bearing capacity analysis of open-ended piles considering the degree of soil plugging[J]. Soils Found 55(5):1001–1014 Klos J, Tejchman A (1977) Analysis of behaviour of tubular piles in subsoil. In: Proceedings of 9th international conference in soil mechanics and foundation engineering, Tokyo, pp 605–608. www.issmge.org Kraftjr L (1990) Computing axial pile capacity in sands for offshore conditions. Mar Geotechnol 9(1): 61–92 Kumara JJ, Kikuchi Y, Kurashina T (2016) Effects of the lateral stress on the inner frictional resistance of pipe piles driven into sand. Int J Geo-Eng 7(1):1 Lehane BM, Schneider JA, Xu X (2005) CPT based desing of driven piles in sand for offshore structures. The University of Western Australia, Perth, west of Australia Murthya DS, Robinsonb RG, Rajagopalb K (2018) Formation of soil plug in open-ended pipe piles in sandy soils. Int J Geotech Eng 15(2021):519–529 O’Loughlin CD, Richardson MD, Randolph MF et al (2013) Penetration of dynamically installed anchors in clay. Geotechnique 63(11):909–919 Olson RE, Flaate KS (1967) Pile-driving formulas for friction piles in sand. Soil Mech Found Div (93): 279–296 Paik K, Salgado R (2003a) Determination of bearing capacity of open ended piles in sand.Journal of geotechnical and geoenvironmental engineering. ASCE 129(1):46–57 Paik K, Salgado R (2003b) Determination of bearing capacity of open ended piles in sand. J Geotech Geoenviron Eng ASCE 129(1):46–57 Paikowsky SG (1990) The mechanism of pile plugging in sand. In: Proceedings of the 22nd offshore technology conference, Houston, TX, OTC 6490, vol 4, pp 593–604 Pu Y (2012) Study on driving refusal of steel pipe pile in large diameter. Port Engineering Technology Randolph MF (2003a) Science and empiricism in pile foundation design. Geotechnique 53(10):847–876 Randolph MF (2003b) Science and empiricism in pile foundation design. Geotechnique 53(10):847–876 Randolph MF, Leong EC, Houlsby GT (1991) Onedimensional analysis of soil plugs in pipe piles. Geotechnique 41(4):587–598 Sa L, Yinghui T, Yangrui Z et al (2013) Premature refusal of large-diameter, deep-penetration piles on an offshore platform. Appl Ocean Res 42(3):55–59 Sharifounnasab M, Ullrich CR (1985) Rate of shear effects on vane shear strength. J Geotech Eng 111(1): 135–139 Skov R, Denver H (1988) Time-dependence of bearing capacity of piles. In: Proceedings 3rd international conference app. stress-wave theory to piles, Ottawa, pp 879–888

1213 Sun L, Jia T, Yan S et al (2016) Prediction of pile running during the driving process of large diameter pipe piles. Ocean Eng 128(2016):48–57 Sun L, Wang Y, Guo W, Yan S, Chu J, Liu X (2017) Case study on pile running during the driving process of large-diameter pipe piles. Mar Georesour Geotechnol 1–13 Szechy CH (1959) Test with tubular piles. Acta Technica 24:181–219 Whitaker T (1976) The design of piled foundation, 2nd edn. Great Britain, Robert Maxwell, pp 26–43 Xie YJ, Zhu HH, Wang HZ, Tao LB (2005) Analytical solution for model of pile hammer impact. Chin J Mech Eng 24(1):171–176 Yan SW, Zhou QH, Liu R et al (2011) Pit bearing capacity effect on status of soil plug during pile driving in ocean engineering. China Ocean Eng 25(2): 295–304 Yan S, Huo Z, Zhao L et al (2012) Research on the factors influencing the driving of very long piles in the Bohai Gulf. Financ Innov 1(1):1–11 Yan S, Li J, Sun L et al (2015a) Difficulties and measures of driving super long piles in Bohai Gulf. Theor Appl Mech Lett 5(2):69–73 Yan S, Jia Z, Liu W et al (2015b) Reserch on the large diameter and supper long pile running under selfweight in the ocean engineering. J Coast Res 73: 809–814 Yan S, Chen H, Jia Z, et al (2016) Research on the mechanism and calculation method for pile-running of long and large diameter piles based on energy conservation method. Ocean Eng 35(3):63–71

O Offshore Project Development ▶ Field Development

Offshore Ship ▶ Offshore Vessel

Offshore Structure ▶ Offshore Structure Design Under Ice Loads

1214

Offshore Structure Design Under Ice Loads Zhenhui Liu Front End Engineering, Aker Solutions ASA, Trondheim, Norway

Synonyms Accidental loads; Ice loads; Offshore structure; Plastic design; Ultimate strength

Definition Offshore structure is an installation of structures in a marine environment with relative far distance to nearest shore, usually for the production and transmission of electricity, oil, gas, and other resources. Typical offshore structures are subsea oil and gas developments, offshore platforms (fixed platforms, semi-submersibles, spars, tension leg platforms, floating production storage, and offloading), offshore wind turbines, and subsea pipelines. Depending on the loading conditions, offshore structures can be made of steel, concrete, or composite materials. Ice loads are referring to the loads exerted to offshore structures from various ice types, such as first-year level ice, multiyear level ice, ice ridge, brash ice, and iceberg. The main focus of this section is the design methodology used for the design of offshore structure under ice loads.

Scientific Fundamentals Limit State Design Principles The offshore structures shall be designed in a way that it can sustain all possible loads during their lifetime without causing human loss and significant economic or environmental pollutions. The designers are encouraged to check the conditions that may lead to structure failure, which are referred as limit states. Following limit states are

Offshore Structure Design Under Ice Loads

defined for offshore structure design under ice actions (ISO19906 2010): • Ultimate limit state (ULS) that generally corresponds to resistance to extreme-level ice event (ELIE), both local and global actions shall be considered. • Serviceability limit state (SLS) that corresponds to criteria governing normal functional use under serviceability-level ice event (SLIE). • Fatigue limit state (FLS) that corresponds to the accumulated effect of repetitive actions. • Accidental limit state (ALS) that corresponds to accidental events and abnormal-level ice event (ALIE), both local and global actions shall be considered. Generally, the offshore structure shall be designed to comply the criteria corresponding to all of the above defined limit states. However, it is challenging to predict the ice loads with high precision. The stochastic characteristics of ice loads increase the complexity of structure design. Permanent plate deflections due to compressive ice loads may happen due to large exposed ice loads (Hänninen 2010). An extreme case is the famous Titanic accident in maritime history back to 1912. Obviously, the cruise ship is not considered to take the iceberg impact loads at that time. Limiting Mechanisms for Ice Loads In order to identify the actual ice loads, three limiting mechanisms are defined. They are namely termed as limit stress, limit force, and limit momentum. (a) Limit stress The ice fails against the structure and the strength of ice determines the ice loads level. This normally gives highest ice loads. The unconfined strength of ice is commonly used to represent the ice strength. (b) Limit force The driving force, such as winds, currents, and the surrounding pack ice, are pushing the ice features against wide structures with thinner pack ice failing behind. The load on the structure is given by the wind and current drag on the ice feature leaning against the structure

Offshore Structure Design Under Ice Loads

1215

plus the pack ice driving pushing on the back of the ice feature. (c) Limit momentum This mechanism corresponds to the ice mass with certain velocity collides with a structure and the momentum of ice mass is insufficient to envelop the whole structure. The contact force builds up as the initial momentum changes. Types of Offshore Structure The design of offshore structure under ice loads largely depends on the loads level of ice events. Meanwhile, the structure types also have significant impacts to the ice loads. The interaction between structure and ice is a complicated process. The physical understandings are still limited. The characteristics of structural geometry shape shall be considered when evaluating the ice loads. Typical offshore structure types are as follows: • Floating production, storage, and offloading unit (FPSO) • Semisubmersible floater • Gravity-based structure (GBS) • Jackup rig • Icebreaker • Offshore supply vessel (OSV) • Offshore oil tanker • Liquefied natural gas carrier (LNG) • Offshore wind turbine Based on the main dimensions of the offshore structures, they can be categorized as shown in

Fig. 1. Figure 2 shows some of the main concepts used for offshore structures (not necessarily for ice loads). Types of Interaction Scenario The interaction scenarios play a crucial role on deriving ice-related loads. For an optimized structure design, the identification of the interaction scenario is of great importance. The typical interaction scenarios are summarized as follows: (a) Vertical-sided structure The ratio between the width of structure and the ice thickness determines the likelihood of possible ice failure modes. The crushing of ice against the vertical wall may cause significant local high pressure, as explained by Jordaan (2001). This type of interaction is normally for fixed structures under relative light ice conditions. Figure 3 shows an illustration of this interaction scenario. (b) Multi-leg This type of interaction has decreased exposed contact area, and consequently, it may have better performance under harsh wave loads. It is normally used for environment where ice is not severe. The presentence of several legs interacting with ice in close vicinity to each other has mutual influences, see the discussions by Karulin and Karlina (2014). The sheltering effect causes unsymmetrical ice loads to legs, which may increase the yawing

Offshore structures

Floating

Ship

Semisubmersible

Fixed

FPSO

Wind turbine

Jackup

Offshore Structure Design Under Ice Loads, Fig. 1 Main offshore structure under ice condition

GBS

O

1216

Offshore Structure Design Under Ice Loads

Offshore Structure Design Under Ice Loads, Fig. 2 Some typical offshore structural concepts with permission of NOAA (2010)

from ice-breaking failure and ice clearance (Fig. 5).

Offshore Structure Design Under Ice Loads, Fig. 3 An illustration of ice sheet crushing with vertical side structure

p-A Relationship for Ice Crushing The ice-structure interaction is a complicated process. The understanding of it is still limited. For simplification, ice crushing failure pressure could be determined by the contact area (Sanderson 1988). The pressure and area relationship is widely used for designing structures under ice actions, see Fig. 6 for an example. It is defined as follows: p ¼ Cp ∙ADp

moment. Figure 4 shows scenarios for a multileg platform operating in ice conditions with different heading angles. The potential jamming effect of broken ice could be another hazard to the multi-leg structures. (c) Sloping-sided structure Sloping-sided structures break ice upwards or downwards. The corresponding ice failure mode is bending failure and the bending failure results generally lower ice loads. This type of structure has been widely applied to various offshore structures, such as jackets in Bohai sea of China (Yue and Xiangjun 2000), wind turbines in ice covered waters (Barker et al. 2005), and the confidential bridge in Canada (Aïtcin et al. 2016). The main loads are

where p is pressure, Cp and Dp are both constants. Constants Cp and Dp are depending on various factors, such as the confinement effects, indentation geometry, area of loading, aspect ratio etc., see the discussion by Johnston et al. (1998). The understandings to the background of the pressurearea relationship are crucial for selecting the right combinations. The pressure p can be either global nominal pressure or local contact pressure, and the constants shall be selected accordingly. The improper selection of constants may cause significant discrepancies on predicting the ice loads. The recommended constants for local pressure and area relationship from ISO 19906 are listed in Table 1.

Offshore Structure Design Under Ice Loads

1217

Offshore Structure Design Under Ice Loads, Fig. 4 An illustration of multi-leg interaction with ice sheet under different heading angles

Offshore Structure Design Under Ice Loads, Fig. 5 Typical ice failure on upward and downward cone

Offshore Structure Design Under Ice Loads, Fig. 6 A typical pressure area relationship plot

O

Local Structure Design Under Ice Crushing In this section, the main principles of the local structure design are presented. The related regulations, the pressure area relationship and the theory behind the plate design equations are shown.

Related Regulations The design of local structural scanting shall follow the rules that classification society has given. The main relevant ice regulations are as follows: • The Finnish-Swedish Ice Class Rules, FSICR (Finish-Swedish 2017)

1218

Offshore Structure Design Under Ice Loads

• The Russian Maritime Register of Shipping ice rules (RMRS 2005) • The unified Polar Class (PC) rules of the International Association of Classification Societies (IACS 2016) • The DNV rules for classification of ships, Part 5 Chapter 1 (DNV 2003) A design patch load (uniform distributed pressure load) shall be established prior to the structure design. Figure 7 shows an example of effective contact area for structure exposed to ice sheet. The detailed procedures on how to derive the effective contact area can be found in related regulations, such as the DNV ice rule (DNV 2003).

equations, together with correction factors accounting various design scenarios. Assuming a three-hinge mechanism for a deformed plate with unit length under uniform pressure p, the plate width is b, as shown in Fig. 8. The critical loads q could be obtained by equaling external virtual work with internal virtual work (Jørgen 2007). External work: We ¼

ðs 0

p∙wðxÞdx ¼ pb∙

dw 2

ð1Þ

Internal virtual work: W i ¼ Mp ðdy þ 2dy þ dyÞ ¼ 4Mp dy

Plastic Plate Strip Analogy The regulations mentioned above are using either elastic or plastic analogy to derive the design Offshore Structure Design Under Ice Loads, Table 1 Summary of constants for local pressure and area relationship, from ISO 19906 (ISO19906 2010) Interaction scenario First-year level ice Thick, massive ice

Pressure type Local Local

Offshore Structure Design Under Ice Loads, Fig. 7 An example of effective contact area

Cp 2.35 7.40

Dp 0.50 0.70

ð2Þ

And we have: b dw ¼ dy 2

ð3Þ

16Mp b2

ð4Þ

So: p¼

ℎ

ℎ

Offshore Structure Design Under Ice Loads, Fig. 8 Plate strip analogy (plastic analysis)

2

Ice sheet

Offshore Structure Design Under Ice Loads

1219

yield line

plate patch load

Offshore Structure Design Under Ice Loads, Fig. 9 Roof-shaped yield line pattern for plate under uniform pressure load

The unit plastic bending moment is defined as follows: Mp ¼ sy W p ¼ sy

t2 4

ð5Þ

where sy is the yield stress. Combining Eqs. (1)–(5), the relationship between plate thickness and the critical external loads can be established. rffiffiffiffiffi b p t¼ 2 sy

ð6Þ

Equation (6) is obtained from plastic analysis for a plate with unit width under uniform distributed loads. For the plate exposed to ice load patches, a two-dimensional plastic analysis may be performed. Figure 9 shows a typical yield line pattern for a plate under uniform pressure load (patch load). The plastic analysis can be used to derive the design equations for plate thickness (Chen and Han 1988). Sobotka presents solutions for plate under loads other than uniform pressure (Sobotka 1989). Based on the failure pattern as shown in Fig. 9, the plastic load-carrying capacity in bending for fully clamped pates is expressed by the following equation, see (Wood 1961):

p¼

12sy t2 l 2 a2

ð7Þ

where αqisffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi called the aspect ratio and defined as   2 b a¼l 3 þ bl2  bl . l is the length of load patch, and b is the patch load height. Equation (7) can be rewritten as: 0sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffiffi b p @ 1 b2 1  pffiffiffi t¼ ∙ 1þ 2 sy 3 l2 3

O

1 bA l

ð8Þ

In IACS (2016), the plate thickness design equation is as follows after let l ¼ s (without the safety factors). t¼

b 2

rffiffiffiffiffi p 1 ∙ sy 1 þ 0:5ðb=sÞ

ð9Þ

References Aïtcin P-C, Mindess S, Langley WS (2016) Chapter 8: The confederation bridge. In: Alexander MG (ed) Marine concrete structures. Woodhead Publishing, London, pp 199–214 Barker A, Timco GW, Gravesen H, Vølund P (2005) Ice loading on Danish wind turbines: Part 1: dynamic model tests. J Cold Reg Eng 41:1–23

1220 Chen WF, Han DJ (1988) Plasticity for structural engineers. Springer-Verlag, New York DNV (2003) Chapter 1: Ships for navigation in ice. In: Rules for classification of ships Part 5. DNV, Høyvik, Norway Finish-Swedish (2017) Finish-Swedish ice class rules, TRAFI/494131/03.4.01.00/2016. Finish Transport and Communications Agency, Helsinki, Finland Hänninen S (2010) Incidents and accidents in winter navigation in the Baltic Sea, winter 2002–2003. Finnish and Swedish Maritime Administration, Helsinki, Finland and Norrkoping, Sweden IACS (2016) Requirements concerning POLAR CLASS. International association of classification societies, London, UK ISO19906 (2010) Petroleum and natural gas industries – Arctic offshore structures 19906. International Standards, Geneva, Switzerland Johnston ME, Croasdale KR, Jordaan IJ (1998) Localized pressure during ice-structure interaction: relevance to design criteria. Cold Reg Sci Technol 27:105–117 Jordaan I (2001) Mechanics of ice-structure interaction. Eng Fract Mech 68:1923–1960 Jørgen A (2007) Design considerations for stiffened plates subjected to ice action. In: TMR4205 (ed) Buckling and ultimate strength of marine structures. Norwegian University of science and technology, Trondheim, Norway Karulin E, Karlina M (2014) Peculiarities of multi-legged platform operation in ice condition. OMAE, San Francisco NOAA (2010) NOAA Ocean explorer gallery: types of offshore oil. [Online] Available at: https:// oceanexplorer.noaa.gov/explorations/06mexico/back ground/oil/media/types_600.html. Accessed July 2018 RMRS (2005) Rules for the classification and construction of sea-going ships. Russian Maritime register of shipping, Saint-Petersburg, Russia Sanderson TJO (1988) Ice mechanics – risks to offshore structures (1st ed). Springer, London Sobotka Z (1989) Theory of plasticity and limit design of plates. Elsevier, North Holland Wood RH (1961) Plastic and elastic design of slabs and plates. The Ronald Press, New York Yue Q, Xiangjun B (2000) Ice-induced jacket structure vibrations in Bohai Sea. J Cold Reg Eng 14:81–92

Offshore Vessel Zhuang Kang and Wen-Chi Ni College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China

Synonyms Offshore engineering vessel; Offshore ship

Offshore Vessel

Definition Offshore vessels are ships that specifically serve operational purposes such as oil exploration and construction work at the high seas.

Scientific Fundaments Composition and Basic Type As mentioned, above, the denotation of offshore vessels is a collective reference and as such includes a wide array of vessels employed in the high sea sector. They can be mainly classified into the following main groups: • • • •

Oil exploration and drilling vessels Offshore support vessels Offshore production vessels Construction/special purpose vessels

Each of this category comprise of a variety of vessels. Oil Exploration and Drilling Vessels

Oil exploration vessels, as the name suggests, help in exploration and drilling of oil at high seas. The main types of exploration vessels are: Drilling Vessels Drill ships are special purpose ships which are used for drilling on the ocean beds at deep seas. Drill ships are inherently ships designed to provide optimum viability while on water, thus making it easy for the conglomerates to engage their services for better qualitative results in the overall scheme of drilling viability and functionality (Gouldin et al. 2017). Drilling vessels can also be used as an analytical vessel to carry out sub-water researching operations in the high seas. The drilling equipment aboard these vessels can penetrate to really greater depths (anywhere over 600 m to over 3000 m) and can be relocated in the high seas as the requirement necessitates. Likewise, the drilling equipment aboard the oil drilling vessels can also be employed to shoal areas to carry out the necessarily required maritime operations. In order to help them stabilize in the water, these vessels utilize equipment like GP systems

Offshore Vessel

1221

Offshore Vessel, Fig. 1 Drill ship. (http://www.ussfreedom.org/home)

and exceedingly strong support cables and ground tackles to keep them firmly positioned in the drilling area. The construction of a drill ship involves a crane-like framework to hoist and lower the required drilling apparatuses from and into the water from a hatchway specifically constructed to pass through the vessel, into the water’s depths to aid the process. This feature of the offshore drilling ships makes them highly economical and conducive to the high seas drilling, in addition to the aforementioned aspects (Fig. 1). Semisubmersible Vessels Semisubmersible vessel is majorly used in marine operations carried out in the high seas like oil drilling and production platforms for oil. In addition, semisubmersible ships are also used as heavy-duty cranes. The semisubmersible vessel was developed because of the need for vessels that could stay afloat and carry out their required functions in the high seas amidst the constant movement of the waves. The concept of a semisubmersible vessel emerged toward the early twenty-first century. According to many sources, Shell Company’s Bruce Collipp is regarded as the pioneer and creator of these big ships. But it is also said at the same time that the idea behind the semisubmersibles was that of Edward Robert Armstrong, who utilized the

theory of landing planes in sea platforms supported by ballast tanks in a columnar form. At first, semisubmersible rigs were designed only to be used in shallow waters. Such rigs could be used in water levels up to 30 m. But later on as the need was felt for rigs which could be operated in more depths, the invention of the marine equipment developed and widened. The first recognized and acknowledged semisubmersible vessel was the one launched by the Blue Water Drilling Company in the year 1961. The name of the rig was the Blue Water Rig No. 1. Another semisubmersible rig was launched in the year 1963 and by 1972; the offshore marine operations had about 30 semisubmersible rigs operating (Minton 1967) (Fig. 2). Offshore Barge A barge is a flat-bottomed boat, especially built for river and canal transport of heavy goods. Barges these days are actually used to transport low-value bulk items as the cost of hauling goods by barges are cheaper. A typical barge measures 195 by 35 ft (59.4  10.6 m) and can carry up to 1500 t of cargo. Other than barges, the different types of shipping vessels that are used are container ships, bulk carriers, and tankers. All in all they serve the same purpose of carrying cargo, goods,

O

1222

Offshore Vessel

Offshore Vessel, Fig. 2 Semisubmersible vessels. (http://www.Fallschirmjäger/wikipedia.org)

materials, and sometimes even vehicles or people from one port to another. A classic barge is very similar to a very large raft. In many cases, a barge is unpowered and has to be moved with the assistance of a tugboat. In this situation, the captain and first mate are aboard the tugboat, not the barge, as the tugboat is providing the power and steering for the barge. On self-powered barges, the crew includes a captain and first mate to steer the boat and manage the crew, and a small superstructure is usually mounted on the rear of the barge (Fig. 3). Offshore Support Vessels

Certain offshore vessels provide the necessary manpower and technical reinforcement required so that the operational processes in the high seas continue smoothly and without any undesired interruptions. Such vessels are called as offshore support vessels. Offshore supply vessels transport the required structural components to the designated high sea sector along with providing assistance to supply freight as well. The constructional aspect of these

vessels can be purpose-built to suit the operational demands. Some of the main types of offshore support vessels are: Anchor Handling Tug Vessel (AHTV) AHTS vessels are a type of supply vessels that supply tugs and anchors to not just oil rigs but also to cargo-carrying barges. Technically, an AHTS is a very huge naval vessel, mainly because of the equipment that it carries – tugs and anchors along with the winches. In order to transport such a heavy bulk in a manner that they are lost while the AHTS is moving, it is but natural that the design and construction of such ships has to be accommodating to fit such equipment easily. In addition to towing and tugging oil rigs, another major feature of such anchor handling vessels is that they also act as rescue vessels for other ships in times of some emergency. If a ship or a boat requires immediate anchor handling or towing or tugging, and if an anchor handling tug is in the oceanic vicinity, then they are a great source of help to such stranded vessels (Fig. 4).

Offshore Vessel

1223

Offshore Vessel, Fig. 3 Offshore barge. (http://www.JeremyA/wikipedia.org)

O

Offshore Vessel, Fig. 4 Anchor handling tug vessel (AHTV). (http://www.BoH/wikipedia.org)

1224

Seismic Vessel For the purpose of seismic survey, seismic waves are the main components that are analyzed. The process involves a seismic detector that shoots such seismic waves to a selected underwater point. The time taken for the waves to refract back to their origin point determines whether that particular subsea area is feasible for the oil drilling purpose. A survey vessel is the one that helps monitor such seismic waves. It is the primary requirement for any shipping concern engaged in or planning to engage in the process of oil and gas excavation from the oceanic reservoirs. A seismic vessel is fitted with all technological gadgets like GPS, computers, nautical charts, and any other equipment that would enhance the process of seismic survey. Such vessels are built very carefully and only in selected locations across the world (Eisner et al. 2011). This is because the entire ship-building process for seismic vessel involves fitting all the necessary gadgets (mentioned above) without missing even a single one. Seismic vessels are more in demand in today’s time considering the

Offshore Vessel

amount of subsea drilling that is being carried out. They are also known as research vessels because in a completely different way, they do help research the oceans and seas (Fig. 5). Platform Supply Vessels (PSVs) Platform supply vessels or PSVs is a type of offshore vessel which is mainly used for transiting essential equipment and additional manpower to reinforce the high seas’ operations. A platform support vessel is, at its broadest and most literal of implications, a much-needed support ship. Synonymously referred to as offshore supply vessels (OSVs), platform supply vessels help to sustain the demands of the constructional and maintenance projects, thus fulfilling a vital necessity in the nature of operations at the high seas. The singularity of OSV ships stems from numerous factors, even aside from its unique role in the high seas constructional sector. Under a broader ambit, supply vessels help to lug not just heavy structural equipment but also smaller yet essential structural components like paving

Offshore Vessel, Fig. 5 Seismic vessel. (http://www.SludgeG/Wikipedia)

Offshore Vessel

material (cement and concrete) and chemical compounds that help in efficient sub-water boring operations. In addition to these, food and provisions to the crew and personnel working in the high seas is also transported by way of these supply ships. Personnel discharged from active line of operations in the high seas are also transported back to the nearest harbor facilities by way of these incoming supply vessels. Since OSV ships transit personnel, these vessels come furbished with cookhouses and other necessary facilities to facilitate an easy transiting for the personnel. In terms of their technical proportion, OSVs can measure anywhere between 65 ft and over 300 m. This aspect about platform supply vessels adds to their operational singularity. A platform support vessel can be custom-built to suit the operational needs of its operators. Consequentially, not all PSVs are employed to transit drilling rig platforms or sub-water cables to help in the oil excavation operations (Dong et al. 2017). They are also utilized for the purposes of curbing the extent of oil spillage in the high seas

1225

and also as handy vessels with fire-controlling instrumentation. Presently, the need for PSVs has started to be felt more and more as compared to the past few years. This is on account of the constant rise in the number of operations in the high seas, which has in turn resulted in the advancement in the construction of the supply vessels. This demand fuelled the need for more of these vessels and coupled with the benefits of modern technologies can very well be considered as a positive thrust in a very viable and highly necessitated medium of operation (Fig. 6). Offshore Production Vessels

Offshore production vessels refer to those vessels that help in the production processes in the drilling units in the high seas. FPSOs (floating production storage and offloading) can be enumerated as an example of these types of offshore ships. The main type of these vessels is: Floating Production Storage and Offloading (FPSO) The FPSO (floating production storage

O

Offshore Vessel, Fig. 6 Platform supply vessels (PSVs). (https://www.marineinsight.com)

1226

and offloading) system is used extensively by oil companies for the purpose of storing oil from the oil rigs in the middle of the ocean and in the high seas. It is one of the best devised systems to have developed in the oil exploration industry in the marine areas. The FPSO, as its name suggests, is a floating contraption that allows oil rigs the freedom not just to store oil but also to produce or refine it before finally offloading it to the desired industrial sectors, either by way of cargo containers or with the help of pipelines built underwater. The use of this system ensures that shipping companies do not have to invest even more money by ferrying the raw and crude oil to an onshore refinery before transferring it to the required industrial areas. In simple terms, the FPSO saves time and money effectively (Huser and Rasmussen 2001) (Fig. 7).

Offshore Vessel

Offshore Construction Vessel

Ships that primarily aid in the construction of various high seas structures are known as offshore construction vessels. Other offshore vessels’ of these type also include those that provide anchorage and tugging assistance and those kinds of ships that help in the positioning of deep sub-water cable and piping lines. Main types are: Diving Support Vessel A diving support vessel, as the name suggests, is a vessel that is used for the objective of diving into oceans. Divers, who dive into the middle of the seas as a part of professional diving process, need proper diving support. This necessary support is provided by such a dive support vessel. The concept of a diving support vessel came into existence four to five decades ago. From that

Offshore Vessel, Fig. 7 Floating production storage and offloading (FPSO). (https://www.maersk.com)

Offshore Vessel

time onward, these ships have been extremely important to the field of commercial diving which forms a vital part of professional diving. It has to be noted that professional diving means diving for the prospect of construction, repairing, and maintenance of oil rigs and other important offshore naval constructions. Such dive support ships are mainly used in the North Sea and the Gulf of Mexico since these are the areas from where crude oil is majorly excavated from subsea sources. Such support vessels are flat-based or flatbottomed because it makes the diving part easy for the divers. Additionally it has to be noted that such ships are equipped with the dynamic positioning system in order to help the vessel used for diving support stay steady on the water. In the absence of the dynamic positioning system, what could happen is that the ship could move away from the intended diving spot which would cause complications to the diver. Another important feature in vessels that enable diving support is the saturation diving system. The saturation diving system enforces the presence of combination of certain important gases like helium and oxygen for the diver.

1227

Without proper saturation diving system, the diver has to go very deep into the oceanic water, which could cause complications like lack of air leading to suffocation (Fig. 8). Crane Vessel As the name suggests, a crane ship is that kind of seagoing vessel which has a crane attached to it. A crane vessel is of great significance when it comes to the aspect of constructing structures in the high seas. It is only because of such vessels that many important constructions are carried out in trickier parts of the seas and oceans. The role and scope of a crane ship is similar to the cranes that are used in day-to-day construction and hauling business activities. The only difference is the fact that the former variation of crane is used in the seas while the latter on firm ground. The designing of the crane vessel has changed in the 800 years of its origin. The first crane ship was created in the fourteenth century, and since then the technology has helped generations and generations of people. In today’s times, along with the basic ship that carries a single crane attached to it, there are also concepts like “semisubmersible vessels” and the “sheerlegs.”

O

Offshore Vessel, Fig. 8 Diving support vessel. (https://www.wikimedia.org)

1228

All such crane vessels are capable of lifting heavy tonnage, but different varieties offer different features and USP to their clients. The main difference can be elaborated as follows: • Common crane vessels: These types of naval cranes are more commonly known around. They were the ones that were first introduced in the fourteenth century, as mentioned above. These cranes can be used to haul and lift around 2500 t. Additionally, another major feature is that it is movable, which means, the crane can be moved to the place where the item to be lifted is located, thus offering lots of flexibility. • Semisubmersible: These types of cranes offer a lot of stability to the equipment that is being carried. As the name goes, semisubmersible cranes submerge partially into the water to give the weight placed on top of them the balance required. This balance provided ensures that the item carried does not topple into the water and thereby cause serious problems not just to the business concerned but also to the marine ecosystem. The weight carrying capacity of such semisubmersible cranes varies

Offshore Vessel

from one naval vessel to another. However, the heaviest limit that such semisubmersibles can carry extends to around 14,000 t. • Sheerlegs: These types of cranes are immovable. In other words, the weight that has to be loaded on them has to be brought to them so that they can be hauled. The weight carrying capacity of such cranes varies from around 50 t to around 4000 t. A crane vessel has enabled to solve the trickiest aspect of construction. Crossing the ocean and helping widespread places to come even closer have become so much easier. Also, in today’s times, with the help of a crane ship, important oil rigs are constructed so as to enable the world to get precious oil from oceanic sources (Fig. 9). Pipe Laying Vessel A pipe laying ship is a maritime vessel used in the construction of subsea infrastructure. It serves to connect oil production platforms with refineries on shore. To accomplish this goal, a typical pipe laying vessel carries a heavy lift crane, used to install pumps and valves, and equipment to lay pipe between subsea structures.

Offshore Vessel, Fig. 9 Crane vessel. (https://www.MarkFromSavannah/wikipedia.com)

Offshore Vessel

Lay methods consist of J-lay and S-lay and can be reel-lay or welded length by length. Pipe laying ships make use of dynamic positioning systems or anchor spreads to maintain the correct position and speed while laying pipe. Recent advances have been made, with pipe being laid in water depths of more than 2500 m. The term “pipe laying vessel” or “pipe layer” refers to all vessels capable of laying pipe on the ocean floor. It can also refer to “dual activity” ships. These vessels are capable of laying pipe on the ocean floor in addition to their primary job. Examples of dual activity pipe layers include barges, modified bulk carriers, modified drill ships, and semi-immiscible laying vessels, among others (King 2008) (Fig. 10). Development History

The history of offshore vessel originates from ocean vessels. In the seventeenth–eighteenth century, the great value of trade from India and the East Indies prompts the various East India companies – and particularly those of England and Holland – to invest in magnificent ocean-going

1229

merchant ships. These ships needed to have capacity for storing large amounts of cargo; they need to be strong and well-armed to fight off pirates or even the ships of rival companies; and they need to be comfortable for their captains and for important passengers, busy making fortunes in the east. These were the most beautiful ships of that time period. The largest classes, outdoing even the biggest warships, were 1200 t in weight. The largest ships of this kind were 50 m long and 12 m wide. With a ratio of 4:1 between length and width, these ships could not achieve a big speed. Speed was not a crucial factor for the East India companies, since they enjoyed the monopoly anyways. The ships used trade winds as assistance in the journey and made just one journey in and out from east per year. With the nineteenth century bringing competition, speed of merchant ships became a factor and the age of clippers came. As a result of the growing demand for a more rapid delivery of tea from China, in 1843 the Clipper era begun. Clippers were very fast-sailing ships with three or more masts and a square rig.

O

Offshore Vessel, Fig. 10 Crane vessel. (https://www.wikipedia.com)

1230

Offshore Wind Turbine

The demand for clippers continued during the “Golden Rush” when there was a need for quick ships that were used for the transportation of gold. The decline in the usage of clippers started with the gradual introduction of steamships. Although clippers could reach much higher maximum speed than steamships, they depended on the wind and thus could not be accounted as punctual. As for steamers, they could keep the schedule and this made the more reliable. The industrial revolution, new mechanical methods of propulsion, and the ability to construct ships from metal triggered an explosion in ship design. The quest for more efficient ships, the end of long running and wasteful maritime conflicts, and the increased financial capacity of industrial powers created an avalanche of more specialized boats and ships. Specialized ships built for entirely new functions, such as firefighting, rescue, and research, also began to appear (Woodman 2005). With the development of offshore engineering, the offshore vessel has also been born.

References

Key Applications

Offshore Wind Turbine

Offshore vessels are ships that specifically serve operational purposes such as oil exploration and construction work at the high seas. There are a variety of offshore vessels, which not only help in exploration and drilling of oil but also for providing necessary supplies to the excavation and construction units located at the high seas. Offshore ships also provide the transiting and relieving of crewing personnel to and from the high seas’ operational arenas, as and when necessitated.

▶ Shallow Foundations

Cross-References ▶ FPSO ▶ Ice Breaking Vessel ▶ Polar Merchant Vessel ▶ Research Ship ▶ Service Ships ▶ Special Marine Vehicle

Dong YL, Wang D, Qin RM (2017) Technical analysis on safe operation of berthing sea facilities of offshore oil support vessel. Value Engineering Eisner L, Stotter C, Mueller MC, Duncan PM, Herndler E (2011) Design of passive seismic monitoring for underground gas storage in the Vienna Basin, Austria. Eage Conference and Exhibition Incorporating Spe Europec Gouldin D, Lancaster J, Boutalbi S, Dietrich E, Toralde, JS (2017) Realizing rig integration: implementing deepwater MPD technology in 6th generation ultradeepwater drillships. Iadc/spe managed pressure drilling & underbalanced operations conference & exhibition Huser A, Rasmussen O (2001) Cost-effective explosion risk management of fpso’s. 1. https://doi.org/10.4043/ 12951-MS King RA (2008) Subsea pipeline engineering. Pennwell Publishing, Tulsa Minton RC (1967) Review of procedures after four years experience in floating drilling. J Pet Technol 19(2):167–174 Woodman R (2005) The history of the ship. Conway Maritime Press, London

Offshore Wind Turbine-Ice Interactions Wei Shi Deepwater Engineering Research Center, Dalian University of Technology, Dalian, Liaoning, China State Key Laboratory of Coast and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning, China

Introduction Climate change caused by the excessive use of fossil fuels has become one of the hot topics in the last few decades and threatens human

Offshore Wind Turbine-Ice Interactions

security and societal development. Serious environmental pollution and energy crises cause people and governments to look for sustainable energy resources. Offshore wind energy is regarded as one of the fastest-growing renewable energy resources in the world. Compared with onshore wind energy, the deployment of offshore wind energy offers another promising solution because of the improved wind conditions, unlimited sites, negligible visual impact, and the possibility of installing extra-large wind turbines (Perveen et al. 2014). Offshore wind energy has significant potential in northern regions with cold climates, such as Northern Asia, North America, and Northern Europe. In these regions, wind turbines may experience icing on the blades or drifting ice during wintertime. A great potential for offshore wind is ready to be tapped in the Baltic Sea, with more than 16 GW of Baltic projects (Recharge News 2016). The Icebreaker project of Lake Erie Energy Development Co. (LEEDCo) would include six wind turbines for a total generating capacity of up to 20.7 MW in Lake Erie, north of Cleveland. According to China’s 13th Five-Year Plan for offshore wind energy (NDRC 2017), nearly 900 MW of offshore wind projects will begin construction in the Bohai Bay Rim area by 2020. Bottom-fixed wind turbines are very suitable for the shallow and intermediate water depths ( 0.5, the pipeline embedment can be treated as e/D ¼ 0.5 with an equivalent uniform surcharge pressure q ¼ (e  0.5D)γ0, where γ0 is the buoyant unit weight of the soil (in kPa/m3)); and Nc, Nq, and Nγ are the bearing capacity factors for the cohesion, for the distributed load, and

for the buoyant weight of soils, respectively. For the clayey seabed under undrained conditions, if neglecting the effects of the pipe geometric curvature (e/D ! 0), the pipe-soil interface adhesion (i.e., the interfacial friction coefficient m ¼ 0), and the internal friction of the soil (i.e., the angle of internal friction ’ ¼ 0), the slip-line field solution can be degenerated into Prandtl’s solution for conventional strip footings, i.e., Nc ¼ 2 + π. With increasing pipeline embedment, the value of Nc decreases from Nc ¼ 2 + π at e/D ! 0 and finally reaches Nc ¼ 4.0 at e/D ¼ 0.5. It has been indicated that the geometric curvature effect is unneglectable when evaluating the ultimate bearing capacity of submarine pipelines. Note that the aforementioned solutions were obtained under the assumption that the seabed soil is described with a perfectly plastic stressstrain relationship. Such approximation is applicable for the soils of low compressibility, which might meanwhile correspond to the general shear mode of failure. However, for a very soft clayey seabed, large settlements of the pipeline may occur under its submerged weight and laying disturbances without general shear failure occurring. In such cases, the limiting criterion for bearing capacity should be the maximum allowable settlement. Seabed Liquefaction Seabed liquefaction is the phenomenon that the seabed sediment loses a significant part of or all its shear strength under the action of ocean waves or earthquake. Both residual and oscillatory mechanisms for the wave-induced pore pressure response in the seabed have been identified in flume experiments and field observations. The residual liquefaction of the seabed is due to the pore pressure buildup under undrained or partially drained conditions, which usually takes place in fine sands or silty soils under severe wave loading and always combined with currents in the offshore field. Besides residual liquefaction, the instantaneous liquefaction (also termed as “momentary liquefaction”) is particularly prone to occurrence in seabed sediments during severe storms, which

O

1252

On-Bottom Stability of Submarine Pipelines

is essentially caused by the instantaneous upward seepage within the upper layer of the seabed under wave troughs. In the instantaneously liquefied layer of the seabed, the vertical gradient of excess pore pressure (jz ) should be identical to the buoyant unit weight of the soil (γ0 ), i.e., the improved criterion for instantaneous liquefaction (Qi and Gao 2018): jz ffi γ0. Based on the analytical solution to Biot’s consolidation equations for porous seabed response to waves (Yamamoto et al. 1978) and the above criterion for instantaneous liquefaction, the maximum depth of instantaneously liquefied layer (zL) under wave troughs can be derived (Qi and Gao 2018): zL ¼

p0 1  g0 Re ½lð1  aÞ þ l0 a

ð2Þ

where p0 is the amplitude of wave-induced excess pressure at the seabed surface; the operator “Re{}” means to take the real part of the complex variable in the brackets; l(¼2π/L) is the wave number; L is the wavelength; α and l0 are the complex numbers related to the properties of the seabed and waves (see Yamamoto et al. 1978). If the pipeline is to be buried in a liquefiable seabed, the designed burial depth should be larger than the maximum depth of instantaneously liquefied layer (see Eq. 2). To keep the buried pipeline vertically stable, the residual liquefaction of the soil around the pipeline needs to be further evaluated. Moreover, under the condition that waves and current coexisting in the field, the seabed liquefaction and the on-bottom stability of the pipeline should be accurately predicted.

Lateral Stability In submarine geological and hydrodynamic environments, the multi-mechanics processes can emerge in the proximity of as-laid pipelines, including shear flow above the seabed, sediment transport along the seabed surface, the excessive pore pressure in the soil, etc. They are generally coupled with each other and have significate influence on the lateral stability of submarine pipelines (Gao 2017).

The triggering mechanisms for the pipeline lateral instability involve not only pipe-soil interactions (Wagner et al. 1989; Zhang et al. 2002; Youssef et al. 2013; Gao et al. 2016) but also flow-pipe-soil coupling process (Gao 2017). Experimental observations (see Fig. 1) with an oscillatory flow tunnel showed that there always exist three characteristic stages during the lateral instability of a pipe shallowly embedded in sands under a storm-like wave loading, i.e., (a) local scour of sands around the pipe, (b) periodic rocking of the pipe with small amplitudes, and (c) pipe breakout from original location (see Gao 2017). In the process of the pipe losing lateral instability, local scour always emerges as an indicator for the flow-pipe-soil coupling effect, which was observed taking place at the rear and front of the pipe. The pipe periodic rocking due to the vortex shedding may increase its penetration into the seabed and further affect the lateral stability. The occurrence of pipeline instability is characterized by a distinct lateral displacement (e.g., dp/D>0.5, where dp is the pipe lateral displacement, see Fig. 1). The criteria for pipeline lateral instability are crucial to the on-bottom stability design. Based on similarity analyses for physical modeling experiments, it was found that the controlling nondimensional parameter of hydrodynamics for pipeline lateral instability is the Froude number pffiffiffiffiffiffi (Fr ¼ Um = gD ) and another parameter is the non-dimensional submerged weight of pipelines (G ¼ Ws/γ0D2, where Um is the maximum velocity of wave-induced water particle movement and g is the gravitational acceleration. Both the scaling of the Froude number and that of the KeuleganCarpenter number (KC ¼ UmT/D, where and T is the wave period) can be concurrently satisfied in the physical modeling with wave flumes. KC number essentially controls the generation and development of vortex around the pipeline under oscillatory flow in waves. A unified formulation of criteria for pipeline lateral instability in waves and currents can be expressed as (Gao et al. 2003) Frcr ¼ a þ b

Ws g0 D2

ð3Þ

On-Bottom Stability of Submarine Pipelines

1253

On-Bottom Stability of Submarine Pipelines, Fig. 1 Characteristic stages during the pipeline losing lateral stability under a storm-like wave loading (Adapted from Gao 2017)

where Frcr is the critical values of Froude number for pipeline lateral instability. In Eq. (3), the two parameters a and b are relative to the hydrodynamic loads (periodic waves or steady current), the end constraint conditions (anti-rolling or freely laid) of a shallowly embedded pipe, and the soil properties of the seabed. On the basis of the results of a series of experiments, the values of these two parameters were determined as (a, b) ¼ (0.07, 0.62) for the anti-rolling pipes in waves and (a, b) ¼ (0.042, 0.38) for the freely laid pipes in waves (5 < KC < 20). But for the freely laid pipes in a steady current (KC ! 1), (a, b) ¼ (0.102, 0.423), indicating the pipes are more stable in currents than in waves due to the inertia effect of wave movements. It should be noted that the above recommended values for the two parameters a and b were based on the results of model tests on a uniform medium sand-bed. The particle size is closely related to sediment transport and further affects the lateral stability of the pipeline. The instability criteria in the unified formulation by Eq. (3) provided alternative expressions to the pipe-soil interaction model by Wagner et al. (1989) for the on-bottom stability of a shallowly embedded pipeline, as addressed by Fredsøe (2016). Besides the aforementioned lateral instability, submarine pipelines could also be under the threat

from tunnel erosion due to the seepage failure of its underneath soil, especially under the action of shear flow near the seabed, which may further bring the spanned pipeline undergo vibrations, i.e., vortex-induced vibrations (Gao 2017). It has been revealed that the two typical scenarios, i.e., the lateral instability of the pipe and the tunnel erosion of the soil, are always competitive between each other in the submarine geological and hydrodynamic environments (Shi and Gao 2018).

Axial Pipe-Soil Interactions As offshore developments extend into deep waters, the relatively high pressure and high temperature (HPHT) becomes a dominant factor for the pipeline safety. The HPHT pipeline would undergo expansion and contraction during startup and shutdown cycles in the operating life, which may induce pipeline walking on the seabed. It should be noted that the pipeline walking is not a limit state; nevertheless, the excessive compressive force can lead to severe global buckling of the pipeline and even the failure of associated infrastructures (Randolph and Gourvenec 2011). The ultimate axial soil resistance (FRu) to a conventional strip footing with flat bottom is generally linked with the normal pipe-soil contact

O

OPC – OLE for Process Control

1254

force (FN) and the interface friction coefficient (m), i.e., FRu ¼ mFN. But for submarine pipelines, the assessment of ultimate axial soil resistance becomes much more difficult than that for conventional strip footings. Due to the effect of pipeline curvature, the integrated normal pipe-soil contact force (FN) would exceed the submerged pipeline weight (WS), i.e., FN ¼ ζWS, by incorporating a wedging factor (ζ): z¼

2 sin y0 y0 þ sin y0 cos y0

ð4aÞ

for clayey soils (White and Randolph 2007) and z¼

1  ð2y0 =pÞ2 cos y0

ð4bÞ

for sandy soils (Shi et al. 2019), respectively. In Eqs. (4a) and (4b), θ0 is the semi-angle subtended at the pipe-soil contact chord. The axial soil resistance expressed with an equivalent friction coefficient could span an order of magnitude, which is related to many influential factors, including the soil types, drainage condition, and the pipe roughness. A theoretical framework was developed within a critical-state context using effective stresses, applicable to any degree of drainage in the soil, quantifying the magnitude and duration of excess pore pressures generated near the pipesoil interface (Randolph et al. 2012). It has been recognized that the axial soil resistance is crucial for assessing the effective axial force along the pipeline and the corresponding global buckling predictions.

Cross-References ▶ Design of Pipelines and Risers ▶ Pipeline Soil Interactions

References Chen WF, Liu XL (1990) Limit analysis in soil mechanics. Elsevier Scientific Publishing, New York

Det Norske Veritas, Germanischer Lloyd (2017) Pipe-soil interaction for submarine pipelines. Recommended Practice DNVGL-RP-F114. https://www.dnvgl.com/ Fredsøe J (2016) Pipeline-seabed interaction. J Waterw Port Coast Ocean Eng 142(6):03116002 Gao FP (2017) Flow-pipe-soil coupling mechanisms and predictions for submarine pipeline instability. J Hydrodyn 29(5):763–773 Gao FP, Gu XY, Jeng DS (2003) Physical modeling of untrenched submarine pipeline instability. Ocean Eng 30(10):1283–1304 Gao FP, Wang N, Zhao B (2013) Ultimate bearing capacity of a pipeline on clayey soils: slip-line field solution and FEM simulation. Ocean Eng 73:159–167 Gao FP, Wang N, Zhao B (2015) A general slip-line field solution for the ultimate bearing capacity of a pipeline on drained soils. Ocean Eng 104:405–413 Gao FP, Wang N, Li JH, Han XT (2016) Pipe-soil interaction model for current-induced pipeline instability on a sloping sandy seabed. Can Geotech J 53(11):1822–1830 Qi WG, Gao FP (2018) Wave induced instantaneouslyliquefied soil depth in a non-cohesive seabed. Ocean Eng 153:412–423 Randolph MF, Gourvenec S (2011) Offshore geotechnical engineering. Spon Press, New York Randolph MF, White DJ, Yan Y (2012) Modelling the axial soil resistance on deep-water pipelines. Géotechnique 62:837–846 Shi YM, Gao FP (2018) Lateral instability and tunnel erosion of a submarine pipeline: competition mechanism. Bull Eng Geol Environ 77:1069–1080 Shi YM, Wang N, Gao FP, Qi WG, Wang JQ (2019) Physical modelling of the axial pipe-soil interaction for pipeline walking on a sloping sandy seabed. Ocean Eng 178:20–30 Wagner D, Murff JD, Brenodden H, Svegen O (1989) Pipe-soil interaction model. J Waterw Port Coastal Ocean Eng ASCE 115(2):205–220 White DJ, Randolph MF (2007) Seabed characterisation and models for pipeline-soil interaction. In: Proceedings of the 17th international offshore and polar engineering conference (ISOPE), Lisbon, pp 758–769 Yamamoto T, Koning HL, Sellmeijer H, Hijum EV (1978) On the response of a poro-elastic bed to water waves. J Fluid Mech 87(1):193–206 Youssef BS, Tian Y, Cassidy MJ (2013) Centrifuge modelling of an on-bottom pipeline under equivalent wave and current loading. Appl Ocean Res 40:14–25 Zhang J, Stewart DP, Randolph MF (2002) Modeling of shallowly embedded offshore pipelines in calcareous sand. J Geotech Geoenviron Eng ASCE 128:363–371

OPC – OLE for Process Control ▶ Central Monitoring System

Open Water Test

Open Water Experiment ▶ Open Water Test

Open Water Test Yunsai Chen1, Qiumeng Zheng2 and Xuewen Ma2 1 Department of Technology, National Deep Sea Center of China, Qingdao, Shandong, China 2 College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China

Synonyms Cavitation test; Open water experiment; Openwater test

Definition The open water test is a propeller model running alone in uniform current, which can be carried out in the model laboratory, circulating water channel and cavitation tunnel. The open water test can estimate the propeller operating performance as a simple and reliable way to determine and analyze propeller performance. Torque, thrust, speed, and rotate speed are tested at the same time and a series of characteristic curves are obtained through the propeller model open water test and provided information for the later research. Propeller Series Diagram is compiled based on the open water characteristic curves obtained from a large number of experimental results in the tank, used for propeller design, calculation and other applications. The B type propeller in the model pool of the Dutch ship is the most famous propeller pattern, while the AU type propeller pattern in Japan is the most frequently used as well. The propeller model test is a convenient method to examine and analyze the performance of propellers, which is significant in studying the

1255

hydrodynamic performance of propeller. It can provide sufficient information for propeller designs and a reliable basis for the development of propeller theory. There are several purposes of open water test: 1. With a set of experiments, drawing the results into a particular graph for design. 2. According to the results, analyzing the influence of various geometry elements on the propeller. 3. As an indispensable means of checking and verifying theoretical methods. 4. Comparing the advantages and disadvantages of various design schemes and choosing the prime by cooperating with self-propelled experiment.

Scientific Fundamentals Historical Development As the most widely used Marine propeller, the performance of the propeller research mainly concentrated in the pool experiments. As far as the propeller itself is concerned, its operating efficiency in a uniform flow is the most basic important performance index, and the open water test is the most commonly used effective tool of studying this kind of performance. To date, the open water test of single propeller has been studied for hundreds of years, while the open water test of combined propeller such as ducted propeller and counter-rotating propeller has been conducted for decades. Basic Classification Model tests carried out in the laboratory. The open water test can be carried out on the propeller, rudder, etc., by the model test in the experimental pool, and the measured data can be sorted out and analyzed to obtain a series of characteristic curves for subsequent calculation. Open water tests of propellers are used in conjunction with tests behind models to determine the wake and relative torque efficiency (Tupper 2013). Also, methodical propeller testing is

O

1256

carried out in a towing tank. The propeller is powered from the carriage through a streamlined housing. It is pushed along the tank with the propeller ahead of the housing so that the propeller is effectively in undisturbed water (Tupper 2013). Records of thrust and torque are taken for a range of carriage speeds and propeller revolutions (advance coefficient) (Tupper 2013). Such tests eliminate cavitation and provide data on propeller in uniform flow. This methodical series data can be used by the designer, making allowance for the actual flow conditions. (Tupper 2013). There have been many methodical series. Those by Froude, Taylor, Gawn, Troost, and van Lammeren are worthy of mention. The reader should refer to published data, if it is wished to make use of these series. A typical plot for a four-bladed propeller from Troost’s series is presented in Fig. 1 (Tupper 2013).

Open Water Test

Numerical Calculation First of all, the numerical algorithm of the open water performance of the propeller with regard to the numerical calculation of the open water performance has been developed very early. As early as the early twentieth century, Lanchester and others began to study the propeller theory and further study was completed by Prandtl. Then Goldstein put forward the Goldstein theory and the Goldstein factor in 1929. Theoretically, the flow field can be simulated by solving the N-S equation and related equations, so as to solve the problems of propeller correlation performance. However, the process of solving the N-S equation becomes very complicated due to some assumptions made in the process of establishing the N-S equation, as well as the complexity of the practical problems and boundary conditions, and the huge amount of calculation seriously restricts the

Open Water Test, Fig. 1 A typical plot for a four-bladed propeller from Troost’s series

Open Water Test

development of this method. After nearly a hundred years of research by related scholars, three classical theoretical methods, namely lift line theory, lift surface theory and surface element method, were formed on the basis of potential flow theory, which greatly promoted the study of propeller hydrodynamic performance. At present, many scholars consider the performance of propeller by building solid model. Solid modeling means that hull, propeller, and other appendages no longer adopt the equivalent alternative method, but build solid model and calculation domain together, in which each model is either static or moving. In the solid modeling calculation, the paddle processing can be divided into three types: multiple reference frame (MRF) method, mixed surface method, and slip surface method. MRF method is to divide the whole computational region into multiple subdomains. Individual subdomains have their own forms of motion such as stationary, moving and rotating, and these subdomains can be considered to maintain the steady state approximation at different moving or rotating speeds. By solving the governing equations of each subdomain and exchanging the flow information of each subdomain on the general interface, the flow information of the whole flow field computing domain can be obtained. If the meshes on both sides of the subdomain interface are not completely consistent, the flow information on the interface is transmitted by interpolation. MRF method is suitable for many conditions of steady flow, especially when the flow area is almost uniform at the boundary. The hybrid plane method also divides the whole computing domain into several independent subdomains. Instead of each of these little domains being seen as a steady state approximation at different velocities of motion or rotation, each little domain is a steady state. It is considered as a steady flow in the subdomain, and a mixed surface similar to boundary conditions is constructed on the interface between the subdomains to transfer the flow information of both subdomains. The mixed plane method can solve the unstable problems caused by the circumferential changes among the subdomains, such as the

1257

steady-state and flow separation, and then obtain a stable solution. When using the slip surface method for calculation, there are multiple subdomains in the entire flow region, and there are relative motions between these subdomains, as well as interfaces between every two of them. During the calculation process, the part of the interface that is connected with the adjacent subdomain is called the internal region, and the other part that is not connected with the adjacent subdomain is called the plane region as solving the plane problem. And the part in dealing with periodic or aperiodic problems is called the periodic region. In addition, while using the sliding grid technology, the grids on the interface are irregular, namely the grids on both sides of the interface are not completely consistent. In other words, the relative movement between two adjacent subdomains should be recalculated to obtain the boundary position of the internal region in the specific calculation. This kind of calculation is complex, requiring a high performance of the computer. Compared with the MRF method and the mixed surface method, the slip surface method has a certain advantage in solving periodic or aperiodic problems. At present, sliding grid technology is often used to transfer flow field information. In the meantime, the calculation methods include lift line method based on potential flow theory, lift surface method, surface element method, and viscous flow method based on RANS equation. Four methods are described below. The lift line method proposed by Goldstein in 1929 is applied to propeller performance prediction. In this method, all the attached vortices of the propeller are concentrated on a spreading line from the blade root to blade tip, which is called the lift line of the propeller. The strength of the lift line changes along the spanwise direction, and the tail vortex surface is formed downstream of the propeller by the change of the strength of the attached vortex. With the circulation distribution, it is possible to obtain the lift force of each microsegment vortex element and then obtain the hydrodynamic performance parameters of the propeller accordingly.

O

1258

Open Water Test

The lift surface method is based on the thin airfoil characteristics of Marine propellers. On the one hand, the thickness part only contributes to the pressure distribution of the blade, which is expressed by the source-sink distribution on the chord surface of the wing. On the other hand, the bending part is the origin of lift, which is represented by the vortex distributed on the chord surface of the wing. The boundary conditions are satisfied on the wing chord. Because the boundary conditions of lift surface method are stricter than the lift line method, it can result in more accurate results. The surface element method is a kind of boundary element method, and its basic idea is to transform the Laplace equation of the incompressible, inviscid, and irrotational potential flow problem into an integral equation on the boundary by using Green formula. Thus, the flow around a three-dimensional object is transformed into the solution of the unknown singular point plane distribution on any object surface. The viscous flow method using RANS equation is to directly solve the RANS equation method to obtain the propeller viscous flow field, so as to obtain the propeller hydrodynamic performance parameters. FINE/Marine, Fluent, etc., are commonly available software.

Principles of Open Water Test The advance speed and rotation speed of the propeller model are obtained according to the similarity theorem of the propeller including geometric similarity, kinematic similarity, and dynamic similarity. The advance coefficient, Reynolds number, and Froude number are presented with dimension analysis method. J¼

VA nD

Rn ¼

VAL n

VA ffi Fr ¼ pffiffiffiffiffi gL

T rn2 D4 Q KQ ¼ 2 5 rn D KT ¼

0 ¼

KT J ∙ K Q 2p

J represents the advance coefficient. KT is the symbol of thrust coefficient and KQ is the symbol of torque coefficient. 0 represents the open water efficiency. The similarity theorem is satisfied when the three parts of the propeller and the model are equal. Furthermore, the effect of the wave is negligible when the paddle shaft is at a certain depth underwater, and the Froude number representing gravity similarity is abandoned. In addition, when the critical Reynolds number(3  105) is met, the influence of viscosity can be ignored. However, the scale effect needs to be considered. Open water characteristics are frequently determined from model experiments on propellers run at high-speed and having diameters of the order of 200–300 mm (Carlton 2012). It is, therefore, reasonable to pose the question of how the reduction in propeller speed and increase in diameter at full-scale will affect the propeller performance characteristics (Carlton 2012). Figure 2 shows the principal features of scale effect, from which it can be seen that the torque coefficient is somewhat reduced for a given advance coefficient while the thrust characteristic is largely unaffected (Carlton 2012). The scale effects affecting performance characteristics are essentially viscous in nature and are primarily due to boundary layer phenomena dependent on Reynolds number (Carlton 2012). Due to the methods of testing model propellers and the consequent changes in Reynolds number between model and full-scale, or indeed a smaller model and a larger model, there can arise a different boundary layer structure to the flow over the blades (Carlton 2012). While it is generally recognized that most full-scale propellers will have a primarily turbulent flow over the blade surface, this need not be the case for the model where

Open Water Test

1259

Open Water Test, Fig. 2 The principal features of scale effect

characteristics related to laminar flow can prevail over significant parts of the blade (Carlton 2012). In order to quantify the scale effect on the performance characteristics of a propeller, an analytical procedure is required (Carlton 2012). There is, however, no universal agreement as to which is the best procedure. In a survey conducted by the 1987 ITTC, it was shown that from a sample of 22 organizations, 41 percent used the ITTC–1978 procedure; 23% made corrections based on correlation factors developed from experience; 13%, who dealt with vessels having open shafts and struts, made no correction at all; a further 13% endeavored to scale each propulsion coefficient, while the final 10% scaled the open water test data and then used the estimated fullscale advance coefficient (Carlton 2012). Hence, similarity theorem is all about kinematic similarity, implemented through equalizing the advance coefficient of the propeller and model. KT ¼ f 1 ð J Þ KQ ¼ f 2 ð J Þ There are two ways to obtain the advance coefficient: In the towing tank, the model rotational

speed is kept constant and the advance speed is changed; in the cavitation tunnel, the advance speed of the model remains still and the rotational speed is changed. The thrust coefficient, torque coefficient, and open water efficiency under different advance coefficients were obtained through experiments and plotted as the propeller characteristic curves (Zhu 2016). The main measuring device for the open water test is data acquisition system and propeller dynamometer, which is classified as a mechanical dynamometer (shown in Fig. 3), electric test dynamometer, and electromechanical integrated dynamometer due to the different power sources. The data acquisition system consists of two parts. One part is a data collection device, which measures data by an open water dynamometer machine and transmutes to the data collection device for filtering, amplifying, and processing. The other part is data acquisition system supporting software. The data acquisition device is connected to a computer with software, which will be processed in the back of the data input, and the software will be able to visualize and move on to the data. At the same time, the software is also a platform for the operation of data acquisition equipment, with the control of data acquisition, system balance, and other functions.

O

1260

Open Water Test

Open Water Test, Fig. 3 J04 Propeller Dynamometer (mechanical dynamometer)

In the preparation stage of the test, the whole set of test equipment including open water dynamometer and data acquisition system is tested and calibrated to obtain the calibrated value. Besides, in the open water test, the rotational speed and advance speed of the propeller should be determined first. The selection of these two values is very important. First of all, the rotation speed of the propeller should take into account the influence of factors such as the material of the propeller itself, and the selection of the advance speed should take into account the influence of factors such as the performance of the trailer. The interval of the advance speed shall not be too large. Otherwise, the test data points will be too small, which will not be able to accurately reflect the trend of the water performance curve of the open water. On the contrary, the interval will be too small to increase the number of tests. Then the experiment can be carried out with the change of advance speed. During the test in the cavitation test tube, the similarity condition must be satisfied that the number of cavitation is equal as well as the coefficient of advance. The cavitation test cylinder is composed of a sealed circulating water cylinder, a driving water pump, a pressure regulating device, and so on. There is an observation window in the working section, and throughout the test, water circulates and is depressed to make the number of cavitation equal to the number of the real

propellers. The test process is observed and recorded with stroboscope and high-speed camera, and the thrust, torque, and other test data of propeller are measured by dynamometer. Propeller tests (open-water tests, cavitation tests) are usually performed in cavitation tunnels (Bertram 2012). A cavitation tunnel is a closed channel in the vertical plane recirculating water by means of an impeller in the lower horizontal part (Bertram 2012). In this way, the high hydrostatic pressure ensures that even for reduced pressure in the tunnel, the impeller itself will not cavitate (Bertram 2012). The actual test section is in the upper horizontal part. The test section is provided with observation glass ports (Bertram 2012). The tunnels are designed to give (almost) uniform flow as inflow to the test section. If just the propeller is tested (with the driving shaft downstream), it is adequately tested in open water (Bertram 2012). Vacuum pumps reduce the pressure in the tunnel and usually some devices are installed to reduce the amount of dissolved air and gas in the water. Wire screens may be installed to generate the desired amount of turbulence (Bertram 2012). Cavitation tunnels are equipped with stroboscopic lights that illuminate the propeller intermittently such that propeller blades are always seen at the same position (Bertram 2012). The eye then perceives the propeller and cavitation patterns on each blade as stationary (Bertram 2012).

Open Water Test

Usual cavitation tunnels have too much background noise to observe or measure the noise-making or hydro-acoustic properties of a propeller, which are of great interest for certain propellers, especially for submarines or antisubmarine combatants (Bertram 2012). Several dedicated hydro-acoustic tunnels have been built worldwide to allow acoustical measurements. The HYKAT (hydroacoustic cavitation tunnel) of HSVA is one of these (Bertram 2012).

Key Applications The open water test is mainly used to measure the hydrodynamic performance of various propellers, such as ducted propellers, pod propellers, and combined propellers. It is also sometimes used to measure hydrodynamic characteristics of rudder and other attachments, such as the open-water test of a connecting rod flap rudder (Zhu 2013). Open Water Test of Pod Propellers Ever since the concept of pod propeller was proposed, after more than 20 years of development, it has been successfully applied in many ship types. Its excellent performance, which has been shown in practical applications, attracts more and more ship-owner and ship designers’ concerns, as well as more and more attention to their research on hydrodynamic performance. The open water test for the pod thrusters is to test the entire pod parts, including the propeller, the pod, the stents, and the fins, as part of the propulsion unit, and the open water test for the pod unit requires the development of a specialized testing device. The complete open water test of pod propeller not only measures the thrust and torque of a propeller, but also measures the thrust of the whole pod unit (Shen 2007). The characteristic quantities such as the lateral force and the rudder moment of the whole unit can be investigated more completely. The dynamometer includes propeller dynamometer and unit force balance. The thrust and torque of the propeller are measured by a dynamometer located in the cabin. The axial force, lateral force, and rudder torque of the whole unit are measured by a three-component force balance. Besides, the

1261

propeller is driven by a motor through a driving shaft. Water tightness is considered in the design of the dynamometer and transmission mechanism as well. The whole test device is composed of free stress part and fixed constraint part. The free force part consists of propeller, cabin, bracket, tail fin, and other parts. The force is measured by propeller dynamometer and three-component balance. It is important that free-stressed parts are not affected by other test equipment. The fixed restraint is secured to the trailer and should be avoided that the force on it affects the balance measurement. The test apparatus is capable of accurately adjusting the submerged depth of the propeller shaft in the subsea and ensuring that the paddle axis is parallel to the horizontal plane. Combined with the test results of the pool and other relevant data analysis, it is concluded that in the open water test of the pod propeller, the bracket clearance should be kept as small as possible, and the hub clearance should be controlled in an appropriate range. Open Water Test of Combined Propellers Compared with common propellers, combined propellers have the great advantage of reducing the radiation noise of propellers, improving the efficiency of open water and the initial critical speed of cavitation. At the same time, if the propeller can match the hull properly, it can even obtain higher propulsion efficiency. The structural features of such thrusters are multicomponent combinations, so that the characteristics of hydrodynamic interference among components will be the focus of their performance research. In order to study the hydrodynamic interaction between the components of the combined propeller, the method of decomposition test may be employed.

New Scientific Discovery Changes in Testing Methods By using the traditional test method, on the one hand, it needs to be operated by many people, and it is easy to bring artificial reading error, and on the other hand, processing the data of these measurements is quite a time-consuming and

O

1262

laborious work. With the rapid development of computer technology, a variety of electrical measuring sensors have appeared continuously, which provides convenient conditions for the computerization of open water test. By using the computer to collect and process the data, we can analyze and modify the program in real-time, reduce the error, and realize the automatic control of the experiment process.

Cross-References ▶ Numerical Simulation Floe Ice–Sloping Structure Interactions ▶ Resistance Test

References Bertram V (2012) Practical ship hydrodynamics (2nd ed) [M]. Elsevier Ltd, United Kingdom Carlton JS (2012) Marine propellers and propulsion (3rd ed) [M]. Elsevier Ltd, United Kingdom Shen H, Yang Y, Yao H (2007) A new experiment and assessment method for the open water performance and component interaction of integrated propulsor [J]. J Ship Mech 11(2):160–170 Tupper EC (2013) Introduction to naval architecture (5th ed) [M]. Elsevier Ltd, United Kingdom Zhu F (2013) Numerical simulation of ship self – propulsion model test [D]. Wuhan University of Technology, Wuhan, China Zhu Q (2016) Numerical prediction method research of ship self-propulsion performance based on hull-propellerrudder system [D]. Jiangsu University of Science and Technology, Jiangsu, China

Open-Water Test

Optical ▶ Fiber-Optic Cable

Optical Compass Qing Zhang College of Automation, Harbin Engineering University, Harbin, China

Synonyms Digital signal processor (DSP); Fiber-optic gyro (FOG); Fiber-optic gyro attitude reference system; Fiber-optic gyro motion sensor; Inertial measurement unit (IMU); Motion reference unit (MRU); Strapdown inertial navigation system (SINS)

Definition Fiber-optic gyro compass is a strapdown inertial navigation system (SINS) with three fiber-optic gyros and three accelerometers. This compass outputs the information of the heading, roll, and pitch. Comparing to the traditional mechanical gyro compass, fiber-optic gyro compass has less setting time, higher measuring accuracy, better dynamic characteristics, and longer service life. It is specially suitable for the navigation and control of high-speed platforms with high rate of turn.

Open-Water Test Scientific Fundamentals ▶ Open Water Test Frame Definitions A fiber-optic gyro compass relates to several basic navigation frames (Li et al. 2013) drawn in Fig. 1.

Operational Challenges ▶ Technical and Economical Barriers on Green Energy Utilization in Shipping

1. The b-frame. Body frame, the strapdown inertial sensor frame, with its origin at the center of mass of the accelerometer and gyro triad and

Optical Compass

1263

Optical Compass, Fig. 1 The frames definition

axes parallel to nominal right-handed orthogonal sensors input axes. 2. The i-frame. Inertial frame, stabilized in the inertial space. 3. The n-frame. Navigation frame is the local level coordinate frame here. Its x axis points to East (E), y axis points to North (N), and z axis points upward (U). Fiber-Optic Gyro In a fiber-optic gyro compass, fiber-optic gyro (FOG) is used for measuring the rotation angle. Recently, FOG is being widely used for military and defense applications, due to its significant advantages such as small size, low cost, light weight, no moving parts, large dynamic range, low power consumption, and possible batch fabrication (Narasimhappa et al. 2014). FOG is a kind of optical gyros and its principle is based on the Sagnac effect, as shown in Fig. 2. After passing through the coupler, the light beam from SLD source is divided into two light beams by the polarizer. The two light beams propagate along the two opposite optical paths in the fiber-

optic ring. If there is no angular velocity (Ω ¼ 0), the CW light beam and CCW light beam arrive the detector simultaneously and interfere with each other. The detector could convert the light intensity of interference into electrical signals. If there is one angular velocity (Ω 6¼ 0), the output of the detector will be changed. The polarizer could also modulate the phase of the light beam by applying voltages to improve the angular velocity detection. The performance of FOG degrades due to the variation in environmental factors such as temperature, vibration, and pressure. Among different types of error in the FOG signal, random drift error leads to decrease the FOG performance over a period of time. The precision of FOG depends on the bias drift and noise in the measurement. FOG has mainly two types of error (i) deterministic error and (ii) stochastic error. Deterministic errors are due to the scale factor, bias, and misalignment which can be eliminated by suitable calibration techniques in the laboratory environment. However, stochastic errors are due to the environmental temperature changes, electronic components, and other electronic equipment interfaced with it. It is difficult to

O

1264 Optical Compass, Fig. 2 Basic structure of the fiber-optic gyro

Optical Compass Coupler

Polarizer

Phase

SLD CW Detector

Ω

eliminate these errors by calibration. Thus, stochastic models are required to characterize these errors, and signal processing techniques are required to suppress these errors. Working Principle In favor of modern technologies, gyrocompass manufacturers have abandoned gimbaled platform and mechanical gyros, and began to use mathematic platform and optical gyros instead. Comparing to the traditional mechanical gyro compass, fiber-optic gyro compass has less setting time, higher measuring accuracy, and better dynamic characteristics. It is specially suitable for the navigation and control of high-speed platforms. Because of the solid-state solution, the strapdown gyro compass has high reliability and is maintenance-free during its service life. Thus, strapdown gyro compass is the current and nextgeneration marine navigator to provide attitude measurements. The heart of a fiber-optic gyro compass is its inertial measurement unit (IMU), whose mechanism is composed of three orthogonal fiber-optic gyros and three orthogonal accelerometers. As depicted in Fig. 3, a full range IMU corresponding to the three axes of the ship b-frame system will measure six degrees of freedom movement relative to n-frame system including the three rotational moments (pitch, roll, and yaw) and the three translational moments (heave, surge, and sway). The basic working principle of a fiber-optic gyro compass is the strapdown inertial navigation algorithm. A block diagram representation of this algorithm is shown in Fig. 4. Strapdown inertial

zb

Heave

yb Surge Roll

Yaw

fiber-optic gyro compass

CCW

o Pitch

xb Sway Optical Compass, Fig. 3 Fiber-optic gyro compass installed in ship

navigation system is a self-contained architecture that double integrates three acceleration components with respect to time and transforms them into the n-frame to deliver position, velocity, and attitude components in real time. The three orthogonal linear accelerations are continuously measured through three-axis accelerometers while three gyroscopes sensors measure the three orthogonal angular rates in an inertial reference frame. Digital signal processor (DSP) is used to calculate the mathematic platform. For short time, the integration with respect to time of the linear acceleration and angular velocity monitored by the gyroscopes results in accurate attitude, position, and velocity. However, sensor errors and mathematical integration over a long time of the fiber-optic gyro compass may

Optical Compass

1265

fn

fb

3x Accelercometers

Coordinate Transformation

v

Velocity Output Velocity Update

C

v

n

Translation Angular Velocity Calculation

ωen Location Matrix Correction

L Position Output

a

Attitude matrix computation

l y

y '

Q

Attitude Output

Quaternion normalization

q

g

g Decomposi -tion

Attitude quaternion update Equivalent Rotation Vector Computation

Δq 3x Fiber-optic gyros

Angular velocity

ωbib

ωbnb

ωie Decomposi -tion

Carrier’ s angular velocity calculation

w ie

Optical Compass, Fig. 4 Strapdown inertial navigation algorithm

cause considerable long-term system errors. Therefore, the fiber-optic gyro compass should work with external position and velocity provided by GPS and LOG to improve the long-time navigation performances. Key Technologies Attitude Updating Algorithm

The three fiber-optic gyros and three accelerometers of the fiber-optic gyro compass are directly connected with the ship b-frame system. The strapdown matrix is usually used as a mathematical platform. Therefore, a key problem in the fiber-optic gyro compass is the real-time solution of strapdown matrices. Therefore, in a strapdown gyrocompass system, attitude updating algorithm is the core of strapdown gyrocompass system algorithm. Real-time updating of ship attitudes is a very important technology in strapdown navigation system, and it is also a key factor affecting the accuracy of the whole system. In order to make the compass system have high precision, it is very important to adopt a high precision attitude updating algorithm. Quaternion algorithms and rotation vector algorithms are the two common methods for

attitude updating of strapdown systems. Quaternion algorithm has the characteristics of small computation and simple algorithm. However, the non-commutative error of quaternion arithmetic will occur when the finite rotation is carried out. Therefore, quaternion arithmetic can only be applied to attitude calculation under the condition of low dynamic motion of carrier. For high dynamic environment, the drift rate of quaternion arithmetic is very serious. By introducing the rotation vector algorithm, the influence of noncommutative error can be compensated. Although the accuracy of the compensation algorithm will be improved with the increase in the number of sub-samples, the corresponding calculation will be more and more large. In practical engineering applications, the appropriate attitude updating algorithm should be chosen according to the output data form of gyroscope and the time requirement of attitude updating algorithm. Rapid Alignment Technology

The navigation parameters (position, velocity, and attitude) of a fiber-optic gyro compass are calculated in navigation frame through the transformation from the body frame to the navigation frame using the attitude matrix (El-Sheimy et al. 2004).

O

1266

The relationship between the navigation frame and the body frame is realized by continuously updating this attitude matrix. To limit the errors in the derived navigation parameters, it is very important to determine the initial value of such matrix with high accuracy. In static ground alignment, the system attitude can be determined directly by using the gravity and earth rate signals obtained by using accelerometers and gyros in the navigation frame. However, the swing of marine will be caused by the wind wave. During the alignment process of SINS, gyros are employed to monitor the components of the earth rotation rate along their sensitive axes to determine the initial attitude of the moving platform. The angular rate error which is decided by the wind wave is much larger than Earth rate. So, the signal-to-noise ratio of gyro’s output is poor, and the frequency band of angular rate error is wide. It is impossible to directly get the Earth rate from gyros. Therefore, a feasible alignment solution for marine SINS may not only use the Earth rate and gravity obtained by using gyros and accelerometers, but also use some external information (GPS, LOG, etc.) (Sun and Sun 2010). The alignment process of compass is generally divided into two steps: coarse alignment and fine alignment. The goal of the coarse alignment stage is to solve the rough coordinate transformation matrix from the carrier system to the navigation system as soon as possible, which provides a good initial condition for the fine alignment stage. Therefore, rapidity is the main performance design index in the coarse alignment process. Generally, there are some errors between the attitude matrix obtained by coarse alignment and the real navigation system, especially the error of heading angle, which is much bigger than the error of horizontal attitude. In addition, the errors of inertial devices, such as the constant drift of gyroscope, will lead to the deterioration of the performance of navigation equipment after the start-up of the equipment. It is usually necessary to estimate and compensate for these errors in the process of fine alignment. The aim of fine alignment is to obtain the attitude angle which is infinitely close to the real value and compensate for

Optical Compass

other errors in the alignment process. Accuracy and rapidity are the two most important indicators of fine alignment. Damping Technology of Strapdown Compass

In strapdown solution, in order to avoid the influence of acceleration information on accelerometer data, it is necessary to select appropriate system parameters to make the system meet Schuler tuning conditions which are the undamped working state. However, when the system works in the undamped state, there are three kinds of oscillation errors caused by various kinds of disturbances. The three kinds are Schuler oscillation error with a period of 84.4 min, Foucault oscillation error with latitude variation, and Earth oscillation error with a period of 24 h. Among those oscillation errors, Foucault oscillation error and Schuler periodic oscillation error are mutually modulated. Those oscillation errors will lead to oscillation errors of navigation parameters in pure inertia solution, and even divergence of navigation errors in long-term operation. Those oscillation errors cannot be ignored. Therefore, in practical applications, the strapdown compass is usually switched between undamped and damped states according to different sea conditions. There are two main working states of a fiberoptic gyro compass: undamped state and damped state. The fiber-optic gyro compass normally works in the damped state which is also called compass state. The compass-loop control is used to find the north and indicate the ship’s course and attitude information. When the ship encounters strong motions such as bad sea conditions or frequent velocity variations, the disturbance motion information is measured by accelerometer, and then controlled by compass channel as part of gravity. In order to reduce the impact of external maneuvering environment on the compass output, the fiber-optic gyro compass needs to enter the undamped state in a short time. A general way to compensate the maneuvering error caused by the motion of the carrier is the “broken pendulum” often used in the platform compass system. This way refers to the accelerometer measurement data. If the sensitive data exceeds one threshold, the fiber-optic gyro

Optical Compass

1267

compass will not calculate the attitude information based on the accelerometer data. Therefore, the interference of errors caused by the acceleration of carrier maneuver can be overcome by an appropriate threshold. Integrated Navigation Technology

With the rapid development of the fiber-optic gyro, the fiber-optic gyro compass will be more accurate, smaller in size, more reliable, cheaper, and lower in energy consumption. However, the navigation error of the fiber-optic gyro compass will accumulate over time, which is difficult to meet the long-distance and long-time navigation requirements. Therefore, the external navigation information from other navigation systems is necessary for the fiber-optic gyro compass to correct the diffuse system error. The common working principle of an integrated navigation system is shown in Fig. 5. Each navigation system provides corresponding navigation information, which is fused by filtering method to obtain more accurate and reliable navigation information. According to different application Optical Compass, Fig. 5 The principle of integrated navigation system

environment and requirement, one or more other navigation modules are chosen for an integrated navigation. The general process of building integrated navigation system can be described as follows: by modeling and analyzing the system structure abstractly, the state equation and measurement equation of the system are established, and the state information or state error information of the system is estimated optimally by Kalman filter, and the optimal estimation is used to correct the navigation parameter information of subsystems.

Typical Applications Navigation At sea, mechanical gyro compass has always been used as a source of course information for ships. The mechanical gyros can sense the angular deviation of the navigation reference coordinate system relative to the inertial coordinate system, and provide this signal to navigation and positioning systems. It can be applied to the satellite positioner ARPA, integrated navigation system, Positon Attitude Velocity

O

SINS Positon Velocity GNSS Positon Attitude Velocity

Positon APS Data Fusion Geophysical navigation

Positon

Velocity DVL

MCP

Heading

1268

AIS, etc. The improvement of the mechanical gyro accuracy is seriously restricted by the unbalanced mass of the high-speed rotating “rotor,” the cross-coupling effect of the rotational degrees of freedom, the moment of inertia of the rotor, the harmful moment of the rotor support, and other factors. Also, the start-up time of the mechanical gyro compass is up to 6 h long. The fiber-optic gyro compass is not affected by this aspect. In addition to providing high-precision course information, it can also provide information of pitch, roll, and ship rotation angular velocity. The fiberoptic gyro compass hardly needs start-up time. Therefore, it will replace the mechanical gyro compass and be widely used in navigation. Survey With the increasing demand for understanding underwater topography and geomorphology, multi-beam bathymetry system is becoming more and more popular as an underwater topographic survey system with the advantages of full coverage, high efficiency, high precision, and high resolution. It has been widely used in underwater completion survey, pipeline route survey, breakwater mapping, before dredging and after dredging survey, coastal zone mapping, revetment survey, port mapping, river survey, IHO special survey, search and rescue, site obstacle survey, pipeline inspection, underwater inspection, object positioning, etc. When Multi-beam bathymetric system is used for bathymetric survey, due to the influence of wind and wave, the surveying ship will inevitably produce three rotational moments (pitch, roll, and yaw) and the three translational moments (heave, surge, and sway), which will lead to the inclination of the coordinate system of the surveying ship and the systematic deviation of the measured water depth. A fiber-optic gyro compass can provide six-degree-of-freedom motion information for ship measurement, and assist multi-beam bathymetric system to make systematic correction. Dynamic Positioning Dynamic positioning ship has become one of the most important marine equipment in the ocean engineering, which consists of measuring,

Optical Fiber

propulsion, and control devices. The accuracy of measurement system has a great influence on the accuracy of ship positioning control. A fiber-optic gyro compass could be used as a motion reference unit (MRU) to measure the ship’s motion. It measures the roll, pitch, and heave of the ship or platform during operation. Comparing the measured data with the preset values, the control system generates control instructions to keep the ship’s position.

Cross-References ▶ Fiber-optic Gyro Attitude Reference System ▶ Fiber-optic Gyro Motion Sensor

References El-Sheimy N, Nassar S, Noureldin A (2004) Wavelet de-noising for IMU alignment. IEEE Aerosp Electron Syst Mag 19(10):32–39 Li Q, Ben Y, Sun F (2013) A novel algorithm for marine strapdown gyrocompass based on digital filter. Measurement 46(1):563–571 Narasimhappa M, Sabat SL, Peesapati R, Nayak J (2014) An innovation based random weighting estimation mechanism for denoising fiber optic gyro drift signal. Optik Int J Light Electron Optics 125(3):1192–1198 Sun F, Sun W (2010) Mooring alignment for marine SINS using the digital filter. Measurement 43(10):1489–1494

Optical Fiber ▶ Umbilical Cable

Optical Fibers ▶ Fiber-Optic Cable

Optimal Control ▶ Intelligent Control Algorithms in Underwater Vehicles

Optimal Design

Optimal Design Mian Li UM-SJTU Joint Institute, Shanghai Jiao Tong University, Shanghai, China

Synonyms Design optimization; Optimized design; Optimum design

Definition Optimal design is usually considered as the design process that seeks the “best” possible solution(s) for a mechanical structure, device, or system, satisfying the requirements and leading to the “best” performance, through optimization techniques. It also refers to the design points that best satisfy objective(s) which are in contrast to non-optimal design. George Dieter has given a formal definition of design as follows: “Design establishes and defines solutions to pertinent structures for problems not solved before, or new solutions to problems which have previously been solved in a different way” (Dieter and Schmidt 2009). Optimal indicates a searching and decision-making process that is required to determine the best possible design alternatives. Optimization techniques are used to evaluate the trade-off among design alternatives and determine the best one(s).

Scientific Fundamentals Brief Background Engineering design process can be viewed as a sequential process. The sequence of design operations includes exploring alternative concepts, formulating a mathematical model, specifying specific subsystems, etc., while the design of complex systems can be broken down into a sequence of design steps. Design solutions come out as a result of repeated trials and errors. With the help

1269

of computer technologies, time-consuming and repetitive operations, like experiments, are replaced by computer program or simulations. Complex problems can be analyzed faster, and designers’ capabilities are extended. The importance of optimal design has been realized in 1980s since the high-quality products from Japanese companies invaded the market of the western world. Mathematical fundamentals for the design process have been developed for a long time, and it is still on its way to maturity. The best way to achieve high quality in a product is to design it from the beginning and assure that it is maintained throughout the manufacturing process. The enemy of quality is variability in performance and manufacturing. In this case, robust design has arisen to reduce variability while simultaneously leading the performance toward the optimal design point (Dieter and Schmidt 2009). To guarantee the product quality, the concept of quality control arose. All actions taken throughout the engineering and manufacturing of a product to prevent and detect product deficiencies and product safety hazards can be regarded as quality control. According to the “80/20 rule,” it is clever to concentrate on the vital few causes that worsen the product quality. Cause-and-effect analysis diagram can be used to identify possible causes of a problem. Control chart is an important quality control tool, which collects and keeps performance data for detecting variations. Since there is more than one possible solution to a design problem, the need for optimization is inherent in a design process. Design optimization methods in engineering design can be summarized by four broad categories: by evolution, by intuition, by trial-and-error modeling, and by numerical algorithms. There is no one universal optimization method for engineering design problems, and different kinds of methods fit for different problems. Computer-aided optimal design (or to be more specific, design optimization) generally starts with an initial or existing design point, and numerical analysis is used afterward to calculate the performance measurements and the sensitivity of the performance measurements with regard to uncertainties in design parameters.

O

1270

New design candidates will be generated during the running of optimization algorithms, while optimum design(s) will be achieved after the execution of the optimization. It is worth mentioning that although we often use “optimal design” and “design optimization” interchangeably, they are not strictly equivalent. The former one usually refers to the whole design process or the optimal solution itself, while the latter usually refers to one important step in the design process or technology used to achieve the design solution(s). Principles of Optimal Design Design System

Designing is a systematic work. A design solution is also called a system (Arora 2004). An original system can be made up of several components which are also systems with their own functions and input/output characteristics, as shown in the diagram in Fig. 1. That is to say, a system can usually be decomposed into interconnected subsystems, which can be further broken down and analyzed at a particular but lower level of complexity. For example, a gas-turbine system contains the components, e.g., compressor, combustor, turbine, etc. Each of the components is a complicated system itself. Meanwhile, the gasturbine system is just one component of a petroleum plant. It is of vital importance to decide whether to represent the design task as a unit or as a collection of components (subsystems).

Optimal Design

with complex functions. Mathematical models have been widely accepted and applied in representing design systems through mathematical relations. The system, as shown in Fig. 1, can be represented by y ¼ f(x), where x, y represent the vectors of input and output quantities, respectively, and f can be equations, algebraic or differential, or a computer-based simulation program. To model a system, we need to generalize the design problem and identify the following model elements: system variables, system parameters, system constants, and mathematical relations. System variables specify different states of the system by assigning different values. System parameters are assigned with one specific value in one particular model statement and can be used to take care of uncertainty or variations when considering robust design. System constants are fixed by underlying phenomenon which cannot be influenced by the designers. Mathematical relations relate to the system variables, parameters and constants using equalities and inequalities, or even implicit formulations. Determination between variables and parameters is subjective but important at the modeling stage. To model a design mathematically, we must be able to define it completely by assigning values to each quantity involved, such as geometric configuration, the material used, and the task it performs. A design modeling study will help increase our understanding on how a system works. Decision-Making and Design Optimization

Mathematical Model

Engineers always use an abstract representation instead of a real system for the purpose of analysis. An abstract description of the real-world system is called a model, which provides an approximate representation of a physical system

Optimal Design, Fig. 1 Design system diagram

A design process can generate more than one alternative in general. A need for making a decision on choosing one or a few of them in this case arises. To evaluate different alternatives and rank them in a rational order, at least one criterion is required. Such criterion may not be unique or may change with time. The design model with the evaluation criterion is a decision-making model or an optimization model. The criterion is called the objective of the model, and the selected “best” design is called optimal design. Design optimization is to select the “best” design solution (s) according to available requirements. To quantitatively formulate a design optimization problem and solve it, a mathematical

Optimal Design

1271

Optimal Design, Fig. 2 Local and global optima

representation is built. x ¼ (x1, x2,. . .,xn)T, in a n-dimensional design space, is the vector of design variables whose value describe a design alternative. The acceptable limits on x are called lower and upper bounds. The objective is represented by a function of design variable, f(x). It is possible that there are multiple objectives in one design optimization problem too. In that case, there will be multiple objective functions, like f1(x), f2(x),. . ., fm(x). Available requirements are constraints by the function relationship among x. hk(x)¼ 0, k ¼ 1,. . ., K and gj(x) 0, j ¼ 1,. . ., J represent equality and inequality constraints, respectively. Any design satisfying the constraints contributes to the feasible design space. Different forms for f, gj, and hk are usually derived from basic equations and engineering laws. Also they can be derived through curve fitting using empirical or experimental data or through simulation modeling, which is the current statement of the complex procedure involving internal calculations and computer programs. In practice, mathematical models in design optimization can be a mixture of above. Then the design optimization problem is formulated as min f ðxÞ x

s:t: gðxÞ  0 hð xÞ ¼ 0

ð1Þ

where x ¼ ½x1 , x2 , . . . , xn T Design optimization involves the selection of design objectives, determination of constraints, and the set of design variables that optimize the objective(s) while satisfying all constraints.

A complete optimization study to find the optimal design(s) could be expensive and time-consuming for large systems. Thus, several iterations, instead of a complete optimization study, are performed until sufficient improvement in the design has been obtained. Local and Global Optima

As shown in Fig. 2, point B and E (point C and F) are minima (maxima) with regard to the values in the local vicinity. They are called local minimum (local maximum). The boundary points A and G are also taken into consideration when determining the overall optimum. From all local minima (local maxima) and boundary points, the smallest one is defined as the global minimum (global maxima). It can be observed that both local and global optima may not be unique. Sometimes an infinity of solutions may be detected. Finding global solutions to optimization problems is important for design optimization. However there is yet no universal solution strategy proven by general optimization theory in practice. To identify the global optimum, a thorough study is conducted to go through all the local optima and determine the global one even under different ranges of parameters. However, this may be difficult from the mathematical viewpoint or expensive from the computational viewpoint. Mathematical methods can be used to identify the solution(s) to the problem. However, to address the solving task in a purely mathematical way while divorcing from the physical significance of the model and its elements can be a tactical error. Optimization problems in design are generally difficult to solve mathematically.

O

1272

Optimal Design

On the contrary, the “best” design solutions may not need to be mathematically proven optima. Typical solving methods in mathematical programming use iterative numerical search procedures. Starting from an initial point, the direction of improvement is identified, and a step is taken along that direction. Consequently, a sequence of points that converge to the minimum can be created. Such numerical iterative computation is driven by local knowledge, which is easy to get but has limited ranges. Global knowledge is superior and results in better techniques but difficult to acquire. Optimization Methods

Analytical Optimization Methods Graphical optimization is a method that finds the optimum solution by drawing the objectives and constraints graphically. Since the graphics can only be drawn on a two-dimensional space, this method can only be used to solve the problems with two design variables. To obtain the optimum solution, the constraints are drawn on the two-dimensional design variable space which forms the feasible region. Then by drawing the iso-objective contours, the design point that makes the objective function reach the minimum in the feasible region is identified as the optimum point. Due to its property and limitations, this method is useful for the illustration of optimization methods. Optimization problems without constraints are called unconstrained optimization problems. For this kind, there exist necessary and sufficient conditions for local minimum. Necessary condition: if f(x) has local minimum at point x*, then the gradient of f(x) at x* is 0. ∇f ðx Þ ¼ 0

ð2Þ

Sufficient condition: if the Hessian matrix H(x*) is positive definite at x*, then x* is sufficiently a local minimum. To obtain a local minimum for a function f(x), which is the objective of an unconstrained problem, we first obtain a solution x* satisfying Eq. (2). Then we check if the Hessian matrix is positive definite at x*. If its Hessian matrix is

positive semidefinite, higher order derivatives need to be checked. For constrained optimization problem, an optimum point can be mathematically obtained using the theorem called Karush-Kuhn-Tucker (KKT) condition. The constraints are added to the objective function by multiplying each with a Lagrange multiplier, resulting in a Lagrange function. The gradient vector of Lagrange function with regard to the design vector x and Lagrange multipliers becomes a zero vector at local minimum. Original constraints and additional restrictions for Lagrange multipliers should be satisfied. More details about KKT condition can be found in the reference (von Laarhoven and Aarts 1987). If the objective f(x) is a convex function defined on a convex feasible domain, the prementioned KKT condition is both necessary and sufficient condition for a global optimum. Numerical Optimization Methods In real practice, finding the optimum solution(s) through mathematical calculations is quite difficult. It is often difficult to solve simultaneous equations which make the gradient vector be a zero vector. Besides, as the number of constraints increases, the process to evaluate many cases in KKT condition for inequality constraints becomes more complicated. It is almost impossible to solve a design optimization problem with mathematical calculations when many constraints exist in the problem. Instead, numerical methods using computer programming are utilized. Various numerical methods are developed specifically for different problems. Numerical methods start from an initial design point and find an optimum in an iterative way. At each iteration, a new design is found. When at least one of the convergence criteria is satisfied, the design in the current iteration is considered as an optimum. The design is improved at each iteration through Eq. (3). xðkþ1Þ ¼ xðkÞ þ DxðkÞ , k ¼ 0, 1, 2, . . .

ð3Þ

where k is the iteration number. A new design x(k+1) is obtained by adding the change of design vector Δx(k) to the current design x(k). The change Δx(k)

Optimal Design

1273

consists of the moving direction d(k) at the point x(k) in the design space and the scalar step size αk in the direction d(k). DxðkÞ ¼ ak d ðkÞ

ð4Þ

The evaluation of αk and d(k) depends on the algorithm used. The determination of αk and d(k) should reduce the objective function f(x(k)) when x(k) is not an optimum yet. This condition is expressed as in Eq. (5).       f xðkþ1Þ ¼ f xðkÞ þ ak d ðkÞ < f xðkÞ

ð5Þ

The sensitivity information, i.e., the (partial) derivative of objective and constraint functions, is used to decide the descent direction in numerical methods. Mathematical derivative functions or finite difference method can be used depending on different situations. The overall steps of a numerical procedure are shown in Fig. 3. Heuristic Optimization Methods Heuristic optimization algorithms are developed by observing different nature behaviors. They are different from classic optimization methods like gradient-

Optimal Design, Fig. 3 General steps of numerical method

based approaches. The search process proceeds toward a solution(s) without caring how the functions are evaluated. Thus continuity or differentiability of the problem functions is not required. In addition, the methods inherently try to determine the global optimum. Since no gradient information is required, heuristic methods are easy to use and program. However, such algorithms usually require a large amount of calculations, and there is no guarantee of obtaining the global optimum. Genetic algorithms (GA) and simulated annealing (SA) are two popular heuristic methods. GA are based on Darwin’s theory of natural selection. The basic idea is to start with a set of randomly generated designs. A fitness value is assigned to each design by using its values of the objective function and penalty function for constrained problems. Processes (e.g., reproduction, crossover, and mutation) which can generate new designs with certain randomness are used to generate new designs. The size of the design set in one iteration is kept fixed, called the population. As more fit members of the set are used to create new designs, the successive sets of designs will have a higher probability of involving better fitness values. The process is continued until a stopping criterion is met. A flowchart of GA is shown

O

1274

Optimal Design

Optimal Design, Fig. 4 Flowchart of GA

in Fig. 4, representing a general procedure of this algorithm. The details of each step can be found in the literature (Arora 2004). The length of strings (used to represent each design) and population size are decided in the initialization stage. The fitness evaluation determines how “good” design points will be in the population. The three operations, reproduction, crossover, and mutation, make more copies of better designs and remove worse designs gradually. New designs with better quality are generated. They also provide GA the capability of jumping out from the local optimum. Designs will converge to the optimal solutions iteration by iteration. SA is a computational stochastic technique for obtaining the global optimum. It is inspired by the thermodynamic process of annealing of molten metals to attain the lowest free energy state. When the metal is cooled slowly enough, it tends to solidify into a structure with the minimum energy. SA is a search strategy imitating the annealing process. The key of the method is to allow occasional worsening moves which may eventually help locate the design to the true global optimum. Details of SA can be found in (von Laarhoven and Aarts 1987). When setting up the problem, the appropriate initial temperature is required. New designs are generated by perturbation, and function values are evaluated. The new

design is accepted for sure if it is a better point, or it is accepted by probability if it is a worse design. The temperature is slowly reduced. Optimal solutions will be gradually reached through the SA procedure. Multi-criteria and Multidisciplinary Design

If there is a set of criteria, f ¼ (f1, f2,. . .,fm)T, the design problem becomes a multi-criteria one: min f ðxÞ x

s:t: g j ðxÞ  0, j ¼ 1, . . . , J

ð6Þ

hk ðxÞ ¼ 0, k ¼ 1, . . . , K Several methods exist to convert the multicriteria formulation into a substitute single-criterion problem which can be solved by single-objective optimization methods. The simplest scalar substitution is obtained by assigning subjective weights, w ¼ (w1, w2,. . .,wm)T, for multiple criteria, and the set of objectives are translated into a scalar f ¼ iwi fi(x). The weights can be considered as the design preference that can be adjusted according to designers’ preferences or different usage scenarios. For example, different combinations of preference parameters can represent different levels of tradeoffs among those criteria. The solution set discovered by assigning different weights can form the

Optimal Design

so-called Pareto set, which includes solutions that cannot improve one criterion without sacrificing others, as shown in Fig. 5. Other approaches suitable for multi-criteria design problems can be found in literature, like value-function method, goal programming (Ignizio 1976), game theory (Vincent 1983), and upper-bound formulation. As discussed above, a system can be decomposed into different levels of subsystems. The designer must identify at which level the

Optimal Design, Fig. 5 Feasible domain and Pareto set of bi-criteria optimization Optimal Design, Fig. 6 Hierarchical decomposition

Optimal Design, Fig. 7 Nonhierarchical decomposition

1275

design optimal solutions are required, while it is possible that the design optima of subsystems (without considering other subsystems) may not be optimum for the entire system. For example, the GnC, vehicle body, and engine are three subsystems of an undersea vehicle system. The optimum design of the GnC may not be the best solution for the entire vehicle if not considering the design of the vehicle body or engine. For large-scale problems, treating the system as a single entity may encounter difficulties for reliable solutions. Instead, the problem can be modeled by a set of independent subproblems which are coordinated by a master problem (or called system problem). Design variables associated with the master problem are called global variables, while those associated with subproblems are local variables. Linking variables are used to represent the original couplings between subproblems. Hierarchical and nonhierarchical partitioning of a system are shown in Figs. 6 and 7, respectively. Decomposition-based approaches for system design require both portioning and coordination. They are employed to improve the overall

O

1276

solution efficiency. This branch of optimization design methods arises as multidisciplinary design optimization (MDO). Robust Optimal Design

Robust design refers to the methods or procedures to develop system products whose performance is insensitive (or least sensitive) to the variations due to uncontrollable factors. As the pioneer of this research area, Taguchi first defined the loss function to evaluate the quality level of the products (Taguchi 1987). The smaller the loss, the more desirable the product. Taguchi method uses a special response variable, signal-to-noise ratio (S/N ratio), which encompasses both the mean and variation in one parameter. Design parameters that primarily affect the S/N ratio are identified, and the level of these parameters is found to minimize the response variations. Since lots of experiments are required in this parameter design, the fractional factorial design of experiments (DoE) is adopted instead of testing all combinations. Taguchi method is still popularly used in the practice although many drawbacks have been pointed out. Later, the robustness concept has been added to the conventional or so-called deterministic optimization. The objective and constraints functions are redefined with additional robustness indices. To distinguish the difference, the design variables determined by solving the conventional deterministic optimization problem

Optimal Design, Fig. 8 Nominal point versus robust point

Optimal Design

where variations (uncertainties) are not considered are called nominal values (or nominal solutions). The robust optimal designs come from the results of the robust optimization problem which takes variations into consideration. The robust optimization problem can be formulated as min f ðx, pÞ x

s:t: gðx, pÞ  0

ð7Þ

xlb  x  xub where p represents the uncertainties in design variables or parameters. One way of defining the robustness is shown as follows. The robustness of the objective function is achieved by reducing the variation in the objective function due to the uncertainties. As shown in Fig. 8, the objective function reaches its minimum at the point A. However, the objective value at this point will be influenced a lot by the small variation in the design variable. On the contrary, Point B and C are less sensitive to the uncertainty in the design variable, thus being more robust. The robustness of the constraint functions is defined such that all constraints should be satisfied whenever design variables or parameters are changing within their variation range. In robust optimization, objective functions can be formulated in different ways. When uncertainties are modeled by probabilistic distributions,

Optimal Design

1277

robust optimization problems can be formulated with the mean and the standard deviations in different ways, as shown below (Park et al. 2006). Weighted Sum with Normalization f new ¼ a

m f ðx, pÞ s f ðx, pÞ þ ð 1  aÞ mf sf

ð8Þ

The new objective function in the robust optimization can be formulated as the weighted sum of the mean and standard deviation of the original objective function f. α is the weighting factor between minimizing the objective value and minimizing the variation of the objective function. A smaller α value will put more emphasis on the robustness. mf* and sf* are the base values for the mean and standard deviation, respectively, used for normalization. Bi-objective Formulation of Robust Optimization  f new ¼ m f ðx, pÞ, s f ðx, pÞ ð9Þ In this formulation, the mean value of the objective and its variation are optimized as two objectives simultaneously.

Constraint Formulation of Robust Optimization The constraint formulation of robust optimization can be shown as Eq. (10). gnew ¼ mg ðx, pÞ þ ks2g ðx, pÞ

ð10Þ

where k is a constant value which reflects the confidence level on the variation of the constraints. For example, when k ¼ 3, the constraints will be satisfied with a probability of 99.865% with normal distributions. When uncertainties are modeled by intervals, robust optimization can be formulated by using the definition of the robustness index (Li et al. 2006). The parameters p with interval uncertainty are represented by their nominal value p0, and the corresponding variation range Δp. p can take

any value randomly in the interval [p0Δp, p0+Δp] without any assumption on the distribution. The robustness of objective and constraint functions is quantified by using the robustness indices f, g, respectively. min f ðx, p0 Þ x

s:t: g j ðx, p0 Þ  0, j ¼ 1, . . . , J n o  ¼ max  f , g  1  0

ð11Þ

lb  xub The robustness of the objective function under interval uncertainties are defined by Eq. (12). It says that the design x0 is objectively robust if the worst objective variation induced by p is within a predefined acceptable variation range Δf0.

f ðx0 , pÞ  f ðx0 , p0 Þ

 f  1 where  f ¼ max

p Df 0

s:t:p0  Dp  p  p0 þ Dp

ð12Þ Eq. (13) defines the robustness of constraints, which represents that x0 is feasibly robust if the worst increase of the constraint function values is still bounded by the absolute constraint value at the nominal parameter value p0. 8 g j ðx0 , pÞ  g j ðx0 , p0 Þ > >

max , > >

> p, j >

g j ðx0 , p0 Þ > > > > > > < if g j ðx0 , pÞ g j ðx0 , p0 Þ g  1 where g ¼ > > > > > > > > > > > > : 0, otherwise s:t: p0  Dp  p  p0 þ Dp, j ¼ 1, . . . , J

ð13Þ After the treatment of the uncertainty using above strategies, the robust optimization problem can be solved through the optimization methods suitable for the deterministic case.

O

1278

Optimal Ship Operations

Cross-References

Optimization Algorithm ▶ Concept Design ▶ Design of Submersibles ▶ Design Spiral ▶ Detailed Design ▶ Empirical Design ▶ Multidisciplinary Design Optimization (MDO) ▶ Preliminary Design ▶ Reliability Based Design (RBD) ▶ Structural Design ▶ Technical Design

References Arora JS (2004) Introduction to optimum design. Elsevier Academic, Amsterdam. ISBN: 9780120641550 Dieter GE, Schmidt LC (2009) Engineering design. Mcgraw-Hill, Boston. ISBN: 9780071271899 Ignizio JP (1976) Goal programming and extensions. Lexington Books, Lexington. ISBN: 9780669000214 Li M, Azarm S, Boyars A (2006) A new deterministic approach using sensitivity region measures for multiobjective robust and feasibility robust design optimization. J Mech Des 128(4):874–883. https://doi.org/10. 1115/1.2202884 Park G-J, Lee T-H, Lee KH, Hwang K-H (2006) Robust design: an overview. AIAA J 44(1):181–191. https:// doi.org/10.2514/1.13639 Taguchi G (1987) System of experimental design; engineering methods to optimize quality and minimize costs, vol 1 & 2. UNIPUB/Kraus International Publications, White Plains. ISBN: 9780941243001 Vincent TL (1983) Game theory as a design tool. J Mech Transm Autom Des 105(2):165–170. https://doi.org/ 10.1115/1.3258503 von Laarhoven PJM, Aarts EHL (1987) Simulated annealing: theory and applications. Springer, Dordrecht. ISBN: 9789048184385

▶ Multidisciplinary Design Optimization (MDO)

Optimization of Propellers ▶ New Technologies in Auxiliary Propulsions

Optimized Design ▶ Optimal Design

Optimum Design ▶ Optimal Design

Orthogonal Frequency Division Multiplexing (OFDM) ▶ Underwater Acoustic Communication

Oscar ▶ Submarine

Optimal Ship Operations

Oslo/Paris Convention (OSPAR)

▶ Human Factors in the Role of Energy Efficiency

▶ Decommissioning of Offshore Oil and Gas Installations

OWT – Offshore Wind Turbine

Outfit ▶ Ship-Fitting Design

1279

OWC – Oscillating Water Column ▶ Power Take-Off System

Outfitting

OWT – Offshore Wind Turbine

▶ Ship-Fitting Design

▶ Analysis of Renewable Energy Devices

O

P

Painting Technology Rui Li School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China

Definition Ships are built on land and sail on rivers or oceans, so the main steel hull and numerous outfitting pieces will be corroded by the industrial atmosphere and the marine environment. Corrosion can cause great damage to ships and reduce the strength of ship structures (Xu 2005). When the steel ship is corroded to a certain degree, the strength of the hull will be reduced to be insufficient to withstand the huge impact of the ocean wind and waves on the hull, and a shipwreck is inevitable. When the various equipment of the ship is corroded to a certain degree, the equipment cannot work and operate normally, which will cause various accidents. In severe cases, the ship will lose control and its self-rescue ability in the ocean, causing disasters finally. Therefore, when the ship is corroded to a certain degree, it has to be scrapped and lose its use-value. The corrosion of steel ships in the ocean is inevitable, but the rate of corrosion can be controlled. In order to prevent the corrosion of steel and prolong the service life of ships, steel, hulls, outfitting steel structural pieces, pipe system, and © Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

cabinet must be rust removal and painted. This kind of surface treatment is called ship painting. In addition to anti-corrosion effects, ship painting also has the effects of exterior decoration and anti-foul (Liu et al. 2011).

Introduction Operation Method of Ship Painting The ship painting method is coordinated with the block construction method of the hull construction and the regional outfitting method of ship outfitting. Therefore, ship painting operations include steel pretreatment, sectional painting, shipboard painting, and finished coat, as shown in the following figure. Among them, the painting of outfitting pieces, the painting of the brackets, bases, strong back, and other outfitting pieces connected with the hull belong to the scope of sectional painting; the painting of other outfitting units and outfitting pieces should be completed at the later stage of unit outfitting and outfitting pieces production, so they are all in-site operations (Fig. 1). Steel Pretreatment Steel pretreatment is the leveling, rust removal (including oxide scale), and protective paint on the steel. The process method and process of steel pretreatment have been discussed in detail above, and the automatic assembly line of steel

1282

Painting Technology

Painting Technology, Fig. 1 Painting stage and process

pretreatment has been briefly introduced, so there is no need to repeat it here (Li et al. 2006). Sectional Painting After the steel pretreatment is made into sections by component processing and structural preassembly welding, the surface of the steel structure will inevitably produce zinc salt, rust, oil stains, moisture, etc., so a second rust removal is required, and then spray primer according to the different requirements of the sections. The secondary rust removal and primer spraying operations for the sections are called sectional painting. In order to control the environmental conditions of the painting operation and ensure the quality of the painting, indoor operations should be used for sectional painting, so the second stage of rust removal is best to use shot blasting in the shot blasting room. It uses the pressure of high-speed flowing compressed air in the air duct to make iron shots impact the rust spots on the metal surface to achieve rust removal. In addition to the iron shot blasting device, the shot blasting room is also equipped with rails and section loading vehicles, iron shot recovery devices and rust dust suction devices to ensure shot blasting operating conditions, and rust removal quality. Outside the house is equipped with sectional dispatching equipment and indoor workplaces for sectional spray primer. The primer should be sprayed immediately after rust removal in sections,

otherwise yellow rust will easily occur and affect the quality of rust removal. Sometimes due to various conditions, it is necessary to carry out sectional painting operations on the field platform. At this time, most of the sectional rust removal uses pneumatic tools, such as pneumatic grinder, pneumatic control wire brushes, etc.; primer spraying uses portable airless spraying equipment (Wang et al. 2019). Shipboard Painting The painting work on the berth (in the dock) before launching the ship and at the dockside after launching is called shipboard painting. The painting operations onboard include rust removal, cleaning, touch-up painting, and spraying of the inner and top coats on various parts of the outer surface of the hull. If there is no subsequent outfitting work for the oil tanks, water tanks, and other liquid tanks inside the hull, painting operations can be completed on the hull (in the dock). However, due to the busy outfitting operation in the ship, the hull deck is easy to wear and tear the paint film and is left to be painted at the later stage of outfitting at the wharf (He et al. 2020). Finished Painting The painting operation before delivery is called finished painting. Finished painting is generally completed within a period of time from the end of the trial voyage to the delivery of the ship, so that

Parametric Roll Resonance

when that ship is hand over to the owner, it will look quite new. However, as long as the shipowner agrees, the finished painting operation can also be carried out in advance. Finished painting operations include the cleaning and touch-up of the outer surface of the superstructure, deck, and deck machinery, as well as the spraying of the last topcoat on the outer surface of the hull; organic solvents are used to clean up grease and other stains before the paint is repaired. The last coat of paint on each part of the outer surface of the main hull is usually sprayed in the dock. Firstly, the bottom of the ship is washed with clean water to remove salt and soil. Secondly, the paint is repaired after drying (e.g., the first paint film is often damaged by the anchoring test). Thirdly, the finish coat is sprayed.

1283

tail. Another example is that the poor paint film of the bottom of the ship at the keel block, insufficient thickness of paint film at the weld seam of the outer plate, and local paint film scratches on the side outer plate will cause electrochemical corrosion in the marine environment (Cho et al. 2016). In order to make up for the deficiencies of anti-corrosion treatment, cathodic protection is generally used as an auxiliary means of anticorrosion for the hull. According to the electrochemical principle, the metal with lower electroplating potential will be used as the anode in the corrosion battery to release electrons, thus causing it to be corroded. Cathodic protection is to polarize the protected metal as a cathode so that it can capture electrons and be protected. According to different polarization principles, there are two kinds of cathodic protection: sacrificial anode method and impressed current method.

Common Paint for Ships Paint is usually composed of binders, pigments, diluents, and additives. Among them, the binder is the main film-forming substance; the pigment is the secondary film-forming substance, which can color the paint film and improve the performance of the paint film; the diluent, a volatile substance is used to dissolve and dilute the paint for operation; the additive is used to make the paint film have specific properties, such as antifouling, corrosion inhibition, and plasticization. Paint can be classified according to binders. The commonly used binders are natural resin, mineral asphalt, and synthetic resin. Synthetic resin is widely used in modern marine paint, mainly including alkyd resin, ethylene resin, epoxy resin, chlorinated rubber, polyurethane resin, and inorganic zinc paint.

Cathodic Protection of the Hull It is not enough for ships to rely on paint to prevent corrosion. For example, exposed copper propellers in water and contact with steel structures such as propeller shafts and stern posts exposed in the water will produce battery effects and cause corrosion of the steel components at the

References Cho D-Y, Swan S, Kim D, Cha J-H, Ruy W-S, Choi H-S, Kim T-S (2016) Development of paint area estimation software for ship compartments and structures. Int J Nav Archit Ocean Eng 8(2):198–208 He X, Wang J, Zhao B, Mu Y, Liu Y, Hou W, Ma T (2020) Nondestructive discrimination of ship deck paint using attenuated total reflection – Fourier transform infrared (ATR-FTIR) spectroscopy with chemometric analysis. Anal Lett 53(17):2761–2774 Huang H (2013) Technology handbook of hull construction. China National Defense Industry Press, Beijing, pp 365–368 Li ZL, Wei JL (2006) Technology of ship production. Harbin Engineering University Press, Harbin, pp 192–194 Liu YJ, Wang J (2011) Technology of ship production. Dalian University of Technology Press, Dalian, pp 160–174 Wang Q, An D, Sun R, Su M (2019) Investigation and source apportionment of air pollutants in a large oceangoing ship during voyage. Int J Environ Res Public Health 16(3):389 Xu ZK (2005) Technology of ship production. The People’s Communication Publishing Company, Beijing, pp 682–688

Parametric Roll Resonance ▶ Parametric Rolling

P

1284

Parametric Rolling

Parametric Rolling Min Gu, Jiang Lu, Shuxia Bu, Jilong Chu, Ke Zeng and Tianhua Wang China Ship Scientific Research Center (CSSRC), Wuxi, China

Synonyms Low cycle resonance; Parametric roll resonance; Parametrically excited roll

Definition Parametric rolling is a dynamic stability phenomenon in which an amplification of roll motion is caused by periodic variation of transverse stability

Stability is increased with strong pushback

Strong pushback, picking up rotation speed

in waves. The phenomenon of parametric rolling is predominantly observed in head, following, bow, and stern-quartering seas when the ship’s encounter frequency is approximately twice that of the ship’s roll natural frequency and the ship’s roll damping is insufficient to dissipate additional energy (SDC 3/WP.5/Annex 4,2016). Figures 1 and 2 shows the process by which parametric rolling develops. If the ship rolls while in the wave trough, increased stability provides stronger pushback, or restoring moment. As the ship returns to the upright position, its roll motion rate is increased, since there was an additional pushback from the increased stability. At that time, however, the ship will roll further to the opposite side because of the greater roll motion rate and less resistance to heeling. Then, if the wave trough reaches the midship section when the ship reaches its maximum amplitude roll, stability increases again and the cycle starts again.

Stability is decreased, ship rolls further

Stability is increased again, strong pushback cycle is repeated

Parametric Rolling, Fig. 1 Development of parametric roll resonance (Belenky et al. 2011; SDC 3/WP.5/Annex 4,2016)

Parametric Rolling

1285 Roll, deg

Phase of wave

20

0

5

10

15

20

25

30

-20 Wave 2

Wave 1 -40

Wave 3

Roll period 1

Wave 4

Roll period 2

Parametric Rolling, Fig. 2 Time histories plots of parametric roll resonance (SDC 3/WP.5/Annex 4,2016)

There are two waves that pass during each roll period (SDC 3/WP.5/Annex 4,2016).

Scientific Fundamentals

o2

o2 DGM e GM

where m ¼ o2me , d ¼ 4 o02 , 2e ¼ 4 o02 e

,

t ¼ oet/2. If the damping coefficient is ignored, the standard Mathieu equation can be obtained as follows:

The roll motion in head or following seas can be expressed as follows:

€ þ ðd þ 2e cos 2tÞ’ ¼ 0 ’

ðI xx þ A44 Þ€ ’ þ N 1 ’_ þ W
 DGM  GM 1 þ cos oe t ’ GM

The solution of the standard Mathieu equation is as follows, and the stability diagram of the Mathieu equation is shown in Fig. 3.

¼0

ð1Þ

where ’: roll angle, N1: linear roll damping coefficient, W: ship weight, Ixx: moment of inertia in roll, A44: added moment of inertia in roll, GM: metacentric height in calm water, ΔGM: the variation of metacentric height in waves, oe: encounter wave frequency, and t: time. The dot denotes the differentiation with time. The roll equation (1) can be rewritten as follows: € þ 2m’_ þ ’

o20


 DGM cos oe t ’ ¼ 0 ð2Þ 1þ GM

where 2m ¼ Ixx NþA1 44 , o0 ¼

qffiffiffiffiffiffiffiffiffiffiffi WGM I xx þA44

, o0: natural

roll frequency. The roll equation (2) can be further rewritten as follows: € þ 2m ’_ þ ðd þ 2e cos 2tÞ’ ¼ 0 ’

ð3Þ

ð4Þ

  1 d 0 ¼  e2 þ O e3 , 2     1 1 d1 ¼ 1  e  e2 þ O e3 , d01 ¼ 1 þ e  e2 þ O e3 8 8     1 5 d2 ¼ 4  e2 þ O e3 , d02 ¼ 4 þ e2 þ O e3 12 12

ð5Þ

From the stability diagram, we see that unstable motion can occur at several different ratios of oe/o0. The shadow area means unstable region. The predominant value of this ratio is d ¼ 4o20 =o2e ¼ 1, meaning that oscillation at the natural frequency occurs if the frequency of encounter is twice the natural frequency. This instability phenomenon is an example of a dynamic motion “bifurcation.” A small initial disturbance 2ε ¼ ΔGM/GMcan trigger a growing oscillation, meaning that a small variation of GM in waves could trigger a growing roll motion, even capsizing in this unstable region. The unstable region becomes large as ΔGM increases. This phenomenon is called parametric rolling.

P

1286

Parametric Rolling

Parametric Rolling, Fig. 3 Stability diagram of the Mathieu equation

Parametric Rolling, Fig. 4 Stability diagram of the Mathieu equation for parametric rolling

The basic value of this ratio is d ¼ 4o20 =o2e ¼ 4, meaning that oscillation at the natural frequency occurs if the frequency of encounter equals the natural frequency. This instability phenomenon is not discussed here. If roll damping is considered as shown in Eq. (3), the solution of the Mathieu equation for parametric rolling is as follows, and the stability diagram of the Mathieu equation for parametric rolling is shown in Fig. 4. 1 d  1 ¼  e2  8

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi e2  ð2m Þ2

ð6Þ

The shadow area means an unstable region, and there is a threshold value ε ¼ 2mfor unstable region. If 2m  ε, it is stable. If 2m < ε, it is unstable, meaning that if 4m < DGM GM and o0/ o ¼ 1/2, parametric rolling could occur.

Typical Parametric Rolling Accident In late October 1998, a C11 class, post-Panamax containership, which is 262 m LBP, and 24.45m Depth with a loaded draft of about 12.5m, eastbound in the north Pacific from Kaohsiung to

Seattle, was overtaken by a severe storm. She carried a deck stow of some 1300 containers. As encounter with the storm became inevitable, the master rode out hove to the rough seas and winds. The storm encounter lasted for some 11 hours, mostly at night. During the period of severest motions, port and starboard rolling of as much as 35–40 degrees was reported simultaneously with extreme pitching. The master later described the ship as absolutely out of control. About 400 containers were lost overboard, and another 400 collapsed or crushed during these motions (SLF45/6/ 7,2002) (Fig. 5). In February 2003, the Wallenius PCTC M/V Aida experienced sudden violent rolling in rough head seas southwest of the Azores. Roll angles as large as 50 degrees were read off the bridge inclinometer. When this incident was postanalyzed, it was found that the condition, in terms of the relation of wave encounter period and natural roll period, was such that parametric rolling was most likely the case. Partly due to this accident, M/V Aida was equipped with a Seaware EnRoute Live system in December 2003 for trial during the winter. In February 2004, on a voyage from Southampton to New York, Aida encountered heading sea with significant wave height 5–6 m and traveled with reduced speed 8–10 knots west

Parametric Rolling

1287

Parametric Rolling, Fig. 5 APL China containership suffered parametric rolling (http:// marineinbox.com/marineexams/parametric-rollingin-container-ships/)

of the Azores. At five different occasions, parametric rolling evolved, with roll angles up to 17 degrees. The strong pitch-roll coupling during head-sea-parametric rolling is clearly demonstrated by the recorded motion time series with the Seaware EnRoute Live system (SLF47/INF.5 2004).

Historical Development Before the accident of the C11 class containership, parametric rolling is mainly dealt with in the cases of following waves (Kerwin 1955) or beam waves (Blocki 1980). In particular, clear experimental records of capsizing due to parametric rolling in following waves were published by Umeda (Umeda et al. 1995). In case of following waves, the encounter frequency is much lower than the natural frequencies of heave and pitch so that coupling with heave and pitch is not important. In addition, added resistance in following waves is generally small. Thus, several successful predictions of parametric rolling in following waves were reported (Munif and Umeda 2000). In case of head waves, however, prediction of parametric rolling is not so easy because coupling with heave and pitch is significant and added resistance cannot be ignored. The effect of dynamic heave and pitch motions on parametric rolling was investigated so far by many researchers and is well established: Restoring

arm variation in head waves depends on dynamic heave and pitch (Taguchi et al. 2006). On the other hand, effect of added resistance on parametric rolling seems to require further investigation. Jensen (Jensen et al. 2007) discussed the effect of surge motion on the probability of parametric rolling in irregular head waves, but their surge model does not include added resistance. Umeda (Umeda et al. 2008) and Umeda and Francescutto (Umeda et al. 2008) executed numerical simulation of parametric rolling in regular and irregular head waves with added resistance taken into account, but their hydrodynamic prediction method for added resistance is different from that for restoring variation. Lu et al. (2011) further developed a numerical prediction method for parametric roll in head waves in which both the restoring variation and the Kochin function for added resistance are calculated with a strip theory.

Key Numerical Method for Parametric Rolling It is widely accepted that degrees of freedom (DOF) of a rigid body in a three-dimensional space are six but can be reduced if constraints are added. First of all, because of head waves, we can assume that a ship runs with the constant course so that there is no sway and yaw motions are two constraints so that the degrees of freedom become four. Then if the heave and pitch motions

P

1288

Parametric Rolling

are assumed to be independent from the surge and roll motions, the heave and pitch motions themselves can be regarded as two constraints so that the degrees of freedom become two. Further, if we assume that the ship runs with a constant speed, the degrees of freedom become finally one. A coupled heave-roll-pitch-mathematical model which is based on a nonlinear strip theory called 3 DOF approach is widely used for predicting parametric rolling. The mathematical model is expressed as (7), (8), and (9). :

ðm þ A33 ð’ÞÞ€z þ B33 z þ A34 ð’Þ€ ’ þ B34 ð’Þ’_ þ A35 ð’Þ€y þ B35 ð’Þy_ ðxG =l, z, ’, yÞ ¼ FFKþB 3 þ FDF 3 ð’Þ ð7Þ ðI xx þ A44 ð’ÞÞ€ ’ þ N 1 ’_ þ N 3 ’_ 3 þ A43 ð’Þ€z þ B43 ð’Þz_ þ A45 ð’Þ€y þ B45 ð’Þy_ ðxG =l, z, ’, yÞ þ FDF ¼ FFKþB 4 4 ð’ Þ 

seakeeping theory. Nonlinear Froude-Krylov forces (FK) and hydrostatic force (B) are calculated by integrating the incident wave pressure around the instantaneous wetted hull surface by two-dimensional strip method or threedimensional panel method. Radiation and diffraction forces are calculated for the submerged hull considering time-dependent roll angle with the static balance retained in sinkage and trim by two-dimensional strip method or threedimensional panel method. The hydrodynamic forces in heave and pitch are calculated at the encounter frequency while those for roll mode are calculated at half the encounter frequency assuming parametric roll occurs. The linear and cubic roll-damping coefficients are used in the mathematic model which are obtained from the roll decay test in the experiment or Ikeda’s method. The model used here also includes the body-nonlinear hydrodynamic coupling between roll and vertical motions, and the nonlinearity of vertical motions is ignored. Equation (8) can be rewritten as below if one only considers Froude-Krylov components in the roll-restoring variation.

ð8Þ

:

ðI xx þ A44 ð’ÞÞ€ ’ þ N 1 ’_ þ N 3 ’_ 3

:  y þ B55 ð’Þ y_ I yy þ A55 ð’Þ €

þA53 ð’Þ€z þ B53 ð’Þz_ þ A54 ð’Þ€ ’ þ B54 ð’Þ’_

¼ FFKþB ðxG =l, z, ’, yÞ 4 ð9Þ

ðxG =l, z, ’, yÞ þ FDF ¼ FFKþB 5 5 ð’Þ

ð10Þ

The 3 DOF approach can also be simplified to 1 DOF approach if the heave and pitch motions are obtained by a strip theory applied to an upright hull.

Aij, Bij, and Cij are the coupling coefficients in

€

_

_

W GZ FKþR&D ðt, XG , zG , y, ’Þ ¼ 0 I xx þ A44 FFKþB ðxG =l, z, ’, yÞ 4 ¼ W


’ þ2m ’ þg ’3 þ GZ FK

€

GZ R&D ¼

_

€

_



ð11Þ

FDF 4 ð’Þ þ A43 ð’Þ z þB43 ð’Þ z þA45 ð’Þ y þB45 ð’Þ y

FK: Only Froude-Krylov and hydrostatic components in roll direction are considered.

W FK+R&D: The radiation and diffraction components in roll direction are also considered.

Parametric Rolling

1289

If the time-varied speed due to the surge motion is considered in 1 DOF approach, 2 DOF numerical approaches can be realized. If the timevaried speed due to the surge motion is considered in 1 DOF approach, 4 DOF numerical approaches can be realized. The time-varied speed due to the surge motion can be shown as follows. €

ðm þ A11 Þ XG

 _ _ ¼ TXG , n  R XG þ FFK 1 ðX G , t Þ  RAW 



T ðXG , nÞ ¼ 1  tp rn

!

_ XG , t

2

D4p K T



ð12Þ   XG 1  wp nDp ð13Þ

_

XG ¼

1 Te

ðT e 0

_

XG ðt Þdt

wave elevation was measured by a servo-needle wave height sensor attached to the towing carriage. Partially Restrained Experiment A multifunctional equipment was used in the partially restrained experiment. The equipment as shown in Fig. 6 consists of five components. The first component is a pedestal and four locking jaws for fixing the equipment to the towing carriage. The second component is a mechanism for keeping the ship model free in heave and measuring the displacement of heave motion and consists of a guide rail bracket, a linear guide rail pair, a displacement sensor using a guide wire, a heave rod, a block, and so on. The third component is three diverging combined sensors using rods for measuring the surge force, the sway force, and the yaw moment in which a strain gauge-measuring technique is applied. The fourth component is a complex movement mechanism for measuring

ð14Þ

where ’: roll angle, m: linear roll-damping coefficient, γ: cubic roll-damping coefficient, W: ship weight, Ixx: moment of inertia in roll, A44: added moment of inertia in roll, Iyy: moment of inertia in pitch, A55: added moment of inertia in pitch, GZ: righting arm, t: time, ζG: heave displacement and θ: pitch angle, and XG: instantaneous shiplongitudinal position. The dot denotes the differentiation with time. Furthermore, T: propeller thrust, R: ship resistance in calm water, and RAW: added resistance in waves.

P

Experimental Method for Parametric Rolling Free Running Experiment Method The ship model was driven by a propeller in regular head seas in the free running experiment. The pitch and roll amplitudes were measured by a MEMS (Microelectromechanical system)-based gyroscope placed on the ship model, and the

Parametric Rolling, Fig. 6 The new equipment for restrained experiment

1290

Parametric Rolling

pitch, roll motions with potentiometers, and roll moment with a double flange torque sensor by fixing a certain roll angle with a locking mechanism. The fourth component is fixed to the ship model, and its weight is regarded as one part of the ship model. The third component is fixed with the fourth component, and the second component is fixed with the third component, and their weights are not part of the ship model for the convenience of arranging and adjusting the center of gravity and moments of inertia. The fifth component is a mechanism for balancing the weight of the second component and third component and consists of a pulley block, a vertical guide rod, a counterweight, and so on. Surge, sway, and yaw motions are always restrained; heave and pitch motions are always free, and roll motion can be free or restrained by the equipment in partially restrained experiments. Therefore, parametric roll, pitch, and displacement of heave can be measured simultaneously. When roll is fixed with a certain angle, the roll moment and the sway force can be measured simultaneously by this equipment, and then the restoring moment can be calculated by roll moment, sway force, and vertical distance between the double flange torque sensor of the equipment and the center of gravity of the ship model. The principal particulars and body plan of the C11 class containership are shown in Table 1 and Fig. 7, respectively. The ship models the free running experiment and partially restrained experiment are shown Figs. 8 and 9, respectively.

The Effect of the Surge Motion on Parametric Rolling The uncoupled roll model (1 DOF) and the coupled surge-roll model (2 DOF) with added resistance taken into account are used to numerically investigate the effect of surge motion on parametric roll. An example of time series is shown in Fig. 10. Free running model experiments, which allow the surge motion and partially

Parametric Rolling, Fig. 7 Lines of C11 containership

Parametric Rolling, Fig. 8 The ship model in free running experiment Parametric Rolling, Table 1 Principal particulars of the C11 containership Items Length: L Draft: T Breadth: B Depth: D Displ.: W CB GM Tj KYY

Ship 262.0m 11.5m 40.0m 24.45m 67508 ton 0.560 1.928m 24.68s 0.24L

Model 4.000m 0.176m 0.611m 0.373m 240.2kg 0.560 0.029m 3.05s 0.24L

Parametric Rolling, Fig. 9 The ship model in partially restrained experiment

Parametric Rolling

1291

4 1DOF

140

2DOF

1DOF

2DOF

120

2

100

1

XG[m]

wave elev on[m]

3

0 0

-1

10

20

30

40

50

80 60 40 20

-2

0

-3

0

t [s]

10

20

30

40

50

t [s]

4

4

1DOF

3.5

2DOF

1DOF

2DOF

3

pitch [degrees]

vel[m/s]

3 2.5 2 1.5 1 0.5

2 1 0 -1

0

10

20

30

40

50

-2

0 0

10

20

30

40

-3

50

t [s]

t [s]

1

1.2

1DOF

0.8

2DOF

1DOF

2DOF

1

roll=10degrees 0.8

0.4 0.2 0 -0.2 0

10

20

30

40

50

GZFK [m]

heave [m]

0.6

0.6 0.4 0.2

-0.4 -0.6

0

-0.8 -0.2

t [s]

20

30

40

50

40

1DOF

2DOF

1DOF

1

2DOF

30

roll=10degrees

20

roll [degrees]

0.8

GZ FK+R&D [m]

10

t [s]

1.2

0.6 0.4 0.2

P

10 0 -10

0

50

100

150

200

-20

0 -0.2

0

0

10

20

30

40

50

t [s]

-30

t [s]

Parametric Rolling, Fig. 10 Comparisons between time series with surge motion and without surge motion, under the condition of the actual Fn¼0.05, l/Lpp¼1.0,

H/l¼0.01, and w¼180 . (1DOF(FK+R&D) and 2DOF (FK+R&D) approaches)

restrained model experiments without surge motion, were also conducted to investigate the effect of surge motion on parametric roll. More comprehensive comparisons are shown in Figs. 11 and 12. The simulations indicate that the effect of the surge motion on parametric rolling is generally small in regular head seas. This is because the difference of the longitudinal ship position is

rather small between the calculations with and without surge motion; consequently, the difference between the relative wave profile around the ship and the change of GZ are very small too, although the ship’s forward speed varies periodically due to the surge motion in regular head seas. This conclusion can be applied to the modeling of the roll-restoring variation with and without the radiation and the diffraction components.

1292

Parametric Rolling

60

Exp without surge

Exp with surge

1DOF(FK)

2DOF(FK)

60 50

roll amplitude [degrees]

roll amplitude [degrees]

50

H/λ=0.01

40 30 20 10 0

Exp without surge

Exp with surge

1DOF(FK)

2DOF(FK)

H/λ=0.02

40 30 20 10 0

0

0.05

0.1

0.15

0

0.05

Fn 60

0.15

60

Exp with surge

1DOF(FK)

2DOF(FK)

Exp with surge

50

1DOF(FK)

2DOF(FK)

50

roll amplitude [degrees]

roll amplitude [degrees]

0.1

Fn

H/λ=0.03

40 30 20 10 0

H/λ=0.04

40 30 20 10 0

0

0.05

0.1

0.15

0

0.05

Fn

0.1

0.15

Fn

Parametric Rolling, Fig. 11 The effect of surge motion on parametric roll as function of Froude number in experiments and simulations with l/Lpp¼1.0, w¼180 (FK: Only Froude-Krylov components in roll direction are considered)

roll amplitude [degrees]

60 50

Exp without surge

Exp with surge

1DOF(FK+R&D)

2DOF(FK+R&D)

H/λ=0.02

40 30 20 10 0 0

Parametric Rolling, Fig. 12 The effect of surge motion on parametric roll as function of Froude number in experiments and simulations with l/Lpp¼1.0, w¼180

0.05

Fn

0.1

0.15

(FK+R&D: The radiation and diffraction components in roll direction are also considered)

Parametric Rolling

1293

The Effect of Parametric Rolling on Heave and Pitch Motions

parametric roll occurs with the amplitudes of about 10 degrees as shown in Fig. 14, heave and pitch motions are affected by parametric roll: Their large and small amplitudes alternately appear. This phenomenon seems like “subharmonic pitch” and “subharmonic heave.” The heave and pitch motions are analyzed in the frequency domain by the Fourier transformation. One distinct observation was that pitch and heave motions in the experiments have both half the encountered wave frequency and the encountered wave frequency components when parametric roll occurs.

The effect of dynamic heave and pitch motions on parametric rolling was investigated so far by many researchers, and it is well established that restoring arm variation in head waves depends on dynamic heave and pitch motions. Coupling from heave, pitch to parametric roll is usually considered, but the effect of parametric roll on heave and pitch motions is ignored. Partially restrained model experiments free in heave and pitch but with a constant roll angle were conducted, and then, partially restrained model experiments free in heave, pitch, and roll for simultaneously measuring parametric roll, pitch, and heave were conducted, and the results are shown in Figs. 13 and 14. The spectra of the ship motions by the Fourier transformation are also shown in Figs. 13 and 14. The results from the experiments indicate the frequency of heave and pitch motions is equal to the encounter wave frequency in the case without parametric roll as shown in Fig. 13, which is consistent with a linear seakeeping theory. When

The Effect of Dynamic Roll Variation on Parametric Rolling Parametric rolling in head seas is a nonlinear phenomenon due to roll-restoring force variation. The calculated roll motions with the 1 DOF approach and the 3 DOF approach are shown in Figs. 15 and 16 together with the results of free running model. The calculations of the rollrestoring variation are performed with and

1.5

pitch[degrees]

2

1 0.5 0 1200 -0.5

pitch spectrum(degrees /s)

1 .0

1220

1240

1260

-1

1280

1300

0 .8

P

0 .6

0 .4

0 .2

0 .0

-1.5

0 .0 0

t [s]

0 .0 2

0 .0 4

0 .0 6

0 .0 8

0 .1 0

0 .1 2

0 .1 4

0 .1 6

0 .1 8

0 .2 0

Frequency (Hz)

0 .2 5

2

heave spectrum(m /s)

0 .3 0

0 .2 0 0 .1 5 0 .1 0 0 .0 5 0 .0 0 0 .0 0

0 .0 2

0.04

0 .0 6

0 .0 8

0 .1 0

0.12

0 .1 4

0 .1 6

0 .1 8

0.20

Frequency (Hz)

Parametric Rolling, Fig. 13 Pitch and heave motions under the constant roll angle in the partially restrained experiment with l/Lpp¼1.0, H/l¼0.01, w¼180 , and Fn¼0.0

1294

Parametric Rolling 10

roll spectrum(degrees /s)

15

roll [degrees]

5 0 1200

8

2

10

1220

1240

1260

1280

1300

-5 -10

6

4

2

0

-15

0 .0 0

t [s]

0 .0 2

0 .0 4

0 .0 6

0 .0 8

0 .1 0

0 .1 2

0 .1 4

0 .1 6

0 .1 8

0 .2 0

Frequency (Hz) 1 .0

pitch spectrum(degrees /s)

1.5 2

1

pitch [degrees]

0.5 0 1200 -0.5

1220

1260

1240

1280

1300

-1 -1.5

0 .8

0 .6

0 .4

0 .2

0 .0 0 .0 0

t [s]

0 .0 2

0 .0 4

0 .0 6

0 .0 8

0 .1 0

0 .1 2

0 .1 4

0 .1 6

0 .1 8

0 .2 0

Frequency (Hz) 0.30

2

0.3

heave[m]

0.2 0.1 0 1200 -0.1

1220

1240

1260

1280

1300

-0.2

0.20 0.15 0.10 0.05 0.00

-0.3 -0.4

heave spectrum(m /s)

0.25

0.4

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

t [s]

Frequency (Hz)

Parametric Rolling, Fig. 14 Roll pitch and heave motions in the partially restrained experiment allowing the roll motions with l/Lpp¼1.0, H/l¼0.01, w¼180 , and Fn¼0.0

without the radiation and diffraction components as shown in Figs. 17 and 18. The prediction of parametric rolling in the 1 DOF approach and 3 DOF approach with Froude-Krylov, radiation, and diffraction components is generally larger than that in the experiments while the prediction of parametric roll with the Froude-Krylov on its own is generally smaller than that in the experiments except for H/l/¼0.01 as shown in Figs. 15 and 16. The prediction of parametric roll with the 1 DOF approach is generally larger than that with the 3 DOF approach as shown in Figs. 15 and 16, while the prediction with the 3 DOF (FK+R&D) approach is closer to

the results in experiments than that with the 1 DOF (FK+R&D) approach.

Key Applications Parametric rolling is one of the five stability failure modes in the second-generation intact stability criteria which include Level 1 and Level 2 vulnerability criteria and direct stability assessment. The main purpose of these criteria is to enable the use of the latest numerical simulation techniques for evaluating the safety level of a ship from an intact stability viewpoint (IMO, Msc.1/Circ.1627 2020).

Parametric Rolling

1295 60

60 1DOF(FK)

Exp with surge

Exp with surge

3DOF(FK)

roll amplitude [degrees]

roll amplitude [degrees]

H/λ=0.01

40

1DOF(FK)

3DOF(FK)

50

50

30 20 10

H/λ=0.02

40 30 20 10 0

0 0

0.05

0.1

Fn

0

0.15

0.05

0.1

Fn

0.15

60 50

roll amplitude [degrees]

3DOF(FK)

1DOF(FK)

Exp with surge

roll amplitude [degrees]

50

H/λ=0.03

40

3DOF(FK)

1DOF(FK)

Exp with surge

60

30 20 10

H/λ=0.04

40 30 20 10 0

0 0

0.05

0.1

Fn

0

0.15

0.05

0.1

Fn

0.15

Parametric Rolling, Fig. 15 Comparisons of parametric roll as function of Froude number in experiments, 1 DOF approach and 3 DOF approach with l/Lpp¼1.0, w¼180

60

60

Exp with surge

roll amplitude [degrees]

roll amplitude [degrees]

3DOF(FK+R&D)

1DOF(FK+R&D)

Exp with surge 50

H/λ=0.01

40 30 20 10

3DOF(FK+R&D)

P

H/λ=0.02

40 30 20 10 0

0 0

0.05

0.1

Fn

0

0.15

0.05

0.1

Fn

0.15

60

60 Exp with surge

3DOF(FK+R&D)

1DOF(FK+R&D)

Exp with surge

50

roll amplitude [degrees]

roll amplitude [degrees]

1DOF(FK+R&D)

50

H/λ=0.03

40 30 20 10

3DOF(FK+R&D)

1DOF(FK+R&D)

50

H/λ=0.04

40 30 20 10 0

0 0

0.05

Fn

0.1

0.15

0

0.05

Fn

0.1

0.15

Parametric Rolling, Fig. 16 Comparisons of parametric roll as function of Froude number in experiments, 1 DOF approach and 3 DOF approach with l/Lpp¼1.0, w¼180

1296 1 0.9

Exp without surge

1DOF(FK)

1DOF(FK+R&D)

0.8

Fn=0.0

0.7 0.6

GZ[m]

Parametric Rolling, Fig. 17 Comparisons of roll-restoring variation in experiments and simulations with l/Lpp¼1.0, H/l¼0.02, w¼180 , and heeling angle 7.3 degrees

Parametric Rolling

0.5 0.4 0.3 0.2 0.1 0 -0.1 0

0.5

1

1.5

2

2.5

3

ξG /λ 1 0.9

Exp without surge

3DOF(FK)

3DOF(FK+R&D)

0.8

Fn=0.0

0.7

GZ[m]

0.6 0.5 0.4 0.3 0.2 0.1 0 -0.1 0

0.5

1

1.5

2

2.5

3

ξG/λ

1 0.9

EXP without surge

1DOF(FK)

1DOF(FK+R&D)

0.8

Fn=0.0

0.7

GZ[m]

0.6 0.5 0.4 0.3 0.2 0.1 0 -0.1 0

0.5

1

1.5

2

2.5

3

ξG /λ 1 0.9

Exp without surge

3DOF(FK)

3DOF(FK+R&D)

0.8

Fn=0.0

0.7 0.6

GZ[m]

Parametric Rolling, Fig. 18 Comparisons of roll-restoring variation in experiments and simulations with l/Lpp¼1.0, H/l¼0.01, w¼180 , and heeling angle 7.3 degrees

0.5 0.4 0.3 0.2 0.1 0 -0.1 0

0.5

1

1.5

ξG /λ

2

2.5

3

Photoelectric Detection Technology in Underwater Vehicles

Parametric rolling is a complicated phenomenon when the ship is sailing in the seas, and the direct stability assessment is related to complex hydrodynamics. The above introduction on parametric rolling could be useful for shipbuilders, shipmasters, shipowners, ship operators, and shipping companies to understand parametric rolling.

1297

Parametrically Excited Roll ▶ Parametric Rolling

Passive Sonar References Belenky VL, Bssler C Spyrou J (2011). Development of second generation intact stability criteria[R]. Hydromechanics Dept. Report, NSWCCD-50-TR-2011/065. Blocki W (1980) Ship safety in connection with parametric resonance of the roll. International Shipbuilding Progress 27:36–53. France WL, Levadou M, Treakle TW, Paulling JR, Michel RK, Moore C (2003) An investigation of head-sea parametric rolling and its influence on container lashing systems. Mar Technol 40(1):1–19 IMO, Finalization of second generation intact stability criteria, Report of the working group (part 1), SDC 3/WP.5/Annex 4,2016. IMO (2020) Interim guidelines on the second generation intact stability criteria, Msc.1/Circ.1627. Jensen JJ, Vidic-Perunovic, Pedersen PJ (2007) Influence of surge motion on the probability of parametric roll in a stationary seas state. Proc 9th International Ship Stability Workshop, Germanisher Lloyd, pp1–9. Kerwin JE (1955) Note on rolling in longitudinal waves. International Shipbuilding Progress 2(16):597–614. Lu J, Min G (2017) Naoya Uneda, Experimental and numerical study on several crucial elements for predicting parametric roll in regular head seas. J Mar Sci Technol 22(1):25–37 Lu J, Umeda N, Ma K (2011) Predicting parametric roll in irregular head seas with added resistance taken into account. J Mar Sci Technol 16:462–471. Munif A, Umeda N (2000) Modeling extreme roll motions and capsizing of a moderate-speed ship in astern waves. J the Society of Naval Architects of Japan 187:405– 408. Sweden, Review of the intact stability code, Recordings of head sea parametric rolling on a PCTC, SLF47/INF.5, 2004. Taguchi H, Ishida S, Sawada H, Minami M (2006) Model experiment on parametric rolling of a post-panamax containership in head waves. Proc 9th STAB, No1, pp 147–156. Umeda N, Hamamoto M, Takaishi Y, Chiba Y, Matsuda A, Sera W, Suzuki S, Spyrou K, Watanabe K (1995) Model experiments of ship capsize in astern seas. J the Society of Naval Architects of Japan 177:207–217. United States, Review of the intact stability code, Head-sea parametric rolling and its influence on container lashing systems, SLF45/6/7, 2002.

▶ Sonar Technology

PDU, Power Distribution Unit ▶ Power Transmission and Distribution

Phase Shift Keying (PSK) ▶ Underwater Acoustic Communication

Photo Multiplier Tube (PMT) ▶ Photoelectric Detection Technology in Underwater Vehicles

Photoelectric Detection Technology in Underwater Vehicles Zhen Ren Tianjin Jinhang Institute of Technical Physics, Tianjin, China

Synonyms Laser carrier intensity modulation (LCIM); Photo multiplier tube (PMT); Photoelectric imaging; Polarization imaging; Range-gated imaging; Underwater device; Underwater target

P

1298

Photoelectric Detection Technology in Underwater Vehicles

Definition Underwater photoelectric detection technology is used for target detecting and imaging in the environment of underwater, using electro-optic detection method. Compared with acoustic detection techniques, photoelectric detection has the advantages of high resolution ratio, no near-field blind area, and fast and convenient for target identification. At present, the underwater photoelectric detection methods include range-gated imaging detection, laser line scanning imaging detection, polarization imaging detection, modulation/demodulation imaging detection, structured light imaging detection, etc. (Cao et al. 2011).

Scientific Fundamentals Compared with land photoelectric imaging system, underwater photoelectric imaging and detection system work in special environment. There are mainly three parts in underwater photoelectric imaging and detection system, including underwater lighting system, underwater imaging lens, and detector (Yuan 2013). Figure 1 shows the working principle. In Fig. 1, laser light source lights the underwater target, and the light reflected by the target enters the optical sensor through the aquatic medium and absorbed scattered by the water at the same time.

Photoelectric Detection Technology in Underwater Vehicles, Fig. 1 Underwater photoelectric imaging and detection system working principle

There are target light, scattering light and backlight showing on the image plane. Target image focuses on the plane of the optical sensor. The photoelectric device takes target image and sends it to the recording device after signal processing. The optical sensor’s imaging quality can be affected by the absorption and scattering of light from the water.

Difficulties of Underwater Photoelectric Detection Since 1963, S.Q. Duntley et al. found that the attenuation of blue and green light in 0.45 mm0.55 mm band by sea water is much smaller than that in other bands (Zhao et al. 2014). The detection of underwater targets and environments such as oceans and lakes by laser irradiation has attracted more and more attention in the world and has also opened up a new way of underwater target detection. Due to the particularity of underwater environment, the key problems of underwater target detection are two aspects: one is how to suppress the backscattering effect of suspended particles in water and improve the imaging contrast; the other is how to overcome the attenuation effect of water on laser energy. Attenuation Characteristics of Light in Water Underwater working system and terrestrial imaging system are different, mainly because of the influence of water on the characteristics of light. The absorption and scattering of water to light are the main factors affecting the quality of underwater imaging. The attenuation characteristic of light in water refers to that the energy of light decreases exponentially in the course of transmission due to the absorption and scattering of water, which limits the propagation distance of light in water. And the scattering of water to light will result in the low contrast of the underwater image. If the light is only affected by the absorption of water in the process of transmission, then the absorption of water can be overcome by increasing the power of the light source. Thus, the imaging distance can be increased. However, due to the existence of scattering, increasing the power of the light source,

Photoelectric Detection Technology in Underwater Vehicles

the power of the target-reflected light and scattered light are increasing at the same time. Then the image contrast obtained by the photoelectric receiver will not be improved. So simply increasing the power of the light source cannot improve the underwater imaging distance. It has been found that the underwater imaging distance is generally about more than 10 m, which is an urgent problem for the underwater optical imaging system, and also the main reason for the application limitation of the underwater optical imaging system. Absorption of Light by Water The absorption selectivity of water to light is obvious. The absorption rate of water is different in different spectral regions. The absorption of water to ultraviolet and infrared bands is stronger, but the absorption to blue-green bands is weaker. In the visible region, absorption of water is the largest in red, yellow, and light-green spectral regions. So color distortion will occur after transmitting light a certain distance underwater. When the underwater imaging distance is relatively long, the image is usually gray. In the water with low turbidity, the absorption in the blue-green band is the smallest, which is the so-called “blue-green window” of underwater imaging. But even in this blue-green window, the underwater transmission of light is greatly affected by the absorption of water. After a 1-m underwater transmission, the attenuation of light intensity reaches at least 4%. In other spectral regions, light is almost completely absorbed several meters away. So even in the blue-green window, the absorption of water will make the imaging distance very limited. Therefore, the influence of water absorption characteristics on the underwater imaging system must be fully considered in the research and analysis of the operating range of the underwater imaging system (Chen et al. 2011). Light Scattering Characteristics of Water Light scattering by water means that when light propagates in water, the direction of light propagation will change due to the action of various medium particles in water. The scattering of sea water is more complex than that of the

1299

atmosphere. There are mainly two types of scattering: the scattering caused by pure water and the scattering caused by suspended particles. These include Rayleigh scattering, Mie scattering and the scattering caused by the refraction of transparent materials. The scattering functions of different sea areas and different water types are quite distinguished. Clean sea water is mainly scattered by water molecules, while turbid water along the coast is mainly scattered by large particles. The scattering mode can be divided into forward scattering and backward scattering according to the direction of scattered light. The scattering of water and particles to light is mainly forward scattering, which generally accounts for more than 90% of the total scattering, while backscattering only accounts for a small part. Forward scattering and backward scattering will affect the quality of the underwater imaging image. Although backscattering accounts for a small proportion, in underwater laser imaging applications backscattering affects image contrast and is the main factor affecting image quality.

Underwater Photoelectric Detection Technology Range-Gated Imaging Detection Technology Instead of using continuous laser, range gating technology uses the pulsed laser to emit the laser light and illuminate the target. The receiving end uses range-gated selection. When the target light reaches the receiver, the gate opens, so that the receiver receives the reflected light from all the scenery in the whole field of view. Before that the gating door has closed, thus eliminating the arrival of the background light during other periods. Its working principle is shown in Fig. 2. The laser illuminates the target actively and then is reflected by the target. Before the light wave reaches the detection receiver, the gate is always in a “closed” state. Only within the very short time when the reflected light of the target reaches the receiver, the gate opens, and the reflected light enters the receiver for imaging. Thus, the target light and scattered light are separated from each other in time, and most of the forward and

P

1300

Photoelectric Detection Technology in Underwater Vehicles

Photoelectric Detection Technology in Underwater Vehicles, Fig. 2 Principle diagram of range-gating synchronization control technology (Jin et al. 2011)

backward scattered light of the laser is eliminated from the optical receiver. And this reduces the background noise formed by the scattered light on the detector and improves the signal-to-noise ratio and contrast of the target image. The laser underwater imaging system, which employs range-gated technology, uses the pulsed laser as the light source. In the process of light transmission underwater, the gate in front of the optical receiver is always closed and only opens at the time when the target-reflected light reaches the detector. At this moment, the receiver receives the reflected light from all the scenes in the whole field of view, including scattered light, targetreflected light, background light, etc. Therefore, the range-gated underwater laser imaging system can eliminate most of the backscattered light, but it cannot be completely eliminated. Moreover, the observation field of the laser underwater imaging system using range-gated technology is narrow. To improve the underwater imaging distance and make the laser irradiate the whole field of view at the same time, the high-energy laser pulse is used to focus on a relatively small area, so that the image observed under the condition of narrow field of view will be clear. The performance of the range-gated imaging system depends on the gated pulse width and laser pulse width. If both are very narrow, only the light near the target can enter the receiver and the

scattered light and background light will be suppressed. This is conducive to the improvement of imaging quality. Laser Line Scanning Imaging Detection Technology Synchronized scanning technology is to synchronize the scanning beam and the receiving line of sight. The imaging technology utilizes the principle that the backscattered light intensity of water decreases rapidly relative to the central axis. It can suppress the backscattered light from space into the receiver, thus overcoming the influence of backscattered light and improving the imaging quality. The image shown in Fig. 3 is a typical optical path diagram of the system. The scanning light and the receiving line of sight are synchronized. The laser and receiver are separated in space. The laser emits continuous narrow beams, and the receiver uses narrow field of view. There is only a small overlap between the two fields of view. The overlap area between illuminated water and receiver is minimized to reduce the scattered light entering the receiver and does not affect the target-reflected light entering the receiver. This effectively reduces the background noise without reducing the reflected light energy, thus effectively improving the imaging distance and image quality. Using synchronous scanning technology, point-by-point detection is

Photoelectric Detection Technology in Underwater Vehicles

1301

Backward one-way scattering light

Laser Scanning Control Device Synchronized Scanning Control

incident light

Backward multiple scattering light Receiver reflected light

Photoelectric Detection Technology in Underwater Vehicles, Fig. 3 Principle of laser synchronous scanning imaging

used to form images. This method can scan a wide area up to 120 , and the effective field of view can reach 70 . The key to the image quality of synchronous scanning imaging technology lies in the tracking and receiving of highly sensitive detectors in the small field of view. The key to the realization of synchronous scanning technology lies in the synchronous control of the scanning beam and receiving the line of sight. The synchronous control methods are divided into mechanical synchronization and signal synchronization. Mechanical synchronization is used often. Principle of Polarization Imaging Detection Each object has a depolarization effect. The depolarization degree of sea water and object to light is different. If polarized light is used to irradiate underwater objects near Lambertine, the approximate depolarization of the object can be obtained according to the scattering theory. According to the knowledge of scattering, different objects have different scattering rates to the same light source. For objects approximate Lambertine, the scattering rate is generally less than that of backscattering light of particles in water. The depolarization of reflected light of objects is different from that of scattering light of particles in water. Therefore, according to the difference of depolarization between the backscattering light of particles and the object reflecting light in sea water, the backscattered light of particles can be suppressed by adjusting the angle of the polarizer in front of

the receiver, and the reflecting light of the object passes through the analyzer to enter the imaging system. Although the energy of backscattered light and target-reflected light are reduced by polarization technology, the degree of their reduction is different, and the backscattered light is reduced more, so the contrast of the image can be improved. There are two kinds of polarization technology: circular polarization technology and linear polarization technology. Both circular polarization technology and linear polarization technology can overcome backscattering to a certain extent and improve the contrast and imaging distance of underwater objects (Dubreuil et al. 2013). Line Polarization Technology

When the polarization direction of the illuminated target light (laser) and the polarization direction of the detector’s front-line polarizer are both horizontal, the reflected light energy and scattered light energy of the object are approximately equal. And the contrast is too small to recognize the image. When the polarization direction of the linear polarizer is perpendicular to the polarization direction of the light source, the reflected light energy received by the detector is much larger than the scattered light energy. So the contrast of the image is related to the angle between the polarization direction of the linear polarizer and the polarization direction of the light source. When the angle is 0 , the image is blurred, and when the angle is 90 , the contrast is maximum, the image is clear.

P

1302

Photoelectric Detection Technology in Underwater Vehicles

Circular Polarization Technology

When the illumination source is right-handed circularly polarized light, the scattered light scattered by particles in water becomes left-handed circularly polarized light, that is, the scattered light becomes left-handed circularly polarized light. When the circular polarizer in front of the detector is right-handed, the backward scattered light of left-handed circularly polarized will be filtered out, and the incident right-handed circularly polarized light will be filtered out by the object. After reflection, the left-circularly polarized light and the right-circularly polarized light account for half of each, and the left-circularly polarized light will be filtered out by the right-circular polarizer in front of the detector. Only the right-circularly polarized light with the same polarization state can enter the imaging system through the polarizer for imaging, that is, the reflected light of the target entering the detector is weakened and then backscattered light is basically eliminated. Using circular polarization imaging technology can reduce both backscattered light and targetreflected light entering the detector, but in different proportions. Most backscattered light is filtered out and most target-reflected light can

reach the detector, that is, the ratio of targetreflected light to backscattered light is improved, and the image quality formed on the detector is improved. To improve, the circular polarization technology can greatly improve the image sharpness. The construction of the underwater polarization imaging system is simple and easy. Only a little modification is needed for ordinary underwater imaging instruments. Two polarizers are prepared. One polarizes the light source and the other analyzes the detected light signal. The light source modulated by polarizer emits fully polarized light, which illuminates the scene through the transmission of medium, and some light is scattered back to the detector by the medium particles. The sketch of underwater polarization imaging is shown in Fig. 4. The underwater polarization imaging system is connected with a circular polarizer on the outside of the digital camera and illuminated by a wide field of view polarization light. The analyzer detector is placed in front of the receiver. And two polarization images, which are perpendicular to each other, are collected. So the contrast and color of the underwater polarization image can be

Y lamphead a point in space

polarizer

X obj

Rsource y

q

Rearn

Z

x

Z obj

analyzer

X

Dome of radius r

Photoelectric Detection Technology in Underwater Vehicles, Fig. 4 Principle of underwater polarization imaging detection (Jin et al. 2011)

Photoelectric Detection Technology in Underwater Vehicles

corrected. The contrast and color of the scene can be greatly improved. Underwater Imaging Technology of Streak Tube The principle of the streak tube imaging system is shown in Fig. 5. The receiving optical system imagines the incident light signal on the slit of the streak camera. The one-dimensional spatial light signal extracted from the slit is focused on the photocathode through the relay lens. The photoelectrons generated on the photocathode are accelerated by the accelerator and focused by the electrostatic focusing pole, and then enter the deflection system (deflection plate). There is a slope voltage that changes linearly at any time on deflection system. The photoelectrons entering the deflection system at different times are affected by different deflection voltage. When the photoelectron beam is enhanced by the image intensifier and reaches the fringe tube screen, it will spread along the direction of the slit and form a clear and visible fringe image on the screen. After the image processing system analysis, two-dimensional information of incident light signal can be obtained. That is, onedimensional information of light intensity along slit direction changing with space and onedimensional information of light intensity perpendicular to slit direction changing with time. A series of two-dimensional images of motion direction can be formed by sweeping with external mechanism, and three-dimensional data cube can be obtained by reconstruction. From the three-

1303

dimensional data cube, the distance image of the observation direction dimension and the contrast image of the motion direction dimension can be obtained directly. Modulation/Demodulation Laser Underwater Imaging Technology Laser carrier intensity modulation (LCIM) technology is a feasible method for underwater range enhancement using coherent imaging detection. Early underwater coherent detection experiments usually used amplitude-modulated continuous laser to illuminate the target. And PMT was used to receive backscattered light and target-reflected light signals, and then the scattered light noise was partially removed by demodulating the amplitude modulated signal. Thus the detection distance could be extended to the detector scattered noise limitation. Subcarrier coherent detection technology is used to separate scattered light noise and reflected light signal in the time domain, thus generating target profile image or distance information. As shown in Fig. 6, a high-speed modulator is used to load the microwave carrier onto the optical pulse, so that the laser pulse can carry microwave signals underwater. After reflection from the underwater target, it is accepted by a high-speed photoelectric detector and a carrier-modulated Lidar system is formed. The backscattering signal of sea water is formed by the superposition of reflected light from a large number of scatterers in water. Due to the random distribution of scatterers, the phase delay of each reflection is Scanning Circuit Scanning Electrode

Trigger signal

light intensity

Image on Fluorescent screen

Space

Time

Time Space incident light

slit

Photocathode

MCP Accelerate d gate

Photoelectric Detection Technology in Underwater Vehicles, Fig. 5 Principle of streak tube imaging

P

1304 Photoelectric Detection Technology in Underwater Vehicles, Fig. 6 Block diagram of the modulated Lidar on optical carrier system (Zhang et al. 2011)

Photoelectric Detection Technology in Underwater Vehicles

Target

Microwave

PD

Modulator

Laser

Controller

uncertain and the coherence is lost. In this case, after the superposition, the information of backscattering at the modulation frequency is largely lost and transformed into a low frequency signal. The phase information of the modulation frequency is not lost because of the coherence of the target reflection, and the high frequency characteristic is maintained. So at the receiving end, the received signal of the system is output by the photoelectric detector, which is divided into two channels. One path passes through a low-pass filter to filter out the signal retaining modulation characteristics. And the other passes through a band-pass filter, whose central frequency is equal to the modulation frequency and whose bandwidth is very narrow, to filter out the scattering noise. The traditional Lidar signal and the modulated pulse signal can be detected on two independent channels of the digital oscilloscope. Finally, the detection data are analyzed by the computer.

Design of Underwater Photoelectric Detection System The underwater imaging system consists of the underwater lighting system, the underwater imaging system, the data transmission system, the storage and display system, etc. (Shirai et al. 2000).

Microwave receiver Microwave signal processing

Low frequency electronics Optical signal processing

Underwater Lighting System It includes the underwater lighting source, transmitting optical system, lighting source mounting bracket, underwater lighting power supply, and controller. Its function is to illuminate underwater targets to meet the need for underwater imaging for light energy. Underwater Imaging System It includes underwater high-speed imaging system, camera power supply, zoom focusing and focusing controller, camera controller, fixed and waterproof seals, and other structures. It is mainly responsible for the photoelectric conversion of the target and clear imaging. Data Transmission System It includes power supply, control and signal transmission, and so on. The Cam Link interface is converted into optical fiber relay transmission mode to realize long-distance transmission. The waterproof and sealed structure is used for power supply, control, and signal transmission. Data Storage Display Processing System It includes host computer, corresponding software and image recording equipment (acquisition card) mainly completes the functions of image storage and playback and can convert data stream files into multiple formats for analysis and preservation after the event.

Physical Properties of Sea Ice

Key Applications In the military field, the underwater photoelectric detection system can be installed on underwater carriers such as submarines, lightning extinguishers, underwater robots, etc. It can be used for underwater target investigation, detection, and recognition, and can be used for mine detection, submarine detection, anti-submarine detection, submarine navigation, and collision avoidance. In the civil field, the underwater photoelectric detection system can be used for underwater engineering installation and maintenance, underwater environmental monitoring, lifesaving salvage, submarine geomorphological exploration, oil exploration drilling location determination, biological research, and other marine development.

1305 carrier for target detection in deep-ocean. Infrared Laser Eng 40(12):2408–2412 Zhao Y, Gai Z-g, Zhao J, Chu S-b (2014) Research on range-gated underwater laser imaging technology. Logist Eng Manag 36(241):270–271

Photoelectric Imaging ▶ Photoelectric Detection Technology in Underwater Vehicles

Photonic Crystal Fiber (PCF) ▶ Fiber Optic Hydrophone

Cross-References ▶ Photoelectric Imaging ▶ Polarization Imaging ▶ Range-Gated Imaging

Physical Ice Management ▶ Ice Management in Offshore Operations

References

Physical Layer

Cao F-m, Jin W-q, Huang Y-w, Li H-l, Wang X, Chu K-l, Liu J (2011) Review of underwater opto-electrical imaging technology and equipment (I) underwater laser range-gated imaging technology. Infrared Technol 33(2):63–69 Chen C, Yang H-r, Wu L, Li G-p (2011) Underwater target detection with electro-optical system. J Appl Opt 32(6):1059–1066 Dubreuil M, Delrot P, Leonard I, Alfalou A, Brosseau C, Dogariu A (2013) Exploring underwater target detection by imaging polarimetry and correlation techniques. Appl Opt 52(5):997–1005 Jin W-q, Wang X, Cao F-m, Huang Y-w, Liu J, Li H-l, Xu C (2011) Review of underwater opto-electrical imaging technology and equipment. Infrared Technol (II) 33(3):125–132 Shirai K, Fujimoto T, Harada T (2000). Underwater imaging system using acoustic holography. In: Proceedings of the 2000 international symposium on underwater technology (Cat. No.00EX418), Tokyo, pp 122–126 Yuan T (2013) The study of the underwater laser imaging system. Thesis, Chuangchun University of Science and Technology Zhang H, Rong J, Li T, Tian L, Tang L, Liang G (2011) Simulation analysis of modulated lidar on optical

▶ Underwater Acoustic Sensor Network

Physical Properties of Sea Ice Qingkai Wang and Zhijun Li State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China

Definition Physical properties of sea ice are the fundamental nature of sea ice, including ice crystal structure, salinity, temperature, and density, which affect other properties of sea ice, such as mechanical, thermal, and electromagnetic properties. Sea ice is

P

1306

a mixture of pure ice, brine, solid salt, and gas. Additionally, the relative contents of phase components change with ice temperature to keep phase equilibrium, which, in turn, affects other properties of sea ice. Therefore, ice porosity (the sum of the brine and gas volume fractions) is another important sea ice physical property. Sea ice can be considered as a medium between atmosphere and upper ocean, which cuts off the direct interaction between the latter two. The changes in the physical properties of sea ice impact the state of atmosphere and upper ocean. Energy exchanges among atmosphere, sea ice and upper ocean in forms of radiation and conduction. Mass exchange also occurs between sea ice and upper ocean such as the rejection of salt from ice into sea water when ice freezes. Sea ice physical properties have a considerable effect on these exchanges. Sea ice exists in the polar regions perennially and further extends to subpolar sea areas in winter (Fig. 1). The production activities such as shipping and gas and oil exploration in the ice-covered water are affected significantly by sea ice. Structure in the ice zone must be designed to withstand extreme ice load. Sea ice mechanical properties are highly dependent on its physical properties. Given the vital function of sea ice on ocean engineering and global climate, a large number of field investigations have been carried out since the middle of the last century to study sea ice physical properties and their effect on ice mechanics. While most of them are conducted when air temperature is relatively high in late spring or summer

Physical Properties of Sea Ice

due to logistics, only a few of them have been carried out in winter or over a complete cycle.

Scientific Fundamentals Sea Ice Growth and Crystal Structure Generally, the seawater where sea ice forms has salinity more than 24.7 ppt leading to the freezing point being higher than the temperature corresponding to maximum density. Therefore, surface cooling of sea water produces an unstable vertical density profile in the upper water which further creates convective mixing. After the initial formation of continuous ice skim, the underlying ocean is isolated from the cold air so the subsequent ice growth is dominated by thermal conduction. Further crystallization occurs by direct freezing of seawater to the underside of the ice, which is called congelation growth. The above process is under calm conditions, while wind- or wave-induced turbulences in the open water areas can cause the ice skim over sea surface rafting and advection. The different grow histories result in varied grain textures. The observation of ice crystal texture is usually conducted by observing thin ice slices under crossed polarized light and photographed. An ice core is cut into several sections with thickness of a few centimeters. These sections are then attached to glass plates and thinned to a millimeter or less using a microtome. The preparation of ice slice should be cautious and is carried out under a low ambient temperature.

Physical Properties of Sea Ice, Fig. 1 Typical sea ice in the (a) Antarctic, (b) Arctic, and (c) subpolar region (Bohai Sea)

Physical Properties of Sea Ice

The most common ice crystal structures are granular and columnar grains (Fig. 2a, b). The granular grain usually has a sphere shape with size at the scale of 102 m. Converse to the isotropy of granular ice, columnar ice usually shows anisotropy in ice mechanics. Such as there is an obvious difference between the uniaxial compressive strength in horizontal and vertical loading directions to ice surface, and the vertical strength is greater than horizontal strength. In the Arctic, first-year ice is often characterized as a thin granular ice layer at the surface underlain by a large fraction of columnar ice layer. While in the Antarctic, the ration between granular and columnar ice is reversed so that the granular ice accounts for more than columnar ice. While for multiyear ice, the crystal structure is much more complicated, which always shows discontinuities in crystal structure related to the changes in the size and shape of crystals. Apart from the common granular and columnar grains, there are also some other grains such as intermediate granular/columnar, mixed granular/columnar, inclined grains, and platelet grains (Fig. 2c). Sea Ice Salinity Ice salinity is usually expressed as the salts (in gram) contained in per kilogram of sea ice. It

Physical Properties of Sea Ice, Fig. 2 Typical crystal structures of Arctic sea ice: (a) columnar, (b) granular, and (c) mixed columnar/granular grains

P

1308

is quoted as a mass fraction in per thousand or practical salinity units (PSU). Ice salinity is usually measured by extracting an ice core, cutting the core into sections, and placing in containers to melt. Ice salinity is then obtained by measuring the electrolytical conductivity of melted samples. Quick operation is necessary because the loss of brine from an extracted ice core occurs as it is removed from ice cover, especially in the warm parts of a core. It is estimated that the salinity underestimation in the bottom layers of an ice core ranges from 1 to 20 ppt in bottom layers for growing sea ice using core-based measurements (Notz et al. 2005). For summer sea ice, the underestimation may be only a few tenths averagely, but it is the main contributor to the scatter of measurement (Eicken et al. 1995). Notz et al. (2005) have developed a nondestructive technique to measure ice salinity in field for growing sea ice based on the impedance measurements between individual thin horizontal platinum wires. However, this method cannot be used to measure salinity in preexisting ice, but must be deployed in an open water before freezing. The salinity of sea ice is usually much lower than that of the seawater from which it has formed. Most of the salt is rejected by sea ice at the advancing ice-ocean interface as it forms. Such rejection can be described using an effective

Physical Properties of Sea Ice

distribution coefficient which is proportional to ice growth rate. The remaining salt within sea ice is not trapped into the ice lattice but becomes concentrated in interstitial liquid brine. After its initial formation, sea ice salinity varies during winter because of processes of brine diffusion, expulsion, and gravity drainage. Of these processes, gravity drainage is considered to dominate the salt loss from sea ice during winter. When an ice floe is cooled, it often has cold top layers and warm bottom layers, which can cause an unstable density profile. The brine pockets at the top with higher densities moving downward. But, this process is dependent of the permeability of the sea ice (e.g., the connectivity of brine channels). It is often assumed that sea ice is permeable for brine transport through connected bine channels as brine volume fraction is above 5–7%. With entering into melt season, the meltwater flushing caused by surface melt can drive brine out of sea ice, which further decreases the salinity. Therefore, for a first-year ice, the vertical salinity profile turns from a “C-shape” during grow season to a “?-shape” after the onset of melt during a cycle (Fig. 3a, b). Multiyear ice is much less saline and usually shows a nearly fresh surface layer (Fig. 3c) because large brine drainage has already occurred in previous seasons. The sea ice bulk salinity is linearly correlated to ice thickness. For

Physical Properties of Sea Ice, Fig. 3 Typical vertical salinity profiles of (a) growing first-year ice, (b) melting firstyear ice, and (c) multiyear ice

Physical Properties of Sea Ice

cold ice, there is a pronounced decrease in bulk salinity with increasing ice thickness. While for warm ice, there is a positive relationship between bulk salinity and ice thickness. Sea Ice Temperature Ice temperature is affected by meteorological conditions such as air temperature and solar radiation. Snow cover over ice surface can also affect ice temperature acting as an insulation. The temporal variation of ice temperature can be investigated using thermistor strings. Core-based measurement is also usually carried out in field observations to measure ice temperature at a certain point of time. A general seasonal evolution of ice temperature is as follows: (1) a cold front propagates through the ice in the fall; (2) sea ice becomes cold and grows in the late fall, winter, and early spring; and (3) sea ice warms to melting point the next summer (Perovich and Elder 2001). The ice/ocean interface temperature is at around melting point. While the air/ice interface temperature varies with air temperature, solar radiation varies with longwave radiation. Additionally, snow cover acts as an insulation for ice leading to a warmer ice temperature. There is a spatial variation for ice temperature with different conditions of ice and snow conditions. Typically, thinner ice and deep snow produce warmer snow/ice interface and internal ice temperatures, while thicker ice and shallow snow result in colder snow/ice interface and internal ice temperatures. The related contents of phase components change as ice temperature varies. The brine volume must decrease or increase to keep phase equilibrium with decreasing or increasing ice temperature. Gas bubbles are expected to form meanwhile. Therefore, ice mechanical properties have strong relationships with ice temperature. Sea ice mechanical strength decreases with increasing ice temperature. Sea Ice Density Sea ice is a multicomponent medium consisting of pure ice and inclusions such as brine solid salt, and gas. The density of sea ice is controlled by the densities and contents of the pure ice, brine, and solid salt as well as the air content in ice. Furthermore, the relative content of each component is

1309

dependent on the ice temperature. There are mainly four different techniques to measure sea ice density including mass/volume, displacement (submersion), specific gravity, and freeboard and ice thickness methods. The advantage and disadvantage of each technique have been presented detailed in Timco and Frederking (1996). Of these techniques, mass/volume method is commonly used in most field measurements by measuring the mass and dimensions of ice samples. For the core-based density measurement, there are two sources of error. The first is because of the measurement uncertainty, and the second is the brine loss during core sampling. The former can be deduced through an error propagation analysis. An accurate identification of the error due to brine drainage is not easy. The underestimation is estimated to range from 5% to 20% (Hutchings et al. 2015; Pustogvar and Kulyakhtin 2016). Sea ice density has been reported over a wide range from 720 kg/m3 to 940 kg/m3, with an average of approximately 910 kg/m3 (Timco and Frederking 1996). This wide range is caused by, on the one hand, the multicomponent nature of sea ice, and in the other hand, the measurement uncertainty of dimensions. In general, density in the ice section above sea level is less than below sea level. This is because the drained brine pockets in the section above sea level can be replaced by air. For first-year ice, density ranges from 840 kg/m3 to 910 kg/m3 in the section above the waterline, and from 900 kg/m3 to 940 kg/m3 below the sea level. For multiyear sea ice, density ranges from 720 kg/m3 to 910 kg/m3 in the section above the waterline; while below the waterline, density has a same range as first-year ice. Sea ice density decreases with the increasing gas content. Timco and Frederking (1996) have calculated the density of gas-free ice with four different ice salinities (0, 2, 5, and 10 ppt) according to equations in Cox and Weeks (1983). It can be considered as the upper-limit value of ice density for an ice with specific temperature and salinity (Fig. 4). Sea Ice Porosity Porosity is defined as the sum of brine and gas volume fractions. Brine and gas inclusions are trapped when ice forms. Brine and gas volumes

P

1310

Physical Properties of Sea Ice

950

Salinity = 10 ppt

Ice density (kg/m3)

Salinity = 5 ppt 940

Salinity = 2 ppt Salinity = 0 ppt

930

920

910 -30

-25

-20

-15 -10 Ice temperature (e C)

-5

0

Physical Properties of Sea Ice, Fig. 4 Calculated ice density versus ice temperature for four different salinities for gasfree sea ice in Timco and Frederking (1996)

vary with ice temperature. When ice is cooled, brine volume is reduced to keep phase equilibrium. Gas bubbles can also form by escaping from liquid brine because of decreased gas solubility. When ice warms, brine volume must be increased. At the same time, gas bubbles are expected to form in brine inclusions because lower density ice melting into higher density liquid forms a void within the inclusions. Brine and gas inclusions can be observed using the image process technique. Recently, computed tomography X-ray imaging method is employed to measure brine and gas inclusions. In addition, there are sets of mathematical formulae to calculate the volume fractions of brine and gas when the temperature, salinity, and density are known (Cox and Weeks 1983; Leppäranta and Manninen 1988). It is noteworthy that the calculation of gas volume fraction requires density with high accuracy. A small error of density measurement can produce a large error to calculated gas volume fraction. Observations show that brine pockets are more vertically elongated and oriented than air bubbles. Brine pockets typically have mean major axis lengths of tenths of a millimeter, and air bubbles are much larger with mean major axis lengths of the order of millimeters. Measurements found that for multiyear ice, brine content ranges from 1% to

Physical Properties of Sea Ice, Fig. 5 Calculated brine and gas volume fractions against normalized ice depth for multiyear ice in the Arctic

15% by volume controlled by the thermodynamic equilibrium between the solid and liquid phases, and gas volume fraction decreases from >20% at the surface to 1:0

ð7Þ

when α  1.0, c ¼ p0sðuzÞ , where p0 o(z) is the effeco

tive vertical stress at depth z. For under-consolidated clays (clays with excess pore pressures undergoing active consolidation), α can usually be taken as 1.0. The bearing capacity of unit pile end in clay can be calculated as: q ¼ 9su

ð8Þ

where Qf,c is the shaft friction capacity in compression, in force units, Qp is the end bearing capacity, in force units, f(z) is the unit shaft friction, in stress units, As is the side surface area of pile, q is the unit end bearing at the pile tip, in stress units,

The shaft friction, f(z), acts on both inside and outside of the pile. The total axial resistance for pile compression is the sum of the external shaft friction, the end bearing on the pile wall annulus, and the total internal shaft friction or the end bearing of the plug, whichever is the lesser. Details of the other code methods (DNV and NGI) can be referred to specific references.

P

1314

Pile Capacity

Ultimate Axial Bearing Capacity in Cohesionless Soils API Method In the API method, the ultimate axial capacity of piles under compression is determined using the equation: Qc ¼ Q

f ,c

þ Qp ¼ fAs þ qAp

available, Table 1 can be used to select the external friction angle. For long piles, f will not increase linearly with overlying pressure. In this case, restricted values of f are defined in Table 1. The unit bearing capacity of pile end in cohesionless soil can be calculated as: q ¼ N q p00,tip

ð9Þ

ð11Þ

where For pipe piles in cohesionless soils, the unit shaft friction f is calculated using the equation: f ¼ Kp00 tan d

ð10Þ

p00,tip is the effective overburden pressure at pile tip, Nq is bearing capacity coefficient, the values of which can be referred to Table 1.

where K is the lateral earth pressure coefficient which is the ratio of horizontal to vertical effective stress, p00 is the effective overburden pressure at calculated points, δ is the external friction angle. For unplugged open-ended driven pipe piles, it is usually assumed that the K values of tensile and compressive loads are all 0.8. For pile with soil plug or close-ended, the K value can be assumed to be 1.0. The capacity of open-ended driven pipe piles is usually lower than that of the closed-ended piles (Paik et al. 2003). If no further information is

CPT-Based Method A simple method called CPT-based method is widely used for assessing pile capacity in cohesionless soils due to its better predictions of pile capacity and the advantages of simple, rapid, and relatively economic (Eslami and Fellenius 1997). This method is applicable for a wide range of cohesionless soils. The four commonly used CPT-based methods include the ICP method, UWA-05 method, Fugro method, and NGI method. More details of these methods can be found in the specific references (API 2011; Jardine et al. 2005; Clausen et al. 2005; Lehane et al. 2005a, b).

Pile Capacity, Table 1 Design parameters for cohesionless siliceous soil (API RP2A)

Density Very loose Loose Medium Loose Medium Dense Medium Dense Dense Very dense Dense Very dense

Soil description Sand Sand-silt Silt Sand Sand-silt Silt Sand Sand-silt Sand Sand-silt Gravel Sand

Soil-pile friction angle, δ Degrees 15

Limiting skin friction values kPa 47.8

Nq 8

Limiting unit end bearing values, MPa 1.9

20

67

12

2.9

25

81.3

20

4.8

30

95.7

40

9.6

35

114.8

50

12

Pile Capacity

Soil Reaction for Piles Under Axial Load The failure of the pile may be related to the bearing capacity, deformation, or settlement of the pile. Soil reaction is the result of interaction between the soil and the pile under load. It is necessary to analyze the soil reaction in order to ensure the pile settlement, deflection, and rotation of the pile are within the acceptable serviceability limits and are compatible with the structural forces and movements. The pile performance and deformation under both axial and lateral need to be predicted in design. The t-z curve is usually used to analyze the relationship between mobilized soil-pile shear transfer (t) and local pile displacement (z) at any depth. And Q-z curve is used to describe the relationship between mobilized end bearing resistance (Q) and axial pile tip displacement (z).

1315

z is the local pile deflection, D is the pile diameter, t is the mobilized soil pile adhesion, tmax is the maximum soil pile adhesion or unit skin friction capacity. The displacement value of 1% of the pile outer diameter (i.e., zpeak/D ¼ 0.01) is generally employed to meet the design purposes. However, Pile Capacity, Table 2 Data of the t-z curves for clays in API method (API RP2A) Clays

z/D (in.) 0.0016 0.0031 0.0057 0.008 0.01 0.02 1

t/tmax (lb/ft2) 0.3 0.5 0.75 0.9 1 0.70 to 0.90 0.70 to 0.90

Axial Load Transfer Analysis and (t-z) Curves API Method API method recommends a t-z curves for noncarbonate soils as shown in Fig. 1. The data to generate the curve are given in Tables 2 and 3. where Pile Capacity, Fig. 1 Typical axial pile load transfer–displacement (t-z) curves

Pile Capacity, Table 3 Data of the t-z curves for sands in API method (API RP2A) Sands

z (in.) 0 0.1 1

t/tmax (lb/ft2) 0 1 1

P

1316

there is great uncertainty for the case where the axial pile stiffness is critical for design. At this situation, it is feasible to take values of 0.25% to 2.0% of the pile diameter. It is necessary to pay attention to the shape of the t-z curve at displacements greater than zmax as shown in Fig. 1. Values of the residual adhesion ratio tres/tmax at the axial pile displacement at which it occurs (zres) are a function of soil stress-strain behavior, stress history, pipe installation method, pile load sequence, and other factors. Generally, the range of tres / tmax is 0.70 to 0.90. Laboratory, in situ, or model pile tests can provide valuable information for determining values of tres / tmax and zres for various soils.

End Bearing Resistance-Displacement, Q–z, Curve API Method The ultimate bearing capacity of the pile foundation can be determined in accordance with the methods described in the previous sections. However, it usually requires a relatively large pile tip displacement to mobilize the full end bearing resistance. In sand and clay, a pile tip displacement as large as 10% of the pile diameter may be necessary for full mobilization. Definitive criteria and precise specifications are absent up to date. Pile Capacity, Fig. 2 Pile end bearing capacitydisplacement curve

Pile Capacity

API recommended a method as shown in Fig. 2 with data in Table 4 for both sand and clay. in which z is the axial pile tip displacement, zpeak is the displacement to maximum soil pile adhesion or unit skin friction, Q is the mobilized end bearing capacity, in force unit, Qp is the end bearing capacity, in force units, D is the diameter of the pile.

Lateral Bearing Capacity and Soil Response in Cohesive Soils In addition to axial load, the lateral load also has an important influence on the pile foundation. For offshore piles, the significant lateral loads and moments are usually inevitable, especially for Pile Capacity, Table 4 Data for pile end bearing capacity-displacement curve (API RP2A) z/D 0 0.002 0.013 0.042 0.073 0.1 1

Q/Qp 0 0.25 0.5 0.75 0.9 1 1

Pile Capacity

1317

foundation such as anchor piles and monopile supporting wind turbines and small platforms. Therefore, the lateral bearing capacity of the pile foundation and the lateral resistance of the soil near the surface should be considered in the design of offshore pile foundation (Gourvenec and Randolph 2011). The method commonly used to design piles under lateral and overturning loads is based on the Winkler modeling method, commonly known as the p-y method (Byrne et al. 2015). Nonlinear load transfer analysis method can be used to analyze the capacity and response of laterally loaded piles using appropriate load transfer curves (p-y curves) for different soil types (Fonseca 2015). The p-y curve method is recommended to calculate the horizontal bearing capacity of pile foundations in API and DNV (Jin 1993).

with depth, XR can be solved by drawing the curves of the two eqs. (12) and (13). The first intersection point of the two curves is XR. This relation does not apply to situations where intensity changes are irregular. In general, the minimum value of XR is about 2.5 times the diameter of a pile D. The relationship between lateral bearing capacity and displacement of piles in soft clay is usually nonlinear. For short term static loads, the p-y curve can be generated according to the data in Table 5. Unless further information is available, the initial slope of the p-y curve of clay can be calculated by the following equation: k¼x

pu Dðec Þ0:25

ð15Þ

where

Lateral Capacity and Response for Soft Clay The following equations are suggested to estimate the lateral capacity of the pile in soft clay: pu ¼ 3su þ gX þ Jsu X=D

ð12Þ

pu ¼ 9su , if X  XR

ð13Þ

x is the empirical coefficient, εc is the vertical strain at one-half the maximum principal stress difference in a static undrained triaxial compression tests on an undisturbed soil sample. For normally consolidated clay, x ¼ 10 is recommended, and for over-consolidated clay, x ¼ 30 is recommended. where

where pu is the ultimate horizontal bearing capacity, su is the undrained shear strength of soil, D is the diameter of the pile, γ is the bulk density of soil, J is a dimensionless constant determined by field tests, with a range of 0.25–0.5, X is the depth below the seabed, XR is the depth below seabed to bottom of reduced capacity zone for uniform soils. For the soil of constant strength with depth, the following formula can be obtained: 6D XR ¼ gD su þ J

ð14Þ

For the nonuniform soil of strength increase

pu is the ultimate lateral capacity, unit of pressure, p is the mobilized lateral resistance, unit of pressure, yc equals 2.5 εc D, y is the local pile lateral displacement.

Pile Capacity, Table. 5 Mobilized lateral resistance – displacement data for short-term static loads (API RP2A) p/pu 0 0.23 0.33 0.5 0.72 1 1

y/yc 0 0.1 0.3 1 3 8 1

P

1318

Pile Capacity

Lateral Capacity and Response for Stiff Clay

where

Hard clay has greater brittleness than soft clay, despite it has nonlinear stress-strain relationship (API RP2A). When establishing the stress-strain curves of hard clay and the p-y curves under cyclic loading, it is necessary to make a proper judgment on the rapid weakening of the bearing capacity of hard clay under large deformation.

Lateral Bearing Capacity and Soil Response in Cohesionless Soils API Method The ultimate lateral bearing capacity of pile in sand can be computed by the following equations. Eq. (16) is for the capacity of shallow soil, and Eq. (17) is for the deep soil. At the given depth, the ultimate bearing capacity should be the minimum value of the calculated pu: pus ¼ ðC1 X þ C2 XÞg0 X

ð16Þ

pud ¼ C3 Dg0 X

ð17Þ

Pile Capacity, Fig. 3 Coefficients C1, C2, C3, as function of f in API method

pu is the ultimate resistance, units of pressure, γ0 is the submerged soil unit weight, D is the pile outside diameter, X is the depth, C1, C2, C3 are coefficients given in Fig. 3.

The lateral bearing capacity–displacement relationship (p-y) of sand is nonlinear. In the absence of reliable data, approximate values at any depth can be approximately determined according to the following equation:


kX p ¼ Apu tanh y Apu

 ð18Þ

where p is ultimate lateral bearing capacity at depth X, k is the rate of increase with depth of initial modulus of subgrade reaction which can be got from Table. 6, y is the lateral deflection at depth X,

Pile Capacity

1319

Pile Capacity, Table 6 Rate of increase with depth of initial modulus of subgrade reaction k (API RP2A) k MN/m3 5.4 11 22 45

f 25 30 35 40

(lb/in3) 20 40 80 165

Cross-References ▶ Monopile Foundations in Offshore Wind Farm ▶ Offshore Pile Driving ▶ Shallow Foundations ▶ Short Pile and Uplifting Capacity ▶ Spatial Variability ▶ Suction Piles

References X is the depth below the original seabed, A is a factor to account for static or cyclic loading conditions as follows: ( A¼

0:9

X 3  0:8  0:9 D

for cyclic loading for static loading: ð19Þ

Other Considerations Pile foundation in offshore engineering is a complex system, from the installation process to loading stage. The contents of pile capacity in this entry only cover the methods for common and simple situations. Some methods, especially the code methods, are based on specific databases. Most of the databases may comprise piles of smaller length and diameter compared with piles in practical projects (Randolph et al. 2005). Some significant issues such as friction fatigue and progressive failure for long and large diameter pile may not be fully integrated in the methods. As a result, caution should be exercised when the selected methods are applied to some circumstances with special conditions. Another significant point is that cyclic loading is an important feature and has critical effects on the capacity of offshore pile foundations (Leblanc et al. 2010). But due to the complexity, cyclic loading is not covered here. Also, some other issues related to the capacity of foundation such as the pipe-pile plugging, pile in carbonate soils, grouted pile in rock, pile groups and so on are not included in this entry. Appropriate paper and books can be referred to address these specific issues.

API (2000) Recommended practice for planning, designing and constructing fixed offshore platforms – working stress design, API RP-2A. American Petroleum Institute, Washington, DC API (2008) Recommended practice for planning, designing and constructing fixed offshore platforms – working stress design, API-RP-2A. 21st edition, errata and supplement 3, March 2008. American Petroleum Institute, Washington API (2011) Geotechnical and foundation design considerations, API 2GEO/ISO 19901-4:2003–Ballot1 Byrne BW, McAdam R, Burd HJ, Houlsby GT, Martin CM, Zdravković L, Skov Gretlund J (2015) New design methods for large diameter piles under lateral loading for offshore wind applications. In: Frontiers in offshore geotechnics III – proceedings of the 3rd international symposium on frontiers in offshore geotechnics, ISFOG 2015, pp 705–710 Clausen CJF, Aas PM, Karlsrud K (2005) Bearing capacity of driven piles in sand, the NGI approach. In: Frontiers in Offshore Geotechnics, 1st 2005, p 677 da Fonseca ACV (2015) Diameter effects of large scale monopiles – a theoretical and numerical investigation of the soil-pile interaction response. Universidade do Porto, Porto DNVGL (2016) Support structures for wind turbines. Standard DNVGL-ST-0126: DNVGL Eslami A, Fellenius BH (1997) Pile capacity by direct CPT and CPTU methods applied to 102 case histories. Can Geotech J 34(6):886–904 Gourvenec S, Randolph M (2011) Offshore geotechnical engineering. Spon Press Taylor & Francis e-Library. Chapter 5 Jardine RJ, Chow FC, Overy R, and Standing J (2005) ICP design methods for driven piles in sands and clays, Thomas Telford, London Jin W (1993) Evaluation of application of p-y curve method in offshore engineering foundation. China Ocean Eng 4:451–466 Karlsrud K, Nadim F (1990) Axial capacity of offshore piles in clay. In: Proceedings of the 22nd annual offshore technology conference, Houston, 7–10 May, 1990, vol 1. Richardson: OTC, pp 405–416. (2–3), A106

P

1320 Karlsrud K, Clausen CJF, Aas PM (2005) Bearing capacity of driven piles in clay, the NGI approach. Frontiers in Offshore Geotechnics, 1st 2005, 775 Kellezi L, Hansen PB (2003) Static and dynamic analysis of an offshore mono-pile windmill foundation. Thomas Telford, London Leblanc C, Houlsby GT, Byrne BW (2010) Response of stiff piles in sand to long-term cyclic lateral loading. Géotechnique 60(2):79–90 Lehane BM, Schneider JA, Xu X (2005a) A review of design methods for offshore driven piles in siliceous sand. UWA report no GEO 05358. The University of Western Australia, Perth Lehane BM, Schneider JA, Xu X (2005b) The UWA-05 method for prediction of axial capacity of driven piles in sand. Frontiers in Offshore Geotechnics, 1st 2005, 683 Paik K, Salgado R, Lee J, Kim B (2003) Behavior of openand closed-ended piles driven into sands. J Geotech Geoenviron 129(4):296–306 Randolph M, Cassidy M, Gourvenec S, Erbrich C (2005) Challenges of offshore geotechnical engineering. In: Proceedings of the international conference on Soil Mechanics and Geotechnical Engineering, p 123

Pipeline End Manifold ▶ Shallow Foundations

Pipeline End Manifold (PLEM) ▶ Decommissioning of Offshore Oil and Gas Installations

Pipeline End Termination ▶ Shallow Foundations ▶ Subsea Connector

Pipeline End Manifold

Pipeline Soil Interactions Yi Wang and Ruiyan Guo College of Safe and Off-shore Engineering, China University of Petroleum – Beijing, Beijing, China

Synonyms Lateral buckling; Pipeline penetration; Pipe-soil interaction; Steel catenary risers; Submarine pipeline; Touchdown point

Definition Submarine pipelines and risers are an important part of offshore oil and gas development engineering, and the seabed pipe-soil interaction is one of the key issues in the design of pipelines and risers. According to the laying state and operation state of pipelines and risers, the results show that the seabed as the foundation of supporting must provide sufficient support to ensure the stability of pipelines and risers. The research on pipe-soil interaction is to accurately predict the fatigue life of pipeline by describing the buried depth and internal force of pipeline in soil and correctly evaluating the effect of soil on pipeline resistance. This kind of research is of great significance to the stability, safety, and economy of pipelines and to the improvement of relevant design codes. Seabed pipe-soil interaction affects various aspects of subsea pipelines and risers during installation and operation, which include the touchdown point (TDP) of the steel catenary risers (SCR) directions, bearing capacity of pipeline and lateral buckling, etc. In this chapter, the research status by scholars in recent years will be introduced in detail.

Soil Types and Classification

Pipeline Penetration ▶ Pipeline Soil Interactions

Soil parameters along the pipeline route are needed for modeling pipe-soil interaction, which can be obtained by carrying out geophysical and

Pipeline Soil Interactions

geotechnical surveys. The soil can be classified by grain size or its plasticity and cohesion. Soils with particles larger than about 0.05 mm are called coarse grained (sands and gravels), while soils finer than this size are called fine grained (silts and clays). Soil is a porous media material comprising solid particles with void spaces containing gas and water. In subsea environments, the water pressure is generally high enough that gas is forced into solution and the soils are saturated with water. Soil behavior depends on the rate at which load is applied to the soil, and generally can be categorized as “drained” or “undrained” behavior (Bai and Bai 2014). If the rate of load is greater than the rate at which pore water in the interparticle voids is able to move in or out of soil interparticle voids, then the soil is said to behave in an undrained manner. If the rate of loading is slower than the rate at which pore water is able to move in or out of soil interparticle voids, the soil is said to behave in a drained manner.

Dynamic Pipe-Soil Interaction at TDP The use of SCR in deepwater developments is increasing, and most of the structural damage of SCR occurs in the so-called TDP where the pipe takes off and lands repeatedly on the soft soils generally encountered in deepwater (Fig. 1). Different pipe-soil interaction models are used in TDP numerical analysis. The rationality and reliability of these models directly affect the accuracy and efficiency of calculation results. At Pipeline Soil Interactions, Fig. 1 TDP of SCR (Fontaine 2006)

1321

present, the most widely used pipe-soil nonlinear models are proposed by Aubeny and Biscontin (2009) and Randolph and Quiggin (2009), which are abbreviated as AB model and RQ model, respectively. Both of them are based on a large number of test results. AB model is mainly developed from the large-scale model test of Langford and Aubeny (2008), while RQ model is summarized from the centrifuge test results carried out by Hodder et al. (2008). Bridge summarized a nonlinear model based on the test results of STIDE and CARISIMA JIP. It was pointed out that the process of pipe-soil interaction can be divided into four stages: penetration, uplift, suction, and reintegration. RQ model refers to the full-scale field test results of Bridge et al. (2004). Different pipesoil interaction models are used in numerical analysis. The rationality and reliability of these models directly affect the accuracy and efficiency of calculation results. As shown in Fig. 2, there are four stages in AB model: initial penetration stage (power function backbone curve), upper pull-up stage (hyperbolic function elastic rebound curve), partial detachment stage (third order polynomial curve), complete detachment stage and repenetration stage (third order polynomial curve). The pipe-soil separation point in AB model can describe the formation of grooves under the pipeline, which is in accordance with the test results, but the effect of soil strength on cyclic weakening is not considered. As shown in Fig. 3, RQ pipe-soil interaction model describes four different states of pipe-soil interaction: noncontact, initial penetration, uplift

P

1322

Pipeline Soil Interactions

Pipeline Soil Interactions, Fig. 2 P-y curve in AB model (Aubeny and Biscontin 2009)

Pipeline Soil Interactions, Fig. 3 P-y curve in RQ model (Randolph and Quiggin 2009)

and repenetration. The curve describes the change of resistance of soil model with the buried depth of pipeline. Curve 1 is the initial penetration, curve 2 is the pull-up process, and curve 3, 4 are the process that the pull-up force increases first and then decreases. Curve 7 represent the repenetration process, which indicates that the soil stiffness decreases when repenetration occurs. As the burial depth continues to increase, the repenetration curve gradually merges into the

initial penetration curve. The variation of resistance in RQ model is related to the pipeline loading path, which can describe the disturbance degree of pipeline movement on the bottom soil to a certain extent. During the interaction between pipeline and seabed, plastic deformation occurs in the soil beneath the pipeline, which explains the reason why part of the soil is pushed by the pipeline to both sides to form a bulge and groove. However, the RQ model does not consider the

Pipeline Soil Interactions

effect of pipe grooving when simulating upsetting. You (2012) has improved the AB model by considering soil weakening with power function, incorporating the repenetration curve into the initial penetration skeleton line with a new formula, and adopting different mathematical formulas for each loading and unloading stage. Aubeny et al. (2015) based on the results of Langford and Meyer’s tests (2010), a new weakening model was formed by considering soil weakening in AB model. The three stages of initial penetration, elastic rebound, and reloading were used to describe the nonlinear behavior of soil, and the effect of soil weakening was taken into account in the new model.

Vertical Pipe-Soil Interaction of Pipeline Pipeline on the seabed will has preliminary embedment which called pipeline penetration. The pipeline penetration is affected by the following fundamental issues, such as geotechnical statement, pipeline laying operations, and scouring from the actions of waves and current. Figure 4 illustrates the definitions of parameters used in the model of pipe penetration (Bruton et al. 2008). To prevent the vertical movement of a pipeline in soil, the pipeline should be neither heavy enough to sink nor light enough to float. The pipelines to be buried should be checked for possible sinking or floatation. Sinking should be considered with maximum content density, such as water filled, and floatation should be considered with minimum content density, such as air filled. The vertical pipe-soil interaction during pipeline penetration can be modeled by soil spring based on Winkler foundation beam theory Pipeline Soil Interactions, Fig. 4 Pipeline penetration in soil (Bruton et al. 2008)

1323

(Limura 2004) or shell model (Yatabe et al. 2002). The effects of deformation mode and the maximum strain of pipelines in different states can be obtained. A module used for assessing pore pressure accumulation in the seabed was designed by Bonjean et al. (2008). The module could assume both the uplifting force exerted on the pipeline and the corresponding soil resisting force. The process of pipeline penetration into the seabed was analyzed by Chatterjee, using the means of large deformation technology (Chatterjee et al. 2012). Considering the effects of strain softening, strain rate, and soil uplift, the formula for calculating the vertical resistance of pipeline was put forward, and a breakthrough in theoretical calculation was achieved. Rossiter and Kenny (2012) examined pipe-soil interaction events during oblique lateral-vertical soil movements using plane strain finite element analysis. The results from this study provide a technical framework to assess complex loading events, such as coupled ice keel/seabed/pipeline interaction. Later, the discontinuous medium contact treatment method in discontinuous deformation analysis was used to simulate buried pipelines, and the feasibility and validity of solving pipe-soil contact with finite element method were discussed (Na et al. 2013). White and Randolph (2007) described the relationship between penetration resistance and the vertical and lateral resistance of pipelines, using both in situ methods in the form of cylindrical (T-bar) and spherical penetrometers. The relationship taking account of the depth of burial and cycles of movement. Two new models of interaction between pipelines and seabed have been proposed: non-weakening model and weakening model (Jiao 2007). In both models, the main line

P

1324

Pipeline Soil Interactions

is used to describe the pipeline penetration, the boundary curve is used to define the resistancedisplacement relationship of the pipeline in large displacement, and a series of formulas are used to describe the resistance-displacement curve in the cyclic process. A predictive model for estimating the compression and shear stresses around a buried pipeline in static conditions has been developed for determining stresses around a buried pipeline and verified using the Alyeska and Soil Box tests (Andrenacci and Wong 2012). Advanced pipe-soil interaction techniques that used to demonstrate benefits that can be realized on typical projects to reduce pipeline walking predictions and the associated mitigation measures were presented (White et al. 2015). Aubeny et al. (2015) formed a new weakening model considering soil weakening based on the test results of Langford and Meyer (2010). It used three stages of initial penetration, elastic rebound and reloading to describe the nonlinear behavior of soil. The interaction between soil and pipeline was studied by controlling the change of soil stiffness during uplift and repenetration. Computational fluid dynamics (CFD) was used to consider seabed soil as fluid and to establish a follow-up grid in a certain area around the pipeline (Hawlader et al. 2015). The computational method requires less computational resources than RITSS and CEL methods, and can also consider strength weakening and strain rate effect. Another research present details of a novel 2D pipe-soil-fluid (PSF) interaction algorithm, which has been developed to offer a more accurate model of the evolution of soil profiles around the pipeline (Griffiths 2012). A large number of parametric 2D CFD models have been run to generate qy1

qy 2

seabed shear stress profiles as a function of seabed and pipe geometry under different wave and current flow conditions. The PSF model has been designed to minimize computational cost but still enable the profile of the soil around the pipe to be tracked.

Lateral Pipe-Soil Interaction of Pipeline Pipeline on-bottom stability design is conventionally based on the static balance between hydrodynamic forces and the soil lateral resistance forces, as shown in Fig. 5. Verley and Lund (1995) developed a soil resistance model applicable for pipelines laying on clay soils. Brennodden and Stokkeland (1992) performed some full-scale model tests for the Troll Phase 1 development. The results of these model tests revealed a significant increase in peak soil resistance (Bai and Bai 2014) (Fig. 6). Based on theoretical analysis and experiments of lateral buckling of a pipe, Palmer and Baldry (1974) correctly interpreted the reason why lateral buckling can occur in a pipe and proposed an analytical formula for the critical pressure. Hobbs (1984) studied the lateral buckling of a perfect straight pipeline on the basis of related work on railroad track and proposed five buckling modes which may occur in the process of lateral buckling. Analytical formulas for critical force, wavelength, and amplitude corresponding to every buckling mode are also presented. Taylor and Gan (1986) considered the initial imperfections and proposed analytical formulas for critical forces of lateral buckling corresponding to mode 1 and mode 2. Finite element (FE) analysis was qy 4

qy 3

qy 5

qy

qx 1 oil

oil qx2 kx1 ky1

kx2 ky2

kx 3 ky 3

kx 4 ky 4

Pipeline Soil Interactions, Fig. 5 Soil spring model

kx 5 ky5

kx6 ky 6

kx 7 ky 7

qx

Pipeline Soil Interactions Pipeline Soil Interactions, Fig. 6 Lateral buckling under cyclic thermal load (Bai and Bai 2014)

1325

Initial condition

heating condition

cooldown condition

used to study the lateral buckling responses of submarine pipelines (Liu et al. 2014), some formulas were proposed to calculate the critical force of lateral buckling. The initial imperfection parameters (initial wavelength and maximum amplitude) are included in these formulas. The stability of submarine pipeline during service is studied by hydrodynamic loading method (Fuping 2001). And the test reflects the coupling effect among wave, pipeline, and seabed. It is found that the lateral instability of submarine pipeline generally goes through four stages: complete stability, sand bed erosion, slight displacement of pipeline, and pipeline instability. It is also found that loading history, soil parameters, and initial settlement of pipeline all affect the stability of pipeline. On the basis of experiments, the empirical relationship of wave-tube-soil interaction for pipeline stability is preliminarily established. Some results simulated the seabed by adding a nonlinear spring under the linear elastic pipeline, and put forward the corresponding analytical model of pipe-soil interaction (Aubeny and Biscontin 2008). The nonlinear spring takes into account the nonlinearity of the load-displacement relationship of the seabed and the separation of pipe and soil. A physical model was used to understand the mechanisms of interaction between pipe and soil through a lateral visualization, and then to simulate the pipe response under combined vertical and horizontal loads (OrozcoCalderon et al. 2012). This entry concentrated on

the results obtained using sideswipe tests with large and short horizontal displacements, and obtained an experimental yielding envelope of the pipe. In the recent years PETROBRAS has developed several projects in deepwater areas of the Santos and Campos Basins, offshore Brazil, where soft clay is predominant. This has motivated the development of an extensive experimental test program for pipe-soil interaction, aimed at increasing the design reliability of subsea pipelines with lateral buckling (Cardoso and Silveira 2010). A new model presented was based on fullscale tests developed at the Institute of Technological Research (IPT) installations over the last 3 years. The experimental results were used to develop a model for the lateral residual friction factor based on dimensionless groups that govern the problem. The aim of this model is to improve knowledge obtained by the industry in recent years, mainly by the JIP SAFEBUCK I and II programs. Another study concerned the lateral buckling critical force of a submarine PIP (pipe-in-pipe) pipeline with one symmetrical initial imperfection on soft foundation (Xinhu et al. 2018). On the basis of 3D beam elements, tube-to-tube interaction elements and pipe-soil interaction elements, 3D finite element model were built for a length of submarine PIP pipeline. The simple empirical formula was proposed to calculate the lateral buckling critical force of a submarine PIP pipeline based on dimensional analysis and finite element

P

1326

results, and the case study was carried out to verify the obtained empirical formula and the results manifest its good accuracy.

References Andrenacci A, Wong D (2012) Evaluation of buried pipeline coatings under soil stress. NACE International, Salt Lake City Aubeny CP, Biscontin G (2008) Interaction Model for Steel Compliant Riser on Soft Seabed. In: Offshore technology conference, Houston Aubeny CR, Biscontin G (2009) Seafloor riser interaction model. Int J Geomech 9(3):133–141 Aubeny C, White T, Langford T et al (2015) Seabed stiffness model for steel catenary risers. In: Frontiers in offshore geotechnics III. CRC Press, Boca Raton, pp 351–356 Bai Q, Bai Y (2014) Subsea pipeline design, analysis, and installation. Gulf Professional Publishing Bonjean D, Erbrich C, Zhang G (2008) Pipeline floatation assessment in liquefiable soil. In: Offshore technology conference, Houston Brennodden H, Stokkeland A (1992) Time-dependent pipe-soil resistance for soft clay. In: Offshore technology conference, Houston Bridge CD, Laver K, Clukey E et al (2004) Steel catenary riser touchdown point vertical interaction models. In: Offshore technology conference, Houston Bruton DAS, White DJ, Carr MC et al (2008) Pipe-soil interaction during lateral buckling and pipeline walking – the SAFEBUCK JIP. In: Offshore technology, conference, Houston Cardoso CO, Silveira R (2010) Pipe-soil interaction behavior for pipelines under large displacements on clay soils – a model for lateral residual friction factor. In: Offshore technology conference, Houston Chatterjee S, Randolph MF, White DJ (2012) The effects of penetration rate and strain softening on the vertical penetration resistance of seabed pipelines. Geotechnique 62(7):573–582 Fontaine E (2006) SCR-Soil Interaction: Effect On Fatigue Life And Trenching. International Society of Offshore and Polar Engineers Fuping G (2001) Experimental study on stability of submarine pipelines under wave action. Doctoral dissertation, Institute of Mechanics, Chinese Academy of Sciences Griffiths T (2012) Development of a novel 2D pipe-soilfluid interaction model for subsea pipeline stability design. International Society of Offshore and Polar Engineers, Mountain View Hawlader B, Dutta S, Fouzder A et al (2015) Penetration of steel catenary riser in soft clay seabed: finite-element and finite-volume methods. Int J Geomech 15(6):04015008 Hobbs RE (1984) In-service buckling of heated pipelines. ASCE J Transp Eng 110:175–189

Pipeline Soil Interactions Hodder MS, White DJ, Cassidy MJ (2008) Centrifuge modelling of riser-soil stiffness degradation in the touchdown zone of a steel catenary riser. In: ASME 2008 27th international conference on offshore mechanics and arctic engineering, Honolulu Jiao Y (2007) Nonlinear load-deflection models for sea floor interaction with steel catenary riser. PhD thesis, Texas A&M University Langford T, Aubeny CP (2008) Model Tests for Steel Catenary Riser in Marine Clay. Offshore Technology Conference Langford TE, Meyer VM (2010) Vertical cyclic testing of model steel catenary riser at large scale. In: Frontiers in offshore geotechnics II. CRC Press, Boca Raton, pp 803–808 Limura S (2004) Simplified mechanical model for evaluating stress in pipeline subject to settlement. Constr Build Mater 18(6):469–479 Liu R, Xiong H, Wu X et al (2014) Numerical studies on global buckling of subsea pipelines. Ocean Eng 78:62–72 Na X, Hong JL, Guang JS (2013) Discontinuous deformation analysis on pipe-soil contact of buried pipeline due to fault. Chin Q Mech 34(2):324–330 Orozco-Calderon M, Equihua-Anguiano LN, Foray P (2012) Experimental yield surface for soil-pipeline interaction in very soft soils. Society of Underwater Technology, London Palmer AC, Baldry JAS (1974) Lateral buckling of axially constrained pipelines. J Pet Technol 26(11):1283–1284 Randolph MF, Quiggin P (2009) Non-linear hysteretic seabed model for catenary pipeline contact. In: Proceedings of the international conference on offshore mechanics and arctic engineering, Honolulu Rossiter C, Kenny S (2012) Evaluation of lateral vertical pipeline/soil interactions. In: Offshore technology conference, Houston Taylor N, Gan AB (1986) Submarine pipeline bucklingimperfection studies. Thin-Walled Struct 4:295–323 Verley RR, Lund KM (1995) A soil resistance model for pipelines placed on clay soils. In: Proceedings of OMAE. Pipeline technology, Copenhagen White DJ, Randolph MF (2007) Seabed characterisation and models for pipeline-soil interaction. Int J Offshore Polar Eng 17(3):193–204 White DJ, Westgate ZJ, Ballard JC et al (2015) Best practice geotechnical characterization and pipe-soil interaction analysis for HPHT pipeline design. In: Offshore technology conference, Houston Xinhu Z, Menglan D, Guedes SC (2018) Lateral buckling critical force for submarine pipe-in-pipe pipelines. Appl Ocean Res 78:99–109 Yatabe H, Fukuda N, Masuda T et al (2002) Analytical study of appropriate design for high-grade induction bend pipes subjected to large ground deformation. J Offshore Mech Arct Eng 126(4):376–383 You JH (2012) Numerical modeling of seafloor interaction with steel catenary riser. Dissertations and theses – gradworks

Piping Technology

Pipe-Soil Interaction ▶ Pipeline Soil Interactions

Piping Technology Ji Wang School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China

1327

in the manufacturing of shipbuilding enterprises. There are many types of pipes with different models and different uses. According to their different transmission media, pipe systems can be divided into steam pipe system, fuel oil and lubricating oil pipe system, compressed air pipe system, and cargo oil and liquefied gas pipe system. According to their different functions, pipe systems can be divided into high pressure pipe system, nuclear power pipe system, high temperature pipe system, low temperature pipe system, chemical medium pipe system, etc. (Xu 2011). According to their different materials, pipes can be divided into three categories: steel pipes, nonferrous metal pipes, and nonmetallic pipes.

Synonyms High chromium duplex corrosion-resisting stainless steel (HDR); Numerical control (NC); Tungsten insert gas (TIG)

Definition Ship piping system refers to the piping system of the ship, which includes all the pipelines, accessories, machinery, equipment, and appliances used to transport fluids. Ship piping system is key to ensuring the normal operation of the ship power plant, deck outfit, ballast systems, and living facilities and to the safe navigation of ships. It is also an important guarantee for the service life of ships. For shipbuilding, ship piping is one of the largest engineering projects of both processing and manufacturing in the workshop and installing and debugging in the field (Rao et al. 2020). For example, the ship piping of a 10,000 DWT grade bulk carrier can account for about 25% of the total workload of shipbuilding. Another example is that piping system of a chemical product transport ship includes dozens of systems, nearly a 1000 types of pipe specifications, and tens of thousands of pipes. Therefore, the processing and assembly of ship pipes is an important part of the construction of the ship structure. In modern shipbuilding, pipe system production is considered as an important processing step

Introduction Pipe Processing Technology The pipe processing workshop is the place where the shipbuilding enterprise processes and manufactures ship pipes. In the modern shipbuilding model, pipe processing workshop is arranged with the principle of group technology, thus establishing a production operation system guided by the principle of manufacturing “intermediate products” of the ship. The pipe processing workshop first decomposes the pipe fitting production tasks according to pipe processing drawings and part lists issued by the pipe design department, together with the tray plan of the piping tray. Then the workshop distributes the decomposed production tasks to different teams, each of which, according to its task, receives the raw materials from the raw material warehouse of the pipe processing workshop and then completes the pipe processing according to the production process of the pipe processing drawing, including the processes of cutting, bending, reshaping and positioning, welding, polishing, testing, and surface treatment (Li 2016). Cutting

Correct cutting is the first step in the pipe processing work. Before cutting, we obtain the theoretical calculation length of the pipe from the design drawing. The cutting length is considered

P

1328

as the overall length of the bending pipe, which is theoretically the overall length of both the straight pipes and the elbow arcs. When the pipe is being bent, the arc length of the elbow part is slightly elongated due to plastic deformation of the material, so the actual cutting length should be slightly shorter than the theoretical length. Elongation is an experience data, which depends on the pipe material, diameter, wall thickness, bending radius, bend size, and the choice of hot or cold bending. Generally, for a pipe of a certain specification and material, the elongation is proportional to the bending angle α. At present, the actual cutting length of a pipe in the factory is usually its theoretical cutting length, and the elongation will be cut off when the pipe is reshaped and positioned. However, if the “welding prior to bending” technology is adopted, the elongation must be considered, usually based on the experience data obtained from the test (Fan 2018). Generally, pipes are cut by the sawing machine or through oxy cutting, but after oxy cutting, iron oxide residue and spatter must be removed. Nonferrous metal pipes and HDR stainless steel pipes should be cut by machine saw or the handsaw. 1. Gas cutting Gas cutting of metals (in reality, oxygen cutting) is currently the most commonly used cutting method for ship piping. Its process is described as follows: first, the metal at the cutting slit is heated with a preheating flame, so that the metal temperature at the starting point of the slit rises to the ignition point (the ignition point of the metal in pure oxygen); then the oxygen flow with high pressure is released and causes the metal to burn (violent oxidization); the slag generated by the burning is immediately blown away by the airflow; continue this process and a smooth slit will be formed in the metal to separate it. 2. Plasma cutting Plasma arc cutting is a processing method that uses the heat of a high-temperature plasma arc to locally melt (and evaporate) the metal at the slit of the workpiece and uses the momentum of the high-speed plasma to remove the molten metal to form a cut. Plasma cutting,

Piping Technology

with different working gases, can cut all kinds of metals that are difficult to cut by oxygen, especially nonferrous metals (stainless steel, aluminum, copper, titanium, and nickel). Its main advantage is that it can reach a high speed when cutting the metal of limited thickness. Especially when cutting ordinary carbon steel sheet, the speed of plasma cutting can be five to six times that of oxygen cutting, with a smooth cutting surface, limited thermal deformation, and a smaller heat-affected zone. Pipe Bending

Rotary draw bending is the main form of cold bend and is also used by most NC pipe bending machines. The pipe bending performed on the pipe bending machines is often divided into two categories: bending without mandrel and bending with mandrel. In order to prevent excessive flattening of the cross-sections of the bending part, the method of bending with mandrel is often used for pipes with relatively thin walls, while the method of bending without mandrel is used for pipes with relatively large wall thickness or with low or even no requirement for cross-section flattening. The schematic diagram of the processing by pipe bending machine is shown below (Fig. 1). The bending forming process is completed with the cooperation of multiple molds. The bending radius of the pipe and the cross-section shape of the bending segment are determined and controlled by the bending die. The clamping die fixes the front end of the pipe on the bending die and gives the pipe a certain clamping force to ensure that the three-in-one rotation of the pipe, the bending die, and the clamping die completes the bending of the pipe. The pressure die supports the outside of the pipe and can move together with the pipe to boost the pipe, thus limiting the decrease in the thickness of the pipe outer wall and the increase in the thickness of the pipe inner wall at the bending segment. The main function of the antiwrinkle die is to reduce the wrinkles caused by pressure on the inner side of the bending position, so an antiwrinkle die must be used in the bending with higher requirements for inner wrinkling or in the bending of large-diameter thin-walled pipes. The mandrel is mainly used in

Piping Technology

1329

Piping Technology, Fig. 1 The schematic diagram of the processing by pipe bending machine

the bending of pipes with relatively small wall thickness, to prevent excessive flattening of the cross section of the bending segment, and the mandrel also has a great influence on the thickness change of the outer wall of the pipe and the rebound of the pipe (Wu 2016). Pipe Reshaping and Positioning

The pipe reshaping and positioning by the pipe reshaping machine is a method of installing the slip-on welding flange on the main pipe. Based on the information of the pipe parts drawing, the pipe reshaping machine is moved to an appropriate position, and a flange is installed on the template, with a steel ring inside the flange, the thickness of which equals to the weld end distance. Then both ends of the pipe to be formed are set into the flange, and the position of the pipe is adjusted according to the drawing. Then the flange positioning work begins to be performed (Fig. 2). Platform pipe reshaping and positioning is another method of assembling slip-on welding flange on the main pipe. The method of marking on the flange surface is used based on the flange bolt hole angle data in the piping parts drawing, and with the help of tools such as flange ruler, level bar, angle ruler, and plumb, the pipe is set on the platform according to certain requirements in order to perform flange positioning. General requirements for pipe reshaping and positioning are that

the end of the pipe should be flush; the surface of the pipe should be clean; the gap between the pipe and the accessories should be uniform and meet the relevant process requirements. Welding

1. Workshop welding of ship pipe fittings Ship pipe fittings refer to semi-finished pipe fittings of all types, batches, materials, and sizes that are welded and produced in the workshop and then sent to the hull block for group welding. The biggest advantage of preparing semi-finished pipe fittings under the conditions of workshop production is that the pipe accessories are easy to assemble, and the functions of various automatic pipe welding equipment and auxiliary welding equipment are given full play. The satisfactory welding quality could also be achieved in some occasions where manual welding is used. As shown in Fig. 3a, an all-position automatic pipe welding machine is used in the workshop to perform pipe-pipe butt welding after preheating. As shown in Fig. 3b, a large all-position automatic pipe welding machine is used in the workshop to perform largediameter pipe-pipe butt welding. As shown in Fig. 3c, a narrow-gap gas welding machine is used in the workshop to perform thick-walled pipe-pipe butt welding.

P

1330

Piping Technology

Piping Technology, Fig. 2 The schematic diagram of the pipe reshaping machine. (1) Column; (2) screw rod; (3) template; (4) hand grip; (5) swivel plate; (6) pedestal; (7) guide rail; (8) guide frame; (9) brake

2. On-site welding of ship pipe fittings On-site welding of ship pipe fittings (Fig. 4) refers to the welding of pipe fittings on the sites of hull block. On-site welding of ship pipe fittings is generally performed in the form of pipe-pipe butt joints, but various welding positions may be required (Figs. 5 and 6), so the automatic pipe welding machines are usually used to ensure high welding quality and reduce welders’ labor intensity. Welding of ship pipe fittings can be summarized into several types: the first type is pipe-pipe butt joint (Fig. 7), pipe-flange butt joint (Fig. 8), and pipe-pipe multipass butt joint (Fig. 9). This type of ship pipe fittings with butt welds are most widely used in ship piping system, and for this type, the standardization and serialization have been formed in the aspects of materials, models and sizes, pressure ratings, etc., for the pipes, pipe flanges, pipe elbows, three-way pipes, and other accessories within the common size range, as shown in Fig. 10. The other type is the branch pipe welding, which is rare among ship pipe fittings within the common size range, because this type of joint can

generally be replaced by a three-way pipe joint; If the branch pipe welding becomes necessary, it must be used for the joint of a non-standardized pipe (or fittings) or a special thick-walled pipe (or fittings) with a tube, which is usually called saddle-shape weld joint in the industry. The most widely used automatic arc-welding equipment in the on-site installation of ship pipelines (block pipe system) is the all-position automatic pipe welding machine. It is an automatic arc welding equipment which can weld fixed pipe joints (with pipe fittings not rotating) at all positions (the meaning of “all-position” is shown in Fig. 11). In Fig. 11, the butt weld pipe joint to be welded does not rotate, but the welding gun (usually a TIG welding gun, namely, an argon tungsten-arc welding gun) rotates more than 360 around the centerline of the groove of the pipe joint. In this way, a variety of welding positions on the pipe surface could be reached by the welding gun: flat welding position, vertical down welding position, overhead position, vertical upward welding position, and multiple welding positions among these four welding positions; because to complete the circumferential weld of a pair of butt-welded

Piping Technology

1331

P

Piping Technology, Fig. 3 The automatic welding method of centralized pipe systems in the workshop

pipes, the welding gun will be at a variety of welding positions, so this arc-welding equipment is called an all-position automatic pipe welding machine. It is a highly automated mechatronic arc welding equipment, because the completion of the welding of the circumferential weld of a pair of pipes requires not only that the welding head rotates around the pipe at a uniform welding speed, but also that the welding current, shielding gas, filler wire, and cooling water are connected to

the corresponding parts of the welding head, as shown in Fig. 12. In order to meet the process requirements of different arc welding and ensure excellent welding quality, sometimes the welding head is required to swing laterally during welding. Therefore, from the appearance, there are many wires, water pipes, gas pipes, and cables led to the pipe welding machine. In order to realize the smooth “three links” of water, electricity and gas, the

1332

Piping Technology, Fig. 4 On-site welding of ship piping system

Piping Technology, Fig. 5 On-site automatic welding of ship piping system (horizontal welding)

Piping Technology

Piping Technology, Fig. 7 Unequal diameter pipe-pipe butt weld joint

Piping Technology, Fig. 8 Pipe-flange butt weld joint

Piping Technology, Fig. 6 On-site automatic welding of ship piping system (horizontal position)

Piping Technology

1333

Piping Technology, Fig. 9 Pipe-pipe multipass butt weld joint Piping Technology, Fig. 11 The schematic diagram of the all-position welding machine

P Piping Technology, Fig. 10 Standard fittings of several pipe flanges

wires, water pipes, gas pipes, and cables of the pipe welding machine must be reasonably arranged. Obviously, the smaller the diameter of the pipe being welded is, the smaller the volume of the pipe welding machine is, but the higher the precision for the mechatronics system of the pipe welding machine is required to be, and the higher the flexibility of the pipe welding machine is required to be.

Pipe-Piece Family Manufacturing The pipe-piece family manufacturing method is another successful application of group

Piping Technology, Fig. 12 The travel carrier pipe welding machine

technology by Ishikawajima Harima Heavy Industries of Japan. In an ideal situation, the various machines needed to manufacture a particular intermediate product family should be set into a group to form a production line. The group of machines can complete all processes as a predetermined process unit, and this method is called “process classification.” This method replaces the

1334

traditional process design method required to manufacture parts. When this method is applied to a pipe workshop, it is called a pipe-piece family manufacturing method. The pipe-piece family manufacturing method is a comprehensive method that simplifies the manufacturing process of the pipes of mixed varieties and mixed batches, such as vent pipe parts manufactured together with other pipe parts. This method requires more complicated plans and schedules than traditional, inefficient, and system-oriented plans and schedules. With this method, mass-manufacturing mode could be adopted for manufacturing complicated varieties of ship pipes, and piping part design, manufacturing technology, and production management could be reasonably arranged, so that the general shipbuilding productivity could be better improved by piping engineering, and the productivity of pipe fittings could be greatly improved, too (Xie 2011).

References Fan Z (2018) Analysis and control of cold bending process of ship pipe. Wuhan University of Technology Li H (2016) Research on application of lean in shipyard pipe processing workshops. Jiangsu University of Science and Technology Rao J, Yu H, Zhou T, Chen H (2020) Research and application of intelligent workshop for ship pipe processing. Mar Technol 1:81–87 Wu S (2016) Research on springback and accurate cutting length of tube bending. Southwest University of Science and Technology Xie Y (2011) Production planning simulation of pipe processing shop in shipyard. Jiangsu University of Science and Technology Xu X (2011) Development and application of efficient welding in marine pipe manufacturing. Weld Technol 40(4):5–8

Planar Motion Mechanism (PMM) ▶ Maneuverability of Polar Vessel

Planar Motion Mechanism (PMM)

Plastic Design ▶ Offshore Structure Design Under Ice Loads

PLR (The Plug Length Ratio) ▶ Offshore Pile Driving

Polar Acoustics Jingwei Yin College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin, China

Polar acoustics (also known as Arctic Ocean acoustics) mainly studies the underwater acoustic environment in the polar region and adjacent sea areas and is a branch of hydro-acoustics. The significant research began during the Cold War (1947–1991) with the advent of the nuclear submarine. The main contents of polar acoustics include the marine environment noise under the ice cover, reverberation characteristics, the characteristics of underwater acoustic channels, and underwater acoustic signal processing. Based on these understandings, polar acoustics are well applied in the polar region, named polar acoustics technology. The presence of ice and its spatial and temporal variability are the main characteristics of the Arctic Ocean that affect the underwater acoustic environment. This phenomenon is particularly prominent in Arctic Ocean, unlike the Antarctica that is covered by ice perennially. The growth and ablation of sea ice make the Arctic acoustic environment unique and interesting.

Ambient Noise The ambient noise in the Arctic Ocean consists of many types and is different from any other sea

Polar Acoustics

1335

area. There is few shipping noise due to less water traffic. Sea ice movement, earthquake, and biological activity are the mainly sources of Arctic Ocean ambient noise. The frequency spectrum range of the Arctic Ocean ambient noise is approximately 1 ~ 1000 Hz, and the peak occurs mainly at two specific frequencies of 15 Hz and 300 Hz (Dyer 1988). The peak at 15 Hz is believed to be generated by ice ridge activity as shown in Fig. 1, and 300 Hz is considered to be caused by temperatureinduced thermal cracks. These two types are the main sources of Arctic noise. Zakarauskas summarized the Arctic ambient noise:

between the upper and lower surface, resulting in thermal cracks (Greening and Zakarauskas 1994b). Thermal cracks are subtle noise phenomenon that takes place on the surface of the ice layer. It usually occurs during the night, and maintenance is 0.05 ~ 0.1 s. Different from the noise produced by the formation of ice ridges, the frequency spectrum of the thermal crack noise is relatively flat, and the noise produced by the ice ridge is mainly in the low-frequency range. 3. Snow Noise

Floating ice is affected by the wind and ocean currents and squeezed to form ice ridges. Collisions, squeezing, and friction between sea ices produce low-frequency noise during the process (Greening and Zakarauskas 1994a).

The polar high atmospheric pressure exists for a long period over the Arctic Ocean, and the east wind prevails in winter. Snow noise become the main noise in the quiet ice area such as huge ice cap in winter and spring. The wind blows the snow particles on the ice cap to rub against it, and then the sound enters the water through the ice layer, creating snow noise. The frequency of this noise is between 2 Hz and 2 kHz.

2. Thermal Cracks Noise

4. Earthquake Noise

As the season change, shrinkage or expansion occurs when the temperature is greatly different

P wave generated by earthquakes have a frequency of 0.1 ~ 5 Hz and carry little energy. The

1. Pressure Ridging Noise

Polar Acoustics, Fig. 1 Frequency spectrums of pressure ridging noise (Greening and Zakarauskas 1994a)

100

P

Noise Level (dB/µPa2/Hz)

90

80

70

60

50

40

1

10 Frequency (Hz)

100

1336

T wave produced by the earthquake has more energy, and the frequency band is 5 ~ 60 Hz. Such waves propagate from the bottom of the sea to the water and reach the ice. This type of noise is more difficult to distinguish from longrange ice ridge forming noise, since the frequency bands of the two are similar. 5. Biological Noise Take the whale noise as an example: the noise emitted by whales is about 15–45 Hz, and the duration is 1–20 s. Generally, there will be 50–100 repetitions, each interval being 1–20 s. There are some animal noise such as seals, but the impact of biological noise on the overall ambient noise in the Arctic is limited. 6. Ice Shore Noise Ice shore noise is caused by the effects of ocean currents, sea breeze, and ice vortex on the coast. Noise levels in this area are generally higher. The main factors affecting the noise level are seawater conditions, water depth, and the size of the waves. T.C. Yang used sonar buoys in Greenland to observe ice shore noise and measured different shore ice conditions separately. The noise level is relatively high when the ice shore is compact and free of ice floes. In contrast, the noise level is relatively low when the shore has scattered floes.

Polar Acoustics

stable upward-refracting sound speed profile with an upper boundary of rough polar ice (Hutt 2012). Baggeroer reports that there are two positive spring layers in Arctic Ocean, halocline at about 40 ~ 50 m depth and syncline at 200 ~ 250 m depth, respectively. When the source is upper the halocline, the sound is constantly reflected at the lower surface of the rough polar ice and can travel a long distance, which act like a surface duct. Acoustic waves with frequencies 15 ~ 30 Hz propagate best because of the rough polar ice scattering and energy conversion between flexural wave and polar ice. As the frequency increases, attenuation increases dramatically, because highfrequency components are scattered out by rough polar ice. Yet very low frequencies, below about 10 Hz, are not effectively trapped by the duct. Urick summarized Arctic Ocean transmission loss shows that for frequencies less than about 100 Hz, propagation is approximately characterized by cylindrical spreading, which is an indication that the surface duct is an excellent waveguide for low frequencies (Urick 1983). Characteristic transmission loss versus range based on numerous measurements is shown in Fig. 2. When the source is near the spring layers, some grazing angle sound are trapped in another duct called “SOFAR” duct. In this duct, the sound can propagate without touching the bottom of the polar ice and the seabed so that travel a long range.

7. Iceberg Melting Noise There are a large number of tiny air bubbles in the water that forms icebergs. They are solidified in the ice due to the pressure. As the iceberg melts in the seawater, the gas in the ice suddenly released and made a sharp crack when the melting surface reaches the air bubbles. A sonar buoy is placed near the iceberg measuring the iceberg melting noise and found that the noise had a flat spectrum.

Propagation The main features of the underwater propagation environment of Arctic Ocean were recognized: a

Reverberation The sound waves emitted by the source impose the scatters and distribute the energy in all directions, i.e., result in scattering waves. The sum of the scattered waves returned to the receiving point constitutes the reverberation. The impact of polar ice variability is a major contributor in the reverberation of Arctic Ocean. The reverberation environment under Arctic ice is characterized by highly variable (and often large) scatter from the water-ice interface and low-volume scatter from the water column. The reverberation intensity is strongly correlated with the ice type and ice

Polar Acoustics

1337

Polar Acoustics, Fig. 2 Characteristic transmission loss versus range based on numerous measurements from the 1960s (Urick 1983)

roughness; sometimes the level of reverberation caused by Arctic ice is more than 40 dB higher than that of sea surface without sea ice (Marsh 1961). J. R. Brown and A. R. Milne found that the scattering intensity of the covered sea ice region increases with the increase of the frequency and the grazing angle through the analysis of the observation data of two observation sites in the Arctic Ocean at different times of the year (Brown 1964). J. E. Burke and V. I. Twersky expressed the ice ridge as a semicylindrical elliptical rigid body and establish a Burke-Twersky model (Burke and Twersky 1966) that describes the reverberation under the ice in 1966, which is widely referenced and modified in following research. In the 1990s, T. C. Yang and T. J. Hayward conducted research on low-frequency Arctic reverberation at different distances using CEAREX 89 test data from the NorwegianGreenland Sea (Hayward and Yang 1993). For the short-range (less than 3 km) direct ice surface reflection reverberation, it is proved that the measured scattering intensity is consistent with the Burke-Twersky model law at the low frequency (24 ~ 105 Hz) when the grazing angle is less than

20 . For the mid-range (5 km ~ 20 km) mixing and reverberation under the ice surface and the seabed, the vertical array was used to separate the underice surface and the seafloor reverberation, and their degree of agreement with the model was verified respectively. For remote (no more than 200 km) very low frequency (10 Hz ~ 50 Hz) reverberation, an Arctic reverberation model based on a normal wave is established, and the model is verified by measurement data. It is pointed out that the effective reverberation intensity depends on the depth of the sound source in this case. Besides, the scope of the active sonar affected by reverberation can reach 200 km. K. LePage and Sehmidt find that Arctic reverberation has great spatial correlation, and halfwavelength correlation can reach 0.99 or more.

Polar Acoustics Technology After the end of the Cold War, the interest in polar acoustics shifted from underwater surveillance to sensing of the Arctic Ocean and engineering application. Polar acoustics technology refers to the application of polar acoustics in the fields of

P

1338

engineering implementation, environmental monitoring, shipping traffic, etc. 1. Acoustic Ice Thickness Measurement According to different measurement principles, sea ice thickness measurement methods are mainly divided into direct measurement methods and indirect measurement methods. Indirect measurement methods are divided into physical detection methods and satellite remote-sensing methods. Direct measurement methods mainly include sampling method of crushed ice, hole drilling method, and resistance heating method. The direct measurement method is to manually work directly on the ice, remove the ice sample, and measure the ice thickness directly. The method has advantages of high measurement accuracy and reliable data, but it is time-consuming and labor-consuming. It is only suitable for small areas and the thin ice thickness measurement. Satellite remote-sensing uses satellite data for ice thickness measurement. This method can be used for a wide measurement range, but there are measurement errors at the intersection, and data reliability is poor. Physical measurement methods include capacitance method, conductivity method, temperature method, electromagnetic induction method, icefreezing degree method, on-site image measurement method, radar laser ranging method, and sonar measurement method. They can realize automatic monitoring of ice thickness for a long time without destroying the ice layer. In particular, in upward-looking sonar measurement method, the obtained ice thickness data has higher measurement accuracy and reliability and is less affected by external environmental factors. Hudson and Wright tested the mooring fixation method in the Beaufort Sea, and in 1990s, Canadian Institute of Marine Fisheries Research develops Ice Profiling Sonar in order to measure the ice ridge thickness and underwater ice appearance of sea ice. Upward-looking sonar is also installed on a nuclear submarine and observes the thickness and morphological characteristics of ice ridges in the Arctic from beneath the ice

Polar Acoustics

sheet. In 1996, ASL Corporation of Canada developed and commercialized the production of the top sonar. In 2008, it developed a new generation of model IPS5, whose ice thickness measurement accuracy in the vertical dimension reaches the order of centimeters, in the horizontal dimension, reaching the order of meters. 2. Acoustic Communication and Navigation Acoustic communication is a useful method of transmitting information in the ocean, especially in the polar region covered with sea ice, as shown in Fig. 3. During the icing period, it is very difficult for vehicles to surface to communicate and obtain location information because of the uncertainty in the floating and thickness of sea ice. Furthermore, the harsh climate conditions in the Arctic are not suitable for long periods of activity. Acoustics solve this problem because the sound can travel a long distance. H. C. Song reported a successful acoustic information transmission over about 2720 km with a data rate of 2 bits/s (Song et al. 2014). More recently, Woods Hole Oceanographic Institution achieved underwater vehicle communication and navigation up to ranges of 70 ~ 90 km at a data rates 5 ~ 10 bit/s (Freitag et al. 2012). 3. Acoustic Thermometry The idea of using low-frequency pulses transmitted over long distances to measure small changes in average ocean temperature was developed in the 1980s. This technique is called acoustic thermometry. The first attempt to carry out acoustic thermometry in the Arctic was the 1993 international experiment called Transarctic Acoustic Propagation (TAP). By examining the modal structure of the received signals, which is affected by bathymetry, ocean structures, and ice thickness, it was deduced that the Atlantic intermediate layer was intruding further into the Arctic Ocean (Hutt 2012). A follow-on project to TAP, and also a US-Russian collaboration, was the Arctic Climate Observations Using Underwater Sound (ACOUS) experiment in 1998. Since the success of ocean

Polar Acoustics

1339

Polar Acoustics, Fig. 3 Gliders and powered AUVs performing oceanographic work beneath the Arctic ice (Freitag et al. 2012)

acoustic thermometry and large-scale ice thickness measurement, the ACOBAR project has been established as a long-term tomography project by the Nansen Environmental and Remote Sensing Center; the ACOBAR experiment consists of a triangle of acoustic transceivers approximately 200 km from each other with a vertical receiver array in the center.

New Arctic Acoustics With the global warming, the Arctic sea ice is decreasing year by year, which makes the acoustic environment of the Arctic Ocean different from that of the 20th century. Henrik Schmidt points that the changes in the environment of the Beaufort Sea severely deteriorated the tracking performance compared to previous deployments (Schmidt and Schneider 2016), and the reason was associated with a previously observed neutrally buoyant layer of warm Pacific water persistently spreading throughout the Beaufort Sea, which severely alters the acoustic environment with dramatic effects for both long- and short-

range acoustic sensing, communication, and navigation. All kinds of changes require us to reinvest to understand the current polar acoustics.

References Brown JRR (1964) Reverberation under Arctic ice velocity and attenuation of sound have been URING September reverberation recordings. Jasa 601(1964):1–4 Burke JE, Twersky V (1966) Scattering and reflection by elliptically striated surfaces. J Acoust Soc Am 40(4):883–895 Dyer I (1988) Speculations on the origin of low frequency Arctic Ocean noise. In: Kerman BR (ed) Sea surface sound: natural mechanisms of surface generated noise in the ocean. Springer Netherlands, Dordrecht, pp 513–532 Freitag L, Koski P, Morozov A, Singh S, Partan J (2012) Acoustic communications and navigation under Arctic ice. Oceans:1–8 Greening MV, Zakarauskas P (1994a) Pressure ridging spectrum level and a proposed origin of the infrasonic peak in arctic ambient noise spectra. J Acoust Soc Am 95(2):791–797 Greening MV, Zakarauskas P (1994b) Spatial and source level distributions of ice cracking in the Arctic Ocean. J Acoust Soc Am 95(2):783–790 Hayward TJ, Yang TC (1993) Low-frequency Arctic reverberation. I: measurement of under-ice backscattering

P

1340

Polar Communications

strengths from short-range direct-path returns. J Acoust Soc Am 93(5):2517–2523 Hutt D (2012) An overview of Arctic Ocean acoustics. AIP Conf Proc 1495(2012):56–68 Marsh HW (1961) Exact solution of wave scattering by irregular surfaces. J. Acoust. Soc. Am 33(3):330 Schmidt H, Schneider T (2016) Environmentally adaptive autonomy for acoustic communication and navigation in the new Arctic. J. Acoust. Soc. Am 140(4):3408 Song HC, Mikhalevsky PN, Baggeroer AB (2014) Transarctic acoustic telemetry. J Acoust Soc Am 136(4):1491–1494 Urick RJ (1983) Principles of underwater sound, 3rd edn. McGraw-Hill, New York. 423p

Polar Communications Qiang Guo1 and L. F. Chernogor2 1 College of Information and Communication Engineering, Harbin Engineering University, Harbin, China 2 V. N. Karazin Kharkiv National University, Kharkiv, Ukraine

Introduction In the twenty-first century, the Arctic and Antarctic regions, where the rich deposits of minerals have been found, are more and more

extensively being developed by humankind. For example, in the Arctic, gas deposits are estimated at 47.3 trillion m3, oil at 90 billion barrels, and gas condensate at 44 billion barrels. Their effective development is impossible without establishing reliable radio communication links with the Arctic and Antarctic regions. According to the estimation by the European Space Agency, the stream of data in the Arctic region will increase tenfold over 2010–2020 (see Fig. 1). At the same time, the organization of communications in the Arctic region is hindered by the features of this region, the atmospheric and geospace structure, including the upper atmosphere, the ionosphere, and the magnetosphere. The Earth’s magnetic field geometry is such that solar energetic particles penetrate into the polar regions, and the aurora, instabilities, geospace medium heating, a significant (by 1–3 orders of magnitude) increase in the electron density of the lower ionosphere, and other processes operate. All these events determine the instability of the atmosphere-ionosphere-magnetosphere communications links and result in considerable difficulties for organizing communications in the polar regions. The instabilities in communications link significantly increase during major variations in space weather, the so-called geospace storms. As

Mbps 300 250 200 150 100 50 . 2010

2011

2012

2013

2014

North America

2015 Europe

2016

2017

2018

2019

2020

Russia

Polar Communications, Fig. 1 Data rates required for the 75–90 N Arctic region (evaluated by European Space Agency)

Polar Communications

is well-known, the geospace storm is comprised of the magnetic storm, the ionospheric storm, and the electric storm. The most prominent geospace storms in the polar regions occur when the ionospheric parameters and geoelectric fields vary by a factor of a few times to tens of times.

Conventional Communications Communications in the polar regions provide radio waves in the frequency band from VLF (3–30 kHz) to VHF–UHF (30 MHz–3 GHz) when the near-Earth medium is used as a communications link. VLF radio waves can propagate in the earthionosphere waveguide at distances, R, of 1,000–10,000 km. VLF communications are not disrupted even during the most severe geospace storms. The major drawback of VLF communication services is that the construction of large antenna systems with spatial sizes of about 100–1,000 m and high-power (of order of 1 MW) radio transmitters is needed and narrow (about 1 kHz) bandwidths are provided. LF radio waves (30–300 kHz) can be reflected from the lower ionosphere over distances to a few thousands of kilometers. During geospace storms, the absorption of these radio waves drastically increases, and the link path length decreases. To provide stable communication services, large antenna systems with tenths of meters in height and high-power (~0.1–1 MW) transmitters are needed. MF radio waves (300 kHz–3 MHz) can provide a ground-wave signal over distances of 100 km, and the signal reflected from the ionosphere can reach at distances of a few hundreds of km. The MF band has almost the same drawbacks than the LF band has. HF radio waves (3–30 MHz) are particularly suitable for providing communication services in the polar regions. The radio waves in this wave band can travel as the ground wave at distances of no more than 50–100 km and as the ionospheric sky wave up to worldwide distances. When the distance reaches 4,000 kilometers, the HF radio wave can travel with a single reflection from

1341

the ionosphere, while at greater distances, the HF wave can propagate in a waveguide with the walls which are usually made up by the ionospheric E and F layers. This waveguide is termed the interlayer waveguide, and the HF attenuation in this waveguide is significantly lower than on multi-hop links. The HF radio waves are mostly subjected to the variations in space weather. The optimal frequency is given by f opt 0:85 f MUF , where fMUF is the maximum usable frequency. This frequency does not exceeds 3fpmax, where f p max

1 ¼ 2p

rffiffiffiffiffiffiffiffiffiffiffiffiffiffi e2 N max : e0 m

Here fpmax is the plasma frequency, e is the electron charge, m is the electron mass, ε0 is the permittivity of free space, and Nmax is the F-region peak density. Under quiet conditions, the value of Nmax is equal to approximately 1012 m3 in the daytime and about (2–3) 1011 m3 at nighttime, resulting in the diurnal variation of fpmax ≈ 9–4 MHz and of fopt ≈ 23–10 MHz, respectively. During a positive ionospheric storm, the Nmax values can increase by a factor of 2–2.5, resulting in fopt ≈ 35–15 MHz. During a negative ionospheric storm, the fpmax decreases by a factor of 3–4, resulting in fopt ≈ 7–3 MHz. It should be noted that during ionospheric storms, the ionospheric D region electron density (50–90 km altitude) may be increased by a factor of 10–100 and the ionospheric E region electron density by a factor of 2–3. The integral absorption coefficient, K, may be increase by a factor of the same magnitude as given by ð 2pf K¼ kds, c s

where f is the radio wave frequency, c is the speed of light, ds is the radio wave path, s is the element, and k is the absorption coefficient, given by

P

1342

Polar Communications

f 2p n : k¼p  2 2 f 4p f þ n2 Here fp is the plasma frequency, and n is the collision frequency. Usually, 4πf2  n2 and k

f 2p n

4p f 3

Communications Based on Radio Wave Scattering

: 2

It is important thatk Nn/f and K f . The transmitter and receiver antennas are small and relatively simple, and the required transmitter powers are small (~1–10 kW) as well. This is the first advantage of HF radio wave service. The other advantage of HF service is that it permits two-way communications at large distances of 1,000–10,000 km. The major drawback of the HF service is that it is profoundly affected by the state of the ionosphere and the space weather, and consequently, the optimal operating frequency should be adjusted almost continuously during the day and during ionospheric storms. During major storms, the HF service can be lost at all. At frequencies greater than 30 MHz, the communications are possible within the straight lineof-sight horizon. The distance to the radio horizon does not exceeds the value given by 3

Rmax

pffiffiffiffiffiffiffiffi pffiffiffiffiffi pffiffiffiffiffi

2RE h1 þ h2 ,

where RE ≈ 6,400 km is the Earth’s radius, h1 is the transmitter antenna height, and h2 is the receive antenna height. For example, when h1 ¼ h2 ¼ 9 m, we find that Rmax ≈ 21 km. For a service with an aircraft (h2 ≈ 10 km), Rmax ≈ 358 km, and with a low-Earth-orbit satellite (h2 ≈ 400 km), Rmax ≈ 2,260 km. The communications with frequencies greater than 30 MHz are relatively weakly dependent on the state of the ionosphere and space weather, because the relative refractive index of the ionospheric plasma is given by

n¼

1

f 2p

f2

and when f 2  f 2p , it differs from unity slightly. Furthermore, the absorption coefficient k f3 rapidly decreases with increasing radio wave frequency.

!1=2 ,

The VHF (30–300 MHz) radio waves can be scattered by the irregularities of the refractive index in the troposphere and the ionosphere, as well as by meteor trails. Consider them in detail. Tropospheric Scattering. Tropospheric scattering occurs from the irregularities in the refractive index, Δn, of the troposphere. Usually, the rootmean-square (RMS) refractive index fluctuations sn ≈ 104–103, and they do not depend on frequency. Since sn 1, the power of the signal scattered by the tropospheric irregularities is very small. To utilize this effect for radio communication, large aperture (~10 m) antennas and highpower (~10–100 kW) transmitters are needed. Such a service provides radio communication over ~100–1,000 km, while this path incurs 50–120 dB of loss at 100 MHz. The maximum propagation distance can be estimated from the following formula: Rmax ¼ 2

pffiffiffiffiffiffiffiffiffiffiffiffi 2RE ht ,

where ht is the altitude of tropospheric irregularities. For example, for ht ¼ 10–15 km, we have Rmax ≈ 720–880 km. The communication based on the tropospheric scattering suffers from seasonal and climatic factors. The major drawback to this kind of service is multipath interference caused by signal fading. As a result, the bandwidth of such a communications channel is limited. Ionospheric Scattering. Over-the-horizon communications, usually at VHF, occur due to scattering by irregularities in the ionospheric D region. The root-mean-square electron fN ¼ density fluctuations are given by s

1=2 ðDN=N Þ2

102  3  102 , and the RMS refractive index fluctuations are given by

Polar Communications

sn

1343 2 1 fp f: s 2 f2 N

It is important that the scattered power is pro

f2 2 = f 4 . The signal portional to s2 , i.e., f 4 s n

p N

power rapidly decreases with increasing frequency, for example, the signal power decreases by a factor of 100 when the frequency increases about 3 times. In the range of 30–70 MHz frequency, the attenuation varies from 90 dB to 120 dB. The maximum propagation distance can be estimated from the following relation: Rmax ¼ 2

pffiffiffiffiffiffiffiffiffiffiffiffi 2RE hi ,

where hi is the altitude of ionospheric irregularities. For example, hi ≈ 90 km yields Rmax ≈ 2,160 km, and the frequency band does not exceed 6 kHz. Electron density irregularities also occur in the ionospheric E and F regions, where they are elongated along the geomagnetic field lines. Such irregularities provide aspect angle scattering and the maximum propagation distance of Rmax ≈ 4,000 km. Meteor Communication. Meteor communication systems operate in an intermittent mode and utilize only single meteor ionization trails that appear sporadically (not meteor showers or streams). The number of such meteors entering the Earth’s atmosphere per day is estimated to be n0 ≈ 1011, while their flux n ≈ 2 103 km2 s1. Small meteors “burn up” in the height range of hm ≈ 80–120 km and form an ionization trail with 1010–1018 m1 electron density per unit of line length. The initial density per unit of volume is N ≈ 1011–1018 m3. The trails persist for ~0.1–10 s. The time of the SNR exceeding the threshold accounts for only 1–10% of the total running time of the system. Scattering from the meteor trails depends on the aspect angle. The maximum range of the meteor channel is 2,000–2,200 km, the channel losses attain 170 dB, and the channel has an instantaneous data rate of ~100–1,000 bit/s. The meteor channels have moderate information data rates

and require moderate transmitter power (~1–10 kW) and relatively simple antennas with an antenna gain of 15–20 dB. The major drawback of meteor channels is the complexity of the system design. The International Telecommunication Union Recommendation ITU-R F.1113, radio systems employing meteorburst propagation, at https://www.itu.int/dms_ pubrec/itu-r/rec/f/R-REC-F.1113-0-199409-I!! PDF-E.pdf describes the construction of two such systems at a realistic commercial cost.

Terrestrial Relay Links These services can be provided by both conventional and new repeaters. Conventional Repeaters. The system requires ~1–10 m antennas, 20–30 dB antenna gains, and ~1–10 kW transmitters. The maximum propagation distance is given by the relation: Rmax ¼ 2

pffiffiffiffiffiffiffiffiffiffiffiffi 2RE hr ,

where hr is the relay station height. For example, substituting hr ¼ 10 m, we have Rmax ≈ 23 km. The small values of Rmax are the major drawback to the conventional repeaters. New Repeaters. Airships provide a relay station with the height of hr ~ 1 km, and stratosphere balloons stable in space can attain heights of hr ≈ 20–25 km. These platforms can support communications at ranges of 226 km and 1,010–1,130 km, respectively.

Cable Links The Russian Optical Trans-Arctic Cable System, ROTACS, (http://www.polarnetproject.net/) project intends to connect the UK, Russia, China, and Japan with optical cable. In the first stage, six pairs of optical fibers are planned to be laid out. The first phase of work is estimated at about $1 billion. Countries in the Arctic region advanced the Arctic Fibre project to connect the UK, Ireland, Canada, the USA, and Japan.

P

1344

Polar Communications

Canada has built Ivaluk Network to serve the needs of Northern Canadians with an optical cable loop of 8,000 km.

Arctic Communications Satellite Links Satellites are practical for providing communications in the Arctic regions. Moreover, this kind of communication is preferable and advanced. The satellites used for these conditions include geostationary and low-Earth-orbit satellites, as well as satellites in highly elliptical orbit. Consider these opportunities in more detail. Geostationary Satellites. In Alaska and the USA, high-quality video and broadband services are delivered by Intelsat, Telesat, and other providers of communication satellite service, when the satellites are at an angle of 9 over the horizon. In Arctic Canada, broadband services and Internet connections are provided by the Telesat Polar Communications, Table 1 An overview of Iridium services. (Data from Iridium homepage (http://www. iridium.com)) Service Voice Circuit switched data Short burst data OpenPort OpenPort aero L-band high speed Broadcast

Iridium 2.4 kbps 2.4 kbps

Iridium NEXT 2.4 kbps 9.6–64 kbps

low 132 kbps 132 kbps N/A

On demand 128–512 kbps 128–512 kbps 512 kbps up–1.5 Mbps down 64 Mbps

N/A

operator via the AnikF1R, AnikF2R, and AnikF3R satellites. In Norway, communications and broadcasts are delivered via the Thor satellite and, in Russia, via the Express satellite. The major drawback of communications via geostationary satellites is that they become unstable at low angles of the satellites over the horizon. Satellites in Highly Elliptical Orbits (HEO). Such a kind of project does not exist yet. Communications through these satellites lack the advantage that geostationary satellites have. Satellites on high elliptical orbit will be repeatedly immersed in the radiation belt, which can shorten the life span of spacecraft electronics components. Low-Earth-Orbit (LEO) Satellites. The Iridium NEXT constellation operates in the L-band at 2.4–132 kbps data rates (Table 1). Gonets System (Russia) is composed of 12 satellites in 1,400 km orbit at 82.5 orbital inclination. The data rate is 2.4–64 kbps, and the frequency used 200–400 MHz. When completed, the Kosmonet satellite project will consist of 48 satellites. The total cost of this project is $0.3 billion.

New Missions Toward the Arctic New missions are the following: (1) Antarctic Broadband (ABB); (2) Arctic Region Communications Small Satellites (ARCSS); (3) Polar Communications and Weather (PCW); (4) Arktika (A); and (5) CASSIOPE/Cascade (CC) (Table 2).

Polar Communications, Table 2 Proposed satellite communication systems (Birkeland 2014) System ABB ARCS PCW A CC Telenor HEO

Frequency band Ka S, X, UHF TBD, UHF

Capacity TBD 3 Mbps TBD Mobile Gbit Broadband

Con’t coverage No No No? Maybe No Yes

Arctic coverage ? Yes Yes Yes Yes Yes

Polar Materials

1345

References

withstand the effect of the polar region climate without sacrificing other performance properties. Reliability, durability, trouble-free operation, and reparability are the requirements for the application of polar materials under polar region conditions. The exploration of the polar regions is largely determined by the availability of materials that are necessary to create technical devices and facilities and can ensure comfort for people who stay and work in severe climatic conditions.

Baldwin P, Anderson V, Chang R, Svitak A, Williams T, El-Nimri S, Kaul D, Perrine M, Abhyankar K (2018) NASA 26 GHz Polar Subnet in 2020+. In: 2018 SpaceOps Conference, p 2556 Birkeland R (2014) An Overview of Existing and Future Satellite Systems for Arctic communication, Conference: ESA Small Satellites Systems and Services Symposium Project: Coastal and Arctic Maritime Operations and Surveillance, May 2014. https://www.researchgate. net/publication/269389702_An_Overview_of_Existing_ and_Future_Satellite_Systems_for_Arctic_Communi cation. https://doi.org/10.13140/2.1.3762.3367 Bradley PA (1996) Propagation of Radiowaves in the Ionosphere, in Radiowave Propagation, IEE Electromagnetic Wave Series 30, Peter Peregrinus Ltd. for IEE, London, UK Davies K (1990) Ionospheric radio. Peter Peregrims, London Freeman JW (2001) Storms in space. Cambridge University Press, London/New York Gonets Leosat System (2013) Gonets.ru webpage. http:// gonets.ru. Accessed Nov 2013 Goodman JM (2005) Space Weather & Telecommunications (The Springer International Series in Engineering and Computer Science). Springer US Iridium Communications Inc. (2013) Iridium next: Advanced technology. http://www.iridium.com/ About/IridiumNEXT/Technology.aspx. Iridium NEXT: Advanced Technology McNamara L (1991) The ionosphere: communications, surveillance, and direction finding. Krieger Publishing Company, Malabar Schunk RW, Nagy AF (2009) Ionospheres: Physics, Plasma Physics, and Chemistry. Second Edition / – Cambridge University Press, Cambridge, UK, – xii, 628 pp

Polar Engineering Antifreeze ▶ Winterization of Polar Engineering

Polar Materials Zhongwu Zhang and Ye Cui College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin, China

Definition Polar materials always refer to materials used in cold climate zones. Polar materials should

Scientific and Engineering Fundamentals Service Environment of Polar Materials Polar Regions

The polar regions are the regions of the planet that surround its geographical poles (the North and South Poles), lying within the polar circles. These high latitude regions are dominated by polar ice caps: the northern resting on the Arctic Ocean and the southern on the continent of Antarctica. These regions include ice and marine sites with islands and straits and a part of the coast. The polar regions are the last unspoiled natural treasures with huge reserves of minerals and resource on earth. In recent years, polar regions, especially Arctic region, have become regions interesting to the global community due to transportation, geopolitical, military, and raw materialrelated reasons. Today, only a small portion of the polar regions can be developed due to the huge infrastructure costs, the required reliable equipment, and the limitations of polar materials. The ability to explore and develop polar regions depends on the materials necessary to create technical installations and facilities for severe climatic conditions in the polar regions. Developing polar materials has become one of the keys to develop polar regions and utilize the polar region resources (Buznik et al. 2018b). The characteristic features of the polar region are extreme natural and climatic conditions such as long-term low temperatures, significant annual temperature gradients (from 60  C to 40  C),

P

1346

strong winds, high humidity, glaciation and snow buildup, the presence of ice caps covering in the seas, a high solar radiation during the polar day, and a low environmental stability. The simultaneous effects of all the factors mentioned above make the polar climate especially severe and the application of polar materials especially complex and strict. Another important characteristic feature is that the polar region environment is sensitive to anthropogenic impacts. Therefore, industrial centers and densely populated settlements are far from the polar regions; the production and transport infrastructure are weak in polar regions; people, raw materials, and equipment need to be brought from the warm continents. Even small accident in polar regions can have serious consequences for humans and the polar region environment. Hence, there are strict requirements for polar materials: polar materials should retain their functional properties as long as possible. Glaciations and snow buildup lead to additional mechanical loads. Sea water can cause severe corrosion. Moisture provides another negative climatic impact, which initiates metal corrosion and degrades the properties and structure of polymeric composites. Under the polar region conditions, this phenomenon is aggravated by negative temperatures and repeated transitions through the melting point of ice, which accelerates corrosion. The most important is that the ships used in polar regions and the related offshore structures may face risks associated with accidents such as iceberg collisions. Obviously, high-quality polar materials should withstand all the severe climate mentioned above, not solely individually or some of them. Characteristic Features of Polar Materials Cold is the main climatic characteristic feature of the polar regions. Long-term service in polar region low temperatures is the biggest challenge for polar materials. However, the impact of cold is not limited to geographical positions; one can identify many of the more severe cold continental areas. So polar materials always refer to materials used in cold climate zones. And polar materials should withstand the effect of the polar region

Polar Materials

climate without sacrificing other performance properties. The important requirements on polar material are their reliability, durability, troublefree operation, and reparability under field conditions. Therefore, structures used in polar regions are more rigorous, more precise, and more discreet than structures used in warmer regions. Development History of Polar Materials At the initial stages of the exploration and research of polar regions, natural materials (wood, wool, leather, coal, ice, and so on) were the main materials for the production of vessel, clothes, household, and building materials. However, the properties of these natural materials are very limited, which is not enough to further develop and explore the polar regions. Hence, from the nineteenth century, anthropogenic materials have replaced natural materials to become the most used materials for producing transport, household, and products for everyday life in polar regions. Recently, the performance requirements for polar materials increase rapidly with the requirements for exploring, utilizing, and developing polar regions. Today, there are two major ways to develop polar materials. The first is the specialized development of materials, and the second is adaptation of the existing materials, giving them additional performance for effective use in the polar regions (Buznik et al. 2017, 2018a, b). Polar Steels

Steel is the main modern construction material. However, it is the most vulnerable material in the polar regions; the vessels used in polar region waterways and the related offshore structures are exposed to risks of brittle fractures due to accidents such as collisions with icebergs. The brittle fracture of steel in polar environments has caused many serious accidents. Moreover, the steels always manifest frost fracture under low temperatures, leading to the destruction of technical facilities. This phenomenon can be attributed to many factors: external impacts, traits of crystalline phases of iron, the microstructures, the presence of inclusions and textures in steels, etc. (Sych et al. 2017).

Polar Materials

Improving the toughness of steels under lowtemperature conditions and preventing the occurrence of brittle fracture have become the main challenges for conventional steels used as polar materials. At present, the special alloying and thermomechanical processing have been used to solve the technical problem for alleviating the brittle fracture and frost cracking and meet the operation requirements in polar regions. The newly developed steels have already been tested in building pipelines, vessels, and the offshore oil platform. In addition, searches have conducted for techniques that would ensure an optimal combination of functional and economic indicators of cold-resistant steels. The properties of steels should be examined carefully and extensively before choosing the certain steel grade. Carbon Steels Carbon steel is the most commonly used structural material in the world. They are cost-efficient in most applications and have good stiffness, high strength, high durability, and recyclability. Since the ductile-brittle transition temperature of carbon steel is generally between room temperature and 40  C, it must be strictly required for steel grade selection, manufacture, assembly, and inspection, when carbon steel is used in polar regions. In general, the polar carbon steels can be divided into four different groups as normal strength steel, high strength steel, extra high strength steel, and ultrahigh strength steel. The normal strength steels (e.g., P215NL pipe steel and grade E steel and steel EW steel certified by classification societies) have yield strengths up to 235 MPa, which are used in pipelines, offshore, and inland applications. For example, P215NL and grade E steel are tough at the temperature of 40  C, which suggests that these steels can be used in few polar areas. Grade EW steel has the transverse impact test energy up to 40 J at temperature of 40  C, and its weldability was improved. These suggest that it is more suitable for welding applications than the other two kinds of steel. The high strength steels (e.g., pipeline steels L245-L390, 11MnNi5-3, 13MnNi6-3, 12Ni14, X12Ni5) have yield strengths exceeding

1347

235 MPa up to 400 MPa. Their ductile-brittle transition temperatures reach 40  C or below. These steels are used in offshore pipelines, offshore fixed applications, and offshore vessels. 11MnNi5-3 and 13MnNi6-3 could work as offshore pipeline steel at 60  C. The Charpy-V impact energy 12Ni14 and X12Ni5 reach 40 J at 100  C and 120  C, respectively. Pipeline steel L320 and L360 could operate about 30 years as gas main. The extra strength steels (e.g., E500, F420690, X10Ni9 and 26CrMo4-2) have yield strength exceeding 400 MPa up to 700 MPa, and their transition temperatures also reach 40  C or below. Many steels in this group were used in nonredundant structures in polar regions around 60  C (Pavel et al. 2016). The ultrahigh strength steels (e.g., L830, S890QL, S890QL1, and S960QL) have yield strength exceeding 700 MPa, and their transition temperatures reach 40  C or below. The pipeline steel L830 or X120 is standardized with impact energy of above 250 J at 30  C. Polar Alloy Steels Polar alloy steels were also developed for offshore or general inland structural application. Steel 09Г2С (09Mn2Si), steel 10Г2, steel 10Г2С1, and steel 16ГС were developed for operating at pole region environments with temperature as low as 70  C in Russia (Panin et al. 2017). For example, steel 14Г2АФ is a ferrite-pearlite-based high-strength alloy steel with low corrosion resistance. It has yield strength and fracture toughness parameter of Charpy U impact of 540 MPa and 110 J/cm2 at 60  C, respectively. Therefore it is recommended for manufacturing vessels and machinery operated at the temperature range of 50  C to 400  C. High-strength low-alloy steels have good weldability and high yield strength (even over 1000 MPa). For example, steel 18Г2Ф is kind of high-strength low-alloy steel developed by Russian. Its yield strength and fracture toughness parameter of Charpy U impact test could reach 440 MPa and 29 J/cm2 at 70  C, respectively. Therefore, it can work at variable temperatures ranging from 60  C to 450  C.

P

1348

Polar Stainless Steels Polar stainless steels are typically used in applications where good corrosion resistance and low-temperature mechanical properties are obligatory. For example, they are used in cargo tanks, storage tanks, shafts, and pressure vessels, especially the pipelines. Polar stainless steels are often categorized to four different main groups: austenitic, ferritic, austeniticferritic (duplex), and martensitic polar stainless steels. Now, several stainless steels were developed in structures and pipes at low temperatures of polar regions. For example, AISI 304, 304L, 316, 316L, 321, and 347 can be used in offshore applications. Polar Steel Welding The welding of polar steel is the most important factor to determine whether the steels can be used in polar region as modern structures, vessels, pipelines, and offshore (Pavel et al. 2018). Modern structures and vessels require the thick-welded steel plates with yield strengths of 690 MPa or more and exceeding plasticity and toughness. In the recent years, some high-strength cold-resistant steels with high plasticity and satisfactory weldability were developed for using as welded parts in the polar region conditions of 20  C. However, some irreversible structural changes are likely to occur due to the influence of the welding thermal cycle during the welding process, which reduces the cold resistance of the welding heat-affected zone in the heat-affected zone. Therefore, the welding techniques become a key problem for using these high-strength coldresistant steels in polar regions. Research shows that reduction of the carbon content and alloying level could increase the mechanical properties of welding joint and lower the HAZ toughness, which implies that the development of highstrength low-alloy steel with good weldability and low-temperature mechanical properties may be an important way to obtain high-performance polar steels in the future. Testing Methods of Polar Steels Steel and welded constructions can rupture rapidly under effect of low temperatures of polar regions. This phenomenon is due to the existence of the ductilebrittle transition temperature below which the

Polar Materials

steels are brittle. The welding defects and fatigue cracks can occur unexpectedly in the stressconcentrated areas under low loads in polar regions. Therefore, good toughness (impact toughness, fracture toughness, crack arrest toughness, and so on) is a desirable character for polar steels used as structural material. Several test methods were developed to analyze the toughness of metals; most common methods are Charpy-V impact, crack tip opening displacement (CTOD) or crack tip opening angle (CTOA), and Nil-ductility temperature (NDT) or drop-weight test (DT) or drop weight tear test (DWTT). Recently, temperature gradient type ESSO test and temperature gradient type double-tension test are developed for evaluating the brittle crack arrest toughness (Shimada et al. 2017). By far the most common toughness test method is the Charpy-V impact test. As a traditional toughness test method, the Charpy-V impact test is easy to operate and clearly shows the toughness of traditional materials. The Charpy-V impact test uses a pendulum with certain weight and speed to impact a standard sized sample. After the collision, the energy absorbed by the sample is recorded to obtain the notch toughness of the test material. The CTOD test was performed by placing the sample in a three-point bending machine and measuring the opening of the crack after applying the load. It obtains the stress intensity factor at the crack tip by calculating the open displacement near the crack tip and using the displacement extrapolation interpolation method. It has become more important in recent years for the CTOD test to have the ability to use a full-size specimen with a crack under the stress corresponding to the load actually used. The DWTT is a method for evaluating the metallurgical quality and brittle fracture of test sample. It measures the impact energy absorbed in the test sample and observes the characteristics of metallurgical defects, fracture properties, and morphology. It can be used to compare welded parts and test “Nil-ductility temperature.” The “Nil-ductility temperature” is obtained by testing multiple samples at different

Polar Materials

gradually decreasing temperatures until the specimen is broken. Nonferrous Metallic Materials

Beside steels, many other metallic materials are also used in polar regions (Buznik et al. 2018a, b; Buznik and Kablov 2017). Among them, aluminum alloys are widely used in offshore structures for their lightweight and good corrosion resistance even in presence of sea water, such as deck structures. The other advantage of aluminum alloys used in polar region is that they are not suffered from the ductile-brittle transition at low temperature. In general, 5xxx and 6xxx series aluminum alloy, with different tempers, are classified for offshore use. 5xxx series products are valid in forms of sheet, strip, and plate and 6xxx series for extruded products. Other metals and alloys, such as titanium alloys, manganese alloys, and copper-based alloys, were also used for constructions and facilities and structural frames in polar regions. High Molecular Compounds

The great interest in the applications of high molecular compounds in polar region is due to their great chemical diversity and broad spectrum as construction, functional, and auxiliary materials. High molecular materials, including oligomers, thermoplastics, thermosets, elastomers, etc., have been widely applied to produce products used in polar regions, such as glues, sealants, coatings, fillers, anti-icing coatings, hydrophobic polymer and oligomer materials, frost- and fireresistant rubbers, weatherproofs, hydrophobic, and tribological coatings. High molecular materials are also used for low-temperature oil- and gasoline-resistant elastomers, ultrahigh molecular weight polyethylene with a high toughness and crack resistance, and high-performance radiationmodified polytetrafluoroethylene and polymer electrolytes. Low temperatures are harmful for high molecular compounds: polymers and rubbers vitrify, crystallize, and lose their serviceability and destruction (Petrova et al. 2016). Various fillers are being sought actively to increase the cold resistance of materials within acceptable cost.

1349

Ceramics Materials

Ceramics materials, including glasses and cements, have been used to produce the heatresistant glasses (used for alarm systems and navigation systems of rescue vessels), various coatings, porous fire-resistant heat-insulating materials, electrode materials for chemical current supply sources operating at low temperatures, and radiation-resistant ceramic materials. Composites

Metallic, ceramic, and polymeric composite materials have been used to produce structural frames, composite protector hydro- and ice-phobic coatings, high-strength hydrophobic CMs with a low coefficient of friction, heat and noise insulation, and composite paint-and-lacquer systems. Other Materials

In addition to the above materials, natural materials were also developed and used in polar regions (Schulson 2015), such as ice, liquid fuels and low-temperature lubricants, electrochromic and heatproof coatings for glasses, frost-resistant textile materials, etc.

Cross-References ▶ Ice Breaking Vessel ▶ Polar Offshore Engineering

References Buznik VM, Kablov EN (2017) Arctic materials science: current state and prospects. Her Russ Acad Sci 87:397–408 Buznik BM, Burkovskaya NP, Zibareva IV, Cherepanin RN (2018a) On the problem of roadmapping of domestic arctic materials science: Part I. Inorg Mater Appl Res 9:31–40 Buznik BM, Burkovskaya NP, Zibareva IV, Cherepanin RN (2018b) On the problem of roadmapping of domestic arctic materials science: Part II. Inorg Mater Appl Res 9:41–46 Panin SV, Maruschak PO, Vlasov IV, Syromyatnikova AS, Bolshakov AM, Berto F, Prentkovskis O, Ovechkin BB (2017) Effect of operating degradation in Arctic conditions on physical and mechanical properties of 09Mn2Si pipeline steel. In: Proceedings of the 16th

P

1350 international scientific conference reliability and statistics in transportation and communication, pp 597–603 Pavel L, Paul K, Vladislav R, Jukka M (2016) Evaluation of applicability of thick E500 TMCP and F500W QT steel plates for Arctic service. Int J Mech Mater Eng 11:4 Pavel L, Paul K, Elena K, Victor O (2018) Study of the sensitivity of high-strength cold-resistant shipbuilding steels to thermal cycle of arc welding. Int J Mech Mater Eng 13:3 Petrova NN, Portnyagina VV, Mukhin VV, Kyzmina ES (2016) Problems of operation of elastomer materials. In: IV Sino-Russian ASRTU symposium on advanced materials and processing technology, pp 129–134 Schulson EM (2015) Low-speed friction and brittle compressive failure of ice: fundamental processes in ice mechanics. Int Mater Rev 60:451–478 Shimada Y, Inoue T, Kawabata T, Aihara S (2017) Effect of specimen size, applied stress and temperature gradient on brittle crack arrest toughness test. Int J Fract 204:245–260 Sych OV, Khlusova EI, Yashin EA (2017) Scientific and technological principles of development of new coldresistant arc-steels (steels for Arctic applications). In: Kozhevnikov A, Tselikova E (eds) 3rd international scientific and technical conference on scientific and technical progress in ferrous metallurgy – SATPIFM

Polar Merchant Ship ▶ Polar Merchant Vessel

Polar Merchant Vessel Shaocheng Di College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China

Polar Merchant Ship

carrying passengers for hire. This excludes pleasure craft that do not carry passengers for hire. Warships are also excluded. As to the unique natural environment of the polar region, some icebreakers are also belonged to this region.

The Reason for the Emergence of Polar Merchant Ships With the continuous exploration of the polar region, the abundant resources of the polar regions are gradually known by human beings. The arctic alone holds 30% of the world’s undiscovered gas reserves and 13% of the world’s undiscovered oil reserves, according to resource exploration (Gautier et al. 2009). Besides, the arctic is rich in beryllium, indium, niobium, platinum, graphite, rare earth and other minerals. In addition, by using the arctic route, the distance between East Asia, Europe, and North America will be greatly shortened, as shown in Fig. 1. For example, the distance from Rotterdam to Yokohama via the Suez Canal is 20,742.40 km. If it goes through the northeast channel, its distance is only 12,038 km, which is reduced by 40%. Likewise, from Seattle to Rotterdam, the northwest passage is 25% shorter than the panama canal route (Borgerson 2008). Considering the cost of canals, fuel, and so on, a single trip would save nearly a million dollars in transportation costs. More and more people’s yearning for polar scenery has also promoted the development of polar mail ship.

Polar Regulations and Influence of Polar Merchant Vessel Synonyms Polar merchant ship; Polar merchantman; Polar trading vessel

Definition The polar merchant vessel is a boat or ship sailing in the polar region in order to transporting cargo or

It is we all known that the geographical environment of the polar sea is different from that of other sea. Cold water, lots of floating ice, and icebergs make it extremely difficult for polar merchant vessel. Therefore, polar ships often need some unique design and navigation routes. In 2006 IACS has issued a unified requirement for polar Marine, Requirements Concerning Polar Class, which is formulated by the nation

Polar Merchant Vessel

1351

Polar Merchant Vessel, Fig. 1 Illustrations for Northwest and current routes (a) from Rotterdam to Seattle; (b) from Rotterdam to Yokohama (Borgerson 2008)

classification societies jointly. The requirement for the design and construction of the polar ships provides a unified standard on the hull structure, machinery, etc. Using additional signs, PC1 ~ PC7, to show polar classification (IACS 2011). This requirement should be used by major classification societies in their classification codes as a basis of classification for polar ships. However, this requirement only provides indicative requirements, which cannot be used as a guide document for polar ship design. Therefore, the implementation and verification levels of the requirements vary from country to country. International maritime organization (IMO) issued a guide International Code for Ships Operating in Polar Waters in December 2002 (IMO 2013). The main contents include: hull structure, subdivision, stability, electrical equipment, fire safety, rescue device, emergency equipment, environmental protection, and so on. Indeed, it is suitable for vessels in the arctic waters. On the base of the code, ships sailing in Antarctic waters are also supplemented. The Polar Code was adopted in 2014 as a mandatory rule for polar

sailing ships, which took effect on January 1, 2017. In terms of the typical design of ice ships, the ship’s plate and deck which is closed to the outside should avoid cold brittle damage at low temperature. In order to restraining the expansion due to ballast water translating to fresh water ice, ballast tank and some similar structures in polar ship should have the appropriate excess volume (10%). Especially, the piping system (including the air permeability pipe) serving the tank should prevent being frozen.

Polar Merchant Ship Categories Polar merchant vessels can be divided into polar bulk carrier, polar container ship, polar tanker, and polar cruise ship. Based on the special environment of the polar regions, polar tanker accounts for a significant proportion of polar ship. Moreover, Polar cruise vessels are mainly used for sightseeing.

P

1352

Polar Merchant Vessel

Polar Bulk Carrier Bulker carrier is a merchant ship specially designed to transport unpackaged bulk cargo, such as grains, coal, ore, and cement, in its cargo holds. Today’s bulk carriers are specially designed to maximize capacity, safety, efficiency, and durability. Polar bulk carrier should pay attention to the cold resistance of their cargo and their own thermal insulation. Yong Sheng

“Yong Sheng” is a polar bulk carrier of Chinese COSCO shipping company, which is shown in Fig. 2. It started from Tai Cang port in 2013 and reached Rotterdam, the Netherlands, via the arctic route. It is the beginning of the arctic voyages of Chinese merchant ships. From then on, Yong Sheng crossed the arctic route four times from 2014 to 2017 and arrived in Europe from China. During this period, several vessels belonged to Chinese COSCO shipping company undertook more than ten commercial voyages. Main Dimension of Yong Sheng Ship

Classification

GRT/NRT Deadweight (summer)

LR, +100 A1, Ice Class 1A Strengthened for heavy cargoes Equipped with container securing arrangement 14,357/6,985 mt 19,561 mt

Max draft (summer) LOA Breadth Depth to main deck Height above keel Max speed

8.42 m 159.99 m 23.70 m 11.95 m 41.10 m 14.80 kn

Polar Container Ship Container ships are cargo ships that carry all of their loads in truck-size intermodal containers, professionally called containerization. They are a common means of commercial intermodal freight transport and now carry most seagoing nonbulk cargo. So far, polar container ships have not been the mainstream of polar merchant Vessel. In other words, polar container ships do not have enough travel times as much as polar oil tankers and polar bulk carriers. Zapolyarniy, a polar container ship, sailed between Shanghai, China, and Dudinka, Russia, sailing through parts of the northeast passage. Polar Tanker A tanker is a ship designed to transport or store liquids or gases in bulk. Due to the abundant natural gas and oil resources in the polar and circumpolar regions, polar tanker accounts for the largest proportion of polar merchant vessel.

Polar Merchant Vessel, Fig. 2 Yong Sheng ship (http://www.coscol.com.cn)

Polar Merchant Vessel

1353

UIKKU

In 1997, UIKKU became the first merchant ship under non-Soviet flag to navigate the entire Northern Sea Route, which is shown in Fig. 3. In the following year, she took part in Arctic Demonstration and Exploratory Voyage (ARCDEV), a research project funded by the European Union to determine the feasibility of year-around navigation in the Northern Sea Route (Transport Research Knowledge Center 2003). UIKKU accompanied by a Russian nuclear-powered icebreaker NS Rossiya to open the way and a research icebreaker Kapitan Dranitsyn to provide facilities to 70 researchers from different countries carried a cargo of gas condensate from Ob river estuary to Europe. General Characteristics (Russian Maritime Register of Shipping)

Tonnage: Displacement: Length: Beam: Draught: Depth: Ice class: Installed power:

11,290 GT 4,937 NT 16,038 DWT 22,654 tons 164.40 m (539.37 ft) (overall) 22.22 m (72.90 ft) 9.55 m (31.33 ft) 12.00 m (39.37 ft) 1A Super RMRS UL 2 Wärtsilä Vasa 12V32E (2 4,920 kW)

Polar Merchant Vessel, Fig. 3 Towing of tanker UIKKU By icebreaker (From Final public report of the ARCDEV project)

Propulsion: Speed: Capacity:

1 Wärtsilä Vasa 12V22D-HF (1950 kW) Diesel electric propulsion 11.4 MW Azipod unit 17 knots (31 km/h; 20 mph) 8 cargo tanks, 16,215 m3 (98%)

Polar Targeting Design

In order to adapt to arctic navigation, people have made a series of changes to UIKKU. Designers have given UIKKU so much power that tankers usually only need to keep one of the two engines working. In addition, hull structures being similar to icebreakers are given to UIKKU. To reduce the friction between the hull and the ice, the ships were also equipped with an air bubbling system (Nathan et al. 1996). Besides, according to IMCO’s nonmandatory requirements, the hull was designed with double hulls to avoid grounding (Gallin et al. 1981). New Polar Tanker – Double Acting Shuttle Tanker A shuttle tanker is a ship designed for oil transport from an off-shore oil field as an alternative to constructing oil pipelines. Both double acting shuttle tanker’s bow and her stern can break the ice continuously. It implements that the sailing bow forward is suitable for open water, and the sailing stern forward is suitable for ice. It settles an

P

1354

Polar Merchant Vessel

economic problem which results from the difference of sailing environment. We should be clear that making the ice broken is not a simply collision when the double acting shuttle tanker sails stern forward, but using fullrevolving propulsor breaks the ice. In this way, we can collapse the ice and at the same time also rotate the ship stern, broaden the channel. However, it is a slow process.

Polar LNG Carrier An LNG carrier is a tank ship designed for transporting liquefied natural gas. Likewise, the polar LNG tanker is a kind of polar tanker. Because of the polar region and its environs owning huge gas reserves, LNG ship is becoming a super star of polar merchant ships with the launching of the Russia Yamal project.

Timofey Guzhenko

Christophe De Margerie

She is completed at 24 February 2009, as shown in Fig. 4. Her sister ship Vasily Dinkov delivered 2007 is the first double acting shuttle tanker.

Christophe De Margerie, as shown in Fig. 5, made its maiden voyage in mid-august 2017. Its owner is Russia’s shipping company, Sovcomflot. In one voyage, she can carry 172,600 m3 of LNG. The ship is 299 m long, 50 m wide and has a draft of 8.42 m. The ship loaded LNG from Hammerfest Norway on August 6, in the absence of icebreaker’s escort, going through the north pole route, across the Bering strait, arriving in South Korea on August 17th. The voyage set a new record on the shortest route across the arctic. In addition, 14 polar LNG carriers will be built for Russia’s Yamal LNG project. This will help customers in Japan, South Korea, and China to speed up cargo turnover and help develop polar route in the arctic. As far as we know, her ice-class was assigned as Arc7, the highest ice class among existing polar LNG carrier. The ship is able to go through ice area independently until the ice is over 2.1 m thick. It is attribute to her bow and stern are

General Characteristics

Type: Shuttle tanker Tonnage: 49,597 GT 21,075 NT 72,722 DWT Displacement: 93,515 tons Length: 257 m (843 ft) Beam: 34 m (112 ft) Draught: 14.2 m (47 ft) Depth: 21 m (69 ft) Ice class: RMRS Arc6 Installed power: 2 Wärtsilä 16V38B (2 11,600 kW) Wärtsilä 6L38B (4,350 kW) Propulsion: Diesel-electric two ABB Azipod units (2 10 MW) Speed: 15.7 knots (29.1 km/h; 18.1 mph)

Polar Merchant Vessel, Fig. 4 Double acting shuttle tanker Timofey Guzhenko (https://rs-class. org/)

Polar Merchant Vessel

1355

Polar Merchant Vessel, Fig. 5 Polar LNG carrier Christophe De Margerie (http://www.sovcomflot.ru/)

covered with 70 mm steel and can withstand 52  C. Furthermore, strong motivation also guarantees that she can travel in the ice area. The total power of this vessel’s propulsion system is 45 MW. Compared to the world’s first nuclear-powered ice-breaker, Lenin, owning 32.4 MW propulsion system, only accounts for around two thirds of Christophe De Margerie’s power.

Polar Cruise Ship Unlike most polar merchant ships, polar cruise vessel often is designed as low ice-class ship. Some of them only stiffen their bow simply, and some of them are modified by scientific research ships. There are two main reasons lead to this phenomenon. Firstly, polar cruise ships choose to sail in summer usually, and their routes are safer than others’. Moreover, polar environmental groups, especially Antarctic ones, have imposed strict controls on commercial shipping to protect the polar environment. For example, International Association of Antarctica Tour Operators (IAATO) divides Antarctic travel vessels into four categories depended on the number of passengers. The number of tourists is from little to large, followed by YA, C1, C2, and CR, respectively. Carrying the more tourists, received the more restrictions.

Ushuaia

Ushuaia is a cruise ship operated by Argentina’s Antarpply Expeditions, which is shown in Fig. 6. She was built for the National Oceanic and Atmospheric Administration. She served the NOAA for 20 years under the names “Researcher” and “Malcolm Baldrige.” CR- Prinsendam

General characteristics (shown in Fig. 7) Length 427 ft (130 m) Capacity 350 passengers Crew 200 C2-Ocean Diamond

Ocean Diamond is a cruise ship operated by Quark Expeditions, which is shown in Fig. 8. She was previously named Song of Flower. Many kinds of entertainment facilities on board are ready. General Characteristics

Tonnage: 8,282 GRT Length: 124.19 m (407.4 ft) Decks: 5

Displacement: 3,433 DWT Beam: 16.03 m (52.6 ft)

Ice class: Speed: 15.5 1D knots Installed power: 2 Wichmann Engines, 7375 horsepower

P

1356

Polar Merchant Vessel

Polar Merchant Vessel, Fig. 6 Polar cruise ship Ushuaia (https://antarpply.com/)

Polar Merchant Vessel, Fig. 7 Polar cruise ship CR- Prinsendam

Le Lyrial

With the increasing popularity of Antarctic travel in recent years, more and more shipping companies are building polar exploration cruise ships specially. These designed polar cruise ships offer more luxurious facilities on board. This makes Antarctic travel not only an adventure, but also an unparalleled enjoyment elsewhere. Le Lyrial is a new cruise ship built by Fincantieri in Ancona, Italy, as shown in Fig. 9. 50 Let Pobedy

There is a special kind of polar cruise ship whose customers are enthusiastic explorers. These explorers’ pursuing is nature’s pole and the limit

of human will. This kind of polar mail ship’s mission tends to be held by heavy icebreakers. The Arktika grade atomic icebreaker, 50 Let Pobedy, is the most famous ship, which is shown in Fig. 10. Since 1989 the nuclear-powered icebreakers have also been used for tourist purposes carrying passengers to the North Pole. In 2008 Quark Expeditions hired this ship to finish expeditions to the North Pole. In October 2013, the vessel carried the Olympic Flame to the North Pole, in the run-up to the 2014 Winter Olympics. In August 2017, Let Pobedy set a new record for transit time to the North Pole.

Polar Merchant Vessel

1357

Polar Merchant Vessel, Fig. 8 Polar cruise ship Prinsendam and Ocean Diamond (http://www.sohu. com/a/192993268_606811)

Polar Merchant Vessel, Fig. 9 Polar cruise ship Le Lyrial (https://us.ponant. com)

P

Polar Merchant Vessel, Fig. 10 Polar cruise ship Let Pobedy (https://www. sohu.com/a/107182071_ 383632)

1358

Polar Merchantman

Main Characteristics

Tonnage: 23,439 GT 3,505 Displacement: DWT 25,168 tons Length: Beam: 30 m Draught: 11 m 159.6 m (98 ft) (36 ft) (524 ft) Depth: 17.2 m Endurance: Crew: 189 (56 ft) 7.5 months Installed power: Two OK-900A nuclear reactors (2 171 MW) Two steam turbo generators (2 27.6 MW) Speed: 18.6 knots (34.4 km/h; 21.4 mph) (maximum)

Polar Offshore Engineering Shoujun Wang CIMC Raffles Offshore Ltd, Yantai, China

Synonyms Floating production storage and offloading (FPSO); Health, safety, and environmental management system (HSE); Mobile offshore drilling unit (MODU); Semisubmersible drilling and production rig (SSDP); The Global Maritime Distress and Safety System (GMDSS)

Cross-References Definition ▶ Ice Breaking Vessel ▶ Navigation of Polar Vessel ▶ Special Marine Vehicle

Reference Borgerson SG (2008) The economic and security implications of global warming. Foreign Aff 2:63–77 Gallin C et al (1981) Ships and their propulsion systems: developments in power transmission. Lohmann & Stolterfoht GmbH, Witten, West Germany Gautier DL et al (2009) Assessment of undiscovered oil and gas in the arctic. Science 324(5931):1175–1179 IACS (2011) Requirements concerning polar class. Part 1, p 1. IMO (2013) International code for ships operating in polar waters Transport Research Knowledge center (2003) Final public report of the ARCDEV project. European Commission, Transport RTD Programme, Brussels. Nathan DM, et al (1996). Development and results of a northern sea route transit model (pp 15–17). Cold Regions Research and Engineering Laboratory (CRREL).

Polar offshore engineering refers to the equipment and technology to carry out scientific investigation, commercial navigation, oil and gas resources development, and tourism and leisure activities in polar regions. It is an important carrier to understand, develop, and utilize polar regions. At present, the international polar equipment is mainly divided into polar scientific equipment, polar ship equipment, polar resource development equipment, and so on.

Introduction In general, the polar offshore engineering is such kind of engineering operated in the Arctic including exploration, development, and utilization of resources in the polar ice area, as well as the detection, protection, or recovery of the polar ocean environment.

The Significance of the Polar Offshore Engineering Development

Polar Merchantman ▶ Polar Merchant Vessel

The arctic region is rich in oil, gas, minerals, and fishery resources. With global warming and the arctic glacier melting, the arctic route has started to become the most efficient energy and materials

Polar Offshore Engineering

channel which connects Europe, Asia, and America. Because polar ocean environment is unique and fragile, environment protection of the polar ocean is significant for the whole human beings. However, human activities, such as commercial activities, scientific investigation, exploitation of resources, adventure tourism, and fishing in the Arctic which is a remote area with harsh climate (low temperature, strong wind, huge waves, floating ice, etc.) and fragile environment, rely on economical, safe, and environmental polar offshore engineering equipment which are suitable for the polar environment. The polar offshore engineering equipment are important tools and platform for us to explore, understand, protect, and exploit the polar region. The polar offshore engineering is an important subject that studies and solves the key technologies involved in the whole life cycle of research, design, construction, operation, and discarding of the polar offshore engineering equipment.

Key Technologies of Polar Offshore Engineering • The Environment and Load of Ice in Polar Region In extreme environment, the impact of ice floe on the structure of the polar marine equipment is significant. The perennial floating ice will cause continuous and periodic extrusion and influence on the structure of the offshore platform. The influence will cause great ice load and possibly form intense ice exciting vibration. How to confirm the proper design ice load is a challenging technical problem. On the one hand, the work experience of the marine engineering in the polar environment is limited. On the other hand, the interaction between ice and the platform is complex, as well as the physical mechanism of the ice breakage. In order to meet the customer’s demand of ice load forecasting for marine equipment,

1359

ABS has explored a series of new methods for numerical simulation of ice load by cooperation with universities and enterprises in recent years. For example, they use the particle-in-cell method to predict the ice load of the dispersed floating ice on the sea structure, the discrete element (DEM) method to explore the consequences of the ice load produced by the whole ice floe on the sea structure, and the traditional finite element (FEA) method to simulate the ice load with the special physical properties of the ice. • Cold and Ice Prevention of Mechanical Systems, Electrical Systems, and Equipment Based on the particularity of the low temperature of the polar environment and the influence of different temperature on the equipment and the function of the system at low temperature, the design and use requirements of the core equipment and system at different temperature grades are selected according to the temperature grade of the low-temperature environment. According to the low-temperature conditions of the polar regions, the reasons for the formation of the platform ice in the lowtemperature environment, the antifreezing and protection of the equipment in the open area, the indoor antifreeze, and the deicing of the platform are studied to ensure the safety of the polar operating platform and the operation of the equipment. • Development and Application of LowTemperature Materials Low temperature is another major challenge for polar offshore operations. Extreme low temperature will not only test the physical condition of the staff on the marine equipment but also have a great impact on the structure, equipment, and materials of the marine equipment. As we acknowledge, winter of the Arctic region usually starts from November to April next year. The average temperature in January is 20  C to 40 C, and the average temperature in the warmest month is only 8  C in August. The toughness of ordinary materials is decreased in the low-temperature environment,

P

1360

and the possibility of brittle failure is greatly increased. The brittle failure is difficult to find out in the early stage, so it is more likely to cause serious consequences, especially in the extreme low-temperature sea conditions of the polar region. The safety problems such as material fracture, pipe and valve plugging, control system failure, and so on should be paid more attention. Therefore, research and development of low-temperature-resistant materials will become the focus of future development. • Communication and Navigation Technology in Polar Regions The global maritime distress and safety system (GMDSS) has been listed as a special A4 sea area because the polar regions cannot be actively covered by INMARSART’s satellites due to its far distance. In addition, the electromagnetic environment of the polar region is more complex than that of the Earth’s magnetic field. Moreover, the development of polar resources depends on the development of underwater communication under ice, which is also a key technology for polar marine engineering equipment. • Ocean Environmental Protection, Monitoring Technology, and Standards in Polar Region The problem of polar environmental protection is a serious problem. In order to protect the fragile ecological environment in the polar region and reduce the chain reaction caused by the development of the polar ocean as far as possible, the International Maritime Organization and other organizations have established the “polar rules” and formally entered into force in January 1, 2017. In spite of this, some scholars believe that the existing pollution prevention measures in the rules are not sufficient to protect the special ecological environment of the polar region. In order to further improve the pollution prevention measures of the rules, the specific provisions and proposals are deeply analyzed with the method of fish bone map analysis and comparative analysis, and the corresponding revisions are put forward suggestions on this basis.

Polar Offshore Engineering

Main Equipment of Polar Offshore Engineering In the polar, the temperature is very low, and the climatic condition is very poor; polar offshore engineering development is facing great challenges. The main offshore engineering equipment currently operating in the polar field includes drilling platforms, FPSOs, drilling vessels, supply vessels, subsea production facilities, and so on. 1. Polar Icebreaker At present, the countries with polar icebreakers in the world are mainly distributed in the near polar region, including Russia, Finland, Canada, the United States, China, and so on. Among them, Russia is the country with the most polar icebreakers. • “NORTH” Level Nuclear-Powered Icebreaker (22220 Type) For the icebreaker as shown in Fig. 1, the length is 170.3 m, the width is 34 m, and the draft is 10.5 m. It is equipped with two new generations of RTM-200 nuclear reactors. Each reactor has a power of 170 MW and can break 3 m of ice. The icebreaker joined the Russian nuclear fleet in December 2017. It can travel in the shallow waters of the Arctic Ocean or in the deep waters and can guarantee the passage of ships with a load of 100,000 tons. 2. Polar Drilling Equipment At present, there are relatively few drilling platforms specially aimed at the polar operations; those that have been put into use are from Norway and Russia, and some of the platforms are made in China. The details are as follows in Fig. 2: • CS50 CS50 is a semisubmersible rig which is registered in Russian Maritime Register of Shipping. For the operation areas in the Barents Sea and in the Kara Sea, drift ice on the sea may occasionally occur. The SMODU shall be designed to operate in occasional first-year drifting thin ice. However, the SMODU shall not have any iceclass notation. The length of pontoon

Polar Offshore Engineering

1361

Polar Offshore Engineering, Fig. 1 “50th anniversary of victory.” (Image from the network: http://www.sohu. com/a/190672530_ 99968045)

Polar Offshore Engineering, Fig. 2 Russian offshore – CS50. (Courtesy of Yantai CIMC Raffles Offshore Ltd)

P

is 118.56 m. The breadth of pontoon is 17.20 m. The spacing of pontoon is 58.00 m. The length of deck is 84.48 m. The breadth of deck is 72.72 m. • North Dragon GM4D North dragon is a semisubmersible drilling rig (the unit) built by YANTAI CIMC Raffles. The rig is equipped and suitable for year-round operations worldwide, inclusive operation on Norwegian Continental Shelf (NCS). Therefore, the design process and

the technical facilities of the unit shall comply with relevant Norwegian shelf rules (PSA Regulation). The pontoon length of the rig is 106.75 m. The breadth of pontoons is 16.20 m. The length of deck is 88.15 m. The breadth of deck is 73.10 m. The height from the bottom of pontoon to double bottom of deck is 42 m, as shown in Fig. 3. • Cat-I Polar Drilling Ship Norwegian Inocean’s Cat-I drilling ship concept design for Statoil, based on

1362

Polar Offshore Engineering

Polar Offshore Engineering, Fig. 3 GM4D – North Dragon. (Courtesy of Yantai CIMC Raffles Offshore Ltd)

Polar Offshore Engineering, Fig. 4 Cat-I Polar Drilling Ship. (Image from the network: http:// www.offshorelm.com/cn/)

its INO-80 drilling ship, added coldresistant devices, etc., which is designed to be suitable for the work in the polar area, which minimizes the impact on the environment and can maximize the concern of the health, safety, and environmental management system (HSE),as shown in Fig. 4.

The ship length is 232 m, the width is 40 m, and the depth is 19 m. The working displacement is 89,800 tons, and the effective load is 22,400 tons. The hull of the ship is reinforced for passing through the ice zone. It can resist the 16-m ice ridge when it is positioned by dynamics and can resist the 8-m underwater ice when anchoring.

Polar Offshore Engineering

1363

Polar Offshore Engineering, Fig. 5 “Sevan 1000” FPSO平 (https://www. eniday.com/en/technology_ en/goliat-norway-offshoreoil-production/)

• “Sevan 1000” FPSO The “Sevan 1000” FPSO was designed by Sevan Marine in 2013. The FPSO is specifically designed for Eni’s Goliat oil field in the Barents Sea in the northern Arctic of northern Norway. The climate is cold, and there is a need for better performance FPSO. The equipment was built by Hyundai Ulsan Shipyard in Korea and completed in 2015, as shown in Fig. 5. Compared with conventional ship types, the cylindrical structure can better withstand the ice drift pressure in different drift directions while avoiding the drift ice floes causing damage to the semisubmersible hull. The cylindrical platform lower space can be used to store more oil than a typical platform unit.

Polar Offshore Engineering Development Trend At present, most countries are actively participated in the establishment of international polar

rules and accelerate the study of polar rules and related supporting equipment. Independent research and development of heavy icebreakers, polar drilling equipment, polar scientific research equipment, polar expedition travel equipment, and related technologies to meet the strategic needs of polar seas and the construction of ice pool laboratory, lowtemperature material laboratory, low-temperature electromechanical system verification experiment, the laboratory verification conditions, and the actual ship verification system are the key development directions of the major base equipment strength countries. In addition, we should energetically cultivate the experienced polar ship handling and management personnel, realize the safe and reliable operation of the equipment in the polar sea area, fully verify the guidelines for the operation of the polar navigation, and continue to improve. At the same time, we should speed up the development of meteorological and insurance services in our Arctic waterway so that the polar region can truly become a “treasure trough” and a “golden waterway.”

P

1364

Polar Propulsion

References Sun Q, Ji G, Wang H et al (2012) Status and development trend of polar drilling equipment. Pet Drill Technol 6: 43–46

Polar Propulsion Chao Wang Harbin Engineering University, Harbin, China

more complicated is the propeller will have a great chance to be in contact with the ice body directly during the ship navigation in the ice area, which makes the propeller suffer ice load directly. This will bring new challenges to the strength verification and the design work of the propeller. Therefore, polar propulsion is not simply an extension of a single discipline. It is a comprehensive science with direct value of engineering application. At present, the research focus of polar propulsion mainly contains the measurement and prediction work of propeller load, the propeller strength verification, and the design work.

Nomenclature V n D r t fr F M Fx Fy Fz Mx My Mz EAR Z Hice Sice Fb Ff αA

Velocity of ship Propeller rotational speed Propeller diameter Radius of the section Time Pitch angle of the section Force Moment Force in the direction of x-axis Force in the direction of y-axis Force in the direction of z-axis Moment in the direction of x-axis Moment in the direction of y-axis Moment in the direction of z-axis Disc area ratio Amount of blades Ice thickness Ice intensity index Maximum backward bending load Maximum forward bending load Apparent angle of attack for the blade section

Introduction Ice-going vessels operate in the ice conditions that present various challenges to the propulsion system performance. Compared with conventional propulsion, the focus and difficulty of polar propulsion are that the conventional hydrodynamic performance, noise, cavitation, and excitation force of the propeller become more complicated due to the addition of ice. What is

Polar Propulsion Requirements and Selection Icebreakers are typically meant to operate in more severe ice conditions than normal ice-going vessels, which means that strength and thrust requirements for the propulsion system need even more special consideration. Operative situations that require good maneuverability include assisting other ships, making ships free from ice, changing direction (astern), operating in narrow ports, and breaking out of channels. In addition to the raw power, some of these operations require precision and good controllability of both bow and stern of the vessel at various speeds. If the icebreaker is specified to have dynamic positioning capabilities, requirements for propulsion system are even more difficult to be satisfied with traditional shaftline and rudder arrangements. Redundancy requirements of higher DP classes result in a need of multiple transversal or azimuthing thrusters at both ends of the ship. In such cases, azimuthing thruster propulsion is highly efficient as it can be used to reduce the total number of the thrusters. The axis of the Azipod propeller is vertical axis, and the propeller can rotate 360 around the axis, and it can obtain the maximum thrust in any direction. It can make the ship rotate in place, move laterally, retreat swiftly, and perform special operations such as steering in the low-speed range. Azipod propeller is divided into the Z-Azipod propeller and podded propulsion system. The structures of the two

Polar Propulsion

propellers are different, but their hydrodynamic performance is similar. For the current widely favored bi-directional dynamic icebreaking, selecting the Azipod propulsion would bring too many benefits. The azimuth thruster eliminates the structure of rudder, tail, and stern tube. It also would simplify the ship stern shape and reduce hull resistance. Besides, it would not be neglected that the maneuverability of polar ship would be outstanding by using Azipod propeller. However, it would be not neglected that adjustable-pitch propellers would be another good choice for polar propulsion. Almost all of the propulsion of icebreakers built and rebuilt in the last two decades apply adjustable-pitch propellers or azimuth thrusters (including Rolls-Royce propellers, Azipod propellers, Schottel propellers, and Steerprop azimuth propellers). Adjustablepitch propellers can use the operating mechanism in the hub to rotate the blades and change the pitch distribution of the blades, which will help to make the main engine power being fully absorbed under various operating conditions. It can not only improve the propeller performance but also reduce fuel consumption and improve economic efficiency. One of the advantages of adjustable-pitch propellers in the ice area is that they could produce more great thrust. This point is of great significance in the current situation of high energy costs. In addition, the effect of free ice in the propeller wake can be eliminated by adjusting the pitch. However, as the design of the propulsion system for the vessels in ice areas, the adjustable-pitch propeller and the Azipod propulsion device both have their own advantages and disadvantages. A new idea that the propulsion device is a Z-type transmission propulsion system has additional conduit with adjustable blades. The advantage is that the conduit has a protective effect on both the blade and the hub and improves the reliability of the propeller. This is particularly important for special propellers that are difficult to maintain after being damaged. The adjustable pitch and the overall rotation of the propeller around the shaft can greatly improve maneuverability of the vessels in ice areas and the efficiency of icebreaking. Adjustable-pitch blades can not

1365

Polar Propulsion, Fig. 1 Azipod propeller and ducted propeller. (Referenced website: http://www.engineer ingsociety.co.uk/pod.html)

only increase the propulsion efficiency in open water areas and the ability to break thick ice but also increase the thrust of the blades during icebreaking operations. The adjustable-pitch propellers and the Azipod propulsion system have been the research direction of icebreakers’ propulsion devices in recent years. From the side, this data statistic also verifies the applicability and rationality of the application of adjustable-pitch propellers and Azipod propulsion system to the icebreaker. Figure 1 shows the Azipod propeller and ducted propeller.

Propeller Load The polar propeller would be subjected to the following three types of loads: inseparable hydrodynamic load, separable hydrodynamic load, and ice load. Separable hydrodynamic load refers to the hydrodynamic load in open water conditions. Inseparable hydrodynamic load refers to the hydrodynamic load considering the influence of ice on the disturbance of the flow field, generally including the blocking effect, proximity effect, and cavitation effect. The ice load is caused by direct physical contact between ice and propeller blade and can generally be divided into two kinds: ice milling load and ice impact load. The division is based on the contact model and the contacting ice block size.

P

1366

Hydrodynamic Load At present, researchers study hydrodynamic loads mainly through the model tests and numerical predictions. People choose the model test as the main test style, and this is because compared with the full-scale test, model test has the advantages of less finical and labor cost as well as less demand for experimental conditions. And the shortcomings of model test are the uncertainty of similarity law between model test and real working condition. Besides, the selection of sea ice material in the model test is also the key to the success of the test. At present, there are frozen ice models as well as nonfrozen sea ice models made from other materials such as nonfrozen breakable synthetic materials. Many scholars around the world have carried out research work on the prediction of propeller hydrodynamic load under ice loading. Among them, Yamaguchi (1993) proposed a lifting surface method to predict the propeller performance considering the interference of flow from ice. Bose (1996) used a three-dimensional unsteady surface element method to predict the performance of a propeller under the conditions of blocking flow. Doucet et al. (1998) predicted and analyzed the fluctuation of axial force of several large skew ice class propellers with the help of panel method PROPELLA. Liu Pengfei et al. (2002) simulated blocking flow conditions with three different ice shapes using the panel method program PROPELLER. Numerical results show that the blade load during the blockage is close to

Polar Propulsion

the experimental results. On this basis, they have made a series of further studies on the hydrodynamic load prediction of propeller surface under the interaction between ice and flow in the following years. They improved the Kutta conditions of the unsteady program and carried out the design of heavy load ice class propeller based on improved panel method (2010). Previous researches on the inseparable hydrodynamic load were mostly based on potential flow theory. Therefore, the fluid viscous effects and boundary layer problems on ice and propeller could not be analyzed. In fact, these factors would show great influence on the performance of propeller. Wang (2013–2018) used the viscous flow theory and CFD overlap grid technology to numerically predict the propeller hydrodynamic performance and induced excitation force during the ice-propeller interaction process and developed the numerical prediction method of the induced excitation force and cavitation excitation force under ice blocking conditions and ice progressive conditions (Fig. 2). Polar propellers are generally under heavy load conditions during icebreaking. It is difficult to avoid cavitation on the surface of the propeller, and the phenomenon of cavitation tends to aggravate the vibration and noise of the propeller, which in turn affects the hydrodynamic performance and strength of the propeller. The propeller-ice-flow interaction process is very complex. In order to simulate the ice-propeller milling and impact conditions, a large number of model tests have been carried out in the ice tank.

Polar Propulsion, Fig. 2 Propeller-ice milling process in cavitation tunnel (Wu et al. 2018)

Polar Propulsion

1367

The difference between the two is not very clear. The load has often been classified as a milling load if the contact lasts more than one revolution, which means the same blade hits the ice block more than twice. In this work, the contact is always considered to be of the milling type when the leading edge of the blade comes into contact with ice, even if the ice block is small and the duration is not enough for a blade to pass. If the blade and ice block velocity geometry is such that the block hits the blade at the back or face side, without leading edge contact, the contact load is classified as an impact load. According to the propeller-ice contact model proposed by Kinnunen (2015), the angle of attack is accordingly one of the main parameters in contact load calculations (Fig. 3). The contact geometry between an ice block and the blade back side depends on the angle of attack as shown in Fig. 5. It is, however, not well-known in practice, since the actual wake factor at the disk level in ice conditions is not known. The propeller can accelerate the ice block before contact, or the ice block can be supported by other ice blocks. Therefore, an apparent angle of attack is used to indicate the contact geometry in this work, assuming the ice block enters into contact at the ship speed, Vs, as shown in Fig. 4. αAis the apparent angle of attack for the blade section, Vs is the ship speed, n is the propeller speed, r is the radius of the section, βr is the angle of advance of the section, fr is the pitch angle of the section. At present, the research on the ice load is mainly obtained by numerical prediction and

However, due to the fact that atmospheric pressure cannot be scaled in the ice pool, the determination of the hydrodynamic load in the ice tank is often performed under the assumption that there is no cavitation on the propeller surface. In order to study the problem of cavitation in ice-propeller interactions, Lindroos and Björkestam (1986) simulated the propeller cavitation under the icepropeller interaction in a cavitation tank for the first time. They placed a flat plate in front of the propeller to induce cavitation. The results showed that the blocking flow will make the propeller vibration and cavitation more serious, which in turn will increase the thrust and torque of the propeller. His study pointed out the importance of the study of the cavitation phenomenon. Sampson (2007) conducted propeller cavitation model tests in Emerson’s cavitation tunnel during the period. The results of the study showed that the cavitation during propeller-ice interaction has a great influence on the strength and performance of the propeller. Cavitation will influence the thrust and torque of the propeller, causing severe vibration and noise, and cause fatigue damage to the propeller blade. Ice Load The ice load is caused by the direct contact between ice and propeller. It accounts for the most important part of the total load on the propeller. The study shows that the ice load is more than one order of magnitude larger than the hydrodynamic load. The contact loads are usually separated into milling-type or impact-type loads.

Polar Propulsion, Fig. 3 Contact length between ice and back side of a blade section (Soininen 1998)

Advance direction Contact length at the back side

Angle of attack line αA

de

Bla

φr

ion ect

s

ide

es

c Fa

βr 2πrn

Vs

Groove due to previous blade Rotation direction

P

1368

Polar Propulsion

Polar Propulsion, Fig. 4 Propeller-ice contact model established by PD theory

Material particles Direction of propeller rotation Y

The definition of the axes

Leading edge

Blade

model test. Sampson carried out a series of ice cutting tests in air test platform and measured the ice load of propeller under ice cutting condition separately. With the development of computing ability, the use of commercial software or self-programming to predict blade ice load has become a mainstream. Compared with model tests, numerical prediction has the advantages of simple calculation, free working conditions, and low investment. However, how to simulate ice material and the fracture process of ice materials during milling process has become the main constraint to the application of numerical prediction. Among them, Hu and Xia (2013) built the propeller-ice contact model based on the ANSYS/ LS-DYNA platform. The sea ice was simulated by SPH method. And the finite element method is used to solve the structural deformation of the blade under ice load. In the same year, the structural dynamic response of propeller blade under different milling areas, advance speeds, and collision angles were studied and analyzed through this numerical model. To handle a large number of discontinuous problems happening in the icepropeller milling process, Ye et al. (2017) introduced meshless method peridynamics and established ice-propeller numerical model. He carried out many prediction calculations to ice impact conditions and ice milling conditions and obtained the variation regularity of the blade ice load with external conditions, as shown in the following picture.

Mixing Load The ice-water mixing load of propeller in ice areas has always been the focus and difficulty in the research. At present, the most effective research methods are model test measurements. Among them, Wang et al. (2005) carried out model test of Azipod propeller milling ice in IOT’s tank and obtained valuable data of the mixing loads as Fig. 6 shows. These graphs except for the carriage speed are plotted over a 1-s interval, the 65th to 66th seconds. In the time series records for the forces and moment, five peaks can be seen because the propeller rotational speed was 5 rps. The carriage speed for the duration of the 65th and 66th seconds was 0.5 m/s. Wang et al. (2007) installed a 6-degree-of-freedom mechanical sensing device at the root of the main blade and successfully measured the ice-fluid mixed load of the blade. There are no well-developed numerical prediction due to the complexity mechanism of fluid-solid coupling. Wang et al. (2017) try to establish the numerical model with PD-FEM-SPH coupling method, but the meshless method makes the calculations work too large being performed. So establishing a numerical method to this kind of problem would be very innovative and of engineering practicality.

Polar Propulsion Strength The strength of polar propulsion is very essential. In order to check the propeller strength more

250

S

65.6

S

66.0

15

20

25

65.0

65.2

65.2 S

65.6

65.4 S

65.6

BLADE My

65.4

BLADE Fy

65.8

65.8

66.0

66.0

Polar Propulsion, Fig. 5 Six degrees of loads measured in model test conducted in IOT ice pool (Wang et al. 2005)

65.0

–50

0 65.8

66.0

–0

65.6

65.8

5

65.4

BLADE Mx

65.4

–5

65.2

65.2

10

65.0

65.0

0

50

100

150

200

250

–10

–15

–20

–25

–50

0

50

100

150

BLADE Fx

N Nm

N

Nm

N Nm

200

0

5

10

15

20

25

65.0

65.0

–50

0

50

100

150

200

250

65.2

65.2

65.4

65.6 S

65.8

S

65.6

65.8

BLADE Mz

65.4

BLADE Fz

66.0

66.0

Polar Propulsion 1369

P

1370

Polar Propulsion

Fb ¼ 27Sice ðnDÞ0:7


0:3 EAR D2 kN Z

ð1Þ

D  Dlimit ,
0:3 EAR Fb ¼ 23Sice ðnDÞ H 1:4 ice  D kN ð2Þ Z 0:7

Dlimit ¼ 0:85  H 1:4 ice

ð3Þ

Polar Propulsion, Fig. 6 Propeller blade structural damaged by ice loads. (Referenced source: DNV Classification Notes No. 51.1)

Ff is defined as the maximum forward bending load on the blade during the ship life cycle:

effectively, many classification societies have formulated special standards for the polar propeller strength and add them into the ice class rules separately. The International Association of Classification Societies (IACS) had collated and arranged the existing regulations to ensure the safe navigation of ships in the ice areas and formulated the IACS ice grade specification in 2008. At present, most of the ice class specifications around the world are very similar to the specifications put forward by IACS. The specification does not only contain the demand for the strength checking under ice load but also provide the requirements for the material properties of propeller. The load given in the IACS ice class rules is only applicable to the propeller, also defined as the maximum load that the propeller is expected to sustain during the life cycle. The load given should be recommended as the total load including hydrodynamic load and ice load. For conventional propeller blades, the design load calculation method introduced by the IACS specification is given by Eq. 1 through Eq. 6. Fb is defined as the maximum backward bending load on the blade during the ship life cycle, D is the propeller diameter, n is the propeller speed, EAR is the disc area ratio, Z is the number of blades, Hice is the ice thickness, Dlimit is the ice thickness index, and Sice is the ice intensity index:

D < Dlimit ,

D < Dlimit

 F f ¼ 250

EAR ½D2 kN Z

ð4Þ

D  Dlimit , !  1 EAR ½D kN F f ¼ 500 Hice Z 1  Dd Dlimit ¼



2D  H ice Dd

ð5Þ

ð6Þ

Polar Propulsion Design Due to the special working environment of the polar ship, it is necessary to consider the influence of the environment, low temperature, and sea ice on the propulsion system. Therefore, the design of the polar propulsion system is different from the conventional propulsion system. The propulsion performance in ice conditions and open water conditions should be considered for the design work. Therefore, it is necessary to perform proper performance analysis under different navigation conditions during the propeller design process. In general, it is essential to determine whether the design of the blades meets the strength requirements according to the ice class rules. Due to the special requirements on strength, the blade section thickness of the ice class

Polar Research and Supply Vessel

propeller will be slightly thicker than that of the conventional propellers. In addition, the trailing edge of the propeller will become blunt in the rules for the radius of the guide circle. For such kind of propeller with a blunt trailing edge, the special blade section shape can cause a large pressure drag, resulting in a decrease in the propulsion efficiency. Usually, the propulsion efficiency of polar ship would be reduced by about 6% compared to a conventional propeller. The too low ambient temperature of the polar propulsion system determines the special design requirements of the main engine, ventilation system, and cooling water system. Thermal insulation measures for these systems need to be taken into account in the design to prevent the low-temperature environment from affecting its normal operation. In order to ensure that the polar ship can navigate in some areas where the noise level is limited, the designed propeller must also be optimized for radiated noise. Of course the propeller-ice contacting behavior could not be ignored; the shape of the blade must be specially designed so that the blade can effectively mill sea ice. The design of the ice class propeller must also be coordinated with the rational design of the hull lines to reduce the amount of sea ice flowing to the propeller. This would be helpful to avoid the blocking effect, noise, and cavitation effect.

Cross-References ▶ Ice Breaking Vessel ▶ Ice Tank Test

References Bose N (1996) Ice blocked propeller performance predictions using a panel method. Trans R Inst Nav Architects 138:213–226 Doucet J, Liu P, Bose N, et al (1998) Numerical prediction of ice-induced loads on ice-class screw propellers using a synthesized contact/hydrodynamic code. Ocean Engineering Research Centre Report No. OERC1998–004 Hu ZKG, Xia PP (2013) Dynamic response analysis of the collision between ice and propeller at high speed. In: Proceedings of the Society for Underwater

1371 Technology Technical Conference (SUTTC2013). Society of Underwater Technology, China Branch, China Ship Scientific Research Center, Shanghai, pp 72–76 Kinnunen A, Lämsä V, Koskinen P, et al (2015) Marine propeller-ice interaction simulation and blade flexibility effect on contact load. In: Port and Ocean Engineering under Arctic Conditions Poac Lindroos H, Björkestam H (1986) Hydrodynamic loads developed during ice-clogging of a propeller nozzle and means to prevent the clogging. Proc Polartech 86:1061–1092 Liu P, Bose N, Colbourne B (2002) A Broyden numerical Kutta condition for an unsteady panel method. Int Shipbuild Prog 49(4):263–273 Liu P, Islam MF, Doucet JM et al (2010) Design study of a heavily loaded ice class propeller using an advance panel method. Mar Technol 47(1):74–84 Sampson R, Atlar M, Sasaki N (2007) Effect of cavitation during systematic ice block tests. Proceedings of the International Conference on Port and Ocean Engineering Under Arctic Conditions Soininen H (1998) A propeller-ice contact Model[D]. Helsinki University of Technology, pp 20–70 Wang J, Akinturk A, Jones SJ et al (2007) Ice loads acting on a model podded propeller blade (OMAE2005-67416). J Offshore Mech Arct Eng 129(3):236–244 Wang J, Akinturk A, Jones SJ, et al (2005) Ice loads on a model podded propeller blade in milling conditions. ASME 2005 24th International Conference on Offshore Mechanics and Arctic Engineering. American Society of Mechanical Engineers, pp 931–936 Wang C, Sun S et al (2017) Numerical prediction of hydrodynamic performance of ice class propeller in blocked flow-using overlapping grids method. Ocean Eng 141:418–426 Wu S, Liu Y, Zeng Z, Zhang G (2018) Influence of ice block on hydrodynamic performance and cavitation of propeller. Ship Build China 59(1):110–121 Yamaguchi H (1993) Investigation on propeller performance in uniform and blocked flow for the open propeller in the IMD ice tank and cavitation tunnel experiments. Technical Report Laboratory Memorandum LM-1993-11, National Research Council of Canada, Institute for Marine Dynamics Ye LY, Wang C, Chang X et al (2017) Propeller-ice contact modeling with peridynamics. Ocean Eng 139:54–64

Polar Research and Supply Vessel ▶ Polar Research Vessel

P

1372

Polar Research Vessel Gang Wu Marine Design and Research Institute of China, Shanghai, China

Synonyms Polar research and supply vessel

Polar Research Vessel

supplemented. The “Polar Code” was adopted in 2014 as a mandatory rule for polar sailing ships, which took effect on January 1, 2017. The polar regulations regulate not only the ice grade, structure, stability, and seaworthiness of polar ships, but also the requirements for environmental protection. The regulations place strict limits on the polar regions, especially the Antarctic, and express trust in the polar research vessel. In other words, polar research ships are polar pioneers. She should fulfill her responsibilities and lead the trend of polar environmental protection and launch the polar green voyage.

Definition Polar research vessel is a special kind of oceanographic research ships, which can also be seen as a special icebreaker. Like most research vessels, polar research vessel has good control performance, improved the navigation and positioning system, and also is equipped with special equipment and instruments necessary for the execution of task. However, based on the geographical environment of the polar regions, polar research vessel should be able to work in harsh ice area for a long time. Therefore, polar research vessels are constructed around an icebreaker hull, allowing them to engage in ice navigation and operate in polar waters. Due to most of ships cannot enter into the polar region, polar research vessels often play different roles.

Typical Polar Research Vessel There are many famous polar research vessels in the world. Since the 1970s, the United States and the Soviet Union have begun to build. Nowadays, Russia have the largest number of polar ships. Japanese polar research vessel owns the comprehensive functions. The American polar star is one of the most famous polar scientific research vessels in history.

Polar Regulations and Polar Research Vessel

Polar Star USCGC Polar Star (WAGB-10) is a United States Coast Guard heavy icebreaker. In 1976, the ship was built by Lockheed Shipbuilding and Construction Company of Seattle, Washington, along with her sister ship, USCGC Polar Sea (USCGC Polar Star – History). Now the polar star is the only heavy icebreaker in the United States, after the USCGC Healy was classified as a medium icebreaker.

At present, involving the polar shipping unified international rules mainly has two aspects. On the one hand, IACS has issued unified requirements for polar Marine, “Requirements Concerning Polar Class,” which is formulated by the nation classification societies jointly (IACS 2011). On the other hand, International maritime organization (IMO) issued a guide “International Code for Ships Operating in Polar Waters” in December 2002 (IMO 2013). On the basis of the guide, ships sailing in Antarctic waters are also

Unique Ship Design Polar Star (Baker and Jones 1998), which is shown in Fig. 1, uses four different methods of electronic navigation to overcome the difficulties of high-latitude operations, and a computerized propulsion control system to effectively manage six diesel-powered propulsion generators, three diesel-powered ship’s service generators, three propulsion gas turbines, and other equipment vital to the smooth operation of the ship. The extensive use of automation and low maintenance

Polar Research Vessel

1373

Polar Research Vessel, Fig. 1 The US coast guard Polar Star

materials has greatly reduced staffing requirements. Polar Star’s three shafts are turned by either a diesel-electric or gas turbine prime mover. This ensures her strong power. The combination of the hull and the reasonable internal structure endows the polar star very good structural strength. It is worth mentioning that the steel used in these structures has good low-temperature strength. In addition, Polar Star’s hull form is designed to maximize icebreaking by efficiently combining the forces of the ship’s forward motion, the downward pull of gravity on the bow, and the upward push of the inherent buoyancy of the stern. The curved bow allows Polar Star to ride up on the ice, using the ship’s weight to break the ice. Under the guarantee of these engineering techniques, polar star is able to break through ice up to 6.4 m thick by backing and ramming and can steam continuously through 1.8 m of ice at 3 knots. Polar voyages are difficult, so the Polar Star provides the crew with comfort living environment as much as possible.

General Characteristics

Class and type: Polar-class icebreaker Displacement: 10,863 long tons (11,037 t) (standard) (continued)

13,623 long tons (13,842 t) (full) Length: 399 ft Beam: 83 ft 6 in Draft: 31 ft (122 m) (25.45 m) (9.4 m) Installed power: Six Alco 16 V-251F diesel engines (6 3,000 hp (2,200 kW)) Three Pratt & Whitney FT-4A12 gas turbines (3 25,000 hp (19,000 kW)) Propulsion: Combined diesel-electric or gas (CODLOG) Three shafts; controllable-pitch propellers Speed: 18 knots (33 km/h; 21 mph) 3 knots (5.6 km/h; 3.5 mph) in 6-foot (1.8 m) ice Range: 16,000 nautical miles (30,000 km; 18,000 mi) at 18 knots (33 km/h; 21 mph) 28,275 nautical miles (52,365 km; 32,538 mi) at 13 knots (24 km/h; 15 mph) Complement: 15 officers 127 enlisted 33 scientists 12-person helicopter detachment Armament: 2 0.50 caliber machine guns Various small arms Aircraft carried: 2 HH-65A Dolphin helicopters

Multiple Mission Polar Star has a variety of missions while operating in polar regions. Frist of all, Polar Star serves as a scientific research platform with five laboratories and accommodations for up to 20 scientists. Researchers can do some work about fields of geology, volcanology, oceanography, sea-ice physics, and other disciplines which only be operated on a polar research vessel. Besides, the polar

P

1374

research vessel is tasked with transporting supplies to polar research stations. For example, during Antarctic deployments, the primary missions include breaking a channel through the sea ice to resupply the McMurdo Research Station in the Ross Sea. Resupply ships use the channel to bring food, fuel, and other goods to make it through another winter. Last but not least, the polar research vessel sails and studies alone in the polar regions. Therefore, it is necessary for researchers on the polar research vessel to own strong self-survival and crisis management ability. It is also an important task to protect themselves and rescue other research vessels in distress. Monumental Achievement Polar Star was back in operation in late 2013, and assigned to Antarctic operations as part of Operation Deep Freeze in early 2014 (Boyle 2013). She was dispatched from Sydney on January 4, 2014, to attempt a rescue of the Russian research vessel Akademik Shokalskiy and Chinese icebreaking research vessel Xue Long trapped at that time in Antarctic ice, the former since 24 December 2013 (U.S. Breaker to Help Russian 2014; U.S. Coast

Polar Research Vessel

Guard Cutter Polar Star 2014). However, on January 8, 2014, the Australian Maritime Safety Authority confirmed that Polar Star had been released to scheduled duties as both vessels had broken free and were proceeding to open water (Antarctic Rescue Operations Complete 2014). In February 2015 Polar Star was involved in the rescue of the Australian fishing vessel Antarctic Chieftain, towing her and her 27 crew to safety, through ocean ice and snow nearly 20 feet deep in the Southern Ocean (http://www.ktvz.com/news/ us-coast-guard-icebreaker-frees-stuck-ship/3128 4578). In February 2017, fire crews from the USCGC Polar Star were to made available to help the New Zealand Fire Service and NZDF Fire Crews in fighting against the Christchurch Port Hills Fires in Christchurch, New Zealand. Shirase New Shirase, as shown in Fig. 2 (Hull number: AGB-5003), was a new Japanese icebreaker operated by the Japan Maritime Self-Defense Force (JMSDF) and Japan’s fourth icebreaker for Antarctic expeditions. She is the successor of the old Shirase (AGB-5002). They have the same name.

Polar Research Vessel, Fig. 2 The Japanese icebreaker Shirase

Polar Research Vessel

1375

New Shirase was launched in April 2008 and was commissioned in May 2009. Since November 2009, She served in 51 Antarctic expeditions. She was able to move at three knots breaking 1.5 m of ice.

and more efficient energy source and more flexible ways to break ice.

General Characteristics

Design Characteristics

Type: Icebreaker Displacement: 12650 t (standard) 20373 t (full) Length: 138 m (452 ft 9 in) Beam: 28 m (91 ft 10 in) Draft: 9.2 m (30 ft 2 in) Propulsion: Diesel-electric Four propulsion motors, 22,050 kW (30,000 hp) (combined) Two shafts; fixed-pitch propellers Speed: 19.5 knots (22.4 mph; 36.1 km/h) (max) Complement: Approx. 175 sailors + 80 researchers Aircraft carried: 3 helicopters

The Development of Polar Research Vessel in Recent Years Polar research vessels in new age mean more than ice-breaking capabilities, longer endurance, and better research facilities. At the same time, the new polar research vessel represents a greener

RRS Sir David Attenborough (Planet Ice and the Dual-Functional 2017)

Tonnage: 15,000 GT (4,475 DWT) Length: 128.9 m (423 ft) Beam: 24 m (79 ft) Draught: 7 m (23 ft) Depth: 11 m (36 ft) Ice class: PC 4 (propulsion system PC 5) Installed power: 2 Bergen B33:45L6A (2 3,600 kW) 2 Bergen B33:45L9A (2 5,400 kW) Propulsion: Diesel-electric; two shafts 2 2,750 kW (Two 5-bladed controllable pitch propellers) + four Tees White Gill thrusters (2 bow + 2 stern ,4 1,580 kW) Two 5-bladed controllable pitch propellers Speed: 17.5 knots (32.4 km/h; 20.1 mph) (maximum) 13 knots (24 km/h; 15 mph) (cruising) 3 knots (5.6 km/h; 3.5 mph) in 1 m (3 ft) ice Range: 19,000 nautical miles (35,000 km; 22,000 mi) at 13 knots Endurance: 60 days Crew: 30 crew 60 scientists Aircraft carried: 1 helicopter

The British Antarctic survey asks currently the UK Cammell Laird shipyard to build a new polar research vessel. “RRS Sir David Attenborough”

P

Polar Research Vessel, Fig. 3 RRS Sir David Attenborough

1376

as shown in Fig. 3, which is used to replace “RRS Ernest Shackleton” and “RRS James Clark Ross” working in the south and the north Pole, expected to be delivered in 2019. The new polar research vessel costs about 200 million pounds. The ship is 128 m long and 24 m wide, owning a selfsustaining capacity of 60 days (polar region), and can carry more than 30 crew members and 60 scientists. Sir David Attenborough will have a twin-shaft hybrid diesel-electric propulsion system. The power plant, which can run with different configurations depending on the mission and operating conditions, produces electricity to two 2,750 kW (3,690 hp) asynchronous electric motors driving two 5-bladed controllable pitch propellers. At an economical cruising speed of 13 knots (24 km/h; 15 mph), she will have an operating range of 19,000 nautical 3D model diagram of RRS Sir David Attenborough miles (35,000 km; 22,000 mi). For maneuvering and dynamic positioning, the vessel will have four 1,580 kW (2,120 hp) Tees White Gill thrusters, two in the bow and two in the stern (Polar Research Vessel). At 3kn speed, it can break 1 m ice, and the iceclass is PC4 (the propulsion system is PC5). The

Polar Research Vessel

ship is equipped with a large number of professional scientific research equipment and instruments and has advanced laboratories for Marine, submarine, and atmospheric research. Researchers can collect the marine environment and biological data through the underwater robot and underwater glider, and at the same time, aerial robots and shipborne environmental monitoring systems can provide detailed polar environmental information. In order to meeting the increasing demands of scientific research, the laboratory space is designed to be reconfigurable and to be extended for building laboratory modules. Xue Long 2 Xue Long 2, which is shown in Fig. 4, is a Chinese new generation of icebreaking research vessel that had entered service in 2019. She is named after Xue Long (China builds first polar research vessel 2018). Design Xue Long 2 measures 122.5 m (402 ft) long, with a beam of 22.3 m (73 ft) and a draft of 8.3 m (27 ft) at full load. She has a designed displacement of 13,996 tones (Xinhua 2017). She has a diesel-

Polar Research Vessel, Fig. 4 First icegoing picture of Xue Long 2

Polar Research Vessel

1377

electric propulsion system, with two 16-cylinder and two 12-cylinder engines, both Wärtsilä 32-series designs, powering two 7.5 MW Azipods that give her a speed of up to 15 knots (17 mph) in open water and 2–3 knots (2.3–3.5 mph) when breaking ice. Xue long2 combines the technology, functional requirements, and environmental protection concept of the international newgeneration research vessel. She adopts the internationally advanced hull form design with double directions icebreaking and owns a 360 Azimuth pod electric propulsion system, DP-2 dynamic positioning system, and capability of impacting ice to fragmentation. She can also realize the 360 free rotation in the polar region and break through the 20-m ice ridge in the polar region. In addition, the ship’s maneuverability will be greatly improved, which can meet the navigation needs of the global unlimited navigation area. The structural strength meets the requirements of PC3, and the ice can be continuously broken at a speed of 2–3 knots on a 1.5 m thick ice layer covered with 0.2 m of snow. At the same time, the entire ship generator set is equipped with an exhaust gas cleaning system, focusing on the protection of the polar environment. Furthermore, Xue Long 2 will be equipped with a smart ship system. It is the first time that China has equipped an intelligent Hull (China Classification Society (CCS) notation: i-ship H) system on a scientific research vessel. And it is also the first time that China has installed a smart Machinery (CCS notation: i-ship M) in an electric propulsion ship. This will effectively reduce the labor intensity of the crew and improve the operational efficiency of the ship. Summarize the evolution of polar research vessel technology over the decades. The main development directions are as follows: hull design, auxiliary ice-breaking capacity, power plant, and hull form design with double directions icebreaking.

Hull Design During the development of the polar research vessel for several decades, the complicated ice conditions brought her a lot of trouble. In order to adapting to the harsh ice conditions, polar research vessel need to have a larger displacement, a more reliable hull structure, and a longer range.

Polar Research Vessel Outlook and Conjecture

References

In this section, research and development with respect to the hull design, assist in ice breaking ability, power plant and doubling ice-breaking design are presented.

Antarctic rescue operations complete. Australian Maritime Safety Authority, 8 January 2014. http://www.amsa. gov.au/media/. Retrieved 13 January 2014 Baker C, Jones SP (eds) (1998) Encyclopedia of bilingualism and bilingual education. Multilingual Matters, P1119

Assist in Ice Breaking Ability In the last years, a variety of auxiliary icebreaking systems have been developed to improve the ice-breaking capacity of polar research vessel. But these systems have only been applied to a few advanced ships and have not yet been popularized. Improvement and popularization of new technologies will make it possible to improve the working environment of polar research vessels. Power Plant Based on polar regulations and people’s growing environmental awareness, we should search for more green energy. Similarly, we should also look for more powerful energy to support us to explore the polar regions. Both nuclear and electric power may be a direction for us, especially electrical propulsion. Doubling Ice-Breaking Design Doubling icebreaking is a very practical icebreaker design for the ship with 360 azimuth propulsion units. The icebreaker with this design can not only use the bow to break ice, but also use the stern to break ice. The new technology of double icebreaking greatly enhances the maneuverability of the polar ship. When a polar ship possessing this design sails in the ice zone, she may take less time to turning around in ice area and she is less likely to get stuck in the ice layers.

P

1378 Boyle A (2013, December 30) How icebreakers work – and why they sometimes don’t work. NBC News. http:// www.nbcnews.com/science/how-icebreakers-worksometimes-dont-work-2D11821223. Retrieved 31 December 2013 China builds first polar research vessel. The Motorship, 17 April 2018. http://www.motorship.com/news101/ ships-and-shipyards/china-builds-first-polar-researchship. Retrieved 19 April 2018 First Chinese-built polar icebreaker gets name. Xinhua, 10 October 2017. http://www.xinhuanet.com/english/ 2017-10/10/c_136669892.htm. Retrieved 19 April 2018 IACS (2011) Unified requirements concerning polar class (International Association of Classification Societies). Available from: http://www.iacs.org.uk/document/pub lic/Publications/Unified_requirements/PDF/UR_I_pdf 410.pdf. Accessed 11 June 2014 IMO (2013) International code for ships operating in polar waters Planet ice and the dual-functional Attenborough. The Naval Architect, January 2017, 37–38 Polar Research Vessel. Cammell Laird Shipyard. https:// www.clbh.co.uk/wp-content/uploads/2014/10/CL-Da tasheet-Polar-Research-Ship1.pdf. Retrieved 15 Octob er 2017 U.S. breaker to help Russian, Chinese ships stuck in Antarctic ice. Reuters, 4 January 2014. https://www. reuters.com/article/2014/01/05/us-antarctica-ship-resc ue-usa-idUSBREA030E520140105. Retrieved 5 January 2014 U.S. Coast Guard Cutter Polar Star to assist vessels in Antarctica. United States Coast Guard Pacific Area, 4 January 2014. http://coastguard.dodlive.mil/2014/ 01/u-s-coast-guard-cutter-polar-star-to-assist-vesselsin-antarctica/. Retrieved 5 January 2014 USCGC Polar Star – History. http://www.uscg.mil/pacarea/ cgcPolarStar/History.asp. Retrieved 17 September 2009

Polar Trading Vessel

Polyester Rope ▶ Cable

Polyethylene (PE) Net ▶ Net Structures: Design

Pontoon Bridge ▶ Floating Bridge

Position Mooring (PM) ▶ Thruster-Assisted Mooring

Position-Holding ▶ Station-Keeping System for VLFS

Positioning Polar Trading Vessel

▶ Station-Keeping System for VLFS

▶ Polar Merchant Vessel

Positioning System

▶ Photoelectric Detection Technology in Underwater Vehicles

▶ External Turret Single Point Mooring System ▶ Internal Turret Single-Point Mooring (SPM) System ▶ Soft YOKE Single Point Mooring System

Polyamide (PA) Net

Position-Keeping

▶ Net Structures: Design

▶ Station-Keeping System for VLFS

Polarization Imaging

Power Take-Off System

1379

where Fpto is the force acting on PTO and V the velocity of the PTO for power generation. When a rotary motion is used for power conversion, the power is given by

POSMOOR, Position-Mooring ▶ Dynamic Positioning in Ice

P ¼ T pto  o

ð2Þ

Power Cable where Tpto is the torque acting on PTO and o the angular velocity of the PTO for power generation. From the formulae for power conversion, it can be easily seen that to generate a large power, two significantly different ways can be adopted:

▶ Cable

Power Take-Off System Wanan Sheng SW MARE Marine Technology and Consultation, Cork, Ireland

Synonyms LIMPET – Land Installed Marine Power Energy Transmitter; OWC – Oscillating water column; PTO – Power take-off; WEC – Wave energy converter

Definition A power take-off of a wave energy converter is a mechanism with which the absorbed energy in the form of mechanical/pneumatic/potential energy from the primary energy conversion stage is transformed into useful mechanical energy for further energy conversion, mostly into electricity if a generator is connected to the PTO.

Scientific Fundamentals Power Conversion Principle For power conversion, it can be made using either translational or rotational motions and their corresponding PTO force or torque. When a translational motion is used for power conversion, the capture power by the PTO is calculated as P ¼ Fpto  V

ð1Þ

1) Either with a very high (translational/rotational) speed but a small force/torque. Therefore, such a system tends to have a very high system reliability, and a high energy conversion efficiency (generally higher than 90% in conventional energy conversion) can be obtained. These can be seen in conventional power generation using steam turbines, which could directly generate electricity to grid (with frequency of 50 Hz or 60 Hz). 2) Or with a very large force when the velocity in the power convention system is low. These happened in most renewable energy converters in wind, tidal, and wave energy systems. Such systems tend to have a low reliability and low energy conversion efficiency. For wave energy conversion, a specific disadvantage is the reciprocating wave force and velocity (with a dominant period about 6–12 s for wave energy conversion (Falcao 2008; Sheng and Lewis 2016a)). The nature of wave energy conversion with a large force and a low speed (both are reciprocating in most cases) presents a serious engineering challenge in practical application in the following aspects: • System and component reliability: fatigue problems with stress concentration • Low energy conversion efficiency: directly linking to the initial capital of cost of energy production Power Conversion To convert the trapped energy by the WEC, different PTOs may be used, including linear PTOs

P

1380

Power Take-Off System

(direct drive or Wells turbine), nonlinear PTOs (impulse turbine), or coulomb PTO (hydraulic cylinder). For a simple linear PTO, the PTO force is proportional to the PTO displacement, velocity, and acceleration, given in an expression following (Babarit et al. 2012):

Following (Zheng et al. 2016a; Evans 1981; Falnes 1999), the average absorbed power from wave can be given as

Fpto ¼ Mpto1 x€ þ Bpto1 x_ þ Cpto1 x

where the asterisk  means the conjugate of the complex vector. This formula indicates that the converted average power P equals the gross power due to the equivalent excitation force, Fex, less the power due to the wave radiations. The equation can be further written as

ð3Þ

where Mpto1, Bpto1, and Cpto1 are constants, independent of the PTO displacement, velocity, and acceleration. It is noted that only the damping term could extract a net power conversion, while other two terms could absorb energy in a part of the wave cycle, but they also feed energy back to wave in the other part of the wave cycle. As such, the overall net power is zero if the energy conversion efficiency is 100% or negative if the efficiency is less than 100%. Wave Energy Conversion Maximization PTO optimization for maximizing wave energy conversion for a given wave energy converter is a very important aspect when designing a wave energy converter and setting the relevant PTO parameters. When examining the maximized wave energy absorption for a wave energy converter, it is generally accepted that the analysis on a linear system will give the correct information on how much wave energy can be converted by the device, since the maximized wave energy conversion for a given wave energy converter is same for both linear and nonlinear PTOs if the PTOs are optimized (see Sheng and Lewis 2016b). For this reason, the maximization of wave energy conversion by a wave energy converter can be simply carried out in frequency domain h     1  i C þ Cpto U ¼ Fex io M þ A þ Mpto þ B þ Bpto þ io

ð4Þ where the bold letters in square bracket mean matrices and the letters with subscript pto correspond to the matrices for the power take-off system and U and Fex are the complex vectors.

P¼

 1 1  Fex U þ U Fex  U BU 4 2

ð5Þ

1 P ¼ Fex B1 Fex 8



1 1 1  U  B1 Fex B U  B1 Fex 2 2 2 ð6Þ This could lead to an overall maximized wave energy conversion: 1 PMAX ¼ Fex B1 Fex 8

ð7Þ

under the following constraint for an optimal velocity: 1 Uopt ¼ B1 Fex 2

ð8Þ

The condition implies that the overall maximal wave energy conversion happens at the resonance of the dynamic system with the PTO damping equalling to the radiation damping. The explanation is given as follows. The solution of Eq. (4) can be simply expressed as

  U ¼ io M þ A þ Mpto   1   1 Fex C þ Cpto þ B þ Bpto þ io

(9)

When in resonance, the following condition must be satisfied:     o2 M þ A þ Mpto  C þ Cpto ¼ 0

ð10Þ

Power Take-Off System

1381

When the system is in resonance, the velocity is given as  1 U ¼ B þ Bpto Fex

ð11Þ

Although the matrices B and Bpto are both real matrices, Eq. (11) cannot be simply interpreted as the optimal velocity U is in phase with excitation Fex. However, if the single motion mode is for wave energy conversion, the velocity is indeed in phase with the excitation. Hence the resonance condition is called as the phase optimal condition. Taking Bpto ¼ B as the amplitude control, Eq. (11) is same as Eq. (8), a condition corresponding to the maximal wave energy absorption, given by Eq. (7). This optimal PTO damping level is the amplitude optimal condition. The maximization of energy absorption by a wave energy converter above actually provides the basic principle for control technologies on how to achieve the maximized wave energy absorption: in regular wave, it can be done simply by adjusting PTO’s Mpto and/or Cpto to make the dynamic system in resonance with the wave excitation to achieve the optimal phase control, while by setting the PTO’s damping level, it is possible to attain the optimal amplitude control (Falnes 1995). When the phase and amplitude are both optimally controlled, the control is optimal. When only the phase or the amplitude is optimized or partially optimized, the control is suboptimal. In reality, suboptimal controls may be more realizable due to less strict constraints. PTO Optimization Fix-referenced WECs (One Motion Mode)

The simplest case would be the fix-referenced wave energy converters where a single motion mode is accounted for wave energy conversion, such as the fix-referenced point absorber using

Pmax ¼

1 4

heave motion (Seabased 2015; CETO Rafiee and Fievez 2015, etc.), the bottom-fixed oscillating surge wave energy converter using the pitch of the flap (Oyster Whittaker and Folley 2012), or the bottom-fixed OWC device, using the heave motion of the fluid in the water column (LIMPET Folley et al. 2006). For such simple devices, the analytical PTO optimization can be easily derived (see Falnes 2002; Sheng and Lewis 2012). Taking a fix-referenced point absorber as an example, its heave motion is used for wave energy conversion, and the solution of the dynamic system is simply given as U3 ¼ F    ex3  1  io M þ A33 þ Mpto þ B33 þ Bpto þ io C33 þ Cpto

ð12Þ where subscript “3” means the heave motion following the convention in the boundary element method. The average wave energy absorption by the PTO is 1 P ¼ Bpto 2 

B33 þ Bpto

2

þ

o2



jFex3 j2

   2 M þ A33 þ Mpto  C33 þ Cpto

ð13Þ The maximal power absorption happens when Bpto ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi h  1  i2 B233 þ o2 M þ A33 þ Mpto  2 C33 þ Cpto o ð14Þ

The maximal average power is calculated as

jFex3 j2 qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

   2ffi B33 þ B233 þ o2 M þ A33 þ Mpto  C33 þ Cpto

ð15Þ

P

1382

Power Take-Off System

When the point absorber is in resonance with incident wave, a condition must be satisfied:     o2 M þ A33 þ Mpto  C33 þ Cpto ¼ 0 ð16Þ we have from Eqs. (14) and (15) as Bpto ¼ B33 PMAX ¼

2 1 jFex3 j 8 B33

ð17Þ ð18Þ

Eq. (18) is a special case of Eq. (7) when a single motion mode is used for wave energy conversion.

Self-Referenced WECs (Multiple Motion Modes)

For massive wave energy production, the wave energy converters may be more likely deployed in the relative large water depth (larger than 50 m) where the wave energy resources are better, and it is more economic for floating wave energy devices. As such, they may use multiple motion modes or relative motions for wave energy conversion. When the relative motion from two motion modes is used for wave energy conversion, the analytical PTO optimization can be still obtained (Falnes 1999) and Sheng et al. (Sheng and Lewis 2016b). Taking the relative heave motion of two bodies as the motion for wave energy conversion as seen in OPT and RM3 floating point absorbers, the dynamic equation is

8h i h i c c > < ioðm33 þ a33 Þ þ b33 þ 33 v3 þ ioa39 þ b39 þ 39 v9 ¼ f 3  Bpto ðv3  v9 Þ io io i h i h c c 93 > : ioa93 þ b93 þ v þ ioðm99 þ a99 Þ þ b99 þ 99 v9 ¼ f 9 þ Bpto ðv3  v9 Þ io 3 io

where m33 and m99 are the mass of the bodies; a33, a39, a93, and a99 the added mass coefficients; b33, b39, b93, and b99 the potential damping coefficients; c33, c39, c93, and c99 the restoring force 0

  c io ðm33 þ a33 Þ þ b33 þ Bpto þ 33 io @   c93 io a93 þ b93  Bpto þ io
 f3 ¼ f9

coefficients; f3 and f9 the complex heave excitation force amplitudes of two bodies; and v3 and v9 the complex heave motion velocity amplitudes of the two bodies.

1   c
 io a39 þ b39  Bpto þ 39 v3 io   c99 A v9 io ðm99 þ a99 Þ þ b99 þ Bpto þ io ð20Þ

Once the dynamic equation is solved, the average power absorption is given as 1 P ¼ Bpto ðv3  v9 Þðv3  v9 Þ 2

ð19Þ

ð21Þ

Both Falnes (1999) and Sheng et al. (Sheng and Lewis 2016b) have given the expressions for the optimized Bpto and the corresponding average power P . Obviously, the detailed expressions are

much more complicated than those in a single motion mode for wave energy conversion (the complicated mathematical expression and derivation can be found in (Sheng and Lewis 2016b; Falnes 1999)). For more general cases with multiple motion modes, the analytical PTO optimizations are more complicated. In fact, they can be made only in some special cases (more details can be found in Pizer (1993) and Zheng et al. (2016b)).

Power Take-Off System

PTO Optimization for Irregular Waves

The PTO optimizations mentioned above are valid only for regular waves. In irregular waves, they can be regarded as a combination of many different regular components of different amplitudes, frequencies, and phases, and for each wave cycle, its period and height are different. To achieve an optimized PTO damping for a given sea state, the trial-and-error method is usually used. For instance, Bull (2014) suggested 200 different damping levels are used to try out the optimized PTO damping for the RM3 BBDB OWC wave energy converter, while Sheng et al. (Sheng and Lewis 2016b) suggested that using Te as a reference wave period for the irregular waves to calculate optimized PTO damping (same method as for regular waves) and the search of the optimized PTO damping levels could be close to the one based on the reference period of Te. As such, the optimized PTO damping can be more easily found.

Key Applications Types of PTO For different types of wave energy converters, the primary converted energy can be in different forms: in the oscillating water columns, it is pneumatic power trapped in the air chamber in the Power Take-Off System, Fig. 1 Basic process of wave energy conversion

1383

OWC devices, the potential power in the overtopping devices or the kinetic power of the body (or bodies) in the oscillating body (bodies) wave energy converters (see Fig. 1). To convert the different forms of the primary converted energy, different types of PTOs are employed: for pneumatic power, it is an air turbine, such as the Wells turbine and impulse turbine (Fig. 2a (Falcao and Gato 2012)); for potential energy, low head water turbines are used (Fig. 2b, the Kaplan low head water turbine in Wave Dragon (Kofoed et al. 2005)); while for the body kinetic power, hydraulic PTO (Fig. 2c, Falcao 2010) or the direct drive PTO (Fig. 2d, Drew et al. 2009) can be used. These PTOs may be the most used PTO technologies, but we should not exclude other types of PTOs, for instance, the mechanical PTO and the recent PTO developments supported by WES (Wave Energy Scotland 2015). Control Technologies Control technologies for wave energy converters have been a hot and interesting topic of research work since the principle of the optimal control for improving wave energy absorption was identified in the 1970s (Budal and Falnes 1977), and since then researchers have been seeking different control technologies to solve the problems of low wave energy conversion efficiency, especially for those small devices (small devices have been

P

1384

Power Take-Off System

Power Take-Off System, Fig. 2 Conventional power take-offs for wave energy conversion.

preferred due to their robustness in structure, and also the smaller the device, the higher the ratio of the capture power over the mass according to (Falnes 2002)). A good review on controls for improving wave energy conversion can be found in (Ringwood et al. 2014). In the previous sections, it has been shown that the maximum energy absorption by a wave energy converter occurs when the device is in resonance. To maximize wave energy conversion, the PTO control system could provide an additional mass or a negative spring to change the converter resonance period, i.e., the wave energy system has a

cancelled intrinsic impedance. More specifically, with setting or changing of the PTO parameters (i.e., the PTO control, see Eq. (3)), the maximal wave energy conversion can be achieved through the device resonance with the incident wave and the optimal damping level of PTO (Evans 1981; Falnes 1980). While in regular waves such an optimal control may be very straightforward, it becomes much more complicated in irregular waves since every wave cycle in irregular waves has different frequencies and amplitudes, and it is practically unknown what would be in the next wave cycle. This applies a challenge for the

Power Take-Off System

control systems since they need the future information to decide the control parameters and to allow the time for the system to make the control. For instance, a latching control through peakmatching requires the information when is the peak in the future. As shown in (Fusco and Ringwood 2012), most of the active control system needs the future information of a time horizon more than 20s, and an accurate prediction of such a long time horizon is really challenging. This essentially becomes one of two barriers in practical control applications for many wave energy converters controls (the other barrier is the physical implementation of the control system, for instance, how the control system provides the required inputs of large forces to make the control working. In (Hals et al. 2011), these two challenges are specially attributed to latching control, but in fact, they are the common challenges for most control technologies: to make the control optimal, the required future information must be known to the control algorithms, and an ideal control system may be required to provide a large force in a rather swift manner). To remove the barriers partially or fully and make the control more practical, different control technologies have been proposed and attempted. For instance, Falcao (2007) and Sheng et al. (2015) developed the different latching control technologies. In these two novel latching controls, the controllers lock the devices when the device motion velocity vanishes, which are same as in conventional latching control technologies, but both latching controls remove the requirement of the future event prediction. In the former method, it is proposed to release the device when the excitation force is larger than a preset threshold, while in the latter method, a simple latching duration is calculated based on the wave statistics (the wave statistics can be reliably forecast hours ahead of real time or calculated from the wave measurement of the last 30 or 60 min. It is generally accepted that wave statistics may not change in 3 h or a longer period). As such, the barrier for requiring the prediction of the future information is removed! To date, many different types of control technologies have been proposed and studied, and

1385

more are being proposed and/or developed. Ozkop and Altas (2017) have reviewed the literature and summarized that more than 30 different type control technologies. The most popular controls in the summary include (short names in the brackets) following the popularity order in the reference: phase control (PhC), latching control (LC), optimal control (OC), PI control (PIC), predictive control (PC), on-off control (OOC), power control (PoC), valve control (VC), reactive control (RC), etc. It should be seen that although different names are used in the control technologies, some of them may be same in principle. Strictly speaking, a full optimal control (OC) is the ultimate goal for all control technologies, by achieving both the phase and amplitude control conditions, such as the predictive control (PC), which is essentially seeking the optimal conditions in the control method. Alternatively, suboptimal conditions are made. For instance, many control technologies are implemented the full or partial phase optimal conditions, including the phase control (PhC), reactive control (RC), latching control (LC), on-off control (OOC), etc. In a rather detailed comparison, Hals et al. (2011) present a conventional optimized resistive loading (RL) and five popular wave energy control technologies. The former is essentially an optimized PTO damping for the given waves, which provides a base for comparison. The compared control technologies include the classic phase control by (i) latching (Falcao 2008; Babarit and Clement 2006) and (ii) clutching (Babarit et al. 2009) and the advanced active controls, (iii) the approximate complex-conjugate control (Nebel 1992), (iv) tracking of approximate optimal velocity (Falnes 2002), and (v) model predictive control (MPC) (Cretel et al. 2011; Brekken 2011). From the comparisons, it can be seen that all the controls are superior to the pure optimized PTO resistive loading (RL), with the MPC control being the best control since in all the compared cases, MPC gives highest energy conversion, generally 200% more capture energy when compared to RL, and also for longer waves, the controls could produce more wave energy. It should be noted that the comparisons are made for wave energy period Te ¼ 6 s, 9 s, and 12 s, all longer

P

1386

than the natural period of the semisubmersed sphere, T0 ¼ 4.4 s.

Cross-References ▶ Wave Energy Converters

References Babarit A, Clement AH (2006) Optimal latching control of a wave energy device in regular and irregular waves. Appl Ocean Res 28:77–91. https://doi.org/10.1016/j. apor.2006.05.002 Babarit A, Guglielmi M, Clement AH (2009) Declutching control of a wave energy converter. Ocean Eng 36:1015–1024. https://doi.org/10.1016/j.oceaneng.200 9.05.006 Babarit A et al (2012) Numerical benchmarking study of a selection of wave energy converters. Renew Energy 41:44–63. https://doi.org/10.1016/j.renene.2011.10.002 Brekken TKA (2011) On model predictive control for a point absorber wave energy converter. PowerTec, 2011 IEEE 19–23 June 2011 Budal K, Falnes J (1977) Optimum operation of improved wave-power converter. Mar Sci Commun 3(2):133–150 Bull D (2014) Pneumatic performance of a nonaxisymmetric floating oscillating water column wave energy conversion device in random waves. In: Proceedings of the 2nd marine energy technology symposium, Seattle, 15–18 Apr 2014 Cretel JAM et al (2011) Maximisation of energy capture by a wave-energy point absorber using model predictive control. In: Proceedings of 18th international federation of automatic control (IFAC), Milano, 28 Aug – 2 Sept 2011 Drew B, Plummer AR, Sahinkaya MN (2009) A review of wave energy converter technology. Proc Inst Mech Eng 223:887–902. https://doi.org/10.1243/09576509JPE782 Evans DV (1981) Maximum wave-power absorption under motion constraints. Appl Ocean Res 3(4):200–203 Falcao AF (2007) Modelling and control of oscillating-body wave energy converters with hydraulic power take-off and gas accumulator. Ocean Eng 34(14–15):2021–2032. https://doi.org/10.1016/j.oceaneng.2007.02.006 Falcao A (2008) Phase control through load control of oscillating-body wave energy converters with hydraulic PTO system. Ocean Eng 35:358–366. https://doi. org/10.1016/j.oceaneng.2007.10.005 Falcao A (2010) Wave energy utilization: a review of the technologies. Renew Sust Energ Rev 14(3):899–918. https://doi.org/10.1016/j.rser.2009.11.003 Falcao A, Gato LMC (eds) (2012) Air turbines. In: Sayigh A (ed) Comprehensive renewable energy, vol 8. Elsevier, Oxford, pp 111–149

Power Take-Off System Falnes J (1980) Radiation impedance matrix and optimum power absorption for interacting oscillating in surface waves. Appl Ocean Res 2(2):75–80 Falnes J (1995) Principles for capture of energy from ocean waves. Phase control and optimum oscillation. http:// folk.ntnu.no/falnes/web_arkiv/InstFysikk/phcontrl.pdf. Accessed 25 July 2013 Falnes J (1999) Wave-energy conversion through relative motion between two single model oscillating bodies. Transaction of the ASME 121:32–38 Falnes J (2002) Ocean waves and oscillating systems: linear interaction including wave-energy extraction. UK, Cambridge University Press Folley M, Curran R, Whittaker T (2006) Comparison of LIMPET contra-rotating wells turbine with theoretical and model test predictions. Ocean Eng 33(8–9): 1056–1069. https://doi.org/10.1016/j.oceaneng.2005.08.001 Fusco F, Ringwood JV (2012) A study of the prediction requirements in real-time control of wave energy converters. IEEE Trans Sustainable Energy 3(1):176–184. https://doi.org/10.1109/TSTE.2011.2170226 Hals J, Falnes J, Moan T (2011) A comparison of selected strategies for adaptive control of wave energy converters. J Offshore Mech Arct Eng 133:031101-1 Kofoed JP et al (2005) Description of the power take-off system on board the wave dragon prototype. In: Second CA-OE workshop on component technology and power take-off, Uppsala, 2–3 Nov 2005 Nebel P (1992) Maximising the efficiency of wave energy plant using complex conjugate control. Proc Inst Mech Eng 206(4):225–236 Ozkop E, Altas IH (2017) Control, power and electrical components in wave energy conversion systems: a review of the technologies. Renew Sust Energ Rev 67:106–115. https://doi.org/10.1016/j.rser.2016.09.012 Pizer D (1993) Maximum wave-power absorption of point absorbers under motion constraints. Appl Ocean Res 15(4):227–234. https://doi.org/10.1016/0141-1187(93) 90011-L Rafiee A, Fievez J (2015) Numerical prediction of extreme loads on the CETO wave energy converter. In: Proceedings of the 11th European wave and tidal energy conference, Nantes, 6–11 Sept 2015 Ringwood JV, Bacelli G, Fusco F (2014) Energymaximizing control of wave energy converters. IEE Control Syst 34(5):30–55. https://doi.org/10.1109/ MCS.2014.2333253 Seabased (2015) Sotenäs wave power. http://www.seabased. com/en/projects/sotenas-wave-pover. Accessed 15 Feb 2015 Sheng W, Lewis A (2012) Assessment of wave energy extraction from seas: numerical validation. J Energy Resour Technol 134:041701. https://doi.org/10.1115/ 1.4007193 Sheng W, Lewis A (2016a) Energy conversion: a comparison of fix- and self-referenced wave energy converters. Energies 8:054501. https://doi.org/10.1063/1.4963237 Sheng W, Lewis A (2016b) Power take-off optimisation for maximising energy conversion of wave activated

Power Transmission and Distribution bodies. IEEE J Ocean Eng 41:529. https://doi.org/10. 1109/JOE.2015.2489798 Sheng W, Alcorn R, Lewis A (2015) On improving wave energy conversion, part II: development of latching control technologies. Renew Energy 75:935–944. https://doi.org/10.1016/j.renene.2014.09.049 WES (2015) Wave energy Scotland initiatives. http://www. hie.co.uk/growth-sectors/energy/wave-energyscotland/. Accessed 15 Feb 2016 Whittaker TJT, Folley M (2012) Nearshore oscillating wave surge converters and the development of Oyster. Philos Trans R Soc A Math Phys Eng Sci 370:345–364. https://doi.org/10.1098/rsta.2011.0152 Zheng S, Zhang Y, Sheng W (2016a) Maximum theoretical power absorption of connected floating bodies under motion constraints. Appl Ocean Res 58:95–103. https://doi.org/10.1016/j.apor.2016.03.015 Zheng S, Zhang Y, Sheng W (2016b) Maximum wave energy conversion by two interconnected floaters. J Energy Resour Technol 138:032004-1. https://doi. org/10.1115/1.4032793

Power Transmission and Distribution

1387

mineral transportation system, surface support system, power transmission, and control system. The power transmission system mainly provides the power for deep-sea mining vehicles, mineral transportation system, and surface support system. It is an important part of the whole mining system and is the basic condition of whether the whole mining system can work properly. It can be regarded as the “nervous system” of the mining system, so it requires very high reliability. Figure 1 shows a typical mining system.

Surface Support System PTD Surface Support System Composition The surface support system is mainly composed of the following equipment: • Mining vehicle launch and recovery system. • Umbilical launch and recovery system.

Jianbo Zhu and Duochang He Zhuzhou CRRC Times Electric CO., LTD, Zhuzhou, Hunan, China

Synonyms

P

PDU, Power distribution unit; PTD, Power transmission and distribution

Definition Deep-sea mining system is a system that can excavate, collect, and transport minerals from the seabed to the mothership (Liu et al. 2014).

System Brief Introduction The system that combines deep-sea mining vehicles with pipeline transportation system is widely regarded as the most promising commercial mining system at the moment. This mining system is mainly composed of deep-sea mining vehicle,

Power Transmission and Distribution, Fig. 1 Typical mining system

1388

• • • • •

Power Transmission and Distribution

Flexible pipe launch and recovery system. Heave compensation system. Pipe lift system. Pipe storage and transfer system. Pipe docking and disassembly system.

Surface Support System Power Requirements There are several kinds of electrical equipment voltage of surface support system: three-phase AC69 0 V, three-phase AC38 0 V (50 Hz) or AC44 0 V (60 Hz), and single-phase AC22 0 V. These types of voltage can be output directly by the ship generator, and the distance from the ship’s distribution cabinet to the electrical equipment is not very far so low voltage can be used directly for power transmission.

Underwater PTD System The power transmission and distribution equipment of the underwater mineral transportation system and mining vehicle covers a large area and is usually installed on deck, but it can’t meet the waterproof requirements if directly installed on the deck. Also it is dangerous to expose the high-voltage equipment on the deck, so it is required to be installed in a container with a protection grade of at least IP65. The output of ship generator is usually AC low voltage, while the input voltage of underwater motor is generally AC high voltage, so the ship electrical output needs to pass through a step-up transformer to obtain the high voltage required by the motor. The voltage of underwater instruments and control systems are usually AC22 0 V, AC11 0 V, DC2 4 V, and DC5 V. These equipment power can’t be transported directly through the low voltage so it also needs to be transported

Low voltage frequency converter or Step-up Low Low voltage soft starter voltage transformer cable cable

High voltage cable

through high voltage. The high voltage is converted to the required AC22 0 V and AC 110 V under the water. The DC2 4 V and DC5 V are available from AC11 0 V via PSU. For lift pump, hose pump, and mining vehicle, the starting current of the motor is large, so soft start equipment is needed. The lift pump needs to adjust speed so frequency converter soft start is needed. The high-voltage frequency converter covers a large area so it is not suitable to install in the container. We can choose the low-voltage frequency converter. The motor of hose pump and mining vehicle has no speed regulation requirement, so we can choose low-voltage thyristor soft starter for economic reason. Buffer station hydraulic station motor power is small and can start directly. The input power from ship is connected to the step-up transformer through the frequency converter or soft starter, and the high-voltage output terminal of the transformer is connected to the outlet box in the container through the high-voltage cable. The high-voltage power and communication fiber is combined together in the outlet box and then connected to the slip ring in the umbilical winch through umbilical. The power is transported to the underwater motor by umbilical via slip ring. Figure 2 is a road map of underwater equipment power supply, and Fig. 3 is a schematic diagram of underwater equipment power supply.

Key Technology of Underwater PTD Deep-Sea Long-Distance High- Efficiency PTD Technology Ship power supply is different from land power supply; the electric power is supplied by ship generators. The power network capacity is generally small and has poor impact resistance. Heavy

Container outlet box

Slip ring on winch Umbilical

Underwater connection box Umbilical

Input low voltage from ship generator

Power Transmission and Distribution, Fig. 2 Road map of underwater equipment power supply

Underwater motor

Power Transmission and Distribution

1389

FromAC690V distribution cabinet PT1 Q1

Q2

Q3

Q4

Q5

KM1

KM2

KM3

KM4

KM5

T1 690/3300

STR1

STR2

V/F

STR3

PT2

T2 690/3300 CT1

PT3

PT4

CT2

Buffer station hydraulic station motor

T4 690/3300

T3 690/3300

Buffer station hose pump motor

CT3

Lift pump motor

T5 690/3300 PT6

PT5

CT4

Mining vehicle motor 1

CT5

Mining vehicle motor 2

Power Transmission and Distribution, Fig. 3 Schematic diagram of underwater equipment power supply

use of nonlinear loads on ships results in a large number of harmonics. It not only seriously affects the power quality of the ship power grid but also interferes the normal operation of other electrical equipment. The current generated at the start of high-power load is as high as four or seven times the rated current; it will have a huge impact on the ship power grid when it starts. On the other hand, because the underwater equipment can work at a depth of 6,000 m (Wang and Wang 2007), such a long-distance transmission of electric power will cause a serious voltage drop of the line, and this will make the motor not stop because the start voltage is too low. Therefore, how to ensure the reliable transmission of underwater electric power over a long distance needs serious consideration. In addition, the underwater load is far away from the power supply, the transmission loss will be very high if the current is too large. But if the voltage is too high, there will be some problems in the manufacture of umbilical. So there are many factors that need to be considered in selecting the transmission voltage level. Online Monitoring and Diagnosis Technology for Insulation and Grounding Circuit of Deep-Sea Circuit Whether the key components such as power supply, umbilical, and transformer can work normally will directly affect the safe and reliable operation

of transmission and distribution system. Most of the insulating materials are organic materials, which are prone to deterioration due to various factors such as electricity, heat, machinery, environment, and so on, resulting in insulation aging, especially in the harsh environment of the ocean, which is very corrosive and complex. Therefore, it is necessary to have a set of reliable scheme to monitor the equipment insulation and line grounding condition in real time so as to detect power supply failure in time, avoid endangering personal safety, and ensure the safe and reliable operation of the whole system.

Development of Deep-Sea Optoelectronic Composite Umbilical Deep-sea optoelectronic composite umbilical is the “nerve and lifeline” of underwater system; it connects electrical equipments on ship and underwater production facilities to transmit the ship power and all communication signals to deepsea mining equipment. In the deep sea, the umbilical is affected by the chemical corrosion of sea water, ocean current movement, sea bottom biological impact and bite, and gravity of relay stations and mining vehicles, which can easily cause functional units and tensile failure. So it’s important to develop high reliability and long life cycle composite umbilical.

P

1390

Power Transmission and Distribution

Binding Technology of Umbilical The umbilical that transmits power to the lift pump and buffer station must be bound and fixed on the pipe; otherwise the umbilical will swing violently under the influence of the current, which will not only produce a huge pulling force on the winch and the underwater connection box on the ship. It will also collide violently with the delivery pipe, which will easily lead to the breakage of the umbilical. The binding scheme should meet the requirements of fast operation on ship, and the binding material should be corrosion-resistant in sea water, have enough friction to fix itself on the pipe, and have enough load bearing capacity to hold the umbilical.

Underwater PTD Mode The main load of underwater system is lift pump motor, buffer station hose pump motor and hydraulic station motor, and mining vehicle motor. Motor power of lifting pump and mining vehicle is very high, for example, the power of lifting pump motor is 800 kW in the Korean mining experiment project, and the power of mining vehicle motor is 550 kW. The power of underwater mining vehicle motor is even more than several MW in the mining system of Nautilus Mining Company of Canada. The water depth of deep-sea mining is generally more than 1000 m. For example, the “Blue Nodule” project in Europe is

Power Transmission and Distribution, Table 1 Comparison of different transmission modes Sequence number 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Index name Line current No load voltage drop Full load voltage drop Terminal voltage control Line reactive capacity Transmission distance Transmission cable number Transmission cable diameter Transmission voltage level Transmission starting equipment Transmission terminal equipment Line loss Equipment area Technology reliability Technology maturity Transmission cable cost Transmission equipment cost Maintenance

AC low voltage transmission Very big Big Very big Complicated

AC high voltage transmission Small Small Small No

DC high voltage transmission Small Very small Small Complicated

Common Near

Common Far

No Far

3 for 3 phase or 2 for single phase Very big

3 for 3 phase or 2 for single phase Small

2 Small

Low

High

High

No

Step-up transformer

No Very big Small High

No or step-down transformer Small Small High

Step-up transformer and rectifier Underwater inverter or inverter and rectifier Small Big Common

High High

High Low

Common Very low

Low

Common

High

Simple

Relatively simple

Complicated

Power Transmission and Distribution

1391

designed with a maximum depth of 6000 m, and four lifting pumps are used. If we use the low voltage from the ship generator to the transmission of such a long distance of high power, the current will be very large and the line voltage drop will be severe, and the underwater motor will not be able to start. Table 1 is the comparison of three common modes of high electric power transmission in long distance. As can be seen from the above table, when the three-phase or single-phase underwater equipment is in long-distance, high-capacity transmission, the AC high-voltage mode is the best scheme. The transmission mode is simple, the efficiency is high, the cost of transmission equipment is relatively low, and the technology is mature. So the input voltage of deep-sea motor is generally three-phase AC300 0 Vat present, while the higher power motor can use three-phase AC600 0 V.

Underwater Motor Start Mode The capacity of the ship power supply network is very small compared with the land power supply network. The starting current of the high-power motor is very large when it starts directly which will have a serious impact on the whole ship power supply, so the underwater motor should choose the proper starting mode. There are several general starting methods of AC motor as follows: frequency converter start, thyristor soft start, and direct start. Table 2 is the comparison of three different motor start methods. As can be seen from above table: (a) Direct start has a great influence on input power supply so it is only suitable for low power motor. (b) It is necessary to use thyristor or frequency converter to start the heavy-duty motor so as to reduce the impact on the ship power grid.

Power Transmission and Distribution, Table 2 Comparison of different motor start methods Sequence number 1.

Index name Start current

2. 3. 4.

Start torque Applicable load Output voltage

5.

Output voltage harmonic Input power factor Influence on ship power Speed regulation function Speed regulation performance Control difficulty Area Reliability Maturity Cost Maintenance

6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Frequency converter start Small

Thyristor soft start Small

Big All loads Continuous adjustable Low

Small Light load or no load Continuous adjustable

Direct start Can be as big as 4 to 7 times rated current Big Big system Can’t adjust

High

No

High Low

Common Common

Low Big

Yes

Yes

No

Excellent

Common

No

Complicated Big High High High Complicated and high cost

Simple Small High High Common Relatively simple and common cost

Simple Small High High Low Simple and low cost

P

1392

Power Transmission and Distribution

(c) We can use frequency converter to start and control speed when the heavy-duty motor has speed regulation requirement. The motor of the lifting pump has a large power and needs to adjust the speed according to the working conditions so it is suitable to start with the frequency converter. Relay station hose pump motor and mining vehicle motor have a large power but do not need to adjust the speed so it is suitable to start with thyristor soft start. Relay station hydraulic station motor power is small so it can start directly.

PTD Equipment PDU PDU is used to switch on and switch off the circuit; it also can show the circuit parameters such as voltage, current, power, and so on. A PDU mainly contains breaker, contactor, meters, protection devices, and other auxiliaries. Breaker is a kind of switchgear which can not only turn on and off normal load current and overload current but also switch on and off short circuit current. In PTD system, there are two types of breakers widely used, molded case circuit breaker and air circuit breaker. Molded case circuit breaker rated voltage from AC38 0 V to AC69 0 V and rated current from 16A to 1600A. Air circuit breaker rated voltage from AC38 0 V to AC115 0 V and rated current from 630A to 6300A. Figure 4 shows a PDU. Figures 5 and 6 are typical molded case circuit breaker and air circuit breaker. Contactor is a kind of electrical appliance used to switch on and break AC/DC main circuits and large capacity control circuits frequently, rated current from 9A to 2600A and rated voltage from AC22 0 V to AC100 0 V. Figure 7 shows a typical contactor. Transformer Transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. The main components are primary coil, secondary coil, and iron core. Main functions are

Power Transmission and Distribution, Fig. 4 PDU

voltage conversion, current conversion, impedance conversion, isolation, voltage stabilization, etc. There are generally three types of transformers used in deep-sea mining system. One is three-phase or single-phase step-up transformer to convert the low voltage from ship generator into high voltage required for underwater equipment. One is single-phase transformer to convert singlephase high voltage that transported to underwater into single-phase low voltage. One is low-voltage transformer which converts the low voltage from ship generator into other required low voltage. Figures 8, 9, and 10 show typical transformers of these three types. Current Transformer Current transformer is an instrument for measuring primary side high current via secondary side small current according to the electromagnetic induction principle. It is composed of closed iron core and winding. Low-voltage current transformer and high-voltage current transformer are

Power Transmission and Distribution

1393

Power Transmission and Distribution, Fig. 7 Typical contactor

Power Transmission and Distribution, Fig. 5 Molded case circuit breaker

P

Power Transmission and Distribution, Fig. 8 Threephase step-up transformer

Power Transmission and Distribution, Fig. 6 Air circuit breaker

commonly used in power transmission and distribution system. Figures 11 and 12 are typical lowvoltage current transformer and high-voltage current transformer.

1394

Power Transmission and Distribution

Power Transmission and Distribution, Fig. 9 Singlephase step-down transformer

Power Transmission and Distribution, Fig. 11 Lowvoltage current transformer

Power Transmission and Distribution, Fig. 10 Lowvoltage transformer

Potential Transformer Potential transformer is an instrument used to convert the primary side high voltage of the line into the standard low voltage of the secondary side. It is used to measure the line high voltage via the secondary side low voltage. Figure 13 is a typical potential transformer.

Power Transmission and Distribution, Fig. 12 Highvoltage current transformer

Frequency Converter Frequency converter is a kind of electric power control equipment which uses frequency

Power Transmission and Distribution

Power Transmission Fig. 13 Potential transformer

and

1395

Distribution,

Power Transmission and Distribution, Fig. 14 Lowvoltage frequency converter

conversion and microelectronic technology to control AC motor by changing the frequency of motor working power supply. Frequency converter is mainly composed of rectifier, filter, inverter, brake unit, drive unit, detection unit, micro-processing unit, and so on. Frequency converter adjusts the voltage and frequency of output power supply by switching on and off internal IGBT. It provides the required power supply voltage according to the actual needs of motor, thus achieving the purpose of saving energy and adjusting speed. Figure 14 shows the typical low-voltage converter.

is fully switched on, and the motor works on the mechanical characteristics under rated voltage to achieve smooth start. The starting process ends when the motor reaches the rated speed, and the soft starter automatically replaces the thyristor with a bypass contactor to provide the rated voltage for the normal operation of the motor. Figure 15 shows the typical low-voltage soft starter.

Soft Starter Soft starter is a kind of motor control equipment which integrates soft start, soft stop, light-load energy-saving, and multifunction protection. The soft starter uses a three-phase opposite parallel thyristor as a voltage regulator and connected between the power supply and the motor stator. When starting the motor with soft starter, the output voltage of the thyristor increases gradually, the motor accelerates gradually until the thyristor

Umbilical Umbilical is a combination of conductor (power conductor or signal conductor or both), optical fiber (single mode or multimode), insulation material, and outer sheath (steel or Kafra). The main parameters include rated voltage, rated current, outer diameter, minimum bending radius, air weight, sea water weight, safe working load, minimum breaking strength, etc. Figure 16 is a typical section of umbilical.

P

1396

Preliminary Design

Power Transmission and Fig. 17 Typical layout of container

Power Transmission and Distribution, Fig. 15 Lowvoltage soft starter

Distribution,

level and is installed on the deck. The transformer and inverter generate mass of heat when in operation so it’s very important for the container to cool down its internal temperature. Figure 17 shows typical internal layout of the container.

References Liu S, Liu C, Dai Y (2014) Status and progress on researches and developments of deep ocean mining equipments. J Mech Eng 50(2):8–18 Wang H, Wang A (2007) Application of soft-starter in deep-sea mining system. World Inverters 12:64–66, 78

Preliminary Design Min Zhao State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China Power Transmission and Distribution, Fig. 16 Typical umbilical sectional view

Offshore Container Offshore container is used to install the PDU, transformer, inverter, and other electrical devices or control system. It usually has IP56 protection

Synonyms Concept design; Design of submersibles; Design spiral; Detailed design; Empirical design; Hydrodynamic design; Multidisciplinary design optimization (MDO); Optimal design; Reliability based design (RBD); Structural design; Technical design

Preliminary Design

Definition Preliminary design of a submersible is a stage of the design of a submersible. The process of the design of a submersible may be referred to in chronological order as the (1) pre-design, (2) design, and (3) post-design, and then the design process is composed of three design phases: (1) basic design, (2) contract design, and (3) detail design. The basic design consists of concept design and preliminary design stages, and preliminary design is the second stage of basic design. Starting with baseline data provided by the selected concept design(s), preliminary design refines and firms up the significant characteristics of systems, constraint, and relative cost estimates. Consequently, it provides a precise definition of the mission system and assurance that the design goal can be attained.

Scientific Fundamentals Introduction to the Design Stage As noted, the design process is composed of three phases called as basic design, contract design, and detailed design shown in Fig. 1. In this stage, the levels of labor, preparation time, and costs associated with each phase increase exponentially as the process progresses. Design creativity and flexibility are essentially limited to the basic design phase – the mission system, including its submersible system, being well defined at the beginning of contract design. The design process, at this point, is discussed from the perspective of the mission system. As has been seen, this system is composed of (I) systems which may be labeled as new construction or existing systems. Design efforts focus on the total or “from scratch” design of new construction systems and on the selection of suitable existing systems and their alteration, if required, to convert them to (I) systems. The submersible, herein, is considered to be a new-construction (I) system (Allmendinger 1990). The basic design is the primary design phase concerned with how best to accomplish what the

1397

potential user/owner of the mission system wants to do underwater as set forth by his mission requirements. Basic design, as considered herein, is composed of the concept design and preliminary design. Concept design develops two or more design alternatives from which design is selected in accordance with specified criteria. Preliminary design advances the selected alternative’s development to the point of entry into the contract design stage. Basic design proceeds, in general, as discussed above, its process is discussed further in the next section. Contract design requires yet further refinement of design and additional detail. It yields contract plans and specifications necessary for interested parties to bid on the construction of new (I) systems or the alteration of existing (I) systems. It also provides contractual documents for the construction and alteration work. Specifications delineate quality standards of material and workmanship as well as setting forth performance expectations for the (I) systems and their subsystem. They also describe tests and trails which must be performed successfully before acceptance of the systems. Detailed design is the final phase of the design process and entails the development of detailed working plans from which the (I) systems are constructed or altered. In one sense, it is not a design phase since all the creative design effort is made in preceding phase, the design being unequivocally defined prior to entering this phase. It does, however, require the greatest amount of work of all the phases and is often undertaken by entities building or altering the system (Allmendinger 1990). Missions in Basic Design Phase As discussed above, the basic design phase leads the process of design, and the missions of this stage, in general, involves (Allmendinger 1990): 1. Development of performance requirements or (I) system capabilities, from the mission requirements. 2. Determination of the principal characteristics of the (I) systems required to achieve these

P

1398

Preliminary Design

PRE-DESIGN POTENTIAL USER/OWNER OF MISSION SYSTEM DESCRIBES WHAT HE WANTS TO DO UNDERWATER: MISSION TASKS

MISSION(S)

MISSION REQUIREMENTS

CONCEPTUAL DESIGN DESIGN CRITERIA PRELIMINARY DESIGN

DESIGN DESIGNER CONCERNED WITH HOW TO ACCOMPLISH WHAT THE USER/OWNER WANTS TO DO UNDERWATER IN AS OPTIMAL A MANNER AS POSSIBLE CONSIDERING DESIGN CONSTRAINTS ACTING

CONTRACT DESIGN

DETAIL DESIGN

CONSTRUCTION, TEST & EVALUATION

POST-DESIGN OPERATION

INPUT TO FUTURE DESIGNS

Preliminary Design, Fig. 1 Design and associated processes (Allmendinger 1990)

MISSION EXTERNAL DESIGN CONSTRAINTS

Preliminary Design

capabilities, which enable new construction systems to be designed and existing systems to be selected and altered if necessary. 3. Estimation of capital and operating costs of (I) systems. 4. Identification of one or a few mission systems from among a series of alternatives which optimally meet performance requirements to the extent possible considering design constraints acting. 5. Refining and firming-up characteristics and cost estimates of the (I) systems composing the optimum concept design(s). The concept design stage of basic design is concerned with the first four of these functions – function four, herein, is based on costeffectiveness as the optimization criterion. The preliminary design stage of this phase is concerned with the fifth function. Concept design, diagrammed in Fig. 2, is the first attempt to translate all the user/owner’s mission requirements into performance requirements and characteristics of the (I) systems composing the mission system. It is often viewed as consisting of feasibility studies and completion of the optimum conceptual design (s) once they are identified by these studies. Feasibility studies are concerned with the development of those performance requirements and associated system characteristics which have significant impact on the costeffectiveness optimization process. Completion of the optimum design(s) involves developing other major performance requirements and characteristics those which are essential in defining (I) systems but which do not have a significant impact on the optimization process (Allmendinger 1990). Feasibility studies create an orderly series of mission system alternatives, all of which meet the mission requirements and are technically feasible, and select one or a few of these alternatives as the conceptual design(s) to be carried on into preliminary design. These alternatives are shown in Fig. 2 as MS1, MS2, . . . MSi, where “i” can be any small to large number depending on the simplicity/complexity of the mission and

1399

optimization techniques used. As indicated in the figure, each alternative is composed of a unique combination of (I) systems. Each (I) system, in turn, has unique capabilities, characteristics required to achieve these capabilities, and costs associated with providing these characteristics. Certain unique (I) systems may appear in more than one combination, but individual combinations are not duplicated in other alternatives. Mission system alternatives may be generated by (1) varying performance requirements with the cascading effect of varying (I) systems’ capabilities, characteristics, and costs and (2) varying (I) systems’ capabilities, characteristics, and costs in ways each of which meets a specific set of performance requirements. Alternatives generated in this manner contain information necessary to conduct the search for the optimum, cost-effective mission system(s). Combinations of (I) systems forming mission system alternatives may vary in number, type/ capabilities, and status. These features are related to functions required to accomplish mission tasks, the time frame for completing these tasks, if critical, and economic considerations. A mission profile, derived from mission requirements, is useful in providing functions and timeframe information – its usefulness increasing as the complexity of the mission increases. This profile is a chronological listing of all events occurring from the mission’s beginning to end and including time-frame data where necessary. The other “exit line” from the optimization process, as indicated in Fig. 2, leads to the optimum mission system(s) identified by this process in a manner suggested by the cost-effectiveness equation. The concept design(s) of the selected mission system(s) can now be completed by developing the primary characteristics of the (I) systems not considered in the feasibility studies. The identification of more than one optimum concept design means that the “optimization curve” is reasonably flat over a limited range of alternatives – that there is little to choose between them. In this instance, the user/owner may select one of them based on subtleties not heretofore considered or more than one may be carried

P

1400

Preliminary Design

MISSION MISSION EXTERNAL DESIGN CONSTRAINTS

MISSION REQUIREMENTS

MISSION PROFILE

MS1 C O N C E P T U A L D E S I G N

MS2

MSi

I11

I21

I12

I22

I1i

I2i

IN1

I31

IN2

I32

INi

I3i

OPTIMIZATION PROCESS

OPTIMIZATION CRITERION

OPTIMUM MS I10

I20

IN0

I30

PRELIMINARY DESIGN

Preliminary Design, Fig. 2 Basic design of mission system (Allmendinger 1990)

forward into preliminary design. The mission system(s) carried forward should have associated performance requirements firming up and provide baseline (I) system characteristics which are further developed and during the preliminary design stage. Preliminary design, as noted, is the second stage of basic design and is concerned with this phase’s fifth function. Starting with baseline data provided by the selected concept design(s), preliminary design refines and firms up the major

characteristics of systems, constraint, and relative cost estimates. Consequently, it provides a precise definition of the mission system and assurance that the design goal can be attained. Figure 1 shows a “feedback line” from preliminary design to the mission requirements, indicating that refinements in the design may reveal technical feasibility reasons for altering performance and, in summary, mission requirements that were overlooked in concept design. These discoveries should be few in number and minor

Preliminary Design

in their effect on the requirements. A significant discovery of this nature would, most likely, raise doubts about the validity of selected concept design(s) and be the cause for repeating the concept design stage or terminating the design altogether (Allmendinger 1990). Regarding basic design, the major systems comprising submersible are summarized in the following outline (Allmendinger 1990): 1. Hull Structure System: (a) Structure System, (b) Special System. 2. Propulsion Plant System: (a) Energy Generating System, (b) Propulsion System, (c) Special Purpose System. 3. Electrical Plant System: (a) Electrical Power Generation System, (b) Power Distribution System, (c) Lighting System, (d) Special Purpose System. 4. Command and Surveillance System: (a) Command and Control System, (b) Navigation System, (c) Communication System, (d) Surveillance System, (e) Special Purpose System. 5. Auxiliary System: (a) Human System, (b) Life Support System, (c) Air, Gas and Miscellaneous Fluids System, (d) Submersible Control System, (e) Mechanical Handing System, (f) Special Purpose System. 6. Outfit and Furnishings System: (a) Fittings System, (b) Hull Compartmentation System, (c) Preservatives and Covering System, (d) Furnishings, (e) Special Purpose System. 7. Armament System (This system applies only to submersibles having offensive/defensive military missions requiring the launching of weapons). The above introduction mostly came from Allmendinger (1990) which was based heavily on Busby (1976). More detailed introduction from Busby (1990) and Funnel (1999). The Process of the Preliminary Design This section discusses the process of the preliminary with the well-known design spiral which serves as a basis for a brief discussion of the entire design process. The design spiral is shown in Fig. 3.

1401

The design spiral – The iterative nature of the overall design process may be modeled by the design spiral shown in Fig. 3. The spiral consists of spokes and loops. The spokes represent design considerations including performance requirements, submersible characteristics, and cost estimates; submersible characteristics are embodied in its arrangement, geometry, six systems groups, and summaries of energy requirements and weight/displacement centers. The loops indicate design iterations with the design’s refinement increasing as the loops spiral inward. Outer loop procedures use empirical formulations and estimates based on similar design data, whereas middle and inner loop procedures are based on the progressively more detailed development of the design considerations utilizing increasingly precise formulations. The intersection of spokes and loops form “points” which are identified alphanumerically. Thus, for example, 3B is a point in the spiral at which the geometric characteristics of the submersible are being considered in the second iteration in a more detailed manner than they were initially at point 3A. At 3B, adjustments are made as the result of both the more detailed consideration of the geometric characteristics required and the impact on geometric of interrelated design considerations for which data were generated at points in spiral preceding 3B. Adjustments are made at other points in the spiral for the same reasons. For the design to converge to a satisfactory solution of the design problem, these adjustments must become progressively similar with each succeeding loop through concept, preliminary, and contract design. This fact is demonstrated in the spiral by the decreased spacing between loops as they spiral inward. Convergence is illustrated by the innermost loop becoming a circle, indicating that all design considerations are fully developed and required no further adjustments. At this point in the spiral, detailed design can begin (Allmendinger 1990). Preliminary design is arbitrarily limited to loops C, D, and E. Note in the Fig. 3 that loops D and E are relatively close together, indicating that only very small adjustments in design

P

1402

Preliminary Design Mission Requirements

Conceptual Design - Loops A-B Preliminary Design - Loops C-D-E Contract Design - Loops F-G

Arrangement 2

Select Point Performance Requirements 1 A

a

12 Cost-Estimate Summary

B

b Geometry 3 Displacement

11 Weight Displacement Center Summary

C D E F

G

Hull 4 Structure

10 Energy Summary Energy Storage System

Detail Design

Propulsion 5 Plant

9 Outfit and Fumishings

Electrical 6 Plant

8 Auxiliary Systems 7 Command and Surveillance

Preliminary Design, Fig. 3 Design spiral (Allmendinger 1990)

considerations are being made at this point. Should preliminary design’s more detailed procedures and exact formulations reveal the need for relatively large adjustments to be made in one or more of the considerations, the validity of the selected concept design alternative may well be questioned. The end result of preliminary design is a well-defined submersible system which meets performance requirements and for which a firm cost estimate exists. As indicated on the spiral, completion of this phase of design marks the beginning of contract design.

The C, D, and E loops – The preliminary design procedures of these loops progressively refine all aspects of the submersible’s design, including those aspects not considered in the concept design phase. Only small adjustments, if any, are required at the spiral’s point at the end of the E loop. Some general comments on these points follow. (1) C, D, E Performance Requirements: Review these requirements in light of the design’s more detailed development. C and D loop

Preliminary Design

procedures may reveal that it is still necessary or desirable to make small changes in some of these requirements. There should be no changes in them as the result of E loop procedures or, in words, they should be fixed at entry into the contract design phase. (2) and (3) C, D, E Arrangement and Geometry Displacement: Obtain a detailed view of the submersible with the location of systems being essentially fixed so that the systems can function properly, routine inspection and maintenance can be made with relative ease, there are no conflicts in space requirements, and the design condition criteria of adequate stability and zero trim are met. These procedures require detailed inboard/outboard profiles and cross-section views to be drawn. A line drawing may also be drawn depicting the envelope’s geometry; this drawing is necessary to obtain accurate data required for hydrostatic and hydrodynamic calculations. (4–9) C, D, E Systems Groups: Develop these systems in sufficient detail to provide the assurance that, both individually and collectively, they will satisfy all performance requirements and very close estimates of sizing and cost data. Direct calculations and preliminary drawings, as contrasted with working drawings, are used extensively. Procedures, for example, may involve the construction and testing of structural and appended envelope models to verify data derived from theoretical strength and hydrodynamic formulations. (10) C, D, E Energy Summary-Energy Storage Systems: Make progressive refinements of electrical power-energy profile and pneumatic storage system based on increasingly precise C, D, E loop SWBS data. Electrical and pneumatic storage systems should be very accurately defined at point 10E. (11) C, D, E Weight-Displacement-Center Summary: Complete this summary in more detail and investigate stability and trim in design and other operating condition as well as in the emergency ascent condition. These procedures will require a breakdown of SWBS systems into their components.

1403

Procedures at 11C and, to a lesser extent, at Point 11D usually indicate that some adjustments in arrangement or system details or both are necessary to attain design condition criteria of neutral buoyancy, adequate stability, and zero trim. They may also indicate that adjustments in envelop geometry and systems influenced by this characteristics are necessary to obtain adequate surface stability. These adjustments, if any, are to be made, should be relatively small on entry into the contract design phase. (12) C, D, E Cost Estimate Summary: Summarize the progressively refined first and annual operating cost estimates obtained in these loops. A close estimate of the submersible’s operating cost per year should be in hand at the beginning of contract design (Allmendinger 1990).

Key Applications Preliminary design is a significant step of the design of submersibles. Here we introduce the autonomous underwater vehicle (AUV) and remotely operated vehicle (ROV). Autonomous Underwater Vehicles (AUV) The applications of the underwater vehicle have shown a dramatic increase in recent years, such as, mines clearing operation, feature tracking, cable or pipeline tracking, and deep ocean exploration. To satisfy different applications, different kinds of development of autonomous underwater vehicles or their systems appear. Martz (2008) applied multidisciplinary design optimization method to the preliminary design of an AUV. Allotta et al. (2011) developed an innovative AUV called Tifone and finished the preliminary design, as is shown in Fig. 4. Salleh et al. (2013) performed preliminary design of AUV with higher resolution underwater camera for marine exploration. Remotely Operated Vehicles (ROV) In the design stage of ROV, in order to make it a free-flying vehicle, floatation is added to

P

1404

Preliminary Design

Preliminary Design, Fig. 4 Preliminary layout of Propeller and Thrusters on Tifone Vehicles (Allotta et al. 2011)

Preliminary Design, Fig. 5 Vehicle’s righting moment (Christ and Wernli 2014)

Righting moment

Righting moment

P

P

P CB

CB

CB CG

CG

CG

W

W

W

neutralize vehicle buoyancy and achieve mobility in Fig. 5 (Christ and Wernli 2014). Thus, one of the key points in preliminary design of an ROV is to realize the performance requirements and, at the same time, to keep its stability. Bowen et al. (2004) finished the preliminary design of a novel light-tethered hybrid ROV for global science in extreme environments. Govinda et al. (2014) studied modelling, design and robust Control of a ROV in preliminary design stage.

▶ Detailed Design ▶ Empirical Design ▶ Hydrodynamic Design ▶ Multidisciplinary Design Optimization (MDO) ▶ Optimal Design ▶ Reliability Based Design (RBD) ▶ Structural Design ▶ Technical Design

References Cross-References ▶ Concept Design ▶ Design of Submersibles ▶ Design Spiral

Allmendinger EE (ed) (1990) Submersible vehicle design. Society of Naval Architects and Marine Engineers, Jersey City Allotta B, Pugi L, Vettori G, Gualdesi L, Bartolini F, Ridolfi A (2011) Preliminary design of autonomous underwater vehicles, Atti del 20 congresso della

Probabilistic Aspects for Ice Loads on Ships associazione italiana di meccanica applicata alle macchine, Bologna Bowen AD, Yoerger DR, Whitcomb LL, Fornari DJ (2004) Exploring the deepest depths: preliminary design of a novel light-tethered hybrid ROV for global science in extreme environments. Mar Technol Soc J 38(2):92–101 Busby F (1976) Manned submersibles. Office of the Oceanographer of the Navy, Arlington Busby RF (1990) Undersea vehicles directory – 1990–91, 4th edn. Busby Associates, Arlington Christ RD, Wernli RL (2014) The ROV manual: a user guide for remotely operated vehicles. 2nd edn. Butterworth-Heinemann, Waltham Govinda L, Salgado-Jimenez T, Bandala-Sanchez M et al (2014) modelling, design and robust control of a remotely operated underwater vehicle. International Journal of Advanced Robotic Systems, 11, pp 1–16 Martz MA (2008) Preliminary design of an autonomous underwater vehicle using a multiple-objective genetic optimizer. Master thesis, Virginia Polytechnic Institute and State University, USA Salleh Z, Ghani MF, Ramli MAH (2013) Preliminary design of autonomous underwater vehicle with higher resolution underwater camera for marine exploration, Journal of Ocean, Mechanical and Aerospace, Science and Engineering, 2, pp 6–12

Preserve Heat ▶ Thermal Insulation

Pressure-Area Relationship ▶ Ship-Iceberg Interactions

1405

Probabilistic Aspects for Ice Loads on Ships Wei Chai Departments of Naval Architecture, Ocean and Structural Engineering, School of Transportation, Wuhan University of Technology, Wuhan, China Department of Marine Technology, Norwegian University of Science and Technology, Trondheim, Norway

Introduction For ships in the Arctic, ice loads caused by ship and ice interaction represent the dominant load. Ice loads on ship hull is random by nature as other environmental loads. The knowledge of ice loads can promote design and operation of ice-capable vessels in Arctic regions. However, due to the complexity of ship and ice interaction process, studies with respect to the ice loads are limited and still under development. Ice loads on ship hull can be calculated by empirical formula and numerical simulation and collected by laboratory experiments and full-scale field measurements. Among these methods, full-scale field measurements are the most effective way to study the properties of ice loads (Ehlers et al. 2015). In this entry, the randomness of ice loads and the reasons that cause the randomness of ice-induced loads are introduced. Previous studies for probabilistic descriptions and analysis of the full-scale measured ice loads on ship hull are summarized in this work. The challenges and future works for studying the stochastic properties of ice loads on ship hull are also described in this entry.

Prism Based SPR (P-SPR) ▶ Fiber Optic Hydrophone

Randomness of Ice Loads to Ships

PRO - Pressure-Retarded Osmosis

Ice loads are caused by the ship and ice interaction process, which depends on the ice conditions, the geometry of ship hull, and the relative velocity between the vessel and the ice features. Generally, for first-year ice, the ship and ice interaction process is initialized by a localized crushing of

▶ Salinity Gradient Power Conversion

P

1406

Probabilistic Aspects for Ice Loads on Ships

the free ice edge, and then the contact area and crushing forces increase as the ship advances and penetrates the ice features. The ice eventually deflects, and the bending stress promotes a flexural failure at a certain breaking distance from the crushing region (Jordaan 2001). The interaction process is illustrated in Fig. 1, and some other kinds of failure mode (e.g., creep, cracking, bucking) may occur separately or in combination during the interaction process. Even though the interaction between ice features and ship hull is governed by deterministic laws of mechanics, ice loads on ship hull are random by nature (e.g.,

Crushing

Fig. 2). The stochastic nature ice loads have has also been validated by various full-scale field measurement campaigns, which are listed in Ehlers et al. (2015) and Suominen (2018). During the full-scale measurement voyages in ice regions, strain sensors are instrumented to measure the (local) ice loads on ship hull. It is seen in Fig. 2 that the time series of measured ice loads on a frame looks like a sequence of impulses with sharp peaks, which indicate that during the ship and ice interaction process, the accumulated crushing force is high enough to initiate bending failure of the ice feature. Such impulses are

Crushing and bending forces and frictional force

Bending

Support force, buoyancy and frictional forces Buoyancy and frictional forces

Rotating Hydrodynamic support force

Sliding Probabilistic Aspects for Ice Loads on Ships, Fig. 1 An illustration of ship and (first-year) ice interaction process (Riska 2010)

500 400

Load [kN/m]

300 200 100 0 –100

0

0.05

0.1

0.15

0.2

0.25 0.3 Time [hours]

0.35

0.4

0.45

0.5

Probabilistic Aspects for Ice Loads on Ships, Fig. 2 Stochastic nature of the ice loads measured on a frame (Lensu 2002)

Probabilistic Aspects for Ice Loads on Ships

Probabilistic Analysis of Ice Loads to Ships For stochastic processes, probabilistic models and methods should be applied to describe their properties. Within the scope of probability theory, standard methods, such as the statistical parameters (e.g., the mean value, standard deviation, skewness, kurtosis), correlation functions, power spectrum, statistical distributions, extreme value statistics, etc., can be applied to analyze the time series of the random load process (Ochi 1990). In this entry, previous studies on the statistical distributions of the measured ice loads, extreme value statistics, and fatigue damage evaluation based on the collected ice load peaks are summarized. Probabilistic Models of Ice Loads In general, the full-scale measurements can be classified as long term and short term. Long-term measurements are usually taken over several winter seasons, and they have been performed only in the Baltic Sea and the Antarctic sea (Kujula 1994). Basically, most of the full-scale measurements are based on the short-term measurements in which the time periods are hours and minutes. Ice load peaks collected by short-term measurements are widely used for probabilistic analysis.

Kheisin and Popov (1973) were the pioneers in introducing the probability theory to study the ice loads on ship hull. In their study, it was found that the number of ice load events in the ship bow region is distributed according to the Poisson law and the measured ice load peaks were found to follow an exponential distribution. Subsequently, there have been plenty of studies on probabilistic models of the measured ice loads on ship hull. Kujala and his colleagues suggested that the Weibull probability distribution or the exponential distribution or lognormal distribution would give the best fit to the ice loads data collected in the Baltic Sea (Kujula 1994; Suominen 2018). Figure 3 presents an example of measured ice load peaks fitted by different probabilistic models. In addition, Jordaan et al. (1993) applied the event-maximum method and found that the tails of ice loads collected in the North Chukchi sea can be fitted as an exponential distribution by using probability paper method. However, from the full-scale measurements of ice loads collected onboard KV Svalbard in the sea area of Spitsbergen in the year 2007, Suyuthi et al. (2013b) mentioned that some sets of (shortterm) ice load peaks cannot be well modeled by the traditional statistical models, such as the lognormal and the exponential distribution. Later, they proposed a generalized probabilistic model, i.e., a three-parameter exponential distribution to provide a better description of these collected 0.02 Observed

Occurence probability

repeated as the ice-breaking process continues and the peak values of the ice loads are referred to as the ice load peaks. There are mainly two categories of sources causing the randomness of ice-induced loads. One is the variation of the ice conditions in the Arctic regions, which includes physical ice properties (such as ice types, thickness, density, porosity, floe size, etc.) and ice mechanical properties (e.g., flexural, tensile, shear, uni- and multiaxial compression strength, and so on). The other is related to the complex ship and ice interaction process in association with different ice failure mechanisms and randomness of flaw in ice features. In addition, ship operations and movements in different ice conditions also affect the icebreaking process and the values of ice loads.

1407

Weibull Exponential

0.015

Lognormal

0.01

0.005

0

0

100

200 300 Load [kN]

400

500

Probabilistic Aspects for Ice Loads on Ships, Fig. 3 Different probabilistic models for fitting the measured ice load peaks (Suominen 2018)

P

1408

Probabilistic Aspects for Ice Loads on Ships

data sets (Suyuthi et al. 2014). As a result, the three-parameter exponential distribution can serve as an effective supplement to the traditional statistical models for describing the measured ice load peaks.

PðÞ ¼ ProbðMN  Þ ¼ ProbðX1  , . . . , XN  Þ

ð1Þ

Former studies of extreme loads prediction are mainly based on the classic extreme value theory, which includes the peak amplitude approach (Ralph and Jordaan 2013) and the asymptotic method (Lensu 2002). For the peak amplitude approach, it is assumed that all the N collected ice load peaks are independent and identically distributed with common distribution, FX(x), such as the Weibull, exponential, and lognormal distributions, described in section “Probabilistic Models of Ice Loads.” Then, the extreme value distribution is given in the form of the power of encountered number of ice loads events as Eq. 2. The relationship between the distribution of ice load peak FX(x) and the extreme value distribution P() is illustrated in Fig. 4. PðÞ ¼ ProbðX1  , . . . , XN  Þ ¼

N Y

ProbðXi  Þ ¼ ½FX ðÞN

ð2Þ

i¼1

In the asymptotic method, a proper number of time windows with equal duration are

P DF

Extreme Value Statistics The extreme value statistics of ice loads are directly related to the reliability of the ice-capable vessels since the ultimate limit states (ULS) are generally based on extreme load effects. Assume that the stochastic process X(t) represents the ice load peaks over a time interval [0, T]. The values X1, . . ., XN, which were derived from the observed process, are allocated to the discrete times t1, . . ., tN in the time interval [0, T]. The extreme value among the N outcomes of the stochastic process X(t) is defined as MN ¼ max {X1, . . ., XN}, and the extreme value distribution for large values of  is expressed as:

Extreme value distribution

Initial distribution

x

Probabilistic Aspects for Ice Loads on Ships, Fig. 4 Illustration of the relationship between the initial distribution (i.e., distribution of ice load peaks) and the extreme value distribution

selected to divide the measured time series into a corresponding number, K, of intervals. The maxima value in each interval is identified. Then, based on the collected maxima data, the type I asymptotic extreme value distribution, i.e., the Gumbel distribution, is applied to estimate the extreme distribution: PðÞ ¼ GY ðÞ

ð3Þ

where Y represents the process of maxima values in the K intervals and GY(y) is the Gumbel distribution with the following expression:  
  yb GY ðyÞ ¼ exp  exp  a

ð4Þ

where α and β are the parameters for the Gumbel distribution and they can be estimated by ordinary fitting of the empirical cumulative distribution, such as the least-square fitting in a probability paper and the method of moment, etc. This method is also known as the Gumbel method. In this method, for small level of exceedance probability l, the corresponding extreme value is given as:

Probabilistic Aspects for Ice Loads on Ships

 ¼ G1 Y ð1  l=K Þ

1409

ð5Þ

In addition to the abovementioned two methods based on the parametric distribution functions, there is another method, named as the ACER (average conditional exceedance rate) method, which can be applied to estimate the extreme distribution of the collected ice load peaks. The ACER method is based on a sequence of nonparametric distribution function and estimates the extreme value distribution by constructing different orders of the ACER functions, which are available for both the stationary and nonstationary date sets. The principle and development of the ACER functions are described in Næss and Gaidai (2009). In this method, with the time series of the measured ice load peaks, the extreme value can be estimated in the following manner: Pð  Þ Pk ð  Þ

exp ððN  k þ 1Þ  bek ðÞÞ

ð6Þ

where k is the order of the ACER function and Pk represents the approximation of the extreme value distribution based on the kth order ACER function. bek(‧) is the empirical ACER function of order k, which can be obtained by applying the existed time series.

Probabilistic Aspects for Ice Loads on Ships, Fig. 5 An example of extreme estimation for the collected ice load peaks based on the ACER1 function

In order to predict the extreme value distribution in the tail region, an extrapolation scheme is applied. This extrapolation technique is based on the observations that for ships and marine structures being considered, the mean upcrossing rate and the ACER functions are in general highly regular in the tail region. The empirical ACER function is assumed to be in the form of: bek ðÞ qk exp fak ð  bk Þck g,   0

ð7Þ

where ak, bk, ck, and qk are suitable constants, which are dependent on the order k. Generally, under the aforementioned assumptions for the tail region of the ACER functions, plotting log|log(bek ðÞ=qk )| | versus log(bk) would give an almost perfect linear tail behavior. In addition to this method, a more robust Levenberg-Marquardt least-squares optimization method can be used to determine the optimal values for ak, bk, ck, and qk. Details of this method can refer to Naess and Moan (2012) and Chai et al. (2016). An example of extreme value estimation for the collected ice load peaks is presented in Fig. 5. Moreover, the performance of the abovementioned three methods applied for estimation of the extreme values of ice load peaks has been systematically reported in Chai et al. (2018a).

P

1410

Fatigue Damage Evaluation In addition to the extreme ice loads statistics, fatigue damage caused by cycle ice loading is also an important issue for Arctic ships navigating in severe ice regions. Generally, fatigue damage evaluation is based on the S-N data in association with the Palmgren-Miner law of damage accumulation. For the ice load-induced fatigue damage, when the time series of ice-induced stress ranges are available, fatigue damage of ship hull can be directly estimated by summing the fatigue damages of all stress cycles according to the linear Palmgren-Miner cumulative rule or estimated by probabilistic manners when the distribution of stress ranges is known. Current studies for fatigue damage of ship hull due to ice loads actions are limited and only for short-term collected ice load peaks and the associated ice-induced stress ranges (Chai et al. 2018b; Suyuthi et al. 2013a). Assessment of fatigue damage for long-term measurements remains undeveloped.

Future Work The abovementioned former studies are focus on the short-term measured ice load peaks. The methods mentioned in this entry can also be extended for long-term studies when relevant long-term measured data is available. Such studies for extreme value analysis of the ice loads and fatigue damage evaluation are directly related to the ultimate limit states and fatigue limit states of the Arctic ship during its service life. In addition, ice thickness is assumed to be the most representative parameter for the severity of the ice conditions. The ice thickness during the full-scale measurement voyage can be regarded as a random process with respect to time space. Due to the stochastic nature of ice loads and ice thickness, it is a challenge to establish a link between the prevailing ice conditions and iceinduced loads. This study would be achieved when the relevant long-term measured data is available. Furthermore, for current rule-based design method for Arctic ships, the reliability-based design method with considerations of the

Probabilistic Aspects for Ice Loads on Ships

randomness and uncertainties of the ice condition and ice loads could be an effective supplement.

References Chai W, Naess A, Leira BJ, Bulian G (2016) Efficient Monte Carlo simulation and Grim effective wave model for predicting the extreme response of a vessel rolling in random head seas. Ocean Eng 123:191–203 Chai W, Leira BJ, Naess A (2018a) Probabilistic methods for estimation of the extreme value statistics of ship ice loads. Cold Reg Sci Technol 146:87–97 Chai W, Leira BJ, Naess A (2018b) Short-term extreme ice loads prediction and fatigue damage evaluation for an icebreaker. Ships Offshore Struct 13(Suppl 1):127–137 Ehlers S, Cheng F, Jordaan I, Kuehnlein W, Kujala P, Luo Y, Ralph F, Riska K, Sirkar J, Oh Y (2015) V. 6 Arctic technology. In: Proceedings of the International Ship Structures Committee (ISSC), Taylor & Francis Jordaan IJ (2001) Mechanics of ice–structure interaction. Eng Fract Mech 68(17–18):1923–1960 Jordaan IJ, Maes MA, Brown PW, Hermans IP (1993) Probabilistic analysis of local ice pressures. J Offshore Mech Arct Eng 115(1):83–89 Kheisin D, Popov Y (1973) Ice navigation qualities of ships. Cold Regions Research and Engineering Laboratory Report, CRREL No. TL417, Hanover, United States Kujula P (1994) On the statistics of ice loads on ship hull in the Baltic. Helsinki University of Technology, Espoo Lensu M (2002) Short term prediction of ice loads experienced by ice going ships. Helsinki University of Technology, Espoo Næss A, Gaidai O (2009) Estimation of extreme values from sampled time series. Struct Saf 31(4):325–334 Naess A, Moan T (2012) Stochastic dynamics of marine structures. Cambridge, New York, United States Ochi MK (1990) Applied probability and stochastic processes: in engineering and physical sciences. Wiley-Interscience, New York Ralph F, Jordaan I (2013) Probabilistic methodology for design of arctic ships. In: ASME 2013 32nd international conference on ocean, offshore and Arctic engineering, American Society of Mechanical Engineers, p V006T007A010-V006T007A010 Riska K (2010) Ship-ice interaction in ship design: theory and practice. In: Encyclopedia of life support systems (EOLSS), developed under the auspices of the UNESCO. Eolss Publishers, Oxford, UK Suominen M (2018) Uncertainty and variation in measured ice-induced loads on a ship hull, PhD thesis, University of Alto, Espoo, Finland Suyuthi A, Leira B, Riska K (2013a) Fatigue damage of ship hulls due to local ice-induced stresses. Appl Ocean Res 42:87–104 Suyuthi A, Leira B, Riska K (2013b) Statistics of local ice load peaks on ship hulls. Struct Saf 40:1–10

Profiling Float Suyuthi A, Leira B, Riska K (2014) A generalized probabilistic model of ice load peaks on ship hulls in broken-ice fields. Cold Reg Sci Technol 97:7–20

Probability of Reliability ▶ Reliability and Safety in Offshore Engineering

Probability Theory ▶ Reliability-Based Design (RBD)

Profiling Float Lu Chen Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China

1411

Scientific Fundamentals Working Principle There are usually three ways in which objects can ascent and descent in water. One is to change the volume of the object without changing the weight; if the volume changed, the buoyancy will be changed; the other is to change the weight while keeping the volume constant, and then the net buoyancy is changed; the third is to increase or decrease the applied external force (Xu 2002; Yu et al. 2001). Early neutral floats changed the net buoyancy by changing their weight to achieve the motion ups and downs, so the volume were relatively large and cumbersome, and repeated measurements could not be performed. After a period of development, a method of changing the volume was used in the design of neutrally buoyant float. The neutrally buoyant floats periodically change their buoyancy by pumping the hydraulic fluid from an internal reservoir to an external bladder, thereby increasing float volume and buoyancy, so repeated measurements can be achieved, and the volume of the float was reduced a lot at the same time.

Synonyms Autonomous Lagrangian circulation explorer (ALACE); Deep-ocean profiling float (DOPF); Neutral float (NF); Regular profiling float (RPF); Self-sustaining profiling automation circulation detector (SPACD)

Definition Profiling float is also called “Autonomous Lagrangian circulation explorer (ALCE)” or “Self-sustaining profiling automation circulation detector (SPACD).” It is a measurement instrument which can freely drift in the ocean, and it uses the Lagrangian circulation method to automatically measure seawater temperature, electrical conductivity (salinity), and pressure from the sea surface to a certain depth and tracks the drift trajectory to obtain the velocity and direction of the current (Xu 2002).

History of Profiling Float The prototype of profiling float is a measurement instrument made by using Euler and Lagrange method to detect the sea surface or deep currents. Profiling floats were developed on the basis of neutral buoyant floats and integrated sensor technology, satellite positioning technology, and communication technology. In the summer of 1955, John Swallow made his first visit to the National Institute of Oceanography to discuss with oceanographers the possibility of making direct measurements of the vertical profile of currents in the deep ocean (Gould 2005). Swallow is the pioneer to develop the neutrally buoyant float. The first floats were constructed at the beginning of 1955 in the National Institute of Oceanography (NIO). At that time, materials and money were in short supply; the standard tubing had too great a wall thickness, so they put the tubes in a bath of caustic soda to thin the wall. Only

P

1412

Profiling Float

6 months after construction started, the first floats were deployed in June 1955. The floats weighed around 10 kg in air but had to be weighed in water in order that they could be ballasted to stabilize at their target depth. This was done by suspending each float from a simple chemical balance mounted above a tube of salt solution (close to a salinity of 35 and mixed by repeatedly lowering a bucket down the tube and hauling it up again to prevent stratification) in the stairwell of the NIO. The density of the saline solution was measured using high school physics techniques (specific gravity bottles). The floats needed only 38 g of negative buoyancy to stabilize at 1000 m, so great care was needed with the weighing and density calculations and to eliminate trapped air bubbles. Floats were used by NIO scientists in Labrador (See, Fig. 1). Though only two worked satisfactorily in the six floats, the method had been demonstrated, and the results were detailed enough to show evidence of tidal variations (Swallow 1955).

However, the concept of neutrally buoyant float had also been developed simultaneously and independently on the other side of the Atlantic. Stommel had also put forward to directly measure the deep currents by using the subsurface neutrally buoyant floats (Stommel 1955). He supposed that deep currents should be tracked through the Sound Fixing and Ranging (SOFAR) channel by the floats creating regular explosions. However, the discovery of an energetic ocean mesoscale exposed the limitations of ship-tracked floats. If the mean ocean circulation were to be revealed, so continuous observations over months would be needed. The problem was addressed by Rossby and Webb (1970); the floats could be tracked by sound transmissions through the SOFAR channel. Then hydrophones could be used to monitor the floats. The first two SOFAR floats (Fig. 2) were deployed in the Sargasso Sea in 1968 and showed that reception of signals was possible at ranges

Profiling Float, Fig. 1 John Swallow (left) and Gordom Volkmann on R. V. Erika Dan in 1962. The float shown here is essentially identical to floats deployed between 1957 and 1970 and using 10 kHz magnetostrictive nickel scroll transducers (Gould 2005)

Profiling Float, Fig. 2 Prototype SOFAR float (Gould 2005)

Profiling Float

of up to 1000 km and that float positions could be determined with an accuracy of the order of 3–5 km and with a life time of 9–12 months. In 1969, a float operating at 380 Hz was tracked for 4 months and confirmed the robustness of the technique. Each float weighed around 430 kg and was over 5 m long. The floats also had a 10 kHz, short-range navigation system to allow their location and subsequent recovery by a ship (Rossby and Webb 1971). The restriction of SOFAR floats at that time to depths near the sound channel axis (due to depth restrictions on the pressure cases) meant that it was not possible to use these floats to explore the vertical structure of currents over most of the water column (Swallow 1977). Thereby, a ship-based system using transponding floats made it possible by improved transducers, and microelectronics was developed by John Swallow and his coworkers (Swallow et al. 1974). The system allowed up to 18 floats to be tracked simultaneously. This ability to interrogate from a wide range of depths allowed tracking of floats at all depths and the achievement of ranges of up to 70 km. The SOFAR floats enabled day-to-day objective mapping of the ocean mesoscale over an area 400 km2 and revealed the longterm propagation of these features (Freeland et al. 1975; Freeland and Gould 1976). From the mid-1970s, acoustically tracked floats were used extensively to further explore the ocean’s mesoscale structure and variability. In the mid-1980s, there was a considerable interest in the potential for the disposal of radioactive waste either below or on the sea bed. Acoustically tracked floats were ideal for investigating the ocean circulation around potential disposal sites (Gould 2005). With the increasing of the investigation depth, the pressure cases of the aluminum tube could not meet the needs. Then floats using glass spheres as pressure cases were developed both in France and in the USA. The floats designed by Webb Research Corporation (WRC) using four glass spheres and transmitting at 260 Hz could reach the depths close to 3000 m with a lifetime of about 4 years (Rees and Gmitrowicz 1989) (Fig. 3).

1413

Profiling Float, Fig. 3 Deep SOFAR float using glass spheres. The uppermost sphere provides buoyancy, the middle two hold batteries, and bottom sphere contains electronics. The float is seen in a deployment cradle that was opened hydraulically when the float was below the sea surface (Gould 2005)

Due to the SOFAR tracking system needed to place the bulky and heavy sound sources on moorings, thus the usage of long-range floats was restricted. For this reason, the smaller and cheaper RAFOS floats were developed by Tom Rossby and his group (Rossby et al. 1986, 1993) to record the signal arrivals from an array of moored sources and transmit the data back to satellites when they surface at the end of their mission. The applications of various types of floats during the 1970s, 1980s, and 1990s on the scientific investigation were extensive and significantly improved our understanding of the oceanic eddy fields (Webb et al. 1970; Gascard 1973; Rossby et al. 1994; D’Asaro et al. 1996). Due to the measurement could not be done repeatedly by means of dropping a ballast weight,

P

1414

Profiling Float

the Autonomous Lagrangian circulation explorer (ALACE) was developed (Davis et al. 1992). It is a novel system which can be tracked globally. ALACE was subsurface float that cycles vertically from a depth where it was neutrally buoyant to the surface where it was located by, and relays data to, System Argos satellites (Davis et al. 1992). This type of float periodically changes their buoyancy by pumping hydraulic oil from an internal reservoir to an external bladder, thereby increasing float volume and buoyancy.

Because of positioning and data relay are accomplished by satellites, ALACEs are autonomous of acoustic tracking networks and are suitable for global deployment. Schematic of ALACE is shown in Fig. 4. After that, the oil bladder regulation device was widely used in the design of profiling float. As the small, low-power, autonomous CTD sensors with good long-term stability were developed by Falmouth Scientific Instruments and SeaBird Electronics, the full temperature and

Profiling Float, Fig. 4 Schematic of an ALACE. To ascend, the hydraulic pump moves oil from internal reservoir to external bladder. To descend, the latching value is opened allowing oil to flow back into internal reservoir. Antenna shown to right is mounted on the top hemispherical endcap (Davis et al. 1992)

ANTENNA PORT

EVACUATION PORT

DAMPING DISK

INTERNAL RESERVOIR 107 v ARGOS TRANSMITTER CONTROLLER AND CIRCUIT BOARDS MICROPROCESSOR BATTERY PACKS PUMP BATTERY PACKS

MOTOR FILTER

HYDRAULIC PUMP LATCHING VALVE PRESSURE CASE

EXTERNAL BLADDER 17 cm

Profiling Float

conductivity profiles were developed, and ALACE floats evolved to P-ALACE floats (Davis et al. 2001). The research of profiling floats began at the end of the Ninth Five-Year Plan (1996–2000) in China. COPEX profiling float was successfully developed by the National Ocean Technology Center of China in 2003. Another type of profiling float HM2000 was developed by 710 Research Institute of China Shipbuilding Industry Corporation (CSIC) in 2015. Although the development of profiling floats started relatively late in China, the Beidou satellite navigation and positioning system developed in China has the ability to determine the geographical location of users. In and around China, twoway brief digital message communication can be realized between the users, the user and the central control system in the Beidou user machine system. The user terminal has two-way digital message communication capabilities and has been successfully applied in profiling floats (Zhang et al. 2009; Wu et al. 2013). Due to the observation-based studies that demonstrated the warming of the deep ocean below 2000 m has significantly contributed to the mean sea level rise (Purkey and Johnson 2010; von Schuckmann et al. 2014), a strong requirement was proposed from the ocean and climate research community to expand the Argo coverage into the deep ocean below 2000 m. This was an essential element of the global ocean observing system envisioned by the OceanObs’09 conference (Garzoli et al. 2010; Church et al. 2011). Then four types of deep-ocean profiling float were developed, Deep Arvor, Deep NINJA, Deep APEX, and Deep SOLO. Deep Arvor and Deep NINJA can reach the depth of 4000 m; Deep APEX and Deep SOLO can reach a greater depth of 6000 m (Zilberman and Maze 2015; Reste et al. 2016). The deep-ocean profiling floats were shown in Fig. 5. Technical Challenge From the development process of profiling float, we can see that the industrial foundation largely determined the performance. The buoyancy

1415

regulation devices evolved from changing weight to changing volume; pressure hull evolved from aluminum housings to alloy hulls to glass spheres, etc., which can stand greater water pressure and explore deeper. However, to design a profiling float with superior overall performance is a systematic engineering. 1. Energy Efficiency The buoyancy regulation system is the basis for achieving ups and downs of the profiling floats, and it determines the performance of the float largely. The power consumption of the motor accounts for about 60% of the total power consumption of the measurement process (Reste et al. 2016). The energy efficiency is not only related to the motor, hydraulic pump, but also related to the control algorithm, the transmission speed of the communication and positioning system, and other factors. 2. Diving Depth The increased diving depth will inevitably lead to an increased difficulty of design. An increased design depth results in lower pump efficiency, higher motor power consumption, and higher requirements to the pressure material. Weight is also an important indicator for evaluating the performance of profiling floats. Lightweight profiling floats facilitate handling and deployment. The weight control is also a systematic project that involves every design element and component of the floats. Therefore, the pursuit of better performance will inevitably increase the cost. 3. System Reliability There are many causes of failure of the profiling floats, such as failure of the communication and positioning function, sensor failure, battery leakage, hydraulic oil leakage, failure of the pressure hull under special conditions, and so on. Reliable satellite transmission is critical to achieving the scientific goal of measuring subsurface currents. Surface drift must be accurately measured so that measurements of the much slower subsurface motions are not contaminated. Positions are not obtained exactly at

P

1416

Profiling Float

Profiling Float, Fig. 5 Deep-ocean profiling floats (http://www.argo.ucsd.edu/pictures.html)

the surfacing and descent times; therefore, it is necessary to extrapolate the observed positions to these times. Because this requires obtaining as many positions as possible, an important design objective for profiling float is to obtain

good surface following so that the antenna is rarely submerged. Another difficult problem is to avoid the loss of prime in the high-pressure pump caused by air bubbles in the hydraulic fluid.

Profiling Float

1417

Profiling Float, Fig. 6 Park & Profile Mission Operation (http://www.argo.ucsd.edu/How_Argo_floats.html)

P

Profiling Float, Fig. 7 Measurement process of float equipped with an ice probe sensor (http://www.argo.org.cn/index. php?c¼index&catid¼17&contentid¼453&f¼show&m¼content)

1418

The system reliability is closely related to the design and development process. Therefore, the reliability runs through the entire process of the floats.

Key Applications in the Argo Plan Argo is a global array of 3800 free-drifting profiling floats that measures the temperature and salinity of the upper 2000 m of the ocean. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection. The measurement process of regular Argo float and high-latitude ice exploration float was shown in Figs. 6 and 7, respectively. The origins of Argo can be found in the 1990–1997 World Ocean Circulation Experiment (WOCE). WOCE is part of the World Climate Research Programme (WCRP) and set out to collect an unprecedented set of observations. WOCE needed to collect data on ocean currents at about 1000 m throughout the oceans.

Cross-References ▶ Autonomous Underwater Vehicle (AUV) ▶ Glider

References Church JA, Gregory JM, White NJ et al (2011) Understanding and projecting sea level change. Oceanography 24(2):130–143 D’Asaro EA, Farmer DM, Osse JT, Dairiki GT (1996) A Lagrangian float. J Atmos Ocean Technol 13:1230–1246 Davis RE, Webb DC, Regier LA, Dufour J (1992) The autonomous Lagrangian circulation explorer (ALACE). J Atmos Ocean Technol 9:264–285 Davis RE, Sherman JT, Dufour J (2001) Profiling ALACEs and other advances in autonomous subsurface floats. J Atmos Ocean Technol 18(6):982–993 Freeland HJ, Gould WJ (1976) Objective analysis of mesoscale ocean circulation features. Deep-Sea Res 23:915–924

Profiling Float Freeland HJ, Rhines PB, Rossby T (1975) Statistical observations of the trajectories of neutrally buoyant floats in the North Atlantic. J Mar Res 33:383–404 Garzoli SL, Boebel O, Brydene H (2010) Progressing towards global sustained deep ocean observations. In: Hall J, Harrison DE, Stammer D (eds) Proceedings of OceanObs’09: sustained ocean observations and information for society. ESA Publ. WPP-306, vol 2 Gascard JC (1973) Vertical motions in a region of deep water formation. Deep-Sea Res 20:1011–1027 Gould WJ (2005) From Swallow floats to Argo – the development of neutrally buoyant floats. Deep-Sea Res II 52:529–543 Purkey S, Johnson GC (2010) Warming of global abyssal and deep Southern Ocean waters between the 1990s and 2000s: contributions to global heat and sea level rise budgets. J Clim 23:6336–6351 Rees JM, Gmitrowicz EM (1989) Dispersion measurements from SOFAR floats on the Iberian Abyssal Plain, pp 64–67. In: Nyffeler F, Simmons W (eds) Interim oceanographic description of the North-East Atlantic site for the disposal of low-level radioactive waste, vol 3. Nuclear Energy Agency/OECD, Paris, 374 pp Reste SL, Dutreuil V, André X (2016) “Deep-Arvor”: a new profiling float to extend the Argo observations down to 4000-m depth. J Atmos Ocean Technol 33:1039–1055 Rossby T, Webb D (1970) Observing abyssal motion by tracking Swallow floats in the SOFAR channel. DeepSea Res 17:359–365 Rossby T, Webb D (1971) The four month drift of a Swallow float. Deep-Sea Res 18:1035–1039 Rossby T, Dorson D, Fontaine J (1986) The RAFOS system. J Atmos Ocean Technol 3:672–679 Rossby T, Ellis J, Webb DC (1993) An efficient sound source for wide-area RAFOS navigation. J Atmos Ocean Technol 10:397–402 Rossby T, Fontaine J, Carter JEC (1994) The f/h float – measuring stretching vorticity directly. Deep-Sea Res I 41:975–992 Stommel H (1955) Direct measurements of sub-surface currents. Deep-Sea Res 2:284–285 Swallow JC (1955) A neutral-buoyancy float for measuring deep currents. Deep-Sea Res 3:74–81 Swallow JC (1977) An attempt to test the geostrophic balance using Minimode current measurements, pp 165–176. In: Angel M (ed) A voyage of discovery, George Deacon 70th anniversary volume. Pergamon Press, Oxford, 696 pp Swallow JC, McCartney BS, Millard NW (1974) The minimode float tracking system. Deep-Sea Res 21:573–595 von Schuckmann K, Sallée JB, Chambers D et al (2014) Consistency of the current global ocean observing systems from an Argo perspective. Ocean Sci 10:547–557 Webb DC, Dorson DL, Voorhis AD (1970) A new instrument for the measurements of vertical

Pure Loss of Stability currents in the ocean. In: Conference on electronic engineering in ocean technology, University College of Swansea, 21–24 September 1870, I.E.R.E. Provc., 19, pp 323–331 Wu W, Qi JC, Zhang J et al (2013) A new design of ARGO floats based on compass system. Meteorological Science and Technology 41(3):459–463 Xu JP (2002) Quest for Argo global ocean observations. Ocean Press, Beijing Yu LZ, Shang HM, Zhang SY (2001) Research on the technology of Argo profiling float. Journal of Ocean Technology 20(3):34–40 Zhang SY, Shang HM, Li WB (2009) Application of Beidou satellite navigation and position system in autonomous profiling exploring float. Ocean Technology 28(4):126–129 Zilberman N, Maze G (2015) Report on the Deep Argo implementation workshop. Ifremer Doc. LPO-15-04, 36 pp

1419

PTM – Passive Towed Mining ▶ Underwater Mining System

PTO – Power Take-Off ▶ Power Take-Off System

Pure Loss of Stability Min Gu, Jiang Lu, Shuxia Bu, Jilong Chu, Ke Zeng and Tianhua Wang China Ship Scientific Research Center (CSSRC), Wuxi, China

Project Execution Plan ▶ Field Development

Synonyms Loss of stability; Ship loses restoring in waves

Propeller Open Water Tests

Definition

▶ Towing Tank Test

Pure loss of stability was firstly named by Paulling as a kind of capsizing mode (1961) and afterward was under research and realization. Germany proposed pure loss of stability to be part of the stability criteria in the development of IMO in the second generation intact stability criteria. The case diagrammed in Fig. 1 shows a large wave approaching the ship from the stern, while the ship is underway with relatively high speed in following seas. If the celerity (speed) of the large wave is just slightly above the ship speed, the duration needed for the large wave to pass or overtake the ship may be long (“long” here means at least an order of magnitude greater than the natural roll period). Once the crest of the large wave is near the midship section of the ship, the righting lever may be significantly decreased. Further, because of the significant duration that this condition may exist, a large heel angle may develop, which could lead to capsize.

Protocol Design ▶ Underwater Acoustic Sensor Network

PSF – Partial Safety Factors ▶ Design of Renewable Energy Devices

PTD, Power Transmission and Distribution ▶ Power Transmission and Distribution

P

1420

Ship is underway in following waves. A large wave is approaching from the stern.

The large wave is overtaking the ship. If the time of exposure to the crest of the large wave is long enough, the stability failure may occur.

The large wave has passed the ship. The ship has regained its stability.

Pure Loss of Stability Typical changes of stability caused by relatively small waves.

Large decrease of the instantaneous GZ curve, caused by the crest of a large wave

Typical changes of stability caused by relatively small waves.

Pure Loss of Stability, Fig. 1 A possible scenario for the development of pure loss of stability (Belenky et al., 2011; SDC 3/WP.5/Annex 3, 2016)

Historical Development The stability in waves often becomes larger at the trough and becomes smaller at the crest comparing with that in calm water (Paulling, 1961). Pure loss of stability was identified during the model experiments in San-Francisco Bay (Paulling et al., 1972, 1975), and considered as a static capsizing mode that ship loses static restoring in waves (Oakley et al., 1974). Many researchers focused on the method to calculate the GZ curve in regular and irregular waves (Kuo et al., 1986; Hamamoto & Nomoto, 1982). One method for calculating the restoring variation in waves was developed by using the strip method of heave and pitch motion instead of the static method (Umeda et al., 2005). The restoring moment in irregular waves is considered a stochastic process (Dunwoody, 1989; Palmquist, 1994; Bulian & Francescutto, 2006). The Grim effective wave is used to

evaluate the probability of capsizing due to pure loss of stability in short-crested irregular sternquartering waves (Umeda & Yamakoshi, 1993). The waves are assumed to be a narrow-banded stochastic process instead of the Grim effective wave (Vermeer, 1990). The concept of a “critical wave” is used to evaluate the probability of capsizing (Themelis & Spyrou, 2007). The effective wave approach combined with the up-crossing theory is used to produce a time-dependent probability of stability failure (Bulian et al., 2008). The application of the split-time method to pure loss of stability is discussed by Belenky et al. (2015). Pure loss of stability is a nonlinear phenomenon involving a large amplitude roll motion, and Spyrou (Spyrou, 1997) suggested that the loss of stability could be related to periodic motion, accumulative broaching, and so on and it is still difficult to be predicted quantitatively. Hashimoto carried out experiments on pure loss of stability

Pure Loss of Stability

in following seas with an initial heel moment induced by cargo shift (Hashimoto, 2009). Jiang Lu further confirmed capsizing due to pure loss of stability may not be reproduced in the simulation and experiment in following seas without initial heel moments (Lu et al., 2019). Umeda firstly pointed out that pure loss of stability in stern quartering waves could not be really pure, and also the heeling moments induced by a centrifugal force due to ship maneuvering motions are the relevant external moments (Kubo et al., 2012). Umeda further argued the capsizing of the actual ship in stern quartering waves could be due to ship maneuvering motions of sway and yaw (Umeda et al., 2019). Jiang Lu further confirmed that the coupling force from the maneuvering sway and roll motions to roll motion is a key factor for pure loss of stability in stern quartering waves (Lu et al., 2020).

Key Numerical Method for Pure Loss of Stability The 4-DOF mathematical model is expressed by the surge, heave, roll, and pitch for pure loss of stability in following waves in the reference (Lu et al., 2019). The 6-DOF mathematical model is expressed by the surge, sway, heave, roll, pitch, and yaw motions for pure loss of stability in stern quartering waves in the reference (Lu et al., 2020). The surge, sway, yaw, and roll motions refer to the well-established models (Yasukawa & Yoshimura, 2015; Umeda et al., 2016) as shown in Eqs. (1)–(4), respectively. The heave and pitch motions are expressed in Eq. (5) and (6), respectively. The heave and pitch motions are calculated at each constant forward speed applied to an upright hull by a strip theory method using an enhanced integrating method of direct line integral to solve the velocity potential (Kashiwagi et al., 2010). The timedomain heave and pitch motions are calculated according to the relative position of the ship to waves as shown in Eqs. (7) and (8), respectively. The control equation for course-keeping by steering is added in the 6-DOF mathematical model as shown in Eq. (9).

1421

  ðm þ mx Þu_  m þ my vr ¼ X H þ XR þ XP þ XW 

ð1Þ

 m þ my v_ þ ðm þ mx Þur ¼ YH þ YR þ YW

ð2Þ

ðI zz þ J zz Þr_ ¼ N H þ N R þ N W

ð3Þ

:

:

ðI xx þ J xx Þ p  mx zH ur  my zH v ¼ K H þ K R þ K W DIf :  Dð’Þ  W  GZ W FK ðxG =l, zG ðtÞ, yðtÞ, w, ’Þ ð4Þ 



ðm þ A33 ðuÞÞ z þ B33 ðuÞz_ þ C33 z_ þ A35 ðuÞ y þ B35 ðuÞy_ þ C35 y ¼ FFK ðuÞ þ FDF ðuÞ 3

3

ð5Þ 

::   I yy þ A55 ðuÞ y þ B55 ðuÞy_ þ C55 y þ A53 ðuÞ z þ B53 ðuÞz_ þ B53 z ¼ FFK ðuÞ þ FDF ðuÞ 5

5

ð6Þ zG ðtÞ ¼ zGa ðuÞ cos ½2p  ðxG =lÞ  dH ðuÞ ð7Þ yðtÞ ¼ ya ðuÞ cos ½2p  ðxG =lÞ  dy ðuÞ

ð8Þ

d_ ¼ fd  K P ðw  wC Þ  K P T D r g=T E

ð9Þ

The subscript H, R, P, and W refer to hull, rudder, propeller, and wave, respectively. Eqs. (7) and (8) are seakeeping mathematical models, and their symbols are listed with the traditional seakeeping method as follows. ζG(t): heave displacement; θ(t): pitch angle; F3FK, F3DF: wave exciting force on heave direction including Froude-Krylov component and diffraction component; F5FK, F5DF: wave exciting moment on pitch direction including FroudeKrylov component and diffraction component; ζGa(u), δH(u): amplitude and initial phase of heaving when the ship’s forward speed is u; and θa(u), δ#(u): amplitude and initial phase of pitching when the ship’s forward speed is u. The dot denotes the differentiation with time. Aij, Bij, and Cij are coupling coefficients for added mass, damping, and restoring coefficients, respectively.

P

1422

Subscripts 3 and 5 denote heave and pitch directions, respectively.

Experimental Method for Pure Loss of Stability The ship model was driven by propellers in stern quartering seas in the free-running experiment. The roll, pitch, and yaw angles were measured by an optical fiber gyroscope placed on the ship model and the roll, pitch, yaw, and rudder angles and the propeller rotation speed was recorded by an onboard system which is connected with an onshore control computer wirelessly. The wave elevation was measured at the middle position of the basin by a servo-needle wave height sensor attached to a steel bridge which is 78 m in length and spans over the basin. Free roll decay tests in calm water were conducted to obtain roll damping coefficients. The speed is a key factor for pure loss of stability. Here the nominal Froude number (Fn) is used for the experiment of pure loss of stability in stern quartering waves by using the same specified propeller rate as in calm water. The specified propeller rate corresponding to one nominal speed in calm water is determined by measuring the instantaneous position of the model ship with a total station system. First, the model is kept near the wave maker manually by two workmen sitting on the carriage. The initial heading of the model is kept referring to the steel bridge which can rotate about its center, up to 45 degrees. Next, the wave-making system starts to generate waves. Then, the propeller revolutions increase up to the specified value according to the order received from the onshore control computer. When the wave train propagates far enough, the model is released free near one wave crest with its initial heading, and then the model automatically runs in stern quartering waves with its specified propeller rate and autopilot course by a course keeping system. The course keeping system includes the 6-DOF optical fiber gyroscope installed on the ship model and a PD control system is used for course keeping. The latter reacts according to the bias between the yaw angle from

Pure Loss of Stability Pure Loss of Stability, Table 1 Principal particulars of the ONR tumblehome Items Length:L Breadth:B Depth:D Draft:d Displ.:W CB GM OG LCB Tj kyy Κzz 2 AR DP δmax

Ship 154.0 m 18.8 m 14.5 m 5.494 m 8507 ton 0.535 1.48 m 2.729 m 2.569 m 14.0 s 0.25 L 0.25 L 2 23.74 m2 5.22 m 35degs

Model 3.800 m 0.463 m 0.358 m 0.136 m 127.8 kg 0.535 0.037 m 0.067 m 0.063 m 2.199 s 0.25 L 0.25 L 2 0.0145 m2 0.129 m 35degs

wave direction measured by the gyroscope and the yaw angle of autopilot course and the yaw velocity measured by the gyroscope. When the ship model is free running in calm water, a disturbance of yaw angle is made, and then the rudder gain is set by the experience according to the reaction of course keeping in calm water. The principal particulars and body plan of the ONR tumblehome are shown in Table 1 and Fig. 2, respectively. The ship model in the free running experiment is shown Fig. 3.

The Effect of Wave on Roll Restoring Variation When the midship section is located on the crest in following seas, the metacentric height is reduced and may be even negative. The righting arm in calm water GZ, the restoring variations in waves with the static balance method GZW-static and with the strip method at different constant forward speeds GZW (for Fn ¼ 0.0, 0.1 and 0.3) are shown in Fig. 4. The stability loss at the wave crest is significant, and if the state of stability loss at the crest exists long enough, the ship may capsize.

Pure Loss of Stability

1423

Pure Loss of Stability, Fig. 2 The ONR tumblehome lines

stability loss at the crest becomes larger as shown in Fig. 5. But the state of stability loss at the crest is not long enough to result in capsizal.

The Effect of Surge Motion on Pure Loss of Stability

Pure Loss of Stability, Fig. 3 The ship model in the freerunning experiment

The Effect of Constant Speed on Pure Loss of Stability The righting arm in calm water GZ and the restoring variations in waves GZW at different constant forward speeds are shown in Fig. 5. The encounter period becomes larger as the ship increases its forward speed, and the state of stability loss at the wave crest becomes larger. The roll angle due to pure loss of stability at different constant forward speeds is shown in Fig. 6, and the roll angle becomes larger as the ship forward speed increases because the state of

The nominal velocity of the ship at Fn ¼ 0.3, the actual velocity of the ship and the wave velocity are shown in Fig. 7. The nominal velocity of the ship is much smaller than the wave velocity, and the maximum actual velocity of the ship is also smaller than the wave velocity. The forward speed is varied in a large range around the nominal speed of the ship due to the surge motion, and the state at the crest exists longer than that at the trough. The righting arm in calm water GZ and the restoring variations in waves GZW with surge and without surge are shown in Fig. 8. The state of stability loss at the crest exists longer than that at the trough because the surge motion causes the state at the crest to exist longer than that at the trough as shown in Figs. 8 and 9. As shown in Fig. 10, the mathematical model with 3-DOF of heave-roll-pitch coupled motions

P

1424

Pure Loss of Stability

Pure Loss of Stability, Fig. 4 Restoring variation in following seas with ’ ¼ 10 degrees, l/ Lpp ¼ 1.25, H/l ¼ 0.05, and w ¼ 0 degree

GZw-stac

GZ

GZw(Fn=0.1)

GZw(Fn=0.3)

GZw(Fn=0.0)

0.3

φ=10 degrees 0.25

GZ [m]

0.2 0.15 0.1 0.05 0 0

0.2

0.4

0.6

0.8

1

ξG/λ

Pure Loss of Stability, Fig. 5 Time-domain restoring variation in following seas with j ¼ 10 degrees, l/ Lpp ¼ 1.25, H/l ¼ 0.05, and w ¼ 0 degree

GZ

GZw(without surge,Fn=0.0)

GZw(without surge,Fn=0.1)

GZw(without surge,Fn=0.3)

0.3

φ=10 degrees

GZ [m]

0.25 0.2 0.15 0.1 0.05 0 0

20

40

60

80

t [s]

fails to predict capsizing because the state of stability loss at the crest is not long enough while that with 4-DOF of surge-heave-roll-pitch coupled motions could appropriately estimate the pure loss of stability in following seas. One key reason is that the state at the crest exists longer than that at the trough due to the surge motion and then the state of stability loss at the crest exists long enough. Therefore, the surge motion is important for predicting pure loss of stability in following seas.

The Effect of Initial Heel Angle on Pure Loss of Stability Without an external heeling moment, once the wave crest passes the ship, the ship will finally return to the upright position with regained stability as shown in Fig. 10 with ’ ¼ 0 degree. The initial heeling angle is set as 8.6 degrees by cargo shift in the experiment and capsizing happens due to pure loss of stability as shown in Fig. 10. For investigating the effect of the initial heeling angle

Pure Loss of Stability

1425

Maximum roll angle [degrees]

Pure Loss of Stability, Fig. 6 The effect of the constant speed on pure loss of stability with an initial heeling j ¼ 8.6 degrees, l/Lpp ¼ 1.25, H/l ¼ 0.05, and w ¼ 0 degree

Sim-3DOF without surge 60 50 40 30 20 10 0 0

0.1

0.2

0.3

Fn

Velocity [m/s]

Pure Loss of Stability, Fig. 7 Comparison between ship velocity and wave velocity with nominal Fn ¼ 0.3, l/Lpp ¼ 1.25, H/l ¼ 0.05, and w ¼ 0 degree

ship actual velocity wave velocity

20 18 16 14 12 10 8 6 4 2 0

ship nominal velocity

Fn=0.3

0

50

100

150

200

250

300

t [s]

P

Pure Loss of Stability, Fig. 8 The effect of surge motion on restoring variation with ’ ¼ 10 degree, l/Lpp ¼ 1.25, H/l ¼ 0.05, and w ¼ 0 degree

GZ GZw(3DOF without surge,Fn=0.3) GZw(4DOF with surge,average Fn=0.3 for heave&pitch) GZw(4DOF with surge,varied Fn=0.3 for heave&pitch)

0.3

φ=10 degrees

GZ [m]

0.25 0.2 0.15 0.1 0.05 0 0

20

40

-0.05

t [s]

60

80

Pure Loss of Stability, Fig. 9 The effect of the sure motion on pure loss of stability with an initial heeling j ¼ 8.6 degrees, l/Lpp ¼ 1.25, H/l ¼ 0.05, and w ¼ 0 degree

Pure Loss of Stability

Maximum roll angle [degrees]

1426

Sim-3DOF without surge

Sim-4DOF

EXP 80

capsizing 60 40 20 0 0.2

0.25

0.3

0.35

0.4

Pure Loss of Stability, Fig. 10 The effect of initial heeling angles on pure loss of stability with l/ Lpp ¼ 1.25, H/l ¼ 0.05, and w ¼ 0 degree (j ¼ 0, 2 ,4 ,6 ,8 degrees)

Maximum roll angle [degrees]

Fn

80

Sim-4DOF(0)

Sim-4DOF(2)

Sim-4DOF(6)

Sim-4DOF(8)

Sim-4DOF(4)

capsizing 60 40 20 0 0.2

0.25

0.3

0.35

0.4

Fn

on pure loss of stability, simulations with different initial heeling angles are carried out as shown in Fig. 10. The roll angles become larger as the initial heeling angles increases, and capsizing happens at the critical speeds due to pure loss of stability. However, the ship could be captured by a wave crest when the ship has a very small initial heeling angle in following seas at a high speed. That is to say, the ship reaches the speed of the wave in this case.

The Effect of the Coupling Forces from the Maneuvering Forces in the Sway and Yaw Directions in Stern Quartering Waves The 6-DOF mathematical model without the coupling forces in the roll direction due to the

manoeuvring force in the sway direction underestimates roll angles and fails to correctly predict capsizing range of critical ship speeds as shown in Fig. 11. This is due to its negative contributions to the roll moment as shown in Fig. 12. The calculated results with the coupling forces in the roll direction due to the manoeuvring force in the yaw direction are smaller than without it, as shown in Fig. 11. This is due to its positive contribution to the roll moment as shown in Fig. 13.

The Type of Roll Motions During Pure Loss of Stability The experimental results of yaw, roll, pitch motions, and rudder angle in stern quartering waves are shown in Fig. 14.

Pure Loss of Stability, Fig. 11 Comparison of maximum roll angle as a function of the Fn between the experimental results and calculated results with the 6 DOF with and without centrifugal force in roll direction due to the manoeuvring forces in the sway and yaw directions with l/Lpp ¼ 1.25, H/ l ¼ 0.05, and w ¼ 30 degrees

1427

Maximum roll angle [degrees]

Pure Loss of Stability

EXP

6 DOF

6 DOF without Kv*U*V

6 DOF without Kr*U*R

90 80 χ=30degrees 70 60 50 40 30 20 10 0 0.2 0.25

capsizing

0.3

0.35

0.4

Fn

Pure Loss of Stability, Fig. 12 The contribution to the rolling moments from the coupling force in the roll direction due to manoeuvring motions in the sway direction

P Pure Loss of Stability, Fig. 13 The contribution to the rolling moments from the coupling force in the roll direction due to manoeuvring motions in the yaw direction

1428

a

yaw - 30 30

roll

rudder angle

pitch

EXP,nominal Fn=0.225,λ/Lpp=1.25, H/Lpp=0.05

[degrees]

20 10 0 -10 0

20

40

60

80

100

120

-20 -30 -40

t [s]

[degrees]

b

yaw - 30

40 30 20 10 0 -10 0 -20 -30 -40 -50 -60 -70

roll

rudder angle

pitch

EXP,nominal Fn=0.275,λ/Lpp=1.25, H/Lpp=0.05

50

100

150

200

250

t [s]

c

yaw - 30 40

roll

rudder angle

pitch

EXP,nominal Fn=0.31,λ/Lpp=1.25, H/Lpp=0.05

20

[degrees]

Pure Loss of Stability, Fig. 14 Yaw, roll, pitch motions, and rudder angle in the free-running experiment with l/Lpp ¼ 1.25, H/l ¼ 0.05, and w ¼ 30 degrees. (a) Stable roll motion far from the critical speed of pure loss of stability. (b) Unstable roll motion near the critical speed of pure loss of stability. (c) Capsizing due to coupled pure loss of stability and broaching

Pure Loss of Stability

0 -20 0

20

40

60

-40 -60 -80 -100

t [s]

80

100

Pure Loss of Stability

A stable periodic roll motion can be found when the ship speed is far from the critical speed of pure loss of stability as shown in Fig. 14a, while an unstable roll motion can be found when the ship speed is close to the critical speed, as shown in Fig. 14b. The capsizing due to pure loss of stability is shown in Fig. 14c, and the yaw angle subtracting the heading angle reaches 20 degrees and the rudder angle reaches the maximum 35 degrees when the ship capsizes. The capsizing occurs due to pure loss of stability before developing the larger yaw angle, i.e., the maximum rudder angle cannot correct the course and obviously broaching stops due to the capsizal of the model. This could be a new phenomenon of capsizing due to coupled pure loss of stability and broaching. As parametric roll, resonant roll, unstable roll motions, and capsizing due to coupled pure loss of stability and broaching could exist during pure loss of stability, further research should be conducted in the future to shed some light on this complex phenomenon.

References Belenky VL, Bssler C, Spyrou J. Development of second generation intact stability criteria[R]. Hyromechanics Dept. Report, NSWCCD-50-TR-2011/065 Belenky V, Weems K, Lin W-M. Split-time method for estimation of probability of capsizing caused by pure loss of stability. Proceedings of the 12th International Conference on Stability of Ships and Ocean Vehicles. Glasgow, UK, 2015 Bulian G, Francescutto A. On the effect of stochastic variations of restoring moment in long-crested irregular longitudinal sea. Proceeding 9th International Conference on Stability of Ships and Ocean Vehicle. Rio de Janeiro, Brazil 2006;1:131–146 Dunwoody AB. Roll of a ship in Astern Seas-metacentric height spectra. J Ship Res 1989;33(03):221–228 Hamamoto M, Nomoto K. Transverse stability of ships in a following sea. Proceeding of the 2nd International Conference on Stability of Ships and Ocean Vehicles 1982:215–224 Hashimoto H. Pure loss of stability of a tumblehome hull in following seas. Proceedings of the 19th International Offshore and Polar Engineering Conference. Osaka, Japan, 2009;21–26 IMO, Finalization of second generation intact stability criteria, Report of the working group (part 1), SDC 3/WP.5/Annex 3, 2016

1429 Kubo H, Umeda N, Yamane K, Matsuda A. Pure loss of stability in Astern Seas-is it really pure? Proceedings of the 6th Asia-Pacific Workshop on Marine Hydrodynamics 2012;307–312 Kuo C, Vassalos D, Alexander JG. Incorporating theoretical advances in usable ship stability criteria. RINA Int conf of SAFESHIP project. Ship Stab and Saf, London, 1986 Lu J, Gu M, Boulougouris E. Model experiments and direct stability assessments on pure loss of stability of the ONR tumblehome in following seas. Ocean Eng 2019;194:106640 Lu J, Gu M, Boulougouris E. Model experiments and direct stability assessments on pure loss of stability in stern quartering waves. Ocean Eng 2020;216:108035 Oakley OH, Paulling JR, Wood PD. Ship motions and capsizing in Astern Seas. 10th Symposium on Naval Hydrodynamics, 1974;1–51 Palmquist M. On the statistical properties of the metacentric height of ships in following seas. Proceeding of 5th International Conference on Stability of Ships and Ocean Vehicle. Melbourne Florida, 1994 Paulling JR. The transverse stability of a ship in a longitudinal seaway. J Ship Res 1961;44:37–49 Paulling JR, Kastner S, Schaffran S. Experimental studies of capsizing of intact ships in heavy seas. U.S. Coast Guard, Tech Rep (Also IMO Doc. STAB/7, 1973), 1972 Paulling JR, Oakley OH, Wood PD. Ship capsizing in heavy seas: the correlation of theory and experiments. Proceeding of 1st International Conference on Stability of Ships and Ocean Vehicle. Glasgow, 1975 Spyrou KJ. Dynamic instability in quartering seas-Part III: Nonlinear effects on periodic motions. J Ship R SNAME 1997;41(3):210–223 Themelis N, Spyrou KJ. Probabilistic assessment of ship stability trans. SNAME 2007;115:181–206 Umeda N, Yamakoshi Y. Probability of ship capsizing due to pure loss of stability in quartering seas. Nav Archit and Ocean Eng: Sel Pap Soc of Naval Arch of Japan 1993;30:73–85 Umeda N, Hashimoto H, Sakamoto G, Urano S. Research on roll restoring variation in waves. Conference Proceedings of the Kansai Society of Naval Architects, 2005 Umeda N, Usada S, Mizumoto K, Matsuda A. Broaching probability for a ship in irregular stern-quartering waves: theoretical prediction and experimental validation. J Marine Sci Technol 2016;21:23–37 Umeda N, Osugi M, Ikenaga Y, Matsuda A. Pure loss of stability in stern quartering waves: revisited with numerical simulations reproducing accidents. In 17th International Ship Stability Workshop, Helsinki, Finland, 2019 Vermeer H. Loss of stability of ships in following waves in relation to their design characteristics. Proceedings of the 4th International Conference on Stability of Ships and Ocean Vehicles, Naples, 1990 Yasukawa H, Yoshimura Y. Introduction of MMG standard method for ship manoeuvring predictions. J Marine Sci Technol 2015;20:37–52

P

Q

Quadrature Amplitude Modulation (QAM) ▶ Underwater Acoustic Communication

© Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

R

Radar Navigation System ▶ Ship Navigation System

extent practicable, eliminate accidents, injuries, and other adverse effects on human health and the environment caused by ship recycling.

Scientific Fundamentals

Radio Navigation System ▶ Ship Navigation System

Range-Gated Imaging ▶ Photoelectric Detection Technology in Underwater Vehicles

Recycling Regulations Wanhai Xu, Enhao Wang and Xifeng Gao State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China

Definition Recycling regulations are the laws, rules, and conventions issued by authorities which are utilized to regulate ship recycling. They are introduced in the attempt to prevent, reduce, minimize, and, to the © Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

Introduction According to the European Commission (EC), around 1000 large end-of-life ships all over the world are dismantled every year to recycle the steel and equipment. Most of this ship recycling takes place in South Asia, often on tidal beaches and under dangerous conditions which lead to health risks and extensive pollution of coastal areas. In fact, old ships contain many hazardous materials including asbestos, polychlorinated biphenyls (PCBs), tributyltin, and large quantities of oils and oil sludge. In order to reduce those negative effects of this industry, some laws, rules, and conventions have been made by national and international institutions. Nowadays, the most widely used and famous ones among them are the Basel convention, the Hong Kong Convention, and the EU Ship Recycling Regulation. The Basel convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal, usually known as the Basel Convention, was open for signature on 22 March 1989 and entered into force on 5 May 1992. It is an international treaty that was designed to reduce the movements of hazardous wastes between nations and specifically to prevent transfer of

1434

hazardous wastes from developed to less developed countries (LDCs). It does not, however, address the movement of radioactive wastes. The Convention is also intended to minimize the amount and toxicity of wastes generated, to ensure their environmentally sound management as closely as possible to the source of generation, and to assist LDCs in environmentally sound management of the hazardous and other wastes they generate. As of February 2018, 185 states and the European Union (EU) are parties to the Convention. Among them, Haiti and the United States have signed the Convention but not ratified it. The Hong Kong International Convention for the Safe and Environmentally Sound Recycling of Ships (or the Hong Kong Convention, for short) was adopted on 15 May 2009 by an IMO Diplomatic Conference of the International Maritime Organization (IMO) held in Hong Kong, China. This Convention covers the design, construction, operation, and preparation of ships so as to facilitate a sustainable ship recycling without compromising the safety and operational efficiency of ships. It also regulates the establishment of an appropriate enforcement mechanism for ship recycling, incorporating certification, and reporting requirements. From 2011, the IMO has developed several guidelines to assist the States Parties in the early implementation of the Convention’s technical standards. The EU Ship Recycling Regulation (1257/ 2013) entered into force on 30 December 2013 to reduce the negative impacts related to the recycling of EU-flagged ships, especially in South Asia. The Regulation is based on the Hong Kong Convention and aims to implement the Convention quickly, without waiting for its ratification and entry into force. To speed up the formal entry into force of the Hong Kong Convention, the Commission proposal for a Ship Recycling Regulation was accompanied by a draft decision requiring member states to ratify the Hong Kong Convention. History Pressure demanding a safer and a more environmentally friendly ship recycling industry has been building up over past decades and has found outlets among politicians and administrations, who

Recycling Regulations

have looked for ways to regulate ship recycling with international common standards. The first attempt at addressing the problem was to try to implement “The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal,” which was adopted in 1989 and entered in force in 1992. The Basel Convention protects the human health and the environment against adverse effects that result from the generation and management of hazardous and other wastes. In particular, the Basel Convention focuses on regulating the transboundary movement of hazardous wastes in its effort to protect developing countries from importing hazardous wastes that they are unable to manage in an environmentally sound manner. However, Basel does not establish a dedicated system for ships. Its provisions, and particularly its system of Prior Informed Consent designating a State of export, did not envisage ships. This has created difficulties in enforcing the Convention to end-of-life ships, especially in the European Union where the Basel Convention is implemented along with an amendment forbidding the export of hazardous wastes to non-OECD countries. Examples of cases where serious difficulties were experienced include the Otapan, the Sea Beirut, the Sandrien, the Margaret Hill, the Tor Anglia, the Onyx, and others. As early as October 2004, the seventh Conference of the Parties to the Basel Convention, in its decision VII/26, invited IMO to consider the establishment in its regulations of mandatory requirements that ensure an equivalent level of control as established under the Basel Convention and also ensure the environmentally sound management of ship dismantling, and “which might include pre-decontamination within its scope.” In 2003, the IMO adopted the IMO Guidelines on Ship Recycling (International Maritime Organisation 2003) and later in 2004 published for the Guidelines for the Development of the Ship Recycling Plan (International Maritime Organisation 2004). The International Labour Organization (ILO) published guidelines regarding safety and health issues in shipbreaking in 2004 which were subsequently translated into the local languages of major ship recycling countries (International Labour Organisation 2008).

Recycling Regulations

Cooperation between IMO, ILO, and the Basel Convention Secretariat resulted in the establishment of a joint working group in 2005 in order to coordinate each party’s activities and reduce regulatory overlaps (International Maritime Organisation 2005). A ship recycling conference organized by Lloyd’s List in April 2005 discussed inter alia the necessity of a mandatory system. The EU adopted its “Waste Shipment Regulation” (WSR) which was fully transposed and implemented from both the Basel Convention and the Basel Ban Amendment in 2006. In 2007, the EC published the “Green Paper on Better Ship Dismantling,” which was further elaborated in the report “An Integrated Maritime Policy for the European Union” (European Commission 2007) and finalized in the document “An EU Strategy for Better Ship Dismantling” in late 2008 (European Commission 2008). Prior to this, as early as January 2008, IMO published its “Draft Convention on Safe and Environmentally Sound Recycling of Ships.” About the same time, the International Organization for Standardization (ISO) launched a new series of standards with regard to the recycling of ships (Engels 2013). It took just over 3 years since IMO agreed to develop a “new legally binding instrument on ship recycling” through an assembly resolution in December 2005 to develop the “Hong Kong International Convention for the Safe and Environmentally Sound Recycling of Ships,” which is also known as the Hong Kong Convention (International Maritime Organisation 2009). And the Hong Kong Convention was finally adopted at a diplomatic conference held in Hong Kong in May 2009. On 30 December 2013, the EU Ship Recycling Regulation (1257/ 2013) (European Union 2013) which was based on the Hong Kong Convention entered into force.

Key Applications Hong Kong Convention Structure

As its core, the Hong Kong Convention contains 21 articles and an annex comprising of another 26 regulations stipulating general provisions as

1435

well as specific requirements for ships, ship recycling facilities, and reports. This annex is followed by additional seven appendices containing a particular range of forms and checklists which are supposed to facilitate compliance with the provisions of the Hong Kong Convention. Furthermore, seven guidelines have been developed under the auspices of the IMO which relate to the implementation of a specific set of major obligations (Engels 2013). Figure 1 clearly depicts the basic structure of it. Applicability

The Hong Kong Convention applies to “ship” and to “ship recycling facilities” of parties. Here, “ship” means a vessel of any type whatsoever operating or having operated in the marine environment and includes submersibles, floating craft, floating platforms, self-elevating platforms, floating storage units (FSUs), and floating production storage and offloading units (FPSOs), including a vessel stripped of equipment or being towed. And “ship recycling facilities” means a defined area that is a site, yard, or facility used for the recycling of ships. However, ships less than 500 GT, warships, naval auxiliaries, or other ships “owned or operated by a Party and used, for the time being, only on government non-commercial service” and ships that are “operating throughout their life only in waters subject to the sovereignty or jurisdiction of the State whose flag the ship is entitled to fly,” if recycled in the same state where they have operated, are exempted from its terms. Even so, each Party shall adopt appropriate measures to ensure such ships act in a manner consistent with this Convention, so far as is reasonable and practicable. With respect to non-Parties ships, Parties shall apply the requirements of this Convention in a manner so as not to afford any favorable treatment (Engels 2013). “Ship recycling” is defined by the Hong Kong Convention as “the activity of complete or partial dismantling of a ship at a Ship Recycling Facility in order to recover components and materials for reprocessing and re-use, whilst taking care of hazardous and other materials, and includes associated operations such as storage and treatment of components and materials on site, but not their further processing or disposal in separate facilities” (Puthucherril 2010). Therefore, the scope of

R

1436

Recycling Regulations

Recycling Regulations, Fig. 1 Structure of the Hong Kong convention

the convention is confined only to activities like scrapping and storage in the recycling yard and does not extend to the remaining steps in the recycling chain. Key Objectives

The Hong Kong Convention is applied to prevent, reduce, minimize, and, to the extent practicable, eliminate accidents, injuries, and other adverse effects on human health and the environment caused by Ship Recycling and enhance ship safety, protection of human health and the environment throughout a ship’s operating life. Major Obligations

Major obligations of the Convention stipulate requirements for ships, requirements for ship recycling facilities, and reporting requirements. Requirements for ships may generally be divided into three parts: (1) Provisions addressing the problem of hazardous materials such as Regulation 4 and Regulation 5 (2) Regulation 9 on the establishment of a ship recycling plan

(3) The far-ranging Regulation 10 on the establishment of a number of different surveys Requirements for Ship Recycling Facilities Regulations 15–23 affect ship-recycling facilities by stating certain standards which must be complied with Regulations 17 and 18 addressing the general requirements and the ship recycling facility plan are central to the regulating chapter on ship recycling facilities. Regulations 24 and 25 contain notification and reporting requirements, thus comprising the final category of obligations. They primarily address the ship recycling facility but require a certain quality of cooperation by the ship owner. By regulating the whole ship recycling process from the intention of the ship owner to recycle a ship until the completion of the recycling procedure and by constantly involving official and private stakeholders, these regulations essentially cover also the recycling process from “cradle to grave.” Entry into Force

This Convention shall enter into force 24 months after the date on which the following conditions are met (Mikelis 2010):

Recycling Regulations

(1) Not less than 15 States have either signed it without reservation as to ratification, acceptance or approval, or have deposited the requisite instrument of ratification, acceptance, approval or accession in accordance with Article 16; (2) The combined merchant fleets of the States mentioned in paragraph 1.1 constitute not less than 40% of the gross tonnage of the world’s merchant shipping; and (3) The combined maximum annual ship recycling volume of the States mentioned in paragraph 1.1 during the preceding 10 years constitutes not less than 3% of the gross tonnage of the combined merchant shipping of the same States. 1989 Basel Convention Basic Scheme

The Basel Convention applies to “transboundary movement” of “hazardous wastes.” The transport is considered “transboundary movement” when it involves any movement of hazardous wastes or other wastes, from one national jurisdiction of one state to or through the national jurisdiction of another state. The waste is “hazardous waste” as is listed in Annex I of the Basel Convention, unless they do not contain the characteristics listed in Annex III. The Basel Convention has proved to be a basis for actions against substandard shipping in developing countries, which has in some cases forced an improvement in practices. However, the Basel Convention regime has been criticized throughout its operation for being ineffective in solving the problems related to ships (University of Southampton 2013). Applicability

Whether ships sent and/or sold for recycling fall within the regulatory scope of the Basel Convention, is contingent upon three elements: (1) The ships have to be classified as waste. (2) The ships have to be subject to transboundary movement. (3) Both the State of Export and the State of Import have to be parties to the Basel Convention.

1437

Generally, the Basel Convention is open and broad in its scope of application in order to encompass as many different kinds of wastes as theoretically and practically feasible. Objectives

The primary objectives of the Basel Convention include minimizing the generation and transboundary movement of hazardous and other wastes and ensuring environmentally sound management of these wastes. The Parties to the Basel Convention are obliged to minimize the generation of hazardous wastes and to promote adequate disposal within the state where such wastes are generated. The goal is to prevent dumping of toxic wastes onto developing countries. This goal is sought accomplished by reducing the generation of wastes and increase the capacity of the generating state to dispose of its own wastes (University of Southampton 2013). Main Obligations

It is of note that the Convention places a general prohibition on the exportation or importation of wastes between Parties and non-Parties. The exception to this rule is where the waste is subject to another treaty that does not take away from the Basel Convention. According to the definition as provided by the Basel Convention, ships sent for recycling operations fall, in principle, within the scope of the Basel Convention. If a State of Export has been established, then it will need to comply with Article 6 and its “prior informed consent” (PIC) regime. Article 4 of the Basel Convention calls for an overall reduction of waste generation. By encouraging countries to keep wastes within their boundaries and as close as possible to its source of generation, the internal pressures should provide incentives for waste reduction and pollution prevention. Parties are generally prohibited from exporting covered wastes to, or import covered wastes from, non-parties to the convention. According to Article 12, Parties are directed to adopt a protocol that establishes liability rules and procedures that are appropriate for damage that comes from the movement of hazardous wastes across borders.

R

1438

Besides, there are some party obligations under the Basel Ban Amendment (Decision III/1). The Basel Ban obligation states that all Annex VII Parties have a special obligation to “prohibit all transboundary movements of hazardous wastes which are destined for operations according to Annex IV A to States not listed in Annex VII.” Other Related Regulations 1982 UNCLOS

The 1982 United Nations Convention on the Law of the Sea (UNCLOS) establishes for its States Parties an overarching framework of rights and obligations relating to maritime affairs whose provisions on the protection of the marine environment (Part XII), according to many states, reflect rules of international customary law. The convention’s overall significance is explicitly recognized by the Hong Kong Convention. As stipulated by the preamble of UNCLOS, its objective is to establish a form of constitutional framework for the oceans focusing on the role of sovereign states within and toward the marine environment with the main objective of preserving sustainability. The fact that UNCLOS is a framework convention means that it has to be filled with substance by other instruments, both regionally and globally (Engels 2013). 1998 Rotterdam Convention

The Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade promotes a regulatory regime concerned with transboundary movements of particular hazardous chemicals. This convention is of particular relevance in the ship recycling context as it serves as an example of a specific set of relevant principles and concepts, such as prior informed consent, which have been agreed upon at the international level regarding transboundary trade with certain chemicals and pesticides. Hence, these considerations might also be relevant with regard to ship recycling, especially if one considers the principal PIC procedure as a means of safeguarding states’ sovereignty.

Recycling Regulations

1972/1996 London Convention

The London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, which is planned to be replaced by its Protocol after successful ratification, is an international instrument which aims at preventing “the pollution of the sea by the dumping of waste and other matter that is liable to create hazards to human health, to harm living resources and marine life, to damage amenities or to interfere with other legitimate uses of the sea.” The London Convention is not directly applicable to ship recycling. The convention and its protocol may rather be considered as a complement to ship recycling initiatives insofar as both abandoning ships and dumping them on the high sea still is considered by some actors as a mean of manage ships at the end of their final life cycle. International Standards and Guidelines

A number of standardization organizations have been providing sets of relevant international and technical instruments, thus inter alia contributing to “harmonization of environmental standards, primarily by facilitating corporate behavior changes.” The most well-known standards are those developed and issued by the International Organization for Standardization (ISO). It uses a similar procedure to develop standards, guidelines, and related information as the OECD and may therefore also be labelled an instance of “network governance.” For ship recycling, the series of standards under ISO 9.000, ISO 14.000, and ISO 30.000 are of particular relevance. European Initiatives in the Fields of Ship Recycling Applicability

The territorial scope of the treaty defined in Articles 52 and 355 TFEU348 limits the scope of direct regulatory measures available to the EU in the field of ship recycling. However, the flag state jurisdiction provides just such an example of extraterritorial jurisdiction, which is one of the fundamental exemptions. Therefore, where these competencies have been conferred to the EU, the EU law would be applicable, regardless of

Recycling Regulations

whether the ship is located within member states’ waters. Additionally, via port state jurisdiction, the EU legislation could also be made applicable to all ships of foreign registries calling at ports of EU member states. Objectives

The overall objective of European initiatives in the field of ship recycling is to “contribute to safer and more environmentally sound treatment of end-of-life ships worldwide.” In the present situation, and with special consideration for the Hong Kong Convention, the EU measures may thus be based upon provisions for the protection of the environment, provisions aiming at improving the working environment, and provisions on the safety of transport at sea. Fundamental Principles

According to Article 191.2 TFEU, environmental measures of the EU shall be based on inter alia, the Precautionary Principle and the Polluter Pays Principle. Potentially hazardous materials shall be identified ex ante as “potential sources of concern,” they shall be listed in inventories which shall accompany each ship in a “properly maintained and updated” fashion throughout its operating life in order to facilitate later recycling operations and minimize related risks to the environment and/or human health, and, with regard to supplementary data regarding hazardous materials, upon request an evaluation shall be conducted “of the association between the Hazardous Material in question and the likelihood that it will lead to significant adverse effects on human health or the environment.” All these aspects can only be fully understood in the context of the Precautionary Principle, as various legal obligations are established requiring action at a point of time when there is no imminent environmental threat. In addition, capacity building via transfer of knowledge might also “raise the standards of protection and precaution in the countries concerned.” As a matter of course, the EU will take these considerations into account when enacting related legislation. The principle of “Polluter Pays,” namely, the 1992 Rio Declaration, Principle 16 states: National

1439

authorities should endeavor to promote the internalization of environmental costs and the use of economic instruments, taking into account the approach that the polluter should, in principle, bear the cost of pollution, with due regard to the public interest and without distorting international trade and investment. Of far greater importance in practice, at least from a European point of view, the principle of “Polluter Pays” has found its way into numerous judgments of the European Court of Justice in recent years. Additionally, the European Commission explicitly is of the opinion that environmentally sound ship recycling is first and foremost the producer’s responsibility and should therefore follow the Polluter Pays Principle. Waste Shipment Regulation (No 1013/2006) The EU fully transposed and implemented both the Basel Convention and the Basel Ban Amendment by adopting its “Waste Shipment Regulation” (WSR). According to this regulation, ship recycling capacity currently available to ships flying the flags of the EU member states is considerably restricted, effectively to the existing Turkish and British ship recycling facilities. Therefore, the practice is that most of European ship owners obviously make use of loopholes and prefer to contract with substandard Asian ship recycling facilities in order not to face the costs and/or administrative burdens resulting from the application of the WSR. The EU Ship Recycling Regulation (No 1257/ 2013) Structure

The EU Ship Recycling Regulation mainly contains 32 articles, comprising of 6 titles and 2 annexes which give the list of hazardous material and their control measures. Figure 2 demonstrates the basic structure of the EU Ship Recycling Regulation. Applicability

The Ship Recycling Regulation applies to large commercial seagoing vessels flying the flag of an EU member state and to ships flying the flag of a third country calling at the EU ports or

R

1440

Recycling Regulations

Recycling Regulations, Fig. 2 Structure of the EU ship recycling regulation

anchorages. In order to ensure legal clarity and avoid administrative burdens, ships flying the flag of a member state covered by the new legislation would be excluded from the scope of the Waste Shipment Regulation (EC 1013/2006). According to the new rules, the installation or use of certain hazardous materials on ships, such as asbestos, ozone-depleting substances, PCBs, PFOS, and anti-fouling compounds, will be prohibited or restricted. Each new ship flying the flag of an EU member state (or a ship flying a flag of the third country calling at the EU ports or anchorages) will be required to have on board an inventory of hazardous materials. Objectives

As is shown in Article 1, the main purpose of this Regulation is to prevent, reduce, minimize, and, to the extent practicable, eliminate accidents, injuries, and other adverse effects on human health and the environment caused by ship recycling. The purpose of this Regulation is to enhance safety and the protection of human health and of the Union marine environment throughout a

ship’s life cycle, in particular to ensure that hazardous wastes from such ship recycling is subject to environmentally sound management. Specially, the Regulation aims to reduce significantly the negative impacts related to the recycling of the EU-flagged ships, especially in South Asia without creating unnecessary economic burdens (Explanatory note 1.2). Major Obligations

Obligations of Owners of “the EU flagged ships” with respect to: (1) Recycling only at a ship recycling facility on the “European List” (which shall be initially published not later than 31 December 2016): see Articles 6 and 16. (2) Preparation of a ship for recycling: see Article 6. (3) Ship recycling plan: see Article 7. (4) Surveys and certificates: see Articles 8, 9, and 10. For requirements for Ship Recycling Facilities to be included in the “European List,” see Articles 13–16 of the Regulation.

Recycling Regulations

1441

Recycling Regulations, Fig. 3 Relationships between typical regulations

Entry into Force and Date of Application

Unlike the Hong Kong Convention, the EU Ship Recycling Regulation makes a distinction between the date of its entry into force and the date of application. The regulation has entered into force on 30 December, 2013, 2 days after its publication in the Office Journal of the EU (Mikelis 2013). The date of application is the date after which ships under the scope of the EU Ship Recycling Regulation will start having to have an Inventory of Hazardous Materials (IHM), to be surveyed, certificated, and recycled in line with the requirements of the EU. The EU Ship Recycling Regulation shall apply from the earlier of the following two dates, but not earlier than 31 December 2015 shall apply: (1) 6 months after the date that the combined maximum annual ship recycling output of the ship recycling facilities included in the European List constitutes not less than 2.5 million light displacement tones (LDT). (2) On 31 December 2018. There are also some provisions of the European Regulations shall apply from different dates which are explained in Article 32(2–4). Please refer to the original text for more information. Relationships Between Typical Regulations Regulations are not independent of each other. Transposition from one regulation or its key mechanisms to binding obligations of another one is common in the process of developing better recycling regulations. Existed conventions and guidelines can be serviced as the basis to the new regulations by giving some pertinent

definitions and basic principles. For example, IMO’s guidelines and the Basel Convention provide guidance to the Hong Kong Convention, facilitating both its understanding and implementation. The Basel Convention published the “Technical Guidelines for the Environmentally Sound Management of the Full and Partial Dismantling of Ships” in 2003 which is a predecessor to the Convention (de Larrucea and Mihailovici 2011). Similarly, parts of the EU legislation of recycling are transposed from the Hong Kong Convention and the Basel Convention as shown in Fig. 3. As for the current existed and used regulations, coordination have been made between their conflicts by adding conflict clauses and other pertinent provisions. Besides, amendments or even some new guidelines and regulations are born from the conflicts and unreasonable places in original regulations. In short, the make and amendment of one regulation are related to others which have similar scopes and conflicts to it.

R Cross-References ▶ Complete and Partial Dismantling ▶ Inventory of Hazardous Materials ▶ Ship Recycling ▶ Ship Recycling Facility Plan ▶ Ship Recycling Plan

References de Larrucea JR, Mihailovici CS (2011) The Hong Kong International convention for safe and environmentally sound management of the recycling of ships

1442 Engels UD (2013) European ship recycling regulation, entry-into-force implications of the Hong Kong convention. International Max Planck Research School (IMPRS) for Maritime Affairs at the University of Hamburg European Commission (2007) Accompanying document to an integrated maritime policy for the European Union. EU-doc. SEC European Commission (2008) An EU strategy for better ship dismantling’, EU-doc. COM European Union (2013) Regulation (EU) No 1257/2013 of the European Parliament and of the Council of 20 November 2013 on ship recycling and amending regulation (EC) No 1013/2006 and directive 2009/16/ EC International Labour Organisation (2008) Safety and health in shipbreaking: guidelines for Asian countries and Turkey International Maritime Organisation (2003) IMO guidelines on ship recycling (5 December 2003) and Annex to IMO-doc International Maritime Organisation (2004) Guidelines for the development of the ship recycling plan International Maritime Organisation (2005) Terms of reference for the joint ILO/IMO/Basel convention working group International Maritime Organisation (2009) Hong Kong international convention for the safe and environmentally sound recycling of ships Mikelis N (2010) The Hong Kong international convention for the safe and environmentally sound recycling of ships. In: Paper presented at UNCTD (United Nations conference on trade and development) (Geneva, 9 December 2010) Mikelis N (2013) An analysis of European regulation on ship recycling. BIMCO’s bulletin No. 6 Puthucherril TG (2010) From shipbreaking to sustainable ship recycling. Martinus Nijhoff Publishers, Leiden University of Southampton (2013) A European initiative on the subject of ship recycling: a legal analysis of the proposed EU ship recycling regulation in the light of the international law applicable to the recycling of ships. LLM (MARITIME LAW) by Instructional course

RED - Reverse Electrodialysis

Reefer ▶ Transport Ship

Reefing Haiming Zhu and Zunfeng Du Department of Naval Architecture and Ocean Engineering, School of Civil Engineering, Tianjin University, Tianjin, China

Definition Reefing refers to a process of building artificial reefs. An artificial reef is a man-made underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, or improve surfing. The typical methods are sinking oil rigs (through the Rigs-to-Reefs program); scuttling ships, rocks, wood, metal; or deploying rubble or construction debris. Other artificial reefs are purposely built (e.g., the reef balls) from PVC or concrete. Shipwrecks may become artificial reefs when preserved on the sea floor. Regardless of construction method, artificial reefs generally provide hard surfaces where algae and invertebrates such as barnacles, corals, and oysters attach; the accumulation of attached marine life in turn provides intricate structure and food for assemblages of fish (Wikipedia 2019).

Scientific Fundamentals

RED - Reverse Electrodialysis ▶ Salinity Gradient Power Conversion

Red Tide ▶ Harmful Algal Blooms

History The construction of artificial reefs can be traced to ancient times. Persians built artificial reefs for blocking the mouth of the Tigris River to thwart Indian pirates (Williams 2006), and Romans built reefs across the mouth of the Carthaginian harbor in Sicily to trap enemy ships (Hess et al. 2001). Artificial reefs to increase fish yields or for algaculture began no later than the seventeenth

Reefing

century in Japan, where rubble and rocks were used to grow kelp. The earliest recorded artificial reef in the USA is from the 1830s, when fishermen used interlaced logs to build artificial reefs (Williams 2006). The interest in establishing coastal artificial reefs increased rapidly in the USA during the twentieth century due to the subsequent increase in recreational and commercial fishing and its expenditures (Bull and Love 2019). It was estimated that about 90% of the intentionally deployed wrecks to serve as artificial reefs correspond to the US locations (Ilieva et al. 2019). The Colonization of Reefing The colonization of artificial reefs is done progressively. In the beginning, devoid of any form of life, they are rapidly colonized by weed and animal classes like sponges, hydroids, bryozoans, bivalve shells, barnacles, acids, anemones, halcyons, and gorgons and finally, after a few years, by corals with calcareous skeletons like Acropora, Montipora, Pocillopora, and Pavonia. This encrusting fauna and flora provide food for sedentary and mobile animals like sea cucumbers, starfishes, sea urchins, crabs, and squids as well as small fishes like snappers, butterflyfish, Priacanthus, triggerfish, demoiselle, sergeant major, etc. In turn, these small fish attract pelagic and predator species such as hinds, morays, kingfishes, mackerels, barracudas, etc. Finally, it formed a marine biological system. Rigs-to-Reefs Common practice for platform removal uses explosives or mechanical techniques below the seafloor to sever the jacket so that it can be pulled out of water and taken to shore for recycling and/or a landfill (Bull and Love 2019). There are other options that entail reefing the submerged sections of the platform structure (BSEE 2017). Rigs-to-Reefs (RTR) is the process of converting end-of-life oil and gas platforms into artificial reefs. Such reefs have been created from oil rigs in the USA, Brunei, and Malaysia. Offshore oil and gas platforms first began functioning as artificial reefs in 1947 when Kerr-McGee, an American energy company, completed the world’s first

1443

commercially successful oil well 11 miles off Louisiana’s shore. In the USA, where the practice started and is most common, Rigs-to-Reefs is a nationwide program developed by the former Minerals Management Service (MMS), now Bureau of Safety and Environmental Enforcement (BSEE), of the US Department of the Interior. And the vast networks of energy platforms in the Gulf of Mexico form what is widely regarded as the largest man-made reef in the world, so the Rigs-to-Reefs initiative first began in the Gulf of Mexico as a way to preserve the habitats that form on the rigs’ steel scaffolding. There are three methods of platform removal and reefing to have been used in the RTR process: (a) tow-and-place platform, (b) partial removal in place platform, and (c) topple-in-place platform. The first and most common removal method, in deepwater applications, involves the use of explosives inside the jacket legs, 15 ft below the mudline. Once the jacket legs are severed by the explosives, the structure is toppled over in a horizontal position on the bottom. This method offers the donor lower costs and time savings. The disadvantage to the use of explosives is the potential mortality of sea turtles, marine mammals, and fish that might be associated with structures, though large numbers of fish are killed, the overall impact to the population was relatively small. The second removal option involves the partial removal of the upper portion of the jacket and placing it on the seafloor next to the standing bottom portion of the jacket. This method is particularly beneficial with deepwater structures that are converted into reefs. The standing vertical portion of the structure, which must provide at least 85 ft of navigable clearance, remains in place and continues to provide beneficial habitat for a large number of pelagic and other reef fish originally associated with the platform. Also, the upper portion that is removed provides an equal or slightly lower profile to compliment the standing section and increases the overall surface area of the structure for habitat enhancement. This type of removal requires a waiver from the Minerals Management Service. The waivers are required, since existing regulations require severing of the 55-jacket legs 15 ft below the mudline. For

R

1444

deepwater operations, this method significantly reduces the removal costs and risks for divers. The third removal option involves divers cutting the jacket legs below the mudline using explosives. Once the legs are severed, the entire structure can be lifted from the sea floor using a derrick barge, towed to a new permitted location, and placed on the bottom in a horizontal or vertical position. Mechanical or abrasive cutters can also be used to cut the legs. This method is typically only used in water depths less than 100 ft. Water depths in excess of 100 ft would significantly increase the risks to divers. There, however, would be no adverse impacts to associated living marine resources. This method is also expensive, labor-intensive, and time-consuming. Although there was no monetary savings using this method, instead of using explosives, the turtles, fish, and encrusting organisms were transported along with the structures to the new reef site. Benefits

First, oil and gas platforms have proven to be excellent artificial reef material. The National Plan cites five major characteristics or standards for artificial reef materials. These standards, together with siting and management, generally determine the success or failure of an artificial reef project. These include function, compatibility, durability, stability, and availability, and oil and gas platforms appear to possess all these characteristics. Second, it is well documented that oil and gas platforms function well as artificial reefs by providing habitat for a variety of species, since many of these species are habitat limited. And the steel members of the platform provide the necessary hard bottom substrate for many of the encrusting organisms critically important in developing reef habitat. Third, oil and gas platforms have proven to be compatible with the marine environment, since generally only the submerged jacket of the structure or that portion of the platform that has never come in contact with hydrocarbons is used. Forth, oil and gas platforms are also very durable and stable, rarely if ever moving from where

Reefing

they were placed. And these platforms also appear to be relatively durable and have a life span of 300 years. Last, during the reefing, partial mechanical removal methods using divers or abrasive cutting tools have provided a method for transferring platforms into reefs with the highest profile in the water column with the least impact on the natural resource and decrease the dangers to sea turtles and marine mammals. Drawbacks

There are several disadvantages to using oil and gas platforms as artificial reefs. One of the disadvantages is the expense in removing these structures. Derrick barge rates currently run between $50 thousand to $100 thousand a day depending on the lifting capabilities of the barge. The size of the structure to be removed determines the size of barge required. This, however, may be turned into a benefit if the savings realized, by not having to take it to shore, can be shared with the entity accepting the ultimate responsibility for the structure. To date, however, the oil and gas industry has dealt only with established state-recognized reef programs. In some areas permitting and meeting state law requirements and the ability to satisfy liability requirements have prevented fishing clubs and private individuals from acquiring platforms as reefs. Another disadvantage is the method of removal. Currently, state-of-the-art techniques required to sever these structures from the seafloor involve the use of explosives. The concern over the use of explosives stems from their potential impact on endangered sea turtles and marine mammals. Scuttling Ships Reefing by scuttling ships is the deliberate sinking of a ship by allowing water to flow into the hull, which can provide an artificial reef for divers and marine life. This can be achieved in several ways – seacocks or hatches can be opened to the sea, or holes may be ripped into the hull with brute force or with explosives. In the USA, scrap materials of opportunity, deployed without assembly or much modification,

Reefing

still account for a large portion of reef construction materials. Vessels have served as components of most state artificial reef programs. Where available, and where depth conditions allow for deployment, vessels remain an important reef material to many reef managers, particularly on the Atlantic coast. The earliest record of intentionally sinking vessels for artificial reef fishing is 1935 when four vessels were sunk by the Cape May Wildwood Party Boat Association. Dozens of steel-hulled ships sunk in coastal continental shelf waters along the Atlantic and Gulf Coasts during World War II still provide commercial and recreational fishing opportunities and diving enjoyment more than 60 years later. To prepare a hulk for sinking as an artificial reef, several things must be done to make it safe for the marine environment and divers. To protect the environment, the ship is purged of all oils, hydraulic fluids, and dangerous chemicals such as PCBs. Much of the superstructure is removed to prevent the hazard of it eventually caving in from corrosion. Similarly, the interior of the ship is gutted of all structures that corrode quickly and would be dangerous to divers if they came loose. The ship is thoroughly cleaned, often with the help of volunteers interested in diving. A significant part of the cost of preparing and sinking the ship comes from scrapping the contents of the ship, including valuable materials such as copper wiring. The hulk’s suitability as a diving site is enhanced by cutting openings in its hull and interior bulkheads to allow divers access. The preparation phase removes a significant amount of weight, so the ship sits higher in the water than normal. The ship must be carefully weighed down by filling some sections with water as makeshift ballast tanks to prevent excessive rolling in port or during towing. The ship is towed to the sinking location, usually in shallow waters. Benefit

First, vessels make interesting diving locations for both recreational divers and technical deep-diving mixed-gas users. Vessels are also regularly utilized as angling sites by recreational fishermen and the charter fishing industry.

1445

Second, vessels used as artificial reefs can, alone or in conjunction with other types of artificial reefs, generate reef-related economic contributions to coastal counties. Especially steelhulled vessels, when selected for sound hull integrity, are considered durable artificial reef material when placed at depths and orientations that insure stability in major storm events. Third, due to high vertical profile, the artificial reefs built by vessels attract both pelagic and demersal fishes. Vertical surfaces produce upwelling conditions, current shadows, and other current speed and direction alterations that are attractive to schooling forage fishes, which in turn attract species of commercial and recreational importance, resulting in increased catch rates for fishermen. Forth, like other artificial reef material, it can augment benthic structure which locally increases shelter opportunities and reef fish carrying capacity in locations where natural structure is sparse or create structure which is more preferable or attractive to certain fish species than locally less complex hard bottom. Drawback

First, vessels were originally designed and utilized for purposes other than artificial reef construction. They can be contaminated with pollutants, including PCBs, radioactive control dials, petroleum products, lead, mercury, zinc, and asbestos. Hazardous wastes and other pollutants are difficult and expensive to remove from ships. Besides, vessels typically provide proportionately less shelter for demersal fishes and invertebrates than other materials of comparable total volume. This is because the large hull and deck surfaces provide few, if any, holes and crevices. This lack of shelter from predation greatly reduces the usefulness of a ship as nursery for the production of fishes and invertebrates. Also, while a high vertical profile can be attractive to pelagic fish species, unless a vessel hull is extensively modified to allow for access, water circulation, and light penetration, most of the interior of the vessel is not utilized by marine fishes and macroinvertebrates.

R

1446

Last, high vertical profile may render some vessels more prone to movement and/or structural damage due to ocean current and wave surge generated by severe storm conditions. And its durability may be compromised by salvage operations during the cleaning process or by the explosives sometimes used to sink these vessels. Although there are some drawbacks in the reefing by them, they are the most common method of building artificial reefs, compared to its advantages.

Cross-References ▶ Decommissioning of Subsea Facilities ▶ Ship Recycling

References Bull AS, Love MS (2019) Worldwide oil and gas platform decommissioning: a review of practices and reefing options. Ocean Coast Manag 168:274–306 Bureau of Safety and Environmental Enforcement (BSEE) (2017) What is the national artificial plan? https://www. bsee.gov/faqs/what-is-the-national-artificial-reef-plan. Accessed 29 Jan 2019 Hess RW, Rushworth D, Hynes MV, Peters JE (2001) Disposal options for ships (No. RAND/MR-1377-NAVY). RAND Corp, Santa Monica Ilieva I, Jouvet L, Seidelin L, Best B, Aldabet S, da Silva R, Conde DA (2019) A global database of intentionally deployed wrecks to serve as artificial reefs. Data Brief, 23: 103584 Wikipedia (2019) Artificial reef. https://en.wikipedia.org/ wiki/Artificial_reef. Accessed 29 Jan 2019 Williams TW (2006) Sinking poor decision-making with best practices: a case study of artificial reef decisionmaking in the Florida keys. Dissertation Virginia Commonwealth University Richmond, Virginia, 122

Regular Profiling Float (RPF) ▶ Profiling Float

Reliability ▶ Reliability and Safety in Offshore Engineering ▶ Reliability-Based Design (RBD)

Regular Profiling Float (RPF)

Reliability Analysis ▶ Reliability-Based Design (RBD)

Reliability and Safety in Offshore Engineering Junkai Feng College of Safety and Ocean Engineering, China University of Petroleum (Beijing), Beijing, China

Synonyms Dependability; Probability of reliability; Reliability; Responsibility

Definition Reliability refers to the ability of the product to complete the specified function under the specified conditions and within the specified time. Safety refers to the ability of structure to bear various possible actions under normal construction and normal use conditions and to maintain the necessary overall stability when and after accidental events.

Introduction Offshore engineering is a field of engineering that principally deals with the methods for recovering hydrocarbon resources from deep beneath the seabed, from the installation stage and operation of fixed platform structures as well as floating platforms, their operation, and the laying of pipelines and supplementary oil/gas transport systems. Recently, phenomenal advancement in science and engineering has been witnessed as a result of rapid growth of the offshore field, particularly in the exploration and development of offshore oil and gas fields in deep waters of the oceans. A competition increase in the areas of development and installation of innovative offshore

Reliability and Safety in Offshore Engineering

structures, systems, and facilities has led to the question of reliability to be a matter of great interest. In addition during designing, installation and operation of offshore structures technical problems arise which relates to safety and environmental issues. However, offshore structures must be designed, built, installed, and operated with an aim that they work reliably, safely, and efficiently for designed periods of time without maintenance and with limited supervision. Generally, reliability is taken to mean operation without failure. When an offshore system as a whole does not do what it was designed for, even though none of its components fails, but then it is still charged against the system reliability. A good example of reliability would be an offshore structure that can continue to operate safely when a system or component fails. It is good to know that a good engineering always involves a balance between safety and reliability. A commonly used definition for a safety of an offshore structure is that it is a state of an offshore structure being safe from undergoing or causing hurt, injury, or loss. Safety is attained by using reliable structures, components, systems, and procedures. The comparative definitions can be summarized by defining reliability as a measure of confidence that the system produces accurate and consistent results, contrary to safety which can be defined as a measure of confidence that the system will not cause accidents.

Reliability as a Probability De Carlo (2013) gives the definition of reliability as the probability that a component (or an entire system) will perform its function for a specified period of time, when operating in its design environment. Thus he gives his arguments that the elements necessary for the definition of reliability are an unambiguous criterion for judging whether something is working or not and the exact definition of environmental conditions and usage. Parnami et al. (2012) also defines reliability as the probability that a component, device, system, or process will perform its intended function without failure for a given time when operated correctly in a specified environment. He also adds

1447

that reliability deals with decreasing the frequency of failures over a time interval and is a measure of the probability for failure-free operation during a given interval. From definition reliability can be mathematically expressed as 1 ð

RðTÞ ¼ PrfT > tg ¼

f ðxÞdx t

where f(x) is the failure probability density function and (t) is the length of the period of time (which is assumed to start from time zero). It is easy to represent “probability of failure” as a symbol or value in an equation, but it is almost impossible to predict its true magnitude in practice, which is massively multivariate. Therefore, having the equation for reliability does not begin to equal having an accurate predictive measurement of reliability.

Key Concepts of Reliability In order to start a discussion on basics of reliability, coverage of the key concepts of probability becomes crucial. Three important independent concepts can be derived as follows from the definition: 1. Time duration 2. Environmental conditions of use that cause a failure or a fault 3. Functioning parameter value or range that consist the error concept Fjeld (1978) elaborates that probabilistic reliability is the only meaningful concept which can be used to obtain a logical and objective distribution of risks and safety requirements in the offshore industry. He gives a clear description that probabilistic reliability is a tool for specifying criteria for how safe offshore engineering works should be and for evaluating design and operational requirements from probabilistic criteria for the installation as a whole. Reliability is restricted to operation under stated conditions. This constraint is necessary

R

1448

since it is impossible to design a system for unlimited conditions. For example, the deep-sea petroleum Gulf of Mexico oil spill, largest marine oil spill in history, caused by an explosion on the Deepwater Horizon oil rig as a result of failure of subsea blowout preventer stack. Thus, there are extremely strict requirements for safety and reliability in offshore and marine engineering.

Reliability and Safety in Offshore Engineering

From their work more clarification is given on the need to emphasis on order of priority as the most effective way of working, in terms of minimizing costs and generating reliable offshore structures. The ability to understand and anticipate the possible causes of failures forms the primary skill and knowledge of how to prevent them. Having the knowledge of the methods that can be used for analyzing designs and data is of much importance.

Objectives of Reliability in Engineering Simiu and Smith (1984) state that the objective of structural reliability is to develop design criteria and verification procedures aimed at ensuring that structures built according to specifications will perform acceptably from a safety and serviceability viewpoint. Structural reliability is also applied to individual components, which are potentially applicable to offshore engineering problems. These include the estimation of failure probabilities, safety indices, and safety (or load and resistance) factors. It is also an essential tool in the risk analysis of the total installation of a structure. However, it has been stated in Ersdal and Langen (2002) that the most obvious choice for establishing quantitative probabilities of failure is to use a structural reliability analysis, taking into account the variability of the nature, uncertainties in load, uncertainties in capacities, and often inspections, maintenance, reserve strength, and air gap. Applying the highlights of decreasing order of priority of the objectives of reliability in engineering from (O’Connor and Kleyner 2012), we can be apply the objectives as follows: 1. To prevent or to reduce the likelihood or frequency of failures by applying engineering knowledge and specialist techniques 2. To identify and correct the roots of failures that occurs regardless of the efforts to prevent them 3. To determine ways of coping with failures that occurs, if their causes have not been corrected 4. To apply methods for estimating the likely reliability of new designs, and for analyzing reliability data

Reliability Theory and Models Gertsbakh (2000) states that an important step in the formal development of the reliability theory is introducing the notion of lifetime. It is defined as the time elapsed since the “birth” of the system till the appearance of certain event which we call “failure.” Fjeld (1978) modern probabilistic reliability theory seems to be the logical tool to obtain an objective distribution of risks. Failure sources which cannot be considered random and therefore cannot be treated by reliability theory/must be eliminated by control and inspection. Random errors cannot be eliminated by inspection and must be covered be safety factors. From the review of many researches, it is a clear that for better understanding of reliability, we need to develop models that show the relation between various components of a system. This aids in tracing the cause of failure or faults of a given component in an event of a system becoming unreliable. Parnami et al. (2012) emphasizes that in system reliability analysis, it is important to model the relationship between various items as well as the reliability of the individual items in order to determine the reliability of the system as a whole. Barlow (2003) highlights that in order to study reliability, you need to transform reality into a model, which allows the analysis by applying laws and analyzing its behavior. Reliability models are broadly classified into two: 1. Static models 2. Dynamic models

Reliability and Safety in Offshore Engineering

1449

Static models assume that a failure does not result in the occurrence of other faults, whereas dynamic models assume that some failures, so-called primary failures, promote the emergence of secondary and tertiary faults, with a cascading effect. A diagram-based model for reliability analysis gives a visual representation of the system’s components thus giving a good understanding of the system. Figure 1 below shows diagram-based models frequently used in reliability analysis. Consisting of the following: 1. 2. 3. 4. 5. 6.

Reliability block diagrams (RBDs) Failure modes and effects analysis (FMEA) Fault tree analysis (FTA) Event tree analysis (ETA) Decision tree approach (DTA) Root cause analysis (RCA)

Design for Reliability Design for reliability (DfR) is a process that incorporates tools and procedures to ensure that a system attain its reliability requirements, under its use environment, for the duration of its lifetime. DfR is mostly used as part of an overall design for excellence (DfX) strategy. DfR is implemented in the design stage of a structure to proactively improve the reliability of a given system.

There are mainly two approaches that can be used in the design for reliability. These are: 1. Statistics-based approach (i.e., MTBF) 2. Physics of failure-based approach Statistics-Based Approach (i.e., MTBF) In this approach reliability design begins with the development of a (structure) model; it uses block diagrams and fault tree analysis models to provide a graphical means of evaluating the relationships between various parts of the system. These models use predictions based on failure rates taken from historical data. Physics of Failure-Based Approach Physics of failure is the method that depends on understanding the physical static and dynamic failure mechanisms. It accounts for variation in load, strength, and stress that lead to failure with a high level of detail, made possible with the use of modern finite element method (FEM) software programs that can handle complex geometries and mechanisms such as creep, stress relaxation, fatigue, and probabilistic design.

Reliability Testing “Failure” definition is key aspect of reliability testing. There are many situations where it is not

R Diagram-Based Models

Inductive

Semi Quantitative

Quantitative

Realibility Analysis

Deductive

FMEA

Semi Quantitative

Quantitative

ETA

FTA

RBD

Reliability and Safety in Offshore Engineering, Fig. 1 Reliability block diagrams

DTA

RCA

1450

clear whether a failure is really the fault of an offshore structure. Probability estimation can be done from previous data sets or through reliability testing. The sole purpose of reliability testing is to discover potential hitches with the design as early as possible and, ultimately, provide confidence that the system attain its reliability requirements. Reliability plays a key role in the evaluation of cost-effectiveness of offshore structure systems. Reliability is measured against the standard of requirements of a given offshore structure system’s specification. Thus, the methodology used to calculate one offshore structure system’s reliability depends on its configuration. Reliability is not only achieved by mathematics and statistics. Reliability can be attained through process and reliability testing. Reliability testing involves exercising an application so that failures are detected and eliminated before an offshore structure is stationed. MTBF (mean time between failures) for repairable components of an offshore structure system and MTTF (mean time to failure) for non-repairable components can be used to calculate reliability. Reliability tests can be done on the offshore structure system for the most likely situations under conditions of normal usage and validate that the expected service can be provided by a given offshore structure. As time progresses, more complicated tests can be applied to reveal subtler defects.

Benefits of Reliability in Offshore Engineering Some of the benefits of reliability are listed as follows: Safety: Some offshore structures fail due to unintended or unsafe conditions leading to injury or loss of life. Reliability engineering tools assist in identifying and minimizing safety risks before their occurrence. Time: Failures which are not planned for cost time to resolve. Using reliability concepts we can reduce failures and loss of time.

Reliability and Safety in Offshore Engineering

Design: Enhancing the design team’s reliability engineering capabilities through training and working closely with reliability professionals to make decisions having fully considered the impact on reliability of the offshore structures. This reduces the need for expensive redesign or rework costs to address reliability related design errors at a later stage. Expectation: Offshore structures work under environmental and use conditions. Creating an offshore structure that matches the expectations imposed by the operators of the structures permits the structure to work as expected. Getting to know the conditions well allows the design to be met without over designing thus optimizing the structure cost and operator’s satisfaction. Distribution: With fewer failures and optimized maintenance work of offshore structure results in fewer spare parts in the overall logistics system. This minimizes the costs for logistics, transportation, and storage for spare parts and eventually service labor costs are minimized. Liability: Offshore structure can cause the loss of property. Failure minimization and damage mitigation caused by any failure reduces the exposure to liability for the property loss.

Conclusion Reliability in offshore engineering is a broad topic to be covered since the offshore structures are complex in nature. A lot of ares which need further research work by the researchers in the area of reliability of these offshore structures, more so in uncertainty quantification, failure analysis of complex systems and life testing of offshore structure and equipment.

References Barlow RE (2003) Mathematical reliability theory: from the beginning to the present time. In: Mathematical and statistical methods in reliability. World Scientific, pp 3–13 De Carlo F (2013) Reliability and maintainability in operations management. Oper Manag 81–84

Reliability-Based Design (RBD) Ersdal G, Langen I (2002) On assessment of existing offshore structures. In: The twelfth international offshore and polar engineering conference. International Society of Offshore and Polar Engineers Fjeld S (1978) Reliability of offshore structures. J Pet Technol 30(10):1486–1496 Gertsbakh I (2000) Lectures in reliability theory with applications to preventive maintenance. Bölüm O’Connor P, Kleyner A (2012) Practical reliability engineering. Wiley Parnami P, Dave R, Singhal N, Sharma AD (2012) Reliability analysis: the mathematical expression. Int J Comput Eng Res 2(3):964–967 Simiu E, Smith CE (1984) Structural reliability fundamentals and their application to offshore structures. National Bureau of Standards

1451

Definition In the development of a product, it is important to ensure its reliability in the design stage, which enables the concept of reliability throughout the full life cycle of product design, operation, maintenance, and decommission. Such a design method is called reliability-based design (RBD). RBD methods take safety factors into consideration to account for uncertainties, so that established target reliability levels for products can be achieved. The main research contents of RBD include uncertainty theory, reliability analysis, and reliability-based design optimization (RBDO).

Reliability Based Design (RBD) ▶ Concept Design ▶ Preliminary Design

Reliability Based Design Optimization (RBDO) ▶ Reliability-Based Design (RBD)

Reliability-Based Design ▶ Risk-Based Design for Ship and Offshore Structures

Reliability-Based Design (RBD) Hao Chen Zhejiang University – Westlake University Joint Training, Zhejiang University, Hangzhou, China

Synonyms Probability theory; Reliability; Reliability analysis; Reliability based design optimization (RBDO); Uncertainty theory

Scientific Fundamentals Uncertainty Theory At present, uncertainty is mainly divided into two categories, including aleatory uncertainty and epistemic uncertainty (Oberkampf et al. 2004). Aleatory uncertainty describes the nature of random variations inherent in physical systems or environments, and epistemic uncertainty is originated from the lack of knowledge or information. The relationship between mastery degree on knowledge and uncertainty is shown in Fig. 1. With the development of science and technology, the understanding of a certain natural phenomenon becomes more and more profound, so the epistemic uncertainty will gradually decrease with the increase of knowledge. However, many natural phenomena have inherent contingency, and sometimes the phenomena are contrary to the conclusions obtained through the existing scientific observation, which reflects the inherent uncertainty of natural phenomena (i.e., aleatory uncertainty). The mathematical theory used to describe uncertainty is the basis for dealing with uncertainty in practical problems. The most popular method of describing aleatory uncertainty is probability theory. The founder of classical probability theory (CPT) was the Swiss mathematician Bernoulli, who established the first limit theorem named Bernoulli law of large number in probability theory. In 1933,

R

1452

Reliability-Based Design (RBD)

Reliability-Based Design (RBD), Fig. 1 The relationship between cognition and uncertainty

A.N. Kolmogorov summarized the basic properties and relations of events and their probabilities with the ideas of set theory and measure theory, established the axiomatic system of probability, and laid the theoretical foundation of probability theory (Durrett 2019). For epistemic uncertainty, the widely used description methods are interval theory (Moore 1966), evidence theory (Shafer 1976) and possibility theory (Zadeh 1978), generalized information theory (Klir and Wierman 2013), etc. With the development of uncertainty theory, many scientists are working on a unified uncertainty theory that can be used to describe both aleatory and epistemic uncertainties. Cui and Blockley (1990) combined probability theory and interval theory to obtain interval probability theory (IPT) and employed it as a method to measure the credibility of evidence in knowledge system. Based on quantum decision theory (QDT), Papageorgiou and Kamperi (2017) proposed a quantum-based decision-making model which can be employed in engineering design; this model can also capture the complexity of human decision making under uncertainty. The proposed model is able to describe not just the aleatory uncertainty but also the subconscious intuitive feelings and cognitions of the decision makers (i.e., epistemic uncertainty). Reliability Analysis The ability of an engineering system or product to accomplish a specified task under certain conditions and specific time is referred to as reliability. In the design stage, the specified function of an engineering system can be expressed as a function of the input variable X ¼ (x1, x2, . . ., xn), which is usually called the state function g(X). The value of state function g(X) can be used to judge whether

the function of engineering system can meet the design requirements. The most commonly used judgment logic is two-valued logic: when the state function exceeds a certain state, the engineering system cannot meet the requirements of a certain function stipulated in the design. This particular state is called the limit state of the function. If the engineering system can meet the functional requirements specified in the design, the system is reliable, otherwise, the system is unreliable. The reliability of the engineering system is usually divided according to the zero point of the state function: 

reliable

gð X Þ < 0

unreliable

gð X Þ  0

ð1Þ

Then the judgment function of two-valued logic can be expressed as:  I ð gð X Þ Þ ¼

1

gð X Þ < 0

0

gð X Þ  0

ð2Þ

Reliability analysis is closely related to the uncertainty theory used to describe the uncertain variables. When the uncertain variable X is described by different uncertainty theories, the reliability analysis method of system state function g(X) is also different. When uncertain variables are described as random numbers by classical probability theory, reliability analysis is called probabilistic reliability analysis. When uncertain variables are described as fuzzy numbers by fuzzy set theory, reliability analysis is named fuzzy reliability analysis. There are two main reliability analysis methods, including probabilistic reliability analysis method and fuzzy reliability analysis method.

Reliability-Based Design (RBD)

1453

Probabilistic Reliability Analysis Method

In probability theory, the uncertain variable X ¼ (x1, x2, . . ., xn) is considered as a random variable obeying a certain probability density distribution, and the value of state function g(X) of the system is also a random variable. In this case, the failure probability Pf of the system can be expressed as: ð ð P f ¼ . . . I ðgðXÞÞ f X ðxÞdx1 . . . dxn

ð3Þ

where fX(x) represents the joint probability density function of the random variable X. It can be observed from eq. (1) that the calculation of failure probability is a multidimensional integration process, and it is very difficult to calculate this integral in practical problems with high dimension. Therefore, various approximate methods for reliability estimation have been established; these approaches are called reliability assessment methods (Moffitt 2010). At present, reliability assessment methods can be divided into four main categories: (1) Reliability Index Approach (RIA): First Order Reliability Method (FORM), Second Order Reliability Method (SORM), etc. (2) Monte Carlo method: Crude Monte Carlo (CMC), Improved Monte Carlo method (IMC), etc. (3) Performance Measure Approach (PMA): Mean Value (MV), Advanced Mean Value (AMV), Hybrid Mean Value (HMV), etc. (4) Approximation model method: Response Surface Method (RSM), Neural network (NN), etc. Fuzzy Reliability Analysis Method

When the judgment logic function is fuzzy membership function or the uncertainty variable is described by fuzzy theory, the reliability analysis is called fuzzy reliability analysis. Fuzzy reliability analysis methods can be divided into two types: (1) Reliability analysis based on fuzzy logic (2) Reliability analysis based on fuzzy variables

Because the development of fuzzy theory is not mature and the calculation amount of the fuzzy theory is far beyond the acceptable range, the fuzzy reliability analysis method has not reached the level of practical engineering applications. Reliability Based Design Optimization (RBDO) The reliability of engineering products is closely related to the design, manufacture, assembly, and management in the process of product development, among which design plays a decisive role in the reliability of engineering products. RBDO adopts the uncertainty theory based on probability theory, and the research focus of RBDO is the influence of uncertain factors on the constraint function of the engineering product design optimization model. In the objective function, value of the uncertain variable is replaced by its mean value. In general, the optimal design points of engineering problems are located on the boundary of feasible region, and the uncertainty change of design parameters or design variables is likely to make the optimal design points fall out of feasible region due to the disturbance. As mentioned above, since most of the constraints that work are important mandatory index requirements such as safety, this means that there is a great possibility that the optimization design point cannot meet the mandatory index requirements of the actual engineering system, that is, the reliability of the optimization design is not up to standard, so it is important to research the reliability-based design optimization methods (Pan and Cui 2020). In RBDO, the optimization model can be formulated as: min f ðd, uX Þ s:t: Pðgu ðd, XÞ < 0Þ < Ptf gd ð d Þ  0 dl  d  du

ð4Þ

ul  uX  uu s or cov is known where d is called design variables, X refers to the random variable and uX refers to the mean value of X, gu and gd represent the uncertain constraint function and the deterministic constraint function,

R

1454

respectively. Pðgu ðd, XÞ < 0Þ < Ptf is called probabilistic constrains. Probabilistic constraints are the biggest difference between RBDO optimization model and deterministic optimization model. There are three common RBDO algorithms to solve RBDO problems, including double loop reliability-based design optimization (DLRBDO), sequential optimization and reliability assessment (SORA), and safety factor based sequential optimization and reliability assessment (SFSORA). DLRBDO

As shown in Fig. 2, DLRBDO algorithm (Allen and Maute 2004) includes the process of reliability analysis, so the algorithm includes two nested iterative processes. The external iteration is the optimization algorithm and the internal iteration is reliability analysis. Since DLRBDO algorithm will lead to a sharp increase in computation, the approximate model can be used to replace the original high-precision state function. DLRBDO algorithm based on approximate model has been widely used in engineering field (Gayton et al. 2003). SORA

SORA algorithm was first proposed by Du and Chen (2002). In SORA algorithm, the relationship

Reliability-Based Design (RBD), Fig. 2 Illustration of double loop reliabilitybased design optimization

Reliability-Based Design (RBD)

between optimization and reliability analysis is no longer nested, but sequential. Reliability analysis is executed after the finish of optimization process, which can greatly reduce the calculation amount. SFSORA

In engineering design, the most common method to ensure reliability is the safety factor method. Pan and Cui (2020) combined SORA algorithm with the safety factor method and put forward a new SORA algorithm based on safety factor, which is called SFSORA.

Key Applications With the development of uncertainty theories and reliability analysis methods, reliability-based design methods have been widely applied to various fields. Based on probability theory, Ronold and Larsen (2000) presented a reliability-based design method and applied it to analyze the safety of a wind-turbine rotor blade against failure in ultimate loading. By using perturbation method, second moment method, and reliability-based design method, Zhang and Liu (2002) put forward a practical and effective method for the reliabilitybased design of automobile components. Zhang

Reliability-Based Design (RBD)

et al. (2003) presented a new reliability-based design methodology by combining the perturbation method and reliability-based design theory, and the proposed methodology was applied to the reliability-based design of gear pairs, and the theoretical formulae of reliability-based design of gear pairs were obtained. Phoon et al. (2003) developed a reliability-based design framework for transmission line structure foundations, and the role of the proposed RBD method is presented within the context of geotechnical limit state design. A design methodology that combines reliability-based design optimization and highfidelity aeroelastic simulations for the analysis and design of aeroelastic structures is proposed by Allen and Maute (2004). In this work, to account for uncertainties in design and operating conditions, a first-order reliability method (FORM) is used to approximate the system reliability. To develop a strategy for solving reliability-based design optimization (RBDO) problems that remains applicable when the performance models are expensive to evaluate, Dubourg et al. (2011) proposed a surrogate model based RBDO method by using the kriging model, and the effective of the strategy is validated by comparing with other approaches available in the literature on three academic examples in the field of structural mechanics. A methodology for reliability-based design and assessment of an ageing fixed steel offshore structure was established by Mat Soom et al. (2016) to support detailed re-assessment applied to the management of the structure’s safety, integrity analysis, and reliability by evaluating the loading acting on the structure. By integrating the coupled corrosion fatigue model into the reliability-based design optimization, Saad et al. (2016) applied the proposed RBDO method to the life cycle cost of the structure subject to deterioration processes of fatigue and corrosion. To maximize the characteristics of tailor rolled blank (TRB) structures, a multiobjective and multicase reliabilitybased design optimization (MOMCRBDO) was developed by Sun et al. (2017) to optimize the TRB hat-shaped structure, and the radial basis function (RBF) metamodel was adopted to approximate the responses of objectives and

1455

constraints, the nondominated sorting genetic algorithm II (NSGA-II), coupled with Monte Carlo Simulation (MCS), was employed to seek optimal reliability solutions. Luo and Hu (2018) presented an efficient reliability-based design tool for stone-filled crib seawalls, in this work, the first-order reliability method is integrated into spreadsheet to facilitate the reliability analysis for practical application. Homaei and Najafzadeh (2020) proposed a reliability-based probabilistic evaluation framework to assess the effect of various parameters on the reliability for the scour depth to be less than a specific value.

Cross-References ▶ Design of Submersibles

References Allen M, Maute K (2004) Reliability-based design optimization of aeroelastic structures. Struct Multidiscip Optim 27(4):228–242 Cui W, Blockley DI (1990) Interval probability theory for evidential support. Int J Intell Syst 5(2):183–192 Dubourg V, Sudret B, Bourinet JM (2011) Reliabilitybased design optimization using kriging surrogates and subset simulation. Struct Multidiscip Optim 44(5):673–690 Durrett R (2019) Probability: theory and examples, vol 49. Cambridge University Press, New York Du X, Chen W (2002, January) Sequential optimization and reliability assessment method for efficient probabilistic design. In International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (Vol. 36223, pp. 871-880), Montreal, Quebec, Canada Gayton N, Bourinet JM, Lemaire M (2003) CQ2RS: a new statistical approach to the response surface method for reliability analysis. Struct Saf 25(1):99–121 Homaei F, Najafzadeh M (2020) A reliability-based probabilistic evaluation of the wave-induced scour depth around marine structure piles. Ocean Eng 196:106818 Klir GJ, Wierman MJ (2013) Uncertainty-based information: elements of generalized information theory, vol 15. Physica, Heidelberg Luo Z, Hu B (2018) Reliability-based assessment and design of stone-filled crib seawalls for shoreline protection. Mar Georesourc Geotechnol 36(8):918–930 Mat Soom E, Abu Husain MK, Mohd Zaki NI, Azman NU, Najafian G (2016) Reliability-based design and assessment for lifetime extension of ageing offshore structures. In: International conference on offshore

R

1456 mechanics and arctic engineering, vol 49941. American Society of Mechanical Engineers, Busan, South Korea p V003T02A044 Moffitt BA (2010) A methodology for the validated design space exploration of fuel cell powered unmanned aerial vehicles (Doctoral dissertation, Georgia Institute of Technology) Savannah, GA, U.S.A Moore RE (1966) Interval analysis, vol 4. Prentice-Hall, Englewood Cliffs Oberkampf WL, Helton JC, Joslyn CA, Wojtkiewicz SF, Ferson S (2004) Challenge problems: uncertainty in system response given uncertain parameters. Reliab Eng Syst Saf 85(1–3):11–19 Pan B, Cui W (2020) Multidisciplinary design optimization and its application in deep manned submersible design. Springer, Singapore Papageorgiou E, Kamperi EE (2017) Quantum-based decision making under uncertainty in the presence of entanglement for the development of optimal strategies in engineering design. Stud Eng Technol 4(1):35–52 Phoon KK, Kulhawy FH, Grigoriu MD (2003) Development of a reliability-based design framework for transmission line structure foundations. J Geotech Geoenviron 129(9):798–806 Ronold KO, Larsen GC (2000) Reliability-based design of wind-turbine rotor blades against failure in ultimate loading. Eng Struct 22(6):565–574 Saad L, Aissani A, Chateauneuf A, Raphael W (2016) Reliability-based optimization of direct and indirect LCC of RC bridge elements under coupled fatigue-corrosion deterioration processes. Eng Fail Anal 59:570–587 Shafer G (1976) A mathematical theory of evidence, vol 42. Princeton University Press, Princeton Sun G, Zhang H, Fang J, Li G, Li Q (2017) Multi-objective and multi-case reliability-based design optimization for tailor rolled blank (TRB) structures. Struct Multidiscip Optim 55(5):1899–1916 Zadeh LA (1978) Fuzzy sets as a basis for a theory of possibility. Fuzzy Sets Syst 1(1):3–28 Zhang Y, Liu Q (2002) Reliability-based design of automobile components. Proc Inst Mech Eng: J Automob Eng 216(6):455–471 Zhang Y, Liu Q, Wen B (2003) Practical reliability-based design of gear pairs. Mech Mach Theory 38(12):1363–1370

Remote Operated Vehicle (ROV) ▶ AUV/ROV/HOV Propulsion System

Remotely Operated Vehicle ▶ Remotely Operated Vehicle (ROV)

Remote Operated Vehicle (ROV)

Remotely Operated Vehicle (ROV) Lian Lian and Zhaoyu Wei School of Oceanography, Shanghai Jiao Tong University, Shanghai, China State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China

Synonyms Remotely operated vehicle; ROV

Definition The Remotely Operated Vehicle (ROV) is a kind of submersible, remotely operated by a crew aboard a supporting vessel, floating platform, or on land. Generally, ROV works on the principle of teleoperation where slave system, in this case it is the ROV body, interacts with hazardous extreme environment and a master system, in this case human operator, is placed at safe and comfortable location (Agba 1995; Costa et al. 2012). Therefore, the ROV can be remotely controlled to perform the underwater activities with the manipulators and other tooling capabilities. The umbilical cable can supply electrical power to the ROV body; meanwhile, the ROV body can also return the video or other data information to the supporting vessel through the umbilical cable.

Scientific Fundamentals ROVs have the largest number in the world, which is the most widely used, most complex, and most powerful submersible as compared to other kinds. In addition, ROVs have the characteristics of strong work applicability, function flexibly extended, no constraint on the work endurance, no risk of the crews, etc. With the umbilical cable, ROVs can perform the

Remotely Operated Vehicle (ROV)

complicated tasks with higher strength and longer duration on a fixed point under the very severe deep sea circumstance (Tao and Chen 2016). System Composition The system composition of an ROV is closely related to its use and working depth. Generally, the ROV system includes eight subsystems, which are ROV body, tether management system (TMS), tether/umbilical cable, launch & recovery system, deck operation & control system, power supply system, manipulator & tooling package. Among all these subsystems, the ROV body, umbilical cable, deck or aboard operation & control system, and power supply system are compulsory (Lian et al. 2015). In addition, other configurations can be added depending on the system size and work demands, for instance, the drilling machine and sampler. The whole ROV system can also be divided into the underwater and above-water parts. The above-water part consists of launch & recovery system, the deck operation & control system, umbilical winch and power supply system; the underwater part consists of the ROV body, tether management system (TMS), manipulator & tooling package (Lian et al. 2015). Undoubtedly, the two parts are connected by the umbilical cable, which can transmit the control signal and power from the supporting vessel to the ROV body. Meanwhile, the ROV body can also return the captured video and other information to the supporting vessel. In the comprehensive consideration of the water depth and work demanding, the ROV body can

1457

be launched and recovered through either the single umbilical cable or the TMS. Diagram of the system composition for the ROV is shown in Fig. 1, and system configuration for the ROV body is shown in Fig. 2 (Lian et al. 2015). ROV Types As for ROV types, there are many different classifications. Depending on size and weight, ROVs can be classified into micro-sized ROV, small-sized ROV, medium-sized ROV, largesized ROV, and super-sized ROV. According to uses, ROVs can be divided into observation-class ROV and work-class ROV. They can also be divided into work-class ROV and heavy duty work-class ROV depending on their work abilities and divided into free-swimming ROV and bottom-crawling ROV according to the motion mode; furthermore, they can also be divided into electric ROV and hydraulic ROV depending on the driving mode (Chen et al. 2018). Small-sized ROVs are relatively simple to control and they are mainly used for underwater observation; therefore, they are observation-class ROV. Medium-sized ROVs commonly have the weight around hundreds of kilograms. Besides the observation function, they are also equipped with manipulators and sonar system; thus, they can dosimple works and are ability to fix their position. Large-sized ROVs always have the weight of several tons. They have very powerful propulsion system, and are equipped with a lot of devices, such as underwater TV, sonar, tooling package, multifunctional manipulators, etc. Super-sized ROVs have the weight of up

Remotely Operated Vehicle (ROV), Fig. 1 Typical system composition of ROVs

R

1458

Remotely Operated Vehicle (ROV)

Remotely Operated Vehicle (ROV), Fig. 2 System composition of the ROV body (Lian et al. 2015)

to dozens of tons, which are typically used for special underwater works, for instance, the pipeline burial. It needs to be mentioned that largesized ROVs are capable of performing very complex heavy duty underwater works; therefore, they are currently the most widely used kind of ROVs on the exploitation of the offshore oil & gas field. Figure 3 shows the images of the ROVs with different size. Historical Development ROVs are the earliest developed and most widely applied submersible among all kinds of submersible. The earliest ROV was designed in 1953 by Dimitri Rebikoff and named as “POODLE,” which was mainly used in the study of archaeology. It had little impact on the ROV development, but it was the origin. Due to limitation of technologies in the early day, the ROVs had a lot of problems, such as leakage, noise, unstable performance, frequent maintenance, hydraulic system being prone to closing down, and so on (Christ 2013). In 1961, the USA army developed a flexibly operated underwater video system “XN-3,” which finally evolved into the cable-controlled underwater research vehicle (CURV). Later, the army improved CURV, which also made a lot of great events. For instance, the CURV II salvaged a

nuclear bomb at the water depth of 869 m offshore the Spanish sea (Fig. 4a). In 1973, the CURV III was emergently sent from San Diego, USA, to Ireland and performed the deepest underwater rescue in history when it rescued two men trapped at depths of 480 m in the sea for 76 h. After that, the US Army also developed a lot of more complex tethered vehicles, including the first small-sized portable observation-class ROV “SNOOPY” (Fig. 4b), and subsequently a fully electric ROV “Electric SNOOPY” equipped with sonar and other sensors. Subsequently, the US Army has input a huge of money into the Hydro Products in San Diego, USA, which promoted the ROV industry to grow in leaps and bounds. At this time, one of the famous ROV is the “TORTUGA.” In the whole year of 1974, only 20 ROVs were produced in the world, including the Fenland “PHOCAS,” Norway “SNURRE,” UK “CONSUB 01,” as well as the Soviet Union “CRAB-400” and “MANTA.” The ROV industry was still insufficient to pry the market occupied by the HOVs (human occupied vehicles) and divers. However, the great change came in the period till to the end of 1982; there were about 500 ROVs all over the world. There was also a great change on the funding source to produce these ROVs. From 1953 to 1974, 85% of the

Remotely Operated Vehicle (ROV)

1459

Remotely Operated Vehicle (ROV), Fig. 3 ROVs with difference size: (a) small-sized ROVs, (b) China “HAIMA”-4500 ROV (Lian et al. 2015), and (c) the world’s biggest subsea robot SMD ultra trencher 1 (Machin 2011)

fund was provided by the government, whereas 96% of this fund for about 350 ROVs was provided by the private companies from 1974 to 1982. At this time, the technology of ROV became matured and stable. The most important thing was that the ROV was accepted by a lot of marine companies. In 1983, there was even an international conference of ROV’83 with the theme of “A Technology Whose Time Has Come!” More advanced countries, such as USA, Canada, France, Italy, Netherland, Norway, Sweden, Germany, UK, and Japan, entered the ROV industry and produced more kinds of ROVs, including the micro-sized observationclass ROV. Some of these ROVs were also

possessed by the society association or academic and research organization. Till the 1990s in the twentieth century, the technology of ROV had become quite matured, and the ROVs acted positively in most of the oceans and performed many kinds of complex works. The US Army’s CURV III could reach the 6128 m water depth, and their advanced tethered vehicle (ATV) even reached 7012 m below the sea surface. The ROV “KAIKO 11000” designed and manufactured by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) even reached the deepest area of the seabed in 1994 (Barry and Hashimoto 2009), the Mariana Trench of the Pacific Ocean. However, in 2003, it was lost in an ocean

R

1460

Remotely Operated Vehicle (ROV)

Remotely Operated Vehicle (ROV), Fig. 4 (a) US Navy’s CURV II vehicle, (b) US Navy’s hydraulic SNOOPY, and (c) Schilling Robotics UHD

investigation due to the break of the neutralbuoyance umbilical cable. The booming offshore oil industry increased the demanding for the advanced submersibles, especially when the works, such as ocean floor drilling and exploitation, could not be finished by the divers due to the high water pressure in deep sea region, which forced the ocean oil industry and ROV developer to cooperate together. For instance, Schilling Robotics UHD ROV could perform a lot of very complex works, such as underwater stalling, operation, and maintenance (Fig. 4c). In the twenty-first century, many ROV manufacturers started to develop the observation-class ROV and medium-sized ROV. As for the ROV education, the European and North American countries have held some training plans to fulfill the demand of ROV operation with the booming ROV industry. Marine Advanced Technology Education (MATE) center aims to encourage the high school and college-aged young engineers into the field of subsea robotics. Today,

the center has already sponsored several international competitions. Key Technologies in Developing the Deep Sea ROV Typically, the ROV is an interdisciplinary system. As for the ROV design, the engineer needs to consider the launch and recovery system, layout configuration of ROV body, propulsion system, maneuverability, as well as the work tools. Among all these design procedures, some of them are called as key technologies and will be introduced as follows: 1. Navigation and position technology With the development of the modern satellites, to lock on a target on land or on the sea surface is relatively easier, while it is quite difficult to get the position of an object underwater. Therefore, the navigation and position is the first problem that should be solved when operating the ROV for sea bottom works.

Remotely Operated Vehicle (ROV)

The operator needs to know the current position of the ROV in the deep sea and the position the ROV is going to. Then the operator can lead the ROV to the next position. 2. Comprehensive control technology The comprehensive control technology is mainly used to distribute the power for the whole system, to control and monitor devices, direction, video surveillance, lights, pan/tilt system, leakage of electricity, leakage of hydraulic oil, and so on. The comprehensive control system is designed with high technology and complex configuration. It is also the head of the ROV system and the key selling point in the ROV industry. The specific key technologies include system control, real-time data inspection, warning, emergency isolation, multidata merging, real-time attitude inspection, touch control, data record and analysis, auto-heading, auto-depth and auto-altitude navigation, etc. 3. Umbilical cable As the important part connecting the ROV body to the sea surface support vessel, the umbilical cable functions as power transmission, communication, control command transmission, data transmission, launch, and recovery. Generally, the umbilical cable consists of optical fiber, electric cable, mechanical part, filler, Kevlar, and other materials, which are integrated through the way of helical winding. Therefore, the umbilical cable is on a high comprehensive level, has large mechanical strength, has good corrosion resistance, and can be repeatedly released and recovered. In addition, the umbilical cable can be designed/chosen according to the working depths. Generally, there are two kinds of umbilical cables, armored cable and neutral buoyancy cable. As the armored cable is so heavy that the length limitation is generally no longer than 6000 m. Undoubtedly, the umbilical cable is one of the key technologies which restricts the development of the 11,000 m ROV system. Thus, to develop the light, high strength, and abrasion-resistant umbilical cable, which can be repeatedly released and recovered, is the hot spot and trend in the future.

1461

Key Applications The ROV has a wide range of applications; some of the specific areas include survey and inspection, deep sea oil & gas production, deep sea mining, military, educational outreach, underwater photography, fisheries and aquaculture, civil construction, and public safety (Tao and Chen 2016; Chen et al. 2014). Survey and Inspection ROVs used for the survey and inspection are clearly observation-class ROVs or observationclass ROVs with payload option. ROVs are our eyes and hands in the deep sea. They can be used for many science and geological surveys, for instance, capturing the images of marine lives and sea floor, sediment sampling, marine life collection, geological drilling and sampling, water sampling, gauging the health index of marine lives and environment, estimating pollution level, searching for new living species and minerals, and so on. Figure 5 shows the images of marine lives observed by the ROVs. Observation-class ROVs can also be used to locate and position the beacon markers, lay the seabed observation network and underwater structures, inspect pipeline, jacket and even the marine hull of vessels. These ROVs usually have the ability to hold their position in strong currents, and are equipped with manipulators, lighting lamp, camera, sonar, and strobe flasher. Deep Sea Oil & Gas Field Mission of ROVs in the deep sea oil & gas field is a traditional and important application (Shukla and Karki 2016). With steep depletion of major onshore and shallow-water-offshore oil fields, new search of fossil fuel is moving toward deep-water and ultra-deep water offshore fields. Previously, companies can employ the divers to do some inspection and installing work in the shallow-water-offshore oil & gas fields, while it is impossible in the deep water. In addition, replacement of divers with robotic devices to accomplish complex tasks is an unavoidable trend with automatization of the overall offshore oil & gas industry. ROVs are used for many

R

1462

Remotely Operated Vehicle (ROV), Fig. 5 Examples of ROV observations of marine life. (a) A galaxy siphonophore, (b) the same siphonophore with tentacles retracted, (c) a manefish, (d) an oarfish, (e) a pair of Paralepididae fishes, (f) a pair of Giganturidae fishes, (g–h) a fish

Remotely Operated Vehicle (ROV)

Thalassobathia pelagica, (i) a cusk eel, (j–k) yellowfin tunas, (h) an ocean sunfish, (m) a sperm whale, (n) siphonophore, and (o) deepstaria reticulum (Macreadie et al. 2018)

Remotely Operated Vehicle (ROV)

different purposes and the important tasks are listed as follows: • Site survey Observation-class ROVs are used to map the seabed before carrying out the activities of installation and drilling. • Drilling assistance Once oil & gas reserves are discovered, mobile drilling platforms such as drill-ship, jackup rig and submersible drilling rig are used to drill the exploratory well at reserve sites. Work-class ROVs are used to assist the drilling; the activities may include collecting fluid samples from seabed for analysis, retrieving a drilling riser connected to a blowout-preventer located on a sea bed, and real time drilling data interpretation for multiple holes in a single dive. • Inspection, maintenance, and repair Metallic offshore structures are naturally facing difficult environmental conditions (i.e., salty water and strong sea tides), inspection work of flaws, corrosion and related cleaning, grinding, installing, trenching, lifting, pulling, bolt handing, and equipment transport can be performed by work-class ROVs (Baker and Descamps 1999). • Mobile inspection Apart from submerged structures, the equipment on the sea surface (i.e., mobile floating platforms, permanent platforms, and ships) also need routine inspection by the observationclass ROVs to improve safety and efficiency of overall production facility. The specific works include inspecting the gauge reading, leakage and surface condition, etc. • Oil spill situations Oil spill can occur at any stage of petroleum industry (i.e., exploration, drilling, production, transportation, refining, and finally distribution) (Fingas 2012), which is one of the major crises for the oil & gas industry. It not only results in huge revenues losses but also severely damages ecological system of marine life. During these accidents, the ROVs with remote sensing, laser fluorosensors, microwave sensors, and other techniques can be

1463

used for many activities such as regular surveillance, detection of spill, and helping in cleaning up operations after spill. Deep Sea Mining The deep sea mining has attracted more and more interests in the past decade, as the seabed is known to contain huge quantities of minerals. Recent discoveries have well illustrated that the rare earth deposits lied in the Pacific Ocean are estimated to be 80–100 billion metric tons. Take American Neptune Minerals for example, the company was established in 2011, which seeks to explore and mine the seafloor massive supplied deposit around volcanic arcs (Bogue 2015). It is known that exhaled supplied-rich mineralized fluids from the hydrothermal vents are often rich in gold, silver, copper, zinc, and lead around the volcano arc. Three unique seafloor production tools of an auxiliary cutter, a bulk cutter, and a collecting machine will be used to mine these massive deposits up to 1000 m. The auxiliary cutter and bulk cutter are used to flatten the rugged terrain close to the volcanic chimneys. Then the collecting machine sucks in the cut material, with the mine deposit harvested and pumped to a ship on the sea surface. A deep sea mining system schematic is shown in Fig. 6. The key components are the bulk cutter, a massive, tracked robotic device (Fig. 7) equipped with 4-m-wide cutting blades and driven remotely by two pilots in a control room on a surface vessel. Undoubtedly, they are also special kinds of ROVs. Military ROVs have been deployed by the navy more than half century, and a famous example as mentioned above was that the USA Navy’s CURV II salvaged a nuclear bomb at the water depth of 869 m offshore the Spanish sea (Christ 2013). ROVs can help the navy to hunt and break the mines. Small-sized ROVs can also be used by the navy for coast guards and port authorities, and have been widely deployed for a variety of underwater inspection tasks, such as explosive ordnance disposal, meteorology, port security, mine countermeasures, maritime intelligence, surveillance, and reconnaissance.

R

1464

Remotely Operated Vehicle (ROV)

Remotely Operated Vehicle (ROV), Fig. 6 Deep sea mining system (Bogue 2015)

Underwater Broadcast and Photography Note that the time-duration for ROVs working in the dangerous and complex sea circumstances is unlimited. If evolved with HD cameras, the

observation-class ROVs can help the filmmakers to capture the footage (The Dark Secrets of the Lusitania 2016). A famous example for using ROVs to film the documentaries is the BBC

Remotely Operated Vehicle (ROV)

1465

Remotely Operated Vehicle (ROV), Fig. 7 Robotic bulk cutter (Bogue 2015)

Wildlife Special Spy in the Huddle. In addition, the scientist or tourists can also use the small-sized and medium-sized ROVs to take photos of marine lives, coral or plants. Fisheries and Aquaculture Small-sized and medium-sized ROVs can be used in the fisheries and aquaculture. One of the typical services provided by the ROVs is to inspect the fish cages, the specific works include checking nets for holes, assuring the integrity of moorings for farms, and retrieving dead fish from the cage for health purposes (Christ 2013). In the shallow-water-offshore region, like the Shandong province of China, farmers keep a lot of sea cucumbers. The current is very strong and the water is turbid due to the mixture of sand from the rivers in this region, but this region is quite suitable for the sea cucumbers. There is a limit for divers to collect the sea cucumbers in a day due to the visibility, physical fitness, as well as the safety consideration. Another reason is that it is also very expensive to employ the divers. If evolved with sonars and suction manipulators, the ROV can collect the sea cucumber more efficiently than the divers. If countering the overall cost, the ROV will be cheaper than the divers.

Civil Construction ROVs used for subsea civil construction are typically higher powered and specification workclass ROV; they are equipped with high pressure 7-function manipulators and tooling package. The specific tasks performed by the ROVs may include moving heavy pieces, guiding large construction pieces into place, laying and burying cables and pipelines, setting and pulling rigging, and setting mattresses, etc. (Christ 2013). Public Safety Public safety is clearly the realm of observationclass ROVs equipped with cameras, sonars, and other tooling capabilities. This mission typically involved periodic inspection and sweep of pier recreational water, first responder to perform search and rescue the public need, such as recreational boater drown, drown person in the recreational water, river or sea.

Cross-References ▶ Atmospheric Diving Suit (ADS) ▶ Autonomous Underwater Vehicle (AUV) ▶ Deep Submergence Rescue Vehicle (DSRV) ▶ Deep Tow System

R

1466

▶ Doppler Velocity Log for Navigation System in Underwater Vehicle ▶ Glider ▶ Human Occupied Vehicle (HOV) ▶ Hybrid Remotely Operated Vehicle (HROV)/ Autonomous and Remotely Operated Vehicle (ARV) ▶ Remotely Operated Vehicle (ROV) in Subsea Engineering ▶ Rescue Bell ▶ Submarine ▶ Submersible ▶ Underwater Lander

References Agba EI (1995) SeaMaster: an ROV-manipulator system simulator. IEEE Comput Graph Appl 15(1):24–31 Baker MJ, Descamps B (1999) Reliability-based methods in the inspection planning of fixed offshore steel structures. J Constr Steel Res 52(1):117–131 Barry JP, Hashimoto J (2009) Revisiting the challenger deep using the ROV Kaiko. Mar Technol Soc J 43(5):77–78 Bogue R (2015) Underwater robots: a review of technologies and applications. Ind Robot 42(3):186–191 Chen ZH, Sheng Y, Hu B (2014) Development status and application of ROV in the ocean scientific investigation. Technol Innov Appl 32(21):3–4. (In Chinese) Chen Y, Lian L, Huang HC, Yang CJ, Song JB (2018) Fundamentals of marine technology. China Ocean Press, Beijing (In Chinese) Christ RD, Wernli RL Sr (2013) The ROV manual: a user guide for remotely operated vehicles. Oxford: Butterworth-Heinemann Costa MJ, Goncalves P, Martins A, Silva E (2012) Visionbased assisted teleoperation for inspection tasks with a small ROV. In: IEEE Oceans, In Proceedings of the Oceans, Hampton Roads, VA, USA, 14–19 October; pp. 1–8. Fingas M (2012) The basics of oil spill cleanup. CRC Press, Boca Raton Lian L, Ma XF, Tao J (2015) Research and development history of the “HAIMA”-4500 ROV. Nav Archit Ocean Eng 31(1):9–12. (In Chinese) Machin J (2011) The Arctic region from a trenching perspective. J Pipeline Eng 10(2):121 Macreadie PI, McLean DL, Thomson PG, Partridge JC, Jones DOB, Gates AR, . . . Flowler AM (2018) Eyes in the sea: Unlocking the mysteries of the ocean using industrial, remotely operated vehicles (ROVs). Sci Total Environ 634:1077–1091 Shukla A, Karki H (2016) Application of robotics in offshore oil and gas industry – A review Part II. Robot Auton Syst 75:508–524

Remotely Operated Vehicle (ROV) in Subsea Engineering Tao J, Chen ZH (2016) Development and application of the “HAIMA”-4500 remote operatedly vehicle. J Eng Stud 8(2):185–191. (In Chinese) The Dark Secrets of the Lusitania. Irish Film News. Retrieved 4 June 2016

Remotely Operated Vehicle (ROV) in Subsea Engineering Guijie Liu College of Engineering, Ocean University of China, Qingdao, China

Synonyms Autonomous underwater vehicle (AUV); Remotely operated vehicle (ROV); Unmanned underwater vehicle (UUV)

Definition ROV is a kind of underwater robot used for underwater observation, inspection, and construction. As the land resources are gradually exhausted, the ocean, which could provide the rich resources for human’s sustainable development, has been paid increasingly attention. The twenty-first century is recognized as the ocean century by the world. With the advantages of safety, economy, and high efficiency, underwater vehicles can replace human beings to complete high-intensity and heavy-duty underwater operations in a deep and high-risk environment. Hence, an underwater vehicle has become an indispensable equipment for understanding, developing, and utilizing the ocean. This paper mainly focuses on the classification, application, design, and development technologies of underwater vehicles.

Concept and Classification Underwater vehicle is a mechanical and electrical device that can freely move in the water, equipped with a vision and perception system. Through the remote control or autonomous operation,

Remotely Operated Vehicle (ROV) in Subsea Engineering

underwater vehicle utilizes manipulator or other tools to replace or assist human beings to complete underwater tasks (Christ and Wernli 2014). Classification of Underwater Vehicles Underwater vehicle can be classified into different types as follows: • Classified by functions: According to different purposes, underwater vehicles can be divided into three categories, operation, observation, and measurement. Among them, the operation underwater vehicles with working manipulators are used for underwater operations such as rescue, salvage, cable laying, operation, and maintenance of offshore oil platform and other production systems. The observation underwater vehicles are nearly as same as the operation one, but they are mainly used to measure the parameters of the objects to be investigated. The measurement underwater vehicle uses cameras, video cameras, and sonar to observe the topography of sea floor or to search for underwater objects. • Classified by modes of motion: According to different motion modes, underwater vehicles can be divided into three categories, floating, crawler, and walking. Most of the floating underwater vehicles are designed with zero buoyancy (or a little positive buoyancy), and the three-dimensional space motion underwater is relied on thrusters. Crawler underwater vehicles, which are driven by crawlers, are mostly used in seabed construction. The walking underwater vehicles use the walking mechanism to walk on the sea floor. At present, the walking underwater vehicle is still in the research and development stage, and few application cases are reported. • Classified by control mode: Underwater vehicles fall into two basic categories: remotely operated vehicle (ROV) and autonomous underwater vehicle (AUV). The difference between ROV and AUV reflects in whether the underwater vehicle is tethered or not. ROV connects the mother ship of submersible by an umbilical cable, which not only transmits power downward but also controls signals

1467

(from the mother ship to ROV) and data/ images (from ROV to the mother ship) in real-time bidirectional transmission. However, there is no physical connection (no tether) between the AUV and the mother ship. The AUV relies on its own power, navigation and positioning sensing system, and intelligent control decision-making system to achieve autonomous navigation. Compared with ROV, AUV has many advantages, such as wide range of activities, deep diving, little risk of umbilical entanglement, ability of performing tasks in complex structures, no large deck support system required, and low operation and maintenance costs. Design and Features of AUV and ROV AUV: AUV is designed to withstand extreme pressure and maintain neutral buoyancy in the deep sea under extreme harsh conditions to reduce the required propulsion energy and improve the efficiency of the vehicle. Therefore, the overall structure of AUV is generally optimized to ensure streamlined shape design of AUV body and to find a balance point between limited volume and system power consumption and battery power consumption, carry sensors according to the design purpose, and maintain the longest endurance capability. In addition, AUV uses modular and standardized design to accomplish many different tasks. Since all mechanical and electronic interfaces inside the body are standard, the selected sensors can be quickly integrated into the load module, and the functions of the new sensors can be integrated into the software of the main system through a software toolkit to synchronize the data flow with the navigation status. As a result, the AUV has stronger endurance and load-carrying capabilities, more automated and safe release, and recovery systems. AUV has strong endurance and load-carrying capacity, more automatic and safe release, and recovery system. The general basic components of AUV include (1) battery, (2) onboard detection equipment, (3) navigation and positioning system, (4) propulsion system, (5) communication system, (6) safety and security system, (7) release recovery system, and (8) deck workstation.

R

1468

Remotely Operated Vehicle (ROV) in Subsea Engineering

ROV: ROV system is mainly composed of support mother ship, deck console, deck power supply unit, ROV lifting system, umbilical cord cable, ROV body, robot, and working tools. It is powered and communicated by a surface mother ship through the umbilical cord cable connecting the ROV body; observed and operated by the mother ship staff through underwater video, sonar, and other special equipment; and can also operate underwater by a manipulator. Since it does not endanger personal safety and power is primarily provided by the mother ship, working underwater can theoretically be if possible. The ROV has hydraulic power system, propulsion system, cloud platform system, video and lighting system, navigation and positioning system, power supply and distribution system, and monitoring system. The underwater stability of ROV can be well maintained by hydrodynamic analysis, reasonable arrangement of installation position of each equipment, and adjustment of center of gravity by ballast block (Dan et al. 2010).

At present, the propulsion devices of underwater vehicles mainly include propeller thruster, hydraulic thruster, pump-jet thruster, magnetic fluid thruster, bionic thruster, track thruster, and so on. Propeller is generally used as the propulsion system of underwater vehicles. However, in some special environments, other types of propulsion systems are used, such as mining robots working under the sea, mostly crawler thrusters. The characteristics of the two underwater vehicles are comprehensively compared as shown in Table 1. Figure 1 shows two observable ROVs developed by author’s team. Figure 2 shows two AUVs developed by author’s team.

Application Fields of Underwater Vehicles With the rapid ocean development, there are increasing number of underwater construction

Remotely Operated Vehicle (ROV) in Subsea Engineering, Table 1 The characteristics of AUV and ROV Type Characteristics Working principles Control systems Communication systems Design methods

AUV No umbilical cord cable required Autonomous decision-making Auto-control Complex control system Wireless communication Underwater communication is not possible Integrated approach Mechanism analysis method。

ROV Need umbilical cord cable Human decision-making Artificial control Simple control system Wire communication Underwater cable real-time communication Integrated approach Direct similarity method

Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 1 Two observation ROVs developed by author’s team

Remotely Operated Vehicle (ROV) in Subsea Engineering

1469

Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 2 Two AUVs developed by author’s team

and building projects. Underwater vehicles can perform observation, camera shooting, measurement, salvaging, and construction operations underwater, and hence they are widely used in ocean development. At present, underwater vehicles are widely applied in many engineering fields, such as underwater engineering, marine scientific investigation, salvaging, marine military, and fishery production. Applications in Underwater Engineering • Underwater structure inspection: Physical location detection and quality measurement of underwater structures, verification and inspection of laying conditions, damage and corrosion, inspection of drilling platforms, wellheads, dams, cracks, and safety conditions of pollution barriers and gates. • Underwater surveillance: Monitor the operation and construction guidance of grouting, piling, trenching, felling, bulldozing, and other aspects of underwater civil engineering. • Submarine topography survey: Map natural or man-made underwater objectives, seabed topography, and seabed profile. • Underwater facility cleaning: Clean and repaint the surface of underwater facilities, clean oil rigs, remove rust, and paint hulls, pipelines, and underwater components. • Underwater target search and recognition: Search and salvage specified objects underwater, sunken ships, abandoned equipment, equipment, etc.

• Installation and maintenance of underwater facilities: Install and maintain underwater pipeline cables, open valve, weld, cut and detonate, replace the sacrificial anode, etc. • Assist diver operation: Assist diver operations, ensure the safety of divers, and transfer construction equipment to divers. Applications in Marine Scientific Expeditions • Marine geological survey: Record the microtopography of the ocean floor, draw a map of the sea floor, and collect sea floor patterns and rock samples. A 3500-meter ROV independently developed by China has observed a rare huge black chimney in the seamount region of the Eastern Pacific Ocean. During operation, a hydrothermal black chimney sample was obtained by a manipulator of ROV, which provides valuable information for ocean research. • Marine life expedition: Measure the biological form on the seabed and collect biological samples. • Marine physics expedition: Observe seawater aquifers, circulating water velocity, salinity, temperature, depth distribution, seawater specific gravity, etc. • Geophysical expedition: Measure the earth magnetic field and investigate oil and gas deposits. • Marine acoustic survey: Observe underwater acoustic characteristics, underwater reverberation, and acoustic models.

R

1470

• Geochemical expedition: Observe the water temperature of the sea floor, the soil temperature of the sediment layer, and the pH value of the sediment. • Marine optics expedition: Observe water transparency, natural light field distribution, light absorption intensity, etc. Marine Military Applications Military underwater vehicles may play a significant role in the naval battle, which may induce a new prospection in the future. Military underwater vehicles can perform a variety of tasks in maritime military confrontations, such as coastal reconnaissance, demining, anti-submarine, communications, and navigation. They make a possibility to quickly seize a military victory with minimal human casualties in naval battles. The functions of military underwater vehicles are listed as follows. • Underwater demining: Underwater vehicle is an optimal equipment to perform antidemining operations. Compared with other anti-demining devices, underwater vehicle has the advantages of low cost and good concealment. • Anti-submarine warfare: Underwater vehicle can search and track submarines in coastal waters, narrow waterways, and straits. It has a better ability to search for submarines than surface ships and submarines. Underwater vehicles are also utilized to set traps for enemy ships in anti-submarine warfare (sonar confrontation, misleading direction).

ROV System Design ROV System ROV, a kind of unmanned underwater vehicle with cable remote control, generally consists of a deck unit (i.e., a control system), a winch retractable system, and a body. Its work flow is as follows: the operator sends orders through the control system, and the commands are transmitted to ROV through an umbilical cable. ROV makes corresponding actions according to the command.

Remotely Operated Vehicle (ROV) in Subsea Engineering

Data collected by the camera and various sensors are also transmitted to the deck unit through an umbilical cable. The umbilical cable, which is a zero-buoyancy cable with certain strength, can guarantee the normal deployment and recovery of ROV. The specific structure of the system is shown in Fig. 3. The ROV system is composed of seven main parts: main frame, floating material, control communication system, power propulsion system, observation and lighting system, manipulator system, and sensor detection system (Guan 2018). • Main frame: The main frame is the carrier of the entire ROV system and its reasonable structural design based on the overall size of the ROV. The main frame should be firm and stable. • Floating material: The common floating materials utilized in underwater vehicles are polymer-based solid material, which is characterized by low density (0.2 to 0.7 g/cm3), low water absorption (less than 3%), high mechanical strength (e.g., compression strength is in the range of 1 to 100 MPa), corrosion resistance, and machinability. Polymer-based solid material could meet various requirements in the underwater environment. It is noted that floating body materials should be selected according to the maximum water depth. • Control communication system: The control communication system is a comprehensive system, which includes collecting, transmitting, processing, and analyzing various information and commands of the ROV. The control system transmits real-time control commands to the ROV through the umbilical cable, and thus the ROV is controlled to perform some specified work tasks. At the same time, the information such as ROV’s depth, attitude, and image is transmitted to the deck unit in real time through the umbilical cable for analysis and processing. • Power propulsion system: The power propulsion system mainly includes two parts, the thruster and the power supply. The power propulsion system supports the mother ship deck to provide power to the ROV through

Remotely Operated Vehicle (ROV) in Subsea Engineering

1471

Umbilical cable spool

Control cabinet

Spool drive motor, speed reducer

Handheld manipulator Ultra-short baseline positioning

Variable angle swing arm

system fixing mechanism Umbilical cable guide pulley block

GPS positioning system antenna

Ship-mounted lifting platform

Shipboard control system

Umbilical

Buoyancy module Carrier frame Thruster Camera

illumination

Submarine cable detection sensor module

5

Sealed cabin

Height

Counterweight ROV underwater carrier part mechanical module Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 3 Block diagram of ROV system

the umbilical cable and drives the thruster to achieve the command-controlled ROV movement. • Observation and lighting system: The observation and lighting system are mainly composed of cameras, sonars, and LED lights. ROV can obtain underwater image through the observation and lighting system, which contributes to ROV in avoiding obstacles, improving the efficiency and safety during operation. • Manipulator system: The manipulator system is the key symbol of ROV’s operating capability, which is an indispensable part in an operating-oriented ROV. The manipulator system is mainly composed of a manipulator, a hydraulic pump, and a control valve. The manipulator has lots of basic parameters, among which the degrees of freedom,

movement space, load capacity, and selection of materials are important parameters for its design. During operating, the operator sends control signals from the control box on the deck of the mother ship, and the control signals are transmitted to the underwater control system through the umbilical cable, which controls the manipulator to complete certain tasks. • Sensor detection system: Sensor detection systems mainly include altimeters, pressure sensors, attitude sensors, temperature sensors, ultrashort baselines, and cable detection sensors. Various underwater detection information collected by the sensors is transmitted to the deck unit through the umbilical cable. Based on the information, the operator analyzes and judges the status of the ROV, which is beneficial to achieve the ROV operation control.

R

1472

Remotely Operated Vehicle (ROV) in Subsea Engineering

ROV System Design Overall Structural Design

In designing ROV, the engineers should make clear the design goal, the operation task, the working mode, and the working environment. The mature ROV technology in worldwide can be referenced in the design of overall structure framework. The ROV body is discretized into several blocks for modular design. The connection among different modules should be concerned during module design, in order to maintain the integration of each module. Some aspects should be carefully considered in the over structural design of ROV. • Compact layout. The limited space in the ROV should be fully used without interference among each part of the ROV. The overall size of the ROV should be optimized for convenient transport and storage. • The technical performance and requirements for the working environment of ROV should be fully taken into consideration, which ensures the normal use of the equipment and avoid interference with each other. • Without interfere normal function, the design of the components and the connection among the modules should be simplified in maximum extent, which is beneficial to facilitate the maintenance of the ROV. • Under full consideration of operational requirements, sufficient spare space should be

y

reserved for ROV system updating and modifications. • The durability, reliability, and stability of control systems and mechanical components in ROV must be ensured. Design of ROV Propulsion System

The thruster is the main power source for the ROV. There are many kinds of thrusters, among which the propeller thrusters are widest utilized. The number of degrees of freedom of ROV in underwater movement is determined by the operation purpose and design requirement. Three degrees of freedom, i.e., forward and backward, up and down, and steering, are the basic mobility requirements of a ROV. The number of thrusters required for ROV is determined by the purpose and design requirements. At present, the layout of thrusters can be divided into five types: single thruster layout, parallel layout of double thrusters, cross layout of double thrusters, annular layout of four thrusters, and conical layout, as shown in Figs. 4, 5, 6, 7, and 8. For arranging thrusters, two points should be paid attention: • The axis should be parallel to the moving coordinate system, which maximizes the efficiency of the thruster. • The axis of three-axis thruster should be reasonably converged to one point. This point

Y

T1

O

propeller1

X

Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 4 Single-pusher arrangement

X

Remotely Operated Vehicle (ROV) in Subsea Engineering

1473

Y

y

propeller1 T1

a O

X

X

a

T2

propeller2

Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 5 Parallel arrangement of dual thrusters

y

Y d1

T1

a propeller1 O

T2

propeller2

X

X

d2

Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 6 Double-thruster cross arrangement

y

Y

R T1 T2

d1 d2

propeller1 propeller2

O

propeller3

d3

T3

propeller4

d4

T4 X

X

Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 7 Ring arrangement of four pushers

should approach to the center of gravity of ROV in order to avoid some harmful movements of ROV and benefit to the system control.

Overall Balance Design

Due to many equipment on ROV, the weight symmetry of ROV should be taken into consideration, in order to maintain the gravity position and

1474

Remotely Operated Vehicle (ROV) in Subsea Engineering

Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 8 Cone arrangement of thrusters

the metacentric position. In practical, it is very difficult to achieve the absolute balance of ROV. Therefore, the arrangement of ROV’s internal equipment should follow some principles: • The primary body should be firstly considered and then other parts. • The global layout should be firstly considered and then local arrangement. • Some certain amount of space should be left, which leaves the room for modification.

coordinate lines and the vertical line should be kept within the range of 0 to 15 . Dynamic Analysis of ROV For studying the motion law of ROV, its kinematic and dynamic modeling should be developed. Kinematics describes the relationship between location and time, while dynamics focus on the relationship between force and motion (Liu et al. 2015). Force Analysis of ROV in Water

In order to ensure the stable motion of ROV, a certain stable height should be guaranteed. The metacentric height of general underwater vehicles should be greater than 7 cm, and the metacentric height of large underwater vehicles should be correspondingly increased. In order to determine the metacentric height, the coordinates of center of gravity and center of buoyancy need to be calculated according to the overall arrangement of ROV. Besides, the coordinates of center of gravity and center of buoyancy of ROV can also be calculated in 3D drawing software. It is necessary to ensure that the line between the barycentric coordinates and the center of buoyancy coordinates passes vertically through the underwater vehicle so that no overturning moment occurs when it is stationary. Otherwise, the general layout of ROV should be adjusted so that the two coordinate positions are equal as far as possible; even if they are not absolutely equal, the angle formed between the two

ROV is mainly affected by buoyancy, gravity, thrust of thrusters, hydrodynamic and umbilical cable interference forces, and the torque generated by these forces during underwater movement. The combined force and moment formed by these forces and moments make the ROV produce six degrees of freedom in space motion. Gravity and Buoyancy: The buoyancy and gravity of ROV are always in the vertical direction. Gravity is represented by P, and buoyancy is represented by B. The gravity center is represented by G, and floating center is represented by C. It is assumed that the coordinates of the center of gravity and the floating center in the x and y directions are coincident (which can be achieved by balancing the weight and buoyancy), and the floating center is higher than the center of gravity in terms of h. Without considering the changes of buoyancy and load, the components of gravity, buoyancy, and moments

Remotely Operated Vehicle (ROV) in Subsea Engineering

on the axes of the ground coordinate system can be calculated by corresponding formulas. Thrust of the Thruster: The thrust generated by the propeller is the power that enables the ROVs to move in their respective degrees of freedom. The thrust generated by the propeller can be calculated from the propeller thrust formula. Water Resistance: In underwater environment, the resistance of ROV mainly consists of two parts: the hydrodynamic force and the interference of the umbilical cable. The calculation of hydrodynamics is complex. There are around 100 parameters relative to hydrodynamic coefficient. Generally, the hydrodynamics is related to the geometry, motion state, and flow field properties of a ROV (Liu et al. 2020). The calculation of the umbilical cable’s interference force is also complex. Generally, it can be calculated by the concentrated mass method, that is, the umbilical cable is regarded as a chain model. In a chain model, the umbilical cable is assumed as a chain including a series of cylinders with finite length and concentrated mass at one point. According to the movement status of the mother ship and ROV, mechanical analysis and calculation are performed on each section of umbilical cable, and then the interference force of umbilical cable on ROV can be obtained. In practical, an approximate estimation method can generally be used to calculate the resistance force of ROV in underwater environment. The resistance to which it is subjected can be estimated by the resistance formula (Fan et al. 2012). ROV Dynamic Modeling and Analysis

According to rigid body dynamics theory and Newton-Euler equation, the six-degrees-offreedom equation of ROV is obtained, and then the dynamic equation is established by combining the four forces of gravity, buoyancy, propeller thrust, and water resistance (Nakamura et al. 2013). The motion posture of ROV corresponding to the next moment can be calculated from the motion posture and external force of the previous moment, which is an indispensable basis for ROV motion control. In order to verify the dynamic effect of ROV, CFD simulation method is often used (Yan et al.

1475

2010). This method uses computer as the tool, uses discrete mathematical method, and uses simulation software to simulate and analyze the mathematical model.

ROV Control System The control system is the core of the ROV, which mainly includes the hardware system and the software system. The hardware system is divided into two parts, the surface control system and the underwater control system. The software system is divided into two parts, an operation part and a monitoring part. The surface control system is responsible for collecting ROV’s control instructions, including digital quantities and analog quantities. The underwater control system is responsible for responding to the control instructions of the surface control system and also feeding back the corresponding status and data in real time. The software system is responsible for sending operation instructions and receiving and processing data. The cooperation of the hardware system and the software system can ensure the normal operation of the ROV. The overall block diagram of the ROV control system is shown in Fig. 9. ROV Control Hardware System The overall system of ROV is complex and it involves many control targets. A large number of sensors and equipment are involved in its control system. Due to the difference among electrical interfaces and communication protocols, there still are different communication rates and specifications, even though the same the electrical standards are utilized. Hence, the integration of various interface standards and flexible configuration modes are compulsory in the design of the ROV’s control system. Moreover, some certain degree of redundancy should be considered for later maintenance, expansion, and upgrade. Common ROV underwater main control units are as follows: • Based on the main control method of PC104. RS232, RS485, AI (analog input), DI (digital

R

1476

Remotely Operated Vehicle (ROV) in Subsea Engineering

Displayer

Joystick

Host computer

Touch-screen

Displayer

Lower computer

Sonar

Thruster

Sensor

Other peripherals

Video

Remotely Operated Vehicle (ROV) in Subsea Engineering, Fig. 9 ROV overall control system block diagram

input), Ethernet and other modules are configured on the interface, which are operated by Windows or Linux system. • Based on embedded systems of single-chip microcomputers. RAM-based embedded hardware is commonly used, which is operated by Linux, uCOSII, and other operating systems, or without an operating system directly. • Based on the PLC of the industrial automation industry, various common interface modules can be configured according to the ROV. Depending on different PLCs, the manufacturer can develop the operating system or use the general operating system. ROV Control Software System The ROV control software system is the core part of the ROV control system. The ROV control software system contains an operation part and a monitoring part. The operation part is the fundamental software, which is responsible for identifying the information of the joystick and operation buttons and communicating with the ROV in real time. Its software interface mainly completes the following functions: • Configure the initialization information of the ROV software. • Configure the initialization information of each sensor, such as communication mode, communication rate and so on. • Control the enable status of the thruster and monitor the thruster speed.

• Feedback the current speed of ROV’s movement in real time. • Feedback the current depth of the ROV in real time, and estimate the ROV dive speed and dive time. • Feedback the current ROVoff-bottom height in real time, combined with the depth parameter of the ROV, and control the ROV movement speed. • Real-time feedback of ROV electronic cabin temperature and monitoring of the operating system temperature of the electronic system. • Real-time feedback of ROV water leakage detection status and monitoring the pressuretight status and waterproof status of the electronic cabin. • Feedback the status of underwater lights and cameras in real time, and check whether they are turned on correctly. • Feedback the operating status of the manipulator in real time, and compare it with video monitoring to ensure the correct operation of the manipulator. • Detect the hydraulic pump pressure in real time to ensure the correct operation of the manipulator, and eliminate errors. • Configure an appropriate debugging window to detect PLC and other internal variables, and troubleshoot the failure rapidly. ROV Motion Control Method The main parameters of ROV motion control are depth (the vertical distance from the sea surface to

Remotely Operated Vehicle (ROV) in Subsea Engineering

1477

the center of gravity of the underwater vehicle), height (the vertical distance from the seafloor to the center of gravity of the underwater vehicle), heading angle, speed, position, and so on. In most ROV designs, in order to obtain good control performances without complicating the system, single-loop closed-loop control is used for these parameters, such as depth loop (auto-depth control), altitude loop (auto-height control), heading angle loop (auto-heading control), speed loop (constant speed control), position loop (automatic positioning), etc. On the basis of the basic circuit of the motion control system, a certain control algorithm is also needed to achieve accurate control of the motion of the underwater vehicle. The common control algorithms include PID control, fuzzy control, adaptive control, and neural network control.

• Acoustic positioning system: Acoustic positioning system is a technology that uses underwater acoustic equipment to determine the position and distance of the vehicle relative to the mother ship. • Inertial navigation system: The inertial navigation system consists of a gyroscope and an accelerometer. By measuring and integrating the ROV’s angular velocity and acceleration, the ROV’s speed, yaw angle, and position in the navigation coordinate system can be obtained. • Imaging sonar: Imaging sonar is an acoustic device whose principle is similarly to a radar. The sonar transducer, equivalent to a radar antenna, can emit sound waves and receive sound waves reflected from the surrounding environment and then produce acoustic images of the surrounding environment.

Sensing and Communication System in ROV

Operating system sensors: Operating system sensors refer to the various sensors that ROVs carry when operating underwater. Different operating systems use different sensors, including electromagnetic detection sensors and acoustic detection sensors. Condition monitoring sensor: To ensure the safety of the ROV system, some sensors are needed to monitor the vehicle. For example, the battery voltage and power detection sensors can reflect the battery usage; the water leakage detection sensors in the sealed cabin can detect the sealing performance of the sealed cabin in real time.

Common Sensor Used in ROV There are three main sensors used in ROVs, navigation and positioning sensors, operating system sensors, and condition monitoring sensors. Navigation and positioning sensors: Navigation and positioning system sensors include depth sensors, gyroscopes, Doppler Velocity Logs, acoustic positioning systems, inertial navigation systems, imaging sonars, etc. The function of navigation and positioning system sensors is collecting information on the position, attitude, and speed of the underwater vehicle in the water and detecting the vehicle’s surroundings. The specific functions of each sensor are described as follows: • Depth sensor: Measure the water depth in respect to vehicle’s position. • Altimeter: Measure the distance between vehicle and sea floor. • Gyroscope: Measure the attitude of the vehicle in the water. • Doppler log (DVL): The Doppler log is used to determine the speed of an underwater vehicle relative to the ocean floor.

Communication Technology The core of the ROV communication system is data exchange between the aquatic equipment and the underwater equipment through a cable. The common methods are optical fiber communication and power line communication. Optical fiber communication: A communication method that uses light waves as a carrier wave and uses optical fiber as a transmission medium to transfer information from one place to another is called wired optical communication. At present, optical fiber has been widely used in the communication system of underwater vehicles due to its

R

1478

Remotely Operated Vehicles (ROVs)

transmission frequency bandwidth, long transmission distance, high interference resistance, and small signal attenuation. The principle of ROV optical fiber communication is as follows: the transmitted information (such as sensor data and video shot by an underwater camera) is firstly converted into an electrical signal at the transmitting terminal. Then it is modulated onto the laser beam emitted by the laser, so that the intensity of the light varies with the amplitude (frequency) of electrical signal. By transmitted through the optical fiber, the detector converts the optical signal into an electrical signal at the receiving end and restores the original information display after demodulation. Power line communication: The use of power carrier communication in the ROV communication can combine the power supply line and the signal transmission line, which can reduce the number of cores in the zero-buoyancy cable. The principle of the power carrier in ROV is the following: the transmitted information is modulated onto the power line through the carrier module. After the power line transmission, it is demodulated on the carrier module at the other end to obtain the transmitted information. Acoustic communication: Affected by seawater, electromagnetic waves diminish rapidly, and they cannot be used as a technical method for long-distance communication, while light waves are affected by the turbidity, absorption, and scattering in the water (Yong and Weigang 2019). Relying on current technology, only stable connections can be achieved over short distances. The propagation speed is fast; although it is affected by the noise, it can realize long-distance communication through filtering. The acoustic communication has stable and reliable applications on the Jiao Long and Deep Sea Warrior deep submersibles. It is assumed as one of the most promising directions in the development of acoustic communication in the future.

imaging, and sensing capabilities; however, they are still not reliable enough to integrate with marine life and to deal with unknown problems. Some challenges are still faced, including underwater communication, positioning measurement, mid-deep navigation, and unpredictable interference. With the continuous expansion of the application field, the underwater vehicle will develop toward smaller size, more compatibility, and higher intelligence, in order to break through the obstacles in the design of unmanned underwater vehicle, which may greatly improve its automation; in addition, some new technologies (e.g., multimedia technology and virtual reality technology) should be applied to underwater vehicles for future development.

Conclusion and Prospect

Remotely Operated Vehicles (ROVs)

Most underwater vehicles now have a certain degree of motion flexibility and superior navigation,

▶ Hydrodynamics for Subsea Systems

References Christ RD, Wernli RL Sr (2014) The ROV manual: a user guide for remotely operated vehicles. Elsevier Ltd, Estados Unidos Dan O, Nabergoj R et al (2010) Identification of hydrodynamic coefficients for maneuvering simulation model of a fishing vessel. Ocean Eng 37(8–9):678–687 Fan S, Lian L, Ren P et al (2012) Resistance calculation and motion simulation for deep sea open-framed remotely operated vehicle based on hydrodynamics test. Oceans IEEE, pp 1–5 Guan H (2018) A brief analysis of Marine underwater robot equipment technology. Automat Appl 7:87–88 Liu G et al (2015) Dynamics modeling and control simulation of an autonomous underwater vehicle. J Coast Res 73:741–746 Liu G et al (2020) A brief review of bio-inspired surface technology and application toward underwater drag reduction. Ocean Eng 199:106962 Nakamura M, Asakawa K, Hyakudome T et al (2013) Hydrodynamic coefficients and motion simulations of underwater glider for virtual mooring. IEEE J Ocean Eng 38(3):581–597 Yan Z, Guohua X, Xiaolong X et al (2010) Determination of hydrodynamic coefficient of micro-open-frame underwater robot. Shipbuild China 01:67–76 Yong Z, Weigang Z (2019) Brief introduction of underwater robot and its development direction. Intelligent Robot 5:41–44

Rescue Bell

Removal of Fixed Platform ▶ Decommissioning of Fixed Platform

Renewable Energy Propulsions ▶ Ship Construction and Operation Impact on Energy Efficiency

Rescue Bell Yong Hu Shanghai Jiaotong University, ShangHai, China School of Transportation, Wuhan University of Technology, Wuhan, China

1479

from sunken submarines, which at that time was still a virtual impossibility. Momsen soon conceived a submarine rescue chamber that could be lowered from the surface to mate with a submarine’s escape hatch and proposed the concept through official channels. While in command of the submarine S-1 (SS-105), in 1926, Momsen wrote to the Bureau of Construction and Repair (BuC&R) recommending the adoption of a diving bell for the purpose of rescuing entrapped personnel from submarines. But this idea was pigeonholed by the bureaucracy, even during his own subsequent assignment at BuC&R. The loss of S-4 with all hands put the Navy very much “on the spot” because of the loss of lives that might have been saved. The pressure of this incident forced favorable action and Momsen, using the aircraft hangar from S-1, designed and built a prototype submarine rescue chamber (Fig. 1).

Synonyms Rescue chamber; Submarine rescue bell

Definition Rescue Bell is one type of submarine rescue system, which can carry submariners from a disabled submarine to the surface. A typical Rescue Bell consists of four major components: a pressure hull, mating skirt, surface support system, and life support system. Some rescue bells also have propellers, imaging system.

R

Scientific Fundamentals Historical Development During the first two decades of last century, in the United States Navy Submarine Force, there were several accidents in which Navy submarines sank with the loss of life. These experiences led submariner Charles B. Swede Momsen to think of technical alternatives for rescuing survivors

Rescue Bell, Fig. 1 Momsen-McCann rescue bell prototype

1480

During the first 3 months of 1928, divers and other salvage personnel were able to raise S-4 and tow her to the Boston Navy Yard, where she was drydocked and repaired. She returned to active duty in October 1928 and was employed thereafter as a submarine rescue and salvage test ship. Momsen went to sea in the reconditioned S-4 to carry out practical experiments and training with the rescue chambers. Work with S-4 helped to develop equipment and techniques that bore fruit a decade later, when 33 men were brought up alive from the sunken submarine Squalus. The first diving bells for rescuing men from submarines were designed by the BuC&R in 1928. The diving bell went through a series of tests off the shores of Key West, Florida. Based on these tests, Momsen had several changes in mind for the bell, and after nearly 2 years of experimentation full of highly interesting results, the final bell was evolved and christened a “rescue chamber.” This success was catalyst for gaining approval for the development of the submarine rescue chamber in 1930. Lieutenant Commander Allan Rockwell McCann was put in charge of the revisions on the diving bell. From July 1929 to July 1931, McCann was assigned to the Maintenance Division, Bureau of Construction and Repair, where he developed the submarine rescue chamber. When the bell was completed in late 1930, it was produced as the McCann Submarine Rescue Chamber (SRC) (Navy designated the first 12 of these as YRC 1-12, YRC-4 was lost aboard the USS Pigeon, at Bataan, Philippines during the first days of WWII. YRC-5 was aboard the USS Widgeon (AM-22) during the Pearl Harbor attack). In 1931, a one-fifth scale model of a diving bell for submarine rescue work was built and tested. Design called for the bell to withstand the external pressure encountered at a depth of at least 300 ft (91 m) of water, and the test showed the model fulfilled this requirement with a factor of safety of about 3.5. The vessel was tested under external pressure, failure occurring in the shell at a pressure of 470 psi (3,200 kPa). Since the head of the vessel remained intact, it was decided to make a test of the head itself in order to determine its strength relative to that

Rescue Bell

of the shell, and if possible to obtain some measure of the stresses occurring under load. The head collapsed at a pressure of 525 psi (3,620 kPa), indicating its strength under external pressure was about 10% in excess of that of the shell. The revised Submarine Rescue Chamber had improvements including a soft seal gasket for sealing the submarine/bell interface skirting, and a floor installed to maintain air-space in the bell during raising and lowering. Momsen in his speech to the Harvard Engineering Society on 6 October 1939 credits Allan Rockwell McCann with the improvements which made the bell operational, safe, and large enough to hold up to eight rescued crewmen and two operators. After the development of the rescue bell, the US Navy was equipped with dozens of rescue bell. After 1970s, the Deep Submergence Rescue Vehicle (DSRV) replaced the rescue bell. In recent years, China continues to develop the modem rescue bell. China has developed a type of movable rescue bell in 1990s successfully. This type of rescue bell has four thrusters. This rescue bell has better mating ability than McCann rescue bell. The working depth of the movable rescue bell is 200 m. The bell has umbilical line for power supply, with a rotary skirt. The mating angle can reach 20 . McCann rescue bell is a simple rescue chamber. Chinese rescue bell has the ability of manned occupied submersible, but the rescue principle is the same as McCann rescue chamber (Fig. 2). In 2008, China has successfully developed a new type of rescue bell, Maneuvering Rescue Bell. The maneuvering rescue bell has a 45 rotary skirt. The rescue bell can be carried by truck, train, or airplane. The high-pressure seawater pump can drain off the skirt water quickly. The energy supply comes from the mother ship, and the rescue bell can work continuously (Fig. 3). Key Technology in the Development of a Rescue Bell In the development of the modem rescue bell, mating skirt and life support system are the key technology. Most equipments are the same as human occupied vehicle and ROV. For the mating skirt, big mating angle, light weight, and reliable

Rescue Bell

1481

Rescue Bell, Fig. 2 China movable rescue bell

Rescue Bell, Fig. 3 China maneuvering rescue bell

R

sealing are the key technical specifications. For the life support system, rescue with pressure is a complicated rescue condition. Under this condition, mating and transfer are very difficult. And the life support system can support the rescuer under high air pressured environment. The McCann bell suffers from severe limitations in strong currents and when dealing with a pressurized submarine or one lying at extreme

angles. The Rescue Chamber is air transportable to a Vessel of Opportunity (VOO) Mother Ship (MOSHIP), which requires little modification to use the system. Transfer Under Pressure (TUP) to and from pressurized environments such as submarines or hyperbaric chambers is not possible with this system, even though TUP is essential where being subjected to ambient pressure may be life-threatening.

1482

The modem rescue bell such as the movable rescue bell and the Maneuvering Rescue Bell can deal with 2.5 knots currents. The extreme angle can reach 45 . The modem rescue bell can mate and rescue at pressurized environments under 50 bars.

Key Applications In 1939, the McCann Rescue Chamber made its debut when it was used to successfully rescue 33 survivors from Squalus. At the time of Squalus’ accident, Lieutenant Commander Momsen was serving as head of the Experimental Diving Unit at the Washington Navy Yard. The submarine rescue ship USS Falcon (ASR-2), commanded by Lieutenant George A. Sharp, was on site within 24 h. It lowered the Rescue Chamber, a revised version of a diving bell invented by Momsen and, in four dives over the next 13 h, recovered all 33 survivors in the first deep submarine rescue ever. McCann was in charge of Chamber operations, Momsen commanding the divers. Although there was no reason to believe anyone was alive in the aft part of the ship, a fifth dive was made to the aft torpedo room hatch on May 25. This run confirmed the flooding of the entire aft portion of the ship. Although there are no other actual rescue cases, the Chinese navy carries out rescue training every year. The training includes mating and rescue submariner testing through actual submarine. Due to the low cost and simple rescue procedures, the rescue bell is still a simple and efficient submarine rescue equipment.

Cross-References ▶ Human Occupied Vehicle (HOV)

References Gray E (2003) Disasters of the deep: a comprehensive survey of submarine accidents and disasters. Naval Institute Press, Annapolis

Rescue Chamber Gu Jinghua, Liu Pingxiao, Yuan Hengrong, Fen Lei, Yan Shuo (2017) The design of life support system of maneuvering rescue bell. China Pers Prot Equip 2(2) Hu Y, Zhang J-F, Cui W-C (2007) Sealing ability research on movable rescue bell. J Ship Mech 11(2):221–230 Keach J (2000) Submerged (Film). NBC, New York. (Television movie. The film does not acknowledge any design flaw and claims the cause is unknown) LaVO C (1994) Back from the deep: the strange story of the sister subs Squalus and Sculpin. Naval Institute Press, Annapolis Maas P (1999) The terrible hours: the man behind the greatest submarine rescue in history. HarperCollins Publishers, New York. ISBN 978-0-06-019480-2. OCLC 41504915 Mao Lanshen, Hu Y (2009) Current situation and development trend of submarine rescue bell. J Ocean Technol 12–18 V2 Xu P, Hu Y (2011) Optimum design and research for rescue chamber. J Ship Mech 10(2):110–119

Rescue Chamber ▶ Rescue Bell

Research Ship Cheng Long Wei and Shuang Ling Dai Key Laboratory of Marine Mineral Resources, Ministry of Natural Resources, Guangzhou, China Guangzhou Marine Geological Survey, Guangzhou, China

Synonyms Research vessel; Survey vessel

Definition A research ship is a special ship or boat designed, modified, and equipped to carry out research at sea, which is carrying scientists and special equipment. Research ships are applied in marine natural science research such as geology, geophysics,

Research Ship

hydrology, meteorology, chemistry, biology, landforms, and so on.

Scientific Fundamentals Development History On the basis of great technological changes and typical characteristics of ship types, there are two main periods in the development history of the world research ships (Wu 2017).

1483

comprehensive research ships “Kexue 1” and “Shiyan 3” built in 1980, etc. There are a few function shortages of research ships in this period (Li 1982). Loud noise and big vibration can’t meet the demand of acoustic experiment research. Survey equipment and laboratories are outmoded and defective. Besides, outdated detection method and small detecting depth and range are difficult to realize multidisciplinary research. And data transmission and processing are unable to complete in the field. What’s more, high speed results in wasting energy.

First Development Period

The first development period of research ships is from the late 1950s to 1980s. Along with the application of electronic computers and the emergence of various kinds of advanced marine survey equipment, modern research ships are built gradually. Compared with the early refitted research ships, research ships in the first generation have qualitative improvements in performance, laboratories and special equipment, etc. (Griffin and Sharkey 1987). There are a series of research ships that are built in the first development period, such as the 6000 t comprehensive research ship “Romenosov” built in the Soviet Union in 1959, the 3400 t hydrographic research ship “Surveyor” built in the United States in 1960, the research ship “ATLANTIS II” built in the United States in 1962, the 3100 t research ship “DISCOVERY” built in the British in 1962, the 4700 t reconstructive research ship “SONNE” built in Germany in 1977, etc. The first reconstructively comprehensive research ship “Venus” is the pioneer of marine research ships in China in 1956 (Zhang 1998). Since that, there are typically representative research ships, such as the first meteorological research ship “Qixiang 1” designed and built independently in 1959, the comprehensive research ship “Dongfanghong” built in 1965, the 3000 t comprehensive research ship “Shijian” built in 1969, the 4400 t comprehensive research ship “Xiangyanghong 09” built in 1978, the ton class comprehensive research ship “Xiangyanghong 10” built in 1979, the 3000 t geological research ship “Haiyangsihao” built in 1980, the 3300 t

Second Development Period

The second development period of research ships is since the late 1980s. As the gradual improvement of the electric propulsion system and the dynamic positioning system, as well as a variety of upgraded research equipment, the design of research ships is more and more automatic and modularized (European science foundation 2009; Zhu et al. 2012). Therefore a series of new advanced research ships replace the overage ships. There are a series of typical research ships in the period, such as the 18,000 t ocean drilling ship “JOIDES” built in the United States in 1984; the 3600 t “Atlantis III” built in the United States in 1997, which is the mother ship of Alvin DSV (Deep Sea Vehicle); the 6300 t ice comprehensive research ship “Maria S. Merian” built in Germany in 2006; the 3000 t comprehensive research ship “Sarmiento de Gamboa” built in Spain in 2007; the 5800 t comprehensive vessel “JAMES COOK” built in the British in 2007; the 57,000 t ocean drilling ship “CHIKYU” built in Japan in 2007; the icebreaker polar research ship “Akademik Tryoshnikov” built in Russia in 2012; the 6000 t new “DISCOVERY” built in the British in 2013; the 3200 t comprehensive survey ships “AGOR 27” and “AGOR 28” built in the United States in 2014; the 6000 t comprehensive survey ship “Investigator” built in Australia in 2014; the 8000 t new “SONNE” built in Germany in 2015; etc. The building of Chinese research ships appears a little delayed from the middle 1980s to the end of the twentieth century (Li et al. 2012). After the

R

1484

Research Ship

research ship “Dongfanghong 2” designed and built independently, the modified ships “Dayang 1” and “Snow Dragon,” and so on, the marine survey in China begins into the deep sea and the polar area. But the limited number of ships is not content with the actual demand of the development of marine survey in China. It enters into the peak development of research ships since the twenty-first century. There are, respectively, advanced research ships such as “Shiyan 1,” “Haiyangliuhao,” “Kexue,” “Xiangyanghong 10,” “Xiangyanghong 03,” “Xiangyanghong 01,” “Zhangjian,” “Jiageng,” etc. Basic Type Different countries have different strategic target, research area, foundation of parent ships, as well as capability of design and production. According to the characteristics and functional requirements of research ships, there are different classification methods (Meng et al. 2017; Wu 2017). Forms of research ships include mono-hull, catamaran, and special hull. According to the gradation standard of the US Federal Oceanographic Facilities Commission (shown in Table 1, FOFC 2001), gradations of research ships include global class, ocean class, regional class, and coastal class based on the ability of navigation and operation. Based on research tasks, they are divided into comprehensive research ships, subject research ships, and special research ships. However, common subject research ships are geophysical survey ships, geological survey ships, acoustic research ships, fishery research ships, meteorological research ships, environmental surveillance ships, buoy receive and release ships, etc. And special research ships are oceanographic drilling ships, polar research ships, space tracking ships, submersible carriers, archaeology ships, etc.

Comprehensive research ships regard multiple marine subjects and research fields as survey objective. They possess comprehensive survey capability of various functions and techniques. They can conduct marine geology, geophysics, geochemistry, biology, hydrometeorology, hydroacoustics, and fisheries and other marine survey. They can carry out comprehensive research from the upper atmosphere to the seabed through the air-sea interface. They mostly work in the ocean near their own sea or further area. Generally speaking, comprehensive research ships have more form values, cruising ability and self-supportability, and better properties, along with more complete survey equipment. Fishery research ships are engaged in the scientific research of fishery resources and fishing ground environment, the experimental study of fishing gears and fishing methods, etc. They are capable of towing different types of fishing nets, collecting plankton or water samples, and carrying fish-finders. A fishery research ship is often designed and built along the same lines as a large fishing vessel, but with space given over to laboratories and equipment storage, as opposed to storage of the catch. Geology research ships are applied in the research of marine geology, geophysics, and geothermics, by the means of seismic, gravity, and magnetic survey and sampling analysis. These studies can obtain the sedimentary and structure of seabed and make further information of the seabed mineral resources. These ships are equipped with special survey equipment as well as laboratories. Oceanographic drilling ships can drill core samples of the seabed and obtain chemical and biological information of them. These ships are equipped with tall derricks, heavy lifting

Research Ship, Table 1 Gradation standard of research ships (FOFC 2001) Gradation Global class Ocean class Regional class Coastal class

Length/meters 70 55–70 40–55 0.4 m, the formula can be approximately simplified to H F ¼ 0:26 þ ðBH M Þ0:5

ð21Þ

Angle of flare c can be eliminated from the formula on the basis of the following triangulation: sin c ¼ c¼

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2

tan f=

sin aþ tan 2 f

arctan ð tan f= sin aÞ

ð22Þ

It can be seen that the ship resistance in floating ice zone can be preliminarily estimated by the

Discrete (Distinct) Element Method (DEM) Discrete element method (distinct element method, DEM) already has a long history of deployment in the field of ice mechanics. Open source implementations are also available. For example, LIGGGHTS implements DEM (Kloss et al. 2012; Morgan et al. 2015; Morgan 2016; Yulmetov et al. 2017) and employed this software to simulate ice structure interaction. Smoothed Particle Hydrodynamics (SPH) and Moving Particle Semi-Implicit Method (MPS) Smoothed particle hydrodynamics (SPH) is one of the Lagrangian methods to handle continuum mechanics. It was originally developed for fluid simulations but is now extended to handle solid mechanics. Some commercial software such as LS-DYNA implements SPH to handle fluid and/or solid simulations. Moving particle semi-implicit (MPS) method was separately developed and investigated with SPH as an implementation of incompressible fluid simulation but can be considered as an implementation of SPH with different spatial discretization schemes. Recently, it is also extended to handle solid mechanics. Ren et al. (2017) deployed this method to simulate the interaction of an ice beam and a large water droplet. Fluid-Structure Coupling Fluid-structure interaction (FSI) is one of the most important but difficult fields of investigation with numerical simulations. However, a few commercial packages implement FSI recently so that it becomes easier. Song, Kim, and Amdahl (Song et al. 2015) employed LS-DYNA to investigate collision of the steel structure with an ice floe. Shigihara, Ishibashi, and Konno (2015) employed STARCCM+ to investigate collision of a ship with a single ice floe. Vroegrijk (2015) also employed

R

1496

Resistance of Polar Vessel

STAR-CCM+ to investigate ship navigation in brash ice channel.

by dynamometer; t, where Fmeans, force measuredP thrust deduction factor; and Pi , total thrust of i

propellers.

Model Test of Ice Resistance

(2) Second Method

The model test of ice resistance is introduced in the Specialist Committee on Ice, Technical Committees and Group of the 28th ITTC. Methods to Determine Ice Resistance Using Self-Propelled Model Test An increasing share of self-propulsion model tests is one of the modern trends in test practices of ice basins. Most leading ice basins took to using selfpropelled models rather than non-propelled models in ice resistance towing tests. Method of Krylov State Research Center

(1) First Method Traditionally, in the KSRC ice basin practices, the self-propelled models have been used to find ice resistance of model in astern mode. In this case, the captive test method is employed when a model is rigidly fixed to the towing carriage via dynamometer and outfitted with running propellers, as shown in Fig. 1. Propeller thrust is measured with special-purpose dynamometers. For a propelled ship model running astern, the ice resistance RI is found from the following force equation:  X  RI ¼  Fmeans þ ð1  tÞ • P i i

ð23Þ

A model with running propellers is towed at a specified speed by towing carriage. The force of model-carriage interaction FI is measured. The speed of propeller rotation is chosen to match the propulsive thrust with the model speed. In this case, a close to full-scale flow pattern around the hull is obtained. Experiments in a continuous ice sheet, when completed, leave a channel packed up with brash ice. This channel after being cleared of brash ice is used to repeat the self-propelled model tests, now in open water. These experiments are conducted at the same speed of propeller rotation and model speed to measure the force of model-carriage interaction FW. The pure ice resistance force RI is calculated based on the test data obtained in ice and open water conditions using Eq. (24): RI ¼ FI þ F W

ð24Þ

It should be noted that the forces FI and FW retain their actual signs when being summed up. Rigid connection between the self-propelled model and towing carriage makes it possible to accurately set the model speed in ice. The force between towing carriage and model measured by dynamometer indicates whether the propeller

Resistance of Polar Vessel, Fig. 1 Astern test setup: 1, dynamometer; 2, ship model hull; 3, propulsion pod model (Specialist Committee on Ice, Technical Committees and Group of the 28th ITTC, 2017)

Resistance of Polar Vessel

1497

thrust is higher than the ice-plus-water resistance or not sufficient to overcome this total resistance. This force is defined by Eq. (25): F I ¼ RI þ RW  T E

ð25Þ

where RW – model resistance due to water and TE – effective thrust of model’s propulsion system. Model tests in a channel cleaned of brash ice make it possible to determine the hydrodynamic resistance force FW more accurately than it is done using the Finnish method because in these tests, the hydrodynamic resistance has practically no wave-making component. In ice basin, the hydrodynamic resistance should be determined following all requirements which are applied to the same kind of experiments when conducted in towing tanks. In these tests the force between model and towing carriage is determined, which is defined according to Eq. (26): FW ¼ T E  RW

ð26Þ

From Eq. (25) follows the ice resistance in Eq. (27) R I ¼ FI þ T E  RW

ð27Þ

Then the final formula for the ice resistance is Eq. (24). Method of Aker Arctic

The ice basin of Aker Arctic is using a different technique involving a series of preliminary open water tests usually carried out in the ice basin itself. Under this method, ice resistance is determined using self-propulsion tests at the ship propulsion point. Model ice resistance is determined in a number of steps. Self-propelled model is tested under bollard pull condition in open water. In this case, the propeller thrust is measured at different propeller speeds. These data are then used to find the speed which provides the specified thrust of propulsion system in bollard pull condition. Towing tests of the model with running propellers are performed in open (ice-free) water with the model fixed to the towing carriage via dynamometer. Propellers are

run at speeds corresponding to 80, 100, and 120% power consumption. In these tests the brake force (which is applied from the towing carriage side to model) is measured versus model speed (at constant number of revolutions that could be different for side propellers and middle propeller). The open water tests give brake force versus model speed. Method of HSVA

HSVA ice basin is using both self-propelled and non-propelled models in ice resistance tests. Ice resistance tests with self-propelled models are performed in a captive setup. The model is towed at a given speed, while propeller revolution numbers are varied. Propeller revolutions range from practically zero to a certain value specified to assure that the force recorded by dynamometer changes its direction (model now pulling the towing carriage). As shown in Fig. 2, a mandatory test condition is practically zero number of propeller revolutions. Based on the results of this test, the ice resistance of model is found. Model Ice in Ice Resistance Experiment Type ice can be divided into two categories: frozen model ice and nonfrozen model ice. The frozen model ice is mainly used in the ice basin laboratory at home and abroad, and the nonfreezing model ice is mostly used in the conventional towing tank laboratory without an ice basin. The frozen model ice is divided into brine ice, urea ice, and EG/AD/S ice. Brine ice, also known as the first-generation model ice, is made from a certain concentration of sodium chloride solution (Schwarz 1977). Urea ice, also known as the second-generation model ice, is made up of a 1.3% concentration of urea solution (Timco 1979, 1980; Hirayama 1983). The EG/AD/S ice, also known as the thirdgeneration model ice, is made from aqueous solutions of three different additives including the mixture of ethylene glycol (EG), aliphatic detergent (AD), and sugar (S) (Timco 1986). With the development of experimental technology and the requirements of ice zone tests, various kinds of nonfreezing synthetic model ice have come out one after another. The advantages

R

1498

Resistance of Polar Vessel

Resistance of Polar Vessel, Fig. 2 Determination of ice resistance by HSVA method (HSVA Report 2012)

of nonfreezing model ice are that it does not require low-temperature manufacturing and it’s easier to control. At present, the main model ice used in ice ship resistance test are fragments of semi-refined paraffin wax and polypropylene material, as shown in Fig. 3. Two Methods to Conduct the Towing Tests The methods to conduct the towing tests can be found in the website of HSVA ice tank (https:// www.hsva.de/our-services/model-testing/tests-inthe-ice tank.html). Towed Propulsion

During the towed propulsion test, the model is connected to the service carriage, which is pushed by the main carriage, via a rigid rod that itself is attached to a load cell at the bows of the model, as shown in Fig. 4. After being accelerated the model is towed at a constant speed. The propeller rpm is changed in four steps from near idling condition through a value close to the self-propulsion point up to a value well above the self-propulsion

condition. Both the thrust of propellers and the coupling force are measured, and therefore the actual propulsion point for the given speed can be determined throughout interpolation from the linear correlation between thrust and pull force. The resistance can be read from the intersection point of the same curve with the axis of ordinates. Fixed Mode Testing

Regardless of the type, each model can be tested in fixed mode. This means the models’ motion is blocked in a number of degrees of freedom, as shown in Fig. 5. This can be partially inferred that only certain directions of motion are blocked or completely – in this case all six degrees of freedom are blocked. Ice-induced vibrations can be investigated in a fixed mode where the model is rigidly connected to the basin floor, and only motions in one or two directions are allowed. Ice loads on a vessel may be determined in a fixed setup where the vessel is rigidly connected to the main carriage and pushed through the ice. A special rotation platform allows testing the

Resistance of Polar Vessel

1499

Resistance of Polar Vessel, Fig. 3 Artificial ice (Kim et al. 2013; Guo et al. 2016; Werff et al. 2015)

Resistance of Polar Vessel, Fig. 4 Model towed by carriage using rigid pole (HSVA Report 2012)

R Resistance of Polar Vessel, Fig. 5 Model directly under the carriage (HSVA Report 2012)

1500

subject, vessel, or structure, under certain oblique angles. In all cases, forces in three axes and moments around these axes are determined by means of a six-component scale. In addition to the forces accelerations, velocities and movements of the structure/vessel will be measured.

Cross-References https://www.hsva.de/our-services/model-testing/ tests-in-the-ice-tank.html

References Enkvist E (1972) On the ice resistance encountered by ships operating in the continuous mode of icebreaking Finnish-Swedish Ice Class Rules[S] (2002) Finnish and Swedish Maritime Administration Guo C, Chang X, Shuai W et al (2016) Experimental study on ship resistance in crushed ice condition. J Harbin Eng Univ 1.01(04):481–486 Hirayama K (1983) Properties of urea-doped ice in the CRREL test basin[R]. Cold Regions Research and Engineering Lab, Hanover HSVA Report, Brash Ice Tests for a pnmax Bulker with Ice Class 1B, 2012. Keinonen A, Browne RP (1991) Icebreaker performance prediction. In: Proceedings of the First International Offshore and Polar engineering Conference. Edinburgh, pp 562–570 Kim MC, Lee SK, Lee WJ et al (2013) Numerical and experimental investigation of the resistance performance of an icebreaking cargo vessel in pack ice conditions. Int J Naval Archit Ocean Eng 5(1):116–131 Kloss C, Goniva C, Hager A et al (2012) Models, algorithms and validation for opensource DEM and CFD– DEM. Prog Comput Fluid Dyn Int J 12(2–3):140–152 Lindqvist Gustav (1989) A straight forward method for calculation of ice resistance of ships. In: Port and Ocean Engineering under Arctic Conditions, Luleaa, p 722 Morgan, D. (2016) An improved three-dimensional discrete element model for ice-structure interaction. In: Proceedings of the 23rd IAHR international symposium on ice Morgan D, Sarracino R, McKenna R, et al 2015 Simulations of ice rubbling against conical structures using 3D DEM. In: Proceedings of the International Conference on Port and Ocean engineering Under Arctic Conditions Ren D, Park J-C, Hwang S-C, Jeong S-Y, Kim S-Y (2017) Brittle failure simulation of ice beam using a fully Lagrangian particle method. In: Proceedings of the 24th International Conference on Port and Ocean engineering under Arctic Conditions (POAC'17) Riska K (2011a) Design of ice breaking ships. Course mateial NTNU

Resistance Test Riska K (2011b) Ship–ice interaction in ship design: theory and practice. Course Material NTNU Riska K, Wilhelmson M, Englund K, et al. (1997) Performance of merchant vessels in ice in the Baltic, Winter Navigation Research Board NO.52[R]. Helsinki, Finnish Maritime Administration Schwarz J (1977) New developments in modeling ice problems. In: Proceeding of the 4th international conference on port and ocean engineering under Arctic conditions, pp 45–61 Shigihara T, Ishibashi D, Konno A (2015) Experimental and numerical investigation of a model-scale ship and ice floe (second report). In: Proceedings of the International Conference on Port and Ocean engineering Under Arctic Conditions Song M, Kim E, Amdahl J (2015) Fluid-structureinteraction analysis of an ice block-structure collision Specialist Committee on Ice, Technical Committees and Group of the 28th ITTC, 2017. Spencer D (1992) A standard method for the conduct and analysis of ice resistance model tests. Laboratory Memorandum Timco G (1979) The mechanical and morphological properties of doped ice: a search for a better structurally simulated ice for model test basins. In: POAC 79: proceedings, vol 1, pp 719–739 Timco GW (1980) The mechanical properties of salinedoped and carbamide (urea)-doped model ice. Cold Reg Sci Technol 3(1):45–56 Timco GW (1986) EG/AD/S: a new type of model ice for refrigerated towing tanks. Cold Reg Sci Technol 12(2):175–195 Vroegrijk E (2015) VALIDATION OF CFD+DEM AGAINST MEASURED DATA. In: Proceedings of the ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2015), OMAE2015-41770 Werff SVD, Brouwer J, Hagesteijn G (2015) Ship resistance validation using artificial ice. In: Omae 2015, Proceedings of the ASME 2015, International Conference on Ocean, Offshore and Arctic Engineering Yulmetov R, Bailey E, Ralph F (2017) A discrete element model of ice ridge interaction with a conical structure. In: Proceedings of the 24th International Conference on Port and Ocean Engineering under Arctic Conditions (POAC’17)

Resistance Test ▶ Towing Tank Test

Resonance Roll ▶ Dead Ship Condition

Resource Assessment

Resource Assessment Zhen Gao Norwegian University of Science and Technology, Trondheim, Norway

Synonyms ECMWF - European Centre for Medium-Range Weather Forecasts; SWAN - Simulating Waves Nearshore

Definition Resource assessment is an evaluation of the longterm available offshore renewable energy resources (in terms of energy or power), including wind, wave, and marine current energy resources. This can be done from a global and regional perspective for site screening/selection or for a specific location for the development of commercial farms. Offshore renewable energy resource can also be distinguished as potentially available resource (assuming that all the energy can be converted into electricity) or technically available resource (which can be practically converted by a given device or technology and therefore is device- and site-specific).

Wind Energy Resource Wind energy refers to the kinetic energy of air in motion, and the total wind energy during a period of t through an area of A normal to the mean wind direction is E ¼ 12 AtrU3, where r is the density of the air and U is the mean wind speed. Then the power is the energy per unit time P ¼ 12 ArU3 . Often, we use the wind power density AP ¼ 12 rU3 for resource assessment and spatial distribution of wind power. In addition to the parameter of mean wind speed, turbulent intensity factor is often estimated based on measurements or simulations, and it is a very important parameter that is related to dynamic loads and responses of offshore wind

1501

turbines, although it is not so important for power estimation. Figure 1 shows the global spatial distribution of average offshore wind power density with respect to the winter and the summer seasons of the Northern Hemisphere (NASA/JPL 2008). It clearly shows the non-uniform distribution of the wind power density around the globe, with larger wind power in northern or southern areas than that near the equator. The equator area has less variation in wind power density (and therefore wind speed) among different seasons, while wind speed in winter is much larger than that in summer for the northern or southern area. Because of the considerations on economics and survivability of offshore wind turbines, it is not expected to see in the near future wind turbines in the middle of oceans, far from the shore. Offshore wind is now being developed from near shore gradually towards deeper waters. The available power in wind is proportional to the cube of wind speed. Therefore, an accurate estimation of the mean wind speed is important for resource assessment. However, the mean wind speed also varies vertically, increasing when the height from the sea surface increases, which is referred to as wind shear. Figure 2 shows the annual mean wind speed distribution offshore Europe for five standard heights. Most of the offshore wind turbines today have a nacelle height between 70 m and 100 m. The mean wind speed at the height of 100 m is larger than 10 m/s for the northern North Sea area, while it is about 8.5–10 m/s for the North Sea and 6–8.5 m/s for the Mediterranean Sea. If we consider a mean wind speed of 12 m/s as the rated wind speed of an offshore wind turbine and a maximum efficient of 50%, a rotor area of 11,600 m2 and therefore a blade length of 60 m are needed to produce 5 MW of electric power. On the other hand, the mean wind speed varies also in time. From a long-term perspective (i.e., 25 years of lifetime), a probabilistic distribution (for example, Weibull distribution) of mean wind speed for a given site is typically established using either measurement data or hindcast data (see Li et al. 2015). Such wind speed distribution can be used in combination with the wind turbine power

R

1502

Resource Assessment

W/m2 1400 1200 1000 850 750 650 550 450 350 250 190 110 70 30

60N 40N 20N EQ 20S 40S 60S 0

40E

80E

120E

160E

160W

120W

80W

40W

0 W/m2 1400 1200 1000 850 750 650 550 450 350 250 190 110 70 30

60N 40N 20N EQ 20S 40S 60S 0

40E

80E

120E

160E

160W

120W

80W

40W

0

Resource Assessment, Fig. 1 Global distribution of offshore wind power density in winter and summer (NASA/JPL 2008)

curve to estimate the annual power output from a turbine or from a farm. As of today, there are many wind resource maps that are already developed at the global level by government or research agencies, as shown in Fig. 1. More detailed regional and local wind resource assessment, using either numerical models or in situ measurements (such as WAsP – Wind Atlas Analysis and Application Program (Mortensen et al. 2005)), is needed for developing commercial offshore wind farms. Satellite-borne remote sensing observations, purpose-built meteorological masts, and groundbased remote sensing techniques (such as SODARs – Sonic Detection and Ranging; LIDARs – Light Detection and Ranging) are developed for specific wind speed measurement and resource assessment (Sempreviva et al. 2008).

Wave Energy Resource Energy in propagating gravity ocean waves contains both kinetic and potential energy, which alternates when the waves propagate. It is the wave kinetic energy that can be absorbed and converted into electricity using a wave energy converter device. For a regular wave with a height of H, the average energy E stored on a horizontal water surface with a unit area is E ¼ 18 rgH2 , where r is the density of the sea water and g is the gravitational acceleration (Falnes 2002). Wave power P, which is the wave energy flux through a vertical plane of unit width perpendicular to the wave propagation direction, is P ¼ cg E ¼ 2 1 2 32p rg TH , where cg is the group velocity and T is the wave period. For example, when H¼2m, T ¼ 10s,we can get P ¼ 40kW/m. For an irregular

Resource Assessment

1503

R

Resource Assessment, Fig. 2 Distribution of annual mean wind speed and wind power density offshore Europe (Troen and Lundtang Petersen 1989)

wave with significant wave height Hs and wave energy period Te, the wave energy flux becomes 1 P ¼ 64p rg2 Te H2s . For example, when Hs ¼ 2m, Te ¼ 10s, we can get P ¼ 20kW/m. It should be noted that the wave power is proportional to wave period and wave height squared. Although they are not sensitive as wind speed for wind power,

there exists a big difference in wave power for small and large waves. Figure 3 illustrates a map of global annual mean wave power (Mørk et al. 2008). This map indicates that the highest levels of average wave power are found in the areas between 40 and 60 in both hemispheres, which are consistent with the observations for global

1504

Resource Assessment

Resource Assessment, Fig. 3 Global distribution of annual mean wave power (Mørk et al. 2008)

mean wind speed distribution as shown in Fig. 1. Like offshore wind resource, it is not possible to utilize all the wave energy in oceans based on the current technology and only the ocean areas close to the shore are relevant. High annual average wave power, typically 40–100 kW/m, is found along the coastlines of northern Europe, North America, South Africa, Australia/New Zealand, and Chile/Argentina. Considering a site with annual average wave power of 40 kW/m and a device of 25% efficiency for electricity generation, the device needs to be at least 500 m long in order to produce 5 MW of electric power. This indicates that a large device is needed, which is particularly challenging when developing commercial wave energy converters since the cost will be high. Wave power at a given offshore site also shows a variation in time. Since wave power is a function of both wave height and period, the long-term variation of wave power can be determined using the long-term joint distribution of significant wave height and spectral wave period (or wave energy period), as shown by Li et al. (2015). For a given wave energy converter device, the power absorption varies with respect to significant wave height and spectral wave period.

A combination of the wave power matrix of the device with the long-term distribution of significant wave height and spectral wave period can be used to derive the annual power output. Global and regional distribution of wave power can be estimated based on wave buoy measurements, satellite remote data, or numerical models. The results in Fig. 3 were based on the data from the ECMWF (European Centre for Medium-Range Weather Forecasts) WAM numerical model, which is calibrated and corrected by Fugro OCEANOR against a global buoy and Topex satellite altimeter database (Mørk et al. 2008). High-resolution numerical models are developed for resource assessment of a specific site, including the prediction of wave energy, heights, periods, and directions. Two types of approaches are used in these numerical models: (1) the deterministic approach, which describes the sea surface evolution accurately in both time and space; and (2) the spectral approach, which provides a statistical description of the wave conditions in space and time. The first approaches can capture all the relevant physics of wave/bottom/shoreline and nonlinear wave-wave interactions, but they are computationally expensive. The spectral

Resource Assessment

approaches provide an approximation of the physics of nonlinear wave-wave interaction, wind forcing, and wave breaking/bottom dissipation. But they are commonly used today and typically are open-source and user-friendly, such as MIKE21 (2008), SWAN (2009), TOMAWAC (2014). A comparison of the different numerical wave models was carried out and can be found in Venugopal et al. (2010).

Ocean and Tidal Current Energy Resource Ocean current might be generated due to many mechanisms, including tidal effect, ocean circulation, and wind generation. Here, we focus on tidal energy. Like offshore wind energy, ocean current energy refers to the kinetic energy in ocean current, which can be characterized using the current speed or velocity. However, since the density of sea water is much larger than that of air, one doesn’t need a very large rotor area of a tidal turbine to achieve the same power production as compared to a wind turbine, although current

1505

speed is typically much lower than wind speed. For example, considering a tidal current velocity of 3 m/s and 50% of efficiency of the turbine, a rotor with a diameter of 30 m (instead of 120 m for wind turbines at the rated wind speed of 12 m/s) can produce 5 MW of electric power. Tidal energy resource can be very well predicted and shows a 12-h variation. It is strongly dependent on the tidal range at different locations. Figure 4 shows a global distribution of tidal range, which represents the tidal current speed and energy (NASA 2006). It shows that a strong location-dependent and places with abundant tidal energy are limited. In Europe, UK and Ireland have large resource, while some areas in the west coasts of Australia, New Zealand, Canada, and the east coast of the USA and China also have large potential to develop tidal energy. Most of the tidal energy resource assessment is performed based on current speed measurements using for example Acoustic Doppler Current Profilers (Thomson et al. 2012) or Marine Radar (Bell et al. 2012), in particular in local straits or channels, where current speed can reach the minimum value for efficient use of tidal turbines and for

R

Resource Assessment, Fig. 4 Global distribution of tidal range (NASA 2006)

1506

commercial development (Bahaj 2013). Numerical models based on 2D or 3D formulations have also been developed and used for resource assessment (Venugopal and Nemalidinne 2014). An offshore site with significant tidal energy resource often has large turbulence and large waves, which might be challenging for structural design of tidal turbines.

Cross-References ▶ Offshore Wind Turbines ▶ Tidal and Ocean Current Turbines ▶ Wave Energy Converters

References Bahaj AS (2013) Marine current energy conversion: the dawn of a new era in electricity production. Phil Trans R Soc A 371:20120500 Bell PS, Lawrence J, Norris JV (2012) Determining currents from marine radar data in an extreme current environment at a tidal energy test site. In: Proceedings of the geoscience and remote sensing symposium (IGARSS). IEEE International, Munich. July 22–27 Falnes J (2002) Ocean waves and oscillating systems – linear interactions including wave-energy extraction. Cambridge University Press, Cambridge, UK Li L, Gao Z, Moan T (2015) Joint long-term environmental conditions at five European offshore sites for design of combined wind and wave energy devices. J Offshore Mech Arct Eng 137(3):031901 MIKE21 (2008) Wave modelling user guide. Danish Hydraulic Institute, Hørsholm Mørk G, Barstow S, Mollison D, Cruz J (2008) The wave energy resources. In: Cruz J (ed) Ocean wave energy – current status and future perspectives. Springer, Berlin/ Heidelberg Mortensen NG, Heathfield DN, Myllerup L, Landberg L, Rathmann O (2005) Wind Atlas Analysis and Application Program: WAsP 8 help facility. Risø National Laboratory, Roskilde NASA (2006) TOPEX/Poseidon: revealing hidden tidal energy. NASA Goddard Space Flight Center Scientific Visualization Studio, Greenbelt. http://svs.gsfc.nasa. gov/stories/topex/ NASA/JPL (2008) Ocean wind power maps reveal possible wind energy sources. https://www.jpl.nasa.gov/ news/news.php?release¼2008-128 Sempreviva AM, Barthelmie RJ, Pryor SC (2008) Review of methodologies for offshore wind resource assessment in European seas. Surv Geophys 29(6):471–497

Responsibility SWAN (2009) SWAN user manual, SWAN cycle III, version 40.72 [Online]. www.swan.tudelft.nl Thomson J, Polagye B, Durgest V, Richmons MC (2012) Measurements of turbulence at two tidal energy sites in Puget Sound, WA. Ocean Eng 37(3):363–374 TOMAWAC (2014). http://actimar.free.fr/mambo/index. php?option¼com_content&task¼view&id¼159& Itemid¼215&lang¼en Troen I, Lundtang Petersen E (1989) European wind atlas. Risø National Laboratory, Roskilde Venugopal V, Nemalidinne R (2014) Marine energy resource assessment for Orkney and Pentland Waters with a coupled wave and tidal flow model. In: Proceedings of the ASME 2014 33rd international conference on ocean, offshore and arctic engineering. Paper No. OMAE2014-24027, June 8–13, San Francisco Venugopal V, Davey T, Girard F, Smith H, Smith G, Cavaleri L, Bertotti L, Lawrence J (2010) EquiMar Project (Equitable Testing and Evaluation of Marine Energy Extraction Devices in terms of Performance, Cost and Environmental Impact) - Deliverable D2.3 Application of Numerical Models. University of Edinburgh, UK

Responsibility ▶ Reliability and Safety in Offshore Engineering

Restoring Moment ▶ AUV/ROV/HOV Stability

Reynolds Number (Re) ▶ Hydrodynamics for Subsea Systems

Ribbon Bridge ▶ Floating Bridge

Rigid Connectors ▶ Connectors of VLFS

Risk-Based Design for Ship and Offshore Structures

Rigid Module and Flexible Connector (RMFC) ▶ Connectors of VLFS

Risk-Based Design for Ship and Offshore Structures Yang Lu, Jing-Zheng Yao, Hui Jia and Liang-Tian Gao College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China

Synonyms Reliability-based design

Definition In engineering applications, as decision support tools, risk and reliability analysis methods are increasingly recognized worldwide. Risk-based design is a process integrating the risk and reliability analysis methods into product design. Risk-Based Ship and Offshore Structures Design introduces risk analysis into the traditional design process, aiming to deal with safety problems reasonably and effectively (Apostolos 2009).

Scientific Fundamentals Principle of Risk-Based Design The International Maritime Organization (IMO) has discussed the target based criteria and given rise to the term “Safety Level” designating the through-life level of acceptable risk associated with a particular ship concept, which may lead to a new guiding principle to attaining safety costeffectively. The concept of “risk” is often associated with unexpected events and with shipping operations being undoubtedly “risky,” which

1507

must be remembered when designing ship and offshore structures. Effective risk management at the design stage is extremely important. At this stage, commencing with concept development or selection, there is the greatest scope to adopt or devise arrangements which will reduce, or even eliminate, particular risks. Risk assessment should be undertaken as an integral part of the design process, so that risk management decisions can be taken in good time. Much of the potential benefit of risk assessment of the design will be lost if it takes place after the design has been firmed up. It should not simply be used to retrospectively justify design decisions already taken. Safety features incorporated into the design will be more secure, long lasting, and effective than those that rely upon the use of safety equipment or the adoption of operating procedures intended to compensate for design deficiencies. Furthermore, as the design and construction work progress, it will become increasingly difficult and costly to incorporate safety related features. Safety considerations in design can be considered in the following hierarchy: (a) Eliminate the hazard (b) Reduce the likelihood of a hazardous event, giving preference to inherent safety over operational safeguards (e.g., procedures) (c) Reduce the consequences of a hazardous event, for example, by reducing combustible fuel inventory; by adopting fail-safe or fault tolerant systems; by protecting structure and equipment from fire. (d) Protect people from the effects; collective protection in preference to individual protection (e) Provide means of escape and evacuation The application of risk-based design is more focused on the concept of high level innovation (shown in Fig. 1), so it is necessary to use knowledge of ship information in all its forms: best practice, engineering evaluation, latest tools and data, and all content of quantitative risk analysis. Risk-based design is a comprehensive approach. The key to understanding this method

R

1508

is the integration of risk assessment in the design process and decision-making towards achieving the overall design goals, as illustrated by framework of Fig. 2. Safety Assessment The hazards caused by risks of ships and offshore structures mainly include the following three

Risk-Based Design for Ship and Offshore Structures

aspects: casualty, environment disruption, and economic loss (Zhang et al. 2003), shown in Fig. 3. (a) The risks of personnel include: potential casualties, fatal accident rates, average individual risk rates, etc. (b) The degree of damage to the environment can be measured according to its recovery time. It

Risk-Based Design for Ship and Offshore Structures, Fig. 1 Riskbased design and innovation (Apostolos 2009)

Risk-Based Design for Ship and Offshore Structures, Fig. 2 Framework for risk-based design (Apostolos 2009)

Risk-Based Design for Ship and Offshore Structures

1509

In general, the ship can meet all kinds of requirements for its use.

Key Applications

Risk-Based Design for Ship and Offshore Structures, Fig. 3 Content of safety assessment (Zhang et al. 2003)

can be generally divided into: 1–12 months, 1–3 years, 3–10 years, greater than 10 years, etc. (c) Economic loss usually refers to material damage and production delay. Security Goals Security goals, like other design objectives, are related to the mission and purpose of ships. Clear security goals are already part and parcel of the design input. Examples of design objectives driven by safety factors include (Christian et al. 2012): Top-Level Goals: (a) No accident can cause loss of the whole ship, such as collision, grounding, fire, etc. (Franz 2010). (b) No loss of human life due to ship related accidents. (c) Low impact to the environment (no air emissions, low noise). (d) When the ship has an accident, the impact will be minimized. Specific Technical Goals: (a) Vessels remain upright and afloat in all feasible operational loads and environmental conditions. (b) Vessels remain upright and afloat in case of water ingress and flooding. (c) The ship structure can withstand all predictable loads throughout the life cycle. (d) Sufficient residual structural strength in the case of breakage. (e) High passenger comfort (no seasickness, low vibration level, low noise level).

Risk Measurement The risk for ship and offshore structures can be expressed by probability and resulting value. In actual calculation, the basic expression of the risk is: R¼

X

pi  c i

I

where pi represents the frequency of occurrence of a single event and ci represents the consequences of the event. Design Phase Using Risk Criteria When adopting risk based ship design method, different risk assessment criteria can be adopted in different design stages. The feasibility design phase of ship engineering: usually, decisions need to be made under the premise of less information, such as project progress, cost budget, etc. Qualitative or semi quantitative risk assessment methods are mainly adopted. The risk matrix of qualitative assessment is shown in Fig.4. The detailed design phase of ship engineering: with the clarity of design objectives and various design parameters and drawing on existing databases, probability based quantitative risk assessment methods can be adopted. At this point, the ALARP principle can be used for quantitative risk assessment of casualty risk, environmental risk, and property risk, as shown in Fig.5. A qualitative ranking of both frequency (from frequent through to incredible) and severity (from catastrophic to negligible) of each hazard is deduced by consensus. These can be amalgamated in matrix form where the risk categories are: A ¼ Intolerable B ¼ Undesirable and only accepted when risk reduction is impracticable

R

1510

Risk-Based Design for Ship and Offshore Structures

Potential Consequences L6

L5

L4

Minor injuries or discomfort. No medical treatment or measureable physical effects.

Injuries or illness requiring medical treatment. Temporary impairment.

Injuries or illness requiring hospital admssion.

Not Significant

Minor

Moderate

Major

Severe

Almost Certain

Medium

High

Very High

Very High

Very High

Likely

Medium

High

High

Very High

Very High

May occur at some time

Possible

Low

Medium

High

High

Very High

Not likely to occur in normal circumstances

Unlikely

Low

Low

Medium

Medium

High

Rare

Low

Low

Low

Low

Medium

Expected to occur regularly under normal circumstances

Like lihood

Expected to occur at some time

Could happen, but probably never will

L3

L2

Injury or illness resulting in Fatality permanent impairment.

Risk-Based Design for Ship and Offshore Structures, Fig. 4 Risk matrix (https://cn.bing.com/)

C ¼ Tolerable with the endorsement of the project safety review committee D ¼ Tolerable subject to normal project review Risk acceptance criteria may be employed in supporting a design for ship and offshore structures when either classification or statutory approval is sought (Ship Right Design and Construction 2018). Linking Risk-Based Design and Acceptance Risk-based design for Ship and Offshore Structures is considered an enhanced variant of the traditional design process, taking safety as an additional design objective. Hence, an additional constraint is entered into the design optimization, as shown below (Jan 2007): Rdesign  Racceptable Risk-Based Design for Ship and Offshore Structures, Fig. 5 ALARP principle (https://cn.bing.com/)

With Rdesign the risk of the considered ship or offshore structures and Racceptable the acceptable risk.

Risk-Based Design for Ship and Offshore Structures

Usually, risk is determined by the frequency and consequences of events. Different risk categories need to be distinguished, such as human life, environment, or property. The design risk Rdesign is typically the sum of some risks associated with different types of accidents, such as collision, fire, or grounding. With the help of risk model, such as fault tree and Bayesian networks, each partial risk can be calculated. The acceptable risk Racceptable of human life and environmental protection is specified by the approval authority (flag state administration and/or classification society). There are two options for determining acceptable risk: relative or absolute. In the first case, a reference design is selected which complies with current rules. In the second case, IMO risk acceptance criteria are used or referenced. Techniques of Quantitative Risk Assessment Quantitative risk assessment is the term most often used to describe the use of statistical or more properly quantitative methods in risk-based design. Quantitative techniques widely used under the risk-based design for Ship and Offshore Structures include: (a) Failure Modes, Effects and Criticality Analysis (FMECA) (b) Fault Tree Analysis (FTA) (c) Event Tree Analysis (ETA) (d) Statistical analysis of historical accident data (e) Reliability analysis of component failure data (f) Data elucidation from structured expert judgment (g) Human error analysis (h) Cost Benefit Analysis (CBA) Decision Making So far the assessment and ranking of risk has been considered. The final stage involves hard decisions where the proposed safety improvements may be difficult and the cost to implement considerable. The principle of As Low As Reasonably Practicable ALARP (see “Design Phase Using Risk Criteria”) shows that tolerable risk is not a simple

1511

pass/fail test. The majority of risks are in the ALARP region where work should be done to reduce the risk further. The owners of each risk must be satisfied that safety arguments, criteria, and decisions are sound and documented so as to provide an audit trail. Peer review and the use of independent safety assessment/audit are also valuable in giving strength to decisions and actions, particularly if later challenged. By taking safety as the target in the design process, the new concept of “safety design” and the development of risk-based design method can deal with ship safety in a systematic and comprehensive way. Risk-based design opens the door to innovation and provides competitive advantages for the maritime industry by facilitating cost-effective safety. It is impossible to optimize the design solutions without risk-based design. This method reflects the trend of target based standards and highlights the advantages of riskbased design methods. It is particularly useful in the face of innovative ship and offshore structures design concepts and alternative design and arrangements. In this case, quantitative risk analysis is the only reliable way to ensure a suitable safety level and set a safety target.

References Apostolos P (2009) Risk-based ship design methods, tools and applications. Springer. 3:97–151 Christian B, Karl-Christian E, Apostolos P (2012) SAFEDOR-the implementation of risk-based ship design and approval. Procedia Soc Behav Sci 48:753–764 Franz E (2010) Assessing fire safety in maritime composite superstructures – A risk-based approach. Division of Fire Safety Engineering, Fire Protection Engineering 3,5 years, Risk Management and Safety Engineering (M.Sc.Eng.), Division of Risk Management and Societal Safety 5:56–58 Jan EV (2007) Offshore risk assessment: Principles, modelling and applications of qra studies. Springer Series in Reliability Engineering. 2:51–76 ShipRight Design and Construction (2018) Risk based designs. Additional Design Procedures 7:14–16. Zhang SK, Bai Y, Tang WY (2003) Risk assessment in marine and ocean engineering. National Defense Industry Press 3:25–49

R

1512

RMRS, Russian Maritime Register of Shipping ▶ Moored Ship in Ice

RMRS, Russian Maritime Register of Shipping

maintain an ROV on its position and/or heading (fixed location or predefined track) by use of its thrusters. ROVs equipped with DP system allow operations close to the seafloor, including station keeping, trajectory tracking, path following, and low-speed maneuvering. Then the pilot can focus on monitoring and planning of operations that demand human intervention or decision making.

Robust Control ▶ Intelligent Control Algorithms in Underwater Vehicles

Routing Layer ▶ Underwater Acoustic Sensor Network

ROV ▶ Remotely Operated Vehicle (ROV)

ROV Dynamic Positioning

Scientific Fundamentals Historical Development DP system was born with the increasing demands of the rapidly expanding oil and gas exploration industry in the 1960s and early 1970s. In the 1960s, the first DP system was introduced for horizontal modes of motion (surge, sway, and yaw) using single-input single-output PID control algorithms in combination with low-pass and/or notch filter (Sørensen 2011). The first ship to fulfill the accepted definition of dynamic positioning was the “Eureka” (1961), as shown in Fig. 1, of about 450 t displacement and 130 ft. length. This ship was fitted with an analog control system, interfaced with a taut wire reference, equipped with steerable thrusters fore and aft in addition to her main propulsion (Fay 1989).

Biao Wang Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai Ocean University, Shanghai, China

Synonyms Dynamic positioning (DP); Dynamic positioning control; Dynamic positioning control system; Dynamic positioning of remotely operated vehicles; Dynamic positioning of underwater robotic vehicles; Dynamic positioning system

Definition The remotely operated vehicles (ROVs) dynamic positioning (DP) is a method to automatically

ROV Dynamic Positioning, Fig. 1 The world’s first DP vessel Eureka (Steinbeck 2017)

ROV Dynamic Positioning

DP system development came in the mid-1970 with the application of Kalman filters and linear quadratic (LQ) optimal controllers. After 1995, nonlinear PID control, passive observer design and observer back-stepping designs have been applied to DP (Fossen 2002). In 1980, the number of dynamic positioning capable ships was about 65, in 1985, the number had increased to about 150. Currently (2013), it stands at over 1,800 and is still expanding (▶ “Dynamic Positioning in Ice” from Wikipedia). DP systems have become more sophisticated and complicated, as well as more reliable. The costs are falling due to newer and cheaper technologies, and the advantages are becoming more compelling as offshore work enters ever deeper water and the environment is given more respect. Computer technology has developed rapidly and some vessels have been upgraded twice with new DP control systems. Position reference systems and other peripherals are also improving and redundancy is provided on all vessels designed to conduct higher-risk operations. DP of underwater vehicles like ROVs and autonomous underwater vehicles (AUVs) has lately received increasing interest from offshore contractors, vendors, and the research community. DP Classification Based on IMO – International Maritime Organization publication 645 (IMO 1994), the classification societies have issued rules for dynamically positioned ships described as Class 1, Class 2, and Class 3. Equipment Class 1 has no redundancy. Loss of position may occur in the event of a single fault. Equipment Class 2 has redundancy so that no single fault in an active system will cause the system to fail. Loss of position should not occur from a single fault of an active component or system such as generators, thruster, switchboards, remote controlled valves, etc. But the loss of position may occur after the failure of a static component such as cables, pipes, manual valves, etc. Equipment Class 3 which also has to withstand fire or flood in any one compartment without the system failing. Loss of position should not occur from any single failure including a wholly burnt

1513

fire subdivision or flooded watertight compartment. Table 1 gives an overview of the IMO dynamic positioning system classification system and the roughly corresponding dynamic positioning system class notations, individual variations exist. Elements of ROV DP System A typical ROV DP system is shown in Fig. 2. The components and their relevance are explained below. The controller computes control forces based on the error between the desired position and the actual position. The desired position is derived from guidance software. The actual position is taken from the navigation system. Control forces must be transformed to thruster commands by thrust allocation matrix (Fossen and Johansen 2006) and then send to thrusters. Thrusters provide DP capability for ROVs. Normally a DP ROV has an over-actuated vector thrust system. A single or multi failure of thrusters will not cause the system to fail according to the specific thruster configuration. Fault-tolerant control algorithms were proposed by researchers (Yang et al. 1998; Ni and Fuller 2003; Omerdic and Roberts 2004). Navigation system indicates the position of ROVs. Ultra short base line (USBL), Doppler velocity log (DVL), or inertial measurement unit (IMU) is used to obtain position information. For some underwater application, integrated navigation combining the above sensors and pressure sensor, altimeter, digital compass, etc. is used to get a more accurate position. Raw data from sensors are processed in order to check for validity and consistency, and filtered by observers such as extended Kalman filter (EKF). The observer continues estimation of ROV status even if sensors fail to provide raw data, referred to as dead reckoning. Environmental disturbances are mainly generated by ocean currents for ROV DP system. It’s inconvenient to measure current forces. The traditional way is to design a robust controller or estimate current forces by an observer. Winds and waves can be neglected in underwater environment.

R

1514

ROV Dynamic Positioning

ROV Dynamic Positioning, Table 1 IMO DP classification

Description Manual position control and automatic heading control under specified maximum environmental conditions Automatic and manual position and heading control under specified maximum environmental conditions Automatic and manual position and heading control under specified maximum environmental conditions, during and following any single fault excluding loss of a compartment (two independent computer systems) Automatic and manual position and heading control under specified maximum environmental conditions, during and following any single fault including loss of a compartment due to fire or flood. (At least two independent computer systems with a separate backup system separated by A60 class division)

IMO DP Class

Corresponding class notations ABS DPS0

LRS DP (CM)

Class1

DPS1

DP (AM)

Class2

DPS2

DP (AA)

Class3

DPS3

DP (AAA)

DNV DPS0 DYNPOSATUS DPS 1 DYNPOSAUT DPS 2 DYNPOSAUTR

DPS 3 DYNPOSAUTRO

GL

NK

BV

DP1

DPS A

DYNAPOS AM/AT

DP2

DPS B

DYNAPOS AM/AT R

DP3

DPS C

DYNAPOS AM/AT RS

Environmental Disturbances +

Desired Position Controller

Thrusters

+

Vehicle

Navigation System ROV Dynamic Positioning, Fig. 2 Block diagram of ROV DP system

The desired position is derived from guidance software. Guidance software includes set-point regulation, trajectory tracking, and path following modules to accomplish different operations. Guidance software continuously computes the desired position according to predefined track or path. Guidance software can also take inputs from joysticks directly. The ROV DP system comparing with ship DP system is listed in Table 2. Scientific Problems to be Solved It’s hard to obtain a precise mathematical model of ROVs. The traditional way of modeling an ROV

is by computational fluid dynamics (CFD) and scaled model test. The mathematical model is just approximation in typical working condition. Environmental disturbances are hard to be measured. There exists error in the estimation of environmental forces by observer. The error can be even more significant without a precise model of ROV. Besides, the forces from umbilical cable grow with water depth as a result of increasing cable length. Proper ways to measure or estimate disturbances need to be found. ROV DP system needs to keep the station in both horizontal and vertical plane simultaneously, increasing complexity of the system. Robust

ROV Dynamic Positioning

1515

controller with good performance in hazardous underwater environment remains in laboratory. Performance of controller is affected by model accuracy, sensor configuration, and sea condition in practical application.

Application Researchers from the Norwegian University of Science and Technology presented a dynamic positioning system for a small size ROV called Minerva in 2011 (Dukan et al. 2011), as shown in Fig. 3. Minerva is equipped with two horizontal

thrusters, two vertical thrusters, and one lateral thruster, accomplishing six degrees of motion. Navigation sensors consist of fluxgate compass, CRS03 silicon rate sensor, Teledyne RDI Workhorse Doppler velocity log (DVL), Kongsberg MRU6, and Kongsberg HiPAP500. The National Instruments (NI) CompactRIO (cRIO) programmed with LabVIEW is used for the implementation and development of the DP controller. Kalman filter (KF) and extended Kalman filter (EKF) are used as observer. The DP system of Minerva consists of signal processing, observer, controller, guidance system, and thrust allocation modules as seen in Fig. 4.

ROV Dynamic Positioning, Table 2 Comparison with dynamic positioning of ships Control parameter

Environmental disturbance

Navigation sensor

Propulsion

ROV Dynamic Positioning, Fig. 3 Minerva ROV (Dukan et al. 2011)

ROV DP Horizontal position Vertical position Heading Ocean current

DVL USBL IMU Digital compass Pressure sensor Thrusters

Ships DP Horizontal position Heading Wind Wave Ocean current DGPS Gyrocompasses Environmental sensor

Main propellers Tunnel thrusters Azimuth thrusters

R

1516

ROV Dynamic Positioning

Commanded thrust

Measurements

Signal Processing

Processed measurement signals Commanded thrust

Observer

Thrust allocation

Controller Observed states

Control force vector Desired states

Guldance & GUI

Operation mode/ task

User ROV Dynamic Positioning, Fig. 4 DP system of Minerva (Dukan et al. 2011)

ROV Dynamic Positioning

1517 The ROV in the horizontal plane measured estimated

12.5 12.4 12.3

North Position [m]

12.2 12.1 12 11.9 11.8 11.7 11.6 11.5 19.4

19.6

19.8

20.2 20 East Position [m]

20.4

20.6

ROV Dynamic Positioning, Fig. 5 Station keeping test of Minerva ROV DP system (Dukan et al. 2011)

ROV Dynamic Positioning, Fig. 6 Trajectory tracking test of Minerva ROV DP system (Dukan et al. 2011)

The ROV in the horizontal plane 12

measured estimated

10

R

North Position [m]

8 6 4 2 0 –2 –4 0

2

4

6

12 8 10 East Position [m]

14

16

18

20

1518

The signal processing module gathers signals from all sensors and checks validation of each signal data frame. Valid signals are passed to the observer module. Invalid signals are discarded and an abortion message is sent to observer module. The observer takes inputs from signal processing module and thrust allocation module. The outputs are estimated states of ROV. The controller module computes control force vector based on error between the desired states and estimated states. The thrust allocation module transforms control force vector to rotation speed of each thruster. The guidance module generates desired states for station keeping, trajectory tracking or path following. Experimental results proved the validity and performance of the DP system. Result of the ROV DP system in station keeping test is shown in Fig. 5. The maximum measured deviation from desired position was 2 cm in North and 3 cm in East direction. The estimated deviation was within 2 cm in both North and East directions. The results of trajectory tracking test are shown in Fig. 6. Maximum estimated cross-track error is 9 cm and measured is 20 cm.

Cross-References ▶ Dynamic Positioning in Ice ▶ Integrated Navigation ▶ Remotely Operated Vehicle

ROV Dynamic Positioning

References Dukan F, Ludvigsen M, Sorensen AJ (2011) Dynamic positioning system for a small size ROV with experimental results. OCEANS, 2011 IEEE – Spain. IEEE Fay H (1989) Dynamic positioning systems, principles, design and applications. Editions Technip, Paris. ISBN:2-7108-0580-4 Fossen TI (2002) Marine control systems: guidance, navigation and control of ships, rigs and underwater vehicles. Dynamic Positioning. Retrieved January, 23, 2019 from https://en.wikipedia.org/wiki/Dynamic_ positioning Fossen TI, Johansen TA (2006) A survey of control allocation methods for ships and underwater vehicles. Intech. IEEE 2006 14th Mediterranean Conference on Control and Automation - Ancona, Italy IMO MSC/Circ.645, Guidelines for vessels with dynamic positioning systems (PDF). 6 June 1994 Ni L, Fuller CR (2003) Control reconfiguration based on hierarchical fault detection and identification for unmanned underwater vehicles. J Vib Control 9(7): 735–748 Omerdic E, Roberts G (2004) Thruster fault diagnosis and accommodation for open-frame underwater vehicles. Control Eng Pract 12(12):1575–1598 Sørensen AJ (2011) A survey of dynamic positioning control systems. Annu Rev Control 35(1):123–136 Steinbeck J (2017) History of DP. Retrieved January, 23, 2019 from https://dynamic-positioning.com/ history-of-dp/ Yang KC, Yuh J, Choi SK (1998) Experimental study of fault-tolerant system design for underwater robots. IEEE International Conference on Robotics & Automation

S

Safety of Offshore Platforms Shuqing Wang and Junrong Wang College of Engineering, Ocean University of China, Qingdao, China

Definition The safety culture in the ocean engineering covers the safety of personnel, platform, and environment, and it is referred to the control of recognized hazards in order to achieve an acceptable level of risk.

Scientific Fundamentals Introduction In ocean engineering, the offshore engineering oil and gas industry is usually regarded as a high-risk sector, where the workers face not only process hazards associated with exploration, storage, and processing of hydrocarbons on the platforms but also other forms of hazards related to the harsh working environment and transportation (BroniBediako and Amorin 2010; Tang et al. 2017). It is generally agreed that the safety of offshore engineering can be grouped into two main categories, namely, personal safety and process safety (Swuste et al. 2016; Tang et al. 2018). The personal safety emphasizes the health and safety of individual employees via minimization © Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

of their exposure to radiations, chemical, noise, extreme vibration, abnormal temperatures, and mechanical, electrical, and ergonomic hazard with the measures such as industrial hygiene monitoring, chemical health risk assessment, medical surveillance, safety awareness program, and the work arrangement to reduce the fatigue of employee (International Labour Organization 2001; Mearns et al. 2003; Mearns and Hope 2005; Venkataraman 2008). The process safety primarily concerns the hazards of offshore engineering related to the spills, fires, explosions, instability, capsizing, and destruction, which cause not only injuries and fatalities but property and environmental damage (Knegtering and Pasman 2009; Swuste et al. 2016). In many instances, the term process safety is usually interchangeable with asset integrity, where the asset integrity management usually covers the entire life cycle of an asset from design to decommissioning and includes management of processes, resources, people, and system (Hassan and Khan 2012). The consequences of the process safety are usually potentially involving multiple injuries and fatalities, and they are more severe than those of the personal safety (Knegtering and Pasman 2009). Typical Safety Issues in Offshore Engineering Safety can be regarded as the absence of accidents or failures. The insight about safety features can be gained from detailed information of accidents

1520

and failures. In the following, several typical catastrophic accidents in offshore engineering, which caused not only major economic and life losses but also serious environmental damage, are provided. Structural Failure Due to the Extreme Environmental Loadings

Although the extreme environment condition occurs quite rarely during the life of offshore structure, the environmental loadings accompanied with this environment condition may exceed the design loading of offshore structure, and this may lead the structure into failure. As one of the extreme environment conditions, the hurricane with high storm surge and waves, heavy rains, and strong winds may have significant influence on the offshore structure. The Hurricane Katrina entered the GOM on August 26, 2005. Prior to hurricane landfall, more than 700 platforms and rigs were evacuated making more than 90% of the oil and 83% of gas production in GOM offline (Feltus 2005). Statistical results have shown that the Hurricane Katrina completely destroyed 44 platforms and severely damaged 21 others (MMS 2006), including some large production facilities. The number of destroyed and severely damaged offshore platforms with different water depth is listed in Tables 1 and 2, respectively (Cruz and Krausmann 2008). In addition, the drilling rigs were also affected. The hurricane destroyed four drilling rigs and severely damaged nine others, and six drilling rigs, including semisubmersible and jack-up units, were set adrift (Ghonheim and Colby 2005; Tubb 2005). In one case, a drilling rig (ENSCO 7500) was moved 193 km south of Louisiana, and Diamond’s Ocean Warwick (75 m jack-up) was carried 106 km by the storm and washed up in Dauphin Island, Alabama. Furthermore, about 100 pipelines were damaged, and 36 of them were 0.254 m diameter or larger, and there were 211 minor pollution incidents of 500 barrels of oil or less in the outer continental shelf due to Katrina (MMS 2006). In the same year, the Hurricane Rita entered the GOM on September 25, and it destroyed

Safety of Offshore Platforms Safety of Offshore Platforms, Table 1 Number of platforms destroyed by hurricanes Katrina and Rita

Water depth (m) d < 30 30 < d < 60 60 < d < 120

Hurricane Katrina Number of destroyed 16 14 14

Hurricane Rita Number of destroyed 30 27 11

Safety of Offshore Platforms, Table 2 Number of platforms damaged by hurricanes Katrina and Rita

Water depth (m) d < 60 60 < d < 120 120 < d < 240 300 < d < 1000

Hurricane Katrina Number of destroyed 6 6 5 4

Hurricane Rita Number of destroyed 7 18 5 2

69 platforms and 1 rig. There were 32 platforms severely damaged, and 13 rigs were set adrift by the Hurricane Rita (Djamarani 2005; MMS 2006). As was the case during Hurricane Katrina, the pipelines were also affected by Rita. The MMS reported that there were about 83 pipelines damaged, and 28 of them were 0.254 m diameter or larger, and 207 minor pollution incidents of 500 barrels of oil or less in the outer continental shelf due to Hurricane Rita (MMS 2006). More than 2000 people lost their life in hurricanes Katrina and Rita. The direct economic losses were about $70–130 billion, and the reconstruction costs were expected to reach about $200 billion. Following the hurricanes, changes have been proposed to operating and emergency procedures, maintenance requirements, and design practices including mooring practices for mobile offshore drilling units (Cruz and Krausmann 2008). Structural Capsizing Due to Fatigue Failure

The offshore structures are exposed to multiple sea states during their service life, which may cause seriously accumulative fatigue damage

Safety of Offshore Platforms

1521

Safety of Offshore Platforms, Fig. 1 Alexander L. Kielland platform capsized in 1980 due to the fatigue crack (Norwegian Petroleum Museum)

and lead the offshore structures to fatigue failure even if the stresses in the critical regions are smaller than the elastic limit (Jia 2008; Song and Wang 2019). The fatigue damage becomes a major cause of damages that occurred on the offshore structures. As illustrated in Fig. 1a, the Alexander L. Kielland platform capsized while working in the Ekofisk oil field in March 27, 1980, and there were about 123 crews killed, making the capsize the worst disaster in Norwegian waters since World War II (Bunn 2018). The accident started with one of the bracings (D-6) failing due to fatigue, thereby causing a succession of failures of all bracings attached to this leg (see Fig. 1b). It was discovered during the investigation that the weld of an instrument connection on the bracing

had contained cracks, which had probably been in existence since rig was built. The cracks had developed over time, and the remaining steel was less than 50%, and the strength of the bracing did not meet the serviceability requirement of the platform. When the leg came loose, the rig almost immediately developed a severe listing. Within 20 min of the initial failure, it capsized completely, floating upside down with just the bottom of the columns visible in the sea (see Fig. 1c). Both the escape and evacuation operations were far away from orderly and had only limited success. Only one lifeboat was in fact launched successfully, one was totally unavailable due to the listing, and others were smashed against the platform during launching in high waves.

S

1522

Safety of Offshore Platforms

Safety of Offshore Platforms, Fig. 2 Platforms destroyed by explosions and fires. (a) Piper Alpha platform accident in 1988, (b) P-36 semisubmersible platform accident in 2001 (Moan 2005)

Structural Destruction Due to Explosion and Fire

Due to the operational errors or technical faults, the oil and gas leaked from the equipment may be ignited, and the offshore structure can be destroyed by the explosions and fires (Moan 2005). The Piper Alpha platform got explosions and fires in July 6, 1988, and it was one of the costliest man-made catastrophes ever occurred either onshore or offshore (Ian 2012). The explosions and fires were initiated by a gas leak from the blind flange of a condensation pump that was under maintenance but not adequately shut down (PA 1990). As presented in Fig. 2a, the Piper Alpha platform was completely destroyed by the explosions and fires. The accidents resulted in the loss of 167 crew members, including 2 crewmen of a rescue vessel, and the economic loss of about $ 3.4 billion. The investigative report pointed out that the main issue that caused the initiation of this accident was the lack of communication between the maintenance team and the control room operations. The Petrobras 36 (P-36), the largest floating semisubmersible platform in the world in that time, experienced two explosions in March 15, 2001. The accident was initiated by the rupture of the emergency drain tank in the starboard aft column due to excessive pressure, and the rupture caused damage to various equipment and installations, leading to the flooding of water, oil, and gas into the column. After 17 min, the dispersed gas caused explosion and fire. At the time there are 175 people on the

platform and 11 were killed. The platform sank 5 days after the explosion with an estimated 1700 t of crude oil remaining on board (Videiro et al. 2002). A series of operational errors were identified as the main cause of the first explosion and also the sinking. Environmental Damage Resulted from Oil Spill

The oil spills accompanied with offshore engineering accidents have significant influence on the environment and ecosystem. In April 20, 2010, the Deepwater Horizon platform, which drilled the deepest oil well in history at a vertical depth of 10,683 m (see Fig. 3a), exploded and caught fire due to ignition of the high-pressure methane gas from the well (Schwartz and Weber 2010). There were 126 crew members on board when the platform caught fire, and 11 missing workers were believed to be dead from the explosion (see Fig. 3b). The oil flowed for 87 days, and the total estimated volume of leaked oil approximated 4.9 million barrels with plus or minus 10% uncertainty, making it the world’s largest accidental spill (Hoch 2010). According to the satellite images, the spill directly affected 68,000 square miles of the ocean (see Fig. 3c) and had affected 8332 species, including more than 1270 fish, 604 polychaetes, 218 birds, 1456 mollusks, 1503 crustaceans, 4 sea turtles, and 29 marine mammals (Biello 2010; Norse and Amos 2013). Research found that the toxins from oil spills can cause irregular heartbeats leading to cardiac arrest and the tuna and amberjack that were

Safety of Offshore Platforms

1523

Safety of Offshore Platforms, Fig. 3 Deepwater Horizon oil spill (https://en.wikipedia.org)

exposed to oil from the spill developed deformities of the heart and other organs that would be expected to be fatal or at least life-shortening (Kerr 2010). In addition, the spill had a strong economic impact to BP and also the Gulf Coast’s economy sectors such as offshore drilling, fishing, and tourism. Estimates of lost tourism dollars were projected to cost the Gulf coastal economy up to 22.7 billion through 2017. The GOM commercial fishing industry was estimated to have lost $ 247 million as a result of post-spill fisheries closures (Sumaila et al. 2012). BP may be required to pay as high as $ 90 billion.

Key Applications Safety Design Design Criteria

Safety design is referred as the design that effectively minimizes the likelihood of accidents/

damages and mitigates their consequences, which has long been a priority in the offshore engineering industries. As uncertainties in the structural resistance and the environmental loads to the structures for all kinds of reasons, the design approaches can be grouped into two main categories, namely the deterministic design approach and the probability design approach. Deterministic Design Method

The deterministic design method, which is also known as working stress design (WSD) method, assumes that all kinds of environmental loadings are combined, and it may fit a certain probability distribution, and the resistance of structure is deterministic. In the design process, the stress of the structure under different environmental loadings should be less than the allowable stress, and a global safety factor is used to quantifying uncertainties of environmental load and structural capacity.

S

1524

The deterministic design method is mainly considered as applicable to special case design problems, to calibrate the usage factors to be used in the WSD method and for conditions where limited experience exists. The detail of the deterministic design method can be found in API RP 2A (2000) for fixed platform and DNV-OS-C201 (2015) for floating platform. Probabilistic Design Method

The probabilistic design method which is also known as load and resistance factor design (LRFD) method assumes that all kinds of environmental loads fit different probability distributions and the structural resistance/capacity is probabilistic and also obeys a certain distribution function as well. According to the probabilistic design method, the target safety level of the structure is obtained as closely as possible by applying load and resistance factors to characteristic reference values of the basic variables. The basic variables are defined as loads acting on the structure and the resistance of the structure or the resistance of materials in the structure. The target safety level is achieved by using deterministic factors representing the variation in load and resistance and the reduced probabilities that various loads will act simultaneously at their characteristic values. The details of the probabilistic design method can be found in DNV-OSC101 (2011). Safety Assessment and Management General

The offshore platforms are systems consisting of structures, equipment, and other hardware, as well as specified operational procedures and operational personnel. Ideally, the system should be designed and operated to comply with a certain acceptable risk level as specified. The safety assessment and management is the process to ensure that the risks of offshore platform are reduced to a level as low as reasonably practicable via hazard identification, risk assessment, and monitoring (Gupta and Edwards 2002). Typical elements of a safety assessment and management process consist of data collection and

Safety of Offshore Platforms

management, risk assessment, inspection and monitoring plan, and strengthening and mitigation measures (International Labour Organization 2001; Li et al. 2012). Data Collection and Management

The data of offshore structure is the foundation of safety assessment and management process, and it can be grouped into two main categories, namely, characteristic data and condition data. 1. Characteristic data: the data represents the structure’s characteristic in initial condition, and it relates to the structure design, fabrication, transportation, and installation process, including the design drawing, analysis results, fabrication planning, transportation and installation report, and other related files. 2. Condition data: the data represents the structure’s characteristics in operation condition, including the inspection data, monitoring data, maintenance and repair report, etc. 3. An effective data management system should be established to save, modify, and update the related data. Safety Assessment

The safety assessment of offshore platforms during operation is necessary in connection with a planned change of platform function; extension of service life; occurrence of overload damage due to hurricanes, explosion, fires, and ship impact; updating of inspection plans; etc. (Moan 2005). The safety assessment should be based on updated data of offshore structure, and the corresponding results can be represented by the safety indicators, which can measure the safety performance of the offshore structure and provide input for the planning of inspection, monitoring, maintenance, and repairs. The procedure of safety assessment is illustrated in Fig. 4. Inspection and Monitoring Planning

Inspection and monitoring are important measures for maintaining safety, especially with respect to fatigue, corrosion, and other deterioration phenomena. The inspection and monitoring data of a

Safety of Offshore Platforms

1525

Safety of Offshore Platforms, Fig. 4 The procedures of the safety assessment (Li et al. 2012)

given structure is actively incorporated in the planning of future activities (Moan 2005). The inspection planning is usually formulated based on the results of safety assessment, which is the overall and strategic arrangement of platform inspection, including the inspection intervals and scope. Typically, the major inspections of offshore structures are carried every 4–5 years, while intermediate and annual inspections are normally less extensive. The optimal inspection interval can be determined with the probabilistic methods. The following items should be included in the inspection planning: 1. Prioritizing which locations are to be inspected. 2. Selection inspection method (visual inspection, magnet particle inspection, eddy current) depending on the damage of concern. 3. Scheduling inspections.

4. Establishing a repair strategy (size of damage to be repaired, repair method, and time aspects of repair). Strengthening and Mitigation Measures

If the safety of offshore structure did not meet the serviceability and safety requirements, some strengthening and mitigation measures should be carried out to strengthen and mitigate the structure. The permanent repairs are made by cutting out component and welding a new component, rewelding, and adding or removing scantlings, brackets, stiffeners, lugs, or collar plates. However, the strengthening and mitigation measures are usually very expensive. The most relevant measure to alleviate the intensity of repair could be achieved by varying the inspection interval or improving the inspection technology. Many approaches regarding the repair cost as a criterion in reliability-based inspection, monitoring, maintenance, and repair planning have been developed

S

1526

(Garbatov and Guedes Soares 2001; Moan 2005; Dong and Frangopol 2015). It should be mentioned that the risk can never be absence, and the implementation of the safety assessment and management never ends, and it should be carried out through the life cycle of offshore structure.

Conclusions The offshore engineering oil and gas industry has large investment and long-period and high-risk features, and the failure of the offshore facilities usually resulted in the loss of economy and life and subsequent pollution of the environment. Safety is a very important characteristic of the offshore engineering oil and gas industry, and it can be ensured by improving the design method and reducing the human and organizational errors and omissions. The safety assessment and management process is a scientific management strategy to identify, measure, and analyze risk and, on this basis to deal effectively with risk, to achieve maximum security at minimum cost. In the future, the safety assessment and management process can be established with multiple data sources and advanced methods to account for complex interactions between the natural environment, the development of naval technology, and human behavior.

Cross-References ▶ Dynamic Behavior and Fatigue ▶ Reliability and Safety in Offshore Engineering

References API RP-2A (2000) Recommended practice for planning, designing and constructing fixed offshore platformsworking stress design. American Petroleum Institute, Washington, D.C. Biello D. The BP spill’s growing toll on the sea life of the gulf. Yale environment 360. Yale School of Forestry & Environmental Studies. Retrieved June 14, 2010

Safety of Offshore Platforms Broni-Bediako E, Amorin R (2010) Effects of drilling fluid exposure to oil and gas workers presented with major areas of exposure and exposure indicators. Res J Appl Sci Eng Technol 2(8):710–719 Bunn (2018) Alexander L Kielland platform capsize accident. Loss Prev Bull 261:12–13 Cruz AM, Krausmann E (2008) Damage to offshore oil and gas facilities following hurricanes Katrina and Rita: an review. J Loss Prev Process Ind 21:620–626 Djamarani M. The stakes are rising. Petroleum Review, December (2005) DNV-OS-C101 (2011) Design of offshore steel structures general (LRFD method), Det Norske Veritas DNV-OS-C201 (2015) Structural design of offshore units (WSD method). Det Norske Veritas Dong Y, Frangopol DM (2015) Risk informed life cycle optimum inspection and maintenance of ship structures considering corrosion and fatigue. Ocean Eng 201:161–171 Feltus A. Katrina takes a terrible toll. Petroleum Economist, October (2005) Garbatov Y, Guedes Soares C (2001) Cost and reliability based strategies for fatigue maintenance planning of floating structures. Reliab Eng Syst Saf 73:293–301 Ghonheim A, Colby C. GoM offshore structures design criteria. SNAME Texas section meeting, 13 December (2005) Gupta JP, Edwards DW (2002) Interently safer design: present and future. Chem Eng J 80(B):115–125 Hassan J, Khan F (2012) Risk-based asset integrity indicators. J Loss Prev Process Ind 25(3):544–554 Hoch M. New estimate puts Gulf oil leak at 205 million Gallons. PBS News Hour Mac Neil/Lehrer Productions, Retrieved 19 Dec 2010 Ian S (2012) Offshore safety management. Elsevier, Oxford International Labour Organization (2001) Guidelines on occupational safety and health management system. Geneva Jia J (2008) An efficient nonlinear dynamic approach for calculating wave induced fatigue damage of offshore structures and its industrial applications for lifetime extension. Appl Ocean Res 30:189–198 Kerr RA (2010) A lot of oil on the loose, not so much to be found. Science 329:734–735 Knegtering B, Pasman HJ (2009) Safety of the process industries in the 21st century: a changing need of process safety management for a changing industry. J Loss Prev Process Ind 22(2):162–168 Li HT, Xu J, Li Y, Ding GL (2012) Structural integrity management of mobile offshore platforms. In: Proceedings of the green ship and marine equipment innovation development and industrialization forum Mearns K, Hope L (2005) Health and well-being in the offshore environment the management of personal health. Health and Safety Executive Mearns K, Whitaker SM, Flin R (2003) Safety climate, safety management practice and safety performance in offshore environments. Saf Sci 41(8):641–680

Salinity Gradient Power Conversion MMS. MMS updates Hurricanes Katrina and Rita damage. Minerals Management Service, News release, 3486, 1 May (2006) Moan T. Safety of offshore structures. CORE report, no. 2005-04 Moan T (2005) Reliability based management of inspection, maintenance and repair of offshore structures. Struct Infrastruct Eng 1:33–62 Norse EA, Amos J (2013) Impacts, perception and policy implications of the BP/Deepwater Horizon oil and gas disaster. Environ Law Reporter 40(11): 11058–11073 PA (1990) The public inquiry in the pipe alpha disaster. Inquiry Commission HMSO, London Schwartz N, Weber HR. Bubble of methane triggered rig blast. Southern California Public Radio Associated Press. Retrieved 29 June 2010 Song XC, Wang SQ (2019) A novel spectral moments equivalence based lumping block method for efficient estimation of offshore structural fatigue damage. Int J Fatigue 118:162–175 Sumaila UR et al (2012) Impact of the Deepwater Horizon well blowout on the economics of U.S. Gulf fisheries. Can J Fish Aquat Sci 69(3):499–510 Swuste P, Theunissen J, Schmitz P, Reniers G, Blokland P (2016) Process safety indicators, a review of literature. J Loss Prev Process Ind 40:162–173 Tang DKH, Leiliabadi F, Olugu EU, Dawal SZM (2017) Factors affecting safety of process in the Malaysian oil and gas industry. Saf Sci 92:44–52 Tang DKH, Dawal SZM, Olugu EU (2018) Actual safety performance of the Malaysian offshore oil platforms: correlations between the leading and logging indicators. J Saf Res 66:9–19 Tubb R (2005) MMS director overview impact of hurricanes Katrina and Rita. Pipeline Gas J 232(11):69–71 Venkataraman N (2008) Safety performance factor. Int J Occup Saf Ergon 14(3):327–331 Videiro PM, Cyranka C, Nunes GC, Melo AP. The accident of the P-36 Platform: the rupture of the emergency drainage tank. In: ASME 2002 21st international conference on offshore mechanics and Arctic engineering, volume 2, Oslo, Norway, June 23–28 (2002)

Sagnac Interferometer (SI) ▶ Fiber Optic Hydrophone

1527

Salinity Gradient Power Conversion Zhen Gao Norwegian University of Science and Technology, Trondheim, Norway

Synonyms SGPC - salinity gradient power conversion; PRO pressure-retarded osmosis; RED - reverse electrodialysis; AEM - anion-exchange membrane; CEM - cation-exchange membrane

Definition Salinity gradient power is the power available from the difference in the salt concentration between sea water and river fresh water and it is often called osmotic power or blue energy. This form of power is available when two solutions with different salinity levels are mixed together. Salinity Gradient Power Conversion (SGPC) is a technology that uses the osmotic pressure, i.e., the chemical potential of concentrated and dilute solutions of salt, to drive a turbine to generate electricity.

Salinity Gradient Power Resource In order to utilize the salinity gradient power, a large amount of both sea water and fresh water are needed. River mouths, where fresh river water discharges to the sea, are naturally potential areas for SGPC development and are widely distributed around the world (Lewis et al. 2011). The estimated technical potential for SGPC is about 1650 TWh/year (Scråmestø et al. 2009).

Technology for Salinity Gradient Power Conversion

Salinity ▶ AUV/ROV/HOV Hydrostatics

Like ocean thermal energy, salinity gradient power is less developed than any other ocean

S

1528

energy. No commercial plant based on salinity gradient power and only a few pilot plants exist today. From the technology point of view, there are two types of SGPC, namely, Pressure-Retarded Osmosis (PRO) and Reverse Electrodialysis (RED), as shown in Fig. 1. In a PRO plant

Salinity Gradient Power Conversion

(Scråmestø et al. 2009), both fresh water and sea water are pumped in two different loops to a chamber where semi-permeable membranes are placed between them and permit only water molecules to pass through. Water flows from the dilute solution (fresh water) to the concentrated solution (sea water) to bring the chemical potentials on

Salinity Gradient Power Conversion, Fig. 1 Illustration of PRO (left, Scråmestø et al. 2009) and RED (right, van den Ende and Groeman 2007) for ocean salinity gradient conversion

Scouring

both sides of the membranes to an equilibrium, which will lead to high pressure on the sea water side and then drive a turbine to generate electricity. The osmotic pressure between sea water and fresh water is in the order of 2.4–2.6 MPa. The sea water is pressurized to about half of the osmotic pressure, before pumped into the chamber. As long as the pressure difference at the membranes between the two fluids is less than the osmotic pressure, the flows from fresh water to sea water continue. The remaining fresh water and the mixed fresh and sea water are then discharged to the river or the sea. The RED approach (van den Ende and Groeman 2007) is essentially to create a salt battery, using ion-exchange membranes, which either let negatively charged ions in anion-exchange membranes (AEM) or positively charged ions in cation-exchange membranes (CEM) pass through. These AEM and CEM membranes are alternately stacked with water-based solutions of different concentrations in between to build up a considerable electrical potential that can be used for electricity generation.

Development and Challenges for Salinity Gradient Power Conversion The concepts of PRO and RED have been proposed in 1970s. However, it is in 2009 that the first PRO power plant with a nominal power of 10 kW was built and started operation by the Norwegian company Statkraft. It uses about 2000 m^2 of membranes to eventually generate 5 kW of electric power (IRENA 2014). In 2014, the first RED plant with a nominal power of 50 kW was built at Afsluitdijk, the Netherlands, using the fresh water from Lake Ijssel and the sea water of the North Sea (Schaetzle and Buisman 2015). The developed prototypes of SGPC devices are very small, with a cost not competitive to other forms of ocean renewable energies. There exist many technical challenges for SGPC devices (Schaetzle and Buisman 2015). Both PRO and RED need a large amount of fresh and sea water, which should be pumped into specific chambers. This requires a large facility and increases the

1529

overall cost. Both PRO and RED plants use membranes, which are very sensitive to fouling, i.e., the accumulation of minerals or marine growth on the membranes and require very clean water. This is a challenge in real world. In the case of a RED plant, the ion composition of the real fresh and sea water is much more complex than that is assumed in the lab tests with simple NaCl solutions. This will make the efficiency of a RED plant lower.

Cross-References ▶ Economic Assessment ▶ Ocean Thermal Energy Conversion ▶ Power Take-Off System

References IRENA (2014) Ocean energy technology brief, 2 June 2014 Lewis A, Estefen S, Huckerby J, Musial W, Pontes T, Torres-Martinez J (2011) Ocean energy. In: Edenhofer O, Pichs-Madruga R, Sokona Y, Seyboth K, Matschoss P, Kadner S, Zwickel T, Eickemeier P, Hansen G, Schlomer S, von Stechow C (eds) IPCC special report on renewable energy sources and climate change mitigation. Cambridge University Press, Cambridge, UK/New York Schaetzle O, Buisman CJN (2015) Salinity gradient energy: current state and new trends. Engineering 1(2):164–166 Scråmestø OS, Skilhagen S-E, Nielsen WK (2009) Power production based on osmotic pressure. In: Waterpower XVI, Spokane, WA, USA, 27–30 July 2009 van den Ende K, Groeman F (2007) Blue energy. Leonardo Energy, KEMA Consulting, Arnhem. Available at: www.leonardo-energy.org/webfm_send/161

SCF (Single Column Floater) ▶ SPAR Platform

Scouring ▶ Iceberg Scouring

S

1530

SCR (Steel Catenary Riser)

SCR (Steel Catenary Riser)

SeaStar TLP

▶ SPAR Platform

▶ Tension-Leg platform

Screen-Force Model

Second Generation Intact Stability Criteria

▶ Aquaculture Structures: Numerical Methods Min Gu, Jiang Lu, Shuxia Bu, Jilong Chu, Ke Zeng and Tianhua Wang China Ship Scientific Research Center (CSSRC), Wuxi, China

Sea Environment ▶ Ship Operational Environment

Definition

Sea Ice Management ▶ Ice Management in Offshore Operations

Seabed ▶ Underwater Lander

Seafloor ▶ Underwater Lander

Seakeeping Experiment ▶ Aquaculture Techniques

Structures:

Experimental

Interim guidelines on the second generation intact stability criteria are approved by the International Maritime Organization (IMO) on 10 December 2020, and IMO Member States are invited to use the interim guidelines as complementary measures when applying the requirements of the mandatory criteria of part A of the International Code on Intact Stability, 2008 (resolution MSC.267(85)), and to bring them to the attention of all parties concerned, in particular shipbuilders, shipmasters, shipowners, ship operators, and shipping companies, and recount their experiences gained through the trial use of these interim guidelines to the organization. The second generation intact stability criteria include five stability failure modes as follows: dead ship condition, excessive acceleration, pure loss of stability, parametric rolling, and surf-riding/ broaching with Level 1, Level 2 vulnerability criteria, and direct stability assessment for each stability failure model. The main purpose of these criteria is to enable the use of the latest numerical simulation techniques for evaluating the safety level of a ship from an intact stability viewpoint (IMO, Msc.1/Circ.1627, 2020).

Historical Development

Seakeeping Tests ▶ Towing Tank Test

The IMO intact stability criteria (resolution A.749(18)) were developed based on the

Second Generation Intact Stability Criteria

experience with ships designed and built quite some years ago – in the 1930s, and the empirical criteria do not and cannot represent the physical properties of modern vessels and a set of performance-based criteria is proposed to be developed (Germany, IMO SLF 45/6/2, 2002). The intact stability code applies to all ships based on two different concepts: general criteria addressing the geometry of the calm water lever arm curve and the weather criterion consisting of a set of empirical formulae. The weather criterion is only based on beam wind and beam waves scenario, and the other stability failure models in quartering, following, and head seas cannot be included. Due to the restriction to the static calm water lever arm curve, dynamic problems endangering ships cannot be assessed. The scenariobased criteria including parametric rolling, pure loss of stability, and excessive acceleration in case of resonance are proposed to be developed (Germany, IMO SLF 46/6/6, 2003). A long-term approach should cover dynamic criteria (Germany, IMO SLF 46/6, 2003). The development of dynamic stability criteria may have the following structure: criteria to avoid large rolling angles (minimum stability requirement), criteria to avoid large acceleration (maximum stability limit), criteria to guarantee sufficient roll damping in dead ship condition (minimum damping requirement), and criteria to avoid broaching (minimum course keeping limit) (Germany, IMO SLF 47/6/4, 2004). The working group on the review of the intact stability code agreed that for three identified phenomena, i.e., pure loss and parametric excitation, behavior in dead ship condition and maneuveringrelated problems (e.g., broaching-to), and necessary preliminary precautionary provisions should be in the code (as new paragraph 1.2 of part A of the draft revised Code) (Germany, SLF 48/4/7, 2005; SLF 48/WP.2, 2005). In order to back up the long-term work tasks, Germany further gave out a proposal of probabilistic intact stability criterion (Germany, SLF 49/5/2, 2006), and Japan gave out proposals on the methodology of direct assessment for stability under dead ship condition and capsizing due to broaching (Japan, SLF 49/5/5, 49/5/6, 2006).

1531

Japan, the Netherland, and the USA believe that the motivation for the development of performance-based criteria for intact stability is derived from the appearance of new types of vessels. These vessels may have unconventional hull particulars or geometry or modes of operation for which there is insufficient operational experience. Performance-based criteria should be applicable to unconventional vessels while the existing intact stability code still be applicable to “conventional” vessels. The performance-based criteria also could be used as an alternative procedure for “conventional” vessels. A framework for the development of new generation criteria for intact stability is proposed by Japan, the Netherland, and the USA, and parametric rolling, pure loss of stability, stability under dead ship condition, and broaching-to are considered (SLF 50/4/4, 2007). The new generation intact stability criteria will be applicable to unconventional types of ships, assessed by vulnerability criteria (Germany, SLF 51/4/1, 2008). Japan gave out a proposal of new generation intact stability criteria as an example (Japan, SLF 51/4/3, 2008). The working group agreed to the framework for the new generation intact stability criteria and the draft terminology for the new generation intact stability criteria (SLF 51/WP.2, 2008). In considering the best way forward on the necessary work for the new generation intact stability criteria, the working group, based on the report of the correspondence group (SLF 52/3/1, 2009 and SLF 52/INF.2, 2009), taking into account the relevant documents submitted to this session, developed a summary of methodology considered for the stability failure modes. The framework of the new generation stability criteria is confirmed including Level 1, Level 2 vulnerability criteria, direct stability assessment, and operational guidance for stability failure models, and the stability failure modes include pure loss of stability, parametric rolling, surf-riding/ broaching, and dead ship condition (SLF 52/WP.1, 2010). The name of “the new generation intact stability criteria” is changed as “the second generation intact stability criteria” in the conference SLF 53, and the structure of the second generation

S

1532

intact stability criteria is updated with five stability failure models such as pure loss of stability, parametric roll, surf-riding/broaching, dead ship condition, and excessive acceleration, and each failure model has multiple levels including Level 1, Level 2 vulnerability criteria, direct stability assessment, and operational guidance (SLF 53/WP.4, 2011). Following an in-depth discussion, the working group prepared an updated version of the draft vulnerability criteria of Level 1 and 2 for pure loss of stability, parametric roll, dead ship, and surf-riding/broaching (SLF 54/WP.3, 2012). The working group prepared a revised plan, identifying the priorities, time frames, and objectives for the work to be accomplished. The working group agreed on the draft vulnerability criteria of Levels 1 and 2 for the failure mode parametric roll, and agreed to the selection of a wave environment for the first and second level vulnerability criteria for parametric rolling. The working group discussed the direct assessment methodologies considering their importance for ships which fail vulnerability levels 1 and 2 and to develop operational guidance when necessary (SLF 55/WP.3, 2013). Subcommittee of ship design and construction (SDC) is established including the working of subcommittee on stability and load lines and on fishing vessels safety. The working group reviewed the second generation intact stability criteria on the base of the correspondence group and prepared a revised plan, identifying the priorities, time frames, and objectives for the work to be accomplished (SDC 1/WP.5, 2014). The working group finalized the draft amendment to the 2008 Intact Stability Code regarding vulnerability criteria and the standards of levels 1 and 2, and further developed the direct stability assessment procedures (level 3) for the five stability failure models. The working group was the view that each criterion should have a single option. On the other hand, the working group was also of the view that the calculation of some parameters may include different options (SDC 2/WP.4, 2015). For the finalization of the second generation intact stability criteria, the working group further

Second Generation Intact Stability Criteria

considered the draft criteria in levels 1 and 2 for the five stability failure modes, further developed the draft explanatory notes for all five failure modes, and further developed the draft guidelines of direct stability assessment procedures and operational limitation/guidance (SDC 3/WP.5, 2016). The working group further considered the draft criteria in levels 1 and 2 for the five stability failure modes, further developed the draft guideline for the specification of direct stability assessment with a view to preparing draft interim guidelines, further developed the draft explanatory notes for all five failure modes with a view completing the draft interim explanatory notes, and further developed the draft guidelines for the preparation and approval of operation limitation and operational guidance with a view to preparing draft interim guidelines (SDC 4/WP.4, 2017). A provisional work plan was drafted with a view to ensuring the finalization of the second generation of intact stability criteria (SDC 5/J.6, 2018). With a view to presenting outcomes ready for finalization, continued progress made by the experts’ group on intact stability including the draft interim guidelines on the specification of direct stability assessment procedures, the draft interim guidelines for the preparation of operational limitation and operational guidance, and the draft interim guidelines on vulnerability criteria for the second generation of intact stability criteria (SDC 6/WP.6, 2019). The draft group on intact stability discussed the best possible method of work to finalize the draft interim guidelines on the second generation intact stability criteria and agree to elaborate on the matters pending in square brackets as a matter of priority, followed by a complete editorial review of the draft guidelines. The draft group agreed to remove all references to the draft explanatory note (SDC 7/WP.6, 2020). Interim guidelines on the second generation intact stability criteria is approved by the International Maritime Organization (IMO) on 10 December 2020 (IMO, Msc.1/Circ.1627, 2020). The explanatory note is under discussion by the correspondence group of the second

Second Generation Intact Stability Criteria

generation intact stability criteria and will be submitted to SDC 8 (Jan., 2022).

1533

progress to the application of operational measures or operational guidance, revising the design or discarding the loading condition (IMO, Msc.1/Circ.1627, 2020).

Application Logic Figure 1 shows the simplified scheme of the application structure of the second generation intact stability criteria. As the simplest options, the vulnerability criteria are presented in two levels: Level 1 and Level 2. The assessment of the five stability failure modes should begin with the use of these levels. Level 1 is an initial check and then, if the ship in a particular loading condition is assessed as not vulnerable for the tested failure mode, the assessment for that failure mode may conclude, otherwise the design would progress to Level 2. If the ship in a particular loading condition is assessed as not vulnerable for the tested failure mode in Level 2, then the assessment would conclude, otherwise the design would progress to the application of direct stability assessment, application of operational limitations, revising the design of the ship, or discarding the loading condition. If the ship in a particular loading condition is not found acceptable with respect to direct stability assessment procedures, then the logic is that the design would then

Vulnerability Criteria of Five Stability Failure Modes Parametric Rolling Parametric rolling is a dynamic stability phenomenon in which an amplification of roll motion is caused by periodic variation of transverse stability in waves. The vulnerability criteria of parametric rolling are shown as follows. Level 1 Vulnerability Criteria of Parametric Rolling

For each loading condition a ship is considered not to be vulnerable to the parametric rolling failure mode if dGM 1
RPR GM

and

VD  V  1:0 A W ðD  d Þ

ð1Þ

In which RPR ¼ 1.87 if the ship has a sharp bilge and otherwise:

S

Second Generation Intact Stability Criteria, Fig. 1 Simplified scheme of the application structure of the second generation intact stability criteria. (IMO, Msc.1/Circ.1627, 2020)

1534

Second Generation Intact Stability Criteria

8
 100Ak > > R ¼ 0:17 þ 0:425 , if Cm,full > 0:96; PR > > LB > <
 100Ak , if 0:94
Cm,full
0:96; RPR ¼ 0:17 þ ð10:625  Cm,full  9:775Þ > LB > >
 > > : RPR ¼ 0:17 þ 0:2125 100Ak , if Cm,full < 0:94; LB 100A 

should not exceed 4; δGM1 is amplitude of the variation of the metacentric height (m) calculated by Eq. (3), and SW ¼ 0.0167. k

LB

dGM 1 ¼

I TH  I TL 2V

ð3Þ

where ITH, ITL are transverse moment of inertia of the waterplane at the draft dH(m) and transverse moment of inertia of the waterplane at the draft dL(m). d H ¼ d þ ddH d L ¼ d  ddL
 L  SW dd H ¼ Min D  d, 2
 L  SW dd L ¼ Min d  0:25dfull , 2

Level 2 Vulnerability Criteria of Parametric Rolling

For each condition of loading a ship is considered not to be vulnerable to parametric rolling if C1
RPR1 ¼ 0:06 or C2
RPR1 ¼ 0:025

ð5Þ

The value for C1 is calculated as a weighted average from a set of waves specified in (IMO, Msc.1/Circ.1627,2020). C1 ¼

N X

W i Ci

ð6Þ

i¼1

ð4Þ

In which Wi is weighting factor according to the wave data specified in (IMO, Msc.1/ Circ.1627,2020). If the Eq. (7) is satisfied, Ci ¼ 0, otherwise Ci ¼ 1.

  dGM ðH i , li Þ GM ðH i , li Þ > 0 and < RPR GM ðH i , li Þ ! rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffiffiffiffiffiffi GM ðH i , li Þ li 2pi or when GM ðH i , li Þ > 0, V PRi ¼  g > Vs  GM 2p Tr

The value for C2 is calculated as a weighted average from a set of waves conditions specified in (IMO, Msc.1/Circ.1627,2020) C2 ¼ " # 12 12 X   X 1 C2ðFni , bh Þ þ ðC2ð0, bh Þ þC2 0, b f þ C2ðFni , b f Þ =25 2 i¼1 i¼1

ð8Þ C2(Fni, β) can be calculated by Eq. (9).

ð2Þ

C2ðFni , bÞ ¼

N X

W i CS,i

ð7Þ

ð9Þ

i¼1

In which Wi is weighting factor for respective wave cases specified in (IMO, Msc.1/ Circ.1627,2020). Also, N is total number of wave cases for which the maximum roll angle is evaluated for a combination of speed and ship heading; Ci is 1 if the maximum roll angle in head and following waves according to one degree of rolling motion exceed 25 and 0 otherwise.

Second Generation Intact Stability Criteria

1535

Pure Loss of Stability The provisions given hereunder apply to all ships, except for ships with an extended low weather deck, for which the Froude number, Fn, corresponding to the service speed exceeds 0.24. Level 1 Vulnerability Criteria of Parametric Rolling

For each loading condition a ship is considered not to be vulnerable to the pure loss of stability failure mode if GM min  RPLA

and

VD  V  1:0 ð10Þ AW ð D  d Þ

where RPLA ¼ 0.05; GMmi is minimum value of the metacentric height (m) calculated as provided in Eq. (11); SW ¼ 0.0334. GM min ¼ KB þ

I TL  KG ∇

L  SW 2



W i C1i ;

i¼1

CR2 ¼

N X

ð14Þ W i C2i ;

i¼1

In which Wi is weighting factor for respective wave cases specified in (IMO, Msc.1/ Circ.1627,2020). Also, C1i and C2i are calculated as follows: ( 1 ’V < K PL1 ¼ 300 C1i ¼ 0 otherwise 8 ’sw > K PL2 > > > > > < 1 K PL2 ¼ 150 for passenger ships C2i ¼ > > > K PL2 ¼ 250 for other ships > > : 0 otherwise ð15Þ In which ’v and ’sw are angle of vanishing stability and angle of heel under action of heeling lever lPL2 ¼ 8(Hi/l)dFN2 specified in (IMO, Msc.1/Circ.1627,2020).

ð12Þ

KB: height of ship buoyance; KG: height of ship gravity; ∇: displacement (m^3).

Level 2 Vulnerability Criteria of Parametric Rolling

For each condition of loading a ship is considered not to be vulnerable to pure loss of stability if max ðCR1 , CR2 Þ
RPL0 ¼ 0:06

N X

ð11Þ

ITL are transverse moment of inertia of the waterplane at the draft dL(m). d L ¼ d  ddL
dd L ¼ Min d  0:25dfull ,

CR1 ¼

ð13Þ

Each of the two criteria, CR1 and CR2 in 2.4.3.1, represents a weighted average of certain stability parameters for a ship considered to be statically positioned in waves of defined height, Hi, and length, li, obtained according to (IMO, Msc.1/Circ.1627,2020). CR1 and CR2 are calculated as follows:

Surf-Riding/Broaching Broaching is a violent uncontrollable turn that occurs despite maximum steering efforts to maintain course. As with any other sharp turn event, broaching is accompanied with a large heel angle, which has the potential effect of a partial or total stability failure. Broaching is usually preceded by surf-riding which occurs when a wave, approaching from the stern, captures a ship and accelerates the ship to the speed of the wave. Surfriding is a single wave event in which the wave profile does not vary relative to the ship. Because most ships are directionally unstable in the surfriding condition, this maneuvering yaw instability leads to an uncontrollable turn – termed “broaching” (SDC 3/WP.5/Annex 5, 2016). Broaching is considered as one of the most dangerous phenomena in following and sternquartering waves for high-speed ships, such as destroyers and fishing vessels.

S

1536

Second Generation Intact Stability Criteria

(

Level 1 Vulnerability Criteria of Surf-Riding/ Broaching

C2ij ¼

For each loading condition a ship is considered not to be vulnerable to the surf-riding/broaching failure mode if L  200 m

or

Fn
0:3

ð16Þ

In which Fn is Froude number corresponding to ship service speed; L is ship length. Level 2 Vulnerability Criteria of Surf-Riding/ Broaching

C¼

W2ðHS , T Z Þ

HS T Z

Nl X Na X i¼0

! wij C2ij

j¼0

< RSR ¼ 0:005 ð17Þ Where W2(HS, TZ) is weighting factor of shortterm sea state as a function of significant wave height HS and zero crossing wave period TZ. Also wij is statistical weight of a wave with steepness (H/l)i and wave length to ship length ratio (l/L)i calculated with the joint distribution of local wave steepness and lengths. Finally, C2ij is a coefficient depends on ship propulsion and resistance characteristics as follows: In which Nl ¼ 80, Na ¼ 100.  pffiffiffiffiffiffiffiffiffiffiffiffi  pffiffiffi 5=2 g L T 01 2 3=2 1 þ n2 pffiffiffiffiffiffiffiffiffiffiffiffi DrDs wij ¼ 4 s r pn ðH s Þ3 j i 1 þ 1 þ n2 8 2 0 sffiffiffiffiffiffiffiffiffiffiffi12 93  2 < L  r  s gT 201 A =5 1 i j  exp 42 1 þ 2 @1  Hs 2pr i L ; : n

ð18Þ In which, n ¼ 0.425; T01 ¼ 1.086TZ; sj ¼ (H/ l)j, varying from 0.03 to 0.15 with increment Δs ¼ 0.0012; ri ¼ (l/L)i, varying from 1.0 to 3.0 with increment Δr ¼ 0.025. The value of C2ij is calculated for each wave, as follows:

if if

  Fn > Fncr r i , s j   Fn
Fncr r i , s j

ð19Þ

pffiffiffiffiffiffi Fncr ¼ ucr = Lg is critical Froude number corresponding to the threshold of surf-riding (surf-riding occurring under any initial condition) which should be calculated for the regular wave with steepness sj and wavelength to ship length ratio ri. The critical nominal ship speed, ucr, is determined by solving the following equation with the critical propulsor revolutions, ncr:

For each loading condition a ship is considered not to be vulnerable to the surf-riding/broaching failure mode if XX

1 0

T e ðucr ; ncr Þ  Rðucr Þ ¼ 0

ð20Þ

The critical propulsor revolutions, ncr, is determined by solving the following equation in (IMO, Msc.1/Circ.1627,2020) 2p

T e ðci ; ncr Þ  Rðci Þ þ 8a0 ncr þ 8a1 f ij

 4pa2 þ

64 1024 a  12pa4 þ a 3 3 15 5

¼0

ð21Þ

Dead Ship Condition Level 1 Vulnerability Criteria of Dead Ship Condition

For each loading condition a ship is considered not to be vulnerable to the dead ship condition failure mode if ba

ð22Þ

In which, a and b are calculated according to 2008 IS Code Part A–2.3, and MSC.1/Circ.1200 Table 4.5.1. Level 2 Vulnerability Criteria of Dead Ship Condition

For each loading condition a ship is considered not to be vulnerable to the dead ship condition failure mode if

Second Generation Intact Stability Criteria

C¼

N X

1537

W i ðH S , T Z Þ  CS,i ðH S , T Z Þ

i¼1


RDS0 ¼ 0:06

ð23Þ

In which, Wi is weighting factor of shortterm sea state as a function of significant wave height HS and zero crossing wave period TZ. CS,i ¼ 1 , :1 ,

CS, i is short-term dead ship stability failure index for the short-termenvironmental condition under consideration, calculated as specified in (IMO, Msc.1/Circ.1627,2020). N is total number of short-term environmental conditions.

if either : the mean wind heeling lever

lwind,tot

exceeds the righting lever, GZ, at each heel to :2 ,

leeward, or the stabe angle under the action

ð24Þ of steady wind, ’S ,

is greater than the angle of failure   ¼ 1  exp r EA T exp , otherwise

Excessive Accelerations When a ship is rolling, the objects in higher locations travel longer distances. A period of roll motions is the same for all the location onboard the ship. To cover longer distance during the same time, the linear velocity must be larger. As the velocity changes its direction every half a period, larger linear velocity leads to larger linear accelerations. Large linear acceleration means lager inertial force (SDC 3/WP.5/Annex 7, 2016). Level 1 Vulnerability Criteria of Excessive Acceleration

For each loading condition a ship is considered not to be vulnerable to the excessive acceleration failure mode if   ’kL g þ 4p2 hr =T 2r
REA1

  ¼ 4:64 m=s2

ð25Þ

In which ’ is characteristic roll amplitude (rad) calculated by Eq. (26); kL is factor taking into account simultaneous action of roll, yaw, and pitch motions; g is gravity acceleration; hr is height above the assumed roll axis of the location where passengers or crew may be present (m), for

to leeward, ’fail,þ , and

which definition, the roll axis may be assumed to be located at the midpoint between the waterline and the vertical center of gravity; and Tr is natural roll period. ’ ¼ 4:43rs=d0:5 ’

ð26Þ

In which, r is effective wave slope coefficient; s is wave steepness as a function of the natural roll period Tr as determined in (IMO, Msc.1/ Circ.1627,2020); and δ’ is nondimensional logarithmic decrement of roll decay. Level 2 Vulnerability Criteria of Excessive Acceleration

S

For each loading condition a ship is considered not to be vulnerable to the excessive acceleration failure mode if C¼

N X

W i CS,i
REA2 ¼ 0:00039

ð27Þ

i¼1

In which, long-term probability index measures the vulnerability of the ship to a stability failure due to excessive acceleration for the loading condition and location under consideration based on the probability of occurrence of short-

1538

Second Generation Intact Stability Criteria

term environmental conditions, as specified in (IMO, Msc.1/Circ.1627,2020); Wi is weighting factor for the short-term environmental condition; and CS,I is short-term excessive acceleration failure index for the short-term environmental condition under consideration, calculated by Eq. (28).

  CS,i ¼ exp R22 = 2s2LAi

ð28Þ

In which, R2 ¼ 9.81 (m/s2); sLai is standard deviation of the lateral acceleration at zero speed and in a beam seaway.

Cross-References ▶ Auxiliary Icebreaking Methods ▶ Human Occupied Vehicle (HOV) ▶ Reliability Based Design (RBD) ▶ Transport Ship ▶ Underwater Mining System

References Germany, Review of the intact stability code, Proposals with regard to the scope of revising the IS Code and the related MSC/Circ. 707, IMO SLF 45/6/2, 2002 Germany, Review of the intact stability code, Towards the development of new intact stability criteria, IMO SLF 46/6/6, 2003 Germany, Review of the intact stability code, Towards the development of dynamic stability criteria, IMO SLF 47/6/4, 2004 Germany, Revision of the intact stability code, Proposal of a probabilistic intact stability criterion, SLF 49/5/2, 2006 Germany, Revision of the intact stability code, Report of the intersessional correspondence group on intact stability, SLF 51/4/1, 2008 Germany, Review of the intact stability code, Dynamic intact stability problems in waves, SLF 48/4/7, 2005 Germany, Review of the intact stability code, Report of the international correspondence group, IMO SLF 46/6, 2003 IMO, Development of new generation intact stability criteria, Report of the working group (part 1), SLF 52/WP.1, 2010

IMO, Development of second generation intact stability criteria, Report of the working group (part 1), SLF 53/WP.4, 2011 IMO, Development of second generation intact stability criteria, Report of the working group (part 1), SLF 54/WP.3, 2012 IMO, Development of second generation intact stability criteria, Report of the working group (part 1), SLF 55/WP.3, 2013 IMO, Development of second generation intact stability criteria, Report of the working group (part 1), SDC 1/WP.5, 2014 IMO, Development of second generation intact stability criteria, Report of the working group (part 1), SDC 2/WP.4, 2015 IMO, Finalization of second generation intact stability criteria, Report of the working group (part 1), SDC 3/WP.5, 2016 IMO, Finalization of second generation intact stability criteria, Report of the working group (part 1), SDC 4/WP.4, 2017 IMO, Finalization of second generation intact stability criteria, Provisional workplan, SDC 5/J.6, 2018 IMO, Finalization of second generation intact stability criteria, Report of the experts’ group on intact stability, SDC 6/WP.6, 2019 IMO, Finalization of second generation intact stability criteria, Report of the drafting group on intact stability, SDC 7/WP.6, 2020 IMO, Interim guidelines on the second generation intact stability criteria, Msc.1/Circ.1627, 2020 IMO, Review of the intact stability code, Report of the working group (part 1), SLF 48/WP.2, 2005 IMO, Revision of the intact stability code, Report of the working group (part 1), SLF 51/WP.2, 2008 Japan, Development of new generation intact stability criteria, Information collected by the intersessional correspondence group on intact stability, SLF 52/INF.2, 2009 Japan, Development of new generation intact stability criteria, Report of the intersessional correspondence group on intact stability, SLF 52/3/1, 2009 Japan, Revision of the intact stability code, A methodology of direct assessment for capsizing due to broaching, 49/5/6, 2006 Japan, Revision of the intact stability code, A proposal of new generation intact stability criteria as an example, SLF 51/4/3, 2008 Japan, Revision of the intact stability code, Proposal of methodology of direct assessment for stability under dead ship condition, SLF 49/5/5, 2006 Japan, the Netherland and the United States, Revision of the intact stability code, Framework for the development of new generation criteria for intact stability, SLF 50/4/4, 2007

Semi-submersible Platform

1539

Self-Organizing Network

Semi-submersible Platform

▶ Underwater Acoustic Sensor Network

Baihui Zhao Shanghai Jiao Tong University, Shanghai, China

Self-Propulsion tests

Synonyms

▶ Towing Tank Test

CUSS I (Continental, Union, Superior and Shell Oil Companies’ Project Mohole); DP (dynamic positioning); LFC (low-frequency cycle); VIM (vortex-induced motion)

Self-Sustaining Profiling Automation Circulation Detector (SPACD) ▶ Profiling Float

Semi-closed Containment System ▶ Modern Aquaculture Structures

Definition A semi-submersible platform is a specialized offshore unit used in a number of specific offshore roles such as drilling rigs, safety vessels, oil production platforms, and heavy lift cranes. They are designed with good stability and seakeeping characteristics. Other terms include semi-submersible, semi-sub, or semi for simplification (https://en. wikipedia.org/wiki/Semi-submersible_platform).

Introduction

Semirigid Connectors ▶ Connectors of VLFS

Semi-submersible Crane Vessel (SSCV) ▶ Decommissioning of Offshore Oil and Gas Installations

Semisubmersible Drilling and Production Rig (SSDP) ▶ Polar Offshore Engineering

Offshore drilling in water depth greater than 500 meters normally requires that operations be carried out from a floating vessel, as the cost on fixed structures are normally unaffordable. Initially in the early 1950s, monohull ships such as CUSS I (Keuren and David 2004) were used, but these were found to have significant heave, pitch, and yaw motions in large waves, and the industry needed more stable drilling platforms. Thus, semisubmersible platform concept came into engineering application soon (Fig. 1). A semi-submersible platform, also known as the column stable drilling platform, which operates mainly in the deepwater area, is a floating production system that enables the drilling and exploitation of offshore oil and gas resource. Most of the floating body is below the water

S

1540

Semi-submersible Platform

Semi-submersible platform can be used as both drilling and production platform. It has a series of advantages such as high safety factor, large deck space (up to 110 m/110 m in length and width), and strong expansion of the topside in the later stage. The deck area and load can be flexibly adjusted according to the actual situation. The platform is also flexible to move, the stability is relatively good, and the reliability is high. In addition, semi-submersible platform can be used for other offshore operation utilizations, including pipelayers, supply vessels, offshore lifting vessels, etc., especially widely used in deepwater oil and gas exploration.

History

Semi-submersible Platform, Fig. 1 North Dragon semi-submersible platform

surface, and the general positioning system is mooring lines, anchoring equipment, and dynamic positioning system (DP). Nowadays, a semi-submersible platform generally consists of a platform body, columns, a pontoon, and a number of support rods – a pontoon submerged under water, providing primary buoyancy, and columns connecting the deck body to the pontoon. A semi-submersible obtains most of its buoyancy from ballasted, watertight pontoons located below the water surface and are away from wave action. Structural columns connect the pontoons and operating deck. The operating deck can be located high above the sea level owing to the good stability and therefore is kept well away from the waves. With its hull structure submerged at a deep draft, the semi-submersible is less affected by wave loadings than a normal ship. However, with a small water plane area, however, the semi-submersible is sensitive to load changes and therefore must be carefully trimmed to maintain stability.

The semi-submersible design was first developed for offshore drilling activities. Bruce Collipp (From “Wikipedia n.d.) of Shell is regarded as the inventor. But Edward Robert Armstrong (From “Wikipedia n.d.) may have paved the way with his idea of “seadrome” landing strips for airplanes in the late 1920s, since his idea involved the same use of columns on ballast tanks below the surface and anchored to the ocean floor by steel cables. When oil drilling moved into offshore waters, fixed platform rigs and submersible rigs were built, but were limited to shallow waters. The first semi-submersible arrived by accident in 1961. Blue Water Drilling Company owned and operated the four column submersible drilling rig Blue Water Rig No.1 in the Gulf of Mexico for Shell Oil Company. As the pontoons were not sufficiently buoyant to support the weight of the rig and its consumables, it was towed between locations at a draft midway between the top of the pontoons and the underside of the deck. It was observed that the motions at this draft were very small, and Blue Water Drilling and Shell jointly decided that the rig could be operated in the floating mode. The first purpose-built drilling semi-submersible Ocean Driller was launched in 1963. Since the emergence of a semi-submersible offshore platform in the early 1960s, it has been widely used in the offshore oil exploration and development. In

Semi-submersible Platform

1541

Semi-submersible Platform, Fig. 2 Distribution of semi-submersible production platform (2008)

1975, the world’s first semi-submersible production platform “DeepSea Pioneer” was built. Most of the semi-submersible production platforms were converted from drilling rigs in the initial stages of the development of floating production facilities. Due to the small number of drilling rigs available for modification since the 1990s, it became less attractive than FPSO. However, with the worldwide exploitation of deepwater and marginal oil fields, semi-submersible production platforms were once again favored by oil exploration companies after the 1990s. Its main operating blocks are mainly in the Brazilian waters, the Gulf of Mexico, the South China Sea, and the North Sea. Fig. 2 shows the semisubmersible production platform operational distribution in 2008 (2008 Semi Floating Production Vessel Poster n.d.).

Structural Features The semi-submersible platform is composed of an upper deck, columns, a lower pontoon or rigs, and anchoring system. The advanced fifth-generation or sixth-generation semi-submersible drilling

platforms are all equipped with DP system. If DP system is not used, the platform is normally connected to the seafloor through the mooring system. Since its appearance, the structure of the semi-submersible platform has undergone many evolutions, and its appearance tends to be simple. Huge pontoon provides the buoyancy required for towing work. The columns connect the pontoon and the upper deck. During operation, the pontoon and large proportion of columns are sunk into the water, which greatly reduces the water surface area and thus reduce heave motion amplitude of the platform. The larger water plane moment of inertia provides the stability required for the platform operation. In order to consider damage stability and cost-effect, the number of columns is generally 4 to 8. The upper deck is the main place for equipment storage and personnel residency, providing work site and arranging production and living facilities. The money-maker of the platform, the rig, is installed on the deck. The accommodation facilities are always designed near helicopter platform, in case of emergency evacuation.

S

1542

Semi-submersible Platform

Semi-submersible Platform, Fig. 3 Offshore support vessel Toisa Perseus with, in the background, the fifthgeneration deepwater drillship Discoverer Enterprise, over the Thunder Horse Oil Field. Both are equipped with DP systems

Dynamic positioning system (DP) is mostly installed on newly built semi-submersible drilling platform, because they are always expected to operate in deepwater area and DP operation can save great time and cost than those of traditional mooring positioning operation. DP system can be composed of 6–8 propellers installed beneath the pontoon, and their directions can be adjusted with 360 degree to counteract the wind load, current load, and second order wave load (Fig. 3).

Construction and Installation Process The construction and installation process of the semi-submersible platform is very complex, timeconsuming, and costly. At present, only a few big companies in the world can afford the construction and operation costs. Some of them can only undertake part of the construction work such as the construction of the hull. Nowadays, some international companies that are famous for their construction of semi-submersible drilling platforms are mainly located in East and Southeast Asia, for instance, Keppel Corporation and Sembcorp Marine Company in Singapore, Samsung Heavy Industries and Daewoo Shipbuilding and Marine Engineering Company in South Korea, and Raffles

Shipyard, Waigaoqiao Shipyard, and Dalian Shipyard in China (Fig. 4).

Vortex-Induced Motion Effect For the conventional semi-submersible platform, the natural periods of roll, heave, and pitch motions are between 40 and 60s; when using the mooring positioning systems, the natural periods of surge, sway, and yaw motions are between one to several minutes, which are far from the general wave energy range that is normally between 5 and 30s. Therefore, the first-order wave motions including heave, roll, and pitch will be quite small and benefit the drilling operation very well. However, under the action of the secondorder low-frequency wave force effect, semisubmersible platform can have obvious slowdrift motion on surge and sway, which has to be borne by mooring system or DP system. In addition wave run-up phenomenon is another important phenomenon often being concerned, especially under severe sea state (Danmeier et al. 2008). Recently, with the application of deepdraft semi-submersible concept, vortex-induced motion (VIM) problem has also arisen to cause much attention.

Semi-submersible Platform

1543

Semi-submersible Platform, Fig. 4 Construction and installation process of semisubmersible platform in different shipyards

Vortex-induced motion (VIM) is one of the hydrodynamic problems for deep-draft semisubmersible platform with large column height. Traditional semi-submersible platforms have relatively low drafts, and the height of the underwater part of the column is small, so its vortexinduced motion is not obvious. However, with the development of petroleum exploration toward the deep sea in recent years, the loading requirements for semi-submersible platforms have been continuously improved, and the draft design draft has also gradually increased, that is, it has developed into a deep-draft semi-submersible platform. The semi-submersible platform is a typical multi-column floating body. The tail of the

column will generate periodic vortex shedding under certain flow conditions. The vortex shedding will generate pulsating pressure. Under certain flow conditions, the vortex will follow the surface of the cylinder and generate alternating falling motion, which leads to the horizontal resonant vibrations that cause vortex-induced motion (VIM). When the natural frequency of the platform system is close to the frequency of vortex shedding, this resonant motion is even more serious, resulting in a large low-frequency cycle (LFC) fatigue damage to the mooring and riser systems. Compared with the highfrequency damage caused by waves, the dynamic tension amplitude caused by the

S

1544

vortex-induced kinematics is much greater, resulting in more severe fatigue problems. In addition, a larger vortex-induced response will also have a greater impact on the platform’s mooring and positioning capabilities. Therefore, in the design stage of mooring and riser systems, accurately predicting the vortex-induced motion characteristics of the platform under the action of the ocean current provides an important reference for checking whether the fatigue lives of mooring and riser systems satisfy the requirements for the whole service life. The characters of VIM of semi-submersible platform are different with those of other offshore structures, such as SPAR platform. Semisubmersible platforms usually consist of a pontoon, cross braces, and multiple columns, so under the vortex-shedding excitation effect, the vortexinduced motion characteristics of the semisubmersible platform are quite different from that of a standpipe or a slender body. For a deepdraft semi-submersible platform, the maximum vortex amplitude A/D can reach 0.5–0.6 (where A is the amplitude of transverse vortex-induced motion, and D is the dimension of platform for dimensionless), which will affect the fatigue life of anchor chain and the hanging catenary riser. The vortex-induced motion is related to the maximum displacement of the platform, which will increase the drag force acting on the platform, especially when the vortex-induced motion is severe, and even affect normal drilling operations. Therefore, the VIM has become a challenge that restricts the development of the deep-draft semisubmersible platform. In addition, VIM of semi-submersible platform is special due to the multi-number of columns. Compared with single column platforms, such as the spar platform, the vortex shedding of each column of semi-submersible is superimposed on each other, and the effect of interference makes the VIM characteristics of the deep-draft semisubmersible platform more complicated. Because the importance of predicting VIM effect during the design stage of deep-draft semi-submerged platform, many studies have been conducted based on theoretical analysis and basin experiment methods.

Semi-submersible Platform

Wave Slamming With the development of global ocean exploration and development, the semi-submersible platform has become one of the main tools for the development of offshore oil and gas by its advantages. The basic structural design and analysis have become the important technical content in the basic design. DNVGL (DNV RP-C103 Columnstabilized units 2005) classification requirements for the basic structural design of semi-submersible offshore platforms include completion of overall strength analysis, local strength analysis, web frame strength analysis, air gap analysis, wave slamming (on lower deck by wave loading) strength analysis, etc. The strength analysis of the lower deck structure when attacked by the wave slamming load is an important part in the basic structural design report. In severe sea state, the wave will impact the lower deck structure, which may lead to serious structural damage. Therefore, it is necessary to consider the effect of wave slamming load on the lower deck during the design process. Classification societies provide some analysis procedure for the wave slamming effect check.

Rule-Based Check Method Rule-based check method is the most easily used method by designers, because they only need to conform to the rules of classification societies and can maintain a high working efficiency. For instance, the DNVGL states that the wave load calculation formula calculates the average slamming pressure (DNV RP-C205environmental conditions and environmental loads 2007): Ps ¼ 0:5r  Cpa  v2 In the formula, Ps – the average attack pressure. r – the liquid mass density, the calculated value of 1025 kg/m3. Cpa – the load coefficient; Cpa ¼ 2π when the flat bottom surface is impacted; Cpa ¼ 5.15 when the smooth cylinder is subjected to impact.

Semi-submersible Platform

v – the relative normal velocity between the water surface and the lower deck surface. According to this formula, for all areas in the lower deck of the semi-submersible probably subjected to wave load impact calculated in the air gap analysis, the relative speed and slamming force at the impact of the wave slamming load on these areas in all wave directions are calculated. With the wave slamming load calculation results, the bottom of deck structure of semisubmersible can be checked by classification societies’ rules. There are many rules for structural strength check. So, this is a convenient working procedure. Nevertheless, the accuracy of this method relies much on the classification societies’ rules, so it is classification societies’ duty to guarantee the feasibility and accuracy of those rules. Numerical Simulation Method Numerical simulation is one of the most important methods to analyze and assess the structural safety of the lower deck structure of semi-submersible platform. There are many commercial codes available being used to do the numerical simulations of wave slamming, including ABAQUS, FLUENT, and LS_DYNA. One of the advantages of numerical simulation method is the relative accuracy that this method can provide, and the slamming process can be shown in much detail in time series. The other advantages of the numerical simulation method is that the simulation results can find some critical weakness points of deck structure, which will help to strengthen the deck structure accurately. Nevertheless, there are also some weak points of this method, one of the most critical one is the high cost of human labor and computation time. For example, it may be a challenge task for a designer to learn and use sophisticated CFD codes such as FLUENT. Furthermore, the simulation results could be versatile for different users (Qinjing et al. 2011). It is believable that with the improvement of IT technology, numerical simulation method will become more and more popular and reliable. At that time, the calculation of many nonlinear phenomena will employ numerical simulation methods during the design phase.

1545

Air Gap Air gap has much relationship with wave slamming effect in previous section. For semisubmersible platforms, the vertical support structure below these platforms, namely, columns, are generally more slender, which is to withstand the wave load, thereby enhancing its ability to work in harsh sea conditions. If the initial air gap of the platform is small, the waves can easily slam the structure of the lower deck and platform directly, which can result in large slamming wave load and cause serious structural damage and endanger the people onboard and even, sometimes, overturning of the platform. So for the platform, air gap must not be too small, so as to avoid damage to the platform. During the design stage of offshore platform, especially semi-submersible platform, air gap is always one of the most critical issues. It is a highly nonlinear problem and plays a very important role in the two major factors – the response of wave height and the platform vertical motion amplitude. When considering the wave height calculation, it normally applies both linear and nonlinear wave theories. If only linear wave theory is used, it will be inevitably underestimating the wave climbing value, which is more serious with the increase of wave steepness. Comparatively, the forecast values by applying both linear and nonlinear wave theories are in better agreement with the experimental values. The other calculation issue is the motion amplitude of the platform. If only fixed platform is considered, the air gap problem can be much simplified, but if the motions of floating offshore platform are considered, the forecast of air gap value will become more complicated, because the phases of both motions and that of wave height need to be both considered. In general, the nonlinear issue of air gap forecast is more accurate than that of the linear forecast value, which is worth exploring and practicing. Air Gap Forecast of the Semi-Submersible Platform For semi-submersible platform, it has two types of deck superstructures – open deck structure

S

1546

Semi-submersible Platform

Semi-submersible Platform, Fig. 5 Wave slamming on semisubmersible platform

and closed deck structure – which refer to whether the deck superstructure of the platform is open design or closed design. In the case of an open design, small waves on the deck or lashing can damage the safety of lives and property facilities on the platform and so it compulsorily required that the air gap of the platform must be kept positive. As for the closed superstructure design, due to the better protection brought by the enclosed superstructure, slight waves slamming will not have a significant impact on the platform deck, so it can be applied to the harsh marine environment. Taking into account the cost of the platform construction, the large distance between the bottom of deck structure and the still water surface, namely, the great design value of the initial air gap, often means increasing construction cost. Therefore, for most latest version semisubmersible platforms, in order to avoid the negative air gap completely, it is more economical to perform local strengthening check than to increase the initial air gap (Sweetman et al.) (Sweetman et al. 2002a). Thus, semi-submersible can withstand some wave slamming without the need to increase initial air gap (Fig. 5). For floating platforms, such as semisubmersible platforms, the interference between platforms motion and wave is serious. Due to the effects of wave diffraction and scattering, the crests of some parts of the platform are often overlapped with each other so that the response of the air gap can be amplified or reduced. Therefore, the forecast of air gap is a high nonlinear problem, and it is quite complicated. At present, CFD and numerical calculation are the most reliable methods for the air gap forecast.

Development of Air Gap Forecast Methods At present, numerical prediction of the air gap mainly includes CFD forecast method and numerical calculation forecast method based on potential flow theory. In addition, basin experiment is also used for air gap prediction. For CFD method, it can provide accurate forecasting results with good visual effect, if the required technologies can be used in a correct way. There are many successful examples in air gap forecasting by some famous CFD tools, for instance, OpenForm, Fluent et al. But CFD method also has its drawbacks, such as high time-consuming and labor-consumption, and insufficient reliability et al. Compared with CFD method, numerical calculation forecast method based on potential flow theory costs much less and easily to be mastered, so it is normally used for engineering application. Many popular commercial tools, for instance, WAMIT, SESAM, MOSES, and AQUA, can be used to do the air gap forecast calculation. Nevertheless, it is also needed to point out that sometimes numerical calculation method can underestimate the relative wave height, and thus may not provide a conservative prediction result (Fig. 6). There are some findings from air gap forecast research. It is found that linear numerical methods often underestimate the extremes of relative wave front rise, so basin model testing is essential for designing a new platform. Sweetman (Sweetman et al. 2002b) believes that it is more economical to allow proper negative air gap phenomena in the extreme sea conditions and to reinforce the local structure, compared to always be without wave slamming. Simos and Fujarra (Simos et al. 2006)

Semi-submersible Platform

1547

Semi-submersible Platform, Fig. 6 Wave slamming simulation for semi-submersible through CFD technology

from the University of São Paulo concluded that the plateau is affected by waves, and the air gap response of the platform will have significant nonlinear characteristics (especially the response wave height around the platform column) when the incident wave’s steepness exceeds 4%. In 2009, Lwanowski et al. used ComFLOW software to conduct a theoretical study of the platform (Bogdan et al. 2009). The software predicts the air gap performance of the platform by capturing the N-S equation combined with the improved VOF method and captures the wave climbing and wave-ups around the platform. The results show that this method can simulate the wave scattering and wave surface distribution around the column accurately. Stansberg et al. used the potential flow software WAMIT to simulate the wave height and air gap around the semi-submersible platform (Stansberg 2007). It was found that the nonlinear method can basically meet the requirements of engineering forecast under some special conditions. However, when the wave steepness is large, there is a big deviation from the test value. In addition, besides replying on calculation method, basin experiment is another alternative way, and it can give relatively more accurate and direct forecasting air gap data. However, similar to the disadvantage of CFD method, basin experiment has the shortcoming of high cost and human labor, which may not be affordable by most scholars.

Reference 2008 Semi Floating Production Vessel Poster Bogdan I, Marc L, Rik W (2009) CFD Simulation of Wave Run-up on a semi-submersible and Comparison with Experiment. In: Proceedings of the 28th international conference on offshore mechanics and arctic engineering (OMAE 2009), Honolulu, Hawaii, USA. ASME Danmeier DG, Seah RKM, Finnigan T, Roddier D, Aubault A, Vache M, Imamura JT (2008) Validation of wave run-up calculation methods for a gravity based structure. In: Proceedings of the 27th international conference on offshore mechanics and artic engineering, OMAE 2008, Estoril, Portugal, 15–20 June 2008 DNV RP-C103 Column-stabilized units, 2005 DNV RP-C205-environmental conditions and environmental loads, 2007 From “Wikipedia.: https://www.wikipedia.org/” Keuren V, David K (2004) Chapter 6: breaking new ground-the origins of Scientific Ocean drilling. In: The machine in Neptune’s garden: historical perspectives on technology and the marine environment. Science History Publications, Sagamore Beach, pp 183–210. ISBN 0881353728. Retrieved 1 March 2014 Qinjing G, Shumin C, Ronggui H, Qinhua X (2011) Strength analysis of submersible platform under wave load slamming. Ship Eng 33–1 Simos AN, Fujarra ALC, Sparano JV, Umeda CH., (2006), Experimental evaluation of the dynamic air gap of a large-volume semi-submersible platform. In: Proceedings of the 25th international conference on offshore mechanics and arctic engineering, Hamburg, Germany, OMAE2006–92352 Stansberg CT (2007) Slow-drift pitch motions and air-gap observed from model testing with moored semisubmersibles. In: Proceedings of the 26th international conference on offshore mechanics and arctic engineering, California, USA, OMAE2007–29536

S

1548 Sweetman B, Winterstein SR, Cornell CA (2002a) Air gap analysis of floating structures: first- and second-order transfer unctions from system identification. Appl Ocean Res 24:107–118 Sweetman B, Winterstein SR, Meling TS (2002b) Airgap prediction from second-order diffraction and stokes theory. Int J Offshore Polar Eng 12:184–188. Palo Alto, United State. ISOPE

Semisubmersible Vehicle (SSV)

by sea state, it is much more stable in waves than surface drones or small vessels. The task of the semisubmersible vehicle autopilot control system is to achieve automatic attitude and depth control.

Scientific Fundamentals

Semisubmersible Vehicle (SSV) ▶ Semisubmersible Vehicle Autopilot Control System

Semisubmersible Vehicle Autopilot Control System Changhui Song School of Engineering, Westlake University, Hangzhou, China

Synonyms Autopilot control system; Semisubmersible vehicle (SSV); Unmanned surface vehicle (USV); Unmanned underwater vehicle (UUV)

Definition The semisubmersible vehicle is a fuel-powered underwater vehicle that most of its structure is below the water surface and its snorkel extends above the water surface. The radio antenna is fixed on the snorkel for real-time data transmission and remote control. Different from traditional unmanned surface vehicles (USVs), the semisubmersible vehicle can use the differential global positioning system (DGPS) mounted on snorkel duct for precise positioning, which has greatly enhanced the opportunity for the use of the semisubmersible vehicle. As the snorkel is the only part of the semisubmersible vehicle to be affected

The autopilot control system of semisubmersible vehicles faces three major challenges: some hydrodynamic coefficients unknown, disturbances from unpredicted sea environments, and the coupling states’ effects. The dynamical performances of the vertical plane control are sensitive to the sharply changing of these coupling states and complex disturbances. Due to the highly nonlinear marine vehicles and the significant environment disturbances, it is a great challenge to control unmanned semisubmersible vehicles (USVs) without knowing the model parameters. Sensor, Control and Communication, and Power System As mentioned in the background above, one of the advantages of this semisubmersible is the capability to maintain the communication link to support vessel or shore station and location updated by GPS transceiver. As a categorized unmanned surface vehicle, the topmast of the surface section must have enough space to put some environmental sensors such as temperature, barometric pressure, speed, and wind direction or popular known as weather sensor station. With the most body submerged, it has enough space to put the most common underwater survey equipment such as obstacle avoidance sonar, side-scan sonar, and dual-frequency echo sounder. Figure 1 shows the control architecture of semisubmersible vehicle. For communication, two types of systems will be provided on this vehicle. As a fact that almost the unmanned and autonomous capability surface vehicles have the mission to deploy on the remote area and very far from support vessel or shore station, the best communication must be based on the satellite system. The other widely used communication method is radio communication.

Semisubmersible Vehicle Autopilot Control System

1549

Semisubmersible Vehicle Autopilot Control System, Fig. 1 Control architecture of semisubmersible vehicle (Kartidjo et al. 2015)

To accommodate the long-endurance capability and operation of many sensors, this vehicle is equipped with a high density of battery as the power source. The main criteria of battery beside the capacity are the longest cycle it has (Kartidjo et al. 2015). 6-DOF Equation of Motion of the Vehicle We formulate the motion of the semisubmersible vehicle using a 6-DOF rigid body model. To

describe rigid body motion, two coordinate systems need to be defined: the global coordinate system and the body-fixed frame. Figure 2 shows the coordinate systems used for vehicle modeling. Based on Newton’s second law, Kirchhoff’s equation of motion in the body-fixed frame of the towing vehicle and the towfish can be written as shown in Eq. (1).

 

 mm u_  vr þ wq  xGm q2 þ r 2 þ yGm ðpq  r_Þ þ zGm ðpr  q_ Þ ¼ Xhyd þ Xprop þ Xint

   mm v_  wp þ ur  yGm q2 þ r 2 þ zGm ðqr  p_ Þ þ xGm ðpq  r_Þ ¼ Y hyd þ Y prop þ Y int mm ½w_  uq þ vp  zGm ðq2 þ r 2 Þ þ xGm ðpq  r_Þ þ yGm ðpr  q_ Þ ¼ Zhyd þ Zprop þ Z int   I xm p_ þ I zm  I ym qr þ mm ½yGm ðw_  uq þ vpÞ  zGm ðv_  wp þ urÞ ¼ K hyd þ K prop þ K int I ym q_ þ ðI xm  I zm Þpr þ mm ½zGm ðu_  vr þ wqÞ  xGm ðw_  uq þ vpÞ ¼ Mhyd þ Mprop þ Mint   I zm p_ þ I ym  I xm pq þ mm ½xGm ðv_  wp þ urÞ  zGm ðu_  vr þ wqÞ ¼ N hyd þ N prop þ N int

ð1Þ

S

1550

Semisubmersible Vehicle Autopilot Control System

dz ð k Þ ¼ k P e z ð k Þ þ k I

XO

k X

ez ðlÞ þ kD

l¼1

e z ð k Þ  e z ð k  1Þ T

ez ðkÞ ¼ zðkÞ  zd

YO

ð2Þ q ZO

ym

p

n

xm r

Zm

w

Zhou et al. (2019) set the sampling period to t ¼ 0.2 S and set the submergence depth of the vehicle to 1 m in the control system. The control parameters used in the control system are:

u

Semisubmersible Vehicle Autopilot Control System, Fig. 2 Coordinate systems of semisubmersible vehicle (Park and Kim 2015)

Eq. (1) is the equation of motion of the semisubmersible vehicle, where [u, v, w]T is the surge, sway, and heave directional linear velocity in body-fixed frame, and [p, q, r]T is roll, pitch, and yaw angular velocity in body-fixed frame. [xGm, yGm, zGm] is the position of the center of gravity of the semisubmersible vehicle. The subscript int refers to the interaction force, the subscript hyd refers to the hydrodynamic force, and the subscript prop refers to the propulsion force. As mentioned earlier, the equation of motion of vehicles is described in the fixed-body frame (Park and Kim 2015). In the actual control system, we pay more attention to the vertical control of semisubmersible vehicles. So the dynamic model can be simplified properly. The vertical plane states of the semisubmersible, such as the depth, pitch angle velocity, and pitch angles, are usually coupled with surge speeds. And these states are often corrupted by the unexpected surge or the sea wind. Moreover, pitch angles and submerged depths should be confined according to the mechanisms of the studied semisubmersible vehicles system.

PID Controller As the starting point and to provide a baseline for comparison of designs, a PID control law was employed. In the digital domain, this control law has the form:

kP ¼ 3, kI ¼ 0:5, kD ¼ p Although the response of the PID controller is stable, the transient and steady-state response is somewhat poor. Moreover, the pitch angle is not well controlled, appears as the semisubmersible vehicle is running through the sea, which indicates that the depth of the vehicle is susceptible to the disturbance from the sea environment. Fuzzy Dynamic Feedback Controller The fuzzy dynamic feedback control algorithm can guarantee robustness against external parameter unknown and poor sea environment. Due to the limited submersible depth, motions of the semisubmersible vehicle are directly influenced by wave forces coming from water surfaces. Therefore, the external disturbances on the semisubmersible vehicle are difficult to be described by mathematical expressions. Moreover, the model parameters of the semisubmersible vehicle are unknown, which makes the controller more difficult. Control parameters of the fuzzy rulebased state-feedback controller are auto-adjusted by fuzzified states errors and surge speeds. Figure 3 depicts the block diagram of the depth control of the semisubmersible vehicle. State Feedback Controller One alternative to PID control is to assume that the system can be adequately represented by linear time-invariant dynamics for a specified surge speed and design a state feedback law for the vehicle. Simplify the system model and describe its state-space model as:

Semisubmersible Vehicle Autopilot Control System

1551

Semisubmersible Vehicle Autopilot Control System, Fig. 3 Fuzzy controller of the semisubmersible vehicle (Zhou et al. 2019)

2

3 e_z 6 7 4 e_y 5 ¼ Ax þ Bds e_q

2

0

u

d s ¼ k ez e z þ k ey e y þ k e q e q 2 3 2 3 ez ez

6 7 6 7 ¼ k ey k ey k eq 4 e y 5 ¼ K 4 e y 5 eq eq

3 ez 76 7 1 54 ey 5 eq a2 u

6 ¼ 40 0 0 a1 2 3 0 6 7 þ 4 0 5 ds bu2

0

32

ð3Þ

ð4Þ

where kez , key , and keq are feedback control parameters. Suppose also that it is decided to place the controlled system poles at lez , ley , and leq in the open left-half of the complex plane. det ðsI  ðA  BK ÞÞ ¼ ðs  lez Þðs ley Þ  s  l eq

The key idea of the feedback control is to assign the eigenvalues predesigned according to the desired performances of the system. The eigenvalues are equal to the roots of the character equation of the considered system if there is no pole-zero cancellation. The poles of the closed-loop system can be located at any place according to the desired control performances if the plant system is fully controllable (Gruyitch 2013). If a state feedback control law is designed for a given surge velocity, the pole assignment problem has a solution if and only if (3) is controllable. Preset the form of the feedback control law as:

With further analysis, the control parameters can be determined as: 8 > >
>   : keq ¼ lez þ ley þ leq be where be is decided by the known parameter Ms (Zhou et al. 2019). Sliding Mode Controller The control parameters cannot be provided for the model-based control algorithm, which leads to the

S

1552

Semisubmersible Vehicle Autopilot Control System

Semisubmersible Vehicle Autopilot Control System, Fig. 4 Dorado vehicle (ISE Ltd. 2017)

undesirable control performances of the system since the depth motion model parameters regarding the unmanned semisubmersible vehicles are unknown. For this purpose, a multi-identification model-based dynamic sliding mode control algorithm is presented for the investigation of system’s control problem on the desired depth. In the proposed algorithm, the average-fitting-error method is used to reduce the excessive redundant model parameters, and thus the optimum model parameters are provided for the control algorithm by switching methods. And the state feedback method is used to bring about the chattering exponential decay of sliding mode controller so as to reduce the settling time. The experimental results of lake trials demonstrate that the proposed algorithm could offer the best model parameters for sliding mode control, and the dynamic sliding mode control with multi-identification models is capable of ensuring BQ-01 vehicle to achieve the ideal control performance (Zhou et al. 2017).

Key Applications Semisubmersible vehicles were first used for military purposes, mainly in anti-mine operations. Only a few countries have mastered the relevant technology and developed equipment, including Canada, France, the United Kingdom, the United

States, and China. In recent years, with the increasing demand for marine surveys, semisubmersible vehicles may expand into the civilian field, for example, ocean seismic survey work. Dorado Vehicle The growing threat from new-generation mines that are increasingly more difficult to detect has stimulated the demand for new mine-hunting systems that offer improved safety and operational efficiency. The Dorado vehicle, shown in Fig. 4, in operational service with the Canadian Department of National Defence, was developed to meet this need, which can be considered one of the first examples of truly autonomous USVs (Young et al. 2006). The Dorado vehicle is capable of towing a sonar towfish at speeds up to 12 knots and depths to 200 m. The towfish was developed to follow the seabed at low altitudes and is fitted with a multibeam side-scan sonar. SeaKeeper Vehicle Based on the experience in the design and production of several generations of MCM vessels, the French company DCN had developed the SeaKeeper, shown in Fig. 5, as an answer to face the challenging threat of modern mines. SeaKeeper was presented for the first time in Brest in June 2003 in the complete configuration including the “dry segment.” SeaKeeper was the

Semisubmersible Vehicle Autopilot Control System

1553

Semisubmersible Vehicle Autopilot Control System, Fig. 5 SeaKeeper vehicle (ISE Ltd. 2018)

S Semisubmersible Vehicle Autopilot Control System, Fig. 6 AN/WLD-1 vehicle (Luca 2017)

latest solution available for sonar reconnaissance against the most modern mines at that time. With a vehicle remotely controlled by radio, it offered the highest level of safety for the crew, together with unmatched performance in terms of area coverage rate. The system, integrated by DCN company, had raised interest in several navies in the world. During 13 days of trials and demonstrations, the

SeaKeeper achieves more than 100 h of sonar operation, showing remarkable reliability for the prototype (Waquet 2003). AN/WLD-1 Vehicle Lockheed Martin’s AN/WLD-1 RMS, shown in Fig. 6, is a key component of the Littoral Combat Ship’s mine countermeasures package (Button

1554

Semisubmersible Vehicle Autopilot Control System

et al. 2009). The system consists of a 7-m semisubmersible autonomous remote multi-mission vehicle (RMMV) which tows the AQS-20A Variable Depth sensor. The RMS has sometimes been referred to as a “snorkeler class” unmanned surface vessel due to the snorkel required above the surface for the system’s diesel engine operation. The RMMV can be preprogrammed to perform autonomously or be manually controlled via line of site or over-the-horizon data link. The Navy successfully concluded the second and final phase of reliability testing of the littoral combat ship (LCS) remote minehunting system (RMS) off the coast of Palm Beach, Florida, enabling the service to progress toward developmental testing, in June 2013. The system completed more than 850 h of testing during 47 missions over a 4-month period.

surface. The strut provides buoyancy, air for propulsion, and radiofrequency coverage for communications and positioning. The 6-m vehicle has a maximum speed of 10 knots and a payload capacity of up to 200 kg. It is designed to be launched and recovered from a ship or deployed from the shore. The vehicle permits a wide range of sensor operations for near-surface and deepwater applications. To date, the vehicle has been successfully operated with sonar’s for the underwater survey and with cameras for above water surveillance. Furthermore, the vehicle has been a leading candidate for towed side-scan sonar operations such as deepwater naval mine warfare, and the vehicle has been evaluated by the UK’s Ministry of Defence under their concept capability demonstrator program.

SASS Vehicle The Survey Autonomous Semi-Submersible (SASS) vehicle, shown in Fig. 7, for Ocean survey was developed by UK company ASV Ltd. (Bertram 2008). The platform which is intended to enhance or even replace conventional survey vessels will provide cost-effective deployment of ocean sensors. SASS involves an unmanned submerged torpedo-like body running below waves with a strong upright strut penetrating the water

USS Vehicle USS vehicle, a predecessor to the Remote Minehunting System, was a diesel-powered air-breathing vehicle with a tall narrow mast and the majority of its structure below the water surface (Alleman et al. 2009). The USS vehicle, shown in Fig. 8 (left), is an autonomous semisubmersible vehicle that could be used for shallow-water hydrographic surveys and surface surveillance. This diesel-powered vehicle has an operational speed of

Semisubmersible Vehicle Autopilot Control System, Fig. 7 SASS vehicle (Bertram 2008)

Semisubmersible Vehicle Autopilot Control System

1555

Semisubmersible Vehicle Autopilot Control System, Fig. 8 USS 6300 vehicle and conceptual model of USS 9500 (Alleman et al. 2009)

Semisubmersible Vehicle Autopilot Control System, Fig. 9 BQ-01 vehicle (Zhou et al. 2019)

S 8 knots with an associated endurance of 48 h in sea state 4. At a survey speed of 4 knots, the vehicle has an impressive endurance of nearly 100 h. The vehicle has a payload capacity of 300 kg for sonars, computers, sensors, winches, and camera equipment. A recently constructed vehicle, the USS 6300 for C&C Technologies in the United States, is fitted with a Klein 5000 side-scan sonar and Simrad EM3002 multibeam sonar for commercial hydrographic survey. USS 9500 will be designed to offer long-range (1500 miles) survey and

surveillance operations within the “Exclusive Economic Zone” (EEZ); this 9.5-m diesel-powered vehicle has been designed to a rugged specification, with the ability to operate in sea state 5/6 at moderate speeds, with a sprint speed of 20 knots and the ability to remain at sea for extended periods of up to 30 days. BQ-1 Vehicle BQ-01 system, shown in Fig. 9, is a semisubmersible vehicle that should not completely submerge

1556

into water, or else some water may flow into it from its chimney and breaks down some important parts equipped inner system. To make sure the USV safety, the pitch angles, and the submerged depth are confined to [15, 15] degrees and [0, 3] m, respectively. The features of BQ-01 are as the followings: its power source is a diesel engine, its body can submerge a certain depth, its breather pipe should not be awash, otherwise some water will enter its control cabinet. The length of BQ-01 is 5.9 m, and the width is 2 m. Its performance basic indices are the maximum surge speed 15 knots, the maximum submerged depth is 3.5 m, and the strongest drag force is 10,000 N@10kn (Zhou et al. 2017, 2019).

Sequential Engineering Waquet P (2003) Mine hunting with drones. Inf Secur 13:98–114 Young H, Ferguson J, Phillips S, Hook D (2006) Wavepiercing autonomous vehicles. IEE Control Eng Ser 69:387 Zhou H, Liu Y, Hu Z, Liu K, Yi R (2017) Switching strategy of dynamic sliding mode control based on multiple identification model set for unmanned semisubmersible vehicle. Def Technol 38(11):2198–2206 Zhou H, Liu K, Xu H, Feng X (2019) Experimentally verified depth control of an unmanned semisubmersible vehicle. IEEE Access 7:94254–94262

Sequential Engineering ▶ Design Spiral ▶ Empirical Design

Cross-References ▶ Autonomous Underwater Vehicle (AUV)

References Alleman P, Kleiner A, Steed C, Hook D (2009) Development of a new unmanned semi-submersible (USS) vehicle. OCEANS 2009:1–6 Bertram V (2008) Unmanned surface vehicles – a survey, vol 1. Skibsteknisk Selskab, Copenhagen, pp 1–14 Button RW, Kamp J, Curtin TB, Dryden J (2009) A survey of missions for unmanned undersea vehicles. Rand National Defense Research Institute, Santa Monica Gruyitch LT (2013) Tracking control of linear systems. CRC Press, Boca Raton ISE Ltd (2017) DORADO, digital image. http://207.102. 77.253/defense.html. Accessed 20 Mar 2021 ISE Ltd (2018) ISE DORADO Semi-Submersible Minehunting Vehicle, digital image. https://ise.bc.ca/ product/dorado/. Accessed 20 Mar 2021 Kartidjo M, Nugroho SA, Wibowo W (2015) Design and analysis of CentrUMS-ITB unmanned semisubmersible vehicle. In: 2015 10th Asian Control Conference (ASCC), IEEE, pp 1–5 Luca P (2017) The Lockheed Martin Remote Mine-hunting System (RMS) provides the primary mine reconnaissance capability for the US Navy’s Littoral Combat Ships. (US Navy), digital image. https://armadainter national.com/2017/12/dangers-of-the-deep/. Accessed 20 Mar 2021 Park J, Kim N (2015) Dynamics modeling of a semisubmersible autonomous underwater vehicle with a towfish towed by a cable. Int J Naval Archit Ocean Eng 7(2):409–425

Service Ships Jie Cui, Cheng Chen, Cong Gao, Xin Chen, Dong-Qing Miao and Wei Xu College of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang, China

Definition Service ships are vessels designed to provide support for commercial ships and industrial vessels; some of them are also used for professional work.

Scientific Fundamentals Composition and Basic Type There are many types of work ships depending on the function, such as tugs, icebreakers, fire boats, etc. A tugboat is a type of vessel that maneuvers other vessels or floating structures. The vessel itself does not have the ability of loading and unloading. And it is mainly used to tow barges loaded with cargo and other different kinds of engineering ships. Towing facilities include towing hook,

Service Ships

1557

Service Ships, Fig. 1 Inland river tug (http://www.quanjing.com/)

Service Ships, Fig. 2 The icebreaker “Bolheim”

towing column, mooring winch, etc., and at the same time, the aft deck has a large working area for operating easily (Wu 2017) (Fig. 1). Icebreakers are special vessels designed to open waterways in ice waters and to rescue trapped vessels. As early as 1857, Sweden built the world’s first real icebreaker “Bolheim”. The hull structure of an icebreaker is quite different from that of a general ship. The ship type, bow, propulsion, and propeller are the main distinguishing areas. Icebreakers generally use two methods (continuous icebreaking and collisional icebreaking) for icebreaking operations. In addition to the use of

their own weight, traditional icebreakers often need to use the cooperation between the front and rear pressure tanks to complete the icebreaking work (Fig. 2). Fireboats are professional ships for firefighting and extinguishing in ships or buildings near the shore. Fireboats look like tugboats, so there are also fire boats that double as tugboats. The ship is equipped with high-power water pump system, high-pressure spray gun, and fire-extinguishing agent, as well as rescue workers and medical equipment. Fire hoses are located on fire towers high above the water or on the top of a thickened mast with a range of more than 40 m. The ship

S

1558

Service Ships

Service Ships, Fig. 3 Fire of ocean-going freighter (http://www.sina.com.cn/)

also has a water curtain in order to get deeper into the fire area. When entering the fire area, the whole ship will be covered by a water curtain. Fireboats have a high speed and good seakeeping and require good maneuverability, so they can perform firefighting missions in narrow waterways or crowded ports (Fig. 3). Development History In the seventeenth century, ships began to use steam engines. The first truly tugboat was the Charlotte Dundas, which was powered by a steam engine and paddle wheels, mainly along the coast of Forth and Clyde near Glasgow. In order to improve the efficiency of propulsion, the propellers began to appear on tugboats in the mid-nineteenth century, and the size and towing capacity of the tugboats also increased significantly. The surge in demand for tugs in the first and second world wars drove the development of tugs, and the pace of tugboat modernization was accelerated by the development and applications of diesel engines, propulsion technologies, navigation technology, etc. Today, tugboats still play an important role in port operations, inland water transport, and marine development (Chen 2010).

Since 1900, Russia has been the first to build icebreakers on a large scale. Most of these icebreakers are used for overseas sailing. Among the early construction of icebreakers, the first vessel to sail in the Arctic was the “Yelmaf”. In 1957, the world’s first icebreaker driven by nuclear power was successfully built. It was the “Lenin” built by the former Soviet Union. Nuclear power technology is a major breakthrough in the field of icebreaking. In 1969, the construction process of modern icebreakers was rapidly developed. The USA used these new technologies to transform the transport ship “Manhattan” into a 115,000 t commercial icebreaker. Since then, a large number of high-quality icebreakers have emerged. In 1980, Canada built a new type of icebreaker, the “Kigoglik”, it mainly uses a spoon-shaped head similar to a reamer, which can greatly reduce the friction between the broken ice crystal and the hull, thus effectively improving the ship’s swing performance. In the 1980s, scientists invented a “bubble drag reduction system” that would prevent the icebreaker from being caught by the ice when it was icebreaking, allowing the ship to continue in the ice.

Service Ships

In 1762, the first fireboat appeared in Paris. At that time, it was mainly to deal with the fires that occurred on the wooden bridge over the Seine and the fires that occurred on the boats. By 1764, there were a total of eight fireboats in Paris which were equipped with handcuff pumps. They did not quit service until the nineteenth century. The rise of the industrial revolution in the nineteenth century brought the busyness of American ports, which increased the risk of fire, making Boston introduce lifeboats for firefighting. In 1888, the Paris Fire Brigade Commander asked the municipality for a steam fireboat, but his request was not met. Until 1931, due to the soaring fuel prices, in order to reduce costs, fireboats began to use diesel drives instead of steam drives (Shi 1990). Key Technology

The tugboat is characterized by its small hull, high power, high tractive force, solid structure, strong fenders, and anti-collision equipment, which make the vessels have good stability and maneuverability. Meanwhile, excellent barking performance is very necessary for the tugboat. During towing operation, the tugboat will have a large heeling because of transverse urgent traction from towing cable. Therefore, in order to ensure the transverse stability, the beam will be relatively large and the length-breadth ratio will be smaller

1559

than that of the ordinary transport ship (Yang et al. 2010). In order to keep the good speediness and reliability of tugboats, double engine-paddle propulsion system is basically applied in modern towboats and sometimes especially for four engine-paddle propulsion system. Meanwhile, adjustable pitch paddles have been utilized in most of boats. For keeping excellent maneuverability, lateral thruster and sometimes full-swing devices will be installed in bow and stern of most towboats, respectively (Fig. 4). Icebreakers generally use two methods: continuous icebreaking and collision icebreaking. In addition to using their own weight, traditional icebreakers generally need to use the cooperation between the front and back water tanks. For example, when heading to break the ice, the back water tank will be filled with water, so that the ship will be upward-headed, so that the front part of the ship will be pressed on the ice, and then the forward water tank will be filled with water, and the back water tank will be drained, so as the ship’s center of gravity moves forward, the purpose of crushing the ice will be achieved. When breaking the ice from left to right, the ballast tanks of the ship will be flooded alternately from left to right, which will make the ship shake from left to right, thus breaking the ice (Bostrom 2018) (Fig. 5).

S

Service Ships, Fig. 4 Operations of tug (http://www.quanjing.com/)

1560

Service Ships

Service Ships, Fig. 5 The icebreaker (http://www.baidu.com)

When the thickness of ice does not reach the designed thickness of icebreaker, the continuous icebreaking method is adopted. Propelled by propellers, icebreakers, which slowly and undulately break through the ice, can sail about 9.2 km/h through the ice. If the ice is thicker than the maximum ice break the icebreaker is designed to be, or if it is in more complex ice accumulation, thick ice zones, and more severe ice ridges, then the impact icebreaking method is used. First, the icebreaker needs to move back a distance of one or two captains and then speed up the collision. The tilting bow of the icebreaker can easily run onto the ice surface, in the thick ice area or encountered ice ridge, through repeated impact of the method of breaking the ice (Wei et al. 2017). The advanced external fire protection system is the core part of the firefighting vessels. External fire protection system consists of external fireextinguishing system, external foam fireextinguishing system, self-spraying water curtain protection system, hydraulic lifting device, and external fire monitoring system. The advanced system design can transfer the ship from the navigational state to the fire state in the shortest time. The arrangement of the external firefighting system should have a certain height from the surface of the water due to the consideration of the scope

of action, and it should be arranged more in the top area of the firefighting vessels, so it is often arranged in the top area of the fireboat. Taking account of the personal safety of the firefighters, remote control of the cab should be used as much as possible, unless manual operation is necessary (Fig. 6). Main deck and left and right sides of the upper deck of firefighting vessels shall be provided with fixed water-spray system devices, protecting the hull, superstructure, and deckhouses with waterspray, including the vertical surface of the base and parts of the fire monitor. Water curtain protection can absorb part of the convection and radiation heat, which can protect firefighters from being burned by large fires. Moreover, it can also prevent glass windows from being cracked by fire. At the same time, fireboat shells can be cooled (Shi 2011). The hull and superstructure of firefighting ships and the peripheral walls of deckhouses must be steel. Doors and window frames on all peripheral walls must also be steel (aluminum). Firefighting vessel’s glass windows (especially the big glass window in the cab) should be equipped with tempered glass that is resistant to air blasts to avoid accidental casualties of crew members and firefighters.

Service Ships

1561

Service Ships, Fig. 6 Firefighting vessels (http://www.pic.sogou.com/)

Key Applications With the advancement of technology and changes in people’s needs, service ships are constantly evolving, and the overall trend is modernization, specialization, and multifunctionality. Along with the drafting object increasing and improved requirement for drafting efficiency, the function for tugboat has been enhanced continuously. More advanced equipment has been utilized, and the tugboats have already entered the scope of high value-added ships. The number of newly built tugboat has already reached an unprecedented level, and the development of tugboats has directed to a functional and intelligent orientation (Tang et al. 2016). The main shipyards for tugboats manufacturing are mainly located in European and American nations and China. The total number of tugboats under construction is currently around 400, and it is the USA which possesses most of the tugboats. There are several decades of history for tugboats manufacturing in our country, and enriching experience has been gathered. The design and manufacturing technology for tugboats has achieved great progress and reached the international advanced level mainly including harbor

tugs, offshore and inshore towboats, and multipurpose stand by ship serving offshore oil platform (Fu 2010).

Versatility Due to the restrictive factors in economics, there are drafting functions as well as fire control, marine salvage, supply, and diving work functions in towboats which present the multifunctionality trend. For instance, the “De Hong” tugboat which was designed by Shanghai Merchant Ship Design and Research Institute in China is mainly used in marine salvage including marine long-distance drafting for salvage boats, wrecked offshore drilling platform, stranded reef ships, and boats lacking of maneuverability. Meanwhile, there are also plugging, drainage, and firefighting ability to wrecked ships, setting sail and anchoring ability for marine platform, drafting ability for buoy and undulant wrecked boat, boat hauling and transportation, and marine residuum collection functions. Moreover, bigger cabin has been arranged during preliminary design phase to load the deck cargo and lance pipe so that this ship can also be used as supply boat.

S

1562

Intelligentization Along with the increasing tasks for towboats and burden reducing requirement for the crew, the various systems on ships are needed to keep pace with the times and become more intelligentized and automated. For instance, the VS468 multifunctional tugboat has already met the DNV’s unmanned cabin on duty requirement. Meanwhile, one respective 10 and 3 cm radars, electronic chart, automatic navigator, echo detector, doppler log meter, electronic gyrocompass, and clinometer have been devised as well. Monitoring and remote control can be set to all pump valves including freshwater, drilling water/ballast water, fuel, brine, and methanol. Moreover, alarm and control system can be offered to safe operation of master and auxiliary equipment, and the engine room “death alarm” function is also configured. And skills in unmanned cabin, automatic steering, computer monitoring, and a series of modern communication navigation equipment have been applied in the towboats which are manufactured by shipyards in Zhenjiang and exported to Egypt (Giron-Sierra et al. 2015). The patents and literatures of various new icebreakers are summarized and analyzed, and some possible design conjectures of new icebreakers are put forward. The icebreaker innovatively designed the bow of a ship with a narrow top and wide bottom, which allows the bow to be easily extended below the ice. When the icebreaking operation is carried out, the ship tilts forward at a small angle, and the conical structure of the ship’s bow underwater reaches below the ice sheet. Through the action of the ship’s ballast water system, the distribution of ballast water is changed to make the ship’s center of gravity move back. The forward hull generates forces that push the conical structure forward, which impacts the ice in both the forward and upward directions, thus realizing the “skid-type” icebreaking process. The idea of a semisubmersible icebreaker was first proposed by Vadim Pikeur, a former Soviet engineer, who proposed an icebreaker that could sail on the surface as well as semisubmersible through specially designed reinforced hulls and “comb” icebreakers. The specific icebreaking method is the lower hull reaches the

Service Ships

predetermined depth and then the ballast water is quickly discharged to make it float and break through the ice with the “comb” type icebreaking mechanism. The main structure of the icebreaker is a lower hull equipped with buoyancy module, ballast tank and main and auxiliary equipment, and a tower of about 20 m. The tower is equipped with a bridge, control system, etc. The icebreaking capacity of semisubmersible icebreakers will be greatly improved compared with current icebreakers, and the icebreaking operation of 5-mthick ice will be carried out. At the same time, because the propeller is under the ice, it can improve the performance of the propeller. The mission of the fireboat is clear, and it is inevitable that the city port must be equipped with the supporting fireboat. Meanwhile, the focus of the design of the fireboat is mainly to select a reasonable host propulsion, a fire pump drive mode, an excellent performance, advanced and reasonable firefighting equipment, and an excellent hull line with good resistance performance. The future development of fireboats also needs to reflect the particularity of the image of the city government. People’s modern aesthetic requirements are constantly improving, and the appearance of fireboats will be very important. In the new situation, modern fireboats have been given a new content and meaning in addition to the necessary fire-extinguishing technology, which means they are used to protect the water environment from pollution.

Cross-References ▶ Ship Overall Design ▶ Ship Structural Design ▶ Special Marine Vehicle ▶ Transport Ship

References Bostrom M (2018) Breaking the ice: a work domain analysis of icebreaker operations. J Cogn Technol Work 3:443–456 Chen XD (2010) The development trend of tugboat. J Ship Eng 5:58–59

Shallow Foundations Fu H (2010) Current situation and development trend of tugboat in China and at abroad. J Ship Boat 4:6–10 Giron-Sierra JM, Gheorghita AT, Angulo G, Jimenez JF (2015) Preparing the automatic spill recovery by two unmanned boats towing a boom: development with scale experiments. J Ocean Eng 95:23–33 Shi YW (1990) Domestic fire-fighting vessels overview and determination of main scales. J Wuhan Shipbuild 4:15–23 Shi HY (2011) “Pearl River” fireboat design and construction. GSI Shipbuilding Technology 1:6–7 Tang CH, Tang HE, Tay PKJ (2016) Low cost digital close range photogrammetric measurement of an as-built anchor handling tug hull. J Ocean Eng 119:67–74 Wei YX, Lin C, Ming WH, Hui ZC, Li LL (2017) Analysis of technological development status of icebreaker. J Mar Technol 3:1–4 Wu JH (2017) Overall design of a new 22210Kw fullrotation tugboat. J Jiangsu Ship 4:1–4 Yang LJ, Hong BG, Inoue K, Sadakane H (2010) Experimental study on braking force characteristics of tugboat. J Hydrodyn 5:343–348

SeSAm ▶ Jacket Platform

SGPC - Salinity Gradient Power Conversion ▶ Salinity Gradient Power Conversion

Shallow Foundations Xiaowei Feng Fugro Australia Marine Pty Ltd, Perth, WA, Australia

1563

Tension leg platform; Triaxial compression; Triaxial tension; Unlimited tension interface; Water depth; Zero-tension interface

Definition Shallow foundations applied offshore are considered as having an embedment depth to foundation diameter (width) ratio less than unity.

Design Approach of Offshore Shallow Foundations Historically, offshore shallow foundations can either be large concrete gravity bases to fix the giant superstructures, or the steel mudmats used as temporary support for jacket platforms prior to piling. As the offshore oil and gas developments move into deep water, shallow foundations have become more diverse, including bucket foundations used as anchors mooring floating platforms and skirted mudmats as permanent supports for subsea infrastructures such as pipeline end terminations and manifolds (PLETs and PLEMs). Recent upsurge in exploiting offshore wind as a clean and renewable energy resource around the world makes the skirted foundations a more attractive option for the foundations of offshore wind turbines in deep water, either as a single foundation or in a multipod arrangement. A number of different applications of offshore shallow foundation systems are illustrated in Fig. 1. The partial safety factor approach, referred as to load and resistance factor design approach (LRFD), is generally preferred in routine design. To allow the overall reliability of a design to be quantified better, the applied loads to the foundations are generally scaled up by the load factors, and the shear strength of the soil is reduced by the material factors.

Synonyms Combined vertical, horizontal and moment loading; Concrete foundation template; Gravity-based structures; International Organization for Standardization; Offshore wind turbine; Pipeline end manifold; Pipeline end termination; Simple shear;

General Loads and Soil Parameters General Loads The general loads applied to a gravity-based foundation under working conditions consist of

S

1564

Shallow Foundations

to Manifold

Pipeline

PLET

Wellhead

to PLET Jumper Mudmat

(a)

(b)

(c)

(d)

(e)

Shallow Foundations, Fig. 1 Application of offshore shallow foundations: (a) GBS (tank-type structure); (b) TLP; (c) jacket; (d) OWT; and (e) subsea mudmats

a

b

c

Hx Hy

V Mx

V Vt

H

M Vc

y

x

T

My z

Shallow Foundations, Fig. 2 General loads applied to offshore shallow foundations

vertical load V, horizontal load H, and moment M (Fig. 2a). The vertical component mainly comprises the weight of the platform and the foundations, whereas the horizontal and moment components are typically due to the environmental forces from wind, waves, and currents. The ratio of M/H indicates whether a structure is prone to sliding or overturning failure. Concrete bucket foundations used for TLPs or the steel bucket foundations in a multipod arrangement are generally subject to tensile loads due to the “push-pull” mechanism (Fig. 2b). For the subsea mudmats supporting PLETs and PLEMs, the loads acting on the foundations typically include the vertical load V, the biaxial horizontal load Hx

and Hy, the biaxial moments My and Mx, and the torsion T (Fig. 2c). The biaxial horizontal loads are induced by the thermal expansion and contraction of the attaching pipelines and jumpers, whereas the moments and torsion are generated by the vertical and horizontal eccentricities. The vertical load is relatively small to the ultimate bearing capacity of the foundation, while the torsional and horizontal sliding or the overturning failure generally governs the design. Soil Shear Strength Used for Design The relevance of stability calculations depends on the choice of appropriate shear strength parameters. The stress paths in the soil under a foundation

Shallow Foundations

1565

Mcyc V Hcyc

τ

τcyc 0

DSS TXE

time

TXC

τ0

DSS

0

τ τa τ0

τ

τcyc

τ τcyc

τa time

time

τa

Δτa

0

Δτa

τcyc

Δτa

0

time

Shallow Foundations, Fig. 3 Simplified stress conditions along a potential failure surface beneath a shallow foundation

are complex. Figure 3 shows that the relevant shear strengths at different locations along a potential failure surface can be approximated to those measured in triaxial compression (TXC), simple shear (SS), or triaxial extension (TXE), which may differ by a factor of two. In engineering practice, most designs adopt an average shear strength in TXC, SS, and TXE conditions to use in standard design approaches. The environmental loading applied to an offshore foundation is cyclic in nature. Therefore, the effects of cyclic loading on the available soil shear strength have to be considered (Andersen and Lauritzsen 1988).

Bearing Capacity Classical Bearing Capacity Theory Figure 4 depicts a shallow foundation subjected to a point load P. The eccentric-inclined load P is decomposed into a vertical component V normal to the base and a horizontal component H, intersecting the center of an equivalent fictitious rectangle for which the bearing capacity is calculated.

P V M H Shallow Foundations, transformation

Fig.

4 Load-equivalent

The “effective width” hypothesis was proposed by Meyerhof (1953) for strip foundations to consider the detachment of the foundation due to an overturning moment resulting from eccentricity of vertical load. The concept of an “effective area” has since been developed for other foundation geometries and more complex loading conditions – including biaxial moment (Hansen 1961; Taiebat and Carter 2002), as shown in Fig. 5. The traditional bearing capacity theory calculates the load-carrying capacity of shallow foundations under combined loading by adopting the concept of effective foundation area in conjunction with modification factors for load inclination, and other boundary conditions including foundation shape and embedment, and soil strength heterogeneity (ISO 2016).

S

1566

Shallow Foundations

a

b

B

y C

Footprint A' V ey

L

ex

x

B

L'

O

O'

D

x

e

H Footprint

Effective area

A

B'

Effective area

y Shallow Foundations, Fig. 5 Definition of effective area for various foundation geometry

Undrained Bearing Capacity

The classical approach for predicting the design unit-bearing capacity is conventionally expressed as Eq. (1) for undrained conditions with uniform isotropic undrained shear strength increasing approximately linearly width depth below mudline (ISO 2016).   kB0 K c qd ¼ F N c su0 þ 4 gm

ð1Þ

where qd is the design vertical bearing resistance (Qd ¼ qdA), F is a correction factor given as function of kB0 /su0, Nc is the undrained plane strain-bearing capacity factor for uniform shear strength (π þ 2), su0 is the undrained shear strength of soil at the foundation base level, and k is gradient of the increase of the undrained shear strength with depth. The superposing modification factor Kc accounts for load inclination, foundation shape, and foundation embedment. Drained Bearing Capacity

Equation (2) is a general formula for determining design vertical bearing capacity for drained conditions   1 qd ¼ g0 B0 N g K g þ s0 v0 N q  1 K q 2

ð2Þ

where Nγ and Nq are the drained bearing capacity factors; γ0 is the submerged unit weight of soil;

s0 v0 is the in situ effective overburden stress at base level; and Kγ and Kq are the correction factors that account for load inclination, foundation shape, and foundation embedment.

Shortcomings of the Classical Bearing Capacity Theory Shortcomings of the classical bearing capacity approach for application to offshore shallow foundations are illustrated in Fig. 6 and include that: (a) The approach uses linear superposition of separate modification factors to account for load inclination and eccentricity. Therefore, the true coupling of horizontal and moment interaction leads to underprediction of load carrying capacity (Fig. 6a). (b) The approach uses the effective area method to account for moment which does not allow for transient tensile resistance mobilized by the generation of negative excess pore pressure (Fig. 6a). (c) The approach defines the load-carrying capacity by the single equivalent allowable vertical load, Vd, adjusted to account for horizontal load and moment (Eqs. (1) and (2)). The factor of safety determined by this approach cannot reflect the true load path for a foundation (Fig. 6b).

Shallow Foundations

1567

a

Failure envelope approach Suction

1

b Hult

Moment, My/ABsu0

0.8

Failure envelope approach No suction

H

0.6 0.4

Load path →A:

0.2 0

-1

-0.8 -0.6 -0.4 -0.2

1 V Vd Vult V Failure envelope approach㸸FoS = Hult/H = 2

2 O

Classical theory

A

0

0.2

0.4

0.6

0.8

1

Classical theory 㸸FoS = Vd/V = 1.5

Load path →A: Classical theory cannot reflect the proximity to failure for the ‘true’ loading path

Horizontal load, Hx/Asu0

Shallow Foundations, Fig. 6 Shortcomings of the classical theory

Advanced Approach Failure Envelopes

As an alternative, the failure envelope approach has been recommended by the ISO guidelines (ISO 2016) for calculating the load-carrying capacity of shallow foundations under multidirectional loading conditions. The failure envelope describes a surface in multidirectional load space which defines the combinations of loads causing failure. A load state that falls within a failure envelope is permissible while a load state that falls outside a failure envelope is nonpermissible. A load state that falls on the failure envelope indicates a factor of safety of unity, i.e., all available capacity is mobilized. Benefits of the failure envelope approach over classical bearing capacity theory include overcoming limitations (a) – (c) listed in the last section, specifically that: (a) The approach accounts for inclination and eccentricity of loading by defining capacities under pure moment and horizontal loading (which form apex points of the envelope), rather than by adjustment of the vertical capacity. (b) The approach allows visual evaluation of the proximity to failure and the factor of safety against any combination of loads, illustrating visually whether a given load is favorable or unfavorable from the direction of the load path relative to the failure envelope.

(c) The approach does not require the effective area principle since moment capacity is defined directly, and solutions exist for both full tension and zero tension assumptions at the foundation-soil interface (Shen et al. 2016, 2017). The effectiveness of the effective area method has been investigated in Feng et al. (2019). Additional advantages of the failure envelope methods include that: • No adjustment is made to the classical bearing capacity theory to consider the effect of torsion. However, the effect of torsion can be determined explicitly by the failure envelope approach (Feng et al. 2014). • The approach provides an indication of the displacement path at failure through the principle of normality (Bransby and Randolph 1998). Determination of Failure Envelopes

There are three main methods for determining a failure envelope in three-dimensional coplanar VHM load space or under the more general six degree-of-freedom-loading conditions. In their initial development, the most common approach was experimental (Gottardi et al. 1999). Plasticity limit solutions can be developed for the combined loading problems using a delicate kinematically admissible mechanism within the soil body (Bransby and Randolph 1998; Randolph and

S

1568

Shallow Foundations

Puzrin 2003). Numerical finite element method has become a more common method to determine the failure envelopes because the pursue of the plasticity limit solutions is generally not straightforward under more complex conditions, including the foundation geometry, the soil conditions and the loading regime, e.g. the six degree-offreedom loading (Feng et al. 2014). General Procedures for Applying Failure Envelopes to Design

In-house program can be developed to assist routine design using the published algebraic expressions of the failure envelopes. A procedure for applying the failure envelopes to design of subsea shallow foundations was provided in Feng et al. (2014), as summarized in Table 1. Undrained Uniaxial Capacity: Fine-Grained Soil

Exact solutions exit for the pure undrained ultimate vertical capacity for a surface strip or circular foundation. For the surface strip foundations, the rigorous value of the vertical capacity factor of Ncv (¼ Vult/Asu0) is 5.14, whereas Ncv ¼ 5.91 and 6.05 for smooth or rough surface circular foundations, respectively. The vertical capacity factor has been determined for other boundary Shallow Foundations, Table 1 Design steps for offshore shallow foundations Step 1 2 3

4

5

6

Details For given foundation geometry, evaluate su0 and nondimensional quantities B/L, d/B, and k Evaluate uniaxial capacities for vertical, horizontal, moment, and torsional loading Reduce ultimate horizontal, moment, and torsional capacities to maximum values available, according to mobilized (design) vertical capacity, v ¼ V/Vult For given angle of resultant horizontal load, evaluate corresponding ultimate horizontal capacity, and similarly for ultimate moment capacity If required, evaluate reduced ultimate horizontal and moment capacities due to normalized torsional loading Evaluate extent to which applied (design) loading falls within H-M failure envelope, and thus safety factors on self-weight V, live loading H, M, T, or material strength su0

conditions, including the foundation geometry, embedment depth, and the degree of soil strength heterogeneity. The shape and depth factors were derived through finite element limit analyses and finite element analyses (Edwards et al. 2005; Gourvenec et al. 2006; Salgado et al. 2004), where only the uniform soil profile was examined. Analytical solutions of the effect of soil strength heterogeneity were first presented for strip foundations in Davis and Booker (1973). Gourvenec and Randolph (2003) examined the effect of soil strength heterogeneity for strip and circular foundations using finite element analysis, but the embedment was not considered. The coupling effect of the foundation shape and soil strength heterogeneity on the vertical capacity factor has been investigated recently for surface-rectangular foundations by Feng et al. (2017a). Figure 7 shows that as the degree of soil heterogeneity increases the shape factor reduces, becoming less than unity for values of kB/su0 less than about 2. The reduction in the shape effect becomes less significant as the foundation varies from a square to a longer rectangle, since the plain strain condition prevails in the soil beneath a longer foundation. The undrained ultimate moment capacity of the foundations with zero-tension interface (ZTI) is generally determined by the effective area method. The pure undrained ultimate moment capacity for surface foundations with unlimited tension interface (UTI) can be determined using the upper-bound limit analysis based on the “scoop” mechanism, giving NcM ¼ 0.69 and 0.67 for a strip and circular foundation on uniform soil, respectively (Randolph and Puzrin 2003). The effect of soil strength heterogeneity on the moment capacity factor can be described by the quadratic expressions for strip and circular foundations (Gourvenec and Randolph 2003). The coupling effect of foundation shape and soil strength heterogeneity on the moment capacity factor was determined by Feng et al. (2017a). Pure undrained horizontal and torsional sliding capacity for a surface rough foundation is straightforward. The horizontal capacity factor for embedded strip foundations was derived from the upper-bound limit analyses by Bransby and

Shallow Foundations

1569

Shallow Foundations, Fig. 7 Shape factor of vertical capacity as function of aspect ratio and degree of soil heterogeneity

1.2 1.15

Shape factor, sc

1.1

B/L↑ = 0.2, 0.33, 0.5, 0.75, 1 1.05 1 0

5

10

15

20

0.95 0.9

0.85 0.8

Randolph (1999). An extension of the solution was made for rectangular foundations by Feng et al. (2017b). Torsion is more relevant to the design of subsea shallow foundations. Finnie and Morgan (2004) investigated the torsional capacity of a surface-circular foundation. The torsional capacity factor for surface-rectangular foundations was derived in Murff et al. (2010). The effect of the foundation embedment on the torsional capacity has been systematically investigated for rectangular foundations in Feng et al. (2017b).

Failure Envelopes for Undrained Conditions

Unlimited Tension Interface The pioneer development of the VHM failure envelopes for skirted foundations under undrained soil conditions ignored the physical embedment and often assumed a surface foundation with an unlimited tension interface (UTI) to represent the tensile capacity provided by the foundation skirts. The idealization is appropriated when the soil resistance due to the work done by shearing in the soil above skirt tip level (e.g., due to the disturbance during installation or scour) is negligible. A close-form expression is available to describe the failure envelopes for a circular foundation with UTI on homogenous soil (Taiebat and Carter 2000) (Fig. 8a).

Degree of heterogeneity, κ = ρB/su0



2 V f ¼ V ult "  2 # M HM þ 1  0:3 Mult H ult jMj  3 H 1 þ H ult

ð3Þ

A closed-form expression is also available to describe the failure envelope for a strip foundation with UTI resting on a deposit with a linearly increasing undrained shear strength with kB/su0 ¼ 6 (Bransby and Randolph 1998) (Fig. 8b). 

2 V f ¼ 1 V ult " 2:5  5 #12 M H þ þ H ult Mult

S ð4Þ

where M* is modified moment parameter given by the expression M  ¼ M  hs H

ð5Þ

where hs is the height of the rotation of the scoop mechanism above the foundation level. The size of the normalized failure envelope reduces with the increasing level of vertical load, as indicated by Eqs. (3) and (4). The normalized

1570

Shallow Foundations

a

b

-1

1.2

VVult = 0, 0.1, 0.3, 0.5, 0.7, 0.9 1

Normalised moment, M/Mult

Normalised moment, M/Mult

1.2

0.8

0.6 0.4 0.2

-0.8

-0.6

0 -0.4 -0.2 0 0.2 0.4 Normalised horizontal load, H/Hult

0.6

0.8

VVult = 0, 0.3, 0.5, 0.7

0.8 0.6 0.4 0.2

-1

1

1

-0.8

-0.6

0 -0.4 -0.2 0 0.2 0.4 Normalised hoirzontal load, H/Hult

0.6

0.8

1

Shallow Foundations, Fig. 9 Example failure envelopes for rectangular foundation under six degree-of-freedom loading

Normalized moment, my=My/Myult

Shallow Foundations, Fig. 8 Example failure envelopes for circular and strip foundations under planar VHM loading

1.2 T/T ult=0,0.25,0.5,0.75,0.9 1.0 0.8 0.6 0.4 0.2

-1.0

-0.8

-0.6

-0.4

0.0 -0.2 0.0

0.2

0.4

0.6

0.8

1.0

Normalized horizontal load, hx=Hx/Hxult FE resutls

size of the failure envelope also depends on the degree of heterogeneity and generally increases with the decreasing degree of heterogeneity of the most common combination of horizontal load and moment acting in the same direction (Gourvenec and Randolph 2003). The normalized failure envelope for rectangular foundations was proposed by Feng et al. (2017a) for varying soil strength heterogeneity, and under six degree-of-freedom loading (Fig. 9). A general algebraic expression was given to capture coupling effects of foundation and soil strength heterogeneity on the normalized failure envelopes for rectangular foundations

Estimated

 "   # M M q H M H 2 þb f ¼ 1a M max jM j H max jM j H max  2 H þ 1 H ult 

(6)

where Hmax and Mmax are respectively the maximum available horizontal and moment capacity by considering the vertical load and torsion mobilization, and

q ¼ 3ð1 þ 0:1kÞ

ð7aÞ

Shallow Foundations

1571

b 1.2

1 0.8 0.6 0.4

d/B=0; κ=0 d/B=0.05; κ=0

0.2

1.2

Normalised moment, m=M*/Mult (θm=90°)

Normalised moment, m=M/Mult (θm=90°)

a

d/B=0.10; κ=0

1 0.8 0.6

d/B=0.05; κ=0 0.2

d/B=0.20; κ=0

-1

-0.8

0 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 Normalised horizontal load, h=H/Hult (θ=0°)

0.8

1

-1

d/B=0; κ=0

0.4

-0.8

d/B=0.10; κ=0

d/B=0.20; κ=0 0 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Normalised horizontal load, h=H/Hult (θ=0°)

1

Shallow Foundations, Fig. 10 Effect of failure foundation embedment on the shape of VMH failure envelopes

a ¼Minð0:9, 1:25  0:17wÞ ∙Maxf0, 1 þ k∙½0:11  0:08Maxð1, wÞg

b ¼ 0:03k∙Minð3, 5  wÞ

ð7bÞ ð7cÞ

where k ¼ kB/su0 w ¼ (B/L )1  4θ/π. When a pure horizontal load is applied at the base of an embedded foundation, the resulting displacement will involve rotation as well as translation. Likewise, if a pure moment is applied at the base of an embedded foundation, the resulting displacement will involve translation as well as rotation. The coupling of horizontal load and moment leads to an oblique failure envelope, and this effect becomes more evident with increasing embedment ratio. The shape of the normalized VHM failure envelopes for skirted strip and circular foundations was proposed in Vulpe et al. (2014). Feng et al. (2014) presented the failure envelopes for the subsea-skirted rectangular mudmat foundation and found that the effect of foundation embedment on the shape of the normalized failure envelopes can be diminished by translating the load reference point to the foundation level (Fig. 10). For skirted rectangular foundations, it was also revealed that the shape of the normalized failure envelopes can be represented by that of surface foundation if d/B7). • Fracture mechanism: Only strong suboceanic earthquakes with a distinct vertical component can cause tsunamis. An initial assessment as to whether the ocean floor has moved vertically can be determined using land fixed points. • Ascertainment of a tsunami: On the coasts and on the offshore islands of Indonesia, tide gauges were installed with GPS components, which monitor the sea level. The data are integrated into the warning process. • Decision-making: Within less than 5 min, the decision can be made as to whether a warning needs to be issued and – if so – to which coastal sections. In the GITEWS, buoys are measurement instruments for the detection and verification of a tsunami in the early developing stage. The most important information, namely, the fast earthquake location and magnitude, without which either a simulation or a warning can be generated, cannot be supplied by buoy systems. Buoy

T

2024

Tsunami Warning Buoy

Tsunami Warning Buoy, Fig. 10 A new GPS design of tsunami warning buoy. (Figure from Kato et al. 2005)

systems for the direct measurement of a tsunami were initially part of the GITEWS concept. The further development of the GPS Shield made it possible to discontinue pursuing the buoy concept. Therefore, buoys have no longer been part of the operational warning system since 2010, so that the high maintenance cost of buoy installations near coastlines can also be omitted (GITEWS 2018). After that, GITEWS has developed model calculation methods to determine the possible extent

of a tsunami across the ocean. The measurement data, such as seismological parameters, GPS measurements of land displacements, and coastal tide gauge measurements of the sea level are being included in the model calculations. This results in a dynamic-updated model that constantly reflects the processes in the ocean and can forecast their future progress. The Tsunami Service Bus (TSB) – the integration platform in GITEWS – realizes the service-oriented architecture (SOA) approach by implementing the Sensor Web

Tsunami Warning Buoy

2025

Tsunami Warning Buoy, Fig. 11 Technical concept of GITEWS. (From website GITEWS 2018)

Enablement (SWE) standards and services (Fleischer et al. 2010). Envirtech Tsunami Detection Buoys The Tsunami Warning System (TWS) designed by Envirtech (website see (Envirtech Tsunami Buoys 2018)) is composed of the following main subsystems (as shown in Fig. 13): • an underwater module (UM) to be installed at the sea bottom in open sea location for the accurate measurement of the tide and the identification of anomalous conditions, • a surface buoy (SB) moored close to the UM to receive via acoustic link the measurement of UM to be transferred via satellite link to a data center (DC) for visualization and analysis, • a data center (DC) on land composed of hardware and software infrastructures for the reception via satellite link of the data of SB and UM to be displayed, stored, and analyzed.

Tsunami Warning Buoy, Fig. 12 GITEWS tsunami buoy (The buoys are no longer in operation as part of the GITEWS since 2010)

The tsunami buoy system comprises two components: the underwater module (UM), anchored to the sea floor, and the surface buoy (see Fig. 14). The surface buoy is composed of three main parts: a subsurface pole, a float (cone + cylinder) in the

T

2026

Tsunami Warning Buoy

Tsunami Warning Buoy, Fig. 13 Tsunami Warning System (TWS) designed by Envirtech. (Figure from Envirtech Tsunami Warning Buoy 2018)

middle, and a turret on the top. The sensors on the sea floor measure the change in height of the water column above by measuring associated changes in the water pressure. The water column height is communicated to the surface buoy by acoustic telemetry and then relayed via satellite to the tsunami warning center. The underwater module detects by itself the presence of a “special” event and starts to operate in event mode. The sea level is acquired every 15 s, and collected data are transmitted to the surface each minute. In few seconds, data arrives to the control center and an alarm procedure is raised. Figure 15 shows the Sumatra event on October 2010, as collected by an Envirtech Tsunami buoy deployed in South China Sea, 2,600 km far the earthquake epicenter on a seabed 4,400 meters deep. The seismic waves reached the underwater module few minutes after the earthquake, setting it in alarm mode (Courtesy SOA –

China). No tsunami followed the event in South China Sea. The buoy has multiple composite functions. In addition to tide and tsunami detection, the buoy can be optionally supplied with further payloads such as a complete meteorological station (single or double), an acoustic doppler current profilers (ADCP) for multicell current data collection and water quality multiparameter probe. The MKIII has been built to remain operational during super typhoons, with sea conditions up to Beaufort 14. In 2010, the buoy proved its great strength when the super typhoon Megi crossed its mooring position in the South China Sea. Summary When the tsunami devastated wide areas around the Indian Ocean in December 2004, the effects and the dangers of a tsunami came into global public consciousness with extensive media

Tsunami Warning Buoy

2027

Tsunami Warning Buoy, Fig. 14 The Envirtech MKIII-002 tsunami warning buoys. (Figure from Envirtech Tsunami Buoys 2018)

coverage. In the memory and perception of tourists and holiday makers, seashore sites may forever bear tsunami-related dangers, resulting in the desire for effective, reliable, and easy-to-use tsunami alarm systems. In the existing modern tsunami warning systems, Global Navigation Satellite System (GNSS) plays a central role, whether in DART system with buoys or in GITEWS without buoys. The key role in these systems is played by GPS. Thanks to the

developments made in GNSS data processing, especially in the framework of the International GNSS Service, a relatively cheap infrastructure of high-tech high-sea buoys can provide a very accurate and efficient tsunami early warning system. One of the challenges of tsunami warning is the application of rapid forecasting, for example, the application in Indonesia, where a tsunami caused by an earthquake in Sulawesi in 2018 killed hundreds of people. A long-term goal of tsunami

T

2028

Tsunami Warning Buoy

Sumatra Earthquake Oct 25,2010 Pressure [mmH20] at ENVIRTECH BPR in South China Sea - Time UTC 4404900 4404850 4404800 4404750 4404700 4404650 4404600 Source: Encirtech S.p.A - Italy - Credits SQA - China 16.10.45

16.08.15

16.05.45

16.03.15

16.00.45

15.58.15

15.55.45

15.53.15

15.50.45

15.48.15

15.45.45

15.43.15

15.38.15

15.40.45

15.35.45

15.33.15

15.30.45

15.25.45

15.28.15

15.23.15

15.20.45

15.18.15

15.15.45

15.13.15

15.10.45

15.08.15

15.00.45

15.03.15

15.00.45

14.58.15

4404550

Tsunami Warning Buoy, Fig. 15 Sumatra event collected by an Envirtech tsunami buoy deployed in South China Sea on October 2010. (Figure from website Envirtech Tsunami Buoys 2018)

assessment is to develop sensors that can detect and measure near-field tsunamis as close to the power generation area as possible. If this is achieved, countries will be able to obtain data more quickly, which could reduce evacuation times.

Cross-References ▶ Deep-Ocean Assessment and Reporting of Tsunamis (DART) BUOY ▶ Meteorological Monitoring and Measurement Buoy ▶ Wave Measurement Buoy ▶ WaveRider Buoy ▶ WaveScan Buoy

Reference DART 4G. https://nctr.pmel.noaa.gov/Pdf/brochures/ dart4G_Brochure.pdf. Accessed on: 27 Nov 2018 Deep-ocean Assessment and Reporting of Tsunamis (DART II). https://nctr.pmel.noaa.gov/Dart/Jpg/ DART-II_05x.swf. Accessed on: 27 Nov 2018 Deep-ocean Assessment and Reporting of Tsunamis (DART) Description. https://www.ndbc.noaa.gov/dart/ dart.shtml. Accessed on: 27 Nov 2018

Deep-ocean Assessment and Reporting of Tsunamis (DART) Tsunami Detection Algorithm. https://www. ndbc.noaa.gov/dart/algorithm.shtml. Accessed on: 27 Nov 2018 Envirtech Tsunami Buoys. http://www.envirtech.com/ Envirtech_Tsunami_Buoys.html. Accessed on: 27 Nov 2018 Envirtech Tsunami Warning Buoy Specifications MKIII-002 Spar Buoy. https://zh.scribd.com/docu ment/49150442/20003-SPE-200-0-Envirtech-Tsuna mi-Warning-System-Surface-Buoy-SpecificationsTsunami-Buoy#download. Accessed on: 27 Nov 2018 Fleischer J, Häner R, Herrnkind S et al (2010) An integration platform for heterogeneous sensor systems in GITEWS–tsunami service bus[J]. Nat Hazards Earth Syst Sci 10(6):1239–1252 GITEWS. http://www.gitews.org/en/concept/. Accessed on: 27 Nov 2018 Gonzalez FI, Milburn HM, Bernard EN et al (1998) Deep-ocean assessment and reporting of tsunamis (DART): brief overview and status report[C]//proceedings of the international workshop on tsunami disaster mitigation, vol 19. NOAA, Tokyo Green DS (2006) Transitioning NOAA moored buoy systems from research to operations[R]. National Weather Service Silver Spring MD International Tsunami Warning Center. http://itic.iocunesco.org/index.php. Accessed on: 27 Nov 2018 Kato T, Terada Y, Ito K et al (2005) Tsunami due to the 2004 September 5th off the Kii peninsula earthquake, Japan, recorded by a new GPS buoy[J]. Earth Planets Space 57(4):297–301

TWS Tsunami Warning System Meinig C, Stalin S E, Nakamura A I, et al (2005) Real-time deep-ocean tsunami measuring, monitoring, and reporting system: the noaa dart ii description and disclosure[J]. NOAA, Pacific Marine Environmental Laboratory (PMEL). 1–15 Milburn HB, Nakamura AI, Gonzalez FI (1996) Real-time tsunami reporting from the deep ocean[C]// OCEANS’96. MTS/IEEE. Prospects for the 21st century. Conference proceedings. IEEE 1:390–394 National Data Buoy Center (NDBC). https://www.ndbc. noaa.gov/. Accessed on: 27 Nov 2018 National Tsunami Warning Center. http://ntwc.arh.noaa. gov/. Accessed on: 27 Nov 2018 NOAA Center for Tsunami Research, Pacific Marine Environmental Laboratory. https://nctr.pmel.noaa.gov/Dart/ index.html. Accessed on: 27 Nov 2018 Pacific Tsunami Warning Center. http://www.weather.gov/ ptwc/. Accessed on: 27 Nov 2018 SAIC Introduces New Generation of Commercial Tsunami Buoy Systems. https://www.oceannews.com/featuredstories/september-feature-story-saic. Accessed on: 27 Nov 2018 Summary of DART II performance characteristics and specifications. https://www.ndbc.noaa.gov/dart/dart2_ pc_1.shtml. Accessed on: 27 Nov 2018 The current deployed DART II location. https://nctr.pmel. noaa.gov/Dart/. Accessed on: 27 Nov 2018 The National Oceanic and Atmospheric Administration, Tsunami. https://www.tsunami.noaa.gov/. Accessed on: 27 Nov 2018 The NDBC – DART Deployment Metadata. https://www. ndbc.noaa.gov/dart_metadata/dartmeta_public.php. Accessed on: 27 Nov 2018 Tsunami, The Great Waves. International Tsunami Information Center. http://itic.ioc-unesco.org/index.php? option¼com_content&view¼article&id¼1169& Itemid¼1137&lang¼en. Accessed on: 27 Nov 2018

2029

Tungsten Inert Gas Welding (TIG) ▶ Welding Technology

Tungsten Insert Gas (TIG) ▶ Piping Technology

Turbine Installation Vessel (TIV) ▶ Jack-Up Platforms

Turret Mooring ▶ Single-Point Mooring

2D, Two Dimensional ▶ Numerical Simulation of Ice-Going Ships

TTR (Top Tensioned Riser)

TWS Tsunami Warning System

▶ SPAR Platform

▶ Tsunami Warning Buoy

T

U

UFR, Umbilical, Flow Line, and Riser ▶ Moored Ship in Ice

Ultra-short Baseline (USBL) ▶ Integrated Navigation ▶ Long Baseline Underwater Acoustic Location Technology ▶ Ultra-short Baseline Underwater Acoustic Location Technology

ULS – Ultimate Limit States ▶ Design of Renewable Energy Devices

Ultimate Strength ▶ Offshore Structure Design Under Ice Loads

Ultrahigh Molecular Weight Polyethylene (UHMWPE) Fiber Net ▶ Net Structures: Design

Ultra-short Baseline Underwater Acoustic Location Technology Zongyong Tang Yichang Testing Technique Research Institute, Yichang, China

Synonyms BATS (Broadband Acoustic Tracking System); Heading sensor (HS); Inertial navigation system (INS); Long baseline (LBL); Motion Reference Unit (MRU); Short baseline (SBL); Super short baseline (SSBL); Ultra-short baseline (USBL)

Ultrashort Baseline (USBL)

Definition

▶ Autonomous Underwater Vehicle (AUV) ▶ Doppler Velocity Log for Navigation System in Underwater Vehicle

The underwater acoustic positioning system can be divided into long baseline (LBL), short baseline (SBL), and ultra-short baseline (USBL) or

© Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8

2032

Ultra-short Baseline Underwater Acoustic Location Technology

super short baseline (SSBL) systems according to the spacing of the elements. Ultra-short baseline positioning system array length is generally on the order of several centimeters to tens of centimeters, usually less than or equal to half a wavelength, and the phase difference between the received signals of each array element is used to solve the spatial position of the target. All array elements form a sound array, which can be mounted at the bottom of the carrier or suspended from the side of the carrier or installed where fluid noise and structural noise are relatively weak. The ultra-short baseline system has high requirements for the installation of the acoustic array. The installation position of each array element before installation needs to be determined in advance, that is, the position deviation of the array element relative to the carrier coordinate system and the installation deviation angle of the acoustic array need to be known (Philips 2003; Vickery 1998). The ultra-short baseline positioning system has the advantages of convenient installation, flexible use, and low system cost, but the positioning accuracy is weaker than the long baseline. Ultra-short baseline positioning systems usually choose the low-frequency or medium-frequency band. If the ultra-short baseline positioning system needs to cover the whole sea depth range, the low-frequency (8–16 kHz) or lower-frequency band is generally selected. The relationship between the operating frequency and the maximum working distance is shown in the following Table. 1. The ultra-short baseline positioning system has two working modes, one is an acoustic response mode, and the detected target sends an inquiry

signal to each transponder, and the interrogated transponder sends back a response signal according to the received command and passes the inquiry signal, and the time difference between the response signals is used to calculate the distance. The other is the synchronous clock mode. The clock system at both ends of the inquiry and response needs to perform highprecision clock synchronization, and the distance is calculated by the time difference from the timing of the synchronization pulse to the receipt of the response signal.

Positioning Principle Ultra-short baseline arrays have different positioning principles for narrowband and wideband received signals. When the signal transmitted by the target is a narrowband signal, the direction finding is performed by measuring the phase difference between the received signal and the different array elements; when the signal transmitted by the target is a wideband signal, the delay difference between the received signals and the different array elements is measured. Perform direction finding positioning (Han et al. 2015). As shown in Fig. 1, the origin of the coordinate is O; the center of the array is the element 2 at the origin; the element 1 and the element 3 are located on the X and Yaxes, respectively; and the distance from the center of the array is L, Z-axis. The bottom is perpendicular to the XOY plane. Let the coordinates of the target be S(x, y, z), then the following relationship:

Ultra-short Baseline Underwater Acoustic Location Technology, Table 1 Relationship between working frequency band and maximum working distance Serial number 1 2 3 4 5

Band Low frequency (LF) Medium frequency(MF) High frequency(HF) Extremely high frequency(EHF) Very high frequency(VHF)

Operating frequency (kHz) 8~16 18~36 30~60 50~110 200~300

Maximum working distance (m) 10,000 3500 1500 1000 100

Note: It is assumed that the noise level of the shipborne acoustic transducer array is less than 95 dB in the operating band and the underwater sound source level of the underwater transponder is greater than 195 dB re1mPa@1m.

Ultra-short Baseline Underwater Acoustic Location Technology

2033

Ultra-short Baseline Underwater Acoustic Location Technology, Fig. 1 Acoustic array positioning principle

R¼

cos a ¼

x R

cos b ¼

y R

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi x 2 þ y 2 þ z2

where α is the angle between the vector and the X-axis, β is the angle between the vector and the Y-axis, and R is the target and the center of the array. For the projection of S on the XOY plane, its angle θ with the X-axis is the target horizontal azimuth y cos b y ¼ tan 1 ¼ tan 1 x cos a R¼

pffiffiffiffiffiffiffiffiffiffiffiffiffiffi x2 þ y2

z¼

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi R2  r 2

where r is target horizontal slant distance and z is target depth. It is assumed that the size of the array is much smaller than the distance between the target and the array, that is, R  L. At this time, it can be approximated that the target is incident from the far field, and the acoustic wave reaching each element is approximately plane-wave incidence, as shown in Fig. 2.

Ultra-short Baseline Underwater Acoustic Location Technology, Fig. 2 Coaxial two-element incident signal positioning principle

The delay difference between the array elements is satisfied. t¼

L cos a c

where c is the measured sound velocity in the sea area of the operation. When the system uses the signal as a narrowband signal and depends on the phase difference between the measured signal and the receiving array element, the target position is calculated (Sun et al. 2014).

U

2034

Ultra-short Baseline Underwater Acoustic Location Technology

x¼

l’X ct 2pL

y¼

l’y ct 2pL

where jx is the phase difference between two elements on the X-axis; jy is two-element phase difference on the Y-axis; and t is the one-way propagation delay of the acoustic signal from the target to the array. When the system uses the signal as a wideband signal, the target position is calculated by using the delay difference. The actual measured value is the sum and R, which can be obtained by the response time measurement. x¼

ltX R L

y¼

lty R L

where tx is delay difference of signals received by two elements of X-axis tx ¼ cosL a and ty is delay difference of two signals received by Y-axis ty ¼ cosL b.

Application and Development Trends The ultra-short baseline positioning system appeared relatively late, and reports on ultrashort baseline positioning systems were first seen in the early 1980s. After more than 40 years of continuous development, the products of a few influential companies occupy most of the world’s markets, Among the more representative companies are iXblue in France, Kongsberg in Norway, Sonardyne and Nautronix in the United Kingdom, LinkQuest and EdgeTech in the United States. France iXblue company’s advantage field for marine science research, the new generation of ultra-deep long-range ultra-short baseline positioning system POSIDONIA2 maximum positioning depth of up to 7000 m, the maximum positioning slant distance of 8000~10,000 m, and positioning accuracy of 0.2% slant distance,

can be applied to deep-sea target tracking and positioning, such as ROV and AUV, and submarine tubing and cable-laying construction. The medium-range ultra-short baseline positioning system GAPS has a 3D geometric acoustic array that combines positioning with an optical fiber inertial navigation system (INS) to provide no less than 500 acoustic channels. Recently, the underwater acoustic communication function has been added to the system. In the depth roadmap mode, it can form an LBL/USBL/INS integrated navigation system together with a long baseline. The Norwegian Kongsberg company has been engaged in the research and development of acoustic positioning systems. Its products have been applied in the field of dynamic positioning and submersible docking. The HiPAP series of ultra-short baseline positioning products have been developed. From 1996 to 2015, three generations of products were launched. HiPAP502/452/ 352/102 is a third-generation product that uses the same hardware and software platform and has a long baseline position function. The new communication and positioning acoustic protocol Cymbal is used in the product, and the positioning accuracy is further improved. The mPAP series is a compact ultra-short baseline positioning system that can be operated on the surface carrier, with a built-in motion sensor and inertial navigation system. It is used for positioning requirements of ROV, tow body, diver, and other targets within 1000~4000 m underwater. The accuracy is 0.45% slant distance. The UK’s Sonardyne company’s strengths are offshore oil and gas development. In 2005, it successfully launched WideBand’s full range of ultra-short baseline products based on broadband digital technology. In 2010, it launched the second generation of ultra-short baseline products of 6G broadband digital technology. The main products are Mini-Ranger2, Ranger2, and Scout. The Mini-Ranger2 is a compact and portable product that can be combined with WSM6+, WRT6, and WM6 transponders. With a working range of up to 10,000 m and an accuracy of 0.1% slant distance, Ranger2 uses the unique multi-pulse stack technology to achieve data update rates of up to 1 s in any water depth

Umbilical Cable

environment, supporting long baseline/ultrashort baseline combined positioning and inertial navigation. The Scout series includes Scout, ScoutPlus, and ScoutPro, which can be used for small target positioning such as ROV and tow body in the range of 500–1000 m. Nautronix products dominate the offshore drilling and mining industry. Its NASDrill-USBL is developed for use in near-shore drilling and other environments that require high noise and harsh environments. The system has a range of 4,500 m and an accuracy of 0.5% slant distance. In 2002, LinkQuest of the United States launched the first diving ultra-short baseline positioning system TrackLink 1500, which quickly became a bestseller. The TrackLink 10,000 series developed in recent years belongs to the lowfrequency remote ultra-short baseline positioning system. Based on its unique acoustic broadband spread spectrum technology, it can provide users with ultra-long-range deep-water communication and tracking and positioning solutions. EdgeTech, formerly known as ORE Marine, and ORE Marine products are TrackPoint II, TrackPoint 3, and TrackPoint 3P. EdgeTech has introduced the long-range ultra-short baseline positioning system BATS. The system is available in three configurations, portable BATS (Broadband Acoustic Tracking System), desktop BTAS, and installation. BATS can be combined with Motion Reference Unit (MRU) and heading sensor (HS) (Jin et al. 2018). With the continuous improvement of marine survey and marine engineering requirements, ultra-short baseline positioning technology has gradually shifted from single positioning mode to integrated positioning mode, such as LBL/USBL, SBL/SUBL, and LBL/SBL/USBL systems; from acoustic positioning to acoustics positioning integrated inertial navigation positioning, Motion Reference Unit; signal system from narrowband to wideband; positioning for a small number of users to provide multi-target targets in the work area; and from single positioning function to multifunctional integration, such as integrated underwater acoustic communication; positioning accuracy is developed from the initial tens of meters to the meter.

2035

References Han YF, Zheng CE, Li Z, Sun DJ (2015) An precision evaluation method of USBL positioning systems based on LBL triangulation. Acta Phys Sin 64(9):94301,1–94301,7 Jin B, Xu X, Zhang T, Sun X (2018) USBL technology and its application in ocean engineering. Navig Position Timing 04:8–20 Philips D (2003) An evaluation of USBL and SBL acoustic systems and the optimisation of methods of calibrationpart 1. Hydrogr J 108:180–125 Sun D, Zheng C, Yeng J, Wu Y (2014) Initial study on the precision evaluation for ultra-short baseline positioning system. In: 2014 Oceans-St. John’s. IEEE, pp 1–7 Vickery K (1998) Acoustic positioning systems. A practical overview of current systems. In: Proceedings of the 1998 workshop on autonomous underwater vehicles (Cat. No. 98CH36290). IEEE, pp 5–17

Ultra-violet (UV) ▶ Fiber Optic Hydrophone

Umbilical Cable Jun Yan1, Zhixun Yang2, Hong Guo3, Xipeng Ying4 and Haitao Hu4 1 State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian, China 2 College of Mechanical and Electrical, Harbin Engineering University, Harbin, China 3 China National Offshore Oil Corporation, Beijing, China 4 Department of Engineering Mechanics, Dalian University of Technology, Dalian, China

Synonyms Armor layer; Electric cable; Filler and wrap; Hydraulic pipe; Metallic tubes; Optical fiber; Sheath; Subsea production systems; Thermoplastic hoses

U

2036

Definition In general, umbilical cable is a kind of integrated functional structure, whose structure is similar to a baby’s helically wound umbilical cord which is widely used in aerospace field (such as between the launch pad and the vehicle or between the space suit and the vehicle), diving (such as the umbilical cable that supplies oxygen for diving suits), and ocean engineering (such as applications to ROV underwater robot and subsea production systems). The purpose of this entry focuses on the umbilical cable which is used in the subsea production systems (Drumond et al. 2018). Subsea production system is widely used in the development of subsea petroleum, petrochemical, and natural gas industries. In general, subsea wellhead, subsea production facilities, and subsea pipeline partly or fully transmit the extracted petroleum, petrochemical, natural gas, and water to the marine-dependent facilities or endtermination interfaces, which realized the development of offshore petroleum, petrochemical, and natural gas industries. The typical subsea production system can be divided as follows: subsea well system (including wellhead and Christmas tree), production system (including manifolds, template, and protective structure), and subsea pipe system (including chemical injection pipeline, subsea umbilical cable, and riser). Compared to other ways, the subsea production system is more suitable for developing deep water, marginal petroleum, and natural gas fields for the reason that it has a huge advantage. Since subsea umbilical cable is one of the main equipments of the subsea production systems, it plays a very important role to keep the operation safe. In another word, it is an indispensable component in subsea production systems, as a lifeline between surface facilities and subsea production systems (Yue et al. 2013). The function of umbilical cables connecting upper floater and subsea production systems is to transmit power, hydraulic power, control and feedback signals, and chemical between them. Power, hydraulic power, and chemical are usually transmitted from top to bottom in one

Umbilical Cable

direction. The control and feedback signals are two-way transmissions (Kliewer 2013). The control signals are usually transmitted from top to bottom, while the feedback signals are usually transmitted from bottom to top, including all kinds of sensor signals and action status. In addition, storage and operation can be performed at specific temperatures within the service life range. Normally, the operation of the umbilical cable is resulted from the joint integration of the above functions and the operation of each component contributes to.

Scientific Fundamentals Structure Composition The structures of subsea umbilical cables are various, which are determined by different environments and functions together. In most cases, there is no existence of unified standard or style. In general, the components of umbilical cables can be classified into two categories: One is the functional components, including the electrical cables, optical fibers, thermoplastic hoses, metallic tubes, and polymeric sheath (Hardee 2010). Another one is the strengthening components, including the carbon fiber rod, armor steel wires, and fillers. Thereinto, electric cable component is mainly used for the transmission of power and control. In addition to electrical communication, it can also be used for signal transmission. Optical fiber component is mainly used to transmit all kinds of signals, which is also used to monitor the status information of the umbilical cable under special circumstances. Pipe component contains different kinds of pipelines, such as steel pipes and hoses, which is used to transmit hydraulic fluid, chemical, petroleum, and natural gas. Filler is used to fill the void and fix the relative position of each component of the umbilical cable (Tang et al. 2014). Armor layer is usually placed outside the umbilical cable, whose function is to improve the axial stiffness and strength of the umbilical and enhance the stability of the subsea umbilical cable with more weight per length. Polymeric sheath is usually wrapped outside electric cables, optical fibers, and other types of pipelines.

Umbilical Cable

2037

Umbilical Cable, Fig. 1 The structure of umbilical cable

Umbilical Cable, Fig. 2 The threedimensional structure of umbilical cable

The function of sheath is to insulate and protect the umbilical cable (Lu et al. 2017) (Figs. 1 and 2). Electric Cable

Electric cable is made up of conductor, insulation, and sheath, and sometimes there is also armor and shield included. Electric cable includes power cable and signal cable. Insulation layer provides dielectric strength and electrical insulation (Beaudonnet et al. 2013). Electric cable component is covered with sheath, which protects the cable component, makes the cable round, and adjusts the size and weight. Shield layer mainly has the function of shielding the magnetic field, while the armor mainly plays the role of enhancement (Yang et al. 2015). Hydraulic Pipe

As a result of different functions of the umbilical cables, hydraulic pipe has different structures, sizes, numbers, and positions. The subsea umbilical cables with steel pipe components are usually used in deepwater ocean due to the much stronger resistance to internal and external pressure

compared with the thermoplastic hoses (Chitwood 2006). Most steel pipes are covered with plastic layers, which can prevent cushion and wear between steel pipes and other components or steel pipes. Optical Fiber

Optical fiber is the most important carrier of communication transmission. There are one or more optical fiber components in the umbilical cable. In general, optical fiber cores are no more than 12 cores. The fiber is suspended in a thixotropic ointment, which can prevent water, keep the fiber position stable, and protect the fiber to the maximum extent at the same time. The stability of light attenuation is maintained in various mechanical and environmental conditions (Williams et al. 2002). The fiber protection tubes are usually high-strength stainless steel tubes with high resistance to lateral pressure and corrosion, while the steel pipe is surrounded by one to two layers of steel wire which is used to enhance the tensile strength of optical fiber cable. The optical fiber cable is covered with sheath, which protects the

U

2038

fiber cable, making the cable round, adjusting the size and weight, and preventing corrosion and cushion.

Umbilical Cable

it is suitable for high mechanical external force (Lu et al. 2017). Filler and Wrap

Sheath

Sheath can be classified into the inner sheath and the outer sheath. The function of the inner sheath is to make the cables round, provide mechanical buffering, reduce friction and anticorrosion, and keep the structure of the umbilical stable. The outer sheath is the last line of defense of the umbilical. In addition to the likeness of the influences of the inner sheath, the outer sheath also has high anticorrosion performance, UV, and seawater resistance. In some umbilical cables, the outer sheath also has the resistance to mold and marine life (Dupont et al. 2002). Armor Layer

Different armor types can be chosen armor according to different uses, environments, and working conditions of the umbilical cables, such as single round steel wire, double (quadruple) round steel wire, and double (quadruple) flat steel wire. Steel wire mainly plays the role of enhancement, providing the ability of tensile, anti-torsion, and anti-pressure for the umbilical cables. At the same time, steel wire also plays a shielding role, which is mainly to shield the magnetic field. Single round steel wire is seldom used, which is mainly used in shallow sea or river where the tension is not high. The advantage of this armored method is the lightness and softness, while the disadvantage is that the tensile strength and resistance are poor. When pulled, the torsion will appear. Different from armored method, the winding direction of the double wire layer is opposite in double (quadruple) round steel wire, so it can keep the torsion balance. Compared with double (quadruple) round steel wire, double (quadruple) flat steel wire has its advantage of reducing the outer diameter of cable and increasing the tensile resistance of umbilical cables. The disadvantage of it is that the cable is so hard that the bending performance is poor. So, we can further combine flat steel wire and round steel wire, which has the advantage of high tensile strength and resistance. Even though the weight is heavier,

The roles of filler are mainly reflected in the following aspects. Firstly, the filler makes the umbilical cable round, which is convenient for the latter process and which is helpful for external strengthening of components. Secondly, the filler improves the tensile strength of the umbilical cable and reduces the friction between the functional components and the layers. Thirdly, the filler can improve the stability of the structure of the umbilical cable and can be used for water resistance material and can be wrapped around the block. Classification In general, umbilical cables contain different component types and specific numbers, according to the actual demand of petroleum and natural gas field engineering, the existing facilities and reserved equipment, and users’ requirements. Therefore, it can be concluded that umbilical cable is a typical custom product (SoDahl and Ottesen 2011). According to the difference between the umbilical cables with pipe component, it can be classified into the umbilical cable with steel tubes and with hoses. According to whether the armor layer is included, it can be divided into the umbilical cable with armor layer and without armor layer. According to the different armor materials, it can be divided into metal armor and nonmetal armor umbilical. According to the application condition of umbilical cables, it can be divided into static and dynamic umbilical cables. There are four common types of umbilical cables as the following: Single Armor Layer Umbilical Cable with Electric Cable, Optical Fiber, Hydraulic Fluid, and Steel Tube

This type of umbilical cable is capable of transmitting power, control, communication, optical communication, hydraulic power, and chemical simultaneously. And the armor layer is made up of round steel wire (Pesce et al. 2010). There is an

Umbilical Cable

inner sheath and outer sheath inside and outside the armor layer, which is suitable for the subsea production systems with electrohydraulic compound control method. Double Armor Layer Umbilical Cable with Electric Cable, Optical Fiber, Hydraulic Fluid, and Steel Tube

The function of this type of umbilical cable is the same as the single armor layer one. What makes a difference is that there are two layers of flat steel wire in this type of cable with only one outer sheath and lining inside. It is also suitable for the subsea production systems with electrohydraulic compound control method. Electrohydraulic Compound Umbilical Cable with Hose

This type of umbilical cable is armored by five layers of round steel wire. The armor can withstand tensile load, increase subsea stability, and protect the internal structure of the umbilical. It is suitable for the subsea production systems with electrohydraulic compound control method. Due to the permeability and self-expansion of the hose, it is suitable for short control distance and low hydraulic requirement particularly. Electrohydraulic Compound Umbilical Cable with Steel Tube

This type of umbilical cable is suitable for the subsea production systems with electrohydraulic compound control method, which is similar to the one with hose. What is different is that this umbilical cable is composed of hose or tube (Zhu et al. 2015). Property of Umbilical Cable Functional Performance

As is mentioned above, the umbilical cables are for the operation demand to meet the corresponding function. Therefore, there is a demand of design indicators in the process according to each function in the production systems. Its design indicators correspond to the functional components (electric cable, optical cable, and hydraulic pipelines). The performances of electric cable and optical cable can be explained

2039

in detail by referring to corresponding entries (Witz and Tan 1995). And the performances of hydraulic pipelines are permeability, corrosion resistance, volume expansion, compatibility, and clean ability. Mechanical Property of Umbilical Cable

In addition to meeting the above executive functional indicators, the strengthening design of umbilical cable needs to consider the corresponding mechanical safety guarantee to ensure the normal operation of other functional components. The mechanical properties of umbilical cables are as follows: 1. Stiffness Structural stiffness is called stiffness for short, which has the ability of structure or component to resist deformation. As an important part of the submarine production system, umbilical cable has undertaken various external static and dynamic loads in the marine environment, such as gravity load, wind load, current load, and wave load. These loads on the umbilical cable are as forces or moments (Custódio and Vaz 2002). The transportation and operation of umbilical cable depend on the stiffness of the umbilical itself. Therefore, the stiffness of umbilical cable is a quite important mechanical property which is the key to determine whether the cable can work safely in subsea production system. The main stiffness indexes of umbilical cable are tensile stiffness, torsional stiffness, and bending stiffness. The axial tension and torque are coupled, due to the helical structure in umbilical cable. When there is axial displacement, axial elongation and torsion can occur simultaneously. The relationship between the force and displacement is shown as follows: 

F Mt





k11 ¼ k21

2 3  DL k12 6 L 7 4 5 D; k22 L

ð1Þ

In the formula, F represents the axial tension, Mt represents the torque, ΔL represents the

U

2040

axial elongation, Δ; represents the torsion angle, and L represents the length of umbilical. k11, k22 are tensile and torsional stiffness. k12, k21 are interaction stiffness. In particular, balance of torsion should be considered during installation to avoid damage because of torsion knotting or torsion accumulation (Skeie et al. 2012). Umbilical cables have complex structures which are made up of multiple layers of materials and formed by cross-wound laying of different angle components. Due to the unbonded mode of each structural layer of umbilical cable, there will be relative sliding between each structural layer and a lot of contact interface and interface friction with the increase of the curvature while it bends. And the bending deformations are also inconsistent for different types of umbilical cables. Umbilical cable is usually in the full sliding state in practical engineering application. Therefore, in general, bending stiffness is estimated with complete sliding models. The greater the angle of armor winding is, the smaller the bending stiffness of umbilical cables is, the better the performance of flexible bending is. 2. Strength Strength is the ability of a structure or component to resist damage. Being similar to the stiffness of umbilical cables, strength is another important mechanical performance. In general, hoop stress, radial stress, and axial stress are included in the stress of typical umbilical cables. The total load capacity of umbilical cable is determined by the ultimate stress state of most vulnerable components. Hoop stress, radial stress, and axial stress are usually combined by the strength yield criterion so as to check whether the stress satisfies the yield strength of the materials. The main strength properties of umbilical cable include maximum tensile capacity and minimum bend radius. Maximum tensile capacity is the failure criterion of umbilical structure with the strain failure of different

Umbilical Cable

components (such as steel tube, armor, polymer, and so on). When the maximum tensile capacity of each component is given, the minimum value of these components is taken as the maximum tensile capacity of the umbilical, which should be greater than the extreme tensile load in the application environment. It is important to ensure adequate safety margin at all operation conditions so as to ensure the normal and safe operation of the umbilical cable. In addition, buckling failure, plastic failure, and functional failure of umbilical cable will be caused by excessive bending during the storage and working operation. Therefore, minimum bend radius is also a key property for the umbilical cable design. 3. Fatigue life During the working operation of umbilical cables, alternating tension and bending load can be generated as a result of the wave and current. As a result, the armor and steel tube are damaged by the fatigue failure. Fatigue is one of the most common failure modes for dynamic umbilical cables, which directly determines the service life of umbilical cable. Therefore, the estimation of fatigue life of umbilical cable is the most important property in the whole design process. Ancillary Equipment In addition to the main equipments, some ancillary equipments of umbilical are needed to ensure that the umbilical cable works normally in subsea production systems. It can be classified as ancillary equipments for connecting and for strengthening. The ancillary equipments for connecting are used to connect the cable and the upper floating body or the underwater development device and to provide functional protection, which include surface umbilical termination, pull-in head, suspension device, J-tube or I-tube seals, subsea umbilical termination, connection box, and weak link. The ancillary equipments for strengthening are used to maintain the overall layout of the umbilical cable and to provide mechanical protection for the joint, including bend stiffeners, bend

Umbilical Cable

2041

restrictors, and buoyancy attachments (Tang et al. 2014).

Southeast Asia and Oceania, mainly in Indonesia and Australia.

Key Applications

Cross-References

Umbilical cable is one of the main equipments of the floating production systems. As a lifeline between surface facilities and subsea production systems, it is a key component of the subsea control systems. Generally, umbilical cable is composed of electrical cable, optical fiber, thermoplastic hose and metallic tube, transmitting hydraulic, power, control signal, chemical, and so on. So far, it is widely used for the development of subsea oil and natural gas during the whole production process in shallow water, deep water, and ultra-deep water (Witz and Tan 1992). The application of subsea umbilical cable has a history of nearly 60 years in ocean engineering. It was in the 1960s that the earliest umbilical cable appeared in a subsea wellhead in Mexico by Shell. In the 1970s, there is a system which is called electrohydraulic compound control system appeared, making it possible to reduce the cross-sectional area of subsea umbilical cable greatly. In addition to subsea hoses, it also includes power cables and data transmission lines. The early subsea umbilical cable was made of thermoplastic hoses until Sandvik used metallic tubes instead of thermoplastic hoses firstly in the 1980s, which was used in Frigg petroleum and natural gas field in northeast Norway successfully. In the twenty-first century, the demand for power increased in the subsea production systems, as the depth increased. Nexans began to develop and produce the world’s first umbilical cable with a high voltage cable (24 V) for BP in 2005. Since then, in subsea deepwater petroleum as well as natural gas fields, the subsea umbilical cable which is characterized with high voltage has been widely used (Fleming et al. 2005). Presently, about 60% of subsea umbilical cables are used in the Atlantic region, mainly in Mexico, Brazil, Norway, and Angola. And about 30% of subsea umbilical cables are used in

▶ Armor Layer ▶ Electric Cable ▶ Filler and Wrap ▶ Hydraulic Pipe ▶ Metallic Tubes ▶ Sheath ▶ Subsea Production Systems ▶ Thermoplastic Hoses

References Beaudonnet G, Chilloux D, Rivière L, Delaëter G (2013) Subsea stations could reduce cost, loads of longdistance umbilicals. Offshore Chitwood JE, Vail WB Iii, Skerl DS, Dekle RL, Crossland WG (2006) High power umbilicals for electric flowline immersion heating of produced hydrocarbons. US. 2008/0149343 A1 Custódio AB, Vaz MA (2002) A nonlinear formulation for the axisymmetric response of umbilical cables and flexible pipes. Appl Ocean Res 24(1):21–29 Drumond GP, Pasqualino IP, Pinheiro BC, Estefen SF (2018) Pipelines, risers and umbilicals failures: a literature review. Ocean Eng 148:412–425 Dupont W, Rinehart R, Mcmanus J (2002) Dynamic umbilicals with internal steel rods. US Patent 6,472,614 B1 Fleming R, Moros T, Ghosh R, Lambrakos K, Robson D (2005) Global configuration design of umbilicals in deepwater. In: ASME international conference on offshore mechanical Hardee C (2010) Longer life top deepwater umbilicals. Offshore Kliewer G (2013) ExxonMobil deepwater umbilicals for Erha North. Offshore Lu Q, Yang Z, Yan J, Yue Q (2014) Design of crosssectional layout of steel tube umbilical. J Offshore Mech Arct Eng 136(4):041401 (7 pages) Lu Q, Yang Z, Yan J, Lu H, Chen J, Yue Q (2017) A finite element model for prediction of the bending stress of umbilicals. J Offshore Mech Arct Eng 139(6):061302 (8 pages) Pesce CP, Ramos R, Silveira LMYD, Tanaka RL, Martins CDA (2010) Structural behavior of umbilicals: part I – mathematical modeling. In: ASME international conference on ocean Qingzhen L, Yuanchao Y, Zhixun Y, Jinlong C, Jun Y, Qianjin Y (2017) Fatigue life prediction of umbilicals

U

2042 considering non-linear stress. Polish Marit Res 24:154– 163 Skeie G, Sødahl N, Steinkjer O, Larsen CM (2012) Efficient fatigue analysis of helix elements in umbilicals and flexible risers: theory and applications. J Appl Math 2012:Article ID 246812, 22 pages SoDahl N, Ottesen T (2011) Bend stiffener design for umbilicals. In: ASME international conference on ocean Tang M, Yan J, Yue Q (2014) Tensile stiffness analysis on ocean dynamic power umbilical. China Ocean Eng 28(2):259–270 Williams MR, Johansen JA, Ross CA, Wendt DE, Joan SA (2002) Shearing arrangement for subsea umbilicals. US. 6,397,948 B1 Witz JA, Tan Z (1992) On the axial-torsional structural behaviour of flexible pipes, umbilicals and marine cables. Mar Struct 5(2–3):205–227 Witz JA, Tan Z (1995) Rotary bending of marine cables and umbilicals. Eng Struct 17(4):267–275 Yang Z, Yan J, Lu Q, Chen J, Yue Q (2015) Multidisciplinary optimization design for the section layout of umbilicals based on intelligent algorithm. J Offshore Mech Arct Eng 140(3):031702 (12 pages) Yue Q, Lu Q, Yan J, Zheng J, Palmer A (2013) Tension behavior prediction of flexible pipelines in shallow water. Ocean Eng Zhu J, Beckers P, Dahan M, Yan J, Jiang C (2015) Shape and topology optimization for complicated engineering structures. Math Probl Eng 2015:Article ID 723897, 2 pages

Umbilical Termination Assembly (UTA) ▶ Decommissioning of Offshore Oil and Gas Installations

UN Convention on the Law of the Sea (UNCLoS) ▶ Decommissioning of Offshore Oil and Gas Installations

Uncertainty Theory ▶ Reliability-Based Design (RBD)

Umbilical Termination Assembly (UTA)

Underwater Acoustic ▶ Underwater Acoustic Sensor Network

Underwater Acoustic (UWA) ▶ Underwater Acoustic Communication

Underwater Acoustic Channel ▶ Underwater Acoustic Sensor Network

Underwater Acoustic Communication Lu Ma2, Gang Qiao2 and Jianmin Yang1,2 1 School of Marine Engineering and Technology, Sun Yat-sen University, Guangzhou, China 2 College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin, China

Synonyms Analog-to-digital (A/D); Digital-to-analog (D/A); Frequency shift keying (FSK); Intersymbol interference (ISI); Layered space-time codes (LSTC); Low earth orbiting (LEO); Low-density parity check (LDPC); Maximum likelihood sequence detection (MLSD); Maximum likelihood sequence estimation (MLSE); Multiple input multiple output (MIMO); Orthogonal frequency division multiplexing (OFDM); Phase shift keying (PSK); Quadrature amplitude modulation (QAM); Signal-to-noise ratio (SNR); Singleinput single-output (SISO); Space-time trellis codes (STTC); Spatial modulation (SM); Trelliscoded modulation (TCM); Underwater acoustic (UWA); Underwater wireless acoustic communication

Underwater Acoustic Communication

Definition Underwater acoustic (UWA) communication is a technique for sending and receiving messages by sound in water. As electromagnetic waves propagate poorly in sea water, acoustics provide the most obvious medium to enable underwater communications. UWA communication is difficult due to limited bandwidth, extended multi-path, refractive properties of the medium, severe fading, rapid time variation, and large Doppler shifts. Compared to terrestrial communication, UWA communication has much lower data rates and shorter communication range.

Scientific Fundamentals Basic System Model A typical UWA communication system for the transmitter and receiver in the presence of UWA channels is shown in Fig. 1. Since acoustic signals have low frequency, the passband samples are often directly generated by the modulation module (Zhou and Wang 2014). After digital-toanalog (D/A) conversion, the passband signal is amplified, passed to matching circuits, and matched to the transducer. At the receiver side, the weak signal is increased in level by a preamplifier, filtered by a simple bandpass filter, and sampled at the passband. Finally, the bit information can be achieved by the demodulation module. From the signal processing point of view, the channel includes the imperfections of the transmitter and receiving circuits. All the modules that are lumped together are called channel

2043

between the D/A module and analog-to-digital (A/D) module. UWA Communication Channels UWA communication channels are generally recognized as one of the most difficult communication media in use today (Stojanovic and Preisig 2009). Acoustic propagation is best supported at low frequencies, and the bandwidth available for communication is extremely limited. Although the total communication bandwidth is very low, the system is, in fact, wideband, in the sense that bandwidth is not negligible with respect to the center frequency. Sound propagates in the water at a very low speed of approximately 1500 m/s, and propagation occurs over multiple paths. Delay spreading over tens or even hundreds of milliseconds results in frequency-selective signal distortion, while motion creates an extreme Doppler effect. All of these factors are the key problems to be solved in UWA communication. Next, we will introduce UWA communication channels from four aspects. Attenuation and Noise

A distinguishing property of acoustic channels is the fact that path loss depends on the signal frequency. This dependence is a consequence of absorption (i.e., transfer of acoustic energy into heat). In addition to the absorption loss, the signal experiences a spreading loss, which increases with distance. The overall path loss is given by Aðl, f Þ ¼ ðl=lr Þk að f Þllr , where f is the signal frequency and l is the transmission distance, taken in reference to some lr.

U

Underwater Acoustic Communication, Fig. 1 UWA communication system

2044

Underwater Acoustic Communication

The path loss exponent k models the spreading loss, and its usual values are between 1 and 2 (for cylindrical and spherical spreading, respectively). The absorption coefficient is a(f ), which can be obtained using empirical formula (Berkhovskikh and Lysanov 1982). Noise in an acoustic channel consists of ambient noise and site-specific noise. Ambient noise is always present in the background of the quiet deep sea. Site-specific noise, on the contrary, exists only in certain places. For example, ice cracking in polar regions creates acoustic noise as do snapping shrimp in warmer waters. The ambient noise comes from sources such as turbulence, breaking waves, rain, and distant shipping. While this noise is often approximated as Gaussian, it is not white. Unlike ambient noise, sitespecific noise often contains significant nonGaussian components. The attenuation, which grows with frequency, and the noise, whose spectrum decays with frequency, result in a signal-to-noise ratio (SNR) that varies over the signal bandwidth. If one defines a narrow band of frequencies of width Δf around some frequency f, the SNR in this band can be expressed as SNRðl, f Þ ¼ Sl ð f Þ=Aðl, f ÞN ð f Þ, where Sl( f ) is the power spectral density of the transmitted signal. For any given distance, the narrowband SNR is thus a function of frequency. Another important observation to be made is that the acoustic bandwidth is often on the order of the center frequency fc. This fact bears significant implications for the design of signal processing methods, as it prevents one from making the narrowband assumption (B  fc) on which many radio communication principles are based. Respecting the wideband nature of the system is particularly important in multichannel (array) processing and synchronization for mobile acoustic systems. All in all, the fact that the available bandwidth depending on the distance has important implications for the design of UWA networks. Specifically, it makes a strong case for multihopping, since dividing the total distance between a source

and destination into multiple hops enables transmission at a higher bit rate over each (shorter) hop. The same fact helps to offset the delay penalty involved in relaying. Since multihopping also ensures lower total power consumption, its benefits are doubled from the viewpoint of energy-perbit consumption on an acoustic channel. Multipath

Multipath formation in the ocean is governed by two effects: sound reflection at the surface, bottom, and any objects and sound refraction in the water. The latter is a consequence of the spatial variability of sound speed. Sound speed depends on the temperature, salinity, and pressure, which vary with depth and location; and a ray of sound always bends toward the region of lower propagation speed, obeying Snell’s law. Near the surface, both the temperature and pressure are usually constant, as is the sound speed. In temperate climates, the temperature decreases as depth begin to increase, while the pressure increase is not enough to offset the effect on the sound speed. The sound speed thus decreases in the region called the main thermocline. After some depth, the temperature reaches a constant level of 4  C, and from there on, the sound speed increases depth (pressure). When a source launches a beam of rays, each ray will follow a slightly different path, and a receiver placed at some distance will observe multiple signal arrivals. Note that a ray traveling over a longer path may do so at a higher speed, thus reaching the receiver before a direct stronger ray. This phenomenon results in a non-minimum phase channel response. The impulse response of an acoustic channel is influenced by the geometry of the channel and its reflection and refraction properties, which determine the number of significant propagation paths, and their relative strengths and delays. Strictly speaking, there are infinitely many signal echoes, but those that have undergone multiple reflections and lost much of the energy can be discarded, leaving only a finite number of significant paths. To put a channel model in perspective, let us denote by lp the length of the pth propagation path, with p ¼ 0 corresponding to the first arrival. In shallow water, where sound speed can be taken

Underwater Acoustic Communication

as a constant c, path lengths can be calculated using plane geometry, and path delays can be obtained as tp ¼ lp/c. The surface reflection coefficient equals 1 under ideal conditions, while bottom reflection coefficients depend on the type of bottom (hard, soft) and grazing angle (Jensen et al. 1994). If we denote by Γp the cumulative reflection coefficient along the pth propagation path, and by A(lp, f ) the propagation loss associated with this path, then Gp H p ð f Þ ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi   A lp , f represents the frequency response of the pth path. Hence, each path of an acoustic channel acts as a low-pass filter, which contributes to the overall impulse response, X   hð t Þ ¼ hp t  t p , p

where hp(t) is the inverse Fourier transform of Hp( f ). Time Variability

There are two sources of the channel’s time variability: inherent changes in the propagation medium and those that occur because of the transmitter/receiver motion. Inherent changes range from those that occur on very long timescales that do not affect the instantaneous level of a communication signal (e.g., monthly changes in temperature) to those that occur on short timescales and affect the signal. Prominent among the latter are changes induced by surface waves, which effectively cause the displacement of the reflection point, resulting in both scattering of the signal and Doppler spreading due to the changing path length. It is beyond the scope of the present treatment to summarize what is known about the statistical characterization of these apparently random changes in the channel response. Suffice it to say that unlike in a radio channel, where a number of models for both the probability distribution (e.g., Rayleigh fading) and the power spectral density of

2045

the fading process (e.g., the Jakes’ model) are well accepted and even standardized, there is no consensus on statistical characterization of acoustic communication channels. Experimental results suggest that some channels may just as well be characterized as deterministic, while others seem to exhibit Rice or Rayleigh fading (Chitre 2007). However, current research indicates K-distributed fading in other environments (Yang and Yang 2006). Channel coherence times below 100 ms have been observed (Preisig 2007) but not often. For a general-purpose design, one may consider coherence times on the order of hundreds of milliseconds. In the absence of good statistical models for simulation, experimental demonstration of candidate communication schemes remains a de facto standard. The Doppler Effect

The motion of the transmitter or receiver contributes additionally to the changes in channel response. This occurs through the Doppler effect, which causes frequency shifting as well as additional frequency spreading. The magnitude of the Doppler effect is proportional to the ratio a ¼ v/c of the relative transmitter-receiver velocity to the speed of sound. Because the speed of sound is very low compared to the speed of electromagnetic waves, motion-induced Doppler distortion of an acoustic signal can be extreme. Autonomous underwater vehicles (AUVs) move at speeds on the order of a few meters per second, but even without intentional motion, underwater instruments are subject to drifting with waves, currents, and tides, which may occur at comparable velocities. In other words, there is always some motion present in the system, and a communication system has to be designed taking this fact into account. The only comparable situation in radio communications occurs in low Earth orbiting (LEO) satellite systems, where the relative velocity of satellites flying overhead is extremely high (the channel there, however, is not nearly as dispersive). The major implication of motioninduced distortion is on the design of synchronization and channel estimation algorithms. The way in which these distortions affect signal detection depends on the actual value of factor

U

2046

a. For comparison, let us look at a highly mobile radio system. At 160 km/h (100 mph), we have a ¼ 1.5  107. This value is low enough that Doppler spreading can be neglected. In other words, there is no need to account for it explicitly in symbol synchronization. The error made in doing so is only 1/1000 of a bit per 10,000 bits. In contrast to this situation, a stationary acoustic system may experience unintentional motion at 0.5 m/s (1 knot), which would account for a ¼ 3  104. For an AUV moving at several meters per second (submarines can move at much greater velocities), factor a will be on the order of 103, a value that cannot be ignored. Non-negligible motion-induced Doppler shifting and spreading thus emerge as another major factor that distinguishes an acoustic channel from the mobile radio channel and dictates the need for explicit phase and delay synchronization in all but stationary systems. In multi-carrier systems, the Doppler effect creates particularly severe distortion. Unlike radio systems, in which time compression/dilation is negligible and the Doppler shift appears equal for all subcarriers, in an acoustic system each subcarrier may experience a markedly different Doppler shift, creating non-uniform Doppler distortion across the signal bandwidth. Modulation Schemes Incoherent Modulation

Most early UWA communications systems used incoherent modulation methods for reasons of simplicity and reliability (Chitre et al. 2008), such as binary frequency-shift keying (2FSK), whose modulation process is presented in Fig. 2. Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. However, there were a number of exceptions, in particular systems that were used in channels with little boundary action, for example, vertical links in deep water. Vertical links using directional transducers on unmanned underwater vehicles (UUVs) and ships are very clean, experiencing little or no delay spread, with the result that the biggest challenge is tracking the carrier phase that changes with respect to range.

Underwater Acoustic Communication

Underwater Acoustic Communication, Fig. 2 Incoherent modulation (2FSK)

Underwater Acoustic Communication, Fig. 3 Coherent modulation (2PSK)

Coherent Modulation

A typical coherent modulation process (binary phase-shift keying, 2PSK) is shown in Fig. 3. Binary phase-shift keying (2PSK) is a digital modulation process that conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). Through the 1980s phase, coherent communication was used almost exclusively for deep water vertical links, but in the early 1990s phase, coherent communication in multipath channels began to attract attention, as incoherent methods were limited to a bandwidth efficiency of approximately 0.5 bits per Hz. Single Carrier Modulation

One major step toward high rate communication is single carrier modulation of information symbols from constellations such as phase-shift keying (PSK) and quadrature amplitude

Underwater Acoustic Communication

2047

modulation (QAM), whose block diagram is shown in Fig. 4 (Zhou and Wang 2014). With symbols s[i] and pulse shaping filter p(t), the transmitted signal is xð t Þ ¼

1 X

s½ipðt  iT Þ,

i¼1

where T is the symbol period. The corresponding passband signal can be obtained by  xeðtÞ ¼ 2 Re xðtÞe

j2p f c t



:

The channel introduces intersymbol interference (ISI) due to multipath propagation. When data symbols are transmitted at a high rate, the same physical channel leads to more channel taps in the discrete-time equivalent model. Advanced signal processing at the receiver side is used to suppress the interference; this process is termed channel equalization. Although widely used for slowly-varying multipath channels in radio applications, channel equalization for fast-varying UWA channel is a significant challenge. Multi-carrier Modulation

Multi-carrier modulation offers an alternative to a broadband single carrier communication. By dividing the available bandwidth into a number of narrower bands, orthogonal frequency-division multiplexing (OFDM) systems can perform equalization in the frequency domain and eliminate the need for complex time-domain

Underwater Acoustic Communication, Fig. 4 Single carrier modulation

equalizers. The OFDM modulation process is described in Fig. 5. OFDM modulation and demodulation can easily be accomplished using fast Fourier transforms (FFT). A shallow water experiment in the Mediterranean Sea yielded good OFDM performance (BER < 2  103) at ranges by to 6 km (Frassati et al. 2005). At the same ranges, the DSSS performance was found to be significantly poorer. OFDM systems often use a guard period (often implemented as a cyclic prefix or zero prefix) between consecutive OFDM symbols to avoid ISI. When the delay spread is long, the prefix length can significantly affect the bandwidth efficiency. Maximum likelihood sequence detection (MLSD) on individual subcarriers using a low complexity PSP can combat ISI when the symbol period is smaller than the delay spread (Morozov and Preisig 2006). Other channel shortening techniques such as sPRE may also be used in future OFDM systems to reduce the prefix length and improve bandwidth efficiency. When using coded OFDM, consecutive symbols are often striped across subcarriers to reduce the error correlation due to fading. However, impulse noise present in some environments can affect multiple subcarriers simultaneously and hence generate correlated errors. The use of a channel interleaver with coded OFDM allows symbols to be distributed over frequency-time plane, thus allowing the code to make maximal use of frequency and time diversity offered by OFDM (Chitre et al. 2005). The knowledge of error correlation due to impulsive noise could be used in future decoding algorithms to improve decoding performance. OFDM systems are very sensitive to the Doppler shift due to the small bandwidth of each subcarrier as compared to the Doppler shift. As the carrier frequency in UWA systems is typically low as compared to the Doppler shift experienced due to movement, the communication systems have to

Underwater Acoustic Communication, Fig. 5 Multi-carrier modulation

U

2048

Underwater Acoustic Communication

Underwater Acoustic Communication, Fig. 6 Spatial modulation

cope with wideband Doppler which results in non-uniform Doppler shift across subcarriers. In Stojanovic (2006), the author presents an algorithm for non-uniform Doppler compensation in OFDM systems based on a single adaptively estimated parameter. In Sharif et al. (2000), the authors present a preprocessor that estimates Doppler shift by measuring the time between two known signals and removes the Doppler shift using a computationally efficient linear interpolator. Being a preprocessor, the technique can be used with any type of modulation and equalization. Spatial Modulation

The process of spatial modulation (SM) is shown in Fig. 6. Information theoretic studies have shown that the capacity of a channel increases linearly with the minimum of the number of transmit and receive antennas. This increase in capacity translates to a corresponding increase in achievable data rate through the use of multiple input multiple output (MIMO) processing techniques and space-time coding. Optimal detection techniques such as MAP and maximum likelihood sequence estimation (MLSE) exponentially grow in terms of complexity with the number of antennas. To address this problem, space-time trellis codes (STTC) and layered space-time codes (LSTC) can be used with suboptimal decoding techniques (Roy et al. 2004). The benefits of MIMO over single-input single-output (SISO) UWA communication systems were successfully demonstrated through an experiment in the Mediterranean Sea using two transmit projectors for STTC and four transmit projectors for LSTC. In another set of experiments

with six transmit projectors, a spatial modulation scheme with an outer block code, interleaver, and an inner trellis-coded modulation (TCM) was demonstrated (Kilfoyle et al. 2005). The experiments demonstrated that the proposed spatial modulation scheme offered increased bandwidth and power efficiency as compared to signals constrained to temporal modulation. For ISIlimited channels, spatial modulation offers the possibility of increasing data rates when simply increasing transmission power does not. In a MIMO-OFDM experiment, the nearly error-free performance was achieved with a 2-transmitter 4-receiver setup at ranges up to 1.5 km using a ½-rate low-density parity check (LDPC) code at a coded data rate of 12 kbps (Li et al. 2007).

Key Applications As efficient communication systems are developing, the scope of their applications continues to grow, and so do the requirements on the system performance (Stojanovic 1999). Many of the developing applications, both commercial and military, are calling for real-time communication with submarines and AUVs, UUVs. Setting the underwater vehicles free from cables will enable them to move freely and refine their range of operation. The emerging communication scenario in which the modern UWA systems will operate is that of an underwater data network consisting of both stationary and mobile nodes. This network is envisaged to provide an exchange of data, such as control, telemetry, and eventually video signals, between many network nodes. The network nodes, located on underwater moorings, robots,

Underwater Acoustic Sensor Network

and vehicles, will be equipped with various sensors, sonars, and video cameras. A remote user will be able to access the network via a radio link to a central node based on a surface station. Moreover, UWA communication plays a crucial role in the frogman information system. Compared with other communication forms such as electromagnetic waves, UWA communication has a longer operating range and more reliable performance.

Cross-References

2049 compensation system for underwater acoustic communications. J Ocean Eng 25(1):52–61 Stojanovic M (1999) Underwater acoustic communication. Wiley, New York Stojanovic M (2006) Low complexity OFDM detector for underwater acoustic channels. In: OCEANS. Article number: 4098876 Stojanovic M, Preisig J (2009) Underwater acoustic communication channels: propagation models and statistical characterization. IEEE Commun Mag 47(1):84–89 Yang WB, Yang TC (2006) High-frequency channel characterization for M-ary frequency-shift-keying underwater acoustic communications. J Acoust Soc Am 120(5):2615–2626 Zhou S, Wang Z (2014) OFDM for underwater acoustic communications. Wiley, Chichester

▶ Underwater Acoustic Communication

References Berkhovskikh L, Lysanov Y (1982) Fundamentals of ocean acoustics. Springer, Berlin Chitre M (2007) A high-frequency warm shallow water acoustic communications channel model and measurements. J Acoust Soc Am 122(5):2580–2586 Chitre M, Ong SH, Potter J (2005) Performance of coded OFDM in very shallow water channels and snapping shrimp noise. In: OCEANS. Article number: 1639884 Chitre M, Shahabudeen S, Freitag L, Stojanovic M (2008) Recent advances in underwater acoustic communications & networking. In: OCEANS. Article number: 5152045 Frassati F, Lafon C, Laurent PA, Passerieux JM (2005) Experimental assessment of OFDM and DSSS modulations for use in littoral waters underwater acoustic communications. In: OCEANS. pp 826–831 Jensen F, Kuperman W, Porter M, Schmidt H (1994) Computational ocean acoustics. Springer, New York Kilfoyle DB, Preisig JC, Baggeroer AB (2005) Spatial modulation experiments in the underwater acoustic channel. J Ocean Eng 30(2):406–415 Li B, Zhou S, Stojanovic M, Freitag L, Huang J, Willett P (2007) MIMO-OFDM over an underwater acoustic channel. In: OCEANS. Article number: 4449296 Morozov AK, Preisig JC (2006) Underwater acoustic communications with multi-carrier modulation. In: OCEANS. Article number: 4098913 Preisig J (2007) Acoustic propagation considerations for underwater acoustic communications network development. In: Proceedings of the first ACM international workshop on underwater networks. pp 1–5 Roy S, Duman T, Ghazikhanian L, McDonald V, Proakis J, Zeidler J (2004) Enhanced underwater acoustic communication performance using space-time coding and processing. In: OCEANS, vol 1. pp 26–33 Sharif BS, Neasham J, Hinton OR, Adams AE (2000) A computationally efficient Doppler

Underwater Acoustic Environment ▶ Underwater Acoustic Sensor Network

Underwater Acoustic Sensor Network Jianmin Yang1,2, Lu Ma2 and Gang Qiao2 1 School of Marine Engineering and Technology, Sun Yat-sen University, Guangzhou, China 2 College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin, China

Synonyms Acoustic modems; Ad hoc network; Cross-layer design; Energy efficiency; High latency; Infrastructureless network; Intelligent algorithm based; Medium access control layer; Multihop network; Neighbor discovery; Network experiment; Physical layer; Protocol design; Routing layer; Self-organizing network; Simulation tools; Underwater acoustic; Underwater acoustic channel; Underwater acoustic communication; Underwater acoustic environment; Underwater wireless acoustic communication

U

2050

Definition Underwater acoustic sensor network is composed of sensor nodes placed on the seabed and in the sea (including fixed sensor nodes and mobile platforms loaded with sensors), sea surface buoy nodes, and two-way acoustic links between them, which could cover a large area of underwater three-dimensional areas. Underwater acoustic sensor network can collect, process, classify, and compress information, and the information could be relayed back to the land-based or ship-based control center through underwater acoustic sensor network node.

Scientific Fundamentals Underwater Acoustic Sensor Network Architecture The network architecture is a basis for designing underwater acoustic sensor network; it can be divided into the following four types. One-Dimensional Underwater Acoustic Sensor Network

One-dimensional underwater sensor network is composed of a single underwater acoustic communication unit; these underwater acoustic communication units collect the required information, process the collected information, and send it to the surface buoy or base station. This underwater acoustic communication unit can be a relatively fixed unit such as a seabed fixed node or anchor node; it can also be a mobile underwater acoustic node, AUV, and other underwater units with certain mobility. One-dimensional underwater acoustic sensor network usually adopts a star network topology, and the data is transmitted in a single hop between the network unit and the remote station on the surface. After these independent hydroacoustic units have collected information, the collected information is processed, and then sent to the surface buoy or base station. This underwater acoustic communication unit can be a relatively fixed unit such as a seabed fixed node or anchor node; it can also be an underwater mobile node, AUV, and other

Underwater Acoustic Sensor Network

underwater units with certain mobility. Due to the networking architecture and task requirements, the one-dimensional underwater acoustic sensor network usually adopts a star network topology, and the network unit and the remote station on the surface adopt a single-hop method to transmit data. Two-Dimensional Underwater Acoustic Sensor Network

Different from one-dimensional underwater acoustic sensor network, two-dimensional underwater acoustic sensor network consists of multiple underwater acoustic communication nodes. All nodes in the network are at the same depth underwater. Usually, the nodes in the network are divided into two categories, ordinary nodes and sink nodes. Ordinary nodes only have horizontal communication capabilities, not vertical communication capabilities. The ordinary node collects and processes the required information and sends the data to the sink node through the horizontal link. The sink node has both horizontal and vertical communication capabilities. Sink nodes receive data packets from ordinary nodes through the horizontal link, and after processing, upload the data packets to the surface buoy or base station through the vertical link. Surface buoys or base stations upload data to satellites or send data to shore-based command centers through radio frequency communication. Two-dimensional underwater acoustic sensor network constitutes a variety of network topologies such as star, grid, or ring according to the needs of the tasks performed. Three-Dimensional Underwater Acoustic Sensor Network

Different from two-dimensional underwater acoustic sensor network, the nodes in threedimensional underwater acoustic sensor network are not completely at the same depth underwater. Three-dimensional communication can be carried out between network nodes. Nodes of different depths are clustered according to their depths, and nodes of the same or similar depth are clustered in the same cluster. Nodes have both horizontal and vertical communication capabilities.

Underwater Acoustic Sensor Network

2051

Underwater Acoustic Sensor Network, Fig. 1 Layered network model of underwater acoustic sensor network

Nodes can communicate with nodes in the same cluster through horizontal links or communicate between clusters or with surface buoys or base stations through vertical links.

acoustic sensor network is mainly divided into the physical layer, data link layer, and network layer, as shown in Fig. 1. The details are as follows:

Four-Dimensional Underwater Acoustic Sensor Network

Physical Layer

Four-dimensional underwater acoustic sensor network is composed of a static three-dimensional underwater acoustic sensor network and mobile underwater mobile acoustic communication units. Mobile underwater acoustic communication units include AUVs, mobile nodes, etc. The information collected by the static network can be sent to the mobile underwater acoustic communication unit, and then sent to the surface buoy or base station through the mobile acoustic communication unit. Since the mobile acoustic communication units in four-dimensional underwater acoustic sensor network have good mobility, the underwater acoustic sensor network of this structure can also combine optical communication and radio communication to meet more different needs. Layered Network Model Compared with land-based radio communication network, the research on underwater acoustic sensor network is still in its infancy. From the perspective of practical application, in order to reduce the complexity of network design, referring to the open systems interconnection (OSI), model, and transmission control protocol/internet protocol (TCP/IP) proposed by the International Organization for Standardization, underwater

Physical layer is responsible for realizing the modulation and demodulation of information flow data. Its main function is to provide transmission media and interconnection equipment for data communication between nodes, and to provide a reliable environment for data transmission. Modulation is performed at the transmitting end, and the digital information represented by “0,” and “1” is modulated into an acoustic signal for propagation in the underwater acoustic channel. At the receiving end, the received acoustic signal is demodulated, and the original bit stream information is restored. Physical layer only transmits digital modulation information composed of “0” and “1” and does not care about the specific meaning of each bit. The goal of the physical layer communication algorithm is to improve the reliability and effectiveness of the communication system as much as possible. Because the multipath effect of the underwater acoustic channel causes signal amplitude fading and inter-symbol interference, the channel bandwidth is limited (Stojanovic and Preisig 2009). The main technologies currently used in the underwater acoustic sensor network physical layer include phase shift keying (PSK), multiple frequency shift keying (MFSK), and orthogonal frequency division multiplexing (OFDM). In addition, in order to achieve robust

U

2052

underwater acoustic communication, the key technologies commonly used in underwater acoustic communication include decision feedback equalization technology, time reversal mirror technology, sparse channel estimation and equalization technology, and wideband doppler compensation technology. Data Link Layer

Data link layer is the middle layer of underwater acoustic sensor network, and its goal is to achieve fair and effective sharing of underwater acoustic channel resources by each network node. When designing the data link layer, while pursuing high throughput, minimize signal delay, and node power consumption. The design and implementation of the MAC protocol is the main research content of the data link layer of the underwater acoustic sensor network. The design of a MAC protocol with high efficiency, high throughput, and low energy consumption is very important to improve the performance of the underwater acoustic sensor network. Although there are many classic, mature, and efficient MAC protocols for land-based wireless sensor network, due to the big differences between underwater acoustic sensor network and land-based wireless sensor network, the MAC protocol suitable for land-based wireless sensor network cannot work efficiently in the underwater acoustic sensor network, and the MAC protocol needs to be designed according to the characteristics of the underwater acoustic sensor network. MAC protocols in underwater acoustic communication are usually divided into two categories, namely, scheduled-based and random competition (Climent et al. 2014). The scheduledbased MAC protocols mainly include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA) protocols. Random competition protocols mainly include ALOHA, carrier sense multiple access (CSMA), multiple access with collision avoidance (MACA), etc. Due to the complex application scenarios of underwater acoustic sensor network, sometimes a single multiple access technology cannot achieve good

Underwater Acoustic Sensor Network

results, and different multiple access technologies should be used in combination. Network Layer

Based on the data link layer providing the transmission function of data frames between two adjacent nodes, the main role of the network layer is to further manage the data communication in the network, through several intermediate nodes, and try to transfer data from the source node to the destination node. Its specific functions include addressing and routing, connection establishment, maintenance and termination, etc. Each node in the network must work together to complete the route selection. The design goals of routing protocols are mainly fast, accurate, and efficient have good scalability, and can quickly find routes. As the topology of underwater acoustic sensor network often changes, routing protocols also could quickly establish routes according to network topology changes (Domingo 2011). While selecting the best path according to the congestion of the network, the control information of maintaining routing should be minimized to reduce the overhead of routing protocol. Evaluation Index Evaluation of the performance of underwater acoustic sensor network mainly uses indicators such as average end-to-end delay, throughput, packet loss rate, and overload. End-to-End Delay

End-to-end delay refers to the average time required from the sending node to the destination node to successfully receive the data packet – the unit is s. End-to-end delay generally consists of three parts: the time the application layer generates the data packet and the time the data packet waits in the cache queue; the time it takes for the data packet to be transmitted and received in the transmitter and receiver; and the time of data packet transmission in the channel. Throughput

Throughput refers to the ratio of the amount of data packets successfully received to the unit simulation

Underwater Acoustic Sensor Network

time; the unit is bps, which is represented by TP in this entry and can be expressed as   TP ¼ Numpr  psize =T where Numpr is the number of successfully received data packets, psize is data package size, and T is simulation time. The average throughput is used to evaluate the efficiency of underwater acoustic sensor network data transmission. The higher the throughput, the greater the amount of data transmitted per unit time, and the better the performance of underwater acoustic sensor network. Packet Loss Rate

Packet loss rate refers to the ratio of lost data packets to the total number of data packets sent in the network, used to evaluate the stability of the underwater acoustic sensor network. It is represented by Lrate in this entry and can be expressed as Lrate ¼ ðNumlt  Numst Þ  100% where Numlt is the number of lost data packets and Numst is the total number of data packets sent in the network. Overload

Overload refers to the ratio of the total amount of data generated by the network protocol control message to the unit simulation time; the unit is bps, which is represented by S in this entry and can be expressed as S ¼ Numc  csize =T where Numc is the number of control packets successfully received, csize is control package size, and T is the simulation time. The greater the overload, the more energy is consumed. Therefore, the overload should be reduced as much as possible when designing the network protocol. Simulation Tools In order to evaluate the performance of underwater acoustic sensor network, it can usually be quantitatively evaluated through simulation or

2053

experiment. Underwater acoustic sensor network tests usually require a lot of preparation work and need to wait for suitable sea conditions and other test conditions, which require a lot of manpower and material resources, and due to the limitations of funds and sea conditions, the network performance test verification is not comprehensive. Software simulation is an effective tool for network performance evaluation. There are many software for network simulation, such as NS2, NS3, and OPNET. NS2

NS2 is an open-source network simulation software based on the split model developed by the University of California, Berkeley. It has the characteristics of expansion and high efficiency. It can work under Windows, Linux, Uinx, or Machitosh operating systems. When using NS2 for network simulation, two programming languages are generally used: C++ and OTcl. The former is used to implement the various modules of the network protocol stack, and the latter is used to write some modules and simulation scripts to configure the network topology, protocol stack, simulation time, and other parameters. The simulation results output by NS2 can be further analyzed using related tools. For example, network animator (NAM) can be used to generate a dynamic network topology map, which can clearly show the process of data packet transfer in the simulation process. Although NS2 has powerful functions and can support wired and wireless network simulation, the publicly released NS2 software cannot be directly used for underwater acoustic sensor network simulation because its wireless channel model and physical layer communication module are not suitable for underwater acoustic sensor network. Therefore, some research institutions have improved the physical layer and channel based on NS2 and developed a series of enhanced versions that can be used for UACN simulation, such as Auqa-Sim, NS-MIRCLE, DESERT, and SUNSET (Petrioli and Petroccia 2012). NS3

NS3 is a discrete event simulation software for network systems developed since 2006, using

U

2054

Underwater Acoustic Sensor Network, Fig. 2 The structure of NS3

GNU GPLv2 open-source agreement. This software is not an extension of NS2 and does not support NS2 application programming interface functions. The structure of NS3 is shown in Fig. 2. The core module is the kernel module of NS3, which is the foundation of the entire NS3 operation and development, including scheduling module, callback module, tracking module, etc. Above the core module is the network module, which contains abstract components such as nodes, network cards, address types, sockets, and packets. The upper layer of NS3 provides helper classes for each module. When writing simulation scripts, users can ignore the details of the module implementation and use the APIs in the helper classes of each module to call the components provided by the module. Above the helper class is the test class, which contains content related to software testing in the module development process. NS3 provides a visualization tool that can dynamically track the flow of data packets in the simulation process. As one of the cores of NS3, the data collection system allows users to easily track the data or events of interest in all directions, and finally collect and visualize output through the interface provided by the system. NS3 is still under continuous development and improvement. The publicly released version includes a simple underwater acoustic sensor network model (Tracy and Roy 2008) that can simulate the MAC protocol of centralized underwater acoustic sensor network. OPNET

OPNET is a commercial discrete event network simulation software, which uses a three-layer

Underwater Acoustic Sensor Network

model of process model, node model, and network model to simulate network behavior. The network model is the uppermost layer, which is composed of nestable subnets, communication nodes, and links for communication between nodes. The network topology and model configuration are completed at this layer; the process model is the lowest layer, using a finite state machine (FSM) describing each state and the transition relationship between states. This layer is the specific location for the realization of communication protocol function simulation and simulation-related control behavior. FSM is a communication behavior program described in C language; the node model defines the internal structure of the node, which consists of a transmitter module, a receiver module, a processor module, and a queue module. Currently, researchers have applied OPNET to underwater network simulation. Mandar et al. (2014) used OPNET to simulate the influence of the channel on the underwater acoustic network, but the lack of reliable underwater acoustic channel model and open source underwater acoustic protocol, as well as the ability to simulate 2D underwater network and other factors limit the simulation effect of OPNET. As a commercial software, the scope of application of OPNET is not as good as the open source simulation software NS2 and NS3, but its convenient way of use is still favored by many scholars.

Key Applications With the continuous exploitation of land resources, people’s development and competition for marine resources has become increasingly fierce. As one of the most powerful helpers for marine development, underwater acoustic sensor network has a wide range of services in both military and civilian fields. In this section, various applications of underwater acoustic sensor network will be introduced. As shown in Fig. 3, the applications of underwater acoustic sensor network can be divided into five aspects: underwater monitoring, disaster prevention and monitoring, military, assisted navigation, and sports.

Underwater Acoustic Sensor Network

2055

Underwater Acoustic Sensor Network, Fig. 3 Applications of underwater acoustic sensor network

Underwater Monitoring Underwater monitoring refers to monitoring the characteristics of the waters in a designated area by deploying an underwater acoustic sensor network. The applications of underwater acoustic sensor network in underwater monitoring mainly include water quality monitoring (Faustine et al. 2014), habitat monitoring (Lopez et al. 2009), and underwater exploration monitoring (Srinivas et al. 2012). Disaster Prevention and Monitoring Natural disasters are usually unavoidable, and natural disasters in water are often more dangerous and cause more serious losses. Therefore, it is very necessary to establish an effective underwater natural disaster monitoring and prevention mechanism. Underwater acoustic sensor network has been widely used in the monitoring and prevention of underwater natural disasters. It is used to monitor and prevent floods (Udo and Isong

2013), underwater volcanic eruptions (Casey et al. 2010), underwater earthquakes and the resulting tsunamis, underwater oil pipeline leaks (Iwendi and Allen 2011), and other types of water disasters.

Military The core of modern warfare is the network. As a part of the integrated land, sea, air, and space network, underwater acoustic sensor network is becoming more and more important in the military. An efficient and reliable underwater acoustic sensor network can greatly assist naval operations. Related researchers have conducted a lot of research on the military application of underwater acoustic sensor network. It has been widely used in mine detection (Williams 2010), submarine monitoring and positioning (Hamilton et al. 2010), underwater monitoring (Caiti et al. 2013), and other fields.

U

2056

Assisted Navigation The underwater environment has great unknowns, uncertainties, and randomness, and these instabilities tend to increase with the increase of depth. In such an unknown and dangerous environment, ships, boats, and even diving enthusiasts need reliable navigation mechanisms to escort them. Due to the particularity of underwater channel conditions, navigation technology on the land cannot be applied well underwater. Therefore, it is very important to design a navigation system that can work well underwater. Through the unremitting efforts of relevant researchers, underwater acoustic sensor network technology has been widely used in the field of underwater-assisted navigation (Guo and Liu 2013). Sports Underwater acoustic sensor network also has a very wide range of applications in water movement. These applications are slightly different from the previous types of applications. Sage et al. (2011) propose an underwater acoustic sensor network for monitoring swimmers’ swimming performance. The swimming performance data monitored by the network can be transmitted to swimmers and coaches at the same time. Marshall (2015) focuses on locating swimmers in swimming pools through the underwater acoustic sensor network, and the experimental results show that this method is more accurate than traditional inertial positioning.

Cross-References ▶ Ad Hoc Network ▶ Underwater Acoustic Sensor Network

References Caiti A, Calabro V, Munafo A, Duca A (2013) Mobile underwater sensor network for protection and security: field experience at the UAN11 experiment. J Field Robot 30(2):237–253 Casey K, Lim A, Dozier G (2010) A sensor network architecture for tsunami detection and response. In: Proceedings of international conference on innovations

Underwater Acoustic Sensor Network and commercial application of distributive sensor network, Washington, pp 28–43 Climent S, Sanchez A, Capella J, Meratnia N, Serrano J (2014) Underwater acoustic wireless sensor network: advances and future trends in physical, MAC and routing layers. Sensors 14(1):795–833 Domingo M (2011) A distributed energy-aware routing protocol for underwater wireless sensor network. Wirel Pers Commun 57(4):607–627 Faustine A, Mvuma A, Mongi H, Gabriel M (2014) Undersea wireless sensor network for ocean pollution prevention: a novel paradigm for truly ubiquitous underwater systems. Wirel Sens Netw 06(12):281–290 Guo Y, Liu Y (2013) Localization for anchor-free underwater sensor network. Comput Electr Eng 39(6):1812–1821 Hamilton J, Kemna S, Hughes D (2010) Antisubmarine warfare applications for autonomous underwater vehicles: the GLINT09 sea trial results. J Field Robot 27(6):890–902 Iwendi C, Allen A (2011) Wireless sensor network nodes: security and deployment in the Niger-delta oil and gas sector. Int J Netw Secur Appl 3(1):68–79 Lopez M, Martinez S, Gomez J, Herms A, Tort L, Bausells J, Errachid A (2009) Wireless monitoring of the pH, NH4+ and temperature in a fish farm. Procedia Chem 1(1):445–448 Mandar C, Rohit B, Soh W (2014) UnetStack: an agentbased software stack and simulator for underwater network. In: Proceedings of the IEEE oceans 2014, pp 1–10 Marshall J (2015) Magnetic field swimmer positioning. IEEE Sensors J 15(1):172–179 Petrioli C, Petroccia R (2012) SUNSET: simulation, emulation and real-life testing of underwater wireless sensor network. In: Proceedings of third workshop on underwater network, pp 12–14 Sage T, Bindel A, Conway P, Slawson S (2011) Development of a wireless sensor network for embedded monitoring of human motion in a harsh environment. In: Proceedings of the IEEE 3rd international conference on communication software and network, pp 112–115 Srinivas S, Ranjitha P, Ramya R, Kumar G (2012) Investigation of oceanic environment using large-scale UWSN and UANETs. In: Proceedings of 8th international conference on wireless communications, networking and mobile computing, pp 1–5 Stojanovic M, Preisig J (2009) Underwater acoustic communication channels: propagation models and statistical characterization. IEEE Commun Mag 47(1):84–89 Tracy L, Roy S (2008) A reservation mac protocol for ad-hoc underwater acoustic sensor network. In: Proceedings of IEEE UComms, pp 95–98 Udo E, Isong E (2013) Flood monitoring and detection system using wireless sensor network. Asian J Comput Inf Syst 1(4):108–113 Williams D (2010) On optimal AUV track-spacing for underwater mine detection. In: Proceedings of IEEE international conference on robotics and automation, anchorage, pp 4755–4762

Underwater Driving Subsystem

Underwater Connector ▶ Subsea Connector

Underwater Device ▶ Photoelectric Detection Technology in Underwater Vehicles

Underwater Distributed Remote Sensing ▶ Underwater Information Sensing Technology

2057

vehicles for polymetallic nodule exploitation have been taken since the 1970s. Because of the relatively flat topography of the seabed in the polymetallic nodule mining area, as well as the mechanical properties of the surface sediment, such as high water content, small bearing strength, and shear strength, researchers have developed a variety of driving mechanisms based on different driving techniques. Typical underwater driving mechanisms include the Tow-sled type, the Archimedes spiral propulsion type, and the crawler selfpropelled type. In the late 1970s, some countries carried out sea trials of Towed type and Archimedes type mining vehicles. Although these two ways are technically feasible, they are not suitable for commercial mining due to low mineral collection rates and difficulty in avoiding obstacles. After that, the focus of researchers gradually turned to the development of crawler driving technology and mechanism.

Underwater Driving Subsystem Wu Hongyun Seabed Mining Department of Changsha Institute of Mining Research, Changsha, China

Synonyms SPDM – Self-propelled type driving mechanism; TSDM – Tow-sled type driving mechanism

Definition Underwater Driving Subsystem – A mechanism or device for driving mining vehicles to carry out mining operations on the seabed.

Introduction The driving mechanism of the deep-sea mining vehicle bears the body weight, interacts with the seabed or overlying sediments to realize the vehicle’s movement on the seafloor. Studies on mining

The Tow-Sled Type Driving Mechanism (TSDM) TSDM usually uses a sled-type bearing chassis. With the traction of the sea surface mining vessel through the lifting pipe, it is available to drive on sediments with low bearing capacity or shear force, and to cross some slopes and small obstacles. In 1978, Ocean Management Incorporated Corporation (OMI) successfully completed three mining tests at a depth of more than 5000 m using a tow-sled hydraulic mining machine (as shown in Fig. 1a) jointly developed by researchers from Germany, Japan, and the United States (ISA 2008). The mechanism has the advantages of a simple structure and little disturbance or damage to the seabed. However, the mechanism cannot accurately control the direction of travel or avoid obstacles autonomously, and cannot travel in accordance with the predetermined track and preset speed, which will reduce the efficiency of seabed mineral resources collection and cause resource waste. Therefore, this kind of mechanism

U

2058

Underwater Driving Subsystem

Underwater Driving Subsystem, Fig. 1 Towsled type driving mechanism. (Yamazaki et al. 1999). (a) Bottom view. (b) Improved towsled mining vehicle

is only suitable for the principle experiments, not for commercial exploitation. Figure 1b shows an improved tow-sled mining vehicle used in towing mining experiment on a sea mountain with a depth of 1700 m in 1997 (Yamazaki et al. 1999).

The Self-Propelled Type Driving Mechanism (SPDM) The self-propelled type driving mechanism is powered by the surface mining vessel through armored cables which could deliver a high

Underwater Driving Subsystem

2059

power level. According to the operator’s remotecontrol instructions, it has the ability to drive along the preset path and control the mode with good surmounting and pass obstacles. Moreover, it can change the driving speed according to nodule abundance to maintain constant production capacity. The self-propelled type driving mechanism is mainly divided into the Archimedes spiral propulsion type and the crawler selfpropelled type.

(c) It has difficulty in obstacles surmounting and turning around. (d) The spiral groove is easily trapped by the sediment, which will significantly affect the driving performance.

Archimedes Spiral Propulsion Type Driving Mechanism The Archimedes spiral propulsion type driving mechanism was originally developed by the US Navy to use as a vehicle in swampy areas. In 1979, the Ocean Minerals Company Corporation (OMCO) carried out a mining test in the Pacific polymetallic nodule mining area. The mining vehicle used in the test adopted this kind of driving mechanism, as shown in Fig. 2a (Schick 1980). Figure 2b shows that the mining vehicle in the shuttle boat shape, developed by French scientists, also uses this type of mechanism (Herrouin et al. 1989). The driving mechanism is driven by hydraulic pressure and has a simple structure. The propelling force generated by the high-speed rotation of the spiral blade in the sea mud makes the mechanism move forward or backward. Despite good traveling performance in swampy areas and snowfields, it is almost impossible to move on hard rock. Subsequently, researchers from France, Japan, Germany, Russia, and China conducted extensive research on the Archimedes type of mechanism. After comparing with the crawler type driving mechanism, the following conclusions were drawn on its disadvantages (Wang 2015).

Crawler Self-Propelled Type Driving Mechanism The crawler self-propelled type driving mechanism adopts the mature universal construction machinery driving technology. A benefit from the large grounding area is that it can be well attached to the seabed and produce high traction. Meanwhile, its good maneuverability, as well as its small impact on the environment, makes it especially suitable for polymetallic nodule mining areas.

(a) The Archimedes type’s static depression depth is much lower than that of the crawler type, which means its bearing capacity is poor. (b) The traction force per vehicle weight of the Archimedes type is far less than that of the crawler type, while the driving power is far more than that of the crawler type. Also, the ratio is about 40:7.4.

Therefore, whether the Archimedes spiral propulsion type driving mechanism is suitable for commercial mining on the soft seabed remains to be further studied.

Crawler Driving Technology and Mechanism on Soft Sediment in Polymetallic Nodule Mining Areas

During the operation of a deep-sea mining vehicle, its driving mechanism interacts with the seabed surface sediment. On the one hand, the driving mechanism cuts and depresses the sediment. On the other hand, the sediment drives and bears the driving mechanism. Compared with land soils, seabed sediments (within 20 cm below the seabed surface) are characterized by high water content, large fluidity, low shear strength and compressive strength, and small friction angle. Within a certain range, the shear strength and compressive strength of the sediment gradually increase with the increase of depth. The deeper the driving mechanism is depressed, the greater the traction is generated. However, the driving resistance will be sharply increased if the depression depth is too large. Ultimately, it affects the driving performance and causes a great disturbance to the marine environment. This puts forward a larger emphasis on the design of the mining vehicle’s driving mechanism, that is, to reasonably design the weight of the mining

U

2060

Underwater Driving Subsystem

Underwater Driving Subsystem, Fig. 2 Archimedes spiral propulsion type driving mechanism. (Welling et al. 1980)

vehicle in the water to control the depression depth. Major factors include a lightweight design and the use of buoyancy materials. Since the shear strength and compressive strength of sediments vary with the depression depth, it is necessary to establish a mechanical model of the compressive and shear stress of deep-sea sediments for the purpose of obtaining the traction force generated by the crawler driving mechanism. Research teams from Germany,

Russia, South Korea, India, Belgium, and China have carried out a lot of experimental research and theoretical analysis. Through the establishment of dynamic system modeling and simulation, researchers studied the interaction between the shape, the parameters, the pitch of the crawler teeth, the width of the crawler and the suspension mechanism, and the influence on the driving performance. Successively, countries have developed crawler type mining vehicles. Figure 3 shows the

Underwater Driving Subsystem

2061

Underwater Driving Subsystem, Fig. 3 Double-crawler mining vehicle of 3500meter deep-sea polymetallic nodules developed in China. (COMRA 2020)

Underwater Driving Subsystem, Fig. 4 Fourcrawler driving mechanisms developed by South Korea (a) (Sup et al. 2016) and GSR of Belgium (b) (Johan et al. 2018), respectively

U

2062

double-crawler mining vehicle of 3500-meter deep-sea polymetallic nodules developed in China. Figure 4 shows the four-crawler driving mechanism of mining vehicles, respectively, developed by South Korea (a) (Sup et al. 2016) and GSR of Belgium (b) (Johan et al. 2018). These two mining vehicles have completed the sea test. Crawler Driving Technology and Mechanism on Hard Ground and Complex Terrain

According to previous exploration data, the polymetallic massive sulfide deposits and cobalt-rich crust plate deposits at the top of the seamount Underwater Driving Subsystem, Fig. 5 Polymetallic sulfide mining vehicle. (Nobuyuki et al. 2018)

Underwater Driving Subsystem, Fig. 6 Fourcrawler driving mechanisms of cobalt-rich crusts mining vehicle. (CIMR 2018)

Underwater Driving Subsystem

have complex micro-topographic features, and the mining compressive strength of the block ore body is no less than 20 MPa, which requires the driving mechanism of the mining vehicle to have good obstacle crossing abilities and adhesion. To develop driving technology and mechanisms of mining vehicles for polymetallic sulfide and cobalt-rich crust, it is possible to learn from some relatively mature technologies and mechanisms of heavy-duty operations in complex terrains, such as vehicles from mountainous areas, or combat vehicles. With different mining processes and test purposes, the driving mechanism developed may differ.

Underwater Information Sensing

Aiming at the commercial exploitation of polymetallic sulfide in the Sorawa-1 mining area of Papua New Guinea, Nautilus Minerals has developed a three-step process of mining area leveling, ore cutting, and particle collection in reference to the open-pit mining process. Based on this process, Nautilus has developed three operating vehicles with double crawler driving mechanisms and carried out tests underwater. The auxiliary cutter begins the work by grinding down the seafloor to make it level enough for the second piece of equipment, the bulk cutter. That machine grinds the resulting slurry up fine enough for the collection machine to suck it up before it is sent to a ship on the surface. Two four crawler mining vehicles were developed based on the mining process of cutting and collecting simultaneously, as shown in Figs. 5 and 6. In 2017, a polymetallic sulfide mining test at a depth of 1700 meters was completed in the Okinawa sea area (Ishiguro et al. 2013; Nobuyuki et al. 2018; Saekyeol et al. 2019). In 2018, a verification test of mining sampling at a depth of 2019 meters was completed in the cobalt-rich crusting contract area of the Western Pacific Ocean (CIMR 2018).

2063 at great depths and transporting said deposits to a floating vessel. United States Patent 9874000 Kim S, Cho S, Lee M (2019) Reliability-based design optimization of a pick-up device of a manganese nodule pilot mining robot using the Coandă effect. J Mech Sci Technol 33(8):665–3672 Minghe W (2015) Exploitation of deep sea solid mineral resources. Central South University Press, Changsha Okamoto N, Shiokawa S, Kawano S (2018) Current status of Japan’s activities for deep-sea commercial mining campaign. In: Proceedings of MTS/IEEE OCEANS Kobe Techno-Oceans (OTO), Kobe, Japan Sup H et al (2016) Robot for mining manganese nodules on deep seafloor. United States patent 9334734B2 Welling CG et al (1980) Ocean mining system and process. United States Patent 4232903 Yamazaki S, Kuboki E, Yoshida H (1999) Tracing collector passes and preliminary. Analysis of collector operation. In: Proceeding of the Third (1999) ocean mining symposium, Goa, India

Underwater Equipment Fix Techniques ▶ Subsea Equipment Installation Technology

References

Underwater Glider (UG) CIMR (2018) Research report on scale sampler of cobalt rich crust. Nov 11, Changsha, China (in Chinese) COMRA (2020) Design report on deep-sea polymetallic nodule mining test project. Dec 30, Beijing, China (in Chinese) Herrouin G et al (1989) A manganese nodule industrial venture: summary of a 4-year study in France. In: Proceedings of the Offshore Tech Conference, Houston, OTC 5997, pp 321–332 ISA (2008) Polymetallic nodule mining technology – current trends and challenges ahead: proceedings of the Workshop jointly organized by the International Seabead Authority and the Ministry of Earth Sciences, Government of India, National Institute of Ocean Technology, Chennai, India 18–22 February 2008, pp 54–81 Ishiguro S et al (2013) Development of mining element engineering test machine for operating in seafloor hydrothermal deposits. Mitsubishi Heavy Indus Tech Rev 50(2) Johan H et al (2018) Subsurface mining vehicle and method for collecting mineral deposits from a sea bed

▶ Glider

Underwater Information Awareness ▶ Underwater Information Sensing Technology

Underwater Information Sensing ▶ Underwater Information Sensing Technology

U

2064

Underwater Information Sensing Technology Shaohua Chen and Xiaodong Li Yichang Research Institute of Testing Technology, Yichang, China

Synonyms Acoustic correlation current profiler (ACCP); Acoustic Doppler current profiler (ADCP); Autonomous underwater vehicle (AUV); Conductivity, temperature, depth (CTD); Environmental characterization optics (ECO); Sound, velocity, temperature, pressure (SVTP); Underwater distributed remote sensing; Underwater information awareness; Underwater information sensing; Underwater surveillance; Unmanned surface vehicle (USV)

Introduction Definition Underwater information perception is a process of gathering sea environment and target signal with acoustic, optical, magnetic, electrical, and other sensors; processing the signal; and obtaining the characteristics of the sea environment and target. Since the sound wave can transmit for a long range in water, the acoustic information attracts extraordinary attention. The final purpose of underwater information perception is to develop ocean underwater surveillance system, understand the variation law of ocean environment, construct a transparent ocean, and help the mankind develop and utilize the ocean. Function of Ocean Information Perception In the era of informatization, if we humans want to study and utilize the ocean, we should first perceive the ocean, gather ocean information, and explore the law of ocean. Ocean information involves a wide range of subjects, including all the aspects of ocean physics, ocean chemistry, ocean biology, ocean

Underwater Information Sensing Technology

geology, etc. Mankind has invented a variety of ocean surveillance equipment to observe the ocean, including coast-based ocean wave monitoring station, ocean meteorological station, ocean tide level station, coastal hydrophone station, high-frequency ground wave radar, etc. The buoy and ocean measuring ship are equipped with the synthesis aperture sonar (SAS), the acoustic Doppler current profiler (ADCP), the acoustic correlation current profiler (ACCP), the optical apparatus, and multiple kinds of seawater sensors. The meteorological satellite and watercolor satellite are equipped with a variety of remote sensing and remote testing apparatus. The seabed-based platforms are equipped with a variety of sensors to measure the ocean dynamic parameters. All the sensors work together to sensing the ocean in three dimensions. The information is analyzed, computed, deduced, and signal processed, to form the ocean wind speed, wind direction, air temperature, air pressure, relative temperature, amount of rain, visibility, tidal wave, sea current vector, sea current profile, surface wind field, surface water temperature and salinity, profile water temperature and salinity, sea depth, ocean magnetic field, seabed configuration, evaporation flux, and the formation mechanism of atmospheric duct, the formation mechanism of sea area flow field and convergence zone, and other ocean physical knowledge library and ocean parameter knowledge library. All the knowledge of ocean environment factors forms a grand ocean ambient situation map, used for evaluating and forecasting the effect of ocean environments on all kinds of ocean exploiting activities (Fang 2005). Functions of Underwater Information Perception The physical fields to perceive include underwater acoustic field, ocean magnetic field, ocean electrical field, ocean optical field, etc. We are interested in the ocean environment information and target information, such as the characteristics of sea ambient noise, underwater target, and sound propagation, which are very important to underwater acoustic research and engineering applications. The ocean environment is complex and variable,

Underwater Information Sensing Technology

changing with area and time. The factors affecting sound propagation include the temperature-saltdepth profile, ocean current profile, turbulence, internal wave, frontal surface, sea-bottom sound speed, etc. (Ling 2013). Ocean underwater information is of great importance in mankind’s exploring activities. For example, the density discontinuity layer in seawater affects the safety of underwater vehicles. As a vehicle goes into the lower density layer, the buoyancy reduces suddenly, resulting in a sharp descent of the vehicle, which may cause serious accidents. The internal wave has effects on the controllability and safety of the vehicle. Tide waves and ocean currents may deviate the vehicle from its course. Sound propagation characteristic is the most important factor that affects the acoustic information perception in the sea. Sound propagation in the sea mainly depends on the distribution of temperature, salinity, and density of seawater. In the deep sea, the difference in sound speed at vertical plane forms the convergence zone and acoustic shadow zone. An underwater vehicle may detect an object at a long range by making use of the convergence zone, and hide itself in the shadow zone. In the shallow sea, sound propagation is affected by meteorological and seabed conditions, which makes the propagation characteristics more complex than in the deep sea (He et al. 2015). As a background interference to underwater information perception, the sea ambient noise has important effect on sonar operating range forecasting and sonar signal processing. Studying the characteristics of the sea ambient noise, including the time and frequency domain feature, spatial distribution, and correlation coefficient, taking full advantage of the differences between sea ambient noise and moving sound sources, to suppress the interferences, are very important to detecting moving source signal buried in strong interferences. The regularity in sea ambient noise may be exploited to estimate the relative ocean parameters, such as the surface wind speed, the amount of rain, the shipping distribution, etc. The above information is also used for the study of oceanography and ocean climate (Chen 2006).

2065

Information perception for the moving sound sources is necessary for national defense security as well as the study of the sea environment. The moving sound sources include military ships, merchant ships, and other underwater vehicles. Information perception of underwater moving sources includes two cases。 In the first case, the target passes not far away from the observer and may be looked as a dominant concentrated source, and the noise information acquired can be used for target acoustic characteristics analysis. In the other case, when the moving source is far from the observer, it actually contributes to the sea ambient noise. Usually, the contribution is within the lower frequency band below several hundred Hertz. Sometimes it reaches the frequency band above 1 kHz near a busy sea route.

Scientific Fundamentals Underwater Information Perception System An underwater information perception system includes shore-based sonars, ship-carried sonars, seabed-based sensor arrays, anchored buoys, floating buoys, autonomous underwater vehicles (AUVs), underwater gliders, wave gliders, unmanned surface vehicles (USVs), etc. Those systems carry sensors to observe and gather underwater information. Ocean observing and information gathering in a great period and space is an important developing trend of ocean information perception. The rapid development of underwater unmanned system provides a wide-range underwater information perception capability with an effective approach. Underwater unmanned systems can be divided into two types: the stationary type and the mobile type. The stationary type mainly includes the seabed-based sensor array and anchored buoy, etc. The mobile type mainly includes AUVs and underwater gliders, etc. Both types have advantages and disadvantages. The mobile type is more flexible when performing a task since it can move. It can move into dangerous or sensitive areas to observe clearly at a short range. The advantage of stationary type are relatively simple in structure, having no dynamic energy expenditure,

U

2066

Underwater Information Sensing Technology

supporting long-time observation and data recording, not generating self-noise, and observing quietly. Structure of Underwater Information Perception System

The underwater information perception system mainly includes the carrier, central control unit, sensors, signal conditioner, data recorder, and battery. A digital signal processor (DSP) will be arranged when real-time data processing is required. A communication unit will be allocated when real-time transmission of the information is requested. The structure of an underwater information perception system is shown in Fig. 1. The underwater information perception system can carry a variety of sensors. Sensors used to sensing acoustic signals include sonars, hydrophones, acoustic vector sensors, etc. For the purpose of making spatial directivity and improving the sensibility to weak signals, the sensors sensing the target and noise information usually operate as an array, such as the hydrophone array, magnetic sensor array, electric sensor array, etc. Sensors used to sense the attitude of a platform are magnetic compasses and pressure sensors. Sensors used to sense the ocean environment include CTD (conductivity, temperature, depth), SVTP (sound, velocity, temperature, pressure), ADCP, ACCP, DO (dissolved oxygen) sensor, ECO

underwater information perception system

battery

communication unit

data recorder

digital signal processor

signal conditioner

sensor

carr ier

Underwater Information Sensing Technology, Fig. 1 Structure of underwater information perception system

(environmental characterization optics) sensors, gamma-ray sensors, etc. The signal conditioner is used to filter and amplify sensor signals. The data recorder is used to record the collected digital signals, with a capacity of several months. The DSP is used to analyze and detect the collected signals, extract the signal features, compute the spatial distribution and motion state, and recognize the attribute of the source. The communication unit is used to transmit information among the distributed sensor nodes with the underwater acoustic modem. Sometimes the underwater information is needed to transmit to the radio data link, and the underwater acoustic/radio unit is used, or a communication buoy is released up to the surface. The mobile nodes such as the AUVs or underwater gliders can rise up to the surface, and transmit information with a radio unit. Underwater Information Perception System of Stationary Type

An underwater information perception system of stationary type gathers information of underwater target or environment by sitting at the seabed or mooring in water. The real-time transmission sub-buoy is a single-point moored system used to monitor ocean environment, as shown in Fig. 2. It can carry ADCPs, CTDs, vertical linear arrays, and vector acoustic hydrophones to gather environmental and sound source information. It boasts the advantages of both sub-buoy and surface buoy in that it is capable to conduct long-time continuous secret monitoring of deep-sea oceanographic environment and timely transmit the collected data to shore-based station. This highly integrated system features secrecy, robust against sabotage, and timely transmission and can be applied to early warning of ocean disaster and military attack. The main performance index is as follows: 1. Operation depth: 4000 m, deployment depth of the mother buoy: 80~300 m 2. Effective range of current measurement and profiling: 0~500 m (double ADCP); temperature and salinity depth: 800 m

Underwater Information Sensing Technology Underwater Information Sensing Technology, Fig. 2 Sub-buoy made by Yichang Research Institute of Testing Technology. (a) Sub-buoy. (b) Releasing untethered communication buoy

2067

tethered communication buoy untethered communication buoy

acoustic sensor 300kHz ADCP

moored communication cable cutting releaser

control unit

battery

75kHz ADCP

(a) Sub-buoy

(b) Releasing untethered communication buoy

Underwater Information Perception System of Mobile Type

innovative platform used to monitor marine environment in middle-/long-distance waters. It features autonomy, real-time transmission, and mobility. It can be equipped with such sensors as CTDs, ADCPs, hydrophones, vector acoustic sensors, etc. The main performance index is as follows:

An underwater information perception system of mobile type gathers information about underwater target or environment by cruising in the sea. Take an underwater glider, C-Glider, as an example. C-Glider, as shown in Fig. 3, is an

1. Mass weight: > K ð t Þ ¼ bðoÞ cos ðot Þdo < p 0 ð1 ð5Þ > > : A ¼ aðoÞ þ 1 KðtÞ sin ðotÞdt o 0

W

2124

Wave Energy Converters

The constant added mass A is often given as the added mass at infinite frequency: A ¼ a ð 1Þ

ð6Þ

After solving the time-domain equation, the instantaneous power is calculated as PðtÞ ¼ Fpto ðtÞ  X_ ðtÞ

ð7Þ

And the average power conversion over a period of T is given by P¼

1 T

ðT 0

PðtÞdt

ð8Þ

Key Applications Oscillating Water Column (OWC) An OWC is a specially designed hollow structure (fixed or floating) with an opening in water and an opening to the air. The partially submerged hollow structure forms a water column and an air chamber, separated by a free surface. When a wave passes the hollow structure, the free surface in the hollow structure moves up and down, such that it can compress or decompress the air in the air chamber if the opening to the air is equipped with a power take-off (PTO) system. In a practical OWC, an air turbine can be used to damp the airflow through the upper opening to create the compressed and decompressed air in the air chamber in such a manner that the wave energy is converted into pneumatic energy. The changing pressure in the air chamber could exhale or inhale an airflow through the air turbine PTO and drive the air turbine PTO in a relatively high rational speed to convert the pneumatic energy into mechanical energy. As a unique and maybe the largest advantage for the OWC devices as pointed out by Evans and Porter (1995), they may be the only wave energy converters which can effectively overcome the challenges for converting the low-frequency motions in waves (~0.1 Hz) into electricity of 50 or 60 Hz. This unique feature allows the PTOs of a high rotational speed to be connected to the generators directly to generate electricity.

Different OWC energy converters have been proposed and studied after the successful OWC navigation buoys with an aim to increase the OWC energy conversion efficiency and capacity for possibly massive wave energy production. These include “Kaimei” (Masuda 1979), Backward Bent Duct Buoy (BBDB) (Masuda et al. 1988) (which is being developed by OceanEnergy Ltd (2017) and currently is in preparation for pre-commercial open sea trials in Hawaii), Spar OWC (Falcao et al. 2012), sloped OWC (Payne et al. 2008), enclosed OWC (Fonseca and Pessoa 2013), as well as the shoreline OWC plants: LIMPET (in decommissioning after generating power to grid for more than 10 years) (Folley et al. 2006), PICO (in decommissioning) (Le Crom et al. 2009; Pecher et al. 2011), and Mutriku (still operational) (EVE 2013). As another successful story in wave energy utilization/production, the LIMPET OWC plant (Scotland, UK), a shoreline OWC wave energy plant, has generated wave power to grid for more than 60,000 h in 2000–2011 (Heath 2012), in a period of slightly over 10 years, and in the last 4 years in its service, the power generation availability reaches 90% (EC 2017). As a pioneer (experimental) wave energy plant, this is a great achievement for the special wave energy technology. Oscillating Bodies This category covers a large range of wave energy conversion technologies, including the conventional point absorbers, attenuators, oscillating surging converters, and many other wave energy converters if their body motions are used for wave energy conversion. Point Absorbers

Point absorbers seem the simplest wave energy converters, which have attracted a lot of attention from researchers and developers, as well as outsiders. The principle of wave energy conversion for point absorbers is very simple and very easy to understand even for people who have no much knowledge about wave energy conversion when he/she watches the up-and-down movements of

Wave Energy Converters

2125

the navigation buoys under the wave action in harbors. Generally, either hydraulic or direct drive power take-offs or other mechanical PTOs can be used to convert the kinetic energy of the device body (bodies) of point absorbers. The well-advanced point absorber technologies include CorPower (fix-referenced point absorber, with built-in control system in the device; see Fig. 2, (CorPower 2017)); CETO (fix-referenced fully submerged point absorber (Rafiee and Fievez 2015)); Wavebob (self-referenced floating point absorber (WaveBob 2011)); OPT (selfreferenced floating point absorber (OPT 2015)) and its relevant reference model 3 (RM3 (Yu et al. 2015)); etc. Attenuators

Pelamis (Yemm et al. 2012), a famous attenuator wave energy converter, may be regarded as the first wave energy converter to reach the precommercial level of development, and even three commercial prototypes were manufactured and deployed in the Portuguese coast in 2009 (but no power has been generated yet) based on the report (EC 2017). The later version (P2) has been

Phase control 5 x energy density

tested in EMEC with the financial support from Eon and Scottish Renewables. The company had finally run into administration in 2014, and Wave Energy Scotland (WES) has bought all IPs from the company (EC 2017). A slightly different form from Pelamis, the raft-type attenuator wave energy converters are now being developed by some organizations, including M4M developed at the University of Manchester, UK, (M4M 2015) and SeaPower in Ireland (SeaPower 2015). Numerical modelling technologies have been widely applied for the attenuator wave energy converters (Zheng et al. 2015) (Fig. 3). Oscillating Surging Services

The Oyster device is an oscillating surging device, developed by Aquamarine Power (Whittaker and Folley 2012). Such an oscillating surging device is reported to have a high energy conversion efficiency (Babarit et al 2012), and an additional benefit could be a possible low initial building cost of the device since it is basically regarded in a 2D extension, rather than a 3D extension like many other devices if a larger device is expected. A significant challenge is the structural reliability

Pneu-mechanical drive train (PTO)

Small & light devices

W Effective install and O&M

Wave Energy Converters, Fig. 2 CorPower point absorber wave energy converters (CorPower 2017)

2126

Wave Energy Converters

Wave Energy Converters, Fig. 3 Pelamis 2 in waves. (From EMEC website: http://www.emec.org.uk/about-us/waveclients/pelamis-wave-power/) Wave Energy Converters, Fig. 4 Oyster device in waves. (Adopted from website: https:// oregonshores.org/article/ rules-ocean-energy-sitingare-horizon)

of such a device, since it is found that the device is frequently plunged into water ahead the wave action (see Fig. 4), indicating large wave slamming forces on the device. Overtopping Devices Tapchan

Tapchan is a fixed overtopping wave energy plant, one of the two pioneer wave energy plants in Norway in the 1980s (in the same period, a fixed OWC plant was built a few hundred meters away, both on the west coast of Norway). Accordingly, this prototype wave energy converter has the following features: • The wave energy is converted to potential energy in an onshore water reservoir. • The generation of electricity is carried out by a standard hydroelectric power plant technology.

Wave Energy Converters, Fig. 5 Tapchan wave energy plant. (Adopted from (Falcao 2014))

Wave Energy Converters

2127

Wave Energy Converters, Fig. 6 Wave Dragon 1:4.5 model tested in sea. (Adopted from the Internet)

• The conversion device is entirely passive and has no moving parts (except the water turbine). • High energy conversion efficiency can be maintained over a broad range of wave heights, frequencies, and directions. The plant was destroyed by a winter storm in 1988 (see https://www.youtube.com/watch? v¼vG6R_R2YyAo) (Figs. 5 and 6). Floating Overtopping WECs

Wave Dragon is a floating overtopping wave energy converter. From the literature, this device may have so far the highest power rating in all single wave energy converters: 12MW (http:// www.wavedragon.net/). A proposed full-scale Wave Dragon with a 7MW rated power is a huge device, with an overall length of 350m between two arms and a displacement of 40,000 m3. In the development, the concept has finished a 1:4.5 scale sea trial in the test site in Nissum Bredning, Denmark (Kofoed et al. 2006).

References AQWA. AQWA user manual. Cited (on 11/04/2020) at http://www.mecheng.osu.edu/documentation/Flu ent14.5/145/wb_aqwa.pdf Babarit A et al (2012) Numerical benchmarking study of a selection of wave energy converters. Renew Energy 41:44–63. https://doi.org/10.1016/j. renene.2011.10.002 CorPower (2017) CorPower: resonant wave power. cited at http://www.corpowerocean.com/

Cummins WE (1962) The Impulse response function and ship motions, report no. 1661, Department of the Navy, David Taylor Model Basin, USA. Cited at http://dome. mit.edu/bitstream/handle/1721.3/49049/DTMB_1962_ 1661.pdf?sequence=1 Drew B, Plummer AR, Sahinkaya MN (2009) A review of wave energy converter technology. Proc Inst Mech Eng A 223:887–902. https://doi.org/ 10.1243/09576509JPE782 EC (2017) Study on lessons for ocean energy development (final report). cited at http://publications.europa.eu/ r e s o u r c e / c e l l a r / 0 3 c 9 b 4 8 d - 6 6 a f - 11 e 7 - b 2 f 2 01aa75ed71a1.0001.01/DOC_1 EMEC (2018) Wave devices. cited at http://www.emec. org.uk/marine-energy/wave-devices/ Evans DV, Porter R (1995) Hydrodynamic characteristics of an oscillating water column device. Appl Ocean Res 17(3):155–164. https://doi.org/10.1016/0141-1187(95) 00008-9 EVE (2013) Mutriku OWC plant. Cited at http://www.fp7marinet.eu/EVE-mutriku-owc-plant.html. 27 Mar 2013 Falcao A (2010) Wave energy utilization: a review of the technologies. Renew Sustain Energy Rev 14(3):899–918. https://doi.org/10.1016/j. rser.2009.11.003 Falcao AFO (2014) Modelling of wave energy conversion. cited at https://fenix.tecnico.ulisboa.pt/downloadFile/ 3779580629428/Wave%20Energy%20Conversion% 20Modelling%201%20to%205(2014).pdf. 30 June 2018 Falcao A, Henriques JCC, Candido JJ (2012) Dynamic and optimization of the OWC spar buoy wave energy converter. Renew Energy 48:369–381. https://doi.org/ 10.1016/j.renene.2012.05.009 Falnes J (2002) Ocean waves and oscillating systems: linear interaction including wave-energy extraction. Cambridge University Press, New York Faltinsen OM (1990) Sea loads on ships and offshore structures. Cambridge University Press, Cambridge Folley M, Curran R, Whittaker T (2006) Comparison of LIMPET contra-rotating wells turbine with theoretical and model test predictions. Ocean

W

2128 Eng 33(8-9):1056–1069. https://doi.org/10.1016/j. oceaneng.2005.08.001 Fonseca N, Pessoa J (2013) Numerical modeling of a wave energy converter based on U-shaped interior oscillating water column. Appl Ocean Res 40:60–73. https://doi. org/10.1016/j.apor.2013.01.002 Heath T (2012) A review of oscillating water columns. Philos Tranas R Soc A Math Phys Eng Sci 370:235–245. https://doi.org/10.1098/rsta.2011.0164 Kofoed JP et al (2006) Prototype testing of the wave energy converter wave dragon. Renew Energy 31: 181–189 Le Crom I et al (2009) Numerical estimation of incident wave parameters based on the air pressure measurements in Pico OWC plant. In: Proceedings of the 8th European wave and tidal energy conference, 7–10 Sept 2009, Uppsala M4M (2015) M4M wave energy conversion device. cited at http://www.mace.manchester.ac.uk/news/research/ m4m-wave-energy-conversion-device.htm Masuda, Y. 1979, Experimental full-scale results of wave power machine Kaimei in 1978. In: Proceedings of the 1st symposium on wave energy utilization, 30 Oct-1 Nov 1979, Gothenburg MasudaY et al (1988) The backward bend duct buoy-an improved floating type wave power device. In: Proceedings of OCEANS ‘88. A partnership of marine interests, 31 Oct-2 Nov 1988, Baltimore Newman JN (1977) Marine hydrodynamics. The MIT Press, Cambridge, MA OceanEnergy (2017) Ocean energy: a world of power. cited at http://www.oceanenergy.ie/. 11 Feb 2018 Ogilvie TF (1964) Recent progress toward the understanding and prediction of ship motions. In: Proceedings of the 5th symposium on Naval Hydrodynamics, 10–12 Sept 1964, Bergen OPT (2015) Ocean power technology. Cited at http://www. oceanpowertechnologies.com/. 15 Feb 2015 Parisella G, Gourlay TP (2016) Comparison of opensource code Nemoh with Wamit for cargo ship motions in shallow water, Research report 2016-23, Curtin University, Australia. Cited at http://cmst.curtin.edu. au/wp-content/uploads/sites/4/2015/06/ParisellaGourlay-2016-Comparison-of-open-source-codeNemoh-with-Wamit-for-cargo-ship-motions-inshallow-water.pdf Payne G et al (2008) Assessment of boundary-element method for modelling a free-floating sloped wave energy device. Part 1: numerical modelling. Ocean Eng 35:333–341 Pecher A et al (2011) Performance assessment of the Pico OWC power plant following the equimar methodology. In: Proceedings of the twenty-first (2011) International Offshore and Polar Engineering conference, 19–24 June 2011, Maui Rafiee A, Fievez J (2015) Numerical prediction of extreme loads on the CETO wave energy converter. In: Proceedings of the 11th European wave and tidal energy conference, 6–11th Sept 2015, Nantes

Wave Energy Utilization Buoy SeaPower (2015) The sea power platform. Cited at http:// www.seapower.ie/ Sheng W, Lewis A (2016) Energy conversion: a comparison of fix- and self-referenced wave energy converters. Energies 8:054501. https://doi.org/10.1063/1.4963237 Taghipour R, Perez T, Moan T (2008) Hybrid frequencytime domain models for dynamic response analysis of marine structures. Ocean Eng 35(7):685–705. https:// doi.org/10.1016/j.oceaneng.2007.11.002 WAMIT (2016) User manual. http://www.wamit.com/ manual.htm WaveBob (2011) WaveBob. Cited at http://wavebob.com/. 19 Sept 2011 Whittaker TJT, Folley M (2012) Nearshore oscillating wave surge converters and the development of Oyster. Philos Trans R Soc A Math Phys Eng Sci 370:345–364. https://doi.org/10.1098/rsta.2011.0152 Yemm R et al (2012) Pelamis: experience from concept to connection. Philos Tranas R Soc A Math Phys Eng Sci 370:365–380 Yu YH et al (2015) Experimental wave tank test for reference model 3 floating-point absorber wave energy converter project NREL/TP-5000-62951, National Renewable Energy Laboratory, US. Cited at Zheng S et al (2015) Numerical study on the dynamics of a two-raft wave energy conversion device. J Fluids Struct 58:271–290. https://doi.org/10.1016/j. jfluidstructs.2015.07.008

Wave Energy Utilization Buoy Mingfang Li Wuhan University of Science and Technology, Wuhan, China

Synonyms Wave energy converters; WEC

Definition Wave energy utilization buoy is a floating power station for generating electrical energy from wave power. The buoy devices being developed include: Powerbuoy, OE buoy, RM3, IPS buoy, and so on. (The examples shown here are not intended to form an exhaustive list and were chosen among the projects that reached the prototype

Wave Energy Utilization Buoy

stage or at least were object of extensive development effort.)

Scientific Fundamentals A Brief Overview of Buoy Wave Energy Device Wave energy is a type of well-concentrated renewable energy when compared to other types of renewable energy (such as solar, wind, etc.). The wave energy resources are huge, utilizing wave energy is desirable in many countries around the world, especially in the countries with long coastal lines and rich wave energy resources. Wave energy researchers and developers have been working in solving the practical problems in wave energy extraction for many years. Though some early optimistic predictions in capturing large wave energy from seas at a competitive rate (for example, 2GW wave power plant producing power at a rate of 1.3 p/kWh has been described in Whittaker et al. 1985) have not been reached, the research and development of wave energy conversion have made a great deal of progress, and some of the wave energy devices have reached the stages of full-scale precommercial or large-scale sea trials. For instance, in 2009, a 1:2.5 scale OE Buoy device (an oscillating water column (OWC) device) finished a sea trial for a period of over two and half years in Galway Bay. (Ocean Energy Ltd. 2018) Recently, OceanEnergy announced its pioneering wave energy convertor OE Buoy will be built by Oregon-based Vigor and deployed at the US Navy’s Wave Energy Test Site on the windward coast of the Hawaiian Island of O’ahu in the fall of 2018, the 826-ton OE Buoy measures 125  59 feet with a draft of 31 feet and has a potential rated capacity of up to 1.25 MW in electrical power production (Wave Energy Conversion Pioneer 2018). More wave energy devices and their developments can be found in Refs. (Falcao 2010; ISSC Specialist Committee 2009) In the development of wave energy, nearshore or shallow water regions are frequently considered for developing wave energy converters/farms due to the closeness to the shore and the easy

2129

infrastructure, for instance, the cable connection and the availability for the operation and maintenance. One important aspect of these developments is the availability of wave energy resources in shallow water regions. Folley and Whittaker (2009) have shown that the wave resources reduce by less than 10% when traveling from a water depth of 50 m to 10 m. Hence the development of wave energy in shallow water regions has been preferred. So far most of the installed wave energy converters are deployed in the water depths of less than 50 m, and most of the proposed wave farms are deployed in the water depths of less than 100 m. Similarly, Johanning et al. (2007) concluded that wave energy converters (WECs) would be very likely installed in the shallow to intermediate depths, typically at around 50 m contour in the open areas for wave energy production. Point absorbers may be the simplest floating buoy wave energy converters, and the main motion mode for power conversation is heave, though other motion modes may contribute to small part of the power conversation. The horizontal dimensions of point absorbers are much smaller than the wavelength, the known devices are Power Buoy, (OPT 2018a) the US reference model (RM3, Yu et al. 2015; Prendergast et al. 2018) and RM6, (Bull et al. 2014; Sheng 2019a), and so on. The main motions of point absorbers are the relative heave motions between buoy and referenced damping panel (or referenced to the sea bed). It is quite straightforward for the cases with only considering the relative heave motions (Falnes 1999a and Sheng and Lewis 2016a). Scientific Fundamentals The study of the hydrodynamics of floating wave energy converters could benefit from previous studies on the, largely similar, dynamics of ships in wavy seas, that took place in the decades preceding the mid-1970s. The presence of a power take-off mechanism (PTO) and the requirement of maximizing the extracted energy introduced additional issues. In this section, we will take the single buoy wave energy converter as an example to illustrate how the device extracts wave energy from regular

W

2130

Wave Energy Utilization Buoy

fd ¼ 0 in calm water), fPTO(t) is the vertical force due to the PTO mechanism, A(o) is the hydrodynamic coefficient of added mass (accounting for the inertia of the water surrounding the body), B(o) is the radiation damping coefficient (accounting for the damping on the body due to energy transfer to waves radiated away), and S is the cross-sectional area of the body by the unperturbed free surface plane (rgSx is the hydrostatic restoring force). We assume the PTO force to consist of a linear damper (coefficient C) and a linear spring (stiffness K): f PTO ¼
Cx_
Kx

ð2Þ

Then the whole system becomes fully linear. In regular waves of amplitude Ao and frequency o, we write {x, fd} ¼ Re ({X, Fd}eiot), where X and Fd are complex amplitudes and Re() means real part of. Then, from eq. 1, we obtain Wave Energy Utilization Buoy, Fig. 1 Wave energy converter. Figure from (Faedo et al. 2017)

X¼ (sinusoidal) waves and converts it into electrical energy. Detailed information on wave energy utilization can be found in the literature (Falcao 2010). The oscillation system consists of a halfimmersed sphere and a linear PTO with one end anchored in the sea bed, as shown in Fig. 1. Theoretical and Numerical Modeling

We assume the waves with small amplitude, which allowed the linearization of the governing equations and the use of the frequency-domain analysis. The hydrodynamic forces on the wetted surface of the body were decomposed into excitation forces (due to the incident waves), radiation forces (due to body motion), and hydrostatic forces (connected with the instantaneous position of the floating body with respect to the undisturbed free surface). As shown in Fig. 1, the body position is defined by the vertical coordinate x (with x ¼ 0 in calm water), the equation of motion is ðm þ AÞ€ x ¼ f d
Bx_
rgSx þ f PTO

ð1Þ

where, fd(t) is the vertical component of the excitation force (acting on the assumedly fixed body,

Fd
o2 ðm þ AÞ þ ioðB þ CÞ þ rgS þ K ð3Þ

Since the system in linear, the excitation force is proportional to wave amplitude, i.e., |Fd| ¼ ΓAo, where Γ(o) is a hydrodynamic coefficient of diffraction force. The time-averaged absorbed power   is P ¼ f d x_ ¼ Co2 X2 =2, which can be written as P¼

  1 B F 2 j Fd j 2
 U
d  8B 2 2B

ð4Þ

where U ¼ ioX is the complex amplitude of the velocity x._ For a given body and given incident regular wave, B and Fd are fixed. Then the absorbed power P depends on X, i.e., on the PTO damping and spring coefficients C and K. The maximum value equal to Pmax ¼

1 jF j2 8B d

ð5Þ

occurs for U ¼ Fd/2B, then combined Eq. 3 we obtain the two optimal conditions,

Wave Energy Utilization Buoy

 o¼

rgS þ K m þ AðoÞ

2131

1=2

C ¼ Bð o Þ

ð6Þ ð7Þ

Equation 6 is a resonance condition: its righthand side is the frequency of free oscillations of an undamped mechanical oscillator of mass m þ A acted upon by a spring of stiffness rgS þ K. Equation 7 shows that the optimal PTO damping should equal the radiation damping. In regular waves, the averaged wave energy density, Pw (per unit surface area) over a wave period is given by 1 Pw ¼ rgA2 2

ð8Þ

where A is the amplitude of regular waves. We define the capture width l ¼ P=Pw , for a body with a vertical axis of symmetry (but otherwise arbitrary geometry) oscillating in heave, it can be shown that lmax ¼

Pmax l ¼ 2p Pw

ð9Þ

where l is the wavelength. If the body oscillates in sway lmax ¼ pl. equation 9 is an important theoretical result, obtained independently in 1975–1976 by Budal and Falnes, Evans, Newman, and Mei, (Falcao 2010) on the maximum power that can be absorbed from the waves, as is the well-known Betz limit for the power coefficient of wind turbines. Maximum Wave-Power Absorption Under Motion Constraints

In practice, most wave-energy devices will have physical limitations placed upon their excursions due to restraints such as mooring lines or piston stroke. Whereas there exists a significant band of wave frequencies and lengths for which the device does not reach these limits, in long waves a relatively small device would, ideally, need to make large excursions to achieve optimum power absorption. Again, larger amplitude waves require larger device excursions for optimum absorption. Evans D V (1981) proposed a simple expression

for the maximum efficiency of power absorption of a buoy when its velocity and hence amplitude is constrained such that its magnitude never exceeds a given multiple of the incident wave amplitude and also for a system of absorbing bodies under global velocity constraints. Here we will briefly demonstrate his conclusion. We consider a regular incident wave condition in a frequency of o, N independently oscillating buoys making simple harmonic motions response to the wave also in the frequency of o, and each buoy can absorb energy from the incident wave field. Let U be the complex N-vector denoting the amplitude and phase of the velocity of each buoy, and B the N  N real, symmetric radiation damping matrix. Let F be the complex N-vector denoting the amplitude and phase of the exciting force on each buoy in its direction of subsequent motion, when all buoys are held fixed. Then the optimized energy absorption can be shown as: 1 Pmax ðUÞ ¼ U  ðB þ 2mI ÞU 2 h i 1 ¼ F s B
1
B
1 ðB þ mI Þ
2 m2 F s 8 ð10Þ for 1 b  B
1 F s ¼ kY k 2

ð11Þ

where * denotes conjugate transpose, β is the constraints of the buoys, m determined by UU 5 β2 and U ¼ (B þ mI)
2BY, Y 5 12 B
1 F. We assume each of the N buoys have constraints on their amplitudes and velocities which may be of the form: jU i j  oAai ¼ bi ði ¼ 1, 2, . . . , N Þ

ð12Þ

where A is the incident wave amplitude and αi are constants governing the permissible buoy amplitude compared to the incident wave amplitude. In normal operating conditions αi ¼ 0(1) but in larger waves αi may be small. We define the capture width l ¼ P/Pw, for a vertically oscillating buoy with a vertical axis of symmetry,

W

2132

Wave Energy Utilization Buoy

Pmax Pw n o l ¼ 1
H ð1
dÞð1
dÞ2 2p

lmax 

ð13Þ

occupied by the sphere. In steeper waves where the ratio may have to be as small as α ¼ 0.5 the captured width never exceeds 40% of the sphere diameter.

where  12 3 1 2oAaB 2M d¼ ¼a ðKaÞ2 l233 jFj ra3

Open Sources for WEC Simulation ð14Þ

where K is the wave number, r is the density of sea water, a is the radius of the buoy, and l is the damping coefficient in heave, nondimensionalized with respect to a typical mass, M. Figure 2 Evans 1981 shows the variation of lmax/2a with Ka for different αi of a half-immersed sphere. It can be seen that, if the amplitude of motion of the sphere is not allowed to exceed the wave amplitude the capture width never exceeds 70% of the sphere diameter in contrast to the result from unconstrained motions where lmax increases indefinitely as Ka ! 0. For sphere amplitudes up to twice the wave amplitude (α ¼ 2), lmax peaks at a value 108% of the sphere diameter showing that energy is being absorbed from outside the region Wave Energy Utilization Buoy, Fig. 2 Variation of maximum capture width/ diameter ratio with wave length for half immersed energy absorbing sphere for different motion constraints. The dashed line denotes unconstrained sphere (Evans 1981)

WEC-Sim (Wave Energy Converter SIMulator) is an open-source wave energy converter simulation tool. The code is developed in MATLAB/ SIMULINK using the multibody dynamics solver Simscape Multibody. WEC-Sim has the ability to model devices that are comprised of rigid bodies, power-take-off systems, and mooring systems. Simulations are performed in the time-domain by solving the governing WEC equations of motion in 6 degrees of freedom. WEC-Sim is a collaboration between the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (Sandia), funded by the US Department of Energy’s Water Power Technologies Office. Due to the opensource nature of the code, WEC-Sim has also had many contributions from external

Wave Energy Utilization Buoy

collaborators. For more details see (Wave Energy Converter SIMulator 2018).

Key Applications There is a wide variety of wave energy utilization technologies, resulting from the different ways in which energy can be absorbed from the waves, and also depending on the water depth and on the location (shoreline, nearshore, offshore). Several methods have been proposed to classify wave energy systems, according to location, to working principle, and to size (“point absorbers” versus “large” absorbers). The classification in Fig. 3 (Falcao 2010) is based mostly on working principle. The floating devices can be classified as wave energy utilization buoy. The examples shown are not intended to form an exhaustive list and were chosen among the projects that reached the prototype stage or at least were object of extensive development effort.

2133

A few devices are briefly described in the following section. OE Buoy (BBDB OWC, RM6) OE Buoy is an Oscillating Water Column wave energy converter deployed by the HMRC (The Hydraulics and Maritime Research Centre) in Cork, Ireland, and is now owned and developed by the company OceanEnergy. The OE Buoy is a version of a device known as the Backward Bent Duct Buoy (BBDB) which was invented in 1986 by wave energy pioneer and Japanese naval commander Yoshio Masuda et al. 1988. It was deployed in half-scale test mode in Spiddal near Galway in Ireland for over 2 years between 2007 and 2009. As of March 5, 2011, the model has been redeployed at the same site, primarily as a data collector for the EU-funded Cores Project. The full-scale pioneering OE buoy developed by OceanEnergy will be built by Oregon-based Vigor and deployed at the US Navy’s Wave Energy Test Site on the windward coast of the Hawaiian Island

W

Wave Energy Utilization Buoy, Fig. 3 The various wave energy technologies (Falcao 2010). The floating devices can be classified as wave energy utilization buoy

2134

Wave Energy Utilization Buoy

Wave Energy Utilization Buoy, Fig. 4 RM6 BBDB device design and dimensions and wells turbine schematic. The width of the device (not shown) is 27 m (Bull et al. 2014)

of O’ahu in the fall of 2018 (Wave Energy Conversion Pioneer 2018). RM6 reference model (see Fig. 4) is an oscillating water column wave energy converter developed by Sandia National Laboratories using a combination of numerical modeling tools and scaled physical models (Bull et al. 2014). Bull et al. (2015) studied the US RM6 BBDB oscillating water column wave energy converter, providing some insights on the BBDB wave energy converters on the optimization of the air turbine PTO, as well as the electricity generation. The systematic study of the power performance of BBDB OWC devices can be found in the literature (Sheng and Lewis 2018, 2016b; Sheng 2019b). Reference Model 3 RM3 is essentially a twobody floating (self-referenced) point absorber, it can also be considered as a fix-referenced PA when the damping panel is fixed (no motion is allowed for it). The following section will take RM3 as an example to illustrate the basic principle of wave energy device conversion of wave energy. The original design of RM3 is shown in Fig. 5. This point absorber consists of two main moving bodies: the surface float of diameter 20 m with a small draft, and the vertical column which is connected to a large reaction plate (30 m in diameter). Overall, the point absorber has a draft of

30 m, and the displacements 848.2 m3 and 680.8 m3 for the vertical column (the cylinder and the reaction plate has been simplified as zero thickness) and for the surface float, respectively. The surface float moves up and down the vertical column in response to the motion of the waves. The reaction plate maintains the vertical column in a relatively stationary position. The relative motion of the surface float with respect to the vertical column drives a mechanical system contained in the vertical column that converts the linear motion of the surface float into a rotary one. The rotary motion drives electrical generators that produce electricity for the payload or for export to nearby marine applications using a submarine electrical cable. This high-performance wave energy conversion system generates power even in moderate wave environments. In converting wave energy, the surface float will very much move in-phase, while the vertical column moves out-of-phase with the passing waves. These in-phase and out-of-phase motions could generate a large relative motion between these two bodies, thus providing good motions for converting wave energy. In the case of a fixreferenced RM3, the vertical column can be taken as a fixed structure. It will be seen that for a floating PA with its relative motions between the moving components being used, it could be beneficial for improving its wave energy conversion efficiency, as well as its

Wave Energy Utilization Buoy

2135

Wave Energy Utilization Buoy, Fig. 5 The RM3 point absorber wave energy converter (Yu et al. 2015).

compliance thus its survivability in the extreme waves (with long wave periods). Following (Sheng and Lewis 2016a), for such floating/self-referenced WECs, the heave motions of the two-body systems are normally

independent of the other motion modes, especially when the motions are small. For power conversion, the relative heave motions of the two bodies are taken, and the corresponding dynamic equation can be expressed as:

ð15Þ

with

ð16Þ where Bpto is the damping coefficient of the PTO for the RM3 device; b33, b39, b93, and b99 are the radiation damping coefficients due to the body motions; B33 and B99 the additional linear damping coefficients caused by the heave motion

of the bodies; f3 and f9 the complex excitations for the heave motions of both moving bodies of the device; v3 and v9 the velocities of the heave motions; m33 and m99 the mass of each body; a33, a39, a93, and a99 the self- and cross-term added masses related to the heave motion of two bodies; and c33, c39, c93, and c99 the corresponding restoring force coefficients for the device. The average power conversion is then given by Eq. 17 below, ð17Þ

W

2136

Wave Energy Utilization Buoy

with the relative velocity solved from Eq. 15, the average power is,

reactance-dependent damping coefficients and Z1 and Z2 are radiation damping and excitation-based values that are calculated using Eq. 19 as:

ð18Þ In the above equation Y1, Y2, Y3, and Y4 are

ð19Þ

where the subscripts r and i denote the real and imaginary parts of the excitation forces f3 and f9. Based on the Eq. 18, an optimized PTO damping for maximizing the wave energy conversion for the wave of a given frequency can be obtained in Eq. 20 and the corresponding maximized power conversion in Eq. 21.

ð20Þ

ð21Þ

The optimized PTO damping and the maximal converted wave energy both vary depending on frequency; hence this optimized condition may only be useful in the regular waves, where the wave frequencies are constant for a given wave. Figure 6 shows the comparison of the maximal capture powers for the fix-referenced and selfreferenced PAs (“fix-referenced” and “selfreferenced” in the legend) and the self-referenced devices are with two different reaction plates (D ¼ 25 m and D ¼ 30 m), more details can be found in Sheng and Lewis (2016a). PowerBuoy PowerBuoys are manufactured by Ocean Power Technologies (OPT) in Pennington, New Jersey

(OPT 2018b) (see Figs. 7 and 8). The outline of the PowerBuoy design process is illustrated by examples from recent development efforts in (Edwards and Mekhiche 2014), which attempts to address the complex multidiscipline and concurrent engineering process required to successfully design, develop, test, and validate of OPT’s PowerBuoy. OPT’s PowerBuoy portfolio includes two power output ranges: up to 3 kW and up to 15 kW, the average output power is deploymentsite dependent. OPT’s products serving the offshore power needs are the PB3 (commercial ready) and the PB15 (under development). Product specifications for the PB3 are shown in Fig. 9. OPT’s PB3 was designed acting as an uninterruptable power supply (UPS) which

Wave Energy Utilization Buoy

2137

Wave Energy Utilization Buoy, Fig. 6 RM3 maximal capture powers in regular waves (D ¼ 25 m and D ¼ 30 m) (Bull et al. 2014).

Considering the levels of validation and maturity that have been achieved through full-scale ocean deployments and accelerated life testing, and based on the American Petroleum Institute (API) Technology Readiness Scale (TRL) of 7 (API 17 N), the PB3 was estimated to have achieved a TRL6.

Wave Energy Utilization Buoy, Fig. 7 PowerBuoy cross sectional view (Parsa et al. 2017)

constantly recharges itself by harvesting energy from the waves. It was developed for offshore remote autonomous applications such as the ones found in the oil and gas industry. It was ocean-deployed, moored, and floats over the point of use and can operate in any ocean depth over 20 meters and up to 1000 meters. In July 2016, OPT deployed its first commercial PB3 PowerBuoy off the coast of New Jersey (Ocean Power Technologies 2018; Parsa et al. 2017)

IPS Buoy The IPS Buoy is a system for generating electricity from ocean waves designed by two Swedish companies, Interproject Service AB (IPS) and Technocean (TO). Figure 10 shows the working principle of the IPS OWEC Buoy. As the buoy A moves up and down with waves, the acceleration tube B, which is open in both ends, will move vertically relative to the water column in it. The water column will “trap” the piston C, forcing it to move relative to the acceleration tube. This pumping motion is mechanically or hydraulically transformed to a rotary motion driving a generator D. A typical IPS OWEC Buoy consists of a round 6–8 meter buoy floating, a 20 meter underwater acceleration tube with a piston, and an energy conversion machinery including an electric generator. The buoy is typically located in 50–100 meters deep water and anchored via a slack mooring arrangement. One such buoy built for 120 kW mean output may produce up to 1.0 GWh

W

2138

Wave Energy Utilization Buoy

Wave Energy Utilization Buoy, Fig. 8 Two PB3 as deployed in the ocean in surface expression (Parsa et al. 2017)

Wave Energy Utilization Buoy, Fig. 9 Product specifications for the PB3 (OPT 2018c)

annually. In the waters west of Scotland and Ireland where the power “content” in the waves is in the order of 50 ~ 70 kW/m wavefront, a 10 m IPS

OWEC Buoy will reach a power of 150–250 kW and produce more than 1.4 GWh of electric energy per year The IPS OWEC Buoy (2018).

Wave Energy Utilization Buoy

2139

Wave Energy Utilization Buoy, Fig. 11 IPS buoy with the piston replaced by a hydraulic turbine. (Falcão A F O et al. 2012) Wave Energy Utilization Buoy, Fig. 10 Working principle of the IPS OWEC Buoy

The piston slides along the central part of the tube that needs to limit the stroke of the piston at both ends. Falcão A F O et.al (2012) proposed using a hydraulic turbine inside the tube to solve the problem of the end-stops, as shown in Fig. 11. In such situations, the dynamics of the IPS buoy can no longer be theoretically modeled as Falnes (1999b) did for a two-body heaving system or as done in (Falcão AF de et al. 2008) for the IPS buoy, for the cross-section of the acceleration tube is nonuniform, the flow inside the tube is also nonuniform, the inertia of the enclosed water cannot be represented by that of a solid body. Besides, apart from the axial force on the piston (or on the hydraulic turbine), the extra-axial force on the noncylindrical inner walls of the tube must be accounted for.(Falcão et al. 2012) In regular waves, for a given buoy and given tube diameter and diameter ratio, maximum wave energy absorption is attained by an infinite number of tube combination mass (tube mass plus tube added mass) tube length and PTO damping coefficient. While in irregular waves, the performance was found to be much poorer (no phase control is considered), even if the tube combination mass,

the tube length, and the PTO damping coefficient are optimized. The use of a hydraulic turbine in the tube instead of a piston was found in general to result in poorer wave energy absorption and to require a longer tube (Falcão et al. 2012). The Sloped IPS Buoy The sloped IPS buoy concept was developed by Edinburgh University as a device that would replace the Solo Duck(Salter 1974) as a confidence-building step in wave energy technology (Salter and Lin 1995). It is based on the axisymmetrical device designed by Interproject Services (IPS). The device is an inclined flat plate with a curved head (approximately 30 m wide and 6 m from front to back), which is inclined at an angle to the vertical (see Fig. 12 and Table 1, Thorpe 1999). The long tail is open to the sea at the bottom and is mainly empty, except for bracing plates. This adds a large inertia to movement in all directions, except for “slope” (i.e., back and forth in the direction of the tail). In this mode, the plates are edged on to the movement and so offer minimal resistance. An important feature of the buoy is the flared ends of the tube containing the water piston. When the movement of the piston exceeds the length of the

W

2140

Wave Energy Utilization Buoy

Wave Energy Utilization Buoy, Fig. 12 Shape and side view of the sloped-IPS Buoy (Thorpe 1999)

Wave Energy Utilization Buoy, Table 1 Summary of the characteristics of the sloped-IPS Buoy (Thorpe 1999) Device width

30 m

Directionality factor Mean power Capture efficiency Power captured Conversion efficiency Generator efficiency Availability Average power out Annual output

0.94 1495 kW 81% 1212 kW 92% 88% 90% 985 kW 7.77 GWh

narrower part of the tube, it will enter the wider section allowing water to flow past it more easily. This flow effectively decouples the piston from the large inertia of the water mass in the tail. This arrangement avoids the shock loading that “end stops” can cause. Salter and Rampen (1993) designed the “wedding cake” multieccentric radial piston hydraulic machine for the sloped IPS buoy, but the piston will be operating in seawater so the durability of the device needs to be assessed specially. Taylor J R M and Mackay I (2001) designed an eddy current dynamometer for the Swedish freefloating sloped-IPS buoy and optimized the sloped-IPS buoy models so that the detailed

response data can be collected for a very wide range of sea conditions. More details of numerical simulation about sloped-IPS Buoy can be found in (Payne et al. 2006, 2015). Summary The ocean has a rich reserve of wave energy. So far, thousands of WEC patents have been proposed or put into practice, the number does not seem to be decreasing: new concepts and technologies replace or outnumber those that are being abandoned. All forms of devices should focus on cost, availability, and survivability to improve the industrial readiness level for large-scale commercial applications.

References Bull D (2015) An improved understanding of the natural resonances of moonpools contained within floating rigid-bodies: theory and application to oscillating water column devices[J]. Ocean Eng 108:799–812 Bull D, Smith C, Jenne D S, Jacob P, Copping A, Willits S, Fontaine A, Brefort D, Copeland G, Gordon M, Jepsen R (2014) Reference Model 6 (RM6): Oscillating Wave Energy Converter. SAND2011–18311 Edwards K, Mekhiche M. (2014) Ocean Power Technologies Powerbuoy ®: System-Level Design, Development and Validation Methodology[J]

Wave Energy Utilization Buoy Evans DV (1981) Maximum wave-power absorption under motion constraints[J]. Appl Ocean Res 3(4):200–203 Faedo N, Olaya S, Ringwood JV (2017) Optimal control, MPC and MPC-like algorithms for wave energy systems: an overview[J]. IFAC J Systems Control 1:37–56 Falcao AFDO (2010) Wave energy utilization: a review of the technologies. Renew Sust Energ Rev 14:899–918 Falcão AF de O, Justino PAP, Henriques JCC, André JMCS (2008) Modelling and control of the IPS buoy. In: Proc. 2nd int. conf. Ocean energy, Brest Falcão AFO, Cândido JJ, Justino PAP et al (2012) Hydrodynamics of the IPS buoy wave energy converter including the effect of non-uniform acceleration tube cross section[J]. Renew Energy 41:105–114 Falnes J (1999a) Wave-energy conversion through relative motion between two single model oscillating bodies. Trans ASME 121:32–38 Falnes J (1999b) Wave-energy conversion through relative motion between two single-mode oscillating bodies [J]. J Offshore Mech Arct Eng 121(1):32–38 Folley M, Whittaker T (2009) Analysis of the nearshore wave energy resource. Renew Energy 34:1709–1715 ISSC Specialist Committee (2009) “Ocean, Wind and Wave Energy Utilization,” Proceedings of the 17th International Ship and Offshore Structures Congress (ISSC), Seoul, Korea, Aug. 16–21 Johanning L, Smith GH, Wolfram J (2007) Measurements of static and dynamic mooring line damping and their importance for floating WEC devices. Ocean Eng 34: 1918–1934 Masuda Y, Yamazaki T, Outa Y et al (1988) The backward bend duct buoy-an improved floating type wave power device[C]//OCEANS'88.'A Partnership of Marine Interests. Proc IEEE:1067–1072 Ocean Energy Ltd., http://www.oceanenergy.ie/ Accessed 7 June 7 2018 Ocean Power Technologies Deploys Commercial PowerBuoy with Energy Storage. https://www. powermag.com/ocean-power-technologies-deployscommercial-powerbuoy-energy-storage/ Accessed 7 Nov 2018 OPT. Ocean Power Technology. Available online: http:// www.oceanpowertechnologies.com/, Accessed 7 Nov 2018a OPT OceanPowerTechnologies https://www.oceanpower technologies.com/powerbuoy Accessed 7 Nov 2018b OPT OceanPowerTechnologies PB3, https://www. oceanpowertechnologies.com/pb3 Accessed 7 Nov 2018c Parsa K, Mekhiche M, Sarokhan J et al (2017) Performance of OPT’s commercial PB3 PowerBuoy™ during 2016 ocean deployment and comparison to projected model results[C]//ASME 2017 36th international conference on ocean, offshore and Arctic engineering. Am Soc Mech Eng:V010T09A021–V010T09A021 Payne G S, Taylor J R M, Parkin P, et al. (2006) Numerical modelling of the sloped IPS buoy wave energy converter[C]//The Sixteenth International Offshore and

2141 Polar Engineering Conference. International Society of Offshore and Polar Engineers Payne GS, Pascal R, Vaillant G (2015) On the concept of sloped motion for free-floating wave energy converters [J]. Proc R Soc A 471(2182):20150238 Prendergast J, Li M, Sheng W (2018) A study on the effects of wave spectra on wave energy conversions[J]. IEEE J Ocean Eng Salter SH (1974) Wave power[J]. Nature 249(5459): 720–724 Salter S, Lin CP (1995) The sloped IPS wave energy converter[C]//2nd European wave energy conference, Lisbon, pp 337–344 Salter S H, Rampen W H S. (1993) The wedding cake multi-eccentric radial piston hydraulic machine with direct computer control of displacement[C]// Proc. 10th International Conference on Fluid Power. 47–64 Sheng W (2019a) Power performance of BBDB OWC wave energy converters[J]. Renew Energy 132: 709–722 Sheng W (2019b) Power performance of BBDB OWC wave energy converters[J]. Renew Energy 132: 709–722 Sheng W, Lewis A (2016a) Power take-off optimisation for maximising energy conversion of wave activated bodies. IEEE J Ocean Eng Sheng W, Lewis A (2016b) Wave energy conversion of oscillating water column devices including air compressibility[J]. J Renew Sustain Energ 8(5):054501 Sheng W, Lewis A (2018) Power takeoff optimization to maximize wave energy conversions for oscillating water column devices[J]. IEEE J Ocean Eng 43(1): 36–47 Taylor J R M, Mackay I. (2001) The design of an eddy current dynamometer for a free-floating sloped IPS buoy[C]//Marine Renewable Energy Conference (MAREC). 67–74 The IPS OWEC Buoy. http://www.ips-ab.com/owec.htm, Accessed 7 Nov 2018 Thorpe TW (1999) A brief review of wave energy [M]. Harwell Laboratory, Energy Technology Support Unit, London Wave Energy Conversion Pioneer, Ocean Energy, Inks Major Deal For Deployment At Us Navy Wave Energy Test Site In Hawaii. http://www.oceanenergy.ie/oe-usa, Accessed 7 Nov 2018 Wave Energy Converter SIMulator. https://wec-sim. github.io/WEC-Sim/, Accessed 7 Nov 2018 Whittaker TJT, Leitch JG, Long AE, Murray MA (1985) The Q.U.B. axisymmetric and multi-resonant wave energy converters. ASME J Energy Resour Technol 107:74–80 Yu YH, Lawson M, Li Y, Previsic M, Epler J, Lou J (2015) Experimental Wave Tank Test for Reference Model 3 Floating-Point Absorber Wave Energy Converter Project 2015; NREL/TP-5000-62951; National Renewable Energy Laboratory, Golden

W

2142

Wave Measurement Buoy Wanan Sheng SW MARE Marine Technology and Consultation, Cork, Ireland

Wave Measurement Buoy

waves (the modern wave measurement buoys may also collect the meteorological and oceanographic data, depending on the purposes of the wave measurement buoys). In most cases, the wave measurement buoys are anchored at seabed to allow some motions so to reduce the environmental loads acting on the buoy (see Fig. 1).

Synonyms Scientific Fundamentals Navy oceanographic meteorological automatic device; NOMAD; Ocean data acquisition system; ODAS; Waverider buoy; Wavescan buoy; Weather buoy

Definition Wave measurement buoys are the special buoys which are commissioned to measure the ocean

Nowadays, wave measuring buoys are essential devices in many applications. Many national and international meteorological and oceanographic services monitor ocean wave characteristics nearly continuously over great expanses of the world’s coastlines and in deep waters. These provide important information for mariners, fishermen, offshore oil workers, weather forecasters,

Wave Measurement Buoy, Fig. 1 Wave measurement and communications. (Adopted from website: https://www. bosai-jp.org/en/solution/detail/29/category)

Wave Measurement Buoy

ocean engineers, harbor authorities, coastal managers, marine scientists, and the public-at-large planning, coordinating, and conducting a variety of maritime activities. The wave measurement buoys are normally anchored to the seabed using a single point mooring system (Fig. 1), which could provide enough flexibility for the motion of the buoy, allowing the buoy following the water particle motions, and therefore, the buoy’s heave motion can be assumed to be the wave elevation (details can be seen in the following section). It should be noted that in many cases, the wave measurement buoys may have equipped with many sensors to measure other environmental and oceanographic parameters for providing more information to different users as mentioned above. One of the advantages for the wave measurement buoys for measuring waves is their capability in long-term measurement: the measured data can be transformed using the direct radio communication or via a satellite (see Fig. 1); and the wave measurement is subject to battery life, and that is why the wave measurement buoys are equipped with solar panels. Principle of Wave Measurement Using Wave Buoys The wave measurement buoys measure the ocean waves on the assumption that the buoys follow the water particles traveling on a circular orbit (in deep water conditions). A good example is shown in Fig. 2 (WaveRider wave measurement buoy). The main measurement unit is the accelerometer which is located on a stabilized platform, so it could measure the up-and-down motion of the buoy (in a nautical term as heave motion), rather than the motions of all 6 degrees of freedom (6-DOFs). The accelerometer measures the heave acceleration, and the double integration of it would lead to the motion of the buoy. It should be noted that the wave measurement buoys follow the water particle motion only for certain wave lengths/periods. The RAO (response amplitude operator) of the heave motion for the 0.9 m WaveRider is shown in Fig. 3. It can be seen that when the wave period is larger than 2.5 s, the

2143

Wave Measurement Buoy, Fig. 2 Setup of the WaveRider buoy (website figure)

RAO is very close to 1.0 (equal to 1.0 when the wave period is larger than 3.0 s). The unit RAO means that the heave motion of the WaveRider buoy is same as that of the wave elevation. When wave period is smaller than 3.0 s, an appropriate correction must be applied to get the correct relation between the buoy’s heave motion and the wave elevation. Another important factor is the buoy’s phase response (“red line” in Fig. 3). When the wave period is larger than 1.7 s, the buoy’s heave motion is in phase with the wave elevation, and for the shorter waves, there will be a large response phase between the heave motion and wave, for which the correction would be much more difficult and the measurement accuracy may be limited (it is also subject to the damping level of the buoy in waves). Comparison of Wave Buoys and Other Wave Measurements One question may be asked that whether the wave measurement buoys can measure the wave accurately. For instance, whether the wave measurement buoys could follow the water particles or whether the buoy could avoid the large wave peaks (3-D waves). To answer this question there

W

2144

Wave Measurement Buoy

Wave Measurement Buoy, Fig. 3 WaveRider buoy response to wave excitation (WaveRider diameter: 0.9 m)

Wave Measurement Buoy, Fig. 4 Wave measurements buoys used in WADIC project

are many comparisons of the wave buoys to other measurement methods. In the WADIC project (Allender et al. 1989), seven different wave measurement buoys (Fig. 4) are used for the comparisons of wave measurements, including wavestaff, wave radar, and laser measurement. The conclusion is that all the

measurements are reassuringly good, and the large differences are found mostly for swells, high frequency waves (0.2–0.5 Hz), and the extreme sea states. In another research work, Liu et al. (2015) studied the wave measurements using wave measurements in laboratory condition. Two wave

Wave Measurement Buoy

2145

buoys are, namely WaveScan (1:8 & 1:16) and ODAS (1:11.25), used for comparisons with the wave measurements of wave probes in the wave tank. The data analysis has shown that the wave buoys measure waves in a very good agreement with the measurements of wave probes. In a recent survey in 2010, Mettlach and Teng (2010) examined the ocean wave measurements around the world, and it is found that the nearly all wave buoys use onboard accelerometers for measuring waves; however, Japan, the Netherlands, South Africa, and the USA have experimented with GPS and D-GPS to produce wave measurements.

Key Applications WaveRider Buoy The Waverider buoys, developed by Datawell BV (http://www.datawell.nl/products/buoys. aspx), use the same sensors in the well-known Directional Waverider MkI, II, III, and 4. For the directional WaveRider 4 (Fig. 5), its sample frequency of the data processing is doubled to 2.56 Hz. The high frequency limit of the heave and direction signals is shifted from 0.58 to 1.0 Hz. With this choice, the high frequency limit of the wave buoy is determined by the hydrodynamic response of the hull, not by the onboard instrumentation. In addition, the DWR4 transmission protocol allows for a superior heave and horizontal displacement resolution. Following is the list that displays the features of Waverider buoys. • Wave motion sensor based on a stabilized platform, accelerometers, and magnetic compass • Measures wave height for wave periods of 1–30 s, accuracy 0.5% of measured value • Measures wave direction • Measures surface current • Measures water temperature • GPS for buoy monitoring and tracking through HF link • Internal logger • Power switch • LED flash antenna

Wave Measurement Buoy, Fig. 5 WaveRider buoy

• 0.9 m (0.7 m) diameter spherical hull of AISI 316 including eccentric mooring eye • Optional Cunifer hull, warranted not to corrode • 1.6 years (10 months) battery life • Optional HF transmitter range 50 km over sea • Optional Iridium SBD module for ocean wide coverage and unlimited range • Optional Iridium Internet module • Optional Argos module for ocean wide coverage and unlimited range • Optional GSM internet module for data transmission via the GSM network • Optional Solar Panel system • Optional hull painting WaveScan Buoy The SEAWATCH WAVESCAN buoy (usually referred to as the WAVESCAN buoy, Fig. 6) is a versatile instrumentation platform that may be used in all applications. It has been designed to

W

2146

Wave Measurement Buoy

Wave Measurement Buoy, Fig. 7 ODAS buoy Wave Measurement Buoy, Fig. 6 WaveScan buoy

provide less drag and large buoyancy, making it well suited for deep offshore locations or areas of strong current forces. The buoy’s hull design is based on the dynamic response and stability requirements from comprehensive wave tank testing. The WAVESCAN buoy is a multiparameter buoy that can be used to collect directional wave data as well as meteorological, oceanographic, and water quality parameters. The buoy also has innovative “wells” for sensor mounting, easing service, and maintenance. Features • The ideal buoy for deep water and severe current conditions • A unique design optimizes wave direction measurements • Multiparameter platform for client’s chosen selection of sensors • Modular shaped hull for easier transport and local assembly • Real-time data transfer and presentation • Full onboard processing of all measured data

Wave Measurement Buoy, Fig. 8 Triaxys Directional Wave Buoy

• Two-way communication link for data transfer and control of a number of buoys • Special mooring design minimizes mooring influence on buoy motions • Successful track record worldwide since 198.

Wave Measurement Buoy

ODAS Buoy An ocean data acquisition system (ODAS, Fig. 7) is a set of instruments deployed at sea to collect as much meteorological and oceanographic data as possible. With their sensors, these systems deliver data both on the state of the ocean itself and the surrounding lower atmosphere. The use of microelectronics and technologies with efficient energy consumption allows to increase the types and numbers of sensor deployed on a single device. Triaxys Directional Wave Buoy The TRIAXYS™ Directional Wave Buoy (AXYS Technologies, http://axystechnologies.

2147

com/products/triaxys-directional-wave-buoy/? open_cat¼40, Fig. 8) is a precision instrument incorporating advanced technologies that make it an easy-to-use, reliable, and rugged buoy for accurate measurement of directional waves. • The TRIAXYS™ sensor unit is comprised of three accelerometers, three rate gyros, a fluxgate compass, and the proprietary TRIAXYS™ Processor. • The TRIAXYS™ provides continuous wave sampling, support for any telemetry, up to 10 Hz motion sampling and up to 32 GB (>5 years) of data logging capacity. • The TRIAXYS™ sensor also uses the WatchMan500™ controller, which is the core

Wave Measurement Buoy, Fig. 9 A NOMAD buoy

W

2148

Wave Measurement Buoy

Wave Measurement Buoy, Table 1 A list of organizations as of July 2010 that have deployed moored wave buoys (Mettlach and Teng 2010) Organization Agency for Assessment and Application of Technology, Indonesia Australian Bureau of Meteorology Caribbean Integrated Coastal Ocean Observing System, Puerto Rico Centre for Environment, Fisheries & Aquaculture, UK Chesapeake Bay Interpretive Buoy System Stations, USA Coastal Data Information Program, Scripps Institution of Oceanography, USA Coastal Ocean Monitoring Center, National Cheng Kung University, Central Weather Bureau, Taiwan Delaware Coastal Management Program, USA Environment Canada

Environment Canterbury Regional Council, New Zealand Gulf of Maine Ocean Observing System, USA Hellenic National Center for Marine Research, Greece Hydrometeorological Service of Vietnam Icelandic Maritime Administration Japan Meteorological Agency King Abdullah University, Saudi Arabia Korean Meteorological Agency Manly Hydraulics Laboratory, Australia Marine Institute, Ireland Marine Institute, Peru Met Eireann, Ireland Météo-France Meteorological Department, States of Jersey, UK Michigan Technological University, USA National Data Buoy Center, USA National Institute for Ocean Technology Stations, India National Marine Service, Italy National Research Council of Thailand Oceanographic Institute of the Navy, Ecuador Peoples Republic of China Ports Authority of Spain South African Weather Service UK Met Office University of Connecticut, USA University of Michigan, USA University of New Hampshire, USA U.S. Army Corps of Engineers, Duck NC, USA Woods Hole Oceanographic Institution, USA

Types of buoys Wavescan

No. 6

0.9-m Waverider ® 2.5-m ODAS (ocean data acquisition system)

16 1

Waverider

20

Small discus

8

Waverider

51

2.5-m discus

8

TRIAXYS™ 3-m discus, 6-m NOMAD (Navy Oceanographic and Meteorological Automatic Device), 1.7-m WatchKeeper™, WatchMate™ Waverider

2 52

3

2-m ODAS Wavescan

12 10

Wavescan Wavescan Small discus 3-m discus 3-m, 6-m NOMAD Waverider TRIAXYS Wavescan 2.5-m ODAS, Wavescan ODAS 3-m discus TRIAXYS Small discus 1.8-m, 2.4-, 3-, 10-, 12-m discus, 6-m NOMAD Wavescan

4 6 1 1 5 7 6 6 9 1 1 105 4

1.7 m Seawatch Wavescan Wavescan Small discus Wavescan, Waverider, TRIAXYS Waverider 3-m ODAS, TRIAXYS Small discus Small discus Waverider Waverider 2.4-m discus

14 8 3 3 14 6 9 2 1 1 1 2

Wave-Ice Interactions

• •

• •

• •

technology used in other AXYS monitoring systems. The TRIAXYS™ Directional Wave Buoy is solar powered. The TRIAXYS™ is easy to handle during deployment and can be rolled off a ship deck without any concern for sensor damage due to spinning. The TRIAXYS™ can also withstand extreme temperatures as its sensor is not subject to freezing. The TRIAXYS wave buoy can be configured with AIS Aid to Navigation to broadcast buoy position and weather information to local vessel traffic. TRIAXYS™ buoys have been deployed in waters from 10 to 300 m. Standard mooring configurations specially designed for wave buoys are available for water depths up to 300 m.

NOMAD Buoy The AXYS NOMAD (AXYS Technologies, http://axystechnologies.com/products/nomadbuoy/) is a unique aluminum environmental monitoring buoy designed for deployments in extreme conditions. The NOMAD (Navy Oceanographic Meteorological Automatic Device) is a modified version of the 6 m hull originally designed in the 1940s for the US Navy’s offshore data collection program. It has been operating in Canada’s Weather Buoy network for over 25 years and commonly experiences winter storms and hurricanes with wave heights approaching 20 m. • Custom configurable with a wide range of sensors for monitoring meteorological, oceanographic, and water quality parameters. • A watertight central compartment houses the electronics payload, and there are two masts for mounting meteorological sensors, telemetry hardware, solar panels, and obstruction lights. • Uses the WatchMan500™ controller to integrate sensor systems and provide onboard data processing, data logging, telemetry, and diagnostic/setup routines. • A variety of telemetry options are available, including UHF/VHF, Inmarsat IsatData Pro,

2149

Iridium, GPRS/HSPA, and CDMA/EVDO (Fig. 9). Summary There are many different types of wave measurement buoys deployed for measuring waves in oceans, and the principle for measuring waves is very similar. The choice of the wave buoys may be depending on many different requirements. For instance, in many applications, wave measurement may be only one of many other measurements: Small buoys are preferred if the wave measurement is the primary parameter and the shorter waves are more important while the large buoys provide more space and buoyance for accommodating more sensors for other measurements. Following table is a summary of the main buoys deployed in 2010 for measuring waves around the world (see Table 1).

References Allender J et al (1989) The WADIC project: a comprehensive field evaluation of directional wave instrumentation. Ocean Eng 16:505–536 Liu Q, Lewis T, Zhang Y, Sheng W (2015) Performance assessment of the wave measurements of wave buoys. International Journal of Marine Energy 12:63–76. https://doi.org/10.1016/j.ijome.2015.08.003 Mettlach T, Teng CC (2010) Concepts for an ideal ocean wave-measuring buoy. In: Oceans 2010, 20–23 Sept 2010, Seattle

Wave-Ice Interactions Hongtao Li Offshore Engineering Technology Center of China Classification Society, Tianjin, China Sustainable Arctic Marine and Coastal Technology (SAMCoT), Centre for Researchbased Innovation (CRI), Norwegian University of Science and Technology, Trondheim, Norway

Introduction As a result of global climate change, it has been observed shrinking of ice extent and increase of

W

2150

Wave-Ice Interactions

Wave-Ice Interactions, Fig. 1 Extent of sea ice in Arctic Ocean (National Snow and Ice Data Center 2018b)

wave height in the Arctic Ocean (Thomson and Rogers 2014; Vizcarra 2018). Figure 1 demonstrates the evident diminishing trend of Arctic Sea ice extent. Ocean waves were recorded even in the order of 100 km into ice cover (Liu and Mollo-Christensen 1988; Meylan et al. 2014). Large wave itself poses as a threat to human activities, such as natural resource exploration, shipping, and tourism. Similarly, structural damages of sea-going vessels and offshore structures because of severe ice condition have been documented. In addition to low temperature, combination of severe wave and ice conditions in Arctic Ocean makes the safe operation in this region challenging. Currently, the stage of modeling wave-ice-structure interaction has not been reached yet. Wave-ice interactions are highly nonlinear and coupled. Waves accelerate the formation of ice in winter season, break ice, mobilize ice around, and bring heat by convection to speed up the melting of ice in warm weather. At the same time, ice refracts, scatters, damps waves, and changes wavelength. Herein, we focus on the effects of ice on waves. To start with, a brief account of sea ice types and forming process is provided. Then, effects of ice on waves and wave-ice interaction theories are

presented. Lastly, this entry concludes with summary.

Growth of Sea Ice Sea water freezes and forms sea ice. This process is different from how iceberg is produced. Iceberg originates from glacier. It should be noted that iceberg is of fresh water ice. In the supercooled sea water, frazil ice firstly forms, which has needle-like crystals form (Rogers et al. 2016). Under the action of current and waves, these fine spicules are swept together to become oil-slick and matte looking grease ice (see Fig. 2a). Then, the evolution phase differs due to different sea states. Under calm sea, grease ice turns into nilas ice. This kind of ice responds to waves like elastic thin sheet that easily bends (Carsey 1992). Nilas ice may interlock with each other (namely, finger rafting, see Fig. 2b), because of the actions from currents or winds. More specifically, nilas ice interchangeably rides over and under each other (National Snow and Ice Data Center 2018c). Thereafter, nilas ice may thicken through rafting and freezing to form smooth continuous ice cover under calm sea.

Wave-Ice Interactions

2151

Wave-Ice Interactions, Fig. 2 (a) Grease ice and pancake ice in waves. (b) Nilas sea ice and finger rafting. (With the permission of Juan Botella. © Juan Botella for PolarTREC). (c) Close look of pancake ice. (d) Pancake ice in waves (see also Fig. 8 in Collins et al. (2017)). (e) Continuous ice cover. ((a) and (d) are reproduced with the

permission of Michael Collins. These images are from the video footage obtained by Michael Collins of the Naval Research Laboratory. © Michael Collins. (c) is reproduced with the courtesy of Junji Sawamura. © Junji Sawamura. (e) is from video footage that was obtained by Altan Turgut of the Naval Research Laboratory. © Altan Turgut)

Under slight to moderate sea, grease ice further aggregates to form pancake ice (see Fig. 2c, d), when the heat loss is sufficiently significant (Rogers et al. 2016; Wang and Shen 2010). The size of the pancake ice is governed by aggregation, bending, collision between ice and slope of sea surface (Shen et al. 2001). If the same environmental condition sustains, pancake ice cements between adjacent floes and thickens through rafting to form rough continuous ice cover (National Snow and Ice Data Center 2018a; Shen et al. 2001). If waves are strong, nilas ice may also evolve into rough continuous ice cover (Fig. 2e) by rafting and ridging. Sea ice growth process is summarized as shown in Fig. 3. For a more detailed description of sea ice, readers are referred to Carsey (1992) for a summary of ice terminologies, Hobbs (2010) for physics of sea ice and Timco, and Weeks (2010) for engineering properties of sea ice. An old but still very valuable article is Weeks and Ackley (1986). Images of various ice types can be found in Fig. 8 of Lee et al. (2017), Antarctic Sea Ice Processes and Climate (2012), and PolarTREC (2018).

Wave-Ice Interactions This section is divided into two subsections. Subsection “Effects of Ice on Waves” demonstrates various mechanisms to change properties of waves during wave-ice interactions. Subsection “Wave-Ice Interaction Models” gives an overview of different theories to model effects of ice on waves. There have been several essential review literatures that summarize the knowledge in this field. Readers are advised to start with Li et al. (2018), Shen (2017), Zhao et al. (2015), and Collins et al. (2017). Hereafter, more comprehensive literature summaries, such as Squire et al. (1995) and Squire (2007), can be referred to. Effects of Ice on Waves To reveal how ice changes waves, Fig. 4 is provided to illustrate the various kinds of processes. This figure shows that a wave pattern, which consists of two harmonic waves (left panel of Fig. 4), attenuates when passing through an ice field. In this process, short waves are dissipated, and long waves with decreased amplitude retain (i.e., ice field acts as a low-pass filter, see the right

W

2152

Wave-Ice Interactions

Wave-Ice Interactions, Fig. 3 Sea ice growth cycle

Wave-Ice Interactions, Fig. 4 Waves are attenuated due to (a) turbulence generated in boundary layer, (b) overwash, (c) vorticity of ice, (d) collision and rafting, (e) wave-induced fracture of ice, and (f) scattering. ((a) and (f) are adapted by permission from Springer Nature

Customer Service Centre GmbH: Springer Nature (Zhao et al. 2015). © The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag, Berlin/Heidelberg, 2015)

Wave-Ice Interactions

2153

Wave-Ice Interactions, Fig. 5 Change of wave parameters during wave-ice interaction

Wave-Ice Interactions, Fig. 6 Two models to describe viscoelasticity of ice

panel of Fig. 4). Various attenuation mechanisms, as shown in the middle panel of Fig. 4, contribute to this phenomenon. Additionally, wave propagation direction alters because of refraction, reflecting and scattering in ice fields (Fig. 4f). Wavelength is modified as well due to the presence of ice. Figure 5 depicts what wave period, wave amplitude, and wavelength represent, which of them are changed and associates with what processes. Wave-Ice Interaction Models The development of wave-ice interaction theories can be traced back to nineteenth century. Nevertheless, most of the research work commenced after 1950s. In what follows, typical theoretical models are presented. Figure 6 depicts two commonly used rheological models, i.e., Kelvin-Voigt model (henceforth denoted as Voigt model) and Maxwell model that consist of spring and dashpots. These two models are often employed to describe the constitutive

relation of ice, i.e., relation between strain, strain rate and stress. Table 1 summarizes the wave-ice interaction theoretical models used to quantify the change of wavelength and amplitude of waves when waves traveling into ice fields. In Table 1, the second column lists abbreviations of each model, and corresponding assumptions for ice and water are tabulated in the two columns that follow. Last column gives the criteria to choose physically meaningful solution results. The forthcoming parts are based on the work of Li et al. (2018) and references cited therein. Two common assumptions of these models are (1) ice layer always stays in contact with water; (2) small-amplitude and small-slope waves (i.e., linear wave theory). Because of linear wave assumption, these models only produce exponential decaying behavior of waves when waves propagating in ice fields. On the contrary, large waves in some regions of Arctic and Antarctic exhibited a different attenuation trend. Regarding VSK, VSDD, and VCWS, in which ice layer is modeled as fluid, immiscibility is assumed between water and ice. According to the fundaments of these models, they can be classified into two groups: (1) physicsbased model and (2) phenomenological model. GW model falls within the first category. This model is applied for each single ice floe in ice field and includes as many physic processes (such as scattering, reflection, and refraction) involved as possible. Other models belong to second group, where all dissipation mechanisms that contribute to waves damping are considered by one parameter – effective viscosity, and concrete physical processes are neglected. Implicitly, the whole ice field is viewed as a heterogeneous media. Hence,

W

2154

Wave-Ice Interactions

Wave-Ice Interactions, Table 1 Wave-ice interaction models (Li et al. 2018 and references therein, reproduced with permission of Tatiana Uvarova) Wave-ice interaction model Mass WK loading model Thin plate GW model Viscous VSK layer model VSLM

Viscoelastic model

Ice Discrete mass point

Water Inviscid

Damping of wave energy by Scattering

Selected wave number (criteria) Two real (Geophysics relevant)

Thin elastic plate

Inviscid

Scattering

Two real (Geophysics relevant)

Viscous fluid layer Thin elastic plate

Inviscid

One complex (least damped wave mode) One complex

VSDD

Viscous fluid layer

Viscous

Viscous damping in ice Viscous damping in water Viscous damping in ice and water

VCWS

Viscoelastic fluid layer (Voigt model) Viscoelastic solid beam (Voigt model) Thin elastic beam

Inviscid

Viscous damping in ice (linear dashpot)

Inviscid

Viscous damping in ice (linear dashpot)

Inviscid

Damping forces due to vertical velocity of beam Viscous damping in ice (nonlinear dashpot)

VCFS

VCRP

VCM

Viscoelastic solid (Maxwell model)

Viscous

Inviscid

these models are also called as effective media continuum models. Conceptually, WK model is suitable for sparsely scattered small ice floes. Intuitively, GW model works well for pack ice. According to previous studies, VSK and VSDD model are more applicable for grease ice. VSLM model fits to be used for high concentration ice field. In contrast, VCFS and VCRP model are more suitable for sea regions that are sparsely populated by ice. In principle, VCWS should be suited for all above mentioned ice types.

Summary This entry gives a concise illustration of growth of sea ice under the influence of waves. Moreover, mechanisms to change waves during wave-ice interaction are listed. Lastly, different wave-ice interaction models are presented. This work

One complex (closest to opengravity wave with least attenuation) One complex (closest to opengravity wave with least attenuation) Two complex (in first quadrant of complex plane) Two complex (in first quadrant of complex plane) One complex (close to wave number of gravity wave)

contributes to easing the efforts of readers when reading pertinent literatures in this field.

Cross-References ▶ Ice Breaking Vessel ▶ Service Ships ▶ Special Marine Vehicle

References Antarctic Sea Ice Processes and Climate (2012) Glossary and image library. http://aspect.antarctica.gov.au/ home/glossary-and-image-library. Accessed 18 Oct 2017 Carsey FD (1992) Microwave remote sensing of sea ice. American Geophysical Union, Washington, DC Collins CO, Rogers WE, Lund B (2017) An investigation into the dispersion of ocean surface waves in sea ice. Ocean Dyn 67:263–280. https://doi.org/10.1007/ s10236-016-1021-4

Weight Hobbs PV (2010) Ice physics. Oxford University Press, Oxford Lee CM, Thomson J, Zone MI, Teams ASS (2017) An autonomous approach to observing the seasonal ice zone in the western Arctic. Oceanography 30:56–68 Li H, Lubbad R, Monteban D (2018) Review of wave–ice interaction studies. In: Proceedings of the 24th IAHR international symposium on ice, Vladivostok, 4–9 June, 2018. International Association for HydroEnvironment Engineering and Research (IAHR) Liu AK, Mollo-Christensen E (1988) Wave propagation in a solid ice pack. J Phys Oceanogr 18:1702–1712 Meylan MH, Bennetts LG, Kohout AL (2014) In situ measurements and analysis of ocean waves in the Antarctic marginal ice zone. Geophys Res Lett 41:5046–5051 National Snow and Ice Data Center (2018a) All about sea ice. https://nsidc.org/cryosphere/seaice/characteristics/ formation.html. Accessed 2 Aug 2018 National Snow and Ice Data Center (2018b) Charctic interactive sea ice graph. National Snow and Ice Data Center. https://nsidc.org/arcticseaicenews/charcticinteractive-sea-ice-graph/. Accessed 2 May 2018 National Snow and Ice Data Center (2018c) Cyrosphere glossary – rafting. https://nsidc.org/cryosphere/glos sary/term/rafting. Accessed 1 Aug 2018 PolarTREC (2018) US Arctic GEOTRACES journals. https://www.polartrec.com/expeditions/us-arctic-geotr aces/journals. Accessed 3 Aug 2018 Rogers WE, Thomson J, Shen HH, Doble MJ, Wadhams P, Cheng S (2016) Dissipation of wind waves by pancake and frazil ice in the autumn Beaufort Sea. J Geophys Res Oceans 121:7991–8007 Shen HH (2017) Wave–Ice Interactions. In Encyclopedia of Maritime and Offshore Engineering (eds J. Carlton, P. Jukes and Y.S. Choo). https://doi.org/10.1002/ 9781118476406.emoe086 Shen HH, Ackley SF, Hopkins MA (2001) A conceptual model for pancake–ice formation in a wave field. Ann Glaciol 33:361–367 Squire V (2007) Of ocean waves and sea-ice revisited. Cold Reg Sci Technol 49:110–133 Squire VA, Dugan JP, Wadhams P, Rottier PJ, Liu AK (1995) Of ocean waves and sea ice. Annu Rev Fluid Mech 27:115–168 Thomson J, Rogers WE (2014) Swell and sea in the emerging Arctic Ocean. Geophys Res Lett 41:3136–3140. https://doi.org/10.1002/2014GL059983 Timco G, Weeks W (2010) A review of the engineering properties of sea ice. Cold Reg Sci Technol 60:107–129 Vizcarra N (2018) Arctic sea ice maximum at second lowest in the satellite record. National Snow and Ice Data Center. http://nsidc.org/arcticseaicenews/2018/ 03/arctic-sea-ice-maximum-second-lowest/. Accessed 29 Mar 2018 Wang R, Shen HH (2010) Experimental study on surface wave propagating through a grease–pancake ice mixture. Cold Reg Sci Technol 61:90–96. https://doi.org/ 10.1016/j.coldregions.2010.01.011

2155 Weeks WF, Ackley SF (1986) The growth, structure, and properties of sea ice. In: The geophysics of sea ice. Springer, New York, pp 9–164 Zhao X, Shen HH, Cheng S (2015) Modeling ocean wave propagation under sea ice covers. Acta Mech Sinica 31:1–15

Waverider Buoy ▶ Wave Measurement Buoy

Wavescan Buoy ▶ Wave Measurement Buoy

Weather Buoy ▶ Wave Measurement Buoy

WEC ▶ Wave Energy Converters

WEC – Wave Energy Converter ▶ Power Take-Off System

WEC: Wave Energy Converter ▶ Wave Energy Utilization Buoy

Weight ▶ AUV/ROV/HOV Hydrostatics

W

2156

Welding Methodology

Welding Methodology ▶ Underwater Welding

Welding Technology Dong Sheng Zhao School of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, China

Synonyms Centimeter (cm); Kilojoule (kj); Melt inert gas welding (MIG); Tungsten inert gas welding (TIG) Welding Technology, Fig. 1 Welding robot

Definition Welding is the process of forming a permanent connection between two or more materials (of the same or different species) through the combination and diffusion of atoms or molecules. Compared with riveting, welding can save about 15–20% of metal materials. Compared with casting, the production of welding structure does not require the production of wood mold and sand mold, nor special smelting and casting equipment. The process is simple and the production cycle is short. Welding is an important link in the construction of ships and marine structures (Wang et al. 2017). The quality and efficiency of welding directly affect the construction cost and quality of ships and marine structures. The development of welding technology is the basis for improving the construction level of ships and marine structures. In terms of shipbuilding technology, before the 1930s, most ship structures were riveted or bolted. Around the Second World War, welding technology began to be widely used in ship structures, and higher requirements have also been put forward for the weldability and welding technology of hull steel (Ma et al. 2017).

The development and application of welding mechanization and automation technology in shipbuilding and marine structures are very rapid. The technology of submerged arc welding and gas-shielded welding began to be applied in the 1950s, and the method of CO2 gas-shielded welding began to be applied in the 1970s. At the same time, various types of automatic welding and semiautomatic welding methods were developed. In the 1990s, welding robot technology becomes more and more perfect and practical. Plasma arc welding, laser welding, laser-arc composite heat source welding, friction stir welding, and diffusion welding have been applied in the construction of ships and marine structures, which have greatly improved the welding precision and quality (Fig. 1).

Introduction Welding Method Arc welding is mainly used in the construction of ships and marine structures. Arc welding includes electrode arc welding, submerged arc welding, gas tungsten arc welding, gas metal-arc welding,

Welding Technology

and plasma arc welding (Welding Society of Chinese Mechanical Engineering Society 2012). Their common characteristic is that the electric arc burning between the electrode and the workpiece serves as the heat source. When forming the joint, the filler metal can be used or not used. Electrode arc welding is the earliest and still widely used arc welding method. It uses coated electrode as electrode and filler metal. The arc is burned at the end of the electrode and the surface of the welder. The coating can generate gasshielded arc and weld under the action of arc heat, and the slag can be formed to cover the surface of the molten pool to prevent the interaction of molten metal from the surrounding gas. The more important function of slag is to produce physical chemical reaction with molten metal or add alloy elements to improve the performance of weld metal. Electrode arc welding equipment is simple, portable, and flexible. It can be used for repairing and welding short joints in assembly, and for welding hard-to-reach parts. Submerged arc welding uses continuous feed wire as electrode and filler metal. When welding, a layer of granulated flux is covered over the weld zone, and the arc burns under the flux layer, melting the end part of the wire and the local base material to form the weld. Under the action of arc heat, part of the flux melts into slag and reacts with liquid metal. The slag floats on the surface of the metal pool. On the one hand, it can protect the weld metal, prevent air pollution, generate physical and chemical reaction with the molten metal, and improve the composition and performance of the weld metal. On the other hand, the weld metal can be cooled slowly. Submerged arc welding can use large welding current. Compared with electrode arc welding, its biggest advantage is good quality and high welding speed. Therefore, it is especially suitable for welding straight and circular joints of large workpieces, and most of them adopt mechanized welding. Tungsten gas arc welding is a method of melting metal into weld by using the arc between tungsten electrode and workpiece. During the welding process, tungsten does not melt and only acts as an electrode. When welding, the inert gas argon or helium gas is used as the

2157 Welding Technology, Fig. 2 TIG welding gun

protective gas, and additional filler metal can be added as required, generally known as TIG welding. This method can control the heat input very well, so TIG welding is an excellent way to connect sheet metal and backing welding. The pulse form of welding current can better control the weld depth and improve the solidification characteristics of the weld pool. TIG welding can be used for almost all metal welding, including steel materials and nonferrous metals, and the weld quality is high, but compared with other arc welding methods, the welding speed is slow, and the thickness of the plates that can be welded is small (Fig. 2).

Gas Metal Arc Welding In this method, the arc between the welding wire and the workpiece is used as the heat source, and the gas from the torch nozzle is used to protect the arc. Common shielding gases are argon, CO2, O2, or a mixture of these gases. When argon or helium gas is used as shielding gas, it is called metal inert gas arc welding (MIG welding). When CO2 is used as a protective gas, it is called carbon dioxide gas-shielded welding. When mixed gas is used as a protective gas, it is called mixed gas arc welding.

W

2158

The main advantage of arc welding is that it can be easily welded in various positions, and it also has the advantages of fast welding speed and high deposition rate. It is suitable for welding of most metals and arc spot welding. In recent years, the requirements for welding precision and quality have been continuously improved. High-precision welding methods such as laser welding, laser-arc composite welding, and friction stir welding have also been applied in the construction of ships and marine structures (Farajkhah and Liu 2016) (Figs. 3 and 4). Welding Technology, Fig. 3 Laser welding

Welding Technology

High Heat Input Welding of Steel In the process of welding, the heat circulation of welding will lead to the thick tissue around the welding seam. These areas with large grain size are called the welding-heat-affected zone. Grain coarsening in the heat-affected zone may lead to the decrease of toughness of welded joints. Compared with the base metal, the toughness loss in the heat-affected zone is generally 20–30% and can even reach 70–80% when serious. Although the width of the weld-heat-affected zone is only a few millimeters in general, the serious decline in Eletrode Laserbeam Work piece

Welding Technology, Fig. 4 Friction stir welding

Welding Technology

the toughness of the coarse crystal region in the heat-affected zone is likely to be the crack source, and the safety of the engineering structure cannot be guaranteed (Hamada et al. 1995). In order to reduce the construction cost and improve the productivity of shipbuilding, shipbuilding enterprises widely adopt 100–500 kJ/cm high heat input welding and develop a series of hull steel for high heat input welding, such as YP355 steel developed in Japan in the early 1980s, and YP390 steel and YP47 steel developed in the mid-1990s. The energy of welding line refers to the heat input amount of welding seam per unit length of time. The expression is: E¼IU/V (kJ/cm), where I (A) is welding current, U(V) is arc voltage, and V(cm/s) is welding speed. Generally, the welding energy greater than 50 kJ/cm in the welding process is called high heat input welding, such as single-side arc welding, gas-electric vertical welding, electroslag welding, etc. Under the welding of high heat input, the microstructure of heat-affected zone of traditional low-alloy high-strength steel will grow rapidly, and the strength and toughness of the welding seam will also be significantly reduced, which is easy to generate welding cold cracks, bringing difficulties to the manufacture of large steel structures. At the same time, with the improvement of steel plate strength, its impact toughness and welding performance are significantly decreased, and the susceptibility of welding crack is increased, which makes it difficult to manufacture large steel structures (Yan et al. 2006). The research and development of low-alloy high-strength steel for high heat input welding must take into full consideration the formation process and control method of the structure in the heat-affected zone. A large number of studies and explorations have been conducted on the characteristics of microstructure and properties of welded joints, microstructure transformation behavior, and the dynamics of austenite grain growth of low alloy and high strength steel, especially for the welding heat-affected zone of the acicular ferrite formation as well as the use of oxide metallurgy welding coarse-grained methods, to improve the toughness of a large

2159

amount of basic research and applied research. The results show that there are many factors influencing austenite grain coarsening and toughness loss in the weld coarse crystal area. The alloy design, purity, metallurgical production process, precipitated phase type, and its composition, shape, size, and distribution of materials all have different effects. According to the above research results, some methods to improve the toughness of steel-heat-affected zone for large wire energy welding are put forward, which are mainly to reduce the carbon content, refine austenite grain by second phase particle precipitation, and promote the formation of acicular ferrite by using the principle of oxide metallurgy. In order to improve the toughness of the heataffected zone, a lot of research work has been carried out successively. The two main methods are reasonable composition design and oxide metallurgy (Wang et al. 2012). Composition Design of Steel for High Heat Input Welding At present, the basic idea of steel composition design for high heat input welding is to reduce the carbon content to ensure the weldability, increase the content of manganese and microalloyed elements, increase the strength, and control the content of impurities such as phosphorus and sulfur. The oxide metallurgy method is adopted to form small dispersed fine inclusions, which can inhibit the austenite body length and control tissue transformation in the welding process, and keep the toughness of the steel coarse crystal area for high heat input welding at a good level. Oxide Metallurgy Technology Grain refinement is an effective way to improve the toughness. The smaller the grain size of the heat-affected zone, the better the toughness. In 1990, researchers at Nippon steel, Japan, first proposed the concept of oxide metallurgy, which controls the composition of oxides and makes them small and dispersed. The size, shape, and distribution of sulfide, carbonitride, and other nonmetallic inclusions are controlled by controlling the small, dispersed, high solubility

W

2160

microinclusion material points in the molten steel. On the one hand, these inclusions prevent austenite grains from growing in the heat cycle of welding. On the other hand, they promote the nucleation of acicular ferrite, so as to refine the fine inclusions in the high heat input welding effectively and improve the toughness of the heat-affected zone. A large number of studies have shown that it is a very effective way to improve the toughness of heat-affected zone by utilizing the fine inclusions in these steels. Oxide metallurgy technology provides a new way of thinking for the development of high heat input welding steel. Welding Deformation and Residual Stress Welding deformation and residual stress are common problems in the welding of ships and marine structures, which have important influence on welding precision and welding quality. The fundamental reason of stress and deformation during welding is that the welding parts are heated unevenly, and the thermal deformation and tissue deformation caused by heating are restrained by the rigidity of the welding parts themselves (Fang 2017). The stress and deformation occurring in the process of welding is called transient stress deformation, while the residual stress and deformation after the completion of welding and the complete cooling of components are called residual stress and deformation. The residual stress and deformation of welding seriously affect the bearing capacity and service life of welding structures (Chen et al. 2015). During welding, the weldment is heated unevenly and the weld zone melts, while the thermal expansion of the high-temperature zone material adjacent to the welding pool is restricted by the surrounding cold state material, resulting in uneven compressive plastic deformation. During the cooling process, this part of the material (such as the two sides of the long weld) that has undergone compressive plastic deformation is also restricted by the surrounding metal and cannot freely contract, and to a certain extent, it is unloaded by stretching. At the same time, the weld pool solidifies and the weld metal cooling shrinkage is restricted, resulting in shrinkage

Welding Technology

tensile stress and deformation. Thus, a shortened uncoordinated strain, called residual strain, or initial strain or inherent strain, is generated in the welded joint area. Welding stress and deformation are caused by the interaction of many factors. The local uneven heat input during welding is the decisive factor for the formation of welding stress and deformation, and the heat input influences the metal movement around the heat source through the internal and external constraints formed by material factors, manufacturing factors, and structural factors, and finally forms the welding stress and deformation. The internal constraint of metal motion around the heat source mainly depends on the thermal physical parameters and mechanical properties of the material, while the external constraint mainly depends on the manufacturing and structural factors. The basic law of welding stress and deformation is consistent with that caused by deformation and uneven temperature, but the process is more complicated. The main performance is that the temperature change range is larger when welding, the highest temperature on the weld can reach the boiling point of the material, and the temperature drops sharply from the welding heat source to the room temperature. The appearance of welding deformation will bring a series of problems (Wang et al. 2018). Once the welding structure is deformed, it often needs to be corrected and is time-consuming. Sometimes, the more complex deformation correction workload may be greater than the welding work, and sometimes, the deformation is too large, may not be able to correct, resulting in waste. For the workpiece that needs to be machined after welding, the deformation increases the machine load and material consumption. The appearance of welding deformation will also affect the beauty and dimension precision of components and may reduce the bearing capacity of structures and cause accidents. The control methods of welding deformation mainly include rigid fixation method, reverse deformation method, reasonable welding sequence selection, and reserved shrinkage allowance method.

Welding Technology

Rigid Fixation Method The method of reducing welding deformation by using external rigid constraint is called rigid fixation method. When assembling the plate, fixing the spliced steel plate on the platform with positioning welding can reduce the wave deformation of the steel plate. To prevent corner deformation, two end plates can be welded at both ends of the joint. In the process of hull construction, several process reinforcing plates are often welded along the joint weld to prevent angular deformation. When applying rigid fixation method, it is necessary to pay attention that the binding effect of the fixture will inevitably increase the welding stress and the possibility of welding crack. Therefore, this method is often used in welded steel structures, but not for cast iron and some high strength steel. Inverse Deformation Method Before welding, the deformation size and direction of the structure are estimated in advance, and the component is installed into a deformation in the opposite direction to offset the deformation caused by the welding process. This method is called reverse deformation method. This method is often used in the construction of ships and marine structures. Select Reasonable Welding Sequence In the process of assembly and welding, the influence on deformation is complicated due to the large number of welding seams. In order to control the deformation, the structure is divided into several parts, assembled and welded respectively, and then the welded parts are assembled into a whole. This allows asymmetrical or larger welds to contract freely without affecting the overall structure. Reserve Shrinkage Allowance Method The shortening of the longitudinal (along the weld direction) and transverse (perpendicular to the weld direction) of the component after welding can be controlled by estimating the weld shrinkage and leaving the shrinkage allowance in advance during the material preparation process. The characteristics of welding residual stress include (Gadallah et al. 2017):

2161

1. Mutual balance. Internal stress, tensile stress, and compressive stress coexist. 2. Follow the principle of stress superposition. The working stress caused by the load can be superimposed with the welding residual stress when the unrelieved stress is used. 3. A phenomenon of stress redistribution. When the stress and residual stress caused by external factors of the welded parts are superimposed, the ductile deformation will occur in this area when the yield point of the base metal is exceeded. 4. Without the occurrence of welding deformation, there is no obvious appearance. After a large number of welding, the appearance may not change, but there is a great stress in the interior. The existence of welding residual stress has the following effects on the safety and service performance of welded joints and even welded structures: Effect on Structural Rigidity When the stress generated by the external load and the residual stress in a certain area of the structure are superimposed to reach the yield point of the material, the material in this area will undergo plastic deformation and further lose the ability to withstand the external load, resulting in the reduction of the effective section area of the structure and the decrease of the stiffness of the structure. When the external load is in the same direction as the longitudinal residual stress, the deformation is greater than that without residual stress. When unloading, the strain relaxation is less than the deformation when loading, and the component cannot be restored to the original size. The larger the tensile stress area in the component, the greater the impact on the stiffness and the greater the residual deformation after unloading. Effect on Stability of Compression Bar Parts When the compressive stress caused by the external load and the compressive stress component in the residual stress are superimposed to reach the yield point of the material, this section loses the ability to bear the compressive stress load further.

W

2162

In this way, the effective cross-sectional area distribution of the bar is weakened, and the stability of the bar is changed. Effect on Static Load Strength and Brittle Fracture When there is a serious stress concentration and a high residual stress in the actual component, and if the working temperature is lower than the critical temperature of brittleness, under the combined action of tensile stress and working stress, the static load strength of the structure will be reduced and brittle fracture will occur under the action of the external load stress far below the yield point. Effect on Fatigue Strength The existence of residual stress makes the stress cycling average of cyclic load deviate, but does not affect its amplitude. As the mean value of the stress cycle increases, its limit decreases, otherwise it increases. Therefore, if there is stress concentration and residual stress, the fatigue strength will decrease. If the residual stress is eliminated under the external load, the residual stress will be weakened. The higher the stress concentration coefficient, more obvious the influence of residual stress. Effect on Stress Corrosion Cracking Stress corrosion cracking is a phenomenon of cracking of structures under the action of low stress in a certain environment. When material and medium match, the time required to produce stress corrosion cracking is inversely proportional to the stress. The greater the tensile stress, the shorter the time of stress corrosion cracking. Stress corrosion cracking can be avoided if residual compressive stress layer can be created on the surface of components that contact with corrosion media. The Influence on Welding Precision and Dimension Stability For the component with residual stress, if the original residual stress field is damaged during machining, and the residual stress can be released or redistributed, the component will be deformed and the machining accuracy will be affected. After the component with residual

Welding Technology

stress is placed for a period of time, the stress relaxation will occur due to aging effect or unstable tissue, leading to the instability of structure size. When the temperature rises, the relaxation will increase significantly and the material with unstable tissue is produced after welding. As the unstable tissue changes over time, the residual stress changes greatly, and the dimension stability of the welded parts is poor. Fatigue Strength of Welded Joints The marine engineering structure is affected by wind, wave, and flow, and the sensitivity of high strength steel to stress concentration is higher than that of low carbon steel. Therefore, the fatigue strength of ocean engineering welding structure must be considered (Yan et al. 2016). Factors affecting fatigue strength of metallic materials (such as stress concentration, section size, surface state and load conditions, the application environment, etc.) also have influence on the fatigue strength of welded structure (Sankaran and Sarma 2003). In addition, some characteristics of the welding structure itself, such as the change of properties of area near weld zone in the joint, welding residual stress, and so on, could also affect fatigue strength of welded structure (Chapatti et al. 2003). The main technological measures to improve the fatigue strength of welding structures are: Specific measures to reduce stress concentration include: 1. Using reasonable structural forms to reduce stress concentration in order to improve fatigue strength. 2. Adopting the welding joint forms with small stress concentration coefficient possibly, such as butt joint. 3. Comprehensive measures should be taken to improve the fatigue strength of joints when fillet welds are adopted (machining the end of the weld seam mechanically, selecting the shape of the joint of plates reasonably, ensuring the penetration of the weld root, etc.). 4. Using surface machining to eliminate various grooves in the weld and its vicinity can reduce the stress concentration in the components to improve the fatigue strength.

Welding Technology

5. Adopting TIG arc or plasma beam-shaping method instead of mechanical processing to make a smooth transition between the weld seam and the base material. Adjust the Residual Stress Field The fatigue strength of the joint can be improved by eliminating the residual tensile stress at the stress concentration or producing the residual compressive stress here. This method can be divided into two types: One is structural integral treatment, such as integral annealing or overloading prestretching; the other is the local treatment of the joint, such as heating, rolling, and local explosion of a part of the joint so that the residual compressive stress is generated at the stress concentration of the joint. Improve the Surface Properties of Materials The fatigue strength of the joint can be improved by surface-strengthening treatment, extrusion with small wheels, tapping the weld surface and transition zone lightly with hammer, or spraying the weld zone with small steel balls. Special Protective Measures The fatigue strength of materials is often affected by the medium, so it is beneficial to apply notched surface coating. Requirement of Marine Engineering Structure for Weld Seam The butt weld of marine engineering structure should be fully welded. The shape of the remaining height of the weld should meet the requirements, and be smoothly transferred to the base material. Fillet welds are usually used for the connection between plates and stiffeners, the fixation of bracket plates, etc. If there is an allowable assembly gap between welds, the weld thickness should be increased accordingly. The important fillet welds, as well as those of strong stress components which may cause fatigue, should be fully welded. The technological measures such as alternating symmetric welding and presurfacing weld bead on groove surface can be adopted when welding (Calle and Alves 2015). Reasonable assembly steps and welding sequence are adopted to control the deformation

2163

caused by the weld to avoid excessive residual stress and crack (Zhao et al. 2017). For the joints of thick components and pipes: 1. Low-hydrogen electrode and reasonable welding technology should be adopted to ensure complete penetration. 2. Preheating should be done before welding, and postwelding heat treatment should be done according to the regulations after welding. 3. The pipe joints shall not be burnt through during welding, the weld surfaces shall be continuous and even, and the joint between the two pipes shall gradually make a smooth transition. It is recommended to use small diameter electrodes for cover welding to improve the fatigue properties of joints. If the project requires polishing the joint of the pipes, the radius of curvature of the surface of the weld seam after grinding shall comply with the relevant design and manufacture regulations.

References Calle MAG, Alves M (2015) A review-analysis on material failure modeling in ship collision. Ocean Eng 106: 20–38 Chapatti MD, Tagawa T, Miyata T (2003) Ultra-long cycle fatigue of high-strength carbon steel part I: review and analysis of the mechanism of failure. Mater Sci Eng A 356:227–235 Chen Z, Chen ZC, AjitShenoi R (2015) Influence of welding sequence on welding deformation and residual stress of a stiffened plate structure. Ocean Eng 106: 271–280 Fang HY (2017) Welding structure. China Machine Press, Beijing Farajkhah V, Liu Y (2016) Effect of fabrication methods on the ultimate strength of aluminum hull girders. Ocean Eng 114:269–279 Gadallah R, Osawa N, Tanaka S (2017) Evaluation of stress intensity factor for a surface cracked butt welded joint based on real welding residual stress. Ocean Eng 138:123–139 Hamada M, Fukada Y, Komizo Y (1995) Microstructure and precipitation behavior in heat affected zone of C-Mn microalloyed steel containing Nb, V and Ti. ISIJ Int 35:1196 Ma YY, Wu YS, Fang ZG (2017) Ship equipment and materials. Chemical Industry Press, Beijing Sankaran S, Sarma V (2003) Low cycle fatigue behavior of a multiphase microalloyed medium carbon steel: comparison between ferrite-pearlite and quenched and tempered microstructures. Mater Sci Eng A 345:328–335

W

2164 Wang HH, Wu KM, Lei XW (2012) Effect of fast cooling process on microstructure and toughness of heataffected zone in high strength pipeline steel X120. Sci Technol Weld Join 17:309–313 Wang GD, Shang CJ, Liu ZY (2017) Steels for marine applications. Chemical Industry Press, Beijing Wang JC, Yi B, Zhou H (2018) Framework of computational approach based on inherent deformation for welding buckling investigation during fabrication of lightweight ship panel. Ocean Eng 157:202–210 Welding Society of Chinese Mechanical Engineering Society (2012) Welding handbook. China Machine Press, Beijing Yan W, Shan YY, Yang K (2006) Effect of TiN inclusions on the impact toughness of low-carbon microalloyed steels. Metall Mater Trans A 37A:2147–2157 Yan XS, Huang XP, Huang YC, Cui WC (2016) Prediction of fatigue crack growth in a ship detail under waveinduced loading. Ocean Eng 113:246–254 Zhao HS, Lie ST, Zhang Y (2017) Elastic-plastic fracture analyses for misaligned clad pipeline containing a canoe shape surface crack subjected to large plastic deformation. Ocean Eng 146:87–100

Winch Liping Sun College of Shipbuilding and Ocean Engineering, Harbin Engineering University, Harbin, Heilongjiang, China

Definition Winch is a mechanical device that is used to pull in (wind up) or let out (wind out) or otherwise adjust the tension of a rope or wire rope (also called “cable” or “wire cable”).

Winch

century BC, winch and pulley hoists were regarded by Aristotle as common for architectural use (Coulton 1974). The yacht Reliance, American defender of the 1903 America’s Cup, was the first racing boat to be fitted with modern winches below decks, in an era when her competitors relied on pulley systems (block and tackle). In its simplest form, it consists of a spool and attached hand crank. In larger forms, winches stand at the heart of machines as diverse as tow trucks, steam shovels, and elevators. The spool can also be called the winch drum. More elaborate designs have gear assemblies and can be powered by electric, hydraulic, pneumatic, or internal combustion drives. Some may include a solenoid brake and/or a mechanical brake or ratchet and pawl device that prevents it from unwinding unless the pawl is retracted (Smith 1999) (Fig. 1). Marine winch is an important lifting and pulling equipment used on boat/ship, on the dock or shore, in the port, on offshore platforms, etc. for anchoring, mooring, towing and weights lifting, or pulling, and there is also subsea winch used for some submarine operations. The main structures of marine windlass comprise drum, gypsy wheel, chain, cable, manual band brake, manual clutch, power system and control system, etc. In addition to drum, many winches have one or two small warping heads. Take marine drum winch, for example, it can have one or two drums with or without warping head. Clients can customize by their needs. Speaking of the commonly

Scientific Fundamentals Historical Development The earliest literary reference to a winch can be found in the account of Herodotus of Halicarnassus on the Persian Wars (Histories 7.36), where he describes how wooden winches were used to tighten the cables for a pontoon bridge across the Hellespont in 480 B.C. Winches may have been employed even earlier in Assyria. By the fourth

Winch, Fig. 1 The form of winch (http://cn.bing.com/)

Winch

used marine winches, they can be anchor winch, anchor and mooring winch, towing/tugger winch, mooring winch, combined windlass like electric single drum combined winch and electric double drum combined winch, and so on (Blanc et al. 2006). Ship winch refers to the winch mounted and used on a ship and it is a necessary deck equipment for the ship, which can be used for ship anchoring, mooring, towing, cargo lifting and cable pulling, and so on. According to drum quantity, there is single drum ship winch, double drum ship winch, and triple drum ship winch; the drum brake device should be able to withstand the winch support load, and it should not rotate after braking. According to drive type, ship winch includes electric ship winch, hydraulic ship winch, electric-hydraulic winch, diesel winch, steam winch, and manual winch; according to the type of drums, the winch drums can be split or undivided as needed; as for the brake type and brake application, there are mainly band, disc, mechanical screw, and spring applied. The main specifications of hydraulic winch consist of rated

2165

load, support load, rope speed, rope capacity, power mode, etc. Ship winches are very useful whenever the ships need to be anchored, stopped, towed, or there are something on ships needed to be lifted or pulled. When a ship reaches a port or pier, it needs to stop, and the ship anchor and mooring winch will be used to help with the ship anchoring and mooring to make sure it stops and keeps in the place safely without moving or drifting; according to ships with different sizes, shapes, and rope capacities, they will choose windlasses with different rated loads and drums; when the ship starts to set sail after the stop, the winch will let in the line attached to the anchor to make the ship leave the port or pier; when a ship needs to be towed under some special circumstances, the winch will connect the ship to the tug boat to implement the towing operations; when there are some loading and unloading operations on ship, the winch will also be used to finish the weights lifting work (Blanc et al. 2006) (Fig. 2). The most common use of winches on ships is for mooring, which means the winches are

Winch, Fig. 2 Ship winch

W

2166

usually located on the fore and after the decks at both sides of the ships. The mooring system can hold a ship in position and prevents the ship from drifting away from a berth. The ship mooring winch performs variety of functions, for example, the winch serves to store the mooring line when it is not in use, to haul the ship in place against environmental forces, or it can also act as a kind of safety device which releases the line load in a controlled way once the force in the mooring line increases to the limit of breakage (Chakrabarti 2005). Mooring winch is the mechanical equipment used by ships to dock at docks; tie-up pontoons, alongside ships; to enter and leave docks; etc. It is commonly called mooring equipment. Mooring winch is mainly composed of mooring lines, mooring piles, cable guide holes, winch, rope wagons, collision pads, etc. The ship can be moored by using a stranding machine to take up the stranding cable. At the bow, the mooring reel is usually driven by the same power as the windlass and can also be engaged or disengaged by clutches. The type of winching equipment required in a particular mooring system depends on the type of mooring line to be handled and whether or not the floating vessel itself must initially tension the mooring lines or test load anchors. A floating vessel often has the means of adjusting mooring line tension, retensioning after anchor drag, and disconnecting individual mooring lines. Main Types and Working Principles There are two types of winch: normal type and automatic tensioning type (Smith 1999). The composition of the normal type winch is similar to that of the windlass, and it can also share a set of driving device with the windlass. Its function is to tighten the cable and tie it to the cable pile. While the automatic tensioning cable winch is provided with a cable winding drum, the cable is wound on the cable winding drum, has a separate driving power, and automatically tightens or releases the cable by taking the tensile force of the cable as a signal, so as to adapt to the influence of tide level and cargo loading and unloading on the ship, and is beneficial to

Winch

reducing the labor intensity of the crew. However, one winch can only hold one rope by itself, so the number of mooring winch need more. The working principle of the automatic tensioning hydraulic cable winch is: when the tension on the cable increases, the pressure of the hydraulic system increases, and when the pressure is greater than the setting value of the constant tension valve, the valve opens, allowing the inlet and outlet of the hydraulic motor to communicate. Under the action of the tension of the cable, the hydraulic motor rotates to release the cable, the tension decreases after the cable is released, and the constant tension valve closes. When the tensioning force on the cable is reduced, the hydraulic pump supplies oil to the hydraulic motor so that the hydraulic motor rotates to tighten the cable in the cable direction. When the pulling force on the cable is balanced with the set value of the constant tension valve, the oil supply of the hydraulic pump bypasses through the constant tension valve. In order to reduce the loss of hydraulic energy, large and small hydraulic pumps are permanently installed in the hydraulic system of the automatic tensioning cable winch. The large pumps are used in normal cable collection and discharge conditions. The small pump is used for automatic tensioning. The load capacity, rope capacity, rope diameter, rated speed, and dimension of the winch vary according to different needs and conditions; they are in the different ranges and can be customized. A marine winch is a piece of marine deck equipment applied for handling ropes or wires, and works by spooling or winding the ropes or wires on a drum with a horizontal axis. Powered by electric or hydraulic motors, the winches on ship are fixed and used for various purposes. The winch can also be divided into the following four types according to the material and characteristic of mooring lines. Windlass The most common method of handling and tensioning chain is through the use of a windlass. The windlass consists of a slotted “wildcat” which is driven by a power source through a gear-

Winch

reduction system. As the wildcat rotates, the chain meshes with the wildcat is drawn over the top of the wildcat and lowered into the chain locker. Once the chain is hauled in and tensioned, a chain stopper or brake is engaged to hold the chain. Windlass has proven to be a fast and reliable method for handling and tensioning chain (Luo et al. 2015) (Fig. 3). Chain Jack Chain jack is a device which reciprocates linearly to haul-in and tension chain. Usually powered by one or more hydraulic cylinders, chain jack engages the chain, pulls in a short amount of the chain, engages a stop, retracts, and repeats the process. Although chain jack can be a powerful means for tensioning chain, it is very slow and is recommended for applications not requiring frequent line manipulation (Luo et al. 2015).

2167

Drum-Type Winch Conventional drum-type winch is the most common method used for handling wire rope. Operation of drum-type winch is fast and smooth. Drum-type winch consists of a large drum on which the wire rope is wrapped. The base of the drum is often fitted with special grooves sized specifically to the size of wire rope being handled. The groves control the positioning of the bottom layer of wire rope on the drum. For subsequent layers of wire rope, an external guidance mechanism such as a level-wind is often used to control positioning of the wire rope on the drum. The tensioning capacity of the winch is a function of number of wraps on the drum. Drum-type winch can be a cumbersome method of handling wire rope for deepwater or high strength mooring systems. As the requirement for line sizes and lengths increases, the size

Winch, Fig. 3 Windlass

W

2168

Winch

Drum-type Winch

Fairlead

Wire rope

Winch, Fig. 4 Drum-type winch

of the winch can become impractical. In addition, when wire rope is under tension at an outer layer on the drum, spreading of preceding layers can occur causing damage to the wire rope (Luo et al. 2015) (Fig. 4). Linear Winch Linear winch is similar in principal to chain jack. Two sets of grippers, one stationary and one translating, are used to haul-in and tension the wire rope. Linear winch is available in a single-acting form, in which the wire rope moves intermittently as the gripper is retracted to begin another stroke, and in a continuous double-acting form, two translating grippers are used alternately for continuous smooth motion of the wire rope. Linear winch is most applicable in a permanent application when high tension and large-diameter wire rope is required. A take-up reel is necessary in this case to coil the wire rope after it passes through the linear winch (Luo et al. 2015). Traction Winch Traction winch has been developed for high tension mooring applications as well as for

handling combination mooring systems. It consists of two closely spaced parallel mounted powered drums, which are typically grooved. The wire rope makes several wraps (typically 6–8) around the parallel drum assembly. The friction between the wire rope and the drums provides the gripping force for the wire rope. The wire rope is coiled on a take-up reel which is required to maintain a nominal level of tension in the wire rope (typically 3–5% of working tension) to ensure the proper level of friction is maintained between the wire rope and the traction winch. This system has been favored for use in high tension applications due to the compact size, capability to provide constant torque, and ability to handle very long wire rope without reduced pull capacity.

Key Applications The rope may be stored on the winch. When trimming a line on a sailboat, the crew member turns the winch handle with one hand, while tailing (pulling on the loose tail end) with the other to maintain tension on the turns. Some

Wind Tunnel Test

winches have a “stripper” or cleat to maintain tension. These are known as “self-tailing” winches. Winches are frequently used as elements of backstage mechanics to move scenery in large theatrical productions. They are often embedded in the stage floor and used to move large-set pieces on and off. Off-road vehicles often carry a winch which may be electrically or hydraulically powered and is wound with rope or a wire cable. If the vehicle loses traction, the winch is used to pull it back to firmer ground. The purpose of windlass/winch is to control the speed of chain (cable) movement when releasing and recovering, and pre-tightening and adjusting the tension of chain (cable) while anchoring. There are some requirements for winch design (Piggott 1977): 1. To ensure that the ship can still tie up when it is subjected to wind force below level 6. 2. The tensile force of the winch shall conform to the requirements of “code for the classification and construction of steel sea-going ships. 3. The wringing speed is usually 15~30 m/min, with a maximum of 50 m/min. When the rated pulling force is reached, it can be reduced to the minimum.

2169 Coulton JJ (1974) Lifting in early Greek architecture. J Hell Stud 94(12):1–19 Luo Y, Wang HW, Yan FS (2015) Design and analysis of station keeping system for floating structures, Harbin Engineering University Press, China Piggott D (1977) Understanding Gliding. Morrison & Gibb Ltd, London/Edinburgh. ISBN: 0-7136-1640-7 Smith M (1999) The Annapolis book of seamanship. Simon & Schuster, New York

Wind Propulsions ▶ New Technologies in Auxiliary Propulsions

Wind Speed ▶ Ship Operational Environment

Wind Tunnel Test Lei Gao Shanghai Rainbowfish Deepsea Equipment & Technology Co. Ltd, Shanghai, China

Synonyms Cross-References

Aerodynamic drag; Artificial air flow; Hydrodynamic coefficients; Submersible

▶ Design of Mooring System ▶ Mooring System

Definition References API RP 2SK (2005) (APE Recommended Practice 2SK), Design and Analysis of Stationkeeping Systems for Floating Structures. American Petroleum Institute Blanc C, Isnard J-L, Smith R (2006) Deepwater oil export systems: past, present, and future. In: Offshore Technology Conference. Single Buoy Moorings Inc., Houston Chakrabarti S (2005) Handbook of offshore Engineering. Offshore Structure Analysis, Inc. Plainfield, Illinois, USA

Wind tunnel tests are tests performed in a tunnel with aircrafts, including wing-in-ground-effect ships, other surface ships, offshore structure models, or submarine and submersible models in different speed artificial air flow, which are the most popular tests in aerodynamic and hydrodynamic research. As the similarity between water and air, wind tunnels are also useful and important tools compared with towing tanks (https://www. en.wikipedia.org/wiki/windtunneltests).

W

2170

Scientific Fundamentals Wind Tunnel Types Different types of wind tunnels can be divided by the top wind speed in the tunnel. These include low-speed wind tunnel, subsonic wind tunnel, transonic wind tunnel, supersonic wind tunnel, and hypersonic wind tunnel (Korsmeyer 1996). A division of various wind tunnels is given in Fig. 1. The wind speed in the tunnel is V, and the speed of sound in the air is c, then the Mach number can be defined by the formula, Ma ¼ V/c. Low-speed wind tunnel, Ma < 0.3. The air density keeps the same when as its speed is zero. Subsonic wind tunnel, 0.3 < Ma < 0.8. The air density becomes different. Transonic wind tunnel, 0.8 < Ma < 1.2. Supersonic wind tunnel,1.2 < Ma < 5. Hypersonic wind tunnel, Ma 5. Submersible or submarine models can be installed in wind tunnel and resistance measurement or flow-field measurement can be carried out. Usually the low-speed wind tunnel is suitable for their tests. Wind Tunnel Test Types A division of various wind tunnel tests is given in Fig. 2.

Wind Tunnel Test, Fig. 1 A division of various wind tunnels

Wind Tunnel Test

These include force measurement, pressure measurement, heat conduction tests, and flowfield observation. Force measurement tests are the basic wind tunnel tests. The resistance, trimming moment, lifting force, and so on can be measured of the model. Pressure measurement tests are important when people want to know the pressure distribution on surface of the model. Heat conduction tests are usually for high speed or super high-speed vessels. As the speed increases, the friction between the air flow and vessels become larger. When it is supersonic or even hypersonic, the heat is large enough to burn the vessel to ashes. Flow-field observation is usually carried out by using smoke or wires, which will show the direction of the air flow. Nowadays, new technologies such as particle image velocimetry are applied since the 1980s.

Historical Development It is believed that the first wind tunnel in the world was built in 1871 by the British. The Wright Brothers built a wind tunnel in 1901 in order to carry out different tests for their aircraft model, whose section area was 0.56 m2 and top wind speed was 12 m/s. With the help of the wind

Wind Tunnel Test

2171

Wind Tunnel Test, Fig. 2 A division of various wind tunnel tests

Wind Tunnel Test, Fig. 3 The Jiaolong sub model in wind tunnel

tunnel their plane flied in the sky 2 years later, which was believed the first plane in the world. In the middle of the last century, wind tunnel tests became widely used by not only aircrafts manufacturers but other company, for example, the car industry. In the 1920s, Jaray started to do wind tunnel tests for cars. He did a good job to decrease the wind resistance of cars by carrying out a lot of wind tunnel tests. The aerodynamic drag takes more than 30% of the total resistance when a car drives at 180 km/h. After World War II, vessel engineers built hundreds of wind tunnels and have made great efforts to reduce the aerodynamic drag by more than 60% (Quix 2015; Forte 2012). Scientists found that aerodynamic and hydrodynamic flow were always based on the same laws, which became the theoretical basis that ship and submarine model tests were widely carried out in wind tunnels. The hydrodynamic

coefficients of submarines or other under water vessels are studied. During the design of the 7000 m deep manned Submersible “Jiaolong,” lots of wind tunnel tests were carried out (see Fig. 3). Different design was compared for better performance and higher safety.

Key Technology in Carrying Out a Wind Tunnel Test There are four elements for successful wind tunnel tests. They are the wind tunnel and fans, the model, measurement device, and model vibrations. 1. The wind tunnel and fans The wind tunnel should be large enough for the model. The cross-sectional area of models should be less than 5% of the wind tunnel.

W

2172

The artificial aero flow produce by fans in wind tunnel should be fairly well distributed and stable for both the time dimension and space dimension. As there is a lot of noise when the fans are working, it is suggested to build the wind tunnels far from living area. 2. The model The model ship and the full-scale ship are geometrically similar. The model should be manufactured with high precision. And there are rudders or fins, which should be manufactured and installed to the model. Sometimes they are too small to be well manufactured. In other cases, manipulators, for example, are usually too complex to be manufactured. The model is simplified in most cases (Owens 2011). How to simplify the model should be recorded. Turbulence stimulators are usually installed on the model as the Reynold Number is not high enough to make the laminar flow turn to turbulence flow. And the roughness of the model skin should be carefully paid attention to. Usually the models are painted with some standard methods. 3. Measurement device Measurement devices are usually divided into three kinds, including force measurement balances, pressure and speed measurement sensors, and aero flow visualization devices. Five- or six-component testing system and the methods for resolving calibrating matrix are proposed in wind tunnel tests. Pressure sensors are developed to capture the high-frequency fluctuation aero flow. Particle image velocimetry technologies are widely applied in recent decades as flow visualization methods. Smoke and thin wires are the traditional and classical methods (Brooks 2014). 4. Model vibrations During wind tunnel tests, aero turbulence, model structure, and aerodynamic forces will make the model vibrate with a high frequency. Model vibrations affect the measurement and the model tests cannot carry out in some cases. Model vibrations should be restrained and controlled.

Winding Wire

References Brooks J (2014) Development of non-intrusive velocity measurement capabilities at AEDC tunnel 9. AIAA 2014-1239 Forte M (2012) Experimental study of an optical fibrebased pressure sensor for boundary layer transition detection. AIAA 2012-2755 Korsmeyer DJ (1996) DARWIN: remote access and data visualization elements. AIAA96-2250 Owens LR (2011) Off-body boundary-layer measurement techniques development for supersonic lowdisturbance flows. AIAA 2011-284 Quix H (2015) Model deformation measurement capabilities at ETW. AIAA 2015-2562

Winding Wire ▶ Cable

Winterization of Polar Engineering Lei Ju and Yongkui Wang College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China

Synonyms Antifreeze of the polar ocean platform; Polar Engineering antifreeze

Definition The polar offshore platform is the carrier of resource exploration, development, transportation, and scientific research activities in polar regions. However, the polar climate is extremely harsh, and the temperature is very low over the years. The Polar Engineering antifreeze is a technology that ensures the safe and efficient operation of the offshore platform in a complex and abominable low-temperature polar region and

Winterization of Polar Engineering

provides a more comfortable working life environment for the staff.

Scientific Fundamentals Polar Low-Temperature Environment In the Arctic region, the winter time is long, the temperature is between
43 C and
26 C, the average temperature is
34 C, the air sea air exchange is strong and the humidity is very high, and the relative humidity is above 95% for most of the time, which shows the fog and thick fog. The ice overlying under the extreme climate has a great influence on the polar ocean platform (Horjen 1989). According to the guidelines for the polar ships issued by the China Classification Society, the polar vessels operating at low temperature or season should take into account the exposure to the ambient temperature of the structure, equipment, and the surface of the system and take appropriate measures of protection or operation control to ensure that the ship and equipment have operational capability in the polar service temperature environment (China Classification Society 2016). Ice Cause, Harm, and Ice Zone Specification Cause of Icing

There are two main reasons for ice formation on the offshore platforms, namely, meteorology and ocean spray. The former is a secondary cause and the latter is the main reason. The meteorological conditions mainly include snow, freezing rain, fog and hail, and so on. The overcooled droplets in the atmosphere form a large amount of icing on the surface of the structure, such as the icing on the cable, the lifesaving equipment, the air vent, and so on (Xie et al. 2017). When the temperature is less than or equal to 0 C, freezing rain will cause obvious ice formation on the platform surface. Freezing fog can also cause ice. The amount of ice generated by freezing fog is usually small, but if the duration of the fog is longer, it may cause an increase in ice accretion. Snow will cause icing

2173

on the horizontal structure of the platform, such as deck. The droplet is caused by the impact of the ocean wave platform. Due to the lower seawater temperature and air temperature, the droplet adheres to the hull, and the heat dissipated rapidly, resulting in ice formation. The conditions for ice spray formation are as follows: the air temperature is below
2 C, the wind speed is greater than 16 knots, and the surface seawater temperature is
1.8 C~6.0 C (Yang 2015). Icing Damage

Polar ice platforms can reach hundreds of tons of ice and may encounter the following phenomena and hazards when operating in low-temperature environments: 1. Ice will affect the platform body, the wet gas condensation, and freezing of the cold surface of deck and cargo equipment, and the splash water and rainwater on the superstructure of the platform are frozen on the exposed surface, which will reduce the stability of the platform. For floating platforms, the weight of icing will increase the heeling moment and reduce the freeboard height (Wold 2014). Ice formation will not only affect the floatability and stability of the platform but also increase the wind area of the platform and increase the wind overturning moment, which may lead to the overturning of the platform. 2. Icing can cause damage to the equipment in the polar working area, such as freezing winches, cranes, valves, covering windows, blocking air outlets, etc. Low temperature will affect the material properties of the platform structure, increase brittleness and thermal expansion, reduce allowable stress and structural reliability, and damage the equipment when used. The windows of the vents are mostly designed with mesh and lattice, which are easy to be covered with ice and snow plugging, which will bring problems to the health and mechanical operation of personnel. The lunar pool is an open area located in the center of the offshore platform; the drilling equipment is operated in this area. The icing will cause the valve to be

W

2174

unable to work and the efficiency to be low (Xie et al. 2017). Icing may affect deck operation of platforms, such as the possibility that lifeboats/lifesaving valves can’t be released properly. 3. Ice can affect the safety of the platform. Saltwater is likely to freeze on the antenna, GPS, radar, and other equipment, affecting the normal work of these devices (Gauthier et al. 1997). If the ice covers the cab windows, it will affect the operator’s line of sight. Ice in the open deck passage of the platform will cause difficulties for the crew to walk. If the ice fall off the superstructure, it will directly threaten the personal safety of the crew (Xue 2013). Icing can reduce the self-rescue capacity of the offshore platform, such as covering fire extinguishing equipment, freezing fire extinguishing water gun valves, and blocking smoke sensors, all of which have a great impact on the safety of the platform.

Winterization of Polar Engineering

that the ambient temperature of the space is
30 C. 2. Heating power requirements for antifreeze and deicing are required: The open deck, helicopter deck, access, and staircase are not less than 300 W/M2; the superstructure is not less than 200 W/M2; the handrail is not less than 50 W/ M2. Antifreeze Design The icing on the polar offshore platforms is mainly caused by seawater splashing. The effective ice protection and deicing design can significantly reduce the ice coverage. Polar antifreeze technology mainly includes five aspects: platform structure design, regional protection, selection of outdoor equipment, heat supply system heating, and coating protection. Polar offshore platforms can be designed frostproof from these five aspects: Platform Structure Design

Ice Zone Specification

In the 1930s, Finland and Swedish Maritime Administration first standardized the ice area enhancement of ships in the Finland-Swedish Ice Class Rules (FSICR). The polar classification requirements issued by the International Association of Classification Societies, including ten major classification societies including China Classification Society, were formally promulgated in 2006, and the hull structure was modified in 2010. In addition, Det Norske Veritas (DNV) also adds the WINTERIZATION entry symbol, which mainly considers the design requirements of the platform for the short-term working in the extremely cold environment and does not consider the ice in the surface. The aim is to ensure that the system and equipment can work properly in the design temperature range and reduce the threat of cold environment to operators (Det Norske Veritas 2008). DNV has the following requirements for ocean engineering projects: 1. In ship or ocean engineering projects of the WINTERIZATION entry symbol, the calculation of space heating heat balance must assume

For the offshore platform, it is possible to design the pile foundation of the platform into large diameter and to make the bottom of the deck more flat to increase the possibility of the ice layer to fall off through its own gravity, in order to effectively reduce the amount of water splashing ice. Increasing the design of smooth surface and vertical surface and reducing the number of small components can reduce the mechanical interlocking of icing and equipment and improve the convenience of deicing and the possibility of icing and falling off. Antifreeze Design in Open Area

The antifreeze design in the open area mainly includes the layout of the windbreak wall, the calculation of the heat load in the antifreeze room, the design of the electric tracing system, and the piping layout. When the offshore platform works in the harsh environment, the deck platform is easy to freeze. It will not only affect the normal work of the equipment but also affect the operation of the crew, so the installation of the protective wall can greatly improve the working conditions. Considering the function of the equipment, the

Winterization of Polar Engineering

platform can install a windbreak for some parts of the open deck machinery. The main equipment for installing the windproof wall is as follows: installation of windproof walls around the main deck, installation of windbreak storehouse in drilling pipe/drilling riser area, lifeboat/salvage yacht installation windproof wall, installation of windproof wall near the bow and stern lifesaving valve, and so on. The crew sometimes needs to work in a room in an open area (such as a winch space). In order to operate the normal equipment in a relatively comfortable environment, a space heater is required to be installed in the room to prevent freezing. It can be used as an electric heater and calculates the power of the antifreeze space heater. The escape channel is an important safety setting. In order to ensure effective identification and use of escape passages under severe cold, the activities and evacuation of personnel are not affected by the ice. According to DNV winterization basic, the escape passage in the open area belongs to the I type antifreeze area, which requires that the area can’t have ice accumulation. Heat tracing is usually used to achieve the above purpose. Electric tracing has the advantages of simple installation, uniform heat dissipation, accurate temperature, high reliability, long service life, and energy saving (Guo and Li 2002). In the layout of polar offshore platforms, the influence of low-temperature weather on the piping system should be considered in order to avoid the occurrence of liquid icing in the piping system. In carrying out piping layout, we should pay attention to the following aspects (Yang 2015): 1. As far as piping system is concerned, try to avoid direct exposure to outdoor lines below the waterline. 2. Discharge pipes shall be installed on icing pipes on the open deck and above the waterline. 3. It is necessary to increase the diameter of the drainage pipeline in the open area to avoid blockage. 4. For water tanks above the waterline, heating pipes should be added to prevent freezing.

2175

Interior Antifreeze Design

The objective of interior antifreeze design for polar offshore platforms is to ensure that under harsh weather conditions, the living conditions of the platform personnel and the normal operation of the equipment are satisfied. The indoor antifreeze of the platform is mainly realized by heating, ventilation, and air conditioning system, and the three are collectively referred to as HVAC system. The heating system of polar offshore platform can be divided into two parts: mechanical area and living area. Because the air conditioning in residential areas has the function of heating, the heating of living areas is a part of the air conditioning system. The main purpose of mechanical zone heating is to protect equipment and pipelines in low-temperature environment, and the way to use them is to use space heaters. The main function of the platform air conditioning system is to make the air to the required state, that is, the air temperature, humidity, air flow speed, and cleanliness are manually adjusted to meet the requirements of human comfort and process production (Yang 2015). Design of Heat Source System

The heat source system is mainly used for the heating of fuel, oil, and other kinds of liquid needed by the power plant and provides the heat source for the heating equipment such as the cabin air conditioner and the heater. Therefore, the heat source system is one of the important systems of polar offshore platforms. The heat source system can be divided into four types according to the working fluids: steam heating system, hot water heating system, hot oil system, and electric heating system. Steam heating has a simple and cheap working substance (water) and is widely used in heating occasions when experience is mature. There are three main types of steam users: room heating, cabin heating, and equipment heating. The hot water in the hot water heating system has a low temperature and a large flow rate. If the heating medium of the heating coil of the air conditioner is changed into hot water, the steady flow of water can be kept in the heating coil, and the danger of

W

2176

the freezing cracking of the heating coil can be reduced. In the actual use of hot water heating systems, antifreeze may be added to hot water (Yang 2015).

Winterization of Polar Engineering

surface by absorbing moisture. At
15 C, the adhesion strength of ice can be reduced to below 30 kPa.

Coating Protection

The special surface materials on the bare surface of polar offshore platforms can also effectively prevent icing, such as sacrificial coatings, superhydrophobic coatings, and water-lubricated coatings. The sacrificial coating can release some small molecules that inhibit the crystallization of supercooled water irreversible and increase the lubricity of ice and material surface, reduce the adhesion strength of ice, and even make the icing naturally fall off (Ayres et al. 2007). The so-called superhydrophobic coating is the coating with water contact angle greater than 150

and the rolling angle less than 10 . The coating has the dual properties of the surface and the multilevel roughness of the low surface energy material, which can reduce the contact area of water or ice to the material surface, enhance the stress concentration of the ice and the material interface, and reduce the adhesion shear strength of the ice. So as to achieve the purpose of delaying icing, and after freezing, the ice adhering to the surface of the coating can be removed by very small force or wind. Meuler et al. have studied the relationship between the ice adhesion strength of a series of materials and the water back contact angle θrec. It is found that the ice adhesion strength is strongly correlated with 1 + cosθrec. The results show that increasing the water back contact angle of the coating helps to reduce the ice adhesion strength and has guiding significance for the design of superhydrophobic anti-icing coating (Meuler et al. 2010). Dou et al. (2014) graft hydrophilic dimethyl hydroxypropionic acid (DMPA) onto polyurethane (PU) substrate to make the coating hydrophilic. The contact angle is only 43 . The mechanism is to separate the ice and the coating

Cross-References ▶ Ice Breaking Vessel ▶ Navigation of Polar Vessel ▶ Polar Materials ▶ Structural Characteristics of Polar Engineering

References Ayres J, Simendinger WH, Balik CM (2007) Characterization of titanium alkoxide sol-gel systems designed for anti-icing coatings: I. Chemistry. J Coat Technol Res 4(4):463–471 China Classification Society (2016) Guide to the polar ships[S]. China Classification Society. Harbin, China Det Norske Veritas (2008, July) Rules for classification of ships new buildings, Pt.5, Ch.1[S] Dou RM, Chen J, Zhang Y F et al (2014) Anti-icing coating with an aqueous lubricating layer. ACS Appl Mater Interfaces 6(10):6998–7003 Gauthier GP, Courtay A, Rebeiz GM (1997) Microstrip antennas on synthesized low dielectric-constant substrates. IEEE Trans Antennas Propag 45(8):1310–1314 Guo H, Li Y (2002) Selection and application of electric heat tracing in marine engineering. China Offshore Platform 3:36–38 Horjen I (1989) Ice accretions on ships and marine structures[R]. The River and Harbour Laboratory, Trondheim Meuler AJ, Smith JD, Varanasi KK et al (2010) Relationships between water wettability and ice adhesion. ACS Appl Mater Interfaces 2(11):3100–3110 Wold LE (2014) A study of the changes in freeboard, stability and motion response of ships and semisubmersible platforms due to vessel icing[D]. University of Stavanger, Stavanger Xie Q, Chen H, Zhang J (2017) Research progress of antiicing and deicing technologies for polar ships and offshore platforms. Chin J Ship Res 12(1):45–53 Xue G (2013) Anti skidding and skidding work of ships in winter. World Shipping 36(03):30–31 Yang Y (2015) Anti freezing and deicing technology for semi submersible drilling platform in Beihai[D]. Harbin Engineering University. Harbin, China

Z

Zero-Tension Interface ▶ Shallow Foundations

© Springer Nature Singapore Pte Ltd. 2022 W. Cui et al. (eds.), Encyclopedia of Ocean Engineering, https://doi.org/10.1007/978-981-10-6946-8