Offshore Energy Structures

Offshore Energy Structures

Madjid Karimirad Offshore Energy Structures For Wind Power, Wave Energy and Hybrid Marine Platforms 1 3

ISBN 978-3-319-12174-1 ISBN 978-3-319-12175-8 (ebook) DOI 10.1007/978-3-319-12175-8 Springer Cham Heidelberg New York Dordrecht London Library of Congress Control Number: 2014954245 Springer International Publishing Switzerland 2014 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. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the Copyright Clearance Center. Violations are liable to prosecution under the respective Copyright Law. 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. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)

Preface Due to the rapid growth of offshore renewable energy structures such as offshore wind and ocean energy devices (such as wave energy converters and tidal current turbines), the science, technology and engineering in this field are seeing a phenomenal development. However, the needed competencies and knowledge are not available in a single reference. Particularly, for hybrid marine platforms, where wind and wave energy devices are combined to use possible synergies through proper combinations, limited information is available. Incredible progress has been made in the last decades in the advancement of offshore energy structures, especially for offshore wind applications. Now, the bottomfixed offshore wind turbines are mature enough to compete with land-based wind turbines. This has given rise to the development of new concepts/structures for deep ocean applications. Floating wind turbines are emerging and several concepts have been commissioned, which produce electricity. Also, wave energy converters are being well-developed during the last decades and several concepts are in the stage of producing electricity. Recently, the combination of wave and wind energy devices in hybrid marine platforms has been the focus of scientists in the field of offshore technology. This generated an obvious need for a book providing the state-of-the-art knowledge in offshore energy structures. Offshore renewable industry has planned for further booming in coming years which needs having more engineers in the offshore energy structures field. This is what this book is about. In this book, the author has tried to avoid sophisticated mathematical expressions. The hope is that engineers with moderate mathematical background can get a proper insight to offshore energy structures by reading this book. However, to read some parts of the book, a proper knowledge of calculus is necessary. The book is written for MSc students and engineers in the field of offshore technology, renewable energy, marine, ocean and coastal engineering. This book can be used in MSc-level courses in departments of civil engineering, mechanical engineering as well as ocean, coastal and marine engineering. This book tries to simply introduce the base for design of offshore energy structures. v

vi Preface The book is about wind turbines, wave energy converters, and combined concepts such as wave-wind energy platforms. This is a book for masters students and engineers willing to study and work in offshore renewable energy business. In general, there is no book in the market covering all these aspects. The book makes a link between available standards and theoretical methods. The basics have been explained and applications in real life are exemplified. Design codes, standards and numerical tools are mentioned. The book is applicable for engineers working in offshore business. It is easy and simple. The author has tried to avoid complicated mathematical points while explaining the physics. The book covers designs applicable in industry while mentioning the practical codes and needed information. Some of the main keywords covered in this book are listed below: Offshore structure Renewable energy Wave energy converters Wind turbines Floating wind turbines Combined wave and wind energy Aero-hydro-elastic Energy structures Structural dynamics Stochastic methods The objectives of the book, considering the design aspects needed for offshore energy structures, are explained in the first chapter. Also, the scope of the book considering the interconnections between different chapters are highlighted in the first chapter. The book consists of the following chapters: 1. Introduction 2. Wind turbines 3. Fixed offshore wind turbines 4. Floating offshore wind turbines 5. Wave energy converters 6. Combined wave and wind power devices 7. Design aspects 8. Wave and wind theories 9. Aerodynamic and hydrodynamic loads 10. Dynamic response analyses 11. Stochastic analyses Finally, I would like to thank my dear family (in particular, my wife) for their support which enabled me to finish this important task. Norway Dr. Madjid Karimirad September 2014

Contents 1 Introduction... 1 1.1 Background... 1 1.2 Objectives... 3 1.3 Scope... 3 References... 5 2 Wind Turbines... 7 2.1 Introduction... 7 2.2 Nacelle... 7 2.3 Hub... 9 2.4 Blades... 10 2.5 Pitch System... 11 2.6 Main Shaft... 13 2.7 Gearbox... 14 2.8 Generator... 15 2.9 Control... 16 2.10 Sensors... 17 2.11 Converter... 18 2.12 Transformer... 19 2.13 Yaw System... 19 2.14 Rotor... 19 2.15 Tower... 19 2.16 Wind Park... 21 References... 21 3 Fixed Offshore Wind Turbines... 23 3.1 Introduction... 23 3.2 Offshore Wind Farms... 24 3.3 A Case Study: Greater Gabbard Wind Farm... 25 3.4 Bottom-Fixed Offshore Wind Turbine Concepts... 32 vii

viii Contents 3.5 Monopiles... 34 3.5.1 Monopile Characteristics... 36 3.6 Jacket Wind Turbine... 40 3.7 Tripile Wind Turbine... 42 3.8 Tripod Wind Turbine... 45 3.9 Gravity-Based Wind Turbines... 46 References... 50 4 Floating Offshore Wind Turbines... 53 4.1 Introduction... 53 4.2 Floating Offshore Wind Projects... 53 4.3 Hywind Project... 54 4.4 WindFloat Project... 57 4.5 Fukushima Project... 60 4.6 Floating Wind Turbine Concepts... 64 4.7 Semisubmersible Offshore Wind Turbine... 65 4.8 Tension-Leg Platform (TLP) Offshore Wind Turbine... 67 4.9 Spar Offshore Wind Turbine... 70 4.10 Unconventional Floating Wind Turbine Concepts... 72 Bibliography... 75 5 Wave Energy Converters... 77 5.1 Introduction... 77 5.2 Wave Energy Resources... 79 5.3 Wave Energy Converter Concepts... 82 5.4 Overtopping Energy Devices... 83 5.5 Oscillating Water Column... 87 5.6 Point Absorber... 89 5.7 Wave Energy Converter Projects... 91 5.7.1 Wavestar (Wave Star Energy)... 92 5.7.2 Pelamis (Pelamis Wave Power)... 93 5.7.3 Wave Dragon (Wave Dragon A/S)... 95 5.7.4 OE Buoy (Ocean Energy Ltd.)... 95 5.7.5 Oyster (Aquamarine Power)... 96 5.7.6 WaveRoller (AW Energy)... 97 5.7.7 LIMPET (Voith Hydro Wavegen Ltd.)... 98 5.7.8 OceanLinx (Oceanlinx)... 98 5.7.9 CETO (Carnegie Wave Energy Limited)... 98 5.7.10 Powerbuoy (Ocean Power Technologies)... 100 References... 102 6 Combined Wave- and Wind-Power Devices... 105 6.1 Introduction... 105 6.2 Combining Offshore Wind and Wave Energy, Why?... 106 6.3 Poseidon: An Example of Combining Wave and Wind Devices... 109

Contents ix 6.4 Synergies of Combined Wave and Wind Concepts... 112 6.5 Hybrid Wave- and Wind-Energy Concepts... 115 6.6 Bottom-Fixed Hybrid Wind-Wave-Energy Concepts... 118 6.7 Floating Hybrid Wind-Wave-Energy Concepts... 122 References... 127 7 Design Aspects... 129 7.1 Introduction... 129 7.2 What is Design?... 129 7.3 General Design Aspects... 130 7.4 Reliability and Limit States... 131 7.5 Economical Aspects of Design... 133 7.6 Environmental Aspects of Design... 133 7.7 Component Design... 134 7.8 Design Principles... 139 7.9 Design Safety... 140 7.10 Design Using Partial Safety Factor Method... 142 7.11 Design Using Direct Simulation of Combined Load Effects... 145 7.12 Design Certification of Wind Turbines... 146 7.13 Design Loads for Offshore Wind Turbines... 151 7.14 Design Load Cases... 157 7.15 Design of Floating Wind Turbines... 159 References... 164 8 Wave and Wind Theories... 165 8.1 Introduction... 165 8.2 Regular Wave Theory... 166 8.3 Modified Linear Wave Theory (Stretching Models)... 169 8.4 Stokes Wave Theory... 171 8.5 Cnoidal and Solitary Wave Theories... 173 8.6 Stream Function Wave Theory... 174 8.7 Validity Range of Wave Theories... 174 8.8 Offshore Waves Versus Nearshore Waves... 175 8.9 Irregular Wave Theory... 176 8.10 Wind Theory... 179 8.11 Spatial and Temporal Variations of Wind... 179 8.12 Wind Distribution (Weibull Long-Term Probability)... 180 8.13 Wind Shear... 181 8.14 Turbulence and Wind Spectrum... 182 8.15 Joint Wave and Wind Conditions... 184 References... 185 9 Aerodynamic and Hydrodynamic Loads... 187 9.1 Introduction... 187 9.2 Blade Element Theory... 187

x Contents 9.3 Aerodynamics of Wind Turbines... 193 9.4 Wind Turbine Aero-Servo Loads... 196 9.5 Wave Loads and Hydrodynamics... 198 9.6 Wave Forces on Slender Structures... 200 9.6.1 Morison Formula for Fixed Structures... 200 9.6.2 Morison Formula for Floating Structures... 201 9.6.3 Morison Formula with MacCamy-Fuchs Correction... 202 9.6.4 Pressure Integration Method... 202 9.7 Breaking Wave Loads... 203 9.8 Large-Volume Structures... 204 9.8.1 Hydrostatic Considerations... 204 9.8.2 Mass and Inertia Loads... 208 9.8.3 Hydrodynamic Considerations... 209 9.8.4 Hydrodynamic Analyses Methods... 210 9.8.5 First-Order Wave Loads... 211 9.8.6 Second-Order Wave Loads... 213 9.8.7 Higher-Order Wave Loads... 220 Bibliography... 220 10 Dynamic Response Analyses... 223 10.1 Introduction... 223 10.2 Dynamics of Single Degree of Freedom Systems... 223 10.2.1 Free Vibration of Single Degree of Freedom Systems... 225 10.2.2 Forced Vibration of Single Degree of Freedom Systems... 229 10.3 Natural Periods of Floating Structures... 230 10.4 Two Degree of Freedom System Dynamics... 233 10.5 Eigen-Value Analysis of Multi Degree of Freedom Systems... 236 10.6 Rigid Body Modes... 239 10.7 Modal Dynamic Analysis for Multi Degree of Freedom System... 239 10.8 Wave-Induced Responses Applying Frequency Domain Analysis... 241 10.9 Response Equations for Offshore Energy Structures... 244 10.9.1 Floating Wind Turbines Aero-Loads Considerations... 245 10.9.2 Simple Vs. Comprehensive Aero-Loads Modelling... 246 10.9.3 Wave Energy Converters Considerations... 247 10.9.4 Solution Methods for Rigid-Body Response-Equations... 247 10.10 Comprehensive Analysis of Offshore Energy Structures... 249 10.10.1 Elastic-Body Response-Equations... 251 10.10.2 Static Finite Element Analysis... 251 10.10.3 Dynamic Finite Element Analysis... 252 10.11 Multi-Body Dynamics Considering Hydrodynamic Interactions... 253 10.12 Some Aspects of Dynamic Response... 255 10.13 Aero-Hydro-Elasticity Applied to Energy Platforms... 256 10.14 Flutter: An Aeroelastic Dynamic Behaviour... 259 10.15 Case Study: Analysis of a Jacket Wind Turbine... 262 References... 266

Contents xi 11 Stochastic Analyses... 269 11.1 Introduction... 269 11.2 Probabilistic and Stochastic Theories... 270 11.3 Spectrum and Spectral Analysis... 274 11.4 Peaks Distribution for General Random Process: Rice Distribution... 277 11.5 1/N Largest Maxima... 279 11.6 Largest Maximum Among N Maxima... 279 11.7 Extreme Value Analysis... 282 11.8 Stochastic Time Domain Analysis Aspects... 284 11.9 Fatigue Damage Assessment: A Stochastic Analysis... 286 References... 288 Short Biography... 289 Bibliography... 291 Index... 299