Offshore Mechanics E-Book

Madjid Karimirad

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 517

Veröffentlichungsjahr: 2018

Beschreibung

Covers theoretical concepts in offshore mechanics with consideration to new applications, including offshore wind farms, ocean energy devices, aquaculture, floating bridges, and submerged tunnels This comprehensive book covers important aspects of the required analysis and design of offshore structures and systems and the fundamental background material for offshore engineering. Whereas most of the books currently available in the field use traditional oil, gas, and ship industry examples in order to explain the fundamentals in offshore mechanics, this book uses more recent applications, including recent fixed-bottom and floating offshore platforms, ocean energy structures and systems such as wind turbines, wave energy converters, tidal turbines and hybrid marine platforms. Offshore Mechanics covers traditional and more recent methodologies used in offshore structure modelling (including SPH and hydroelasticity models). It also examines numerical techniques, including computational fluid dynamics and finite element method. Additionally, the book features easy-to-understand exercises and examples. * Provides a comprehensive treatment for the case of recent applications in offshore mechanics for researchers and engineers * Presents the subject of computational fluid dynamics (CFD) and finite element methods (FEM) along with the high fidelity numerical analysis of recent applications in offshore mechanics * Offers insight into the philosophy and power of numerical simulations and an understanding of the mathematical nature of the fluid and structural dynamics with focus on offshore mechanic applications Offshore Mechanics: Structural and Fluid Dynamics for Recent Applications is an important book for graduate and senior undergraduate students in offshore engineering and for offshore engineers and researchers in the offshore industry.

Leseprobe

Table of Contents

Cover

Title Page

About the Authors

Preface

Acknowledgements

1 Preliminaries

2 Offshore Structures

2.1 Ship‐shaped Offshore Structures

2.2 Oil and Gas Offshore Platforms

2.3 Offshore Wind Turbines

2.4 Wave Energy Converters

2.5 Tidal Energy Converters

2.6 Combined Offshore Energy Systems

2.7 Multipurpose Offshore Structures and Systems

2.8 Submerged Floating Tunnels

2.9 Floating Bridges

2.10 Aquaculture and Fish Farms

References

3 Offshore Environmental Conditions

3.1 Introduction

3.2 Wave Conditions

3.3 Wind

3.4 Currents

3.5 Joint Distribution of Waves and Winds

3.6 Oceanographic and Bathymetric Aspects

3.7 Scour and Erosion

3.8 Extreme Environmental Conditions

3.9 Environmental Impact of Offshore Structures’ Application

References

4 Hydrodynamic and Aerodynamic Analyses of Offshore Structures

4.1 Introduction

4.2 Wave Kinematics

4.3 Wave Loads on Offshore Structures

4.4 Tides and Currents Kinematics

4.5 Current Loads on Offshore Structures

4.6 Wind Kinematics

4.7 Wind Loads on Offshore Structures

4.8 Aerodynamic Analysis of Offshore Wind Turbines

References

5 Fundamentals of Structural Analysis

5.1 Background

5.2 Structural Analysis of Beams

5.3 Mathematical Models for Structural Dynamics of Beams

5.4 Frame Structures and Matrix Analysis

5.5 Plate Theories

References

6 Numerical Methods in Offshore Structural Mechanics

6.1 Structural Dynamics

6.2 Stress Analysis

6.3 Time‐Domain and Frequency‐Domain Analysis

6.4 Multibody Approach

6.5 Finite Element Method

6.6 Nonlinear Analysis

6.7 Extreme Response Analysis and Prediction

6.8 Testing and Validation of Offshore Structures

6.9 Examples

References

7 Numerical Methods in Offshore Fluid Mechanics

7.1 Introduction

7.2 Potential Flow Theory Approach

7.3 CFD Approach

References

8 Mooring and Foundation Analysis

8.1 Mooring Considerations

8.2 Soil Mechanics

8.3 Foundation Design

References

Index

End User License Agreement

List of Tables

Chapter 03

Table 3.1 Beaufort scale, and wind and wave conditions: this guide shows roughly what may be expected in the open sea.

Chapter 04

Table 4.1 Long‐term North Atlantic wave conditions based on significant wave height and second mean period.

Table 4.2 Terrain roughness parameter

z

0

and power law exponent

α.

Table 4.3 Shape function for different geometries.

Chapter 05

Table 5.1 Relations between distributed load, shear and moment.

Table 5.2 Relations between distributed load, shear and moment and strain energy.

Chapter 06

Table 6.1 Scaling ratios that are used in testing of marine and offshore structures.

Table 6.2 RAOs of surge, heave and roll motions of the floating body.

Table 6.3 Properties of a SFC in full scale.

Table 6.4 Estimated scale factors for use based on Froude’s laws.

Chapter 08

Table 8.1 Details of the mechanical properties of steel used in offshore applications.

Table 8.2 Proposed formulas for the proof load and breaking load of mooring lines.

Table 8.3 Typical values of soil modulus of elasticity.

List of Illustrations

Chapter 01

Figure 1.1 Schematic layout, different chapters and their roles in forming the present book,

Offshore Mechanics: Structural and Fluid Dynamics for Recent Applications

.

Chapter 02

Figure 2.1 Schematic layout of an FPSO offshore oil and gas field; the ship‐shaped offshore structure (FPSO) is moored by a turret‐mooring system. The shuttle tanker, drilling rig, umbilical and risers are shown as well.

Figure 2.2 Artistic layout of the fixed‐type offshore structure.

Figure 2.3 Artistic layout of the floating‐type offshore structure.

Figure 2.4 Relation of rotor diameter and rating power of wind turbine rotor during the time evolution.

Figure 2.5 Alpha Ventus monopile offshore wind turbine supplied by Adwen in the North Sea.

Figure 2.6 University of Maine’s VolturnUS 1:8 floating wind turbine.

Figure 2.7 Hywind floating wind turbine.

Figure 2.8 Wind turbine hub during installation.

Figure 2.9 Categorization of WECs based on the working principle in which energy can be absorbed.

Figure 2.10 A schematic representation of a hydraulic PTO.

Figure 2.11 Prototypes of (a) Pelamis wave energy converter (WEC) on site at the European Marine Energy Test Centre and (b) Wave Dragon WECs.

Figure 2.12 (a) La Rance, France, and (b) scale model of the power station.

Figure 2.13 SeaGen, in Strangford Lough.

Figure 2.14 Physical model of an SFC (semisubmersible with rotating flaps combination) placed into ocean basin.

Figure 2.15 A numerical model of a submerged floating tunnel (SFT) with pontoons.

Figure 2.16 Different possible types of floating bridges: continuous pontoon type, separated pontoon type, semi‐submerged foundation type and long‐spanned separated foundation type.

Figure 2.17 (a) The Homer Hadley Bridge (left) and the Lacey V. Murrow Memorial Bridge (right); (b) the Hood Canal Bridge; (c) the William R. Bennett Bridge.

Figure 2.18 World fisheries and aquaculture productions in 2012, both inland and marine.

Figure 2.19 Schematic layout of a small fish farm consisting of four fish cages; the shared mooring system and anchoring are shown as well.

Chapter 03

Figure 3.1 Classification of the spectrum of ocean waves according to wave period.

Figure 3.2 Particle motion for deep waters.

Figure 3.3 Swell at Lyttelton Harbour, New Zealand.

Figure 3.4 Shoaling effect: increase in the amplitude of waves due to decrease in the speed of wave motion as it travels toward shallow waters.

Figure 3.5 World’s dominant winds.

Figure 3.6 Sea breeze.

Figure 3.7 World’s largest gyres.

Figure 3.8 Offshore Meteorological Met Mast (Alpha Ventus Offshore Wind Park).

Figure 3.9 Features of the sea floor, including trenches, mid‐ocean ridges, basins, and island arcs. For more information, refer to Stewart (2008).

Figure 3.10 Clear‐water scour and live‐bed scour. For more information, refer to Arneson

et al

. (2012). Normally, clear‐water scour produces higher scour depth compared to live‐bed scour. As some of the soil particles in suspension during live‐bed scour fall down on soil, this reduces the size of scour.

Chapter 04

Figure 4.1 Different environmental loads on an offshore wind turbine.

Figure 4.2 Boundary conditions imposed on the Laplace equation to derive an equation of motion for the free surface waves.

Figure 4.3 Relation of wave number and wave frequency for different

kh

values and infinite water depth.

Figure 4.4 Summation and components of four different free surface waves with different amplitudes, frequencies and phases.

Figure 4.5 JONSWAP spectrum for short‐term representation of wave condition with 10 m significant wave height and 12 second mean wave period.

Figure 4.6 A monopile offshore wind turbine as an example of a fixed offshore structure.

Figure 4.7 Forced oscillation of a sphere in unbounded fluid.

Figure 4.8 Forced surge oscillation of a circular cylinder in the limit of zero frequency is akin to oscillation near a plance boundary.

Figure 4.9 Profile of tidal currents (left), wind‐induced currents (center) and the summation of these two (right).

Figure 4.10 Boundary layer and separation of flow at the surface of a circular cylinder.

Figure 4.11 Distribution of mean wind speed in 10 min intervals based on Rayleigh model.

Figure 4.12 Probability distribution of the turbulence intensity function can be approximated by a normal distribution function.

Figure 4.13 A power spectral density function of a wind condition.

Figure 4.14 Wind speed as a function of height based on logarithmic and power law approaches.

Figure 4.15 Control volume for studying thrust force on a wind turbine; linear momentum theory approach.

Figure 4.16 Control volume for calculating thrust force and torque for a horizontal axis wind turbine by considering the rotational wake effects.

Figure 4.17 Comparison of power efficiency by considering or neglecting the rotational effects of a wind turbine. Dashed line shows the Betz limit in which rotational effects are neglected.

Figure 4.18 Wind turbine blade and cross section. Main characteristics of a cross section of a wind turbine blade are shown.

Figure 4.19 Angle of attack for a cross section of a wind turbine based on the twist angle and wind relative velocity.

Figure 4.20 Different shapes of a wind turbine’s cross sections at different radii of the wind turbine.

Chapter 05

Figure 5.1 Rigid and hinged connection of beams; a hinged connection does not carry the moments between different elements, while the rigid connections (e.g. welded beams) carry moments between elements. Dashed lines present the deformed beams under external loads.

Figure 5.2 Different types of boundary conditions, supports and their corresponding reaction forces and displacements.

Fx

A

, 

Fy

A

, 

Mz

A

are support reaction forces (in the x and y directions) and moment at point A.

u

A

,

v

A

,

φ

A

are displacements (in x and y directions) and slope at point A.

k

x

,

k

y

,

k

φ

denote linear horizontal, vertical and rotational stiffness. Δ

x

, Δ

y

, Δ

φ

denote horizontal and vertical deflections and rotation (e.g.

).

Figure 5.3 Different approaches for expressing equilibrium conditions for a beam under loads.

Figure 5.4 Superposition principal illustration.

Figure 5.5 Mechanism, determinate and indeterminate structures.

Figure 5.6 Different types of joints; moment (hinge), axial force and shear force releases; N, Q and M are the normal axial force, shear force and bending moment, respectively; positive sign conversion is shown.

Figure 5.7 Reaction forces and internal loads diagram for a beam under uniform pressure.

Figure 5.8 Internal force diagram for a part of a beam subjected to point force, bending moment and distributed load (positive value is in the Y‐direction).

Figure 5.9 Stress–strain curve representation.

Figure 5.10 Infinitesimal cube about point of interest and stress state.

Figure 5.11 Plane deformations resulting in normal and shear strains.

Figure 5.12 Mohr stress circle.

Figure 5.13 Schematic layout of a beam subjected to transverse loading.

Figure 5.14 Schematic layout of a ship‐shaped structure in waves; sagging and hogging load cases; the structure can be roughly presented as a beam subjected to weight and buoyancy forces distributed along the beam.

Figure 5.15 Torsion of a solid circular‐section beam.

Figure 5.16 Schematic of a thin‐walled closed‐section beam subjected to torsion.

Figure 5.17 I‐profile terms for calculation of torsion constant; see Equation 5.26.

Figure 5.18 Distribution of shear stress in part of a thin‐walled open section subjected to torsion (truncated component just for illustration and clarification of terms used in equations).

Figure 5.19 Distribution of shear stress in open and closed sections.

Figure 5.20 Schematic layout of a gravity‐based bottom‐fixed wind turbine and a simplified modelling using a few beams with diffident cross sections and section stiffness.

Figure 5.21 Pure bending of beam; radius of the curvature is shown for the deformed case.

Figure 5.22 A tapered cantilever beam with a circular section subjected to point load.

Figure 5.23 Shear stress and shear force in a cantilevered beam subjected to a point load.

Figure 5.24 Curvature of the deformed neutral axis and transverse displacement.

Figure 5.25 Load intensity, reaction forces, shear force, bending moment, slope and deflection of a beam and their relation; positive moment and shear force convention are shown in Figure 5.6.

Figure 5.26 Simplified structural beam‐model of a bottom‐fixed turbine.

Figure 5.27 A pinned‐pinned beam subjected to compressive load.

Figure 5.28 End‐condition effect on effective length and end‐condition constant for buckling of a beam with different support conditions.

Figure 5.29 Critical stress plotted versus the slenderness ratio, highlighting the safe and buckling (unsafe) regions based on elastic (Euler formula) and inelastic stability limits.

Figure 5.30 The natural frequency percentage deviation compared to the experimental values for first and second modes; non‐slender beams were studied. The Bernoulli–Euler model has almost 105% error for the second‐mode natural frequency value compared to experiments.

Figure 5.31 The schematic layout of a ship‐shaped structure (i.e. a floating production storage and offloading [FPSO] vessel) subjected to wave loads.

Figure 5.32 Tripod bottom‐fixed wind turbine; an example of a space frame structure; the support structure is made of a few beams connected at joints.

Figure 5.33 External loads and deflections of a beam; for 3D frames, each beam has six degrees of freedom at each end. Here, a beam in a plane is assumed which has three degrees of freedom at each end (two translations and one rotation).

Figure 5.34 Transverse and bending loads to present

, while other deflections are zero.

Figure 5.35 Global and local deformations and deflections of end 1 of a beam.

Figure 5.36 Schematic layout of a submerged tunnel.

Figure 5.37 Simplified frame representing the submerged tunnel section shown in Figure 5.36.

Figure 5.38 Plane stress, membrane state versus bending state.

Chapter 06

Figure 6.1 A SDOF system (a) and a free body diagram of the system (b).

Figure 6.2 An undamped two degrees of freedom MDOF system.

Figure 6.3 A damped two degrees MDOF system with external loadings.

Figure 6.4 Constant initial acceleration for numerical integration.

Figure 6.5 Constant average acceleration for numerical integration.

Figure 6.6 Linear acceleration for numerical integration.

Figure 6.7 The Ocean Tank of the Ocean Technology Laboratory – LabOceano.

Figure 6.8 Definition and basic parameters of the examined FB.

Figure 6.9 Hydrodynamic model of the examined FB.

Chapter 07

Figure 7.1 Two offshore platforms, discretized for hydrodynamic analysis based on the potential flow theory approach.

Figure 7.2 (a) Cylinder used to study the force heave motion. It is assumed that L> > D; therefore, it can be represented in the heave direction by (b) a 2D model. The slip boundary condition is imposed by defining the strength of the number of sources on the perimeter of the circle.

Figure 7.3 Cavity problem and a structured grid used for discretization of the domain.

Figure 7.4 Cavity problem for a Reynolds number equal to 100: (a) shows the results of comparison with another numerical model; and (b) iso‐pressure contours in the cavity box.

Figure 7.5 Marker function used in the VOF method to distinguish between different fluids.

Figure 7.6 Definition of the level set function for free surface flow.

Figure 7.7 Modeling a standing wave with the level set method and comparing the numerical results with an analytical solution.

Figure 7.8 Immersed boundary grid points used to study hydrodynamic loads on a wind turbine.

Figure 7.9 CFD simulation of a floating wind turbine on a rectangular structured grid by the level set and immersed boundary methods.

Figure 7.10 Coordinate system for solving the NS equations is mapped from (a) x–y to (b)

.

Figure 7.11 Contravariant velocities in the

coordinate system.

Figure 7.12 Simple mapping function to map a uniform grid to a non‐uniform stretched grid.

Figure 7.13 Stretching grids used to discretize a 2D numerical wave tank.

Figure 7.14 Mapped coordinate system for grid generation around a structure.

Figure 7.15 Elliptical grid generation methods to discretize the domain around a half a cylinder.

Figure 7.16 Comparison of structured and unstructured grid. (a) Structured grid, (b) unstructured grid, (c) example of structured grid, (d) example of unstructured grid.

Chapter 08

Figure 8.1 Different types of mooring lines.

Figure 8.2 Stud and stud‐less mooring chain links.

Figure 8.3 Components of steel wire rope that are used in offshore engineering.

Figure 8.4 S‐N design curves for mooring lines of different types.

Figure 8.5 Spread symmetric mooring line layout (Figure 8.5a) and a turret mooring system (Figure 8.5b).

Figure 8.6 A catenary side 2D view (a) of a mooring line and forces that act on an element of the mooring line (b).

Figure 8.7 A typical tension leg platform (TLP) station kept with tendons.

Figure 8.8 Free body diagram of a TLP.

Figure 8.9 Schematic layout of a gravity‐based structure on elastic soil.

Figure 8.10 A layer of soil subjected to constant load.

Figure 8.11 A layout of a shallow foundation with its main design parameters.

Figure 8.12 Coefficient of friction for sand (cohesionless soils), which depends on soil type, material type and roughness of foundation.

Figure 8.13 Element of a pile subjected to axial load.

Figure 8.14 Shear stress and displacement relationship for cohesive (clay) material.

Figure 8.15 Shear stress for a pile in cohesive soil.

Figure 8.16 Element of a pile subjected to lateral load.

Guide

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Offshore Mechanics

Structural and Fluid Dynamics for Recent Applications

Madjid Karimirad

Queen’s University BelfastUK

Constantine Michailides

Cyprus University of TechnologyCyprus

Ali Nematbakhsh

University of California, RiversideUSA

This edition first published 2018© 2018 John Wiley & Sons Ltd

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Library of Congress Cataloging‐in‐Publication Data

Names: Karimirad, Madjid, author. | Michailides, Constantine, 1978– author. | Nematbakhsh, Ali, 1984– author.Title: Offshore mechanics : structural and fluid dynamics for recent applications / by Madjid Karimirad, Queen’s University Belfast, UK, Constantine Michailides, Cyprus University of Technology, Cyprus, Ali Nematbakhsh, University of California, Riverside USA.Description: First edition. | Hoboken NJ, USA : Wiley, 2018. | Includes bibliographical references and index. |Identifiers: LCCN 2017043079 (print) | LCCN 2017044707 (ebook) | ISBN 9781119216643 (pdf) |ISBN 9781119216636 (epub) | ISBN 9781119216629 (cloth)Subjects: LCSH: Offshore structures–Hydrodynamics.Classification: LCC TC1665 (ebook) | LCC TC1665 .K38 2018 (print) | DDC 627/.98–dc23LC record available at https://lccn.loc.gov/2017043079

Cover design by WileyCover image: © BenGrasser/Gettyimages

About the Authors

Dr Madjid Karimirad is Senior Lecturer (Associate Professor) in Marine and Coastal Engineering in the School of Natural and Built Environment, Queen's University Belfast (QUB), UK, since March 2017. Prior to joining QUB, he was Scientist at MARINTEK (Norwegian Marine Technology Research Institute) and SINTEF Ocean, Trondheim, Norway. Dr Karimirad has been researching in the field of marine structures and offshore technology with more than 10 years of work and research experience. He has a strong background in academia and industry, including postdoctoral and PhD research, working expertise, and competencies in the offshore oil and gas business. Dr Karimirad got his PhD in 2011 in Marine Structures from the Norwegian University of Science and Technology (NTNU). He has been employed by CeSOS (Centre for Ships and Ocean Structure), a Centre of Excellence (CoE) in Norway. Dr Karimirad served as postdoctoral academic staff at CeSOS, and his postdoctoral was part of the NOWITECH (Norwegian Research Centre for Offshore Wind Technology) program. Dr Karimirad obtained his MSc (2007) in Mechanical Engineering/Ships Structures and his BSc (2005) in Mechanical/Marine Engineering from the Sharif University of Technology, Tehran. In addition, he has worked in industry as Senior Engineer at the Aker‐Kvaerner EPCI Company. Offshore renewable energy (ORE) structures and oil/gas technologies are among his interests, and he has carried out different projects focusing on these issues. Dr Karimirad has served as editor and reviewer for several international journals and conferences; also, he has been appointed as topic and session organizer of the International Conference on Ocean, Offshore & Arctic Engineering (OMAE). His knowledge covers several aspects of offshore mechanics, hydrodynamics, and structural engineering. The work and research results have been published in several technical reports, theses, book chapters, books, scientific journal articles, and conference proceedings.

Dr Constantine Michailides is a Lecturer in Offshore Structures in the Department of Civil Engineering and Geomatics, Cyprus University of Technology, Cyprus, since July 2017. He holds a BSc, MSc, and PhD in Civil Engineering from Aristotle University of Thessaloniki (AUTh), Greece. He did a PhD in marine and offshore engineering in hydroelasticity of floating structures and wave energy production; for his PhD research, he awarded by AUTh and International Society of Offshore and Polar Engineering (ISOPE). In May 2013, he joined Centre for Ships and Ocean Structures (CeSOS) and Centre for Autonomous Marine Operations and Systems (AMOS) in the Department of Marine Technology at the Norwegian University of Science and Technology as Postdoctoral Researcher until January 2016, when he was appointed as Senior Lecturer in the Department of Maritime and Mechanical Engineering, Liverpool John Moores University, UK. Dr Michailides has performed research on numerical analysis, experimental testing, and structural‐field monitoring of offshore and coastal structures and systems. His research focuses on global and local numerical analyses of offshore structures and systems (oil and gas, and renewable energy), fluid–structure interaction, hydrodynamics and hydroelasticity, ocean energy devices, offshore wind technology, offshore combined energy systems, physical model testing, structural health monitoring, optimization, genetic algorithms, and floating bridges and tunnels. Recent interests include computational fluid dynamics (CFD) and reliability analysis for offshore engineering applications. Dr Michailides is a member of research and professional bodies in marine and offshore engineering technology like ISOPE, International Ship and Offshore Structures Congress (ISSC), Technical Chamber of Greece, and Engineering and Physical Sciences Research Council (EPSRC) Peer Review Associate College. He authored more than 40 research papers in peer‐reviewed journals and conference proceedings in the field of marine and offshore engineering.

Dr Ali Nematbakhsh is an expert in the field of computational fluid dynamics (CFD) and numerical modeling, with 9 years of experience in these fields. He is currently Project Scientist at University of California, Riverside. He received his PhD in 2013 from Worcester Polytechnic Institute in Massachusetts in the field of Mechanical Engineering. During his PhD, he wrote original code to model nonlinear hydrodynamic loads on floating wind turbines. Right after his PhD, he was invited to be a Postdoctoral Researcher at Center of Ships and Ocean Structures (CeSOS) at Norwegian University of Science and Technology, where he further developed and used his numerical model to simulate different offshore structures, including floating wind turbines, wave energy converters, barges, and monopiles. Dr Nematbakhsh also has extensive knowledge in high‐performance computing using parallel CPUs and GPUs, which enable him to simulate complex and nonlinear offshore engineering problems. Dr Nematbakhsh is a member of the American Society of Mechanical Engineers. His research has been published in more than 15 papers in international conference proceedings and scientific journals.

Preface

Offshore industry has seen rapid development in recent years. New marine structures have emerged in different fields such as offshore oil and gas, marine renewable energy, sea transportation, offshore logistics and sea food production. As a result, new concepts and innovative offshore structures and systems have been proposed for use in the oceans. An obvious need exists for a book which provides the capabilities and limitations of theories and numerical analysis methods for performing dynamic analysis for the case of recent applications in offshore mechanics. This book covers the needs for the required analysis and design of offshore structures and systems. Particular emphasis has been given to recent applications in offshore engineering. This includes ship‐shaped offshore structures, fixed‐bottom and floating platforms, ocean energy structures and systems (wind turbines, wave energy converters and tidal turbines) and multipurpose offshore structures and systems. Theoretical principles are introduced, and simplified mathematical models are presented. Practical design aspects for various offshore structures are presented with handy design guides and examples. Each example is followed with an analytical or a numerical solution. Additionally, special attention has been paid to present the subject of computational fluid dynamics (CFD) and finite element methods (FEM) that are used for the high‐fidelity numerical analysis of recent applications in offshore mechanics. The book provides insight into the philosophy and power of numerical simulations and an understanding of the mathematical nature of the physical problem of the fluid–structure interaction, with focus on offshore applications.

The book helps students, researchers and engineers with a mid‐level engineering background to obtain insight on theories and numerical analysis methods for the structural and fluid dynamics of recent applications in offshore mechanics. The main key feature of the book is using “new” applications for describing the theoretical concepts in offshore mechanics. Furthermore, the present book not only covers traditional methodologies and concepts in the field of offshore mechanics, but also includes new approaches such as novel CFD and FEM techniques. Nowadays, due to the rapid increase of computational resources, offshore industry is using various advanced CFD and FEM tools to design offshore structures. Therefore, qualified graduated students and engineers need to be familiar with both traditional methodologies and new methods applied in offshore mechanics proper for recent applications. The book helps engineers and researchers in the field of offshore mechanics to become familiar with recently applied trends and methodologies.

This book covers the fundamental knowledge of offshore mechanics by teaching the reader how to use numerical methods for design of different concepts in offshore engineering. Recent methodologies for hydrodynamic and structural analysis of offshore structures are introduced and explained. The authors believe that a graduate student or an engineer in offshore industry should be well familiar with these concepts. The book is intended for graduate students, researchers, faculty members and engineers in the fields of offshore engineering, offshore renewable energy (wind energy, wave energy and tidal energy), marine structures, ocean and coastal engineering, fluid dynamics and mechanical engineering. The readers of the book must have basic offshore engineering knowledge and interest related to the analysis and design of recent applications in offshore mechanics. The presented theories and applications are developed in a self‐contained manner, with emphasis on fundamentals, concise derivations and simple examples. Some of the main key words covered in this book are as follows:

Offshore mechanics; structural dynamics; fluid–structure interaction; hydrodynamics; fluid dynamics; ocean energy devices; offshore wind; multipurpose floating platforms; offshore structures; wave energy converters; floating wind turbines; combined wave and wind energy; finite element method (FEM); computational fluid dynamics (CFD)

The book consists of the following chapters:

Preliminaries

Offshore Structures

Offshore Environmental Conditions

Hydrodynamic and Aerodynamic Analyses of Offshore Structures

Fundamentals of Structural Analysis

Numerical Methods in Offshore Structural Mechanics

Numerical Methods in Offshore Fluid Mechanics

Mooring and Foundation Analysis

Acknowledgements

Dr Karimirad would like to thank his family (in particular, Soosan and Dorsa) for their support which helped him to finish this important task.

Dr Michailides would like to thank his wife, Christina, and his son, Evangelos, for inspiring him; and also his mentor, Professor Demos Angelides, for teaching him about marine structures.

Dr Nematbakhsh would like to thank his wife, Nafiseh, for her support during writing this book.

Dr Madjid Karimirad, Queen’s University Belfast (QUB), Belfast, UK

Dr Constantine Michailides, Cyprus University of Technology (CUT), Limassol, Cyprus

Dr Ali Nematbakhsh, University of California, Riverside (UCR), USA

October 2017

1Preliminaries

Compared to inland structures, offshore structures have the added difficulty of being placed in the ocean environment. Hence, offshore structures are subjected to complicated loads and load effects. Important factors affect the design, functionality, structural integrity and performance of offshore structures, including but not limited to: fluid–structure interaction, intense dynamic effects, nonlinear loadings, extreme and harsh weather conditions and impact pressure loads. Offshore industry has seen rapid development in recent years. This includes the emergence of new marine structures in different areas such as offshore petroleum, marine renewable energy, sea transportation, offshore logistics and seafood production. As a result, new concepts and innovative offshore structures and systems have been proposed for use in the oceans.

An obvious need exists for a book providing the limitations and capabilities of theories and numerical analysis methods for structural and fluid dynamic analysis of recent applications in offshore mechanics. This book attempts to provide a comprehensive treatment of recent applications in offshore mechanics for researchers and engineers. The book covers important aspects of offshore structure and system analysis and design. Its contents cover the fundamental background material for offshore structure and system applications. Particular emphasis has been paid to the presentation of recent applications from the required theory and their applicability. The book covers recent applications in a broad area. This includes ship‐shaped offshore structures, recent fixed‐bottom and floating oil and gas platforms, ocean energy structures and systems (wind turbines, wave energy converters, tidal turbines and hybrid platforms), multipurpose offshore structures and systems, submerged tunnels and floating bridges for transportation purposes and aquacultures (fish farms).

Many of the applications of the theoretical principles are introduced, and several exercises as well as different simplified mathematical models are presented for recent applications in offshore engineering. In this book, practical design aspects of the aforementioned offshore structures are presented with handy design guides and examples, simple description of the various components for their robust numerical analysis and their functions. Additionally, special attention has been paid to present the subjects of computational fluid dynamics (CFD) and finite element methods (FEM) along with the high‐fidelity numerical analysis of recent applications in offshore mechanics.

The book makes available an insight into the philosophy and power of numerical simulations and an understanding of the mathematical nature of the fluid and structural dynamics, with focus on offshore mechanics applications. The current book helps students, researchers and engineers with mid‐engineering background gain good insights on theories and numerical analysis methods for structural and fluid dynamics for the cases of recent applications in offshore mechanics. Figure 1.1 presents the schematic layout of the book and shows different chapters as well as their roles in shaping this book.

Figure 1.1 Schematic layout, different chapters and their roles in forming the present book, Offshore Mechanics: Structural and Fluid Dynamics for Recent Applications.

The key features of the book are using “new” applications for describing the theoretical concepts in offshore mechanics, and covering both traditional and recent methodologies used in offshore structure modelling. Most of the books currently available in the field of offshore mechanics are based on using traditional oil, gas and ship industry examples to explain the fundamentals of offshore mechanics. Therefore, the reader becomes familiar with the basic concepts very well, but his or her viewpoint will remain limited to the traditional applications. This book tries to address this limitation by covering some recent applications, such as: offshore wind farms, ocean energy devices, aquaculture, floating bridges and submerged tunnels.

Furthermore, the current book not only covers traditional methodologies and concepts in the field of offshore mechanics, but also includes new approaches such as CFD and FEM techniques. The material in this book will help graduate students get needed knowledge in offshore industry for recent applications. Currently, due to the rapid increase in speed of computational resources, offshore industry is using various advanced CFD and FEM tools such as ANSYS and ABAQUS to analyse offshore structures. Therefore, qualified graduated students and engineers need to be familiar with both traditional methodologies and new methods applied in offshore mechanics proper for recent applications.

Structural fluid mechanics of offshore structures, the theories applied to recent applications and proper case studies to explain analytical and numerical methods make the core of this book. The hydrodynamic, stochastic dynamics and structural analyses are the book’s focus. What makes this book distinct from similar available books is that it covers recent applications in offshore industry by providing suitable examples. Simplified examples help students, researchers and engineers to understand the subjects and know how to use proper methods.

This book will help engineers and researchers in the field of offshore mechanics to become familiar with new trends and methodologies that have been applied recently. Different new offshore concepts such as offshore energy harvesters, floating bridges, submerged tunnels, multipurpose platforms, hybrid floaters as well as fish farms are going to play important roles in the future of offshore industry. Furthermore, new numerical techniques such as advanced CFD and FEM methods are currently used in industry.

We believe that the new offshore concepts that are now the focus of academic investigations gradually will be adopted by industry and probably result in greater popularity of this book. This book helps readers to learn the basic concepts of offshore mechanics not only by traditional standard applications, but also by applying these concepts for new structures in offshore engineering. In addition, it introduces the fundamentals of new numerical techniques that are emerging in offshore industry.

The book covers the fundamentals of offshore mechanics by teaching the reader how to use these concepts for traditional and (more specifically) current demands in offshore industry. The examples, given throughout the book, are for offshore structures that have been recently designed or are currently under development. For example, different offshore wind farms have been installed in Europe in recent years, and several projects are ongoing for harvesting energy from waves. We believe that a graduate student or an engineer in offshore industry should be well familiar with these concepts.

The methodologies for hydrodynamic and structural analyses of offshore structures are introduced and explained in this book. By learning the basics of the new methodologies, the reader has enough background to further expand his or her knowledge based on the needs in a specific industry. Throughout the chapters, special attention is given to familiarize the reader with numerical methods. These numerical methods cover both structural and hydrodynamic analysing of offshore structures.

This book is intended for graduate students, researchers, faculty members and engineers in the fields of: offshore structural engineering, offshore renewable energy (wind energy, wave energy and tidal energy), marine structures, ocean and coastal engineering, fluid dynamics and mechanical engineering. Its reading level can be considered as introductory or advanced. However, readers must have basic offshore engineering knowledge and interest related to the analysis and design of recent applications in offshore mechanics. The presented theories and applications are developed in a self‐contained manner, with an emphasis on fundamentals, concise derivations and simple examples.

The book has eight chapters. The first chapter introduces the book and explains its scope and objectives. The second chapter covers offshore structures, explaining different concepts such as ship‐shaped, oil and gas platforms (bottom‐fixed and floating), ocean energy devices (e.g. wind turbines, wave energy, ocean tidal turbines and hybrid platforms), multipurpose floaters, submerged tunnels, floating bridges and aquaculture and fish farms. The third chapter covers metocean and environmental conditions; in particular, wind, wave and current conditions, joint distribution of wave and wind, oceanography, bathymetry, seabed characteristics, extreme environmental conditions and environmental impacts of offshore structures. The fourth chapter explains the wave, wind and current kinematics as well as aerodynamic and hydrodynamic loads. This covers coupled hydrodynamic and aerodynamic analysis for offshore structures. Chapter 5 covers structural analysis and fundamental structural mechanics. This includes beam theories, stress–strain relation as well as buckling, bending, plate and plane theories and similar basic theories useful for studying the structural integrity of offshore and marine structures. In Chapter 6, the stress analysis, dynamics analysis, multibody formulation, time‐domain and frequency‐domain simulations, finite element methods, nonlinear analysis, extreme response calculation as well as testing and validation of offshore structures are discussed. The seventh chapter is dedicated to computational methods for fluid mechanics covering potential theories (i.e. a panel method covering radiation and diffraction as well as excitation forces). Computation fluid dynamics (CFD) is the core of this chapter, and different practical theories are included in this chapter. The eighth chapter covers mooring and foundation as well as theories related to soil mechanics and soil–foundation interaction.

The objective of the present book is to help the readers on different levels – namely, knowledge, comprehension, application, analysis, synthesis and evaluation – whenever they are dealing with physical problems that exist in offshore mechanics, especially with recent applications. As a result, the readers of the book will be able to: (a) exhibit learned material by recalling facts, terms and basic concepts; (b) demonstrate understanding of facts and basic concepts; (c) solve problems by applying acquired knowledge, facts, techniques and rules in a different way; (d) examine and split any possible information into parts by identifying motives or causes, making inferences and finding evidence to support solution methods; (e) compile information in a different way by combining elements in a new pattern; and (f) present and defend opinions by making judgments about relevant information based on a set of criteria.

In Chapter 2, we will review and present important information for different types of offshore structures, and we will try to identify an outline of their numerical analysis needs and the methods that have been used up to now. The types that will be presented are ship‐shaped offshore structures, oil and gas offshore platforms, offshore wind turbines, wave energy converters, tidal energy converters, multipurpose offshore structures and systems, submerged floating tunnels and aquaculture and fish farms. For all the types of recent applications of offshore structures, categorization and basic design aspects are presented.

In Chapter 3, we will present important information about the generation and the process of propagation of different environmental conditions that may affect the structural integrity of recent applications of offshore structures. Different environmental processes like the wave, wind, current, scour and erosion are described appropriately in connection with possible effects that they have on all the different types of offshore structures that are examined. Moreover, the effect of joint analysis on wind and wave is presented. Finally, insight is presented about the estimation of extreme environmental conditions that have straightforward relation with the survivability of offshore structures.

In Chapter 4, we deal with the three dominant excitation loading conditions that influence the lifetime of offshore structures: the wave, tidal and wind loadings. Wave kinematic theories that exist for addressing regular and irregular waves are presented. Moreover, methods for estimating the wave loads induced by inviscid flows in members of offshore structures are presented, too. In addition, tide and current kinematic methods are presented with emphasis on methods for estimating the current loads on offshore structures. Wind kinematic methods that have application for the design of offshore structures are presented along with numerical methods for estimating the wind loadings. Finally, fundamental topics of the required aerodynamic analysis for the design of offshore wind turbines are presented. Emphasis is on presenting numerical methods for estimating the aforementioned environmental loadings and on how these loads are used compared to different numerical tools.

In Chapter 5, some of the important principles of statics and dynamics and how these are used to determine the resultant internal loadings in an offshore structure are initially presented. Furthermore, the concepts of normal and shear stress are introduced along with the strains induced by the deformation of the body. Moreover, important information about the appropriate development of structural elements of offshore structures is presented. Beams and plates, and methods for developing numerical models with the use of these types of structural elements for the structural analysis of offshore structures, are presented.

In Chapter 6, numerical methods that are used in offshore engineering for the structural response dynamic analysis of different types of offshore structures are presented. Dynamic loadings dominate the response of offshore structures. Numerical methods for the development of numerical models and tools for the dynamic analysis of offshore structures in both frequency and time domain are presented. Also, special cases where a multibody approach is needed or nonlinear phenomena exist, and numerical methods for handling these special cases, are presented. Methods for estimating or predicting numerically the extreme response values of different components of offshore structures (e.g. mooring lines, pontoons of a semisubmersible platform and tower of a wind turbine) are presented. Finally, the fundamental required process for the development of a physical model test of an offshore structure is presented.

In Chapter 7, the different possible numerical methods that exist in offshore fluid mechanics are presented. Initially, the bases of potential flow theory models are presented and explained. Afterwards, a comprehensive presentation of CFD‐based models in offshore engineering is presented. Details about the discretization of the Navier–Stokes equation on rectangular structures’ grids, with details about the advection, viscous and pressure terms and mass conservation equation, are presented. Possible numerical methods for solving the Navier–Stokes equations, incorporating the Poisson equation, the effects of free surface and the volume of fluid method, are presented. Moreover, the discretization of the Navier–Stokes equation in a mapped coordinate system (which can be used for different types of moving offshore structures) is presented. Finally, methods for discretization of level set function and of reinitialization of the equation of motion are presented in connection with use for the numerical analysis of offshore structures.

Chapter 8 presents the effects of different possible foundation systems that are used in offshore engineering. Initially, different mooring line systems are described, with emphasis on catenary and taut mooring systems; the appropriate numerical modelling of these mooring line systems is presented and explained. Afterwards, fundamental theories for the numerical analysis of soil in offshore areas are presented, with focus on possible soil–structure interaction effects that should be taken into account. Finally, the chapter presents design aspects for the case of foundations that are used in offshore engineering, like piles, caissons, direct foundations and anchors.

2Offshore Structures

2.1 Ship‐shaped Offshore Structures

Oil and gas demand will not decrease in the near future unless substantial changes and developments happen in renewable and sustainable energy technologies. Oil prices may increase and change world economics again. This leads oil companies and countries to be keen to explore new offshore fields in deeper water, in harsher conditions and in areas with longer distance to shore.

Offshore oil and gas have seen a movement from deep water (500 to 1500 m) to ultra‐deep water (more than 1500 m) (Lopez‐Cortijo et al., 2003) in the past decade, and several oil and gas subsea facilities have been installed in offshore sites with water deeper than 2000 m (TOTAL, 2015). This is mainly due to energy supply development limits and policies, as well as the world economy and increased energy consumption. To develop these offshore fields, ship‐shaped structures are widely used, particularly in sites with no (or limited) pipeline infrastructure. However, the application of ship‐shaped offshore structures is not limited to deep water, and these structures may be considered in near‐shore oil and gas terminals (Paik and Thayamballi, 2007).

In moderate‐depth and relatively shallow offshore sites (less than 500 m in depth), bottom‐fixed platforms (e.g. jackets) have been widely used for oil and gas development. However, they are not feasible in deep water (500+ m depth). Floating‐type offshore structures (e.g. semisubmersibles) are considered for deep‐water and ultra‐deep‐water areas. In Section 2.2, fixed‐type and floating‐type offshore oil and gas platforms are discussed. The current section is dedicated to ship‐shaped offshore structures.

Several alternatives exist for production, storage and offloading. The produced oil and gas should be transported to shore for further processing and use. All types of floating platforms (e.g. spar, semisubmersible and tension leg platform) need systems and infrastructures, such as pipelines and other associated facilities, to store and transport the products. The processed oil may be stored in platforms and transported via pipelines to shore.

Before the oil and gas can be transferred to shore or stored for offloading, the product should be processed. Normally, the rig flow is separated into water, gas and oil. The gas may be compressed and stored, or flared (burned to atmosphere). The stored gas can be used for reinjection in later phases of oil production. The water is drained and normally reinjected to enhance oil production in nearby wells. The oil is further processed to obtain necessary crude oil characteristics.

An oil tanker converted to an FPSO (floating, storage, processing and offloading) or FSO (without processing) vessel, or a vessel built for this application, is a very attractive alternative for field development compared to ordinary floating platforms (Devold, 2013). If the structure is equipped with drilling, the unit is called an FDPSO (floating, drilling and production, storage and offloading) vessel.

By using shuttle tankers, the produced and processed oil and gas can be transported to shore from the ship‐shaped unit. Thus, the ship‐shaped structure is an active unit combining several functions, which reduces infrastructure needed for transporting products to shore. Development of oil and gas fields in deep water and ultra‐deep water with limited access to pipelines has been extensively enhanced using economical ship‐shaped units.

Numerous types of research about design, engineering, construction, installation and operation covering structural integrity, cost and reliability of these structures have been carried out; nevertheless, the first ship‐shaped structures were in place 40 years ago. The first FPSO was built in 1977, and currently more than 270 FPSOs are installed worldwide.

There are similarities and differences between ship‐shaped offshore structures and trading tankers. The number of conversions has grown in recent years, and several oil tankers have been converted to FPSOs during that time (Biasotto et al., 2005). The structural geometry of ship‐shaped units and oil tankers is similar. Ship‐shaped structures (similar to other types of oil and gas platforms) are designed for a specific offshore site with specific environmental conditions for which the design is tailored (ABS, 2014). Oil tankers like other merchant ships can avoid harsh weather or change their heading angle. However, ship‐shaped structures are located in a defined location and are subjected to environmental conditions at the site (Hwang et al., 2012).

The other important parameter is that the trading ships are regularly checked, surveyed and repaired (i.e. by dry‐docking to maintain the ship in proper condition). But the structural integrity of ship‐shaped units is considered to cope with their long‐term safety demands. Risk assessment and management plans for field development are initiated very early in the concept selection phase, and the project’s feasibility may be questioned regarding converting an oil tanker or designing a new‐built unit (Mierendorff, 2011).

Another difference between an oil tanker and FPSO is that the FPSO has a production and process unit. In converted FPSOs, the production/process plant is constructed in modular form and added onto the deck of the oil tanker. Regarding the storage, the newly built ships and converted units are the same, and the processed oil is stored in tanks of the units. During offloading, the oil is pumped to shuttle tankers using a flexible floating discharge hose (Karimirad and Mazaheri, 2007). Figure 2.1 shows a schematic layout of a turret‐moored FPSO; the shuttle tanker is moored to the FPSO for offloading.

Figure 2.1 Schematic layout of an FPSO offshore oil and gas field; the ship‐shaped offshore structure (FPSO) is moored by a turret‐mooring system. The shuttle tanker, drilling rig, umbilical and risers are shown as well.

Although loading and unloading of trading ships are normally performed in protected ports at still‐water conditions, the loading and offloading (ballast, transient and fully loaded conditions) of ship‐shaped offshore structures are subjected to major loading (Terpstra et al., 2001). Ship‐shaped offshore units are installed permanently at a specified location and hence similar to other offshore structures, designed to withstand 100‐year environmental conditions. For converting oil tankers, the structural integrity of the hull should be checked with respect to offshore industry standards (compared to shipbuilding industry standards) to confirm durability and reliability (Ayala‐Uraga, 2009), in particular the interfaces between the hull and topside.

Although the shipbuilding industry’s standards are more cost‐effective, it is not easy to apply these to ship‐shaped offshore structures due to differences between the shipbuilding and offshore industries in requirements, background, tradition and culture of staffs. Moreover, there are many interface matters complicating the design, for example topside–hull interactions. These issues should be considered during the design of new‐built units or conversion of oil tankers to FPSOs (Paik and Thayamballi, 2007).

Ship‐shaped offshore structures are used for storage and processing of natural gas as well. Floating liquefied natural gas (FLNG) production is the only option for some fields, although the cost associated with production, liquefaction, storage and transferring using FLNG can be greater compared to land‐based LNG units (Anonymous, 2005). However, this technology helps natural gas to be produced, liquefied, stored and transferred at sea (Shell, 2015), which is required in marginal gas fields and offshore‐associated gas resources. There are unique characteristics for LNG‐FPSO design, such as:

Restricted space

Platform motion

LNG sloshing in the inner storage tank and offloading system (Gu and Ju, 2008).

2.2 Oil and Gas Offshore Platforms

Offshore petroleum industry has seen continuous technological development for exploring, drilling, processing and producing oil and gas during the past 65 years. The key motivations for such nonstop progress are reducing cost, increasing safety, decreasing environmental impact, increasing remote‐control operations and reducing accidents. Hence, new fixed‐ and floating‐type offshore structures have been developed to answer industry requirements. More cost‐effective concepts and more efficient installation methods should be developed to overcome offshore industry challenges.

Many offshore structures are unique in design, engineering, construction, transportation, installation, accessibility, maintenance, operation, monitoring, decommissioning and so on. Hence, some concepts are less attractive than others, considering the existing knowledge, and more research is needed to reduce the associated costs (both capital and operational) of such offshore installations while increasing their durability and reliability. One of the key points in offshore structures design is accounting for the fact that such installations have no fixed onshore access, and they should stay in position in different environmental conditions.

Offshore oil and gas exploration started in the nineteenth century. The first offshore oil wells were drilled in California in the 1890s and in the Caspian Sea. However, offshore industry was born in 1947 when the first successful offshore well appeared in the Gulf of Mexico. Since 65 years ago, innovative structures have been placed in increasingly deeper waters and in more hostile environmental conditions. More than 10,000 offshore platforms have been constructed and installed worldwide. The most important deep‐water and ultra‐deep‐water offshore petroleum fields are located in the Gulf of Mexico, West Africa and Brazil, known as the Golden Triangle (Chakrabarti, 2005).

Offshore shallow water reserves have been depleted, and offshore petroleum industry has moved to explore deep water and ultra‐deep water. Offshore exploration and production of oil and gas in deep water created new challenges for offshore technology. Several offshore structures have already been installed in deep water. Furthermore, new oil and gas fields have been discovered in ultra‐deep water, and offshore petroleum industry has moved to ultra‐deep water in the past decade. However, several of these fields are small, and their development requires novel concepts and innovative structures to present competitive and cost‐effective solutions.

In general, offshore structures are divided into two main types: fixed and floating. Fixed‐type offshore structures are fixed to the seabed using their foundation, while floating‐type offshore structures may be (a) moored to the seabed, (b) dynamically positioned by thrusters or (c) allowed to drift freely. However, there is another innovative group of structures that are partially fixed to the seabed, and their stability is ensured using guyed lines and floatation devices. Among those structures are articulated columns, guyed towers and compliant platforms (Johnson, 1980).

Fixed‐type offshore structures – for example, jackets, gravity‐based structures and jack‐ups – have been widely used for oil and gas production in moderate and shallow waters. Figure 2.2 shows a schematic layout of bottom‐fixed offshore structures. As water depth increases, fixed‐type structures become more expensive, and the installation of bottom‐fixed structures in deep water is very challenging.

Figure 2.2 Artistic layout of the fixed‐type offshore structure.

The guyed tower is an innovative and cheaper alternative to fixed‐type structures (Finn, 1976). Guyed towers can deflect easier under wave and wind loads, compared to fixed‐type structures. The structure is supported by piles extending from the seafloor and mooring lines attached to the platform helping the structure resist harsh conditions. The Lena (Exxon’s Mississippi Canyon 280‐A) platform represents the first commercial application of the guyed tower concept for offshore drilling and production platforms. The Lena platform was installed in 305 m water depth (Power et al., 1984). The other famous compliant platforms installed in the Gulf of Mexico are Amerada Hess’ Baldpate in 502 m and ChevronTexaco’s Petronius in 535 m. Petronius, the world’s deepest bottom‐fixed oil platform and one of the world’s tallest structures, was completed in 2000 (Texaco Press, 2000).

Moving further in deep‐water and ultra‐deep‐water areas using fixed‐type offshore structures is not feasible. Moreover, alternative solutions such as compliant towers are becoming expensive; hence, the only practical option is floating structures. Floating offshore structures have been widely considered for developing deep‐water oil and gas fields. In Section 2.1, ship‐shaped offshore units (i.e. FPSOs) were discussed. In addition to ship‐shaped structure, the main floating‐type structures are spar, tension leg platform (TLP) and semisubmersible; see Figure 2.3. The world deepest floating oil platform is Perdido, which is a spar platform in the Gulf of Mexico in a water depth of 2438 m. Perdido started production in 2010 (Shell, 2010).

Jacket

: Jacket structures, also called templates or lattices, are three‐dimensional space frame structures consisting of tubular members (legs and braces) that are welled. Jackets are the most common offshore structures used for offshore petroleum drilling and production. Jackets normally have four to eight legs, which are not normally vertical to increase the stability under environmental loads and corresponding overturning moments. Piles penetrating soil fix the structure to seabed; the piles are also tubular members and are driven (hammered) through the jacket legs into the sea bottom. The pile design is highly affected by soil conditions and seabed characteristics. The jacket structure provides an enclosure for well conductors. The platform topside (superstructure) consists of 2–3 decks with drilling units and production facilities. Jackets are widely applied in shallow and moderate water depth around the world. However, water depth is not the only decision‐making parameter, and in areas with more moderate environmental conditions, it may be possible to use a jacket structure in deeper water depth (i.e. environmental conditions in the Gulf of Mexico are moderate compared to the North Sea).

Jack‐up