Wave Forces on Offshore Structures

by Turgut 'Sarp' Sarpkaya

Overview

A thorough understanding of the interaction of waves and currents with offshore structures has now become a vital factor in the safe and economical design of various offshore technologies. There has been a significant increase in the research efforts to meet this need. Although considerable progress has been made in the offshore industry and in the understanding of the interaction of waves, currents, and wind with ocean structures, most of the available books concentrate only on practical applications without a grounding in the physics. This text strives to integrate an understanding of the physics of ocean–structure interactions with numerous applications. This more complete understanding will allow the engineer and designer to solve problems heretofore not encountered, and to design new and innovative structures. The intent of this book is to serve the needs of future generations of engineers designing more sophisticated structures at ever increasing depths.

Product Details

ISBN-13:	9780521896252
Publisher:	Cambridge University Press
Publication date:	02/26/2010
Pages:	338
Product dimensions:	7.10(w) x 10.00(h) x 1.00(d)

About the Author

Dr Turgut 'Sarp' Sarpkaya is Distinguished Professor at the US Naval Postgraduate School, Monterey, CA. He is an internationally recognized authority in fluid mechanics research and was named by Cambridge University as one of the world's one thousand greatest scientists. 'Sarp', as he is known to friends and colleagues, is the recipient of the Turning Goals into Reality Award by NASA, and he was selected Freeman Scholar by the American Society of Mechanical Engineers. Sarpkaya received his PhD from the University of Iowa, followed by postdoctoral work at MIT. He was the Thomas L. Fawick Distinguished Professor at the University of Nebraska and taught at the University of Manchester. He was named Professor and Chairman of Mechanical Engineering at the Naval Postgraduate School in 1967 and Distinguished Professor in 1975. His research over the past 50 years has covered the spectrum of hydrodynamics. His oscillating flow tunnel and the vortex-breakdown apparatus are two among several unique research facilities he has designed. Sarpkaya has published more than 200 papers and has explored for the Defense Advanced Research Projects Agency (DARPA) numerous classified projects dealing with the hydrodynamics and hydroacoustics of submarines. He served as chairman of the Executive Committee of the Fluids Engineering Division of the American Society of Mechanical Engineers (ASME) and the Heat Transfer and Fluid Mechanics Institute. He is a Fellow of the Royal Society of Naval Architects and Marine Engineers, Fellow of the ASME, and Associate Fellow of the American Institute of Aeronautics and Astronautics.

Table of Contents

Preface xi

1 Introduction 1

1.1 Classes of offshore structures 3

2 Review of the fundamental equations and concepts 7

2.1 Equations of motion 7

2.2 Rotational and irrotational flows 9

2.3 Velocity potential 11

2.4 Euler's equations and their integration 13

2.5 Stream function 15

2.6 Basic inviscid flows 16

2.7 Force on a circular cylinder in unseparated inviscid flow 17

2.8 Slow motion of a spherical pendulum in viscous flow 20

2.9 Added mass or added inertia 22

2.10 An example of the role of the added inertia 30

2.11 Forces on bodies in separated unsteady flow 31

2.12 Kinetic energy and its relation to added mass 33

3 Separation and time-dependent flows 39

3.1 Introduction and key concepts 39

3.2 Consequences of separation 42

3.3 Body and separation 47

3.4 Strouhal number 52

3.5 Near wake and principal difficulties of analysis 56

3.6 Lift or transverse force 58

3.7 Free-stream turbulence and roughness effects 58

3.8 Impulsively started flows 64

3.8.1 Introductory comments 64

3.8.2 Representative impulsively started flows 65

3.9 Sinusoidally oscillating flow 69

3.9.1 Introduction 69

3.9.2 Fourier-averaged drag and inertia coefficients 75

3.9.3 Experimental studies on C_d and C_m 76

3.9.4 Transverse force and the Strouhal number 85

3.9.5 Roughness effects on C_d, C_m, C_L, and St in SOF 90

3.9.6 A critical assessment of the Morison equation 95

3.9.7 Oscillatory plus mean flow or the in-line oscillations of a cylinder in steady flow 98

3.9.8 Forced oscillations of a cylinder in a trough 104

3.9.9 Oscillatory flow in a smaller U-shaped water tunnel 107

4 Waves and wave-structure interactions 109

4.1 Surface gravity waves 109

4.1.1 Linear wave theory 110

4.1.2 Higher-order wave theories 115

4.1.3 Character of the forces predicted 117

4.1.4 Random waves 119

4.1.5 Representative frequency spectra 121

4.2 Wave-structure interaction 122

4.2.1 Principal factors of analysis and design 123

4.2.2 Design wave and force characterization 125

4.2.3 Force-transfer coefficients 127

4.2.4 A brief summary of the literature giving explicit C_d and C_m values 135

4.2.5 Suggested values for force-transfer coefficients 138

4.2.6 Effects of orbital motion, coexisting current, pile orientation, interference, and wall proximity 139

4.2.7 Pipe lines and wall-proximity effects 155

4.2.8 Wave impact loads 166

5 Wave forces on large bodies 172

5.1 Introduction 172

5.2 The case of linear diffraction 175

5.3 Froude-Krylov force 176

5.4 The case of a circular cylinder 177

5.5 Higher-order wave diffraction and the force acting on a vertical cylinder 181

5.6 Closing remarks 184

6 Vortex-induced vibrations 186

6.1 Key concepts 186

6.1.1 Nomenclature 190

6.2 Introduction 192

6.3 Added mass, numerical simulations, and VIV 203

6.4 Governing and influencing parameters 204

6.4.1 Parameter space 204

6.4.2 Uncertainties 207

6.4.3 Mass and structural damping 208

6.4.4 f_vac, f_com, and added mass 209

6.5 Linearized equations of self-excited motion 211

6.6 Unsteady force decomposition 213

6.6.1 Lighthill's force decomposition 215

6.7 Limitations of forced and free vibrations 217

6.7.1 General discussion 217

6.7.2 Amplitude and phase modulations 219

6.8 Experiments with forced oscillations 223

6.8.1 A brief summary of the existing contributions 223

6.8.2 Detailed discussion of more recent experiments 227

6.9 The wake and the VIV 232

6.10 Self-excited vibrations 240

6.11 Discussion of facts and numerical models 250

6.12 Suppression devices 252

6.13 Evolution of numerical models 255

6.14 Experiments with advanced models 262

7 Hydrodynamic damping 265

7.1 Key concepts 265

7.2 Introduction 265

7.3 Elements of damping 267

7.3.1 Stokes canonical solutions 268

7.4 Previous investigations 270

7.5 Representative data 272

7.5.1 Solid cylinders 272

7.5.2 Perforated cylinders 274

7.5.3 Three-dimensional instabilities 275

7.5.4 Closing remarks 280

References 285

Index 321