Mechanics of Wave Forces on Offshore Structures

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Turgut Sarpkaya Michael Isaacson

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CINCINNATI LONDON

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.\ (From an original by D . Muller, and reproduced with the permission of Canaco Inc.)

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Preface

Van Nostrand Reinhold Company Regional Offices :

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Copyright © 1981 by Litton Educational Publishing, Inc. Library of Congress Catalog Card Number: 80-20237

ISBN : 0-442-25402-4

All rights reserved. No part of this work covered by the copyright hereon may

be reproduced or used in any form or by any mean~-graphic, electronic, or

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and retrieval systems-without peimission of the publisher.

Manufactured in the United States of America Published by Van Nostrand Reinhold Company 135 West 50th Street, New York, N.Y. 10020

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Published simultaneously in Canada by Van Nostrand Reinhold Ltd. 15 14 13 12 11109 ' 8 7 6 5 4 3 2 1

Library of Congress Cataloging in Publication Data Sarpkaya, Turgut, 1928Mechanics of wave forces on offshore structures. Includes bibliographical references and indexes. 1. Offshore structures-Hydrodynamics. 2. Ocean joint author. waves. I. Isaacson, Michael, 1949II. Title. TC1650.S26 627'.98 80-20237 ISBN 0-442-25402-4

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Offshore technology has experienced extremely rapid development since the 1940 s, and a thor_ough understanding of the interaction of waves with off­ shore structures has now become a vital factor in the safe and economical design of such structures. There has been a corresponding increase in research efforts to meet this need, but results are widely scattered throughout literature. The present text is a modest effort in response to the clear need to assemble and organize the wide ranging research efforts pertment to the central topic of wave forces on offshore structures. However, the intention is specifically not to present a compendium of experimental data and theoretical results. Rather, emphasis is placed on describing the vitally important physical concepts and un­ derlying principles. Observations, laboratory and field experiments and theory have been kept continually in mind in the selection of topics and in their exposi­ tion. This is essential if the reader is to deal with a novel problem which might not entirely overlap with presently available results. In fact , in many instances the understanding of the limitations of the theoretical and experimental results and a sound judgment are the designer's most important recipes. The text is intended to be both of fundamental interest to researchers, scien­ tists and .graduate students , as well as of immediate practical value to engineers involved in the design and construction of offshore structures. It may serve as a convenient text for graduate courses relating to wave forces', as well as for self­ study by engineers interested in problems of wave forces on offshore structures. A good background in mathematics and fluid dynamics is assumed. Even so, for sake of completeness, the fundamental concepts and governing equations of fluid motion are reviewed in Chapter 2 . Subsequent chapters deal in tum with v

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PREFACE

PREFACE

flow separation and time-dependent flows , wave theories, wave forces on small bodies, wave forces on large bodies , spectral methods, dynamic response and hy­ droelastic oscillations, and modelling of offshore structures . Each chapter is reasonably self-contained and the reader should find no serious difficulty in ap­ proaching anyone chapter independently of the others. A comprehensive list of references is provided at the end of each chapter. As such, the book can serve also as a reference tool and perhaps as a point of departure for research. Units of quantities are referred to fairly infrequently, but whenever this is the case the British System has been adopted in view of its widespread use in the United States. Because of the wide range of topics covered, it has not been possible to main­ tain a consistent and distinct set of notation throughout the text without some overlap of symbols. However , the notation within any single chapter should be reasonably consistent and is defined wherever first encountered . A text of this sort, which attempts to help bridge the gap between theoreti­ cians and practicing engineers , cannot hope to fulfill the needs or expectations of all those within this wide spectrum . Indeed, not all topics related to ocean wave interaction with structures could be or are treated. More specifically, the text does not deal with such topics as wave interaction with breakwaters, seawalls and other coastal structures, coastal processes and scour, harbor design, and wave interaction with ships and ship-like vessels. Furthennore, highly specialized top­ ics such as the discrete vortex model are not described in detail. The contents of the 9 chapters reflect the collective experience in teaching, research and consulting of the authors and their assessment of the relevance of the material treated. Although most of the text describes material that is available in the technical literature , a number of original results and interpretations have been included. There are many people to thank for aiding us in this effort. Professors Charles Dalton, of the University of Houston; John H. Nath, of Oregon State University; and Dr. Wayne W. Jamieson, of the National Research Council of Canada, each read the manuscript and gave helpful criticisms. Many graduate students have worked with us on this subject, notably Neil J. Collins, Neil MacKenzie, Farhad Rajabi, and Ray L. Shoaff. Many others devoted countless hours in carrying out experiments and evaluating data. Mr. Jack McKay's ingenuity penneated the de­

sign and construction of many -research equipment which was invaluable in ob­ taining some of the results presented here. Sincere appreciation is also expressed here for the extensive research support and willing cooperation extended through the years by the representatives of the federal agencies, particularly the Office of Naval Research, the National Science Foundation and the Civil Engineering Lab­ oratory of the Naval Construction Battalion Center (port Hueneme, California)

and the National Science and Engineering Council of Canada. Special apprecia­ tion is also extended to our families for their support.

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This book is dedicated to the designers and builders of offshore structures and to researchers in this field. Their concern for the advancement of the state of the art motivated Our work. We sincerely hope that our efforts, modest relative to their monumental achievements, will meet with their approval. T . S. Monterey, California M. I. Vancouver, Canada

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ContentsPREFACE

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I. INTRODUCTION 1.1. 1.2. 1.3. 1.4. 1.5.

Classes of Offshore Structures The Role of Offshore Engineering Rese.arch Historical Development Ouiline of the Text References

2. REVIEW OF TIlE FUNDAMENTAL EQUATIONS AND CONCEPTS 2.1 .

Equations of Motion 2.1.1. Equation of Continuity 2.2. Rotational and Irrotational Flows 2.3. Velocity Potential 2.4. Euler's Equations and Their Integration 2.5. Kinetic Energy

2K Stream Function

2.7. Basic Flow Patterns 2.8. Force on a Cylinder 2.9. Generalization of the C~ 2.10. An Example 2.11. References

1 5 8 11 12 14 14 16 17 18 20 22 23 25 25 32 41 43 ix

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