Practical Ship Hydrodynamics Volker Bertram pot

Practical Ship Hydrodynamics Practical Ship Hydrodynamics Volker Bertram Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd First published 2000  Volker Bertram 2000 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data Bertram, Volker Practical ship hydrodynamics 1. Ships – Hydrodynamics I. Title 623.8 0 12 Library of Congress Cataloguing in Publication Data Bertram, Volker. Practical ship hydrodynamics / Volker Bertram. p. cm. Includes bibliographical references and index. ISBN 0 7506 4851 1 1. Ships – Hydrodynamics I. Title. VM156 .B457 2000 623.8 0 12–dc21 00-034269 ISBN 0 7506 4851 1 Typeset by Laser Words, Madras, India Printed in Great Britain by Preface ix 1 Introduction 1 1.1 Overview of problems and approaches 1 1.2 Model tests  similarity laws 4 1.3 Full-scale trials 8 1.4 Numerical approaches (computational fluid dynamics) 9 1.4.1 Basic equations 9 1.4.2 Basic CFD techniques 14 1.4.3 Applications 15 1.4.4 Cost and value aspects of CFD 19 1.5 Viscous flow computations 22 1.5.1 Turbulence models 23 1.5.2 Boundary conditions 26 1.5.3 Free-surface treatment 28 1.5.4 Further details 29 1.5.5 Multigrid methods 31 1.5.6 Numerical approximations 32 1.5.7 Grid generation 34 2 Propellers 37 2.1 Introduction 37 2.2 Propeller curves 39 2.3 Analysis of propeller flows 42 2.3.1 Overview of methods 42 2.3.2 Momentum theory 44 2.3.3 Lifting-line methods 45 2.3.4 Lifting-surface methods 46 2.3.5 Boundary element methods 49 2.3.6 Field methods 50 2.4 Cavitation 51 2.5 Experimental approach 54 2.5.1 Cavitation tunnels 54 2.5.2 Open-water tests 55 2.5.3 Cavitation tests 56 2.6 Propeller design procedure 56 2.7 Propeller-induced pressures 60 3 Resistance and propulsion 62 3.1 Resistance and propulsion concepts 62 3.1.1 Interaction between ship and propeller 62 3.1.2 Decomposition of resistance 65 3.2 Experimental approach 68 3.2.1 Towing tanks and experimental set-up 68 3.2.2 Resistance test 69 3.2.3 Method ITTC 1957 71 3.2.4 Method of Hughes Prohaska 73 3.2.5 Method of ITTC 1978 74 3.2.6 Geosim method of Telfer 75 3.2.7 Propulsion test 75 3.2.8 ITTC 1978 performance prediction method 76 3.3 Additional resistance under service conditions 80 3.4 Simple design approaches 83 3.5 CFD approaches for steady flow 83 3.5.1 Wave resistance computations 83 3.5.2 Viscous flow computations 90 3.6 Problems for fast and unconventional ships 91 3.7 Exercises: resistance and propulsion 95 4 Ship seakeeping 98 4.1 Introduction 98 4.2 Experimental approaches (model and full scale) 99 4.3 Waves and seaway 101 4.3.1 Airy waves (harmonic waves of small amplitude) 101 4.3.2 Natural seaway 106 4.3.3 Wind and seaway 109 4.3.4 Wave climate 4.2 4.4 Numerical prediction of ship seakeeping 117 4.4.1 Overview of computational methods 117 4.4.2 Strip method 121 4.4.3 Rankine singularity methods 127 4.4.4 Problems for fast and unconventional ships 130 4.4.5 Further quantities in regular waves 132 4.4.6 Ship responses in stationary seaway 132 4.4.7 Simulation methods 134 4.4.8 Long-term distributions 136 4.5 Slamming 138 4.6 Exercises: seakeeping 146 Discourse: hydrodynamic mass 148 5 Ship manoeuvring 151 5.1 Introduction 151 5.2 Simulation of manoeuvring with known coefficients 152 5.2.1 Introduction and definitions 152 5.2.2 Force coefficients 153 5.2.3 Physical explanation and force estimation 158 5.2.4 Influence of heel 163 5.2.5 Shallow water and other influences 164 5.2.6 Stopping 164 5.2.7 Jet thrusters 165 5.2.8 CFD for ship manoeuvring 166 5.3 Experimental approaches 169 5.3.1 Manoeuvring tests for full-scale ships in sea trials 169 5.3.2 Model tests 175 5.4 Rudders 177 5.4.1 General remarks and definitions 177 5.4.2 Fundamental hydrodynamic aspects of rudders and simple estimates 181 5.4.3 Rudder types 188 5.4.4 Interaction of rudder and propeller 190 5.4.5 Interaction of rudder and ship hull 193 5.4.6 Rudder cavitation 195 5.4.7 Rudder design 200 5.4.8 CFD for rudder flows and conclusions for rudder design 201 5.5 Exercise: manoeuvring 203 6 Boundary element methods 207 6.1 Introduction 207 6.2 Source elements 209 6.2.1 Point source 209 6.2.2 Regular first-order panel 211 6.2.3 Jensen panel 215 6.2.4 Higher-order panel 218 6.3 Vortex elements 223 6.4 Dipole elements 226 6.4.1 Point dipole 226 6.4.2 Thiart element 227 6.5 Special techniques 229 6.5.1 Desingularization 229 6.5.2 Patch method 230 7 Numerical example for BEM 236 7.1 Two-dimensional flow around a body in infinite fluid 236 7.1.1 Theory 236 7.1.2 Numerical implementation 237 7.2 Two-dimensional wave resistance problem 238 7.2.1 Theory 238 7.2.2 Numerical implementation 241 7.3 Three-dimensional wave resistance problem 242 7.3.1 Theory 242 7.3.2 Numerical implementation 247 7.4 Strip method module (two dimensional) 250 7.5 Rankine panel method in the frequency domain 253 7.5.1 Theory 253 7.5.2 Numerical implementation 261 References 265 Index 269 Preface The first five chapters give an introduction to ship hydrodynamics, which is in my opinion suitable for teaching at a senior undergraduate level or even at a postgraduate level. It is thus also suitable for engineers working in industry. The book assumes that the reader has a solid knowledge of general fluid dynamics. In teaching, general fluid dynamics and specific ship hydrodynamics are often mixed but I believe that universities should first teach a course in general fluid dynamics which should be mandatory to most engineering students. There are many good textbooks on the market for this purpose. Naval architects should then concentrate on the particular aspects of their field and cover material more suited to their needs. This book is organized to support such a strategy in teaching. The first chapter is an introduction to computational fluid dynamics, and Chapters 2 to 5 cover the four main areas of propeller flows, resistance and propulsion, ship seakeeping and manoeuvring. It is recommended that this sequence be followed in teaching. The first five chapters try to find a suitable balance for practical engineers between facts and minimizing formula work. However, there are still formulae. These are intended to help those tasked with computations or programming. Readers with a practical interest may simply skip these passages. The final two chapters involve more extensive formula work and are more specialized. They may be reserved for graduate and post-graduate teaching and will help understanding and developing boundary element codes. Field methods are not covered in depth here, as my colleague Milovan Peric has already co-authored an excellent book on this particular topic. I tried in vain to find a similar suitable textbook for boundary element methods which would be both easy to understand and address the typical problems encountered in ship flows. As I could not find such a book, I wrote two chapters intended to support me in my teaching and to be of use for many colleagues. The book is supplemented by some public domain software written in Fortran which is available for downloading in source code on www.bh.com/companions/0750648511. The software consists of small programs or subroutines which may help in developing own codes. Some of the programs have been written by myself, some by Professor S ¨ oding, and some by colleagues. Feel free to download the software, but there is no additional documentation available except for the in-program comments. I will not answer questions about the software, but you can comment on which programs you ix x Preface felt difficult to understand. We may then either update the documentation or take the software off the website. There is no guarantee that the programs are completely debugged and of course neither I nor the publisher will take any responsibility for what happens if you use these programs. Furthermore, the software is public domain and you may not sell it to third parties. Despite all this, I have worked with most of the software myself without any problems. The website will be updated more often than the book, and there will be a short read.me file on the web with some information on the available software. This book is based largely on lectures for German students. The nucleus of the book was formed by lectures on ship seakeeping and ship manoeuvring, which I have taught for several years with Professor Heinrich S ¨ oding. I always felt that we should have a comprehensive textbook that would also cover resis- tance and propulsion, as ship seakeeping and manoeuvring are both interwoven strongly with the steady base flow. Many colleagues helped with providing material, allowing me to pick the best from their teaching approaches. A lot of material was written and compiled in a new way, inspired by these sources, but the chapters on ship seakeeping and manoeuvring use extensive existing material. Thanks are due to Seehafen-Verlag Hamburg for permission to reprint text and figures from the Manoeuvring Technical Manual, an excellent book unfor- tunately no longer in print. Thanks are due to Hansa-Verlag Hamburg for permission to reprint text and figures from German contributions in Handbuch der Werften XXIV. Countless colleagues supported the endeavour of writing this book by supplying material, proof-reading, making comments or just discussing engineering or didactic matters. Among these are (in alphabetical order) Poul Andersen, Kai Graf, Mike Hughes, Hidetsugu Iwashita, Gerhard Jensen, Meinolf Kloppenburg, Jochen Laudan, Maurizio Landrini, Friedrich Mewis, Katsuji Tanizawa, Gerhard Thiart, Michel Visonneau, and Hironori Yasukawa. Most of all, Professor Heinrich S ¨ oding has supported this book to an extent that he should have been named as co-author, but, typically for him, he declined the offer. He even refused to allow me to dedicate this book to him. I then dedicate this book to the best mentor I ever had, a role model as a scientist and a man, so much better than I will ever be. You know who. Volker Bertram [...]... model to extract information that can be scaled (transformed) to the full-scale ship 1 2 Practical Ship Hydrodynamics Despite continuing research and standardization efforts, a certain degree of empiricism is still necessary, particularly in the model-to -ship correlation which is a method to enhance the prediction accuracy of ship resistance by empirical means The total resistance can be decomposed in... Traditionally, unless the new ship design was close to an experimental series or a known parent ship, the design process incorporated many model tests The process has been one of design, test, redesign, test etc sometimes involving more than 10 models each with slight variations This is no longer feasible due to time-to-market requirements from shipowners and no longer 4 Practical Ship Hydrodynamics necessary... methods which use harmonic functions as elementary solutions Spectral methods have no practical relevance for ship flows The interested reader may find some introduction in Peyret and Taylor (1985) 1.4.3 Applications Practical CFD applications for ship flows concentrate mainly on the ship moving steadily ahead A 1994 survey at ship model basins showed inviscid BEM computations for wave-resistance and offshore... automatically the flow about a ship with an undeformed (rigid) water surface The double-body potential flow is only used as an approximate 16 Practical Ship Hydrodynamics solution for other methods (boundary layer, wave resistance, seakeeping) The simultaneous consideration of viscosity and wavemaking was subject to active research in the 1990s reaching the threshold of practical application by the end... ‘measured mile trials’, as ships were tested between measured miles near the coast for different ship speeds The ship speed can be measured ‘over ground’ (relative to the earth) or ‘in water’ (relative to the water) The speed in water includes currents and local flow changes Historically, various logs have been developed, including devices towed behind the ship, on long rods alongside the ship, electro-acoustic... and incompressible is called potential flow In potential flows the components of the velocity vector are no longer independent from each other They are coupled by the potential The derivative of the potential in arbitrary direction gives the velocity component in this direction: u v w E vD Dr Three unknowns (the velocity components) are thus reduced to one unknown (the potential) This leads to a considerable... Boundary element methods (BEM) BEM are used for potential flows For potential flows, the integrals over the whole fluid domain can be transformed to integrals over the boundaries of the fluid domain The step from space (3-d) to surface (2-d) simplifies grid generation and often accelerates computations Therefore practical applications for potential flows about ships (e.g wave resistance problems) use exclusively... speed (e.g ship speed), A a reference area (e.g wetted surface in calm water) The factor 1 is introduced in analogy to stagnation pressure 2 q D 1 Ð V2 Combining the above equations then yields: 2 cs Ð 1 Fs 2 D Fm cm Ð 1 2 s Ð V2 Ð As s m Ð V2 Ð Am m D s m Ð As Ð Am Vs Vm 2 6 Practical Ship Hydrodynamics This results in cs D cm , i.e the non-dimensional coefficient c is constant for both ship and model... density, the modulus of elasticity is downscaled by from full scale to model scale 1.3 Full-scale trials Trial tests of the built ship are an important prerequisite for the acceptance of the ship by the shipowner and are always specified in the contract between shipowner and shipyard The problem is that the trial conditions differ from both model test conditions and design conditions The contract usually... initial period where shipyards performed the analyses in-house the pendulum swung the other way with shipyards now using almost exclusively outsourcing as the sensible option 22 Practical Ship Hydrodynamics The main part of the variable costs and response time is created in grid generation There is considerable potential to improve this part of the CFD process: ž By making grid generation more user-friendly . Data Bertram, Volker Practical ship hydrodynamics 1. Ships – Hydrodynamics I. Title 623.8 0 12 Library of Congress Cataloguing in Publication Data Bertram, Volker. Practical ship hydrodynamics / Volker. Practical Ship Hydrodynamics Practical Ship Hydrodynamics Volker Bertram Butterworth-Heinemann Linacre House, Jordan Hill, Oxford. full-scale ship. 1 2 Practical Ship Hydrodynamics Despite continuing research and standardization efforts, a certain degree of empiricism is still necessary, particularly in the model-to -ship correlation which