Principles of naval architecture second revision

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Content: Principles of Naval Architecture Second Revision Volume II · Resistance, Propulsion and Vibration Edward V. Lewis, Editor Published by The Society of Naval Architects and Marine Engineers 601 Pavonia Avenue Jersey City, NJ
Copyright @ 1988 by The Society of Naval Architects and Marine Engineers. It is understood and agreed that nothing expressed herein is intended or shall be construed to give any person, firm, or corporation any right, remedy, or claim against SNAME or any of its officers or members. Library of Congress Catalog Card No. 88-60829 ISBN No. 0-939773-01-5 Printed in the United States of America . First Printing, November, 1988 ii
Preface The aim of this second revision (third edition) of the Society's successful Principles of Naval Architecture was to bring the Subject Matter up-to-date through revising or rewriting areas of greatest recent technical advances, which meant that some chapters would require many more changes than others. The basic objective of the book, however, remained unchanged: to provide a timely survey of the basic principles in the field of naval architecture for the use of both students and active professionals, making clear that research and engineering are continuing in almost all branches of the subject. References are to be included to available sources of additional details and to ongoing work to be followed in the future. The preparation of this third edition was simplified by an earlier decision to incorporate a number of sections into the companion SNAME publication, ship design and Construction, which was revised in 1980. The topics of Load Lines, Tonnage Admeasurement and Launching seemed to be more appropriate for the latter book, and so Chapters V, VI, and XI became IV, V and XVII respectively, in Ship Design and Construction. This left eight chapters, instead of 11, for the revised Principles of Naval Architecture, which has since become nine in three volumes. At the outset of work on the revision, the Control Committee decided that the increasing importance of high-speed computers demanded that their use be discussed in the individual chapters instead of in a separate appendix as before. It was also decided that throughout the book more attention should be given to the rapidly developing advanced marine vehicles. In regard to units of measure, it was decided that the basic policy would be to use the international system of Units (S.I.). Since this is a transition period, conventional U.S. (or "English") units would be given in parentheses, where practical, throughout the book. This follows the practice adopted for the Society's companion volume, Ship Design and Construction. The U.S. Metric Conversion Act of 1975 (P.L. 94-168) declared a national policy of increasing the use of metric systems of measurement and established the U.S. Metric Board to coordinate voluntary conversion to S.I. The Maritime Administration, assisted by a SNAME ad hoc task group, developed a Metric Practice Guide to "help obtain uniform metric practice in the marine industry," and this guide was used here as a basic reference. Following this guide, ship displacement in metric tons (1000 kg) represents mass rather than weight, (In this book the familiar symbol, A, is reserved for the displacement mass). When forces are considered, the corresponding unit is the kilonewton (kN), which applies, for example, to resistance and to displacement weight (symbol ~ where W = pAg) or to buoyancy forces. When conventional or English units are used, displacement weight is in the familiar long ton unit (2240 (Continued) Hi
PREFACE
lb), which numerically is 1.015 X metric ton. Power is usually in kilowatts (1 kW = 1.34 hp). A conversion table also is included in the Nomenclature at the end of each volume The first volume of the third edition of Principles of Naval Architecture, comprising Chapters I through IV, covers almost the same subject matter as the first four chapters of the preceding edition. Thus, it deals with the essentially static principles of naval architecture, leaving dynamic aspects to the remaining volumes. Chapter I deals with the graphical and numerical description of hull forms and the calculations needed to deal with problems of flotation and stability that follow. Chapter II considers stability in normal intact conditions, while CHAPTER III discusses flotation and stability in damaged conditions. Finally, Chapter IV deals with principles of hull Structural Design, first under static calm water conditions, and then introducing the effect of waves which also are covered more fully in Volume III Chapter VIII, Motions in Waves. For Volume II it seemed desirable, on the basis of subject matter and space requirements, to include Chapter V, Resistance, Chapter VI, Propulsion and Chapter VII, Vibration. The first two of these were covered in a single chapter in the preceding edition. The new chapters have been extensively revised, with considerable new material, particularly dealing with high performance craft and new propulsion devices. Chapter VII, Vibration, which is the third in Volume II, has been almost completely rewritten to take advantage of new developments in the field.
May 1988
EDWARD V. LEWIS Editor
iv
Table of Contents Volume II
Preface ....................................
Page iii
Acknowledgments ..........................
Page vi
Chapter 5
RESISTANCE
J.D. VAN MANENand P. VAN OOSSANEN,Netherlands
Netherlands
1. Introduction ...........................
1
2. Dimensional Analysis ....... , ..........
5
3. Frictional Resistance ..................
7
4. Wave-making Resistance ..............
15
5. Other Components of Resistance ...... 27
Maritime Research Institute, Wageningen, The
6. Uses of Models........................
53
7. Presenting Model Resistance Data .... 62
8. Relation of Hull Form to Resistance .. 66
9. Advanced Marine Vehicles ............
93
Chapter 6
PROPULSION
J.D. VAN MANEN and P. VAN OOSSANEN,Netherlands Maritime Resarch Institute, Wageningen, The
Netherlands
1. Powering of Shi~s .....................
127
2. Theory of Prope ler Action ............
131
3. Law of Similitude for Propellers ...... 143
4. Interaction Between Hull and
Proreller ....... : ....................
145
5. Mode Self-propulsIon Tests ........... 153
6. Geometry of the Screw Propeller ..... 164
7. Cavitation .............................
171
8. Propeller Desi~ ......................
183
9. Ducted Propel ers .....................
213
10. Other ProЈulsion Devices .............
225
11. Ship Stan ardization Trials ............ 240
Chapter 7
VIBRATION
WILLIAMS. VORUS,Professor, University of Michigan
1. Introduction ...........................
255
2. Theory and Concepts ..................
257
3. Analysis and Design...................
279
4. Criteria, Measurement, Post Trial
Correction ...........................
306
Nomenclature ...................................
317
Index ............................................
322
v
Acknowledgments The authors of Chapters V and VI, J.D. van Manen and P. van Oossanen, wish to acknowledge their indebtedness to the author of Chapter V in the preceding edition, Frederick H. Todd. Extensive use has been made of the original text and figures. The authors also wish to recognize the assistance provided by U. Nienhuis of the Maritime Institute Netherlands in working through the entire text a second time, making additions and corrections whenever necessary. And valuable ideas and suggestions regarding high-speed displacement and planing hulls in Section 9 of Chapter V were provided by Daniel Savitsky, Director of the Davidson Laboratory and are acknowledged with thanks. The author of Chapter VII, William S. Vorus, expresses his appreciation of the pioneering work of Frank M. Lewis, as distilled in Chapter X of the preceding edition of this book, which provided a foundation for the new chapter. He appreciates the reveiw and comments on early drafts by Edward F. Noonan, of NFK Engineering Associates, Inc., and John P. Breslin of Stevens Institute of Technology. The Control Committee provided essential guidance, as well as valuable assistance in the early stages. Members are:
John J. Nachtsheim, Chairman Thomas M. Buermann William A. Cleary, Jr. Richard B. Couch Jerome L. Goldman Jacques B. Hadler Ronald K. Kiss Donald P. Roseman Stanley G. Stiansen Charles Zeien
Finally, the Editor wishes to thank all of the authors for their fine work and for their full cooperation in making suggested revisions. He acknowledges the indispensible efforts of Trevor Lewis-Jones in doing detailed editing and preparing text and figures in proper format for publication.
May 1988
E. V. LEWIS Editor
vi
CHAPTER
V
Res·.stance I PJ.. Dva.nvaOnosMsaanneenn
Section 1
Introduction
1.1 The Problem. A ship differs from any other large engineering structure in that-in addition to all its other functions-it must be designed to move efficiently through the water with a minimun of external assistance. In Chapters I-III of VoL I it has been shown how the naval architect can ensure adequate buoyancy and stability for a ship, even if damaged by collision, grounding, or other cause. In Chapter IV the problem of providing adequate structure for the support of the ship and its contents, both in calm water and rough seas, was discussed. In this chapter we are concerned with how to make it possible for a structure displacing up to 500,000 tonnes or more to move efficiently across any of the world's oceans in both good and bad weather. The problem of moving the ship involves the proportions and shape-or form-of the hull, the size and type of propulsion plant to provide motive power, and the device or system to transform the power into effective thrust. The design of power plants is beyond the scope of this1 book (see Marine Engineering, by R.L. Harrington, Ed., SNAME 1971). The nine sections of this chapter will deal in some detail with THE RELATIONSHIP between hull form and resistance to forward motion (or drag). Chapter VI discusses propulsion devices and their interaction with flow around the hull. The task of the naval architect is to ensure that, within the limits of other design requirements, the hull form and propulsion arrangement will be the most efficient in the hydrodynamic sense. The ultimate test is that the ship shall perform at the required speed with the minimum of shaft power, and the problem is to attain the best combination of low resistance and high propulsive efficiency. In general this can only be attained by a proper matching of hull and propeller. Another factor that influences the hydrodynamic design of a ship is the need to ensure not only good 1 Complete references are listed at end of chapter.
smooth-water performance but also that under average service conditions at sea the ship shall not suffer from excessive motions, wetness of decks, or lose more speed than necessary in bad weather. The assumption that a hull form that is optimum in calm water will also be optimum in rough seas is not necessarily valid. Recent research progress in oceanography and the seakeeping qualities of ships has made it possible to predict the relative performance of designs of varying hull proportions and form under different realistic sea conditions, using both model test and computing techniques. The problem of ship motions, attainable speed and added power requirements in waves are discussed in Chapter VIII, VoL III. This chapter is concerned essentially with designing for good smooth-water performance. Another consideration in powering is the effect of deterioration in hull surface condition in service as the result of fouling and corrosion and of propeller roughness on resistance and propulsion. This subject is discussed in this chapter. As in the case of stability, subdivision, and structure, criteria are needed in design for determining acceptable levels of powering. In general, the basic contractual obligation laid on the shipbuilder is that the ship shall achieve a certain speed with a specified power in good weather on trial, and for this reason smoothwater performance is of great importance. As previously noted, good sea performance, particularly the maintenance of sea speed, is often a more important requirement, but one that is much more difficult to define. The effect of sea condition is customarily allowed for by the provision of a service power margin above the power required in smooth water, an allowance which depends on the type of ship and the average weather on the sea routes on which the ship is designed to operate. The determination of this service allowance depends on the accumulation of sea-performance data on similar ships in similar trades. Powering criteria in the form of conventional service allowances for both
2
PRINCIPLES OF NAVAL ARCHITECTURE
sea conditions and surface deterioration are considered
in this chapter.
The problem of controlling and maneuvering the
ship will be covered in Chapter IX, Vol. III.
1.2 Types of Resistance. The resistance of a ship
at a given speed is the force required to tow the ship
at that speed in smooth water, assuming no interfer-
ence from the towing ship. If the hull has no appen-
dages, this is called the bare-hull resistance. The power
necessary to overcome this resistance is called the tow-
rope or effective power and is given by
P _RV
(1)
E-
T
a
where PE = effective power in kWatt (kW) RT = total resistance in kNewton (kN) V = speed in m / sec
or ehp = RT Vk / 326
(lb)
where ehp = effective power in English horsepower Rr = total resistance in lb V = speed in knots k .. To conyert f~om horsepower to SJ .. umts there ~s
only a slIght dIfference between EnglIsh and metrIc
horsepower:
hp (English) X 0.746 = kW hp (metric) X 0.735 = kW
Speed in knots X 0.5144 = m / sec
. This total resistance is made up of a number of different components, which are caused by a variety of factors and which interact one with the other in an extremely complicated way. In order to deal with the question more simply, it is usual to consider the total calm water resistance as being made up of four main components .. (a) The frictional resistance, due to the motion of the hull through a viscous fluid. (b) The wave-making resistance, due to the energy that must be supplied continuously by the ship to the wave system created on the surface of the water. (c) Eddy resistance, due to the energy carried away by eddies shed from the hull or appendages. Local eddying will occur behind appendages such as bossings, shafts and shaft struts, and from stern frames and rudders if these items are not properly streamlined and aligned with the flow. Also, if the after end of the ship is too blunt, the water may be unable to follow the curvature and will break away from the hull, again giving rise to eddies and separation resistance. (d) Air resistance experienced by the above-water part of the main hull and the superstructures due to the motion of the ship through the air. The resistances under (b) and (c) are commonly taken together under the name residuary resistance. Further analysis of the resistance has led to the iden- tification of other sub-components, as discussed subsequentIy.
The importance of the different components depends upon the particular conditions of a design, and much of the skill of naval architects lies in their ability to choose the shape and proportions of hull which will result in a combination leading to the minimum total power, compatible with other design constraints. In this task, knowledge derived from resistance and propulsion tests on small-scale models in a model basin or towing tank will be used. The details of such tests, and the way the results are applied to the ship will be described in a later section. Much of our knowledge of ship resistance has been learned from such tests, and it is virtually impossible to discuss the various types of ship resistance without reference to model work. 1.3 Submerged Bodies. A streamlined body moving in a straight horizontal line at constant speed, deeply immersed in an unlimited ocean, presents the simplest case of resistance. Since there is no free surface, there is no wave formation and therefore no wave-making resistance. If in addition the fluid is assumed to be without viscosity (a "perfect" fluid), there will be no frictional or eddymaking resistance. The pressure distribution around such a body can be determined the- oretically from considerations of the potential flow and has the general characteristics shown in Fig. l(a). Near t~e nose, the pressure is .increased above the hydrostatIc pressure, along the mIddle of the body the pressure is decreased below it and at the stern it is again increased. The velocity distribution past the hull, by Bernoulli's Law, will be the inverse of the pressure distribution-along the midportion it will be greater than the speed of advance V and in the region of bow and stern it will be less. Since the fluid has been assumed to be without viscosity, the pressure forces will everywhere be normal to the hull (Fig. l(b)). Over the forward part of the hull, these will have components acting towards the stern and therefore resisting the motion. Over the after part, the reverse is the case, and these components are assisting the motion. It can be shown that the resultant total forces on the fore and after bodies are equal, and the body therefore experiences no resistance.2 In a real fluid the boundary layer alters the virtual shape and length of the stern, the pressure distribution there is changed and its forward component is reduced. The pressure distribution over the forward portion is but little changed from that in a perfect fluid. There is therefore a net force on the body acting against the motion, giving rise to a resistance which is variously referred to as form drag or viscous pressure drag. In a real fluid, too, the body experiences friction~l resistance and perhaps eddy resistance also. The flUId immediately in contact with the surface of the body is 2 This was first noted by the French mathematician d' Alembert in 1744, and is known as d'Alembert's paradox.
RESISTANCE
3
carried along with the surface, and that in the close vicinity is set in motion in the same direction as that in which the body is moving. This results in a layer of water, which gets gradually thicker from the bow to the stern, and in which the velocity varies from that of the body at its surface to that appropriate to the potential flow pattern (almost zero for a slender body) at the outer edge of the layer (Fig. l(c». This layer is called the boundary layer, and the momentum supplied to the water in it by the hull is a measure of the frictional resistance. Since the body leaves behind it a frictional wake moving in the same direction as the body (which can be detected far astern) and is contin-
ually entering undisturbed water and accelerating it to maintain the boundary layer, this represents a continual drain of energy. Indeed, in wind-tunnel work the measurement of the velocities of the fluid behind a streamlined model is a common means of measuring the frictional drag. If the body is rather blunt at the after end, the flow may leave the form at some point-called a separation point-thus reducing the total pressure on the afterbody and adding to the resistance. This separation resistance is evidenced by a pattern of eddies which is a drain of energy (Fig. 1(d). 1.4 Surface Ships. A ship moving on the surface of the sea experiences frictional resistance and eddymaking, separation, and viscous pressure drag in the same way as does the submerged body. However, the presence of the free surface adds a further component. The movement of the hull through the water creates a pressure distribution similar to that around the submerged body; i.e., areas of increased pressure at bow and stern and of decreased pressure over the middle part of the length. But there are important differences in the pressure distribution over the hull of a surface ship because of the surface wave disturbance created by the ship's forward motion. There is a greater pressure acting over the bow, as indicated by the usually prominent bow wave build-up, and the pressure increase at the stern, in and just below the free surface, is always less than around a submerged body. The resulting added resistance corresponds to the drain of energy into the wave system, which spreads out astern o~ the ship and has to be continuously recreated. (see Section 4.3). Hence, it has been called wave-making resistance. The result of the interference of the wave systems originating at bow, shoulders (if any) and stern is to produce a series of divergent waves spreading outwards from the ship at a relatively sharp angle to the centerline and a series of transverse waves along the hull on each side and behind in the wake (Fig. 7). The presence of the wave systems modifies the skin friction and other resistances, and there is a very complicated interaction among all the different components.
Section 2
Dimensional Analysis
2.1 General. Dimensional analysis is essentially a means of utilizing a partial knowledge of a problem when the details are too obscure to permit an exact analysis. See Taylor, E. S. (1974). It has the enormous advantage of requiring for its application a knowledge only of the variables which govern the result. To apply it to the flow around ships and the corresponding re-
sistance, it is necessary to know only upon what variables the latter depends. This makes it a powerful tool, because the correctness of a dimensional solution does not depend upon the soundness of detailed analyses, but only upon the choice of the basic variables. Dimensional solutions do not yield numerical answers, but they provide the form of the answer so that every

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