Proceedings of the 17th International Towing Tank Conference, ITTC'84, Volume 2, Goteborg, Sweden

17TH INTERNATIONAL TOWING TANK CONFERENCE

GOTEBORG, SEPTEMBER 1984

PROCEEDINGS

VOLUME 2

SSPA

GOTEBORG, SWEDEN

P1984-5

VOL.2

.1. 1Vm41

The 17th International Towing Tank Conference was held from 8th through 15th September 1984 in Goteborg, Sweden, the Park Avenue Hotel being the Conference Centre.

The official Opening Ceremony and toe first General Session were both in-cluded within a Sunday Conference Tour, followed by a week featuring ten regular Technical Sessions linked to the work of the appropriate

Technical Committees, one separate Session on New Facilities, four spe-cial Group Discussions on topics of current interest, and the final General Session. In addition there were a number of scheduled Meetings of the Advisory Council and the Executive Committee, and informal Meetings of the different Technical

Committees. A Social Program was

arranged for the Conference partici-pants and accompanying persons. The

Conference was attended by 191

Dele-gates and Observers from 25 different countries, accompanied by 64 ladies.

The 17th ITTC Proceedings have been published in two Volumes, the first

of which was distributed by air _mail

ten weeks ahead of the Conference to

all the Delegates and Observers

recog-nized by the Executive Committee at its February 1984 Meeting.

PREFACE

Volume 1 includes the Reports of the Executive Committee and the Advisory Council and of the ten Technical Committees, together with organizational material pertinent to the

17th Conference.

Volume 2 includes the Contributions

and Replies to the Dis-cussions of the Committee Reports, Introductions to

and Summaries of the Grout)

Discussion Material, selected Contributions on New Facili-ties and Instrumentation, formal Addresses delivered at the Conference, and Recom-mendations and Guidelines for the future work of the Confer-ence and the Technical

Com-mittees.

We feel that the Reports of the Tech-nical Committees met a very high stand-ard, which proved to stimulate a lively

discussion, itself reflected in an

outstanding number of Written Contri-butions and Oral Discussion summaries retyped for the second Volume of the

Proceedings.

The Organizers are grateful for the efforts contributed to and for the

keen interest shown in all aspects of

.1r7177.11.

Special thanks are due to the Chairmen and Members of the Technical Committees

as well as to the Chairmen and Opening Speakers of the Group Discussions and

to the invited Guest Speakers.

We further extend our thanks to all those members of the SSPA staff and others who

contributed their time and spirit to the

Goteborg in May 1985

Hans Lindgren

President 17th ITTC

success of the Conference and their devotion to the completion of these Proceedings.

The printing of this Volume was made possible by a grant from the Martina Lundgren Foundation for Maritime

Research.

Nils H. Norrbin Secretary 17th ITTC

LOCAL ORGANIZING COMMITTEE Dr H. Lindgren

Dr N.H. Norrbin Ms B. Frylinger

LADIES PROGRAM COMMITTEE Ms M. Bjorklund Ms B. Frylinger

CONVENTION BUREAU

Gothenburg Convention Bureau

EDITOR Dr N.H. Norrbin ASSISTANT EDITOR Mr C.S. Ohlsson TYPING Ms L. Fredrikson Ms M. Williams

C771

17TH INTERNATIONAL TOWING TANK CONFERENCE

PROCEEDINGS VOLUME 2

CONTENTS

PAGE

PREFACE 3

LOCAL ORGANIZING COMMITTEE, ETC 4

CONTENTS 5

PROGRAM OF THE 17TH ITTC 9

CONFERENCE PHOTOGRAPH 14

CONFERENCE OPENING CEREMONY ₁₇

INAUGURAL SPEECH 17

CONFERENCE ADDRESS 18

FIRST GENERAL SESSION ₂₅

SESSION ON RESISTANCE 27

DISCUSSIONS ₂₇

REPLY BY THE RESISTANCE COMMITTEE ₆₁

SESSION ON PROPELLERS ₆₅

DISCUSSIONS ₆₅

REPLY BY THE PROPELLER COMMITTEE ₈₁

SESSION ON CAVITATION ₈₇

DISCUSSIONS 87

REPLY BY THE CAVITATION COMMITTEE 104

ADDITIONAL CONTRIBUTIONS TO THE REPORT OF

THE CAVITATION COMMITTEE ₁₀₈

SESSION ON POWERING PERFORMANCE 117

DISCUSSIONS 117

REPLY BY THE PERFORMANCE COMMITTEE 144

SESSION ON HIGH-SPEED MARINE VEHICLES 149

DISCUSSIONS 149

REPLY BY THE HIGH-SPEED MARINE VEHICLES COMMITTE ₁₅₅

COMMITTE REPORT ERRATA ₁₅₈

SESSION ON MANOEUVRABILITY ₁₆₁

DISCUSSIONS ₁₆₁

REPLY BY THE MANOEUVRABILITY COMMITTEE ₁₉₃

SESSION ON SEAKEEPING ₂₀₃

DISCUSSIONS ₂₀₃

17:1714

PAGE

SESSION ON OCEAN ENGINEERING 247

DISCUSSIONS 247

REPLY BY THE OCEAN ENGINEERING COMMITTEE 271

SESSION ON PERFORMANCE IN ICE-COVERED WATERS 277

DISCUSSIONS 277

REPLY BY THE PERFORMANCE IN ICE-COVERED

WATERS COMMITTEE 283

SESSION ON INFORMATION AND PRESENTATION 287

DISCUSSIONS 287

REPLY BY THE INFORMATION COMMITTEE 292

SESSION ON NEW FACILITIES 295

NEW MODEL TEST FACILITIES 295

EXTENSIONS OR MODIFICATIONS TO EXISTING FACILITIES 304

INSTRUMENTATION AND MEASURING TECHNIQUES 311

GROUP DISCUSSIONS 319

SESSION la: ON FULL SCALE MEASUREMENTS 319

la-1 Introduction of the Subject 319

la-2 Invited Contributions 321

la-3 Free Discussion 339

SESSION lb: ON NEW WAVEMAKER DESIGN AND EXPERIENCE 343

lb-1 Discussion Topics for Multi-Element

Wavemakers 343

lb-2 Discussion Topics for Double-Flap Wavemakers 344

lb-3 On a New Single-Flap Wavemaker 345

Appendix A-C (lb-1) 345

Appendix D-F (1b-2) 357

Appendix G (1b-3) 363

SESSION 2a: ON STABILITY TESTING AND CORRELATION 367

2a-1 Introduction of the Subject 367

2a-2 Invited Contributions 368

2a-3 Additional Prepared Contribution 374

2a-4 Free Discussion 375

SESSION 2b: ON FULL-SCALE WAVE DATA AOUISITION AND

ANALYSIS 377

2b-1 Introduction of the Subject 377

2b-2 Invited Contributions 381

2b-3 Additional Prepared Contribution 388

2b-4 Free Discussion 390

VISIT TO THE SSPA FACILITIES 393

EXECUTIVE COMMITTEE AND ADVISORY COUNCIL MEETINGS 395

SECOND GENERAL SESSION AND CLOSING CEREMONY 399

RECOMMENDATIONS CONCERNING RULES AND GUIDELINES FOR

THE OPERATION OF THE ITTC 403

PAGE

COMPOSITION OF THE EXECUTIVE COMMITTEE ₄₀₆

GENERAL ADDITIONAL GUIDELINES FOR THE OPERATION OF THE ITTC 406 RECOMMENDATION TO MEMBER ORGANIZATIONS TO SUPPORT

A RESTRUCTURING OF THE RESISTANCE, PROPELLER,

CAVITATION AND PERFORMANCE COMMITTEES 407

RECOMMENDATIONS CONCERNING THE WORK OF THE INFORMATION GROUP

AND THE TECHNICAL COMMITTEES ₄₀₉

INFORMATION GROUP ₄₀₉

RESISTANCE AND FLOW COMMITTEE 410

PROPULSOR COMMITTEE ₄₁₀

CAVITATION COMMITTEE ₄₁₁

POWERING PERFORMANCE COMMITTEE ₄₁₁

HIGH-SPEED MARINE VEHICLE COMMITTEE ₄₁₂

MANOEUVRABILITY COMMITTEE ₄₁₃

SEAKEEPING COMMITTEE ₄₁₄

OCEAN ENGINEERING COMMITTEE ₄₁₅

PERFORMANCE IN ICE-COVERED WATERS COMMITTEE ₄₁₆

COMMITTEES OF THE 18TH ITTC ₄₁₇

EXECUTIVE COMMITTEE 417

ITTC SECRETARIAT ₄₁₇

TECHNICAL COMMITTEES 418

ITTC ADVISORY COUNCIL ₄₁₉

8-15 September 1984

Technicca P/LopLam and Sociat Event Pakattet Ladie6 Pkognam

Saturday 8 September

Afternoon (Park Avenue Hotel)

13.00 - 14.30 (Sandberg Hall) MEETING OF THE EXECUTIVE COMMITTEE

14.45 - 15.30 (Room 3A-B)

MEETING OF THE EXECUTIVE COMMITTEE AND THE CHAIRMEN OF THE TECHNICAL COMMITTEES

16.00 - 17.00 (Room 3A-B)

MEETING OF THE ADVISORY COUNCIL

17.00 - 19.00 (Conference Desk) REGISTRATION

Evening (Park Avenue Hotel)

18.00 - 19.00 (Taube Hall) WELCOME GATHERING

08.00 - 10.00 (Conference Desk) 18.00 - 20.00

REGISTRATION

All Day Program

09.00 - 12.00

CONFERENCE BOAT TOUR TO MARSTRAND ISLAND Buses from the hotels at 09.00 for old steamer S/S Bohuslan, departing from Stenpiren at 09.30

PROGRAM OF THE 17TH ITTC

Sunday 9 September

11,671MI

Technicat Pnognam and Sociat Evekt6 Pan_attet Lad-6 Pkognam

12.45 - 13.30 (Carlsten Fortress, Knights' Hall)

OPENING CEREMONY

Inaugural speech: Mr A.Norling, Governor

of Goteborg och Bohus lan

13.30 - 14.15 (Knights' Hall)

13.30 -

14.15

GENERAL SESSION GUIDED TOUR OF FORTRESS BUILDINGS

Session Chairman: Dr H. Lindgren

14.30 (about) (Battery Hall)

CONFERENCE LUNCHEON

Passenger ferry at about 17.00 for KoOn and buses to Goteborg, returning at

about 19.00.

Monday 10 September

Morning (Park Avenue Hotel Banquet Hall)

8.30 -

12.00

SESSION ON RESISTANCE

Session Chairman: Prof T. Inui

Afternoon (Park Avenue Hotel Banquet Hall) Afternoon

13.30 -

17.00

SESSION ON PERFORMANCE

Session Chairman: Dr H. Lindgren

Morning (Park Avenue Hotel Banquet Hall) Morning and Afternoon

08.30 -

11.45

SESSION ON HIGH-SPEED MARINE VEHICLES

Session Chairman: Mr W.A. Crago

12.00 - 14.30

SIGHT-SEEING TOUR OF GOTEBORG with visit to the Volvo factories

Buses from the Park Avenue Hotel at 12.00

Evening

19.00 - 20.00

RECEPTION AT THE CITY HALL "B6RSEN", given by the City of Goteborg

Tuesday 11 September

09.00 - 16.00

EXCURSION TO THE PROVINCE OF HALLAND, including visits to Gunnebo Mansion and Tjoleholm Castle

Technicat PnogAam avid Sociat Event Panattet LadieL Pkoviam

Afternoon (Park Avenue Hotel Banquet Hall)

13.15 - 16.15

SESSION ON PROPELLERS

Session Chairman: Prof J.P. Breslin

16.45 - 19.45

SESSION ON CAVITATION

Session Chairman: Prof J.P. Breslin

Wednesday 12 September

Morning (SSPA and Chalmers University

Campus)

09.15 - 1C.45 VISIT TO SSPA

Buses from the hotels at 08.45

11.00 - 12.00 (Palmstedt Hall) SESSION ON NEW FACILITIES

Session Chairman: R Adm P. O'Dogherty

12.15 - 13.00 (Palmstedt Hall) SESSION ON INFORMATION

Session Chairman: R Adm P. O'Dogherty

The Conference Photograph of Delegates and Observers taken prior to a Conference Luncheon at the Student Union Restaurant.

Afternoon (Chalmers Lecture Hall Building)

14.30 - 16.00

GROUP DISCUSSIONS - Parallel Sessions la &b la FULL SCALE MEASUREMENTS

Discussion Chairman: Dr B. Della Loggia

lb NEW WAVEMAKER DESIGN AND EXPERIENCE Discussion Chairman: Prof B. Johnson

Technicat PnovLam and Sociat Event Patattet Ladiez Pkognam

16.15 - 17.45

GROUP DISCUSSIONS - Parallel Sessions 2a &b 2a STABILITY TESTING AND CORRELATION

Discussion Chairman: Prof 0. Krappinger

2b FULL-SCALE WAVE DATA ACQUISITION AND ANALYSIS

Discussion Chairman: Dr N. Hogben

Buses from the Lecture Hall Building for the Conference Hotels at 18.00

Evening

19.00

BUFFET AT STORA TEATERN

hosted by the Swedish Shipbuilders' Association

Buses from the hotels at 18.45

20.00 - 22.00 (about)

BALLET PERFORMANCE AT STORA TEATERN

Thursday 13 September

Morning ( Park Avenue Hotel Banquet Hall) Morning and Afternoon

08.30 - 16.00

EXCURSION TO THE PROVINCE OF VASTERGOTLAND, including visits to the Rorstrand China Factory and Museum, and to Ldckii Castle by Lake Vanern

Afternoon (Park Avenue Hotel) Buses from the Park Avenue Hotel at 08.30

08.30 - 12.00

SESSION ON MANOEUVRABILITY

Session Chairman: Dr E. Nikolaev

13.30 - 17.00 (Banquet Hall) SESSION ON PERFORMANCE IN ICE

Session Chairman: Prof O. Krappinger

17.30 - 18.30 (Room 3A-B)

MEETING OF THE ADVISORY COUNCIL

18.45 - 19.45 (Room 3A-B)

Technical P/togAam and Social Event6 PanatZet Ladiez Pnogkam

Friday 14 September

Morning (Park Avenue Hotel Banquet Hall)

08.30 - 12.00

SESSION ON SEAKEEPING

Session Chairman: Dr N.H. Norrbin

Afternoon (Park Avenue Hotel Banquet Hall)

13.30 - 17.00

SESSION ON OCEAN ENGINEERING

Session Chairman: Dr M.W.C. Oosterveld

Evening (Park Avenue Hotel Banquet Hall)

20.00

CONFERENCE DINNER & DANCE

Saturday 15 September

Morning (Park Avenue Hotel)

08.30 - 09.30 (Room 3A-B)

MEETING OF THE ADVISORY COUNCIL

09.30 - 10.30 (Room 3A-B)

MEETING OF THE EXECUTIVE COMMITTEE

11.30 - 12.30 (Banquet Hall)

GENERAL SESSION AND CLOSING CEREMONY

Session Chairman: Dr H. Lindgren

Afternoon (Park Avenue Hotel)

14.00 - 15.00 (about)

MEETINGS OF NEW EXECUTIVE AND TECHNICAL COMMITTEES

CONFERENCE PHOTOGRAPH

I Sharma 31 Oltmann

61 Yang 91 Clarke 120 Banacki 150 Maruo

2 Cheng 32 van Berlekom 62 Nikolaev 92 Price 121 Powell 151 Takezawa

3 Himeno 33 Frylinger 63 Clauss --93 Gerritsma 122 Maeda 152 Giovachini

4 Biskoup 34 Pattullo 64 Murdey 94 Reis 123 Nagamatsu 153 Patel

5 van Gent 35 Tamura 65

Varsamov 95 Suhrbier 124 Chung 154 Molnar

6 Hoekstra 36 Rocchi 66 Krappinger 96 Couch 125 Rowe 155 Faresi

7 Dyne 37 Takahashi 67 Naka take 97 Yang 126 Gu 156 Bovis

8 Lee, C.M. 38 Sukselainen 68 Lee, C.-S. 98 Wang 127 Cox 157 Loukakis

9 Kose 39 Koyama 69 Schuster 39 Andrew 128 van Oortmerssen 158 Schmiechen

10 Ferguson 40 Yovev 70 Tatinclaux

100 129 Marsich 159 Johnson, B.

11 Fujino 41 Garcia-Gomez 71 Col latz

101 Parkin 130 Rye 160 Hwang

12 Savitsky 42 Strasser 72 Glover .102 Journee 131 Breslin

161 Wu

13 Nakamura 43 Oosterveld 73 Morgan 103 Edstrand

132 Bhattacharyya 162 Della Loggia

14 Ohkusu 44 Ruggiero 74 Gross 104 Chen 133 Carlier 163 Sheng, C.P.

15 Holtrop 45 Baba 75 Jarzyna 105 BjUrheden 134 Kitagawa 164 lvanov

16 Halliday 46 Perez-Sobrino 76 Alexandrov 106 Crago 135 van der Meulen 165 Lorenz

17 Jourdain 47 Al6ez 77 O'Dogherty 107 Murakami 136 Baquero 166 Pittaluga

18 Johnsson, C.-A. 48 Nizery 78 Brockett 108 Beukelman

137 Coppola 167 Motora

19 Kostilainen 49 Nomoto 79 Yosifov 109 Colombo

138 Sheng, Z.-Y. 168 Takagi

20 MUller-Graf 50 Tanibayashi 80 Chislett 110 Lecoffre 139 Kato 169 Lau

21 Williams 51 Accardo 81 Yu 111 Walderhaug 140 Goranov 170 Cardo

22 Palkemo 52 NuTiez 82 Tupper 112a Knowles 141 Dern

171 Urushidani

23 Yamamoto 53 Alekseyev 83 Leinweber 1125 Huang 142 Zhu 172 Russo Krauss

24 Rutgersson 54 Ferdinande 84 lnui 113 Moor 143 Cho 173 Goodman

25 Harvald 55 Mori 85 Lin 114 Wei tendorf 144 Hogben 174 lkehata

26 Namimatsu 56 Abe 86 Loid 115 Kobylinski 145 Norrbin

27 Kjeldsen 57 Huse 37 Rodenhuis 116 Lackenby 146 Luise

28 Abkowitz 53 Yokoo 38 Wehausen 117 van Oossanen 147 Bailey

29 Ward 59 Burcher 89 Lindgren 118 Wilson 148 Yamanouchi

117.177417

The 17th ITTC was officially opened at a Ceremony in the Knights' Hall of the Carlsten Fortress on Sunday 9 September

1984.

Speeches were given by Dr. Hans Lindgren, President of 17th ITTC and Managing Director of SSPA Maritime Consulting AB, by Mr. Ake Norling, Governor of GOteborg

and Bohus LLn (Inaugural Speech), by

THE CONFERENCE OPENING CEREMONY

The natural harbour of Marstrand with approaches from different quarters has been used as long as people have sailed in these waters. Marstrand was a strong-hold for the vikings and its history

is forever connected with the sea. With shipping, trade, naval warfare, fishing and, alas, devastating fires. The wooden houses huddled up against the wind are even today in great danger,

Dr. Hans Edstrand, former Director General if a fire should start somewhere among

of SSPA (Conference Address), and by them.

Mr. William A. Crago, Test Facilities

Director of British Hovercraft Corp. Ltd. Looking at Marstrand today it's hard

to believe the important role it once

INAUGURAL SPEECH BY MR A. NORLING played in the history of Scandinavia.

Until the middle of the 17th century

Ladies and Gentlemen! Honoured Guests! _{it belonged to the united}

Denmark--Norway and for a long period it even

We are very happy that you have once _{competed with Goteborg in economic}

again chosen to have an International _{significance. When pirates and hostile}

Towing Tank Conference here in GOteborg _{war-ships were a constant threat, ships}

on the west coast of Sweden. _{sailed from Marstrand in convoys for}

the south of Europa and the Far East.

Not being a technician myself I wisely _{For periods of variable length,}

re-desist from plunging into the technolo- _{turning roughly once per century, the}

gical field which is yours by profession. _{herring the silver of the sea}

-Nor am I a historian but I think that _{used to appear in shoals of incredible}

the surroundings here simply demand an _{amplitude. During those periods Marstrand}

historical briefing. _{really flourished. I hardly need to say}

that herring is scarce these days at

Gothenburg and the coastal region nearby _{least in comparison with the herring}

have ancient traditions concerning ship- _periods.

building and naval architecture. Frequent

rock-carvings a few miles from here _{This fortress was built during the}

dating 3000 years back are indicative _{Swedish time which began in 1658.}

of the strongest in Europe. The construction of these huge walls must have cost tremendous efforts. Part of the work was done by

prisoners, as the fortress served as a prison as well.

One of the prisoners, a notorious thief with the nickname Lasse-Maja, is legendary in Sweden. The name Lasse-Maja is composed of one male and one female part, which refers to one of his peculiarities. He often committed his crimes dressed up as a woman. Very few prisoners

left the fortress alive but Lasse-Maja did. He even ended up as a candidate to the Swedish parliament. The ladies will hear more about the

fortress in a short while.

As I said Marstrand and GOteborg were once rivals in significance, strange as it may seem today. Marstrand today is a charming sea-side resort. It has a shipyard though.

GOteborg on the other hand has

de-veloped to be the second largest city of Sweden with about half a million inhabitants - about the same

size as the Norwegian capital, Oslo.

Goteborg has the biggest port in

Scandinavia, a worldwide network of commercial contacts and an advanced industry with companies as Volvo, SKF

and, of course, the Swedyards.

The two remaining shipyards in Goteborg have specialized in ship repairs and offshore products. As a matter of fact

the GVA shipyard and a handful of other companies such as Stena AB and Consafe

have managed to give Goteborg a

posi-tion as an offshore centre in Scandinavia.

Our host company, SSPA, has been instru-mental in this achievement and I rest assured that the responsibility for the Conference is in competent hands.

I hope that you will find the contacts and the discussions with skilled

col-leagues from other nations rewarding. I also hope that you will have a jolly good time while you are here. With these words I declare the 17th International Towing Tank Conference opened.

CONFERENCE ADDRESS BY DR H. EDSTRAND

In the Book of Genesis in the Bible there is a description of Noah's Ark. It agrees surprisingly well with the present day opinion concerning the proportions of the main dimensions. The length is given to 300 yards and the breadth to 50 yards. Noah chose an L/B figure of six. A quite reason-able value. However, it is, of course, unlikely that Noah carried out model

tests before his decision.

In historical time the first, or one of the first, to carry out model ex-periments in our field was the French priest Edmond Mariotte. Around 1650 he demonstrated the functions of water mills (Moulins de la Seine) at the Castle Chantilly and in Paris.

One of the earliest proposals known for

the use of towed models for the

investi-gation of ship resistance is that of the two Swedes Christofer Polhem and Emanuel Swedenborg. In a paper (concern-ing ships' speed at sea) they recom-mended the Royal Swedish Academy of Sciences in 1717 "that ship model

Fredrik Henrik af Chapman is the first Swede known to have carried out ship model investigations. He was responsible for the Swedish

Naval Shipyard at Karlskrona in the

south east of Sweden. (A naval base

still of interest to the Swedish Navy and also, as we suspect, to the navies and submarines of other nations, as you may have noticed from your

news-papers).

Around 1760 Chapman arranged a towing tank with ship models towed by falling weights at his farm, Skarva, outside Karlskrona. The dimensions of the tank were 68 x 15 x 4 ft. In 1794, at the

age of 73, he carried out systematical investigations in this tank. For example, he tested logs with systematically varied angles of entrance and runs.

Chapman died as a bachelor in 1808, 87 years of age. He worked hard at his hydrodynamic problems up to the last day

of his life.

The 200 or 250 years after Mariotte are characterized by rapid progress and two lines of development can be distinguished: one experimental and one mathematical-analytical.

Concerning the experimental line one name must be mentioned especially - the Englishman William Froude, who in 1869 formulated his "Law of Comparison", stating the conditions under which model tests could be used to predict full-scale ship

resistance.

From 1900 and on many new ship towing tanks were established with experi-mental arrangements based on William

Froude's Law.

In Sweden the first new small towing tank was built in 1921, connected with the Royal Institute of Technology in Stockholm, and for almost twenty years it was the only tank in

Scandinavia. Our host establishment, SSPA in Goteborg, was opened in 1940. Dr. Lindgren's and my predecessor, Dr. H. F. Nordstrom, was successively in charge of both these

establish-ments.

It is impossible for me to enumerate all the ship towing tanks built during the last years. I personally believe that there are too many. National prestige, fear of competition and other reasons have forced nations and firms to over-establish in this field. The enormous investments are not

giving the return they ought to.

ITTC

In May 1932 an International Hydro-mechanical Conference took place in Hamburg. This Conference was initiated and organized by the German Towing Tank in Hamburg (die Hamburgische Schiffbau-Versuchsanstalt). The Proceedings of this Conference were published in 1932, "Hydromechanische Probleme des Schiffsantriebs". In an after-dinner speech at this

Confer-ence one of the delegates, Mr John de Meo, pleaded strongly for international tech-nical cooperation in the field of ship propulsion. Professor L. Troost of the Wageningen Tank in the Netherlands took up this idea and invited his colleagues present in Hamburg to come to the

Netherlands in 1933 to discuss what form the cooperation of the tanks should take.

11.7707

of Tank Superintendents (this was the name of the ITTC at that time) took place in the Hague in the Netherlands,

on July 13 and 14, 1933. It was attended

by 23 delegates.

The discussions, which were informal and confidential, led to the appoint-ment of a committee of four (Baker,

Barrillon, Kempf, Troost) to set down the general conclusions in a more definite way. Thus apparently already at the first Conference a Committee was necessary in order to sum up all the different opinions.

Before World War II three further Conferences were held - in London 1934, in Paris 1935 and in Berlin 1937.

The first International Conference of Ship Tank Superintendents after the war took place in London in 1948. Since then a Conference has been held every third year in various countries.

Among the scientific and technical achievements of the Conference I will mention only a few. In 1935 in Paris the formula for calculating friction resistance was agreed upon. In Madrid the ITTC 1957 Model-Ship Correlation Line was adopted. In 1978 in the Hague the ITTC Member Organizations were recommended to use the 1978 ITTC Performance Prediction Method for Single Screw

Ships.

For some reason the ITTC has always been very popular. The demand for invitations for Delegates increases all the time. Not only professionals

in tankery, but also university professors, consultants and ship-builders' and shipowners' representa-tives have shown considerable interest.

In the Preface to the Proceedings of this Conference, Volume 1, Dr. Lindgren asks: "Will ITTC still exist 30 years

from now, ...?" My answer is "No!" At least not in its present form. You simply cannot afford it.

At SSPA we had in the past two men who were directly responsible towards the shipbuilders and shipowners, and thus built up the reputation SSPA may have had. They were Mr. Rodstram and Mr. Warholm. Today it is Mr. Loid, Mr. Williams and Mr. van Berlekom. None of these five persons have ever

had anything to do with the Confer-ence. I think the picture is the same at most establishments.

The Head of the Tank is a Delegate of the Conference. His duties at home mostly concern administrative and economic matters. Besides the Tank Leaders the Conference mainly consists of Technical Committee Members. They are hydromechanical scientists, professors from universities and so on. They travel around the world to each other places, have Committee Meetings and write more or less

sophisticated Committee Reports, which are of little immediate use

to those responsible towards ship-builders and shipowners.

I believe my old friend and colleague Mr. David Moor expressed the situation very clearly in 1969 in Rome when he

said, discussing the Resistance Committee Report: 'Why all this, why

Kr:CM

not instead try to give us a good and reliable method to correct for blockage

effect?"

Remember also the costs involved. To keep a Member on a Committee is expensive. For a Tank establishment to keep somebody as Chairman or Secre-tary in a Committee is very expensive indeed. One has to calculate with something between half-time and full-time for three years and added resources. It will hardly pay back.

I suggest that you decrease the size and the scope of the Conference, say down to the size of the present

Advisory Council. Abandon the elaborate and expensive system with large Tech-nical Committees and use smaller groups for more immediate problems in the experimental field - just what the

ITTC from the start was meant to do. The work of the present Technical Committees is of course of great value, but it does not belong to tankery, but to the

mathematical-analytical line and ought to be taken care of by the represen-tatives of Education, the Technical

Universities.

Since 30 years ago, when I was the Secretary of the Conference last time it met here in Goteborg,

have followed the work of the

Conference very closely in different positions in different Committees.

Against the background of the very serious economic situation for ship-builders, shipowners and the offshore industry, at least in the Western Hemisphere, Europe and America, I believe it is necessary for the

ITTC to do something to rationalize its work and bring down the costs

Involved.

After all, the main task for the ITTC must be the same today as the one John de Meo pleaded for 52 years ago, namely for customers to get the

same or at least a similar answer, when investigating the same techni-cal problem at different experimental

facilities.

May be you had not expected me to say just what I have said. I hope, however, that you will take my ideas under serious consideration. I believe this is

impor-ant for the future and may mean the >urvival of many ship towing tanks.

I wish all the Delegates and Observers some interesting days and I wish you all a pleasant stay in our country.

Dr. Hans Lindgren, wellcoming old and new friends in ITTC

Mr. Ake Norling, opening the 17th Conference

Mr. William Crago, speaking Dr. Hans Edstrand, delivering

Listening, and arguing, in the Knights' Hall

The Kongandlla Folk Dancers

137/77t101

The first Meeting of the Conference in General Session took place immedi-ately after the Opening Ceremony, the full Executive Committee presiding.

The Chairman introduced the Report of the Executive Committee and read the obituary notices. He asked the Conference to rise in memory of their five colleagues Mr. Michail Michailidis, Dr.

Y. N.

Prishchemikhin, Dr. George Hughes, Mr. Robert N. Newton and Prof. Stanko Silovi6, the latter deceased in late June of 1984.

The Chairman further observed with great regret the unfortunate absence due to illness of two eminent col-leagues, Prof. Dick van Manen and Mr. Phil Eisenberg.

The Chairman next briefly reviewed the activities of the Executive

THE FIRST GENERAL SESSION

Chairman: Dr. H. Lindgren

Committee, and he invited the Conference to comment on the two Recommendations placed before it on new Rules of Organization and on a new Composition of the Executive Committee, based on rearranged Geographical Areas.

(See Report of the Executive Committee

in Proceedings, Volume 1, p. 11-22.

Separate copies of the Recommendations were distributed at the Session.) The

Conference adopted the above Recom-mendations. Additional Recommendations

were announced to be presented at

the final General Session. (All the

Recommendations approved by the Conference are included at the end

of this Volume.)

The Secretary informed the Conference about procedures for the Technical Sessions and other activities during the forthcoming week.

.1r67171,

M. NAMIMATSU and R. TASAKI

-Ishikawajima-Harima Heavy Industries Co., Ltd., Yokohama, Japan

ON DATA AND PRESENTATION OF THE COOPER-ATIVE EXPERIMENTAL PROGRAM

The authors would like to correct a mis-print in a table of the pressure distri-bution which was presented to the Re-sistance Committee through "1983 Report on the Cooperative Experiments on Wigley Parabolic Models in Japan". The Cp value

of IHI model at Z/D = -0.20, x/(L/2)

--0.2 for Fn = --0.25 on page 6.6 should be corrected from "-0.040"to"-0.093". Fig1 is the corrected figure corresponding to Fig. 13 of the Committee Report. It

is found that the agreement of the re-sults is much improved.

The trim coefficients for Wigley hulls are plotted in Fig. 9 of the Committee Report. In the figure, the half values are plotted for the Japanese models. The trim coefficients of the Japanese models

SESSION ON RESISTANCE

Chairman: Prof. T. Inui

Resistance Committee Memberships: J.H. McCarthy (Chairman) - M. Hoekstra (Secretary) E. Baba M. Fancev A.M. Ferguson L. Larsson V.C. Patel I. Tanaka

-Y. Yovev

Discussion of the Report and the Draft Recommendations of the Resistance Committee. (Cf Proceedings, Volume 1, p. 75-138.)

I. DISCUSSIONS

are however nondimensionalized by the model length. All the data of Wigley models are plotted in Fig. 2. The results of the four models are in good agreement

with each other.

0.03 21

0.02

0.01

0.0 Whoa

R9.1 Pressure distribution on the Wigley hulls (Z/ D=0.2 )

BSHC I HI X SRI TOKYO A. 9 0

0°

0.20 0.30 0.40 0.50 Fn=1E,(81-7_

17711Villis

The sinkage of a ship is caused by the velocity increase around the hull and the trim is caused by the longitudinal asymmetry of the force including the effect of ship waves and skin friction.

Fig. 9 of the Committee Report shows the

sinkage at fore end. However it may be better to plot the mean value of fore and aft sinkage, considering the above physi-cal meaning of the sinkage.

Fig. 3 shows the reanalysed data of sink-age for Wigley hulls expressed by

o =

117 (c5A + F)

whereF and dA are the sinkage of fore and aft end respectively, g is the gravitational acceleration and U is the ship speed. This expression seems to be rational from the view point of hydro-dynamical force acting on the hull sur-face and has been used in the Workshop

on Ship Wave-Resistance Computations [1].

The values at the lower Froude numbers scatter because of errors in the ment. An error in the sinkage measure-ment can be evaluated as the effect of seiche in towing tanks [2].

In Fig. 3 the solid line is the sinkage calculated by using the wave potential. The wave potential is expressed by Michell's thin ship approximation and the vertical pressure force can be

cal-culated as

Fz = -pU

ff

x 3z dx dz

where wave potential of thin ship

approximation

f: hull offset y = f(x,z)

The calculated result has humps and hollows and it qualitatively agrees with

the experimental results. The dotted (2) tarj A a ,P cPx8 'ft'cRek.0% 0.05- ° x. ,ffla4,,g,96 X

Calculated by using double rnodel flow

Xta 0

0 BSHC

o IH I .SRI

a TOKYO

Fi9.3 The sinkage of Wigley hulls

0.4 0.5

Calculated by using

wave potential

line is the sinkage estimated by using the double model flow [3]. The calcula-tion gives a constant value of a and corresponds well to the experimental value at the lower Froude numbers where the sinkage is very small. Behaviour of the sinkage at the low speed has been discussed by Kajitani et al. taking into account the viscous effect [4].

References

Proceedings of the Workshop on Ship Wave-Resistance Computations,

DTNSRDC, Bethesda (1979, 1983)

TASAKI, R. and OGIWARA, S.: "Effect on Seiche on Measurement of Sinkage in Towing Tanks". The 4th Meeting of JSPC, Papers on Marine Hydro-dynamics, to be published (1984)

OGIWARA, S.: "Calculation of Poten-tial Flow Field around a Ship Hull and its Application". IHI Engineering

Review, Vol. 17, No. 2 (1984)

[4] KAJITANI, H., NAMIMATSU, M., OGIWAPA

S., TANAKA, H., HINATSU, M.: "An

Evaluation of Resistance Components

on Wigley Geosim Models (2.

Con-sideration on the Effect of Viscosity at Low Speed)". KSNA, to be published

(1984)

KMErile,

R. TASAKI and S. OGIWARA -

Ishikawajima-Harima Heavy Industries Co., Ltd.

Yokohama, Japan

ON THE EFFECT OF SEICHE ON MEASUREMENT OF SINKAGE IN TOWING TANKS

Introduction

The Resistance Committee reports on the

attitude of model ships in the

compara-tive experimental program. The sinkage

was presented by the following

nondimen-sional expression in the Workshop on Ship

Wave-Resistance Computations [1],

a .

(6

+F)

V2 A

where g is the acceleration of gravity,

V the model speed, and 5A and SF are the

aft and fore sinkage respectively. The

Japanese report of Wigley models also

uses this expression [2]. The expression

exaggerates values at the low speed

where the sinkage is small itself and

errors are liable to occur in the

measure-ment. The expression tends however to a

limiting value for V =

0 and gives a

clue to examine the validity of

mathe-matical models [3], [4].

Herewith the authors show that the effect

of seiche is predominant in the error of

sinkage measurement in towing tanks and

suggest a cure to remove it.

Investigation with a Mathematical

Model

2.1 Mathematical Model

(1)

The coordinate system is shown in Fig.

1

where a is the tank length, h the water

depth and x the position of a carriage

measured from the starting end of the

tank. The elevation of water surface

Fig.I Coodinate sYstem

observed from the carriage running at a

speed V is written for the seiche of

unit amplitude with a single node as,

Z

= cos(Lx) cos

_a

_{(71Vgh x:xo} + (p) =

V

= cos(7) cos(Trf

+ 0) (2)

where xo: the carriage runs with a

con-stant speed from x = xo

(4)

: arbitrary phase of seiche at

x = X0

= x/a,

0

-

xia,

0 = cp-7-fo

f =

\i(TE/V = 1/Fh = A/L(1/Fn)

Fh: water depth Froude number

Fn: ship length Froude number

When the sinkage measurement is done over

a measuring range between x = x2 = Cla

and x2 =

2a, the mean elevation of water

surface over the range is expressed as

2

1

S =5 cos()7 cos(71-1-0)d

_c2S1

1

= Pcos0 + Qsin0

(3)

where P and Q

are the functions of f,

ci and

2, and

is to be an arbitrary

phase. The amplitude of S is defined as

the seiche amplitude factor,

SF =

!SI =,/P2+Q2 =

1

f(f2+1)(1cos71A cosTrfA)

-uX(f2-1)

2fsin7rX sinTrfA+

+(f2-1)(cos7A-cosTrfA cos276}1

(4)

where

X = 2 2E = El 2 1

SF presents the effect of seiche on the

sinkage measurement and is a function of the following three parameters:

the water depth Froude number, Fh = V/Vgh

the ratio of the length of measuring

range to the tank length, X

the position of the range, that is, the ratio of the distance between the middle point of the range and the tank front to the tank length, c.

2.2 Characteristics of Seiche Am2litude Factor

Effect of the length of measuring range

The effect of the length of measuring range, X, is shown in Fig. 2 for the case where the middle point of the measuring range coincides with that of the tank

length. The effect is noticeable and the

shorter the measuring range 8 the

smaller the effect. It is recommended for making accurate measurement of the sinkage to use the mean value of sinkage

over 1/2 length of the tank for Fh<0.2

and 1/4 length for Fh>0.2.

10 0.6 z,0.4 0 2 0.0 00

Effect of the position of the measuring

range

The effect of the position of measuring

range, c, is shown in Fig. 3 for the

case where the length of measuring range is half the tank length. It is concluded that the effect is negligible when the range includes the middle point of the tank as the usual towing tank practice.

0.5 0, 0.3 02 0.1 = 0 0.0 0 2 0 4 0.6 aFh-V I

F3.g.3 Seiche amplitude factor (Effect of measuring position)

Humps and hollows of the amplitude factor

The amplitude factor has humps and hollows dependent upon the water depth Froude number. Froude numbers which correspond to humps and hollows are roughly esti-mated by the following formulae:

Hurps at Fh = X/(2n)

Hollows at Fh = X/(2n-1) n=1,2,3...

Effect of seiche in a progressive test

Long towing tanks make frequently pro-gressive speed tests in a run. This is however unfavourable for the sinkage measurement because a calculation shows that in the low speed range the error

due to seiche of a progressive test can

be ten times as large as of a speed test in one run [5].

3. Practical Examples

As the sinkage is proportional to V2, the differences between the experimental

measurIng cl,s tar, tank lei-4th 1/4 2/4 3/4 _______ T.... 02 04 0.6 0.8 F I 0

Fig 2 Seiche amPlitude factor (Effect of measuring distance)

13771

o's at the two successive Froude numbers may be regarded as the variations of data when the differences of the Froude

num-bers are small. Fig. 4 shows an example

of the variation of c for a Wigley model. In the figure the solid lines are the a's calculated by SF for the seiches of

given amplitudes T (mm) and the dotted

lines by the given uniform vertical

dis-The effect of seiche on the sinkage measurement for practical ship forms is

given in Table 1. The seiche 1 mm in

amplitude which is assumed in Table 1 is

usually observed in towing tanks, and brings about the following order of vari-ations in the sinkage measurement in

towing tanks:

These variations are not more than 10 % of the values to be measured and can be neglected in usual tests. Attention

should be paid however to the latent influence of seiche as the amplitude grows possibly even up to more than 3mm

[6]. The effect of seiche on the sinkage measurement is relatively large for a fine ship form. Further, the periods of seiche in the towing tanks are of the

Table 1 EXAMPLES OF EFFECT OF SEIM ON MEASUREMENT OF SINKAGE

Remarks : Amplitude of seiche is assumed to be 1.0mm.

Length of tank : 210m Depth of water 5.0m

Length of model : 6m Measuring range : from 65m to 155m

T : Tanker M : Medium speed ship C : Container ship W : W1gley model

5-

x sinkage

Stn.& of Wiver Model

161 1980. 12. 26 21mm). frfel(125 13'5' 0.75 1.0

_,

\

%,.. JAW `... 1'.

WWII".

.1.7467111.1:1,11....t Jatr41. .,...- ..- - . FnwV/4i17.-i 0.10 0.20 0.25 0.30 FhwVA4(gh) 0.11 0.22 0.27 0.33 var. due to seiche in mm 0--0.20 0.007 0.44 0.004 0.55 0.003 0.56 0.002 Kinds of ship T M C W T M C W

TMC

W

TMCW

Sinkage In mm 3.7 2.6 2.2 1.0 14.6 10.6 9.0 5.0 - - 14.6 8.4 - - - 13.5 0- 0.12 0.09 0.07 0.03 0.12 0.09 0.08 0.04 0.08 0.04 0.05 Percentage due to seiche 5 8 9 20 3 4 5 9 4 7 4

placement z (mm). The scattering of 0.1 mm for Fn < 0.07

the data is the order of the variation 0.2 mm for 0.07 < Fn < 0.16

due to seiche. 0.4 mm for 0.16 < Fn < 0.20

0.6 mm for 0.20 < Fn < 0.40

Tank lencth 210.0 M Measdrment Water deoth 5.0 M Start at X1 65.0 M

Model 'meth 6.0 M End at x2 155.0 M

00 0.i 0 2 0.3 Ffl.45F 0.4

Fig.4 Variation of 0- of a Wiley model

0.04

. 0.03

002

2 0.0,

I I I . PE91* 1

order of a minute. Attention should be paid when adjusting the zero point for

sinkage measurement.

4. Conclusion

The effect of seiche on the sinkage measurement in towing tanks is investi-gated by using a simple mathematical model and practical examples, and it is shown that attention should be paid to the effect when doing the elaborate experiments, for instance, comparative experiments and geosim tests. Recently numerical methods and new tank test techniques have made rapid progress and brought many interesting and useful findings. These findings should be finally examined through rather conven-tional tank tests. It seems that the more development in ship hydrodynamics requires the more accurate tankery work. It is desired that a little more tankery problems are added to the discussions

of the Committee.

References

The Proceedings of The Workshop on Ship Wave-Resistance Computations, DTNSRDC, Bethesda (1979, 1983)

Cooperative Experiments on Wigley Parabolic Models in Japan, presented to the Resistance Committee of

17th ITTC, Varna (1983)

KAJITANI, H., NAMIMATSU, M., OGIWARA, S., TANAKA, H. and

HINATSU, M.: "An Evaluation of Resistance Components on Wigley Geosim Models (2. Consideration on

the Effect of Viscosity at Low Speed) ". KSNA, to bepublished (1984)

OGIWARA, S.: "Calculation of

Poten-tial Flow Field around a Ship Hull

and its Application". IHI Engineering

Review, Vol. 17, No. 2 (1984) pp1-7

TASAKI, R. and OGIWARA, S.: "Effect of Seiche on Measurement of Sinkage in Towing Tanks". Papers on Marine Hydrodynamics, the 4th Meeting of JSPC, to be published (1984)

FUKASE, T.: "The Effect of Seiche on Tank Tests". KSNA, Vol. 157

(1975) pp 57-62

CHEN, F.-S. and XU, T.-Q. - Shanghai Ship and Shipping Research Institute, Shanghai, China

ON WAVE-PATTERN RESISTANCE OF GEOSIMS

The wave-pattern measurements of 1 .8 m

Series 60 Cb = 0.60 4210 W, carried out

in No. 1 tank of SSSRI in July 1981 and

April 1982, were submitted to the Resis-tance Committee ofthe17th ITTC. In Nov. 1983, the same work on a 3.84 m wood model of the same lines in No. 2 tank of

SSSRI was done.

1. Model and Tank

The model:

Lines: Parent model 4210W of

Series 60, Cb = 0.60 Lpp x B x T: 3.84 x 0.512 x 0.205 m Wetted surface: 2.514 m2 Displacement: 241.6 kg Trip wire: 0 1 mm at stn. 19 The tank:

LxWxh

192 x 10 x 4.5 m Water depth: 4.2 m

2. Test Condition and Result

The wave-pattern and wave profile along hull side were measured in November 1983. The water temperature was 1598 C. The signal of wave height was picked up by a wave probeofKGY-2 type and recorded on

the XWT-type recorder. The signal of a photo-cell indicating the position of

the model relative to the generated

wave was also recorded on the XWT

re-corder. The wave probe was placed at a transverse distance Y = 1.096 m from the centre line of the model, i.e. Y/L =

0.285. The calculation according to

Sharma's method was used. Fig. 1 shows

the amplitude functions for 12 Fr number. The curves of Cwp-Fr were shown in Fig.2 together with the results of 1.8 m model

tested in the No. 1 tank in July 1981.

-la

1:7711,4,

IIIMIN111111111

pa mom= mommunto

111111111111111

MITIMMAMMIMMEMME

WIMINMEMM MMEMMEEN

Plinc MM.

_mil

Els

Fig. 1 Amplitude Functions

3437

-3

333

Fig. 2 Cwp curve of Geosims

It is clear that there is a certain effect of the size of the model on wave-pattern resistance, the smaller model gives the smaller value of resistance.

In order to study the effect of the transverse position of the probe on the measured wave pattern resistance, 5

positions, i.e. Y/L = 0.185, 0.235, 0.285, 0.335, 0.385, were used, and the results are shown in Fig. 3. It can be

Fig. 3 Cwp at different Y/L

14 204,0 20 ;A. Az 0.25 43 eSS"

a

0.5

0.5

as

a

0

Fig. 4 Wave profile alongside the hull surface

seen that the result is similar to that obtained on the 1.8 m model in smaller tank, and the effect of Y on wave-pattern resistance is slightly significant at higher Fr number only.

Fig. 4 shows the wave profile along the hull surface at above mentioned 12 Fr,

where c is the non-dimensional wave height relative to the undisturbed water

surface (non-dimensional with U, ./2g).

Anyhow, by comparing Fig. 2 with Fig. 7

on page 82 of the proceedings of the 17th ITTC, it can perhaps be concluded that the effect of the size of model on the value of Cwp is not very large, and the effect of the accuracy of the

measuring instruments may be an important

factor.

K. MORI - Hiroshima University Hiroshima, Japan

ON THE REPORT OF THE RESISTANCE COMMITTEE

The report of the cooperative experimen-tal program is invaluable. The data base which is reported to be published will contribute much for the developments in the related fields. The contributors must be greatly appreciated.

Let me make a comment to one of the con-clusions that "A general point worth no-ting is the danger of using too small a model." This conclusion seems to be drawn from the results of 2.0 m -Yokohama- mo-del, 1.8 m SSSRI-model (both for the glo-bal measurements) and 1.2 m -Hiroshima-H-model (for the local measurements). It -a5

...41,

[

.

... o, 24,99. _ ,,pr O. 33'76 _{1_} e

.

JOF... o '--as-,,, rf 0 °

.

/ f- - -.!---' -1- -.-- - -I'

0 '

o

Fr

= _-0. _35-24 o

.

'

.

. di

.

.

6 a

.

.

F,

-- o. 3697 ,

MIPS

I ..

IIIINOSIII

,

.

smillin

I:

-1111111.01111111111

NI Einniiiii

---1

1 I

.

.

1,7_0.36,06

I 1111

111E1

QS -- --:-l'

119.

1--r =-- 0,3 946

iuvuuuuuauuu

6 .. ' ;

.

-r-e

III

Ind

1111

ill=

1 L .

MI Er, _-. froM ME I

1 i e

CHM

_{a .} I 0 45

1117177roirA

is true that the Yokohama-model is a little isolated in the Wigley resistance test and so the SSSRI-model in Series 60

of wave pattern resistance. These

differ-ences, however, should not be attributed

ox x

10

Fig 1-a Momentum thickness. Wigley hull

X/t = 0.9

@ Extrapolation of Hiroshima-H

to

a

= 3.2 x 106

0 Hiroshima H . Hiroshima M 0 NMI Yokohama 2

Fn 0.20 0.16 0.21

-x 10-6 0.8 3.2 7.4 1.4 1.4

Fig 1-b Momentum thickness. Wigley hull

X/t = 1.0 (AP)

only to the size of models. Experimental errors, which can be included in the larger models also, must be carefully examined before drawing such an impor-tant "warring". Even larger models show different curves. ell -1- x 10' ell x 10 10 10 0.5

Keel Fraction of girth OWL

0 Hiroshima H 4- Hiroshima M Yokohama 2

Fn 0.20 0.21

-Rn x 10-6 0.8 3.2 1.4 1.4

Fig 1-c Momentum thickness. Wigley hull

X/t = 1.1

S Extrapolation of Hiroshima-H to Rn = 3.2 x 106

0.5

Keel Fraction of girth OWL

0 Hiroshima H + Hiroshima M 5 4 Yokohama 2

Fn 0.20 0.21

--6

R. x 10 0.8 3.20 1.4 1.4

Fig 1-d Momentum thickness. Wigley hull

X/t. = 1.2

0.5

Keel Fraction of girth OWL

x 10-6 0.8

0 Hiroshima H + Hiroshima M Yokohama 2

0.20 0.21

-3.2 1.4 1.4

Keel

0.5

As mentioned briefli, in the Report, the

Reynolds number effects are included in the results. The results of Hiroshima-H, shown in Fig. 11, are examined from this

standpoint of view.

The flat plate boundary layer theory tells us that the momentum thickness is pro-portional to Rn1/51 where Rn is the Rey-nolds number. Under this assumption, we extrapolated Hiroshima-H (Rn=0.8x10G) to Rn=3.2x106 at which Hiroshima-M is

carried out.

The calculated results are shown in Fig. la-d by double circles. They show

rather good agreements with Hiroshima-M except x/R=1.1. The discrepancies still remaining should be regarded as experi-mental errors which are possible in

other results also.

The wave pattern resistanceof Series 60 SSSRI must also be defended. The results are obtained by a presently-available wave-analysis method, though it is not mentioned precisely. It cannot include the Reynolds number effects. If there is a way to exclude them, as done for the momentum thichness, the discrepancies may be reasonable.

As one of the researchers who are under-taking experiments by making use of

rather small models raging from 1.2 m to 3.0 m, the discusser strongly insists to delete the word "danger". He rather hopes to draw a positive conclusion for small models through the present cooperative

program, for small models can contribute much especially for basic researches.

HAJIME MARUO - Yokohama National Univer-sity, Yokohama, Japan

ON THE UNDERSTANDING OF THE BOW-WAVE-BREAKING

The wave-breaking phenomena around a hull moving in calm water have drawn atten-tion of naval architects for the first time when Baba has pointed out that the wave-breaking at the bow becomes an ori-gin of another resistance component of the ship. Though various kinds of hypo-thesis have been proposed so far in or-der to provide theoretical exposition for the wave-breaking, rational elucida-tion seems to have been out of our reach. Baba tried to interpret this phenomenon with an analogy to the hydraulic jump in the shallow water flow, according to some phenomenological similarity between two phenomena, and several reproductions of this idea have followed after this, such as the free-surface-shock-wave con-cept by Miyata. However, the hydrodyna-mic analogy between the wave-breaking around a hull and the hydraulic jump in shallow water has never been supported by rational analysis, and it seems to become a dominant opinion among experts in ship hydrodynamics that these phenom-ena should be interpreted by different theoretical bases in spite of their

superficial similarity. Another idea con-cering the inception of wave-breaking is the existence of a thin shear layer at the free surface in front of the bow like the boundary layer, which can bring the

separation bubble at the stagnation point and is considered to relate pri-marily to the inception of wave-break-ing. Though the shear layer obviously has some connection with the wave-break-ing, its theoretical foundation is not easy to understand. There exists a shear flow near the stagnation point in the

corner separation, so that the shear layer, if it exists, should be of vis-cous origin. However the visvis-cous shear

layer at the free surface is hardly legi-timated by Newtonian principles of hydro-dynamics, unless some abrupt change at the free surface, which brings an extreme curvature or discontinuity, takes place.

Several experimental studies have been conducted at Yokohama National University in order to elucidate the mechanism of inception of wave-breaking. The result was reported at Symposium on New Develop-ments of Naval Architecture and Ocean Engineering held at Shanghai in September

1983, which is not referred to in the Report of Resistance Committee

unfortu-nately. The study begins with the

inspec-tion of the bow wave configurainspec-tion of ships in full scale by means of photo-graphs, and it is suggested that there are four types of wave-breaking feature. Among them, there is a case of a full hull form in full load condition, by which one can observe a few row of short waves like ripples or wrinkles around the stem. These waves are so steep that breaking takes place at their crests. This type of breaking waves will be converted to fully developed chaotic breakers at higher speed. An analytical exposition has been given to this phenomenom, by means of the low speed theory of wave-making in two-dimensions. In order to examine phenomena when the wave-breaking takes place in detail, experiments with wedge-shaped models are conducted in the towing tank. The free surface elevation in front of the wedge along the centre line is measured by the servo-type wave probe and photographs are taken in order to observe the condition of the free surface. Remarkable difference is ob-served in the wave pattern between the case of apex angle less than 1200 and

that of larger apex angle. In the latter case, there is a swell ahead of the stem, and behind this swell, one can observe

short waves just in front of the stem. The wave-breaking takes place first at these short waves at higher speed. The height of the swell grows up as the speed increases until the so-called spilling breaker appears at the top of the swell and develops into fully tur-bulent breaking waves. Thus the incep-tion of the wave-breaking takes place in the large swell. In case of smaller apex angles, however, the swell is not observ-ed and the breaking of waves takes place at the short waves only. In the model experiment, capillary waves or waves of surface tension are observed over the free surface in front of the stem, in-dicating the strong influence of the

sur-face tension. Therefore the scale effect due to the surface tension is present between model scale and full scale.

On summarizing the above investigation, one can conclude that the breaking of waves at the bow is a phenomenon which

is common in waves in deep water, like the breaking of waves of large

ampli-tudes. It takes place when the wave generated in front of the blunt bow

exceed a certain criterion of wave height

or wave steepness. The breaking waves

which appear in front of full hull forms

are spilling breakers. This fact

discri-minates the wave-breaking from the spray formation of high speed vessels, because the latter is accompanied by so-called

plunging breakers. The shear layer at

the free surface does not become the primary origin of the bow-wave-breaking, but it is a result of the disturbance of

HAJIME MARUO - Yokohama National University, Yokohama, Japan

ON COMPUTATIONS OF SHIP WAVES AND WAVE RESISTANCE BY THE SLENDER BODY THEORY

The application of the slender body

theory to ship hydrodynamics was pro-posed more than twenty years ago. In contrast with the remarkable success of the slender body theory in aero-dynamics, it has been revealed that the

formulation in ship hydrodynamics yields only very disappointing results in nu-merical computation by this theory. The wave resistance of a ship predicted by it differs much from measured results, and it has been regarded so far even that the slender body theory is useless

for the practical purpose of prediction of ship wave resistance. Though much development has been observed in the slender body theory for oscillating ships in waves, progress in the problem of steady forward motion is rather poor.

In his formal contribution to 16th ITTC, the present author introduced a new for-mulation of the slender body theory for

a ship with constant forward speed. It is based on a suitable asymptotic expan-sion of the Kelvin source along its track. The approximate expression for the

velocity potential near the hull is

given in the form like

=+

Sbl (1,2 with

(v--= I

a (x,y',z') ln 1,) (z-z')2ds 1 (y-y'₎₂ + (z+z1)2 C (x)

where a(x,y', z') is the density of two-dimensional sources distributed along

the contour C(x) of the transverse

sec-tion of the hull. The expression for (1)2

has been given in Proceedings Vol. 2 of

the 16th ITTC, page 23. The source

den-sity is determined by the solution of the boundary value problem on the hull surface, which is much simpler than that of the Neumann-Kelvin problem. The wave resistance is expressed by the formula

R = pK2 flfdxf

V(x,y)exp(iYoxVV +

w 7 0 b(x) z iKDyv)dyl2dv + 7pfdx f v(1-Koz)ds -C(x) fdx'f V (1-Koz1)ds"

_[(x2x1)2

C(x')

{KOXX1)1]

K2Y

_po

{K (x-x')1+o

2(:%

7

_')Y1

where Vn = 9,1)1/11 V z=0

There is a difference between the above expression and the corresponding formula given in 16th ITTC. The attenuation

fac-tor 1 - Koz which represents the effect

of the depth of singularities is taken into account in the present formulation.

The wave pattern and wave resistance of the Series 60, CB= 0.60 model at Froude number 0.304 are computed for example. Experiments of the same model has been conducted in the towing tank. The com-parison of computed and measured

con-tours of the free surface is shown in

Fig 1, and the wave profile alongside the hull is shown in Fig 2. In spite of the complex hull form of Series 60, the agreement is fairly good. Fig 3 gives the computed point of the wave resist-ance of the resistresist-ance curve determined by the towing test. The curve obtained by the Michell theory is also shown. The result is quite encouraging and fur-ther computation of ofur-ther cases are

171:741111

References

MARUO, H.: "New Approach to the Theo-ry of Slender Ships with Forward Ve-locity". Bulletin of Faculty of Engi-neering, Yokohama National University,

31 (1982)

MARUO, H., IKEHATA, M., TAKIZAWA, Y., MASUYA, T.: "Computation of Ship Wave Pattern by the Slender Body Approxi-mation". Journal of the Society of Naval Architects of Japan 154(1983) pp. 9-16

Fig. 2 - WAVE PROFILE ALONGSIDE THE MODEL

Fig. 1 - CALCULATED AND MEASURED WAVE PATTERN

2

0 ' 0.20

SLENDER BODY THEORY

--- MICHELL THIN SHIP THEORY

o-- MODEL EXPERIMENT [Cr CY-1 K

- 0.27

025 030 0:35

Fn Fig. 3 - WAVE RESISTANCE COEFFICIENT

J.H. CHUNG - Busan National University, Busan, South Korea

ON THE REPORT OF THE RESISTANCE COMMITTEE

I wish to make a brief comment on the numerical studies of the low Froude number problems of the Resistance Committee. The topic of numerical com-putation of wave resistance at low Froude numbers has been presented on the agenda of this Committee. Baba and Hara (1977) presented a procedure for the numerical calculation of wave resistance of con-ventional ship forms. They evaluated wave resistance by a numerical method such as the one developed by Hess and Smith (1964) for nonlifting bodies. And also, Maruo and Suzuki (1979) determined the distribution of Rankine source over the double model in the uniform flow by the method of Hess and Smith. In the Resistance Committee Report it is stated that the present numerical methods are

not satisfactory for predicting the wave

resistance of conventional ships. I would like to suggest that the numerical

computation of wave resistance at low Froude numbers might be calculated by Boundary Element Method.

5

4

References

BABA, E. and HARA, E.: "Numerical

Evaluation of a Wave-Resistance

Theory for slow Ships". ICNSH Report, Berkeley, (1977)

HESS, J.L. and SMITH, A.M.O.:

"Cal-culation of Nonlifting Potential Flow About Arbitrary Three Dimen-sional Bodies". JSR, Vol. 8, No. 2,

(1984)

MARUO, H. and SUZUKI, K.: "Wave Resistance of a Ship of Finite Beam Predicted by the Low Speed Theory".

JSNA, Vol. 142, (1977)

WU, J.-H. and LI, S.-M. - Wuhan Institute of Water Transportation Engineering, Wuhan, China

ON THE LOW SPEED THEORY

1. Boundary Value Problem and Its

Solution

The boundary value problem of the

non-dimensionalized velocity potential (ID can

be described as V2cp = 0 n.94, = 0 J J h = -Fr201+IDiWy(10 (33+Fr231.) = -Pr2(2311 + +YBil)(Paig) PESF (1-4) V (4) 0 at infinity (1-5) for x1 (1-6) V - 0(

1)

1./XT P C V (1-1) PCSB (1-2) PESF (1-3)

As Baba has done, we consider that

where (491., is the double-body disturbed

velocity potential, qow is an additional

velocity potential to Qr. It is assumed

that D....

= 0(1)

3 1 r D j

--

1 w(4D = 0(Fr4-2n) n = 0,1,2,...; m = 1,2,3,...; j,1 = 1,2,3 then h = hr +h w hr hw (1-7) (1-8) ( 1 - 9 ) = -Fr2011-iyraj) = 0(Fr2) (1-10') = -Fr2(D1+D.(4)

_3r3

_{D.+19.(P 9.)(.0}

JWJW

₌ -Fr2(91+3j(Pr9j)Qw = 0(Fr)

Substituting equation (1-7) into (1-4),

expanding (pr. from the exact free surface

to plane x3 = 0 and

(f)w

to the curved sur-face x3 = hr by using Taylor series ex-pansions, and noticing the equations

(1-8,9,10',10) we find LB = D(x1,x2) + 0(Fr) where LB = 33 Fr2[(1-31(pr

'ail

+2(14-31(pr)32kor312+ 02(Pr)2322] (1-12) D(X1,X2) = 31[(1+91(Pr)hr1+2[hr32(Dr] (1-10) D 32

where D = ,D - , (j,1=1,2,3), Equation (1-11) is Baba's slow ship free

I jl 9xj9xl

n (j = 1.2.3) is the component of the surface condition. Here we have neglected

outward unit normal vector, and all van- the higher order terms.

ables in the equations (1-1) through

(1-6) have been nondimensionalized by L Let

(1 )

(2)

),,,, = Q + (0

and let

(.1)

(1)

_{and cp(2)}

_{satisfy the}

following conditions:

at(y)

= 'fatrexp(ixy)dx

ats(y) = ff9trscprexp(ixy)dx

(1-17)

By utilizing Fourier Integral Transforma-

method of solving the Q(1), we have

tion and asymptotic analysis method, we

find

cp(26)=ff

a(Q)G(p,Q)dS -Re -1)-T

SB Q 27

7

7 CP(1)(p)

= -ReTTT fsec2e(vp)

fsec2ede(v-p)foK-K0

B(Y) exp[K(x iw)]dK

-IT v T

.

--

3 7 2 r

A(y)

-

Re i f sec2013(1,0)exp[K,(x,-iw)]de

K-vsec20

exp[K(x,-iw)]dKlde+

_7 0 2

Rev f sec2eA(yo)exp[Ko(x3-14)Jde

2112

_2

2

(1-14)

kernel function

r(Y,u)

=

E Fr2jK(3)

j=0

2 2

E [2at(y-u)ulut+ I Etts (y-u)utus]

K (°)- tri

s=1

(1-16)

472(lui-Fr2u)

ffx("(y,z)K(i-1)

(z,u)dz

the notation in above equations is

defined as

(1-18)

where

where, amplitude function

B(y)=BF(y) +Fr2ffF(y,u)BF(u)du

_-.

A (y)

= DF (y) + Fr2ffr (y,u) DF (u) du

B =472Fr2y2H(y)/Iy1

F 1

D(y) = ffD(x)exp(ixy)dx

(1-15)

H(y)=ffa(Q)exp[q3 lyl +i(qiyi+q2y2)]dSQ

G(P,Q)=[(xl-q1)2+(x2-q2)2+(x3-q3)2]-1+

+[(x1-(11)2,(x2-(212)2+(x,102]-i

(1-19)

The source strength density a(Q) is

de-termined by the following equation

1 (2)

0(Q)=[n.(v.p).cp"+ n.a.cp0)] (1-20)

_211J

3 ₃

3

finally, the solution of cpw can be

ex-pressed as

x =

(x1,x2)

y =

(y1,y2) = K(cose,sine)

(A) (B) V2Q(1)

= o

V2(.02) 0 X3<0

_{u =}

_(u1,u2)

_z =

(z1,z2)

v = 1/Fr2

(1)(1) D L cp(2) = 0

_X3.0

(11 (2)

n. .cp"=-n.D.cp" PES

Ko

vsec20

y0=K0(cose,sine)

7 7 7 7 B

w = xicose +x sine

(11 (2) 2

Vcp"

VQ"

0

at infinity

On the other hand, by distributing source

vq)(1) 1

vq)(2).0(

1

--,- +.3

for

) x

density o on the body surface and the

image of the body, and utilizing the same

LP w (P)=fis G )G (P,Q)caSQ- fsec2 e

(v

p ) 2 r A(y)+B(y)exp[K (x +ic4)]dK + J K-K, o 3 0 + ReTIivT sec20[A(17,)+B(y0)]* 7 2 exp[K0(x3+iw)]dK (1-21)

The first integral of the r.h.s. of the equation (1-21) cannot produce wave motion, and has no contribution to the wave resistance. If the contribution of

source density o to ww is neglected, and

so is the nonuniformity effect of th.:

free surface, that is, B(y)=0 and A(y)=

DF(y), the solution formula (1-21) of

(4)w

is then returned to the asymptotic form developed by Baba.

2. The Contribution of Hull Boundary Condition to (1)w We let ( 2 ) (2 ) (2) m + (I) -r (2-1)

and make CPr(2) and Q(2)

w be determined by

the following boundary value problems:

(C) (D) ( V2Q(2)=0 V2)2u)w=0 x3<0 (2) a''Pr 'CI /13(Pw(2 )=113(Pr(2 ) n.a.(4)(2)=-n.3.(49(1) n. .cp(2)=0 3 r J J J w pESB Vcp(2),

0V

(pw(2) at infinity (2) 1 Vcpw =Of) for x1--. \TXT

The function (4)(2)is so decomposed that

it is convenient to survey its

charac-ters. Because V(4)(I)= 0(Fr2) it is

ob-vious that LB

q)(2)=

0(Fr4), and cp(2) =

r

= 0(Fr2). At the same time, noticing

that V(p(1)= 0(Fr2) when D(x11x2)=0(Fr2), one may come to the conclusion that

V(p(2)= 0(Fr4). Hence, (f)(2) is a high

w(I)

order term relative to (4) . And the

boundary value problem (C) expresses a double-body flow mathematically, so it has no contribution to wave resistance. Then one can conclude that if it is only interested in wave resistance, the

potential function (4)(2) can be neglected.

It proves that it is reasonable to ex-clude wetted surface condition for

solving the additional velocity potential

3. An Analytic Solution of 2-D Slow Ship Wave Velocity Potential

For two-dimensional problems , the

bound-ary value problem can be simplified as

follows v2(pw o x <0 (3-1) (V)c3 +

_{a(x)TN)w.D(X1)}

D 32 1 X3=0

(3-2)

p E SB (3-3) ni3iQw+n33ocpw=0 no upstream wave where 2m = D(xi) = [1-3(1 +--a) r)2, x30 Dx. B(Pr a(xi) = (1 + 3x )2

so there are a flow function IPw and a

complex potential W.

W(Z) = (Pw + Z = x1+ iX3

By neglecting hull boundary condition (3-3) and utilizing complex function

(3-4)

(3-5)

17:147t9117

analysis one may find complex wave

velocity dW

i r

exp[ -iuf (2) ] J du

j

1.-Jexp [ iuf ( t ) ] dt+ dZ 7

-

- a( t ) +exp[-ivf(Z)] jD(t) exp[ivf(t)]dt a (t) (3-7) where dt f(t) =

j

a(t)

when D(t) is an odd function and a(t) is an even function, the resistance co-efficient can be expressed as

CO

Cw= 16Fr2(

f

ap tt-))

sinv f(t)dt]2 (3-9) 1+5

Here we require that (S, which is

in-troduced to ensure the existence of w(z), is a constant number larger than

zero.

If one does not consider the nonuniform-ity of the free surface, that is, a(x1)-=1, formula (3-9) can be simplified as follows

Cw 16Fr2[ JD(t) sinvt dt]2

For a half-floating circle

3 t-1 f(t) = t- + in 2(t2-1) 4 t+1 (3-8) (3-10) (3-11)

the wave resistances of the circle have been evaluated. By comparing the

numeri-cal results of C defined by the formula

(3-9) with that defined by the formula (3-10), we find that the nonuniformity of the free surface will eliminate the phenomena of the "humps and hollows". This shows that the uniformity of the

free surface cannot be neglected.

D.M. ZHU - Harbin Shipbuilding Engineer-ing Institute, Harbin, China

ON AN OPTIMUM HULL DESIGN METHOD

Many people have made great progress in estimating wave resistance. The

success-ful methods they developed will certain-ly stimulate the effort of optimum design of ship forms. But some difficulties are

still lying in the way.

Some of my colleagues [3] have been try-ing to exploit a feasible optimization method, and attempting to find out if simple theory can be used in practical design somehow. To remove the trouble of waviness occurring in many optimization methods, which is one of the main obstac-les Impeding the practical use of those methods, they put forth a "Damping Water-line" method. Combined with C.C. Hsiung-s optimization technique [1], their method showed encouraging results in optimum design of hull for high speed transom

ships (HSTS).

Optimization of ship forms for wave re-sistance has great significance to HSTS, for which the wave resistance constitutes a great sector in total resistance.

Un-fortunately, the waviness and distortion occured in many optimization techniques blocks their way to practice.

They have [2], using Hsiung-s method, rectified by the method of "Fictitious Extension Length" to cope with the tran-som stern, predicted successfully the wave resistance coefficient of HSTS. Using "Tent Function" f..(x,z) in Michell

13

Integral,the coefficient Cr is expressed by a quadratic form of the offsets. It

supplies an objective function for opti-mization. But wavy forms were obtained.