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The first International Symposium on Shipboard Acoustics, held in Noordwijkerhout (The Netherlands) in 1976, was a meeting of invited experts, each having considerable expertise in ship acoustics. Many of the participants were dealing with research on various ship acoustical subjects, and it proved to be a good idea to discuss future investigations and new techniques. At that time acousticians learned to use realtime signalprocessing techniques and attempts were made to establish sound level prediction methods based on semifundamental considerations instead of the methods using empirically obtained data. Time was pressing as it was assumed that, in view of the adoption of Recommendation 141 of the International Labour Conference in 1970, authorities would soon make appropriate provisions to protect seafarers from the ill effects of noise. This resulted in several national recommendations followed by the IMO Code on noise levels aboard ships which was adopted by the IMO Assembly in 1981. After that, pressure on the authorities was increased further by the decision of the European Community to protect labourers against harmful noise at their workplaces, including ships. Legally enforceable noise limits will therefore become normal in the future.
SHIPBOARD ACOUSTICS Shipboard Acoustics Proceedings of the 2nd International Symposium on Shipboard Acoustics ISSA ' 86, The Hague, The Netherlands, October 7-9, 1986 Organized by the Netherlands Organization for Applied Scientific Research (TNO) TNO Institute of Applied Physics (TPD) in co-operation with Maritime Research Institute Netherlands (MARIN) National Foundation for the co-ordination of Maritime Research in the Netherlands Royal Netherlands Navy edited by J. BUITEN TNO Institute of Applied Physics (TPD) Delft, The Netherlands 1986 MARTINUS NIJHOFF PUBLISHERS ~. a member of the KLUWER ACADEMIC PUBLISHERS GROUP lIiII DORDRECHT / BOSTON / LANCASTER • Distributors for the United States and Canada: Kluwer Academic Publishers, 101 Philip Drive, Assinippi Park, Norwell, MA 02061, USA for the UK and Ireland: Kluwer Academic Publishers, MTP Press Limited, Falcon House, Queen Square, Lancaster LAI lRN, UK for all other countries: Kluwer Academic Publishers Group, Distribution Center, P.O. Box 322, 3300 AH Dordrecht, The Netherlands ISBN -13:978-94-010-8070-5 e-ISBN -13 :978-94-009-3515-0 DOl: 10.1007/978-94-009-3515-0 Copyright © 1986 by Martinus Nijhoff Publishers, Dordrecht. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publishers, Martinus Nijhoff Publishers, P.O. Box 163, 3300 AD Dordrecht, The Netherlands. PREFACE The first International Symposium on Shipboard Acoustics, held in Noordwijkerhout (The Netherlands) in 1976, was a meeting of invited experts, each having considerable expertise in ship acoustics. Many of the participants were dealing with research on various ship acoustical subjects, and it proved to be a good idea to discuss future investigations and new techniques. At that time acousticians learned to use real-time signal-processing techniques and attempts were made to establish sound level prediction methods based on semi-fundamental considerations instead of the methods using empirically obtained data. Time was pressing as it was assumed that, in view of the adoption of Recommendation 141 of the International Labour Conference in 1970, authorities would soon make appropriate provisions to "protect seafarers from the ill effects of noise". This resulted in several national recommendations followed by the IMO "Code on noise levels aboard ships" which was adopted by the IMO Assembly in 1981. After that, pressure on the authorities was increased further by the decision of the European Community to protect labourers against harmful noise at their workplaces, including ships. Legally enforceable noise limits will therefore become normal in the future. In many countries recommendations with respect to maximum allowable sound pressure levels in the crew accomodations and work area aboard ships were already taken into account by ship owners, long before the existence of the Recommendations. Shipyards are confronted with the problem of how to fulfil the requirements at the lowest possible costs, a situation which does not essentially differ from that in 1976. In addition however, modern ships tend to be of a lighter construction and as a consequence, the acoustic countermeasures have to be light. Yards are constructing ships that are more specialized and technically more complicated than in the past; acoustical standard solutions are of little use for these vessels. The yards are compelled to find solutions that have' flexibility in the design stage and standardization in the production stage. The consultant is confronted with rapid and drastically changing demands of owners and yards, which require fast and highly precise answers. He should have perfect knowledge of the results of research and has to transform these into practical tools. Much more often than before, he has to combine disciplines, which makes it difficult to be an expert in one of them. In the past ten years research workers have experienced a rapidly growing demand on research, followed by a sharp decrease of funds. Their tools changed dramatically compared with preceding decennia, in capabilities as well as in the necessary investments, especially in computer hardward and in software. They discovered that solutions of rapidly increasing quality could be given, but that costs increased correspondingly. Many developments VI in the vJide area of "noise" and "vibration" force the scientist to extend eXisting, or to establish new data bases. Increasing demands on research cause increasing specialisation and, for the research worker an increasing need for open discussions with colleagues. Society however, requires methods that are simple to handle, and industry wants to protect its trade secrets. In spite of the conflicting demands of the different parties involved in design, construction and management of ships, and those in charge of the crew and passengers, much has been attained in the last decennium. At a symposium on shipboard acoustics and vibrations only some recent highlights and experiences can be emphasized in a limited number of papers. The discussions, which will be added to this issue later, will certainly complete the papers presented. We trust that the contributions to this book will give rise to an exchange of ideas on the application of research results, on subjects for future research and on the necessary standardization. The Organizing Committee expresses its thanks to the authors who shaped this symposium. The efforts of the Netherlands Organization for Applied Scientific Research (TNO) and the members of the TNO Corporate Communication Department are gratefully acknowledged. The editor would like to thank his colleagues of the TNO Institute of Applied Physics (TPD) and Dr. A. de Bruijn of SACLANT ASW Research Centre for their assistance, and the authors who made this task a pleasant one. August 1986 J. Buiten TABLE OF CONTENTS PREFACE 1. A. de Bruijn, W.H. Moelker, and F .G.J. Absil Prediction Method for the Acoustic Source Strength of Propeller Cavitation v 2. A. Colombo, P. Ausonio, L. Grossi, and L. Accardo 21 Propeller Induced Noise and Vibration Reduction: Acquired Experience in Design and Testing Approach 3. J. van del' Kooij 43 Experimental and Analytical Aspects of Propeller Induced Pressure Fluctuations 4. T. Sasajima, N.Nakamura, and A. Oshima 63 Model and Full Scale Measurements of Propeller Cavitation Noise on an Oceanographic Research Ship with Two Different Types of Screw Propeller 5. Wei Yi-mai 75 A Study of Simulation and Elimination of Propeller Sinqing 6. B. Bajic, J. Tasic, A. Dzubur, and I. Jovanovic 91 Propeller Noise: Some Topics from the Activities of Brodarski Institute 7. J.H. Janssen, and W.H. Moelker 103 Some Experiments on the Transmission of Propeller Cavitation Noise into the Ship's Structure 8. J.I. Smull in 121 Quiet High-Speed Yachts and Water Jet Applications 9. J.R. Chapman 135 Model-Scale Measurements of the Transmission and Radiation of Hull-Borne Vibrational Energy Using Frequency/Wavenumber Analysis 10. M. Purshouse 155 Underwater Noise Radiation Due to Transmission through the Cooling Water System of a Marine Diesel Engine 11. A.R. Clark and P.S. Watkinson Measurements of Underwater Acoustic Intensity in the Nearfield of a Point Excited Periodically Ribbed Cylinder 177 VIII 12. Zhu Xiqing 189 Sound Generation from a Moving Shell 13. E. Bonetti and P. Calcagno 201 Low Noise Levels as the First Task of a Vessel. A Description and Some Remarks about Acoustic Quieting Design Criteria and Features of Saclant ASW Centre Oceanographic Research Vessel 14. J. 0degaard 217 Ship Noise Criteria. Do They Reflect the Present Level of Noise Reduction Technology? 15. P. Hynna 233 A Literature Survey Concerning Propeller as a Noise Source and Prediction Methods of Structure-Borne Noise in Ships 16. P. Calcagno, R. Maltese, and F. Pinazzi 245 Applications o"f Two Mathematical Approaches to Predict Airborne Noise Levels in Ship Superstructures 17. R. Kinns 265 Some Observations on the Achievable Properties of Diesel Isolation Systems 18. J.G. van Bakel Acoustic Transfer Functions of Flexible Shaft Couplings; Measurement Method and Results 279 19. A.D. Sykes 295 Random Vibration of Multiterminal Mechanical Systems 20. P. Tilmann 317 The Influence of the Internal Impedance on Vibration Reduction 21. G. Mancuso and F. Sacchi 335 Main Propulsion Diesel Generator Sets with Acoustic Enclosure and Double Resilient Mounting for Low Noise Application 22. B. E. Douglas 353 Flexural Wave Damping in Ship Hulls, Decks and Bulkheads 23. S. Weyna , 365 Determination of Acoustic Properties of Ship's Sound Reducing Floors 24. A. Blanchet, G. Chatel, and A. Paradis Study of Structure-Borne Noise Transmission Inside Cabins by Sound-Intensity Measurements 377 25. M.J.A.M. de Regt Experiments on Sound Reducing Floors Including Visco-Elastic-Damping on Board a Rhine Cruise Vessel IX 393 PART I LECTURES PRESENTED AT THE SYMPOSIUM PREDICTION METHOD FOR THE ACOUSTIC SOURCE STRENGTH OF PROPELLER CAVITATION A. DE BRUIJN*, W.H. MOELKER, F.G.J. ABSIL TNO INSTITUTE OF APPLIED PHYSICS (TPD) , DELFT, THE NETHERLANDS 1. INTRODUCTION Ship propeller cavitation is considered to be one of the most impor- tant sources of underwater noi se. Furthermore it often contri butes con- siderably to the noise level aboard the ship. Much research has been carried out in this field in order to reduce the extent of cavitation by a proper blade design. Also through the use of model simulation techniques more insight into the cavitation performance has been gained. An important overview about this subject has been presented by ISAY [1]. Modern computer-based design techniques,(cf. KERWIN [2], VAN GENT [3]) applying three-dimensional lifting surface theories, have improved con- siderably the insight into the hydromechanical aspects. For example, the pressure distribution on the blades gives the position where cavitation probably will occur. The price to be paid to reduce the cavitation is mostly the decrease of propulsion efficiency. This is the reason that in the design phase the con- sequence of noise reduction has to be known at a very early stage. Mostly nothing more is known but the propulsion power, rotation speed, diameter of the propeller etc., so the noi se and vi br,ation anal i st is 1 eft with empi ri ca 1 methods to predi ct the acoustic source strength or the hull- induced vibrations. Prediction of the hull-pressures induced by the cavitation has been the subject of considerable investigations. NOORDZIJ [4J has attempted to deve- lop a calculation scheme for estimating the cavitation volumes at any blade position. By calculating the volume variations he was able to determine the pressure amplitudes exerted on the hull. The agreement with experiments is quite limited but useful in comparative studies. Up ti 11 now a cheaper, but st i 11 re 1 i ab 1 e, method is the semi -empi ri ca 1 approach. The method is based on the compari son of a great number of experimental data taken from as many ships as possible. By statistical regression it has been attempted to find the significant parameters which describe the induced hull-pressures. A successful evaluation of this approach for hull-induced pressures at the two lowest blade-rate frequen- cies is given by HOLDEN et al [10]. * Currently employed at: SACLANT ASW Research Centre, La Spezia, Italy Buiten, J. (ed), Shipboard Acoustics. ISBN 90-247-3402-7. © 1986.' Martinus Nijho!! Publishers, Dordrecht. [...]... broadband, but the ratio ilp is mostly made up by the generation of sweep tones to obtain the best signal-to-noise ratio The result of the measurement depends heavily on the location of the hydrophone in the first experiment From extensive investigations it has been found that the best location is the centre of the sheet cavitation when the sheet has started its collapse stage To obtain a reasonably unique... 2,1 (dB) 8,8 TABLE 3: Mean deviation of the calculated volume velocities in dB as the results of the standard deviation of the variables of the prediction method The interpretation of the data gives some information on the importance of each vari ab 1e The size of the propeller appears important Thi sis quite understandable, since it is the major factor for scaling The factor K'Q appears also to be... in the accomodation areas of the ship The correlation between the harmonic pressure content, as measured above the propeller tip, and the vibration harmonic content measured at a stern point on the main deck is shown in Fig 8 It must be pointed out that the experienced pressure harmonic content was not previously foreseen by theoretical calculation (by considering the ship model wake field) nor by the. .. gives an indication about the quality of the propulsion configuration It is a measure for the propeller load The larger the value the more the propeller is loaded In the various speed conditions of the sh i p KI Q does not vary very much The quantity (KQ/ J5) 0.25 is related to 8 the parameter B , well-known in 1iterature We should consider it a p variable which indicates the difficulty in the design It... determining the voZ·ume velocity of propeUer cavitation In the first ("silent") experiment the transfer function is measured and it is determined by a reciprocal technique for practical reas'ons In the second ("sailing") one the noise or vibrations due to the propeller cavitaThese tion at an arbitrary point in the accommodation are measured results represent the combining effect of the source strength of the. .. carried out, generally at the Italian Navy Cavitation Tunnel (CEIMM) During these experiments, visual observation of the cavitating behaviour of the propeller is used to discover the inception of each phenomenon at various propeller operating points and cavi tation index values (cavitation bucket) A survey of the type and extension of the cavitation in correspondence with the most signi ficant full-scale... good correlation exists at the afterbody and an acceptable correlation at the navigation bridge Furthermore, the complete vibration survey on the ship showed very low amplitudes throughout the classical low frequency range, as had been foreseen The explanation for the relatively high noise levels in the aftermost part of the ship can be found in Fig 4c, showing the harmonic content of the measured induced... sheet-cavitation and tip-vortex cavitation These types are mainly responsible for the noise generated aboard the ship or underwater The main question is now what is the relation between the cavitation picture and the noise generated An a-priori answer cannot be given, since there is no suitable mathematical sol ution on the relation between the noise and the picture Model experiments can give reliable solutions... or predictable, although the progress in this field is quite impressive It is of prime importance to eliminate the transfer function before judging the source strength of various propellers This paper concentrates on the determination and evaluation of the cavitation source strength This is a first step in the prediction scheme for the noise aboard the ship Transmission of the propeller noise should... Calculations learn that the variation in volume velocity level is about 3 to 4 dB around the mean value in all frequency bands In view of the uncertainty of the value of the wakefield we may conclude that it still leads to an acceptable spread in the volume velocities The best'way to check the validity of the method is to measure the volume velocities aboard a number of other ships outside the collection . SHIPBOARD ACOUSTICS Shipboard Acoustics Proceedings of the 2nd International Symposium on Shipboard Acoustics ISSA ' 86, The Hague, The Netherlands, October 7-9,. Mean deviation of the calculated volume velocities in dB as the results of the standard deviation of the variables of the prediction method The interpretation of the data gives. of the type of ship. 8. PREDICTION FORMULA The volume velocity in third-octave frequency bands of a fictitious equivalent monopole in the position of the upper part of the