INTERNATIONAL SOUND AND VIBRATION DIGEST Published by THE INTERNATIONAL INSTITUTE OF ACOUSTICS AND VIBRATION (IIAV) Volume 2, Number 1 Date: August 9, 1996 Editor-in-Chief: Malcolm J. Crocker, Auburn University, USA Assistant Editor: Dragana Obradovic, Auburn University, USA Editorial Board: Duan-shi Chen, Jiao Tong University, Shanghai, CHINA Frank Fahy, ISVR, Southampton University, UK Jean L. Guyader, INSA de Lyon, FRANCE Colin H. Hansen, University of Adelaide, AUSTRALIA Hanno Heller, DLR, Braunschweig, GERMANY Nikolay Ivanov, Baltic State University, St. Petersburg, RUSSIA Finn Jacobsen, Technical University of Denmark, DENMARK G. Krishnappa, Institute for Machinery Research, NRC, CANADA Conny Larsson, Uppsala University, SWEDEN Martin V. Lowson, University of Bristol, UK Leonid M. Lyamshev, Andreev Acoustics Institute, Moscow, RUSSIA Eric Marsh, Penn State University, USA M.L. Munjal, Indian Institute of Science, Bangalore, INDIA David E. Newland, The University of Cambridge, UK Michael P. Norton, University of Western Australia, AUSTRALIA A. Selamet, Penn State University, USA Andrew F. Seybert, University of Kentucky, Lexington, USA Jan W. Verheij, TNO, Delft, THE NETHERLANDS. Current number of subscribers: 1203 To send a submission to the IS&V DIGEST or to subscribe or unsubscribe, send information by E-mail to yanas@eng.auburn.edu. TODAY'S DIGEST CONTENTS ITEM 1. INTRODUCTION. ITEM 2. NEW SCIENTIFIC SOCIETY: The International Institute of Acoustics and Vibration (IIAV). ITEM 3. FIFTH INTERNATIONAL CONGRESS ON SOUND AND VIBRATION: Adelaide, Australia., Dec 15-18, 1997. ITEM 4. FOURTH CONGRESS PROCEEDINGS AVAILABLE. ITEM 5. THIRD CONGRESS PROCEEDINGS STILL AVAILABLE. ITEM 6. 15TH ICA PROCEEDINGS AVAILABLE. ITEM 7. ISVR CONFERENCE ANNOUNCEMENT: Southampton, UK, 14 -17 July 1997. ITEM 8. SPECIAL SAME CONGRESS SESSIONS: Atlanta, GA, USA. ITEM 9. ACOUSTICS FAQ AVAILABLE ON WEBSITE. ITEM 10. NOISE AND HEARING GROUP HOSTED BY NIOSH. ITEM 11. READER QUESTION. ITEM 12. RESEARCH ACTIVITIES AT GERMAN AEROSPACE RESEARCH ESTABLISHMENT DLR. ITEM 13. NEW BOOKS: 1) Sound Intensity: second edition, 2) Active Control of Vibration. ITEM 14. BOOK: Recent Trends in Hearing Research. ITEM 15. CONFERENCE PROCEEDINGS: Psychoacoustics: Sound Perception and Noise Effects. ITEM 16. RESEARCH IN ACOUSTICS, DYNAMICS AND VIBRATION IN WESTERN AUSTRALIA. ITEM 17. CENTRE OF EXCELLENCE FOR TECHNICAL ACOUSTICS, IISc, Bangalore, India ITEM 18. TECHNICAL PAPER: Research Into Pneumatic Active Vibration Control. ITEM 19. TECHNICAL PAPER: Anderson Localization and Quantum Chaos in Acoustics. ***************************************************************************** ITEM 1. INTRODUCTION. ***************************************************************************** We are pleased to bring you the next issue of the ISV DIGEST. We are sorry for the considerable delay since the last issue. But we expect to be able to continue publication every two or three months now without difficulty provided that we receive sufficient news items from readers. So don't forget to send us your news items soon! The digest is now being published by the INTERNATIONAL INSTITUTE OF ACOUSTICS AND VIBRATION (IIAV). The digest will be free of charge to members of the IIAV, but starting in 1997 there will be a moderate charge for non-members who wish to continue to receive the DIGEST. As explained in ITEM 2, the IIAV is a new democratic international scientific society and membership as member or associate is open to individuals from all countries. So far over 150 individual members have joined from 30 different countries. In addition 12 scientific societies have become affiliated with the IIAV. On behalf of Sir James Lighthill, of London, England, the first President of IIAV and the officers and directors, it is my pleasure to invite you to consider becoming a member if you are not already. Members, as part of their dues, will receive not only the DIGEST but also a refereed journal the INTERNATIONAL JOURNAL OF ACOUSTICS AND VIBRATION (IJAV) which will initially be published quarterly starting at the end of 1996. As the IIAV membership grows additional services will be provided for IIAV members. It is planned to make full use of all modern electronic means of communication to assist members in the future. Complete details about IIAV are given in ITEM 2. The first congress officially sponsored by IIAV was a great success. This was the Fourth International Congress on Sound and Vibration. It took place in the beautiful city of St. Petersburg, Russia, June 24-27, 1996. Not only did the congress have a strong technical program, but it had a varied and exciting cultural program. The book of proceedings is now available (see ITEM 4.) Plans are already well underway for the Fifth International Congress on Sound and Vibration. It will be held at the University of Adelaide, at Adelaide in South Australia, December, 15-18, 1997. The General Chairman is Professor Colin Hansen. He is planning an excellent technical program and we hope that you will put this date on your calendar and make plans to attend. We are sure that you will enjoy a genuine Australian welcome with great hospitality. We are pleased to inform you that back issues of the ISV Digest are available on the Auburn University Gopher (Academic Areas and Departments-College of Engineering-Department of Mechanical Engineering). We hope that you are finding the ISV DIGEST useful. We should be interested to hear your comments and to receive items for inclusion in the next issue. These should be sent to yanas@eng.auburn.edu. Malcolm J. Crocker Editor-in-Chief ***************************************************************************** ITEM2. NEW SCIENTIFIC SOCIETY (IIAV). ***************************************************************************** THE INTERNATIONAL INSTITUTE OF ACOUSTICS AND VIBRATION (IIAV) President: Sir James Lighthill,England; Vice Presidents: Hanno Heller, Germany and David Newland, England Executive Director: Malcolm Crocker, USA The International Institute of Acoustics and Vibration (IIAV) incorporated in June 1995, is a non-profit scientific society whose membership is open to qualified individuals in all countries. DIRECTORS: Duan-Shi Chen, China; Zbigniew Engel, Poland; Jean Guyader, France; Colin H. Hansen, Australia; Finn Jacobsen, Denmark; G. Krishnappa, Canada; Martin V. Lowson, England; Leonid M. Lyamshev, Russia; Antonio M. Mendez, Argentina; M. L. Munjal, In dia; Michael P. Norton, Australia; Mitsuo Ohta, Japan; Andrew F. Seybert, USA; and Jan W. Verheij, The Netherlands; PURPOSE The Institute shall advance the science of acoustics and vibration by creating an international scientific society that is responsive to the needs of scientists and engineers in all countries whose primary interests are in the fields of acoustic s and vibration. The Institute shall cooperate with scientific societies in all countries and with other international organizations with the aim of increasing information exchange by sponsoring, cosponsoring or supporting seminars, workshops, congresses and publishing or providing journals or other publications. The Institute will provide an electronic International Sound and Vibration Digest (ISVD) and before the end of 1996 a paper refereed journal will be published and provided for all members as par t of their dues. MEMBERSHIP There shall be six classifications of membership in the Institute including: Fellow, Member, Associate, Student Member, Emeritus Member, and Honorary Fellow. All memberships entitle a member to receive the publications of the Institute and to attend Institute meetings. Those entitled to vote at Institute meetings are restricted to Fellows, Members and Emeritus Members. Fellows, Members, Emeritus Members and Honorary Fellows are eligible to hold office. Membership as Member is open to all th ose who have at least a baccalaureate degree or its equivalent from an accredited institution and who are employed or have been employed in an activity related to acoustics and/or vibration. Membership as Associate is open to all persons who wish to supp ort and promote the activities of the Institute, but who do not meet the criteria for membership as Member. DUES The membership dues are $80 per year. Membership dues for those from some countries will be at a lower rate. Members will begin receiving the electronic ISVD immediately on joining the Institute and the journal before the end of 1996. OFFICERS AND DIRECTORS The officers of the Institute shall be the President, the President-Elect, the Immediate Past President, the Vice President for Professional Relations, the Vice President for Communications, the Secretary and Treasurer. The Presid ent, President-Elect and Immediate Past President shall hold office for two years. The other officers shall hold office for four years. The directors of the Institute shall hold office for four years. The officers and directors shall be elected by the members of the Institute. The first election shall be conducted after the total membership of the Institute exceeds 100 members. COOPERATING SCIENTIFIC SOCIETIES The Institute recognizes that many scientific societies with interests in acoustics and/or vibration exist in different countries. It is the purpose of the Institute to supplement their activities and to cooperate with t hem for the good of scientists and engineers throughout the world. To that end, existing scientific societies will be encouraged to become affiliated with the Institute as cooperating member societies. MEMBERSHIP APPLICATION FORM If you are interested in joining the IIAV, please fill in the form and return it by fax or e-mail (see following). Application for:: ( ) Member ( ) Associate 1) Name: _____________________________________ 2) Address: ___________________________________________________________ Fax: ____________________________ E-mail : ___________________________ 3) Degrees (Institutions and dates): ____________________________________________________________________________ 4) Employment (with dates ): _____________________________________________________________________________ 5) Signature & Date:____________________________________________________ 6) Payment Form: ( ) Check Please send in US dollars drawn on US bank. ( ) Bank Transfer Auburn National Bank - Auburn, AL USA, Tel: 334 821 9200 ABA Number 062202574 - Account Number 10308743 ( ) Credit Card (Visa or Master Card) Card Number _______________________________ Card Type & Expiration Date _______________________________ Please return this form to: Dr. Malcolm J. Crocker, Executive DirectorSecretariat Office IIAV Dept. Mech. Eng. 201 Ross Hall, Auburn University, AL 36849-5341, USA (Tel: 334-844-3310, FAX: 334-844-3306) e-mail: mcrocker@eng.auburn.edu ***************************************************************************** ITEM 3. FIFTH INTERNATIONAL CONGRESS ***************************************************************************** FIFTH INTERNATIONAL CONGRESS ON SOUND AND VIBRATION University of Adelaide Adelaide, South Australia AUSTRALIA General Chair: Colin H Hansen December 15-18, 1997 CONGRESS PROGRAMME The Congress programme will include keynote addresses, tutorials on specialized topics and invited and contributed papers in specialized areas of sound and vibration. The Fifth Congress follows previous congresses held in the USA, Canada and Russia in 1990, 1992, 1994 and 1996. Several hundred people attended each previous congress. KEYNOTE PAPERS The following keynote addresses will be presented in plenary sessions. "A century of shock wave dynamics" Sir James Lighthill, UK "Recent developments in Statistical Energy Analysis" Frank Fahy, UK "Helicopter rotor aeroacoustics" Hanno Heller, Germany "Recent developments in acoustics" Malcolm Crocker, USA "Vibration suppression through smart damping" Dan Inman, USA "Active control of structurally radiated sound" Chris Fuller, USA "Developments in digital analysis techniques for diagnostics of bearings and gears" Bob Randall, Australia "Hearing protectors: are they the cheapest and quickest solution?" Samir Gerges, Brazil CONTRIBUTED PAPERS covering theoretical and experimental research in the following areas are solicited: Active noise control Active vibration control Aeroacoustics Architectural acoustics Boundary element and finite element methods Condition monitoring and diagnostics Damping - passive and active Environmental/community noise Human response to sound and vibration Inverse methods Low frequency noise and vibration Machinery noise and vibration control Materials for noise and vibration control Measurement techniques Mechanisms of human hearing Modal analysis Musical acoustics Noise control elements Non-destructive testing Non-linear acoustics and vibration Numerical methods Occupational noise exposure and control Outdoor sound propagation Scattering of sound Signal processing Sound intensity Sound sources Sound transmission Statistical energy analysis Structural acoustics and vibration Structural intensity Transportation vibration and noise Underwater acoustics Vibration and shock Vibration sources Wavelet analysis SCIENTIFIC COMMITTEE (CHAIR: Malcolm J. Crocker) David Bies, Australia Simon Braun, Israel Norm Broner, Australia Marion Burgess, Australia Christian Carme, France Alan Cummings, UK Zbigniew Engel, Poland Frank Fahy, UK Neville Fletcher, Australia Chris Fuller, USA Samir Gerges, Brazil Barry Gibbs, UK Stewart Glegg, USA Richard Guy, Canada Uwe Hansen, USA Hanno Heller, Germany Ken Heron, UK Hugh Hunt, UK Dan Inman, USA Nickolay Ivanov, Russia Finn Jacobsen, Denmark Adrian Jones, Australia Richard Kohoutek, Australia Krish Krishnappa, Canada B. Andrew Kugler, USA Sen Kuo, USA Sir James Lighthill, UK Joseph Mathew, Australia Yasuo Mitani, Japan David Newland, UK Alexei Nikiforov, Russia Kam Ng, USA Michael Norton, Australia Mitsuo Ohta, Japan Jie Pan, Australia P.K. Raju, USA Yitshak Ram, Australia Bob Randall, Australia David Rennison, Australia Scott Snyder, Australia Scott Sommerfeldt, USA David Swanson, USA Nobuo Tanaka, Japan Osman Tokhi, UK Jan Verheij, Netherlands M. Wahab, Australia Hugh Williamson, Australia PUBLICATIONS Abstracts of contributed papers proposed for presentation at the Congress should be sent as soon as possible and must be received by the Congress Secretariat no later than March 15, 1997. The date for notification of acceptance of abstracts is May 15, 1997. Abstracts should be approximately 200 words in length. If the abstract is accepted, the paper must be typed on special manuscript sheets which will be supplied by the Congress Secretariat. The complete manuscript will be printed in the Congress Proceedings, and must be received no later than August 15, 1997. All written papers and lecture presentations will be in English. EXHIBITION Companies are invited to take part in the exhibition which will include instrumentation and electronics, acoustical apparatus and materials, sound and vibration isolation devices and software. Exhibition information and booth and table reservations are available from the Congress Secretariat. SOCIAL PROGRAM The University of Adelaide is located close to the entertainment centre of a city with over one million people. Adelaide is well known for its lack of traffic jams, cleanliness and clean air as well as for parks and gardens, pure beaches and natural wildlife parks. It is recognized as Australia's leader in high tech industry and is also close to the premier wine producing areas of Australia. Special, unique excursions and activities will be arranged for delegates before, during and after the Congress. LODGING Participants will be accommodated in a number of hotels within 15 minutes walk of the University. Accommodation costs will vary from $AUD30 per night for student style accommodation (shared facilities) to $AUD160 per double for a 5 star hotel. Details of accommodation and reduced congress rates will be circulated at a later date. All accommodation is a short drive (15 mins) from the International airport and is easily accessed by shuttle bus or taxi. FURTHER INFORMATION The Congress registration fee is $460 AUD for members of IIAV and $540 for others for registration prior to May 30, 1997. For registration between May 30, 1997 and November 10, 1997, the fees are $490 AUD for members of IIAV and $570 AUD for others. For registration after November 10, the fees are $570 AUD for members of IIAV and $650 AUD for others. The registration fee includes the book of proceedings, lunches a reception and an Australian BBQ in a natural wild-life park. Please make checks or bankdrafts payable in Australian dollars drawn on an Australian bank for the registration fee payable to 5th Congress and mail to the Congress Secretariat. Alternatively, payment may be made by VISA or MASTERCARD, if you quote your card number, expire date and provide a signature. Those desiring to participate in the Congress should fill out the reply form and send it back to the organizing committee. REPLY FORM (Please return to the Congress Secretariat) NAME____________________________________POSITION_____________________________ ADDRESS_______________________________________________________________________ ______________________________________________________________________________ TELEPHONE_________________FAX____________________E-Mail_______________________ I plan to attend the Congress 0 I would like further information 0 I intend to give a paper with the title of __________________________________ I enclose an abstract 0 (Abstracts due by March 15, 1997 at the latest) My company would like to exhibit a product at exhibition 0 _______________________________________________________________________________ Papers accepted for the Congress will require a written version in Book of Proceedings. Written papers following the typing instructions and not exceeding 8 finished pages should be submitted by August 15, 1997 to the Congress Secretariat. All correspondence should be sent to the Congress Secretariat: Congress Secretariat/ Colin H Hansen, General Chairman Fifth International Congress on Sound and Vibration Department of Mechanical Engineering, University of Adelaide TEL: +61-8-8303-5460 FAX: +61-8-8303-4367 E-mail: chansen@mecheng.adelaide.edu.au ***************************************************************************** ITEM 4. FOURTH INTERNATIONAL CONGRESS PROCEEDINGS NOW AVAILABLE. ***************************************************************************** The Fourth International Congress on Sound and Vibration sponsored by The International Institute of Acoustics and Vibration (IIAV) was held in St. Petersburg, Russia, June 24-27, 1996. Over 250 papers were presented on all aspects of acoustics and vibration by participants from 35 countries. The three volume book of proceedings is 2050 pages long and contains 316 papers. It is available from IIAV for $145 plus $25 airmail from IIAV, P.O. Box 13, Auburn, AL. 36831, USA. Please send total of US $170 drawn on a US bank to this address or send credit card number (VISA or Master Card) and expiration date by e-mail to yanas@eng.auburn.edu or fax to 334-844-3306. **************************************************************************** ITEM 5. THIRD INTERNATIONAL CONGRESS PROCEEDINGS STILL AVAILABLE ***************************************************************************** The Proceedings of the Third International Congress on Sound and Vibration held in Montreal, Canada, June 13-15, 1994 is still available. The Congress was attended by over 300 participants from 35 countries. The three volume book of proceedings contains 264 papers in its 2100 pages on all the modern theoretical and experimental topics currently under investigation by engineers and scientists with an interest in the technical aspects of acoustics and vibration. The proceedings is available for $135 US in the USA and $135 plus $40 airmail in other countries. Checks should be made in US dollars to International Scientific Publications and drawn on a US bank and mailed to ISP, Box 13, Auburn, AL 36831, USA, orders can also be sent by fax to 334-826-7149. Payment can also be made by credit card (visa or mastercard). Give card number, expiration date as it appears on the card. **************************************************************************** ITEM 6. 15TH ICA CONGRESS PROCEEDINGS ***************************************************************************** The Proceedings of the 15th International Congress on Acoustics is now available. The complete proceedings consists of four volumes with a total of 2400 pages. More than 500 papers are covering all aspects of acoustics. These papers represent the latest discoveries in their respective fields, and give the reader a unique opportunity to acquire information. The ICA Proceedings can be ordered by e-mail: or by fax: +47 73 59 14 12 or write to The Acoustical Society of Norway, DELAB, N-7034 Trondheim, NORWAY The price is NOK 1500 plus shipment (for the US: NOK 225/375 surface/air mail) (for Europe: NOK 175/225 surface/air mail) ********** Truls Gjestland SINTEF DELAB truls.gjestland@delab.sintef.no tel: +47 73 59 26 45 fax: +47 73 59 43 02 ***************************************************************************** ITEM 7. ISVR CONFERENCE ANNOUNCEMENT, Southampton, UK, 14-17 July 1997 ***************************************************************************** SIXTH INTERNATIONAL CONFERENCE ON RECENT ADVANCES IN STRUCTURAL DYNAMICS 14-17 JULY 1997 at The Institute of Sound and Vibration Research University of Southampton, England Papers are invited on any aspects of Structural Dynamics from any branch of engineering, but with the main emphasis being of the topics listed below. Two parallel sessions are planed in the following topic: analytical methods, numerical methods, dynamics of modern materials, condition monitoring and diagnostics, system identification and inverse problems, modal analysis and identification, passive vibration control, active vibration control and smart structures, nonlinear analysis, random vibration of nonlinear structures and optimization, vibro-acoustics, sonic fatigue, experimental techniques, vehicle dynamics and biomechanics. All paper presented at the conference will be published in book form, which will be available at the Conference. Two copies of abstracts of approximately 500 words should be submitted to: Dr. N.S. Ferguson ISVR, University of Southampton Southampton SO17 IBJ, UK or Fax +44 (0) 1703 593033 or E-mail: mzs@isvr.soton.ac.uk In addition to formal, presentation of papers, there will be a work-in-progress session (WIP) to provide a forum for presentation of ongoing work. Interested individuals should submit a 200 word summary by 31 March 1997. Those accepted should submit a 4 page description by 10 May 1997. The conference is being organized by the Institute of Sound and Vibration Research, Wright Laboratory, Wright-Patterson Air Force Base, OH and Old Dominion University, Norfolk, VA. Further information is available by contacting Howard Wolfe, (513) 255-5200 x456, Fax (513) 255-6684 or E-mail: howard@msmail.fibg.wpafb.af.mil or Chuck Mei, (804) 683-3733, Fax (804) 683-5344 or E-mail:chmei@aero.odu.edu. ***************************************************************************** ITEM 8. SPECIALIZED ASME CONGRESS SESSIONS, Nov. 17-22, 1996 ***************************************************************************** Technical sessions on Active Noise Control ASME International Mechanical Engineering Congress & Exposition (IMECE) The Active Noise control technical group of the NCAD is organizing sessions for the 1996 IMECE to be held in Atlanta on November 17-22, 1996. The theme for 96 IMECE meeting is "Systems Approach to Noise Control and Acoustics Developments". Papers are sought on all aspects of active noise control and in the technology/industrial areas of automotive/rail/ground transportation systems, aerospace/naval systems, and commercial systems (domestic and industrial). Authors should submit three copies of abstract to one of the organizers. Acceptance is based on a formal peer review of the full paper. All papers must conform to ASME journal standards and will be published in a bound volume. Organizers: 1) Gary H. Koopmann, Center for Acoustics and Vibration, 157 Hammond Building Penn State, University Park, PA 16802 Phone: 814 865 2761, FAX: 814 863 7222, email: ghk@kirkof.psu.edu 2) Koorosh Naghshineh, Western Michigan Univ/Dept of Mech & Aero Eng/ Kalamazoo, MI 49008 Phone: 616 387 3333, FAX: 616 387 3358, email: naghshineh@wmich.edu ***************************************************************************** ITEM 9. ACOUSTICS FAQ AVAILABLE ON WEB SITE ***************************************************************************** The Acoustics FAQ is now posted to the alt.sci.physics.acoustics Usenet group. It is also available from Michael Carley's Web Site at URL: http://www.mme.tcd.ie/~m.carley/Acoustics/faq.html The FAQ includes basic acoustics questions and answers, resource pointers and a list of national acoustical societies. Offers for further additions or ideas are welcomed. Andrew Silverman e-mail: Enviro@measure.demon.co.uk ***************************************************************************** ITEM 10. NOISE AND HEARING GROUP HOSTED BY NIOSH ***************************************************************************** A new listserver group has been established for researchers, acousticians, audiologists, industrial hygienists and safety professionals interested in the biological basis of noise effects on the ear. The group "noise_and_hearing" is hosted on the Centers for Disease Control and Prevention listserver. Dr. Rick Davis of the National Institute for Occupational Safety and Health is the list organizer. Discussion subjects include impact noise, hearing protector research and educational materials as well as many others. To become a subscriber send the following one line message: subscribe noise_and_hearing to the address list lists@list.cdc.gov. There is a digest available which condenses an entire days activity into one message. To the same address send the single line message: subscribe noise_and_hearing-digest The list is open to everyone having an interest in the effects of noise on the ear. -Rick Davis, Ph.D. Bioacoustics NIOSH From: Davis, Rickie R. ***************************************************************************** ITEM 11. READER QUESTION ***************************************************************************** For a demonstration in a course on electro acoustics I would like to simulate the development of the quality of sound recording. For that purpose I search specifications of typical sound recording devices of different ages (frequency response, dynamic range ...). If anybody has a hint I would be glad to get a message. Kurt Heutschi, Switzerland e-mail: kurt.heutschi@empa.ch Tel. CH - 01 823 47 43 ***************************************************************************** ITEM 12. RESEARCH ACTIVITIES AT GERMAN AEROSPACE RESEARCH ESTABLISHMENT DLR ***************************************************************************** THE GERMAN AEROSPACE RESEARCH ESTABLISHMENT DLR, BRAUNSCHWEIG RESEARCH CENTER UNDER CONTRACT TO AIRBUS INDUSTRIE CONDUCTS AEROACOUSTIC TESTS ON FULL-SCALE AIRBUS A320 FAMILY LANDING GEARS IN THE GERMAN DUTCH WIND TUNNEL (for further information contact DLR, Institut f|r Entwurfsaerodynamik, Abteilung Technische Akustik in D-38108 Braunschweig, Germany: by Fax Germany = +49 531 295 2320, or e-mail ieata@text6.ea.bs.dlr.de) Airframe noise during the landing approach of large commercial jet-engine propelled aeroplanes has long been suspected to be of the same order as the noise of throttled engines. Moreover several of the quiet, modern Jumbo-planes have difficulties in complying with approach noise limits as specified by ICAO in the ANNEX 16 (Vol. 1) Chapter 3 due to possibly excessive airframe noise. Deploying landing gears and/or flaps and slats could increase the flyover noise by up to 10 dB beyond that of the "clean configuration". Flyover noise tests where actual aircraft in a landing approach configuration had been used revealed the problem without however allowing the actual identification of the individual sources on landing gears and/or wing slat/flap configurations in sufficient detail. A modern landing gear, for example, exhibits a highly complex geometry. Any model-scale tests in wind tunnels, necessarily employing scaled models of landing gears, are at best capable of reproducing the major components - pylon, wheels, wheel-well - while necessarily neglecting any of the minor components which nevertheless could dominate the overall noise, especially if data are to be obtained in the noise certification measure EPNL. Previous aeroacoustic tests on small scale landing gear models seemed to indicate a broadband low frequency spectrum resulting from the very landing gear, while obviously not showing any noise in the mid-to-high frequency band. This was always suspected not to be the true picture. In December of 1995 the DLR Braunschweig (Institute of Design Aerodynamics, Technical Acoustics Division) under contract to Airbus Industrie conducted aeroacoustic tests on a FULL-SCALE and "real-life" landing gear of an Airbus 320 in the German Dutch Wind Tunnel (DNW). The overall sound measured turned out to be of the same order as that of some of the more quiet aeroengines. Moreover, a substantial amount of mid-frequency sound energy is radiated, being caused by the numerous smaller components on and near a real landing gear. Discrete-frequency tones were observed which were superimposed on the broadband spectrum, some of which changed their frequency in concert with speed, others maintained their frequency independent of the "flight"-speed, providing important hints on the underlying source mechanisms. Both 2-wheel and 4-wheel configurations were tested and several configurational changes were tried - such as providing aerodynamic shaping to certain structural components - to study the effects in detail and asses the potential for penetrating the "ultimate barrier", i.e. to try and reduce landing gear noise as such. Complementing these research efforts, additional tests are now planned where full scale sections of Airbus wings will be tested in the German Dutch Wind Tunnel (DNW). THE GERMAN AEROSPACE RESEARCH ESTABLISHMENT DLR, BRAUNSCHWEIG RESEARCH CENTER WITHIN A EUROPEAN UNION SPONSORED RESEARCH PROJECT LEADS EXPERIMENTS ON HELICOPTER ROTOR AEROACOUSTICS WITH TESTS IN THE GERMAN DUTCH WIND TUNNEL (for further information contact DLR, Institut f|r Entwurfsaerodynamik, Abteilung Technische Akustik in D-38108 Braunschweig, Germany by Fax Germany = +49 531 295 2320, or e-mail ieata@text6.ea.bs.dlr.de) Sponsored by the European Union in the framework of the IMT project HELISHAPE "Rotorcraft Aerodynamics and Aeroacoustics" a model rotor test in the 6 x 8 m open-jet test section was conducted in the period 17 - 30 August, 1995. The test objectives were (1) to evaluate noise reduction techniques conceptually and operationally and (2) to validate aerodynamic and acoustic codes developed or improved by the 16 EU-partners. A highly instrumented model rotor of 4.2 m dia. with modern airfoils and exchangeable tips (provided by Eurocopter France, ECF) was employed. Simultaneous aerodynamic blade surface pressure and acoustic measurements as well as Laser Light Sheet (LLS) flow visualization were conducted (jointly by DLR and DNW) within the 2 week test entry. Test partners in this project were Eurocopter Deutschland, Eurocopter France, ALFAPI (Greece) and DLR (which was responsible for test coordination and conduct). Some key results will be presented at the 22nd European Rotorcraft Forum in Brighton, UK, Sept. 17-19, 1996 (Paper No. 52). Participation in a follow-on research project again sponsored by the European Union, titled HELIFLOW (an acronym for Improved Experimental and Theoretical Tools for Helicopter Aeromechanic and Aeroacoustic Interactions) was awarded. DLR will be actively involved in two Tasks, namely "Sideward Flight" and "Tail Rotor Noise". THE GERMAN AEROSPACE RESEARCH ESTABLISHMENT DLR, BRAUNSCHWEIG RESEARCH CENTER STARTS A RESEARCH INITIATIVE ON CAVITY PRESSURE OSCILLATIONS (for further information contact DLR, Institut f|r Entwurfsaerodynamik, Abteilung Technische Akustik in D-38108 Braunschweig, Germany by Fax Germany = +49 531 295 2320, or e-mail ieata@text6.ea.bs.dlr.de) The renewed practical interest in reducing the intense pressure oscillations in deep and shallow cavities exposed to grazing external flow has recently led to a research initiative of the DLR. Transonic flow conditions are of particular interest because of the efficiency by which sound is generated in this regime. Visualization studies are being carried out, aiming at a more detailed understanding of the dynamics of the shear layer spanning the cavity as well as the cavity-internal pressure wave feed back in shallow cavities (first results, see JSV 1996, H. Heller, J. Delfs: Cavity Pressure Oscillations: The Generating Mechanism Visualized). Especially the quasiperiodic nature of the oscillations is investigated and its significant consequences with respect to active suppression techniques. It is intended to visualize the spatial structure of the most important first few oscillation modes. Based on these pre-studies an aerodynamically/ aeroacoustically improved passive control of the mean flow will be designed, as well as non-periodic strategies of active control. THE GERMAN AEROSPACE RESEARCH ESTABLISHMENT DLR, BRAUNSCHWEIG RESEARCH CENTER INVESTIGATES THE EFFECT OF NONUNIFORM PISTON-ENGINE ROTATIONAL SPEED ON GENERAL AVIATION PROPELLER NOISE RADIATION (for further information contact DLR, Institut f|r Entwurfsaerodynamik, Abteilung Technische Akustik in D-38108 Braunschweig, Germany by Fax Germany = +49 531 295 2320, or e-mail ieata@text6.ea.bs.dlr.de) Due to increasing public complaints about aircraft noise, General Aviation aeroplane noise certification limits are likely to become more stringent in the future. Many of today's light propeller-driven aeroplanes, however, will only be able to comply with such limits if either low noise propellers and/or efficient engine exhaust mufflers are installed. In response to this development, noise tests were performed by the DLR-Institute of Design Aerodynamics, Technical Acoustics Division, in the German-Dutch Wind Tunnel (DNW) on a full-scale propeller-driven aircraft with its 150 kW piston engine operating at different power conditions. The subsequent data-analysis revealed a strong effect on propeller noise radiation caused by the (typical) nonuniform rotational speed of the driving piston engine which had not yet been considered in any existing propeller noise prediction scheme. As a consequence of such periodic speed variations (within one revolution) unsteady aerodynamic propeller loads occur which in turn give rise to additional noise radiation. It turned out that a typical nonuniformity of about plus or minus 2% of the average rotational speed may enhance propeller noise levels by up to 6 dB (in terms of the overall A-weighted level) compared to those for strictly uniform operational conditions. Future noise reduction efforts must therefore account for this phenomenon since the related unsteady noise source mechanisms are most effective at low blade- tip speeds (i.e. for "low-noise" propellers in particular). Results have been presented at the INTER-NOISE 95 Conference, Newport Beach, USA, July 10-12, 1995, Proceedings pp. 195 - 198. Hanno Heller Head Technical Acoustics Division DLR Braunschweig, Germany ***************************************************************************** ITEM 13. NEW BOOKS AVAILABLE. ***************************************************************************** 1. SOUND INTENSITY: Second Edition by F.J. Fahy, ISBN 0-419-19810-5, E & F.N. Spon, London, 1995, 295 pages, 29.99 Britishpounds (US $51.50). This is an excellent book for all those concerned with sound intensity measurements. The material in the first 1989 edition has been reorganized, brought up to date and supplemented. The first edition's nine chapters have been extended to eleven in the second edition. The book begins with a brief introduction and then includes discussions of sound propagation: conservation of mass, the fluid momentum equation, wave equation, and sound radiation from vibrating surfaces. The discussion continues with material on sound energy, propagation of sound energy and sound intensity in plane waves and two and three-dimensions. Chapters five and six are devoted to principles of sound intensity measurement and sound intensity instrumentation and calibration. Errors are treated in the next chapter. The remaining chapters are devoted to determination of sound power using sound intensity and other applications including noise source localization, measurement of sound absorption, transmission loss (sound reduction index) of partitions, sound intensity in ducts, etc. The book contains 186 references to the many papers on sound intensity theory and applications in the literature. It is illustrated with a host of figures and other examples taken from the references. This book is written by a well known acoustician who is expert in the field. The treatment is masterly and since the book is available in paperback it can be obtained for only a moderate cost. It is a bargain for such a technical book. An extended review will appear in the next edition of the digest. 2. ACTIVE CONTROL OF VIBRATION by C.R. Fuller, S.J. Elliott and P.A. Nelson, ISBN 0-12-269440-6, Academic Press, London, 1996, 332 pages. US $75.00. This valuable book is a companion to the earlier 1992 book by Nelson and Elliott titled ACTIVE CONTROL OF SOUND also published by Academic Press. The present book has nine chapters together with five appendices. The book begins with an introduction to mechanical vibration and waves in structures and then continues with discussions on feedback and feedforward control. Chapters are included on the use of distributed transducers for active control of vibration and active control of vibration in structures and active vibration isolation. The book concludes with descriptions of active structural acoustic control in both plate and cylindrical structural systems. Although the book obviously strongly reflects the authors' varied and different research interests and backgrounds and is not completely comprehensive in its coverage of all topics, it is a valuable addition to the limited number of books in this important area. A more comprehensive review will appear in one of the next issues of the digest. 3. ACTIVE NOISE CONTROL SYSTEMS - Algorithms and DSP Implementations. by Sen Kuo and Dennis R. Morgan, ISBN 0-471-13424-4, Wiley-Interscience, New York, 1996, 389 pages plus software disk, US $74.95. This book contains nine chapters and nine appendices. In addition it has an accompanying software disk. Both digital system processing (DSP) hardware and adaptive signal processing algorithms are discussed in detail. The book begins with an introduction to active noise control (ANC) and continues with adaptive transversal filters. Then discussion is included on both broadband and narrowband feedforward ANC. Then multiple-channel and feedback ANC are described. The book concludes with discussions of on-line secondary-path modelling techniques, ANC structures and algorithms and ANC applications. A considerable number of ANC applications are covered including control of room-noise, exhaust noise control, ANC headsets, ANC in enclosures, free-field radiation control, beam and plate vibration, etc. This book will be very helpful to those who wish to understand better the practical aspects of ANC systems and the signal processing and DSP implementation needed. 4. PRINCIPLES OF VIBRATION by Benson H. Tongue, ISBN 0-19-510661-X, New York, 1996, 464 pages, US $65.00. This is a vibrations textbook in eight chapters with four appendices. The book includes a considerable amount of elegant mathematics and the author is obviously very competent and knowledgeable about his topic. Some readers will be surprised by the rather informal and conversational writing style. The book contains a considerable amount of useful practical information, particularly in Chapter 7 entitled "Seat of the Pants Engineering". The book includes problems at the end of each chapter and answers to selected problems at the end of the book. The book will be of use to students in the classroom, but will also be of interest to more mature students who desire a blend of the classical treatment of fundamental vibration theory together with well chosen discussions on approximate approaches and experimental methods. On the whole the informal, relaxed writing style succeeds and many students and other readers will find the book accessible and very useful. 5. SHOCK AND VIBRATION HANDBOOK Fourth Edition, Editor-in-chief Cyril M. Harris, ISBN 0-07-026920-3, McGraw-Hill, New York, 1996, 1484 pages,US $125. This book has 44 chapters and an index. Some chapters review basic theory and others more applied topics including measurement techniques, material properties, vibration measurement instrumentation, transducers, human response to shock and vibration, etc. Other chapters are a mixture of theory and experimental results or practical information. All the important fundamental steady state vibration topics are covered. Besides the more conventional vibration topics, non-linear vibration and transient response to step and pulse functions are discussed. Five chapters are devoted to shock excitation theory and practice. Important topics such as modal analysis, mechanical impedance and condition monitoring of machinery are included too. Surprisingly there does not seem to be a chapter devoted to the important new topic of active vibration control. The book is however truly encyclopedic in nature covering a large number of topics. Many of its authors are well known and considering the book's length and comprehensive nature, the price seems quite reasonable. I am sure that many engineers concerned with vibration problems will want to obtain a copy. It is planned soon to include extended reviews of all of the books featured in ITEM 13 of the ISV Digest in a later edition. Malcolm J. Crocker mcrocker@eng.auburn.edu ***************************************************************************** ITEM 14. BOOK ***************************************************************************** RECENT TRENDS IN HEARING RESEARCH. Festschrift for Seiichiro Namba. Edited by Hugo Fastl, Sonoko Kuwano and August Schick. Oldenburg: BIS-Verlag 1996, 402 pages, author index, subject index, biography and a select list of publications of Seiichiro Namba (Osaka University). Price: 20 US Dollar, 2000 Yen, 30 DM or equivalent currencies. Buyers from abroad: Please pay in bank-notes directly (enclosed in a letter); you will get a sales invoice. We want to avoid high bank charges. Kaeufer in Deutschland ueberweisen den Betrag auf das Konto von August Schick: Nr. 144 2982 300 bei der Oldenburgischen Landesbank, BLZ 280 200 50 (bitte vergessen Sie nicht Ihre Adresse). Order from: Prof. Dr. August Schick, Oldenburg University, Institute for Research into Man-Environment-Relations, P.O. Box 2503, 26111 Oldenburg, Germany Fax: +49-441-798-8261 (E-Mail: Schick@Psychologie.uni-oldenburg.de Contents 1. Noise quality (Seiichiro Namba) 2. Masking effects and loudness evaluation (Hugo Fastl) 3. Loudness adaptation (Bertram Scharf) 4. The detection of frequency modulation (Brian C.J. Moore and Aleksander Sek) 5. Short-term memory for pitch (Andrzej Rakowski) 6. Musical Communication (Edward Carterette and R.A. Kendall) 7. Some current trends in temporal processing (Mary Florentine and Soren Buus) 8. Continuous judgment of temporally varying sounds (Sonoko Kuwano) 9. Theory and method in perceptual evaluation of complex sound (Birgitta Berglund and R.F. Soames Job) 10. Noise annoyance research: Purpose and progress (Martin Taylor) 11. Noise exposure (Zheng Darui) 12. Cross-cultural psychoacoustics (August Schick and Holger Hoege) 13. Category-subdivision scaling - A powerful tool in audiometry and noise assessment (Juergen Hellbrueck) 14. Noise induced health hazards - With special regards to physiological noise susceptibility (Gerd Jansen) ***************************************************************************** ITEM15. CONFERENCE PROCEEDINGS: Psychoacousics: Sound Perception and Noise Effect ***************************************************************************** Members of the graduate college "Psychoacoustics: Sound Perception and Noise Effects" at the University of Oldenburg send you greetings. This is an interdisciplinary college where research groups from the fields of acoustics, medical physics, psychology a nd sociology are cooperating. In 1993, a conference on psychological acoustics was held in Oldenburg and we would like to offer the reader of this Digest the possibility to obtain the book of proceedings. The book is divided into 11 chapters, including fo r example - physiological processes and otoacoustic emissions (with papers from Glenis Long, Bertram Scharf and others) - temporal discrimination (e.g. Brian Moore, M.-C. Botte) - loudness perception and sound evaluation (Martin Taylor, S. Namba, Y. Suzuki) - Acoustical orientation (L. Rosenblum and others) - Noise and performance (Dylan Jones, St. Hygge, W. Schoenpflug) ... The price for the book is $20. Those interested in ordering the book, or in getting further information (abstracts), please send an e-mail to the following address: klatte @ psychologie.uni-oldenburg.de August Schick ***************************************************************************** ITEM 16. RESEARCH IN ACOUSTICS, DYNAMICS AND VIBRATION IN WESTERN AUSTRALIA ***************************************************************************** Centre for Acoustics, Dynamics and Vibration, University of Western Australia: A Centre for acoustics, dynamics and vibration is currently being set up at the University of Western Australia. The Director of the Centre is Professor M.P. Norton. The primary objectives of the Centre will be to actively undertake collaborative contract research with government and industry, to encourage postgraduate research in acoustics, dynamics and vibration by financing externally funded top up scholarships, to act as a focal point for the advancement of acoustics, dynamics and vibration in this re gion, to manage short courses and conferences, and to undertake collaborative research and teaching exchange with overseas affiliates. The Centre will comprise the following: University of Western Australia - Department of Mechanical and Materials Enginee ring, SVT- Engineering Consultants. Lynx Engineering, Worley Engineering & BHP Engineering. Management of the Centre will be undertaken through a Management Advisory Board which will comprise a Director and five other board members. The function of the Ma nagement Advisory Board is to oversee the management and funding of the Centre. Current Research within the Centre for Acoustics, Dynamics and Vibration, University of Western Australia 1. Unwrapped phase spectral analysis for wave propagation in gas piping systems R. Pederson & M.P. Norton Comparing the internal wall pressure fluctuation and pipe response measurements in industrial piping systems in the frequency domain involves the use of single input/single output linear systems with uncorrelated input and output noise. The unwrapped phas e spectrum has been identified as a means of extracting information about the propagation of hydrodynamic, acoustic and structural waves in piping systems. Propagation has been successfully identified from internal wall pressure fluctuation measurements o f flow downstream of an orifice plate under laboratory conditions and from response measurements of flow downstream of a sonic choke in an offshore gas flowline. 2. Fatigue of steels with non-zero mean loadings Y. Gong & M.P. Norton Modifications to existing mean load correction models are being developed. Steel specimens have been subjected to tension-compression type fatigue tests under strain/load control. Some of the combinations of amplitude and mean value are in the vicinity of yield point. Results indicate that the effects of mean value on fatigue life depend on the strain range concerned, say, for strain amplitudes in the elastic range, positive mean strains prolong fatigue life and negative mean strains shorten life. The cyc lic softening and mean stress relaxation/cycle dependent creep process, associated with material properties, have also been studied to understand the fatigue mechanism. Several models are proposed for life prediction under non zero mean strain and/or mean stress. 3. Laminar boundary layer receptivity to transverse structural vibration W.K. Chiu, J. Soria & M.P. Norton The development of stimulated Tollmien-Schlichting waves in a boundary layer as a result of forced leading edge vibration is discussed. Two major sets of experiments are reported on. A #stable case# is used to isolate the forcing function imposed by the v ibrating leading edge, and the development of the stimulated response of the Tollmien-Schlichting wave in the boundary layer due to leading edge vibration is investigated in the #unstable case#. The leading edge vibration is the only disturbance introduce d in the laminar boundary layer. The characteristics of the disturbance is such that the global plate vibration levels are at least 25 times less than the leading edge tip vibration. This leading edge vibration can be interpreted as the inhomogeneous boun dary conditions imposed on the fluid dynamic problem, and gives rise to an acoustic wave mode in the test duct. However, the oscillatory velocity field imposed by this acoustic wave mode is negligible compared to the oscillatory velocity field imposed by the leading edge vibration. The velocity oscillations imposed by the acoustic wave mode are not the cause of instability because the velocity profiles at x < 150 mm do not resemble a Stoke's shear wave. The experiments were performed with the stagnation p oint of the flow incident on the leading edge located slightly below the tip of the leading edge. No flow separation was observed. The experimental results were compared with a set of results obtained by Chiu and Norton where the stagnation point was loca ted slightly above the tip of the leading edge. The experimental results in the present case reveal that, prior to reaching branch I of the neutral stability curve, the boundary layer response to leading edge vibration is independent of the location of th e stagnation point of the flow incident on the leading edge. However, comparison of the stimulated response shows that the development of the Tollmien-Schlichting wave is drastically affected by the change in the location of the stagnation point from a po sition slightly above the tip of the leading edge to that slightly below the tip of the leading edge. This can be attributed to the upstream movement of the region of adverse pressure gradient when the stagnation point is moved from a position above the t ip of the leading edge to that slightly below it. 4. Dynamic stress/strain and vibration velocity correlations D. Karczub & M.P. Norton The work is concerned with the conversion of vibrational velocity levels (measured or predicted) to dynamic stress or dynamic strain levels for fatigue analysis, and the development of new methods for determining dynamic stress from vibration measurements . These new methods use multi transducer techniques similar to those used for structural intensity measurements. A theoretical approach to the analysis of dynamic stress and velocity in structures is also developed which involves separating the propagatin g and evanescent wave components of the response. The purpose of this approach is to concentrate on the underlying physical facets which determine narrow-band and broad-band spatial distributions of dynamic stress and velocity, and hence identify the unde rlying physics of relationships between dynamic stress and vibration velocity. The results demonstrate far field correlations between dynamic strain and velocity, the effect of evanescent waves on far field correlations in near field regions, narrow band and broad band spatial distributions of dynamic strain and predicted dynamic strain, spectral predictions of maximum dynamic strain using spatially distributed measurements of velocity, and crest factors for dynamic strain and velocity. The structures con sidered are a clamped beam, a simply supported beam, a cantilevered beam, a simply-supported beam with a point constraint, a clamped rectangular plate, a free field cylindrical shell with an annular ring (simulating the mass and inertia of a flanged joint ) half way along its length, and a three dimensional piping network system. The accuracy of the predictions suggest that measurements of vibrational velocity can be used for conservative predictions of maximum dynamic stress. They also show that the veloc ity measurements are as effective as strain gauges for the measurement of maximum dynamic strain in frequency bands due to the difficulties associated with the selection of correct locations for installation of strain gauges. Additionally, the use of velo city measurements avoids the need to install permanent strain gauges at a number of cross sections. 5. Acoustic behavior of enclosures with modally reactive boundaries K. Sum and J. Pan Effect of lightweight and modally reactive walls on the sound pressure response and reverberation time in rooms is investigated in the medium frequency range. The modal coupling method is used to predict the magnitude and phase response of the sound fiel d in a coupled panel/cavity system at the medium frequencies. Preliminary results of the characteristics in the response of the medium frequency sound field and the effect of acoustical/structural coupling on the characteristics are obtained. 6. Band-limited power flow in coupled structures N. Farag, N. Kessissloglou and J. Pan The prediction of the dynamic response and vibrational power flow in general 3-dimensional coupled beam and plate structures is the concern of this project. At the arbitrary loading conditions, all wave types may be excited simultaneously in the structur e. The interaction of different wave types at the coupling boundaries is therefore expected. Suitable for the low and medium frequency range, the receptance method is developed which allows the prediction of the detailed structural response and power flo w components carried by the different wave types through the joint boundaries and at any cross section of the beam and plate structure. 7. Active Noise and Vibration Control: Active noise control in enclosures (J. Pan), active noise barriers (J. Pan), active control of structural wave transmission through ribs (J. Pan), mechanisms and active control of nonlinear structural vibration (J. Pan); active noise control headsets (J.P an & M.P. Norton) Associate Professor M.P. Norton Department of Mechanical & Materials Engineering University of Western Australia Nedlands 6009 WA mpn@mech.uwa.edu.au or nortonuwa@eworld.com ***************************************************************************** ITEM 17. ***************************************************************************** CENTER OF EXCELLENCE FOR TECHNICAL ACOUSTICS AT THE INDIAN INSTITUTE OF SCIENCE M L MUNJAL With increasing industrialization and consequent urbanization, the environment is getting more and more noisy. While machinery noise affects the industrial workers only, automotive noise affects everybody - drivers, passengers, passers-by and the neighborhood. Of late, globalization of industries in India has thrown up another problem. Automobiles, earth moving equipment and machine tools, etc. cannot be sold abroad, particularly to the western countries, primarily because these do not satisfy the ambient noise limits prescribed in those countries. Even in India, public awareness about the harmful effects of excessive noise exposure has been increasing. It is being increasingly recognized that noise is not only a nuisance but also is often a measure of wasted energy, or an indication of a badly designed/fabricated/maintained machine, or a symptom of a malfunction. Central Pollution Control Board of the Department of Environment has gazetted limits on noise exposure of industrial workers, noise radiation by new and old automobiles, etc. Ministry of Environment and Forests has included noise in the environmental impact analysis required for new industries. For the last 25 years, Prof. Munjal has been providing consultancy for automotive and industrial noise control. Obviously, a handful of consultants like him cannot serve the entire country of India's size. Moreover, the most cost effective way for noise control is to control it at the source, or better still, to design for quietness. Design engineers need to be taught how to design for quietness through continuing education courses. Quieter Technologies need to be adopted where available and developed where necessary. Appreciating this need, Department of Science and Technology of the Government of India identified Technical Acoustics as one of the important emerging areas and decided to set up a "Center of Excellence for Technical Acoustics" (CETA) here at the Indian Institute of Science with Prof. Munjal as the resource person. This center is deemed as a constituent of Department of Mechanical Engineering of the Institute at this stage. If and when it develops to its full size, it may be separated from the department and located in a separate building as an independent entity. The primary objectives of CETA includes: a. Dissemination of knowledge about quieter technologies to different sections of industry by means of short courses; b. Development of Quieter Technologies where necessary; c. Acting as a clearing house for all problems about noise pollution referred to it by the Central Pollution Control Board and or State Pollution Control Boards in India; d. Developing a course on designing for quietness for the engineering undergraduates; e. Offering consultancy services for control of noise from existing machines or industries; f. Creating public awareness about development of quieter socio-religious living habits; and g. Collaborating with similar centers/institutions abroad through exchange visits for development of quieter technologies. Center of Excellence for Technical Acoustics will get all infrastructure funding from the Department of Science and Technology. However, it is supposed to earn most of its working expenses from industrial consultancy. This is the first Center or Institute of this kind in India and indeed in South Asia. ***************************************************************************** ITEM 18. TECHNICAL PAPER ON ACTIVE CONTROL ***************************************************************************** RESEARCH INTO PNEUMATIC ACTIVE VIBRATION CONTROL IN SLOVAKIA PAST AND PRESENT George Juraj STEIN, Igor BALLO Institute of Materials and Machine Mechanics SLOVAK ACADEMY OF SCIENCES Racianska 75 ; P. O. Box. 95 SK-830 08 Bratislava, SLOVAK REPUBLIC tel.: +427-378 2965, fax.:+427-372 909 e-mail (INTERNET): ummsste@savba.savba.sk 1. INTRODUCTION This paper deals with the research into electro-pneumatic 1 DOF active vibration control system based on the combined effect of the feed forward (compensation) and feed back ("sky-hook") principles. This topic follows closely the research of an electro-hydraulic system, described previously [1]. It is based on theoretical and simulational results of Dr. Marian GAJARSKY, former with this Institute [7,8]. Some results related to proposed use as a driver's seat for earth moving machines are given. These research activities date back into early eighties and are being still pursued. The results are covered to some extent by former Czechoslovak Patents. 2. THEORETICAL CONSIDERATIONS In his Ph.D. thesis Dr. GAJARSKY considered a 1 DOF oscillatory system with an air spring. He discussed the influence of properties of the air spring on the air spring elongation. He discussed the air flow through an orifice and showed that when the absolute pressure before the orifice is approx. twice as much as the absolute pressure behind the orifice the fluid flow through the orifice is supercritical and linear relation between the orifice cross-section area and the mass fluid flow holds. If the orifice cross-section could be proportionally controlled by an electric signal (voltage) in an electro- pneumatic proportional fluid flow transducer the inflow and outflow of the fluid into and from the air spring could be controlled in proportional manner. Further he applied the state equation of the ideal gas to the mass of air enclosed in the air spring and derived relation between the changes of this air mass, the changes in air spring internal absolute pressure and the dynamic force exerted by the air spring as an actuator of the active vibration control system. From these equations emerged the description of an electronic controller, facilitating active vibration control and taking into account various dynamic behaviour of the electro-pneumatic proportional transducer. Theoretical considerations and both analogue and digital simulations have shown that a positive vibration control effect could be achieved. These encouraging theoretical results were summarized in [7] and later in abridged form in [4,8,10]. Following an experimental investigation was started, despite some doubts about the validity of the quasi-static theory applied for this dynamic case (i.e. the use of simplified formulas for fluid flow, validity of closed system equilibrium thermodynamic laws applied to a thermodynamically "open" system, etc.). 3. EXPERIMENTAL INVESTIGATION - FIRST STAGE An existing dummy driver's seat system with a scissors type mechanism hydraulic damper and an air spring tested at the Institute's vibration simulator [4,10] was employed. The pneumatic system of the dummy seat was pneumatically "opened" i.e. a three-port proportional electro-pneumatic transducer was pneumatically linked to the air spring. The inlet port was connected to the reservoir of a compressor, the outlet port was connected to the air spring and the exhaust port via an exhaust silencer to the free atmosphere. The main concern at that time was the uncertainty whether the transducer would be fast enough to handle the required air flows into the air spring and out into the atmosphere. Measurements were undertaken with the scissors type mechanism fixed and the relation between the sinusoidal control voltage driving via a voltage to current converter the transducer coil and dynamic changes of the air pressure in the air spring of constant elongation. A nearly linear, frequency proportional relation in the frequency band of interest (1. to 6. Hz) was measured, validating the theoretical prerequisites and encouraging further experiments. The design of a linear controller, based on the theoretical considerations previously derived, was initialized. An analogue computer was used and the frequency domain approach was applied. After some elaboration a suitable controller structure was designed, the parameters were optimized by a trial and error approach, as the fluid flow properties of the transducer and the pneumatic part of the system could not be measured by available instruments. The seat dummy was subjected to vertical vibration excitation. Tests with sweeped harmonic excitation and narrow band random excitation were undertaken. The first stage experimental results showed that by suitable controller "tuning" the vibration control at a given frequency was nearly perfect, as the theory suggested [2,4,7,10]. The active compensation system worked as a narrow-band band stop filter. When the vibration control properties were evaluated according to standardized procedure of the ISO 7096:82 Standard a one and half improvement in the vibration control (by 3.5 dB) was attained. At that stage this result was deemed to be not good enough to justify the use of such a complicated and energy-consuming vibration control system. 4. SECOND STAGE RESULTS After some analysis of the first stage experimental results [3,5,9] modification of the active vibration control system was undertaken: 1. The hydraulic damper was disposed of. It was found, that due to bad installation of the hydraulic damper it had adverse effects on the system's performance and in fact was of no much use. 2. Instead a "sky-hook" damper was employed, i.e. a feed back loop was used [11-13]. An accelerometer was mounted onto the seat cushion and the amplified sensor's output signal was connected to one input of the linear electronic controller. 3. A correcting network was included into the controller to compensate for the dynamic properties of the combination of the electro-pneumatic transducer and the air spring. 4. Based on the controller set up on the analogue computer a new controller made of standard electronic components (op amps. and passive components) was built. At this stage it was not considered as necessary to pay much attention to a digital controller, based e.g. on a DSP, as the problem could be solved by an analogue controller as well. The active vibration control system was predetermined for use in situations in which a random excitation was stipulated, hence a satisfactory behaviour under harmonic excitation was not deemed as sufficient. Extensive tests with stationary random vibration excitation were performed. The power spectral density (PSD) of the vertical vibration acceleration used had a prescribed form, as given by the ISO 7096:82 Standard [14]. This Standard defines the prerequisites and procedure for laboratory tests and evaluation of vibration control properties of driver's seat for earth moving machinery under simulated working conditions in a reproducible manner. The crucial variable is the so called "corrected weighted rms value of the vertical acceleration at the seated driver - a*" determined by a prescribed procedure The Standard also incorporates limit values on seat characteristics, which enable to discriminate between driver's seats with good vibration control properties and the poor one. It seems that vibration control in earth moving machines is of great concern as prolonged exposure to excessive vibrations may impair irreversible health risk to the earth machine driver as described in various epidemiological studies. This was also the motivation behind this work. Results of seat evaluation according to the ISO 7096:82 Standard [14] : (2nd class - tractor-scraper, 3rd class - wheeled tractor or loader. In both cases M = 75 kg, excitation as specified by the Standard; t...exposure time according to the ISO 2631-1:85 Standard - fatigue decreased proficiency boundary @ 2 Hz [15]) 5. CONCLUSION The results of this study show that the vibration control improvement due to introduction of the compensation (feed-forward) loop is approx. THREEFOLD (approx. 10 dB) in comparison with good passive driver's seat. Hence the uninterrupted exposure time t for the seated driver could be considerably increased, without impairing a health risk due to the exposure to excessive vibration. Hence the machine could be used without health risk to the driver for an uninterrupted whole working shift. Also the operation speed of the machine or vehicle could be increased to facilitate better utilization of the expensive machine. An important question is the energy consumption. As derived in [6] the energy consumption of a parallel pneumatic system is mainly due to the need to maintain the required pressure drop between the source of compressed air and the free atmosphere to guarantee super-critical fluid flow in the proportional electro-pneumatic transducer.A compressed air source with absolute pressure of 9 bar was used. An indirect method for estimating the average energy consumption was used, based on the average energy demand of the compressor, without taking efficiency and losses into account. For a simulated driver's mass of M = 75 kg and vibration excitation of approx. 90 % of that prescribed for the second machine class the estimated value was 960 W, 70 W of which was contributed by the compensation control part. This is in fair agreement with the theoretical value of 677 W [6,9], in view of errors introduced by the approximative method used. The research on this topic is still in progress. It is hoped to report on further results in the future. Note: Only relevant English papers and selected papers in the native Slovak language are quoted: [1] Stein, G., J., Ballo, I.; 1995 RESEARCH INTO ACTIVE VIBRATION CONTROL IN SLOVAKIA PAST AND PRESENT. In this Journal. Vol. 1. No. 4. May 5th 1995, [2] Ballo, I.; 1988 PARALLEL ACTIVE VIBRATION CONTROL SYSTEM. Noise Control Conference. Krakow, Poland, Sept. 5-7, 1988. Proceedings: Vol.1, p. 31-39. [3] Ballo, I. - Gajarsky, M. - Stein, J.; 1992 ACTIVE ELECTRO-PNEUMATIC VIBRATION CONTROL SYSTEM FOR DRIVER'S SEAT. Sixth International Conference on the Theory of Machines and Mechanisms. Liberec, Czechoslovakia, Sept. 1992, Proceedings Vol. B., pp. 11-16. [4] Ballo, I. - Stein, G. J. - Gajarsky, M.; 1992 ELECTRO-PNEUMATIC ACTIVE VIBRATION CONTROL SYSTEM FOR DRIVER'S SEAT OF EARTH MOVING VEHICLES. Noise Control Conference, Krakow, Poland, Sept. 1992, Proc. pp.15-18. [5] Ballo, I.; 1993 ACTIVE VIBRATION CONTROL SYSTEMS FOR DRIVER'S SEAT OF EARTH MOVING VEHICLES. Archives of Acoustics 18, (1993), No.2.,pp.183-195. [6] Ballo, I. POWER REQUIREMENT OF ACTIVE VIBRATION CONTROL SYSTEMS. To be published in Vehicle System Dynamics. [7] Gajarsky, M.; 1984 SOME PROPERTIES OF AN ACTIVE ELECTROPNEUMATIC VIBRATION CONTROL SYSTEM. (In Slovak) Strojnicky casopis 35 (1984), No. 1-2, pp.51-65. [8] Gajarsky, M.; 1984 COMPENSATION ELECTRO-PNEUMATIC ACTIVE VIBRATION CONTROL SYSTEM. (In Slovak). Fourth Conference on the Theory of Machines and Mechanisms. Liberec, Czechoslovakia, Sept. 1984, Proceedings, pp. 1/15-9/15. [9] Ryba, D. - Marsh, C. - Ballo, I.; 1993 HARDWARE INFLUENCES ON CONTROL ALGORITHMS FOR ADVANCED SUSPENSION. Proc. of 13th IAVSD Symposium, Cheng Du, China, August 1993, pp. 411-424. [10] Stein, G. J. - Ballo, I. - Gajarsky, M.; 1992 ACTIVE VIBRATION CONTROL SYSTEM FOR THE DRIVER'S SEAT. 25th ISATA Silver Jubilee Conference. Florence, Italy, June 1992, Dedicated Conference on Mechatronics. Proceedings pp.183-190. [11] Stein, G., J. - Ballo, I.; 1994 AKTIVER PNEUMATISCHER SCHWINGUNGSSCHUTZSYSTEM FUER FAHRERSITZE. Congress DAGA'94, Dresden, Germany, March 1994, Preprints pp. 541-544. [12] Stein, G., J.; 1994 LABORATORY EXPERIENCE WITH DRIVER'S SEAT WITH AN ACTIVE VIBRATION CONTROL SYSTEM. Colloquium on Machine Dynamics'94. Prague, Czech Republic, April 1994, Proc. pp. 81-84. [13] Stein, G., J.; 1995 SOME RESULTS OF SIMULATION OF AN ACTIVE VIBRATION CONTROL SYSTEM. Colloquium on Machine Dynamics'95. Prague, Czech Republic, February 1995, Proc. pp. 1851-190. [14] ISO 7096:82, Earth moving machinery - Operator seat - Transmitted vibration. First edition 1982-02-15. [15] ISO 2631/1:85, Evaluation of human exposure to whole body vibration - Part 1: General requirements. First edition 1985-05-15. --- Stefan Markus, Assoc.Prof., M.Sc. (Eng), D.Sc. INSTITUTE OF MATERIALS AND MACHINE MECHANICS Phone: (+42 7)254751 SLOVAK ACADEMY OF SCIENCES, Racianska 75, P.O.BOX 95 Fax: (+42 7) 253301 830 08 Bratislava 38, Slovak Republic E-mail INTERNET:markus@umms.savba.sk ***************************************************************************** ITEM 19. TECHNICAL PAPER ***************************************************************************** ANDERSON LOCALIZATION AND QUANTUM CHAOS IN ACOUSTICS D.SORNETTE Laboratoire de Physique de la Matire Condensee, CNRS URA 190 Universite de Nice-Sophia Antipolis, Parc Valrose, B.P. 71, 06108 NICE Cedex 2, France (email: sornette@naxos.unice.fr) Abstract : Examples of our recent interdisciplinary research on acoustic wave propagation using concepts and tools borrowed from the fields of Anderson localization and quantum chaos are reviewed. The common Ariane thread of these works is the study of the effect of interferences between wavelets following complex paths. The complex paths come about from either the multiple scattering events in disordered systems or from multiple reflections off the walls of cavities. We discuss experimental results on surface acoustic waves propagating on rough surfaces, which exhibit Bragg resonant enhanced localization at the band edges. A new theoretical/numerical model, coined the Wave Automaton, devised to calculate the wave propagation in the time domain, is introduced and used to show new results on the time-dependent properties of wave propagation in the multiple-scattering regime and will also allow us to test a new non-destructive evalution scheme in this regime, which demonstrates the possibility to detect and identity the position of new defects in a multiple scattering medium. We also mention the possibility of using a random medium with saturable gain to create a laser. In a second part, we present some results of our endeavor to develop a theory of high frequency vibrations of structures, a field which is very important for engineering applications and is plagued by the absence of a reliable theory. Among other results, we mention a full wave theory of room acoustics in the high frequency regime (or more generally of acoustic waves in cavities), based on semi-classical expansions a la Van Vleck, allowing to explain Sabine's law as well as the time-dependent response of a given enclosure. 1-Waves in random media Three regimes of transport characterize waves in random media [1] : 1) at scales below the mean free path, the transport of wave energy is propagative (i.e. ballistic) with non-zero effective phase and group velocities; 2) at scales larger than the mean free path, the transport of wave energy is diffusing, with a zero average velocity and a characteristic effective diffusion coefficient. This is the regime of radiation transfer in stellar atmosphere or that of light in milk or that of high frequency ultrasonic waves in composite systems and austenitic steel for instance; 3) for sufficiently large disorder (technically when the Ioffe-Regel criterion is reached, namely when the mean free path becomes so small as to be comparable to the wavelength), there appears a new characteristic scale, the localization length, beyond which the wave does not expand anymore and is trapped as in an effective cavity [2] created by the coherent interferences between multiply scattered wavelets in the random system. 1.1 Band-edge localization and spatial textures of surface acoustic waves in weakly disordered surface acoustic wave superlattices. The extreme sensitivity of wave propagation on the presence of disorder near remnant geometric Bragg resonances (band edges) has been exhibited experimentally using surface acoustic waves on very weakly corrugated solids with thousands of grooves etched at their surface [3]. Anderson localization is identified by measuring the spatial structure of proper modes with an optical diffraction experiment (Raman-Nath effect) and is found to occur most strongly precisely at the two borders of a remnant stop-band. Exponentially decaying localized modes are decorated by a speckle-like wave pattern, which constitutes an observable fingerprint of the random system. The amplitude of this spatial wave structure is found to exhibit a marked maximum at band-edges thus providing a novel signature of localization, which is used to probe localization in the interior of the remnant stop-bands. Related experiments on surface acoustic waves and their theoretical analysis have been reported previously [4-7]. 1.2 The "wave automaton" (WA). The WA model [8] is a lattice model of wave propagation in arbitrary media of any dimension in the time domain. It is efficient for calculations on large systems (1024 by 1024) over long times (several 106 inverse band widths). Instead of starting from a wave equation or a hamiltonian which needs to be discretized for numerical implementation, the model is defined by the set of S-matrices (in the time domain), one for each node, describing the interaction of the wave field with the scatterers (modeled by the S-matrix at each node). Similarly to a cellular automaton, local rules thus control the dynamical propagation of the waves which exactly obey an unitarity condition, thus conserving the norm of the wave function and the energy at all times. Note however that the word "automaton" may be misleading because the wave is characterized by a local flux amplitude which takes complex values, corresponding to an amplitude and a phase, and not just discrete values. A remarkable property of the WA is that the structure of the S-matrices is determined solely from general symmetry consideration (time-reversal invariance and conservation of energy at the nodes of the lattice). These conditions allow one to get a complete classification of both the different types of waves that are compatible with given symmetries and of the different media that are compatible with a given discretized lattice structure. Remarkably, we have shown that different wave equations, like the hyperbolic wave equation, the Klein-Gordon equation, the Schrdinger equation [9], the Dirac equation [10], etc, are all particular realizations of the WA occurring for special values of the parameters coding the S-matrices. The exposition of the general method of construction of the S-matrices is done in [11]. We have calculated the properties of the WA for a class of parameters in the periodic case (same S-matrix on all nodes) and have exhibited the form of the Bloch modes, the dispersion relation and the modal density. We have carried a detailed study of the time-dependent transport of wave packets in 2D-random systems. The scattering of a Bloch wave in a periodic system by a single impurity (modeled by a different S-matrix on a single node) has been obtained analytically, which allowed us to derive the elastic mean free time and mean free length as a function of the model parameters and the frequency. Many results have been obtained on wave packets in random media (obtained by taking different S-matrices for each node), using extensive numerical simulations on a parallel computer. We have particularly studied the different regimes (ballistic, diffusive, localized) which appear as the wave packets spread over the random media and have compared these numerical results with weak localization predictions. In particular, we have discovered that the diffusion regime of wave transport in 2D beyond the mean free path is in fact a sub-diffusion [13], characterized by the radius of gyration of the expanding wave packet which grows as R ~ tn, with the exposent n<1/2 decreasing continuously as the disorder increases (i.e. mean free path decreases). The dependence of the exponent as a function of disorder has been explained by analytical calculations using weak localization techniques. This sub-diffusion can be understood in two ways : 1) from weak localization in 2D which essentially recognizes the existence of coherent interferences between arbitrarily complex wave paths when propagated forward and backward; 2) from the geometrical fractal structure of localized eigenmodes in 2D. 1.3 Non-destructive evaluations using ultrasonic waves in multiple-scattering heterogeneous media. We address the question of the identification of a new defect (a damage crack for instance) in a composite medium or a polycrystalline system. Standard ultrasonic non-destructive testing techniques rely on the measurement of the wave which is singly reflected by the scatterer. However, suppose that the medium is highly heterogeneous. In order to minimize the background reflections from the surrounding heterogeneities, low frequencies are used, which lead however to a severe loss of spatial resolution. Here, we report on a technique relying on state-of-the-art analytical calculations, which allows one to identify a new scatterer of the same scattering strength as the typical heterogeneities of the medium, in the large frequency regime, with a resolution of the order of the mean free path of the ultrasonic wave in the scattering medium. The technique consists in measuring the transmission or reflection speckle patterns at different frequencies before and after the introduction of the defect. Then, the average of the square of the difference of the speckle patterns before and after the introduction of the new defect over several tens of frequencies can be shown to be related to the space derivative of the Green function of the diffusion equation with a point source located at the position of the new defect [14,15]. A fit between the theoretical prediction obtained by solving the diffusion equation and the experimentally obtained averaged speckle patterns allows one in principle to retrieve the position of the defect. We have tested this theory by performing extensive numerical simulations with the "wave automaton" in a 2D system of size 256 by 512, a mean free path of 10 and a new scatterer added on one node at different positions inside the system. The positions retrieved from the proposed scheme are in remarkable agreement with their actual values [15]. Potential applications of our approach can be found in medical and industrial imaging in highly scattering systems. We can thus conclude that it is possible to "see" new defects through apparently completely opaque systems using the intrinsic coherent nature of the wave field in random systems! 1.4 Random distributed feedback tunable laser A laser needs two ingredients : 1) a gain so as to amplify pre-existing wave background and 2) a cavity to provide a feedback of the amplified photons which are returned to the amplified medium. Here, we report on the numerical test of the idea proposed a few years ago [16] that Anderson wave localization in a random media can lead to the existence of effective cavities (the localized eigenmodes) which are suitable for the laser feedback. Using the "wave automaton", we have constructed a weakly lossy disordered medium with disorder, presenting in addition a weak saturable gain on a single node of the lattice. Numerical simulations have shown that, starting from an initial white spectrum for the weak background wave noise, coherent amplification of a single frequency occurs, ultimately leading to the existence of a single frequency in the spectrum at large time, hence the demonstration of the laser effect in a disordered system. The "cavity" comes from the Anderson localization effect, as can be verified from the fact that the spatial distribution of the wave energy corresponding to the selected frequency turns out to be precisely one of the linear modes of the disordered medium (in absence of gain) which has the strongest overlap with the node on which the gain is applied. By sweeping the position of the node on which the gain is applied, various different frequencies are selected (in fact as many as the number of nodes) with varying spatial structures, thus leading to the concept of a random distributed feedback tunable laser [17]. In a sense, this result illustrates that a random medium acts similarly to the superposition of many different periodic systems. Similar ideas should be relevant to create coherent phonon sources from heterogeneous media. 2- Acoustic waves and quantum chaos. In 1989, we proposed to use the analogy between the problems of the field loosely called "quantum chaos" and those encountered in high frequency vibrations [18,19] to develop new methods of analysis and new techniques of calculations in this last field. The high frequency (HF) regime is defined as the regime where the wavelength of the wave of interest is small compared to the characteristic size of the structure. As a consequence, many modes participate in the response function of a system in the HF regime. Apart from rough approximations as in the Statistical Energy Analysis approach, there are essentially no theory to tackle this domain. In engineering applications, the HF regime is often encountered and pose formidable problems that are rarely satisfactorily addressed. The analogy and the ensuing techniques described briefly below have been developed in an attempt to improve on this state of affairs. 2.1 Spectral properties The basic question is to quantify the amount of information contained in complex spectra. In contradistinction with common wisdom, we have shown that a lot of information can be extracted beyond the smooth density of state approximation, in particular in the fluctuations of the density of state around its smooth average. In order to illustrate the method, we have examined two different systems : 1) a 3D elastodynamic experiment on aluminium blocks [20] and 2) numerical computations of the vibrations of 2D thin plates [21]. The measured spectra are analyzed with techniques borrowed from the theory of random matrices. The main conclusion is that fluctuations of the spectrum on small scales (involving a few mean eigenfrequency spacings) are well described by the model of Gaussian Orthogonal Ensemble (GOE) of random matrices. In addition, we show that the large scale oscillations of the spectrum (large frequency differences) are due to short periodic orbits (i.e. rays following trajectories that close on themselves) in the corresponding "classical" system (obtained by taking the "eikonal" limit of infinite frequency) and thus yield informations on the size and shape of the aluminium blocks! The influence of the classical ray trajectories is also felt on the eigenmodes of vibrations. It can be shown that some of them present a partial localization of the spatial vibration amplitude pattern ("scar") in the neighborhood of periodic orbits followed by geometrical rays. This result is important for the multipolar nature and the acoustic radiation efficiency of the structure [22]. An efficient and reliable numerical scheme has been developed to compute the acoustic radiation directivity and the total acoustic power radiated by isolated eigenmodes and by finite bandwidth excitations of a membrane of arbitray shape over the whole frequency domain [22]. Results have been obtained for the case of a membrane having the shape of a stadium. This stadium shape, while being simple enough, is in fact representative of the generic properties of complex structures presenting chaotic ray trajectories. The radiation directivity is given by the Fourier transform of the vibration amplitude distribution on the membrane and localization in emission directivty is thus simply controlled by the "scars" of eigenmodes made by resonance on periodic ray orbits. The dependence of the radiation efficiency as a function of the ratio cM/c of the membrane wave velocity cM over the air sound speed c and its important fluctuations from mode to mode has been explained by the theory of random matrices [22]. In the presence of absorption, always present in an experimental situation, eigenfrequencies overlap and any measured spectrum usually takes the form of a complicated "herb"-like function, generally believed to contain no information beyond the average density of state. It turns out that we have been able to show that two-point correlation functions of the spectrum can allow one to identify the nature of the underlying system (integrable or chaotic ray trajectories described respectively by Poissonian or GOE random matrix statistics) and in the same token to get access to the value of the dissipation [23]. In particular, there is a strong interplay between GOE statistics and dissipation that leads to severe erroneous errors when neglected as done in the past. Since most structures for engineering applications are in the GOE or multiple-GOE universality class, our results bear important applications. During this work, new efficient algorithms which allow the computation of a large number (hundreds to thousands) of eigenfrequencies for clamped and freely supported plates and for 3D elastodynamical problems have been developed. An equivalence between the vibration problem of a thin plate and that of a membrane with a complex boundary condition has also been shown [21]. This last result allows to circumvent the problems of stability and precision associated to the calculation of thin plate vibration eigenfrequencies. Also, we have extended the algorithm to calculate a large number of eigenfrequencies and eigenmodes of coupled membranes of arbitrary shapes and study the statistical properties of the spectrum and eigenmode fluctuations [24]. Our results emphasize the large sensitivity of the detailled structure of the spectrum of a classically chaotic system with respect to perturbation such as couplings. However, the global statistical properties are very robust as they pertain to only a few different universality class. 2.2 Time-dependent properties : geometric theory of wave dynamics in chaotic enclosures. Spectral properties are only one facet of waves. As for transport of waves in random media described in =A71, the time-dependent properties of waves in cavities can provide new insights. Furthermore, it turns out to be the relevant view point for the problem of room acoustics, in which one is interested in describing the transient behavior of an acoustic wave launched from a source in an enclosure. Interesting links between the theoretical foundation of room acoustics, whose full wave theory has until recently been lacking, and chaotic ray trajectories in billiards have been recently studied, enabling a better quantification of the various regimes [25,26]. Recently semi-classical time-dependent Green function for the hyperbolic wave equation has been constructed using a summation over quasi-recurrent classical ray trajectories [27]. The finite resolution of the wave problem associated to the smallest wavelength allowed us to introduce a natural coarse-graining which permits to partition the classical rays into bundles forming a Cantor set [28] We have shown the existence of contributions in the sum which correspond to precursors to the classical ray arrival times., which embody the physics of multiple interferences and more precisely a diffraction correction associated to the presence of odd numbers of focal points along the classical ray trajectories. Our global formulation and Green function construction over the classical ray trajectories suitably enriched by their relevant phases and amplitudes provide a very good agreement with the direct numerical integration of the wave equation for integrable as well as for various billiard shapes, such as the Sina=EF and stadium billiards. In conclusion, this short review has shown a few examples where new interesting physics can spring out of analogies between different fields. I would like to thank warmly my collaborators C. Vanneste, O.Legrand, P. Sebbah, P. Mortessagne, D. Delande, R. Weaver, C. Schmit, O. Bohigas and S. de Toro Arias. REFERENCES [1] D.Sornette, "Acoustic waves in random media: I Weak disorder regime", Acustica 67, 199 (1989); "II Coherent effects and strong disorder regime", Acustica 67, 251 (1989); "III Experimental situations", Acustica 68, 15 (1989) [2] D.Sornette et B.Souillard, "A mean field approach to Anderson localization", Europhys.Lett. 13, 7-12 (1990) [3] J.P. Desidri and D. Sornette, "Band-edge localization and spatial textures of surface acoustic waves in weakly disordered 1D-superlattices, Europhys. Lett. 23, 165-170 (1993) [4] L.Macon, J.P. Desidri and D.Sornette, "Surface acoustic waves in a simple quasi-periodic system", Phys.Rev.B 40, 3605 (1989) [5] J.P. 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