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British acoustical society
Journal of Sound and Vibration (1972) 25 (4), i-v
BRITISH ACOUSTICAL
SOCIETY
All enquiries should be addressed to the Secretary, British Acoustical Society, 1 Birdcage Walk, London S.W.l (Telephone: 01-930 7476). 1. MEETINGS: PROGRAMME FOR 1972-73
4 January 1973, at Chelsea College, London, a meeting on “Appliance noise”: measurement techniques and assessment procedures for a range of appliances, excluding large plant installations. Details from Dr H. G. Leventhall, Chelsea College, Pulton Place, London S.W.6. 8 February 1973, at the Institution of Civil Engineers, London, a meeting on “Construction noise”: joint with the Acoustics Group, Institute of Physics. Details from The Meetings Officer, Institute of Physics, 47 Belgrave Square, London S.W.1. 22 March 1973, at the National Physical Laboratory, Teddington, a meeting on “Coherent light methods for the study of mechanical vibrations”, joint with the Acoustics and Optics Groups of the Institute of Physics: the application of holographic techniques, including speckle pattern interferometry, to the analysis of vibration patterns of engineering components. Details from Dr R. W. B. Stephens, Chelsea College, Pulton Place, London S.W.6. 27 March 1973, at the Fisheries Research Laboratory, Lowestoft, a meeting on “Sonar in fisheries”, joint with the Society for Underwater Technology. The meeting will discuss advances in the application of sonar to fisheries, e.g. in the detection of fish, especially at long ranges, in the measurement of their abundance and in study of their behaviour. Details from R. A. Mitson, Fisheries Research Laboratory, MAFF, Lowestoft, Suffolk. 25-27 April 1973, at Chelsea College, London, the Spring Meeting of the Society, with sessions on musical acoustics, aerodynamic noise, speech and hearing, vibrations; the Rayleigh Gold and British Acoustical Society Silver Medal Addresses and special lectures. Annual Dinner of the Society. Details from Dr H. G. Leventhall, Chelsea College, Pulton Place, London S.W.6. 11 May 1973, at the Institution of Mechanical Engineers, London, a meeting on “Develop-
ments in high-fidelity systems”, joint with the Acoustics Group, Institute of Physics: the development of high-fidelity reproduction with special reference to magnetic tape cassette, multi-channel stereophonic and loudspeaker reproduction systems, and noise reproduction. Details from The Secretary, British Acoustical Society, 1 Birdcage Walk, London SWlH 9JJ. June 1973 (date to be announced) at the Institute of Sound and Vibration Research, Universsity of Southampton, a meeting on “Noise from prime movers”: four sessions on the sources of noise of machine elements, turbine engines, reciprocating engines, and electrical and hydraulic prime movers. Details from Professor T. Priede, I.S.V.R., University of Southampton, Southampton SO9 5NH. 6 July 1973, at Chelsea College, London, a meeting on “Visco-elasticity in acoustics”, joint with the Acoustics Group, Institute of Physics and the Society of Environmental i
ii
BRITISH ACOUSTICAL
SOCIETY
Engineers : discussion of the role played by visco-elasticity in acoustical phenomena with particular reference to the damping of sound in structural materials. Details from Dr R. W. B. Stephens, Chelsea College, Pulton Place, London S.W.6. A notice is published before each meeting showing the detailed programme, names of speakers, registration fees, etc. This is available from the meeting organizer or the Secretary of the Society. A registration fee is charged for all meetings to cover the cost of organization and refreshments. There is a differential between the fee for members and that for non-members. Summaries of the papers to be given are available at the meetings, and these are subsequently embodied in the Proceedings of Society, issued to all members of the British Acoustical Society free. Papers are not published in full by the Society but are considered for publication in the Journal of Sound and Vibration which also publishes reports on each meeting. Details of membership of the Society are available from the Secretary. 2.
NOISE ADVISORY
COUNCIL
The Council has just given favourable welcome to the official “Code of Practice for Reducing the Exposure of Employed Persons to Noise”, prepared by the sub-department of the Department of Employment’s Industrial Health Advisory Committee and published by H.M. Stationery Office. It has itself published a report on “Traffic Noise: the vehicle regulations and their enforcement”, price 5Op from H.M. Stationery Office. 3. PROCEEDINGS STRUCTURAL
OF THE B.A.S. MEETING ON “APPLICATIONS
OF EXPERIMENTAL
AND THEORETICAL
DYNAMICS”
These proceedings, of the B.A.S. meeting which was recently held at the Institute of Sound and Vibration Research, the University of Southampton, are available bound in (paper) book form from the I.S.V.R. at f6 each. Applications should be made direct to the Institute. 4.
PROCEEDINGS
OF A SYMPOSIUM
ON NON-LINEAR
DYNAMICS
All the papers which were presented at the Symposium which was recently held at Loughborough University of Technology have been bound and are available from the Department of Transport Technology at Loughborough University of Technology, at f4.50 each (surface postage). Applications should be made direct to the Department. 5.
BRITISH ACOUSTICAL
SOCIETY SPRING
MEETING
1972 :
LOUGHBOROUGH
Plenary Session
The Spring Meeting this year was held at Loughborough University on 5-7 April. The attendance of 110 was rather smaller than the previous year because only two areas were covered instead of the three of the first Spring Meeting. The two subjects, Aerodynamic Noise Sources in Industry and Ultrasonics in Industry, did however attract lively audiences as will be seen from the detailed reports below. The plenary session was held on Thursday afternoon, mainly to award the Rayleigh Gold Medal to Professor S. S. Stevens and the British Acoustical Society Silver Medal to Dr C. L. Morfey. The presentations were made by the President, Professor D. G. Tucker and were followed by two very interesting lectures by the recipients of the medals. Details of these lectures have already been included in Journal of Sound and Vibration. The afternoon was rounded off by a stimulating and provocative lecture by Professor Cohn Cherry entitled “Conversation and mood - an experimental approach”.
BRITISH ACOUSTICAL SOCIETY
.. 111
This plenary session was followed in the evening by the Annual Dinner of the Society which proved a very successful and enjoyable evening. J. W. R. GRIFFITHS Aerodynamic Noise Sources in Industry
Noise sources in which the noise is generated by aerodynamic mechanisms occur extensively throughout industry. Despite this situation, however, industrial aerodynamic noise sources have yet to be afforded the attention given to the related phenomenon in the transportation field. To partially rectify this situation the Society organized as part of the 1972 Spring Meeting, a session on “Aerodynamic Noise Sources in Industry”. Fifteen papers in all were presented in three sessions, each of five papers followed by a discussion period. It is of interest to note that thirteen of these papers were presented by authors directly involved with this type of industrial noise source. The other two papers were by authors in universities involved with contract work for industry. The introductory session under the chairmanship of T. Smith (C. A. Parsons), commenced with a paper on acoustic fatigue of structures followed by a paper on community response to industrial noise, both important aspects of industrial aerodynamic noise. In the opening paper Dr L. Yeh (English Electric/ AEI Turbine Generators Ltd.) described the evolution of an empirical method for predicting the life expectancy of gas circuit components for nuclear reactors. These components have to withstand without failure, in-service noise levels in excess of 160 dB for periods of up to twenty years. Although much lower, the noise levels discussed by P. Sutton (Esso Petroleum) in his paper on community response to industrial noise, could just as effectively result in the closure of plant. In this paper the results obtained by using the two existing methods for rating industrial noise (BS4142 and IS0 R/1996) were compared. It was concluded that of the two the British Standard, BS4142 provides the more accurate prediction. Following these two introductory papers, the session continued with two papers on mdustrial gas turbine noise. C. W. Freeman (Rolls-Royce (1971) Ltd.) in his paper discussed the noise characteristics of gas turbines and the manufacturer’s method of reducing the noise from this type of source. Messrs. Hickmann and Percy (Industrial Acoustics Co. Ltd.) in the paper following described the design and installation of the noise reduction treatment applied to 8 x 15 MW gas turbine generator sets located in a power station in a residential area of London. The over-riding criterion in this case was to avoid community response which the installation has since satisfied. In the last paper in the session R. M. Taylor provided details of the design and performance of the silencers his company evolved to reduce the noise produced by two-double-acting reciprocating compressors. In addition to noise in the audio-range the two compressors produced high pressure pulsations at the compressor shaft speed of 250 rpm (4.16 Hz). The existence of this infrasonic component was not appreciated initially and after some unforeseen difficulties was satisfactorily suppressed by incorporating a Helmholtz resonator into each exhaust duct. General discussion on these five papers completed the first session. The second session chaired by G. Berry (AIRO), was devoted entirely to control valve noise. Opening the session D. Headon (Gas Council ERS) presented the attitude of a major user of control valves to the problem of valve noise, indicating the areas of this subject in which there is a general dearth of knowledge and/or a conflict of opinions. His paper was followed by three others by authors representing valve manufacturers: A. Nelson and P. Smagghe (Masoneilan Ltd.), B. M. Williams (GEC-Elliott Control Valves) and J. Hall (Lincoln Valves). These three papers presented each of the manufacturers methods for predicting and/or reducing the noise produced by their products. Following these in the final paper of the session Dr P. 0. A. L. Davies and D. J. Small (ISVR) described and interpreted the results of their experimental investigation of valve noise characteristics, a
iv
BRITISH ACOUSTICAL SOCIETY
paper often at variance with the previous three. During the discussion period the important point emerged that the noise levels associated with a control valve depend a great deal on the pipework into which it is fitted. The normal accepted methods for predicting valve noise, which are derived empirically, can often give erroneous results when applied in practice. This arises due to the pipework, into which the valve was fitted for the derivation of the test data, acting as an acoustic band-pass filter. Unless these characteristics are reproduced in the pipcwork in the final location then the predicted noise levels will be in error. The final session chaired by Dr M. V. Lowson (Loughborough University), contained a miscellany of papers, the first of which, by J. B. Erskine (ICI Billingham), dealt with the calculation and control of noise from pressure venting systems. The author presented the approach of an operator of large chemical plant to the problem of vent noise, describing empirical methods derived for predicting its parameters and also for reducing it. E. G. Spalding (Delta-P International), in the paper following, described the design, construction and performance of silencers for high pressure vents, which his company manufactures. These two papers made an interesting comparison. Three authors, Drs Leventhall, Palmer and Roberts (Chelsea College) were responsible for the next paper on noise sources in oil and gas combustion processes. Dr Leventhall presented the paper which described the investigation at Chelsea College into the noise produced by industrial gas and oil burners. Switching to a completely different subject W. Waddington and J. B. Erskine (ICI Billingham) presented a paper on flow induced noise and vibration in a transverse heat exchanger. When operating, this fundamentally passive item of plant generated a pure tone which produced vigorous community response in addition to excessive vibration levels on the heat exchanger shell. The pure tone was eventually traced to the coincidence of the vortex shedding frequency of the tubes with the fundamental transverse acoustic resonance of the heat exchanger shell. Eventually the pure tone was successfully suppressed by inserting thin plates into the tube banks to detune the heat exchanger resonance. The final paper of the session, by R. J. Davies (Acoustic Technology Ltd.), reviewed the noise of airfin coolers. This item of plant is used extensively in the petrochemical industry and consists of a large bank of finned tubing, force-cooled by a large diameter axial flow fan mounted underneath. Work to date has resulted in the derivation of empirical methods for predicting the noise of and also of reducing the noise from these coolers. As with the previous sessions a general discussion followed the technical papers, after which the chairman proposed a vote of thanks to T. Smith, the session organiser, who after thanking the delegates and authors for attending, declared the meeting closed. T. SMITH Ultrasonics in Industry
Research and industrial applications of ultrasonics are frequently done by different people in different places and communication between them is essential. However, in practice, opportunities for such communication in general are not frequent and even less in the form of personal contact and discussion, creating a need for meetings of this kind. Answering this need the Society selected “Ultrasonics in Industry” as one of the sections of its Spring Meeting in 1972. In three sessions sixteen papers were presented, two of which were given by authors from abroad: one from the U.S.A. and one from Poland. There was a good balance between academic activity and industry, half of the papers being from universities and half from industry or industrial research centres. Most of the work covered was in connection with non-destructive testing and various measurements related to it; however, two papers were devoted to high power applications. The first session was started off by A. E. Crawford (H. Tinsley & Co. Ltd.) surveying the latest developments on high power ultrasonic transducers. This was followed by J. L. Bello and R. W. B. Stephens (Imperial
BRITISH ACOUSTICAL SOCIETY
V
College, Chelsea College) talking about various aspects of ultrasonic welding. One of the novelties was the study of the power required to form a good weld under different conditions, clarifying the adverse effects of both too low and too high power on the strength of the weld. After these two papers on high power ultrasonics followed two on acoustic holography. P. C. Calvert (Bristol Polytechnic) reported on his work done previously at Loughborough University of Technology using the Pohlman cell for recording the ultrasonic hologram. He found this acousto-optical image converter to be simple and cheap with the additional advantage of having a very wide angle of acceptance, but its poor sensitivity imposed limitations in practice. R. Kumar and A. Lafferty (Imperial College) also used the Pohlman cell for photographing the hologram. Their aim was to investigate the sound field within hollow cylinders, applying holographic techniques. High temperature objects are always difficult to study ultrasonically and J. D. Lavender (Steel Casting Research Association) and P. J. Emerson (British Cast Iron Research Association) fused their steel stand-off bars to their castings under test. By looking at the attenuation they were able to find out in time if the quality of a batch of castings was deteriorating, so that a lot of wastage could be saved. D. R. Peck and E. R. Dobbs (Lancaster University) presented their results on generating and receiving ultrasound electromagnetically, i.e. without contact or any couplant. This method is applicable to the testing of high temperature metal objects, but unfortunately its sensitivity is very limited. H. G. Tattersall (N.D.T. Centre, U.K.A.E.A., Harwell) described his work on ultrasonic scatter in various emulsions; his interesting results will help in the understanding of other types of scattering systems. P. D. Hanstead and R. C. Wyatt (C.E.G.B., Portishead) have developed a unique ultrasonic visualisation technique for N.D.T. giving an instantly visible real 3D image (not an illusion!) of defects in an object. D. Cook (British Rail, Derby) measured the depth of propagating cracks of test pieces on the fatigue testing machine, using ultrasonic surface waves. G. L. Wilson (Pennsylvania State University, U.S.A.) reported on his technique for measuring the bulk loss factor of small solid specimens by immersing them into a container full of water and observing the decay time. The expanding field of stress wave emissions was reviewed by R. W. B. Stephens (Chelsea College). Commercial flaw detecting probes are satisfactory as long as regarding only simple everyday flaw detection, but before using them for laboratory measurements they must be checked thoroughly. M. G. Silk and B. H. Lidington (N.D.T. Centre, U.K.A.E.A., Harwell) checked a large number of commercial probes and presented many results worth remembering. K. R. Whittington (Tube Investments Ltd.) described the recent progression of his arrangement of electronically focussed arrays for testing steel tubing at high speed. C. R. Theumer (British Rail, Derby) talked about a multiple probe array developed by BR specifically for testing rails and making use of the mode conversion of waves at the boundary of a defect. P. J. Highmore (Loughborough University of Technology) investigated the wave propagation through a multilayered medium, in practice consisting of thin sheets of steel and plastic sandwiched together, showing a very low frequency resonance of a low Q and surprisingly no upper harmonics. The final paper was given by Z. Jagodzinski (University of Gdansk, Poland) on the graphical analysis and radiation efficiency of ultrasonic transducers, covering both the magnetostrictive and the piezoelectric type. Virtually all the lectures were followed by lively and stimulating discussions and some additional general discussion time was also available before each meeting was brought to a close. J. SZILARD
BRITISH ACOUSTICAL
SOCIETY
All enquiries should be addressed to the Secretary, British Acoustical Society, 1 Birdcage Walk, London S.W.l (Telephone: 01-930 7476). 1. MEETINGS: PROGRAMME FOR 1972-73
4 January 1973, at Chelsea College, London, a meeting on “Appliance noise”: measurement techniques and assessment procedures for a range of appliances, excluding large plant installations. Details from Dr H. G. Leventhall, Chelsea College, Pulton Place, London S.W.6. 8 February 1973, at the Institution of Civil Engineers, London, a meeting on “Construction noise”: joint with the Acoustics Group, Institute of Physics. Details from The Meetings Officer, Institute of Physics, 47 Belgrave Square, London S.W.1. 22 March 1973, at the National Physical Laboratory, Teddington, a meeting on “Coherent light methods for the study of mechanical vibrations”, joint with the Acoustics and Optics Groups of the Institute of Physics: the application of holographic techniques, including speckle pattern interferometry, to the analysis of vibration patterns of engineering components. Details from Dr R. W. B. Stephens, Chelsea College, Pulton Place, London S.W.6. 27 March 1973, at the Fisheries Research Laboratory, Lowestoft, a meeting on “Sonar in fisheries”, joint with the Society for Underwater Technology. The meeting will discuss advances in the application of sonar to fisheries, e.g. in the detection of fish, especially at long ranges, in the measurement of their abundance and in study of their behaviour. Details from R. A. Mitson, Fisheries Research Laboratory, MAFF, Lowestoft, Suffolk. 25-27 April 1973, at Chelsea College, London, the Spring Meeting of the Society, with sessions on musical acoustics, aerodynamic noise, speech and hearing, vibrations; the Rayleigh Gold and British Acoustical Society Silver Medal Addresses and special lectures. Annual Dinner of the Society. Details from Dr H. G. Leventhall, Chelsea College, Pulton Place, London S.W.6. 11 May 1973, at the Institution of Mechanical Engineers, London, a meeting on “Develop-
ments in high-fidelity systems”, joint with the Acoustics Group, Institute of Physics: the development of high-fidelity reproduction with special reference to magnetic tape cassette, multi-channel stereophonic and loudspeaker reproduction systems, and noise reproduction. Details from The Secretary, British Acoustical Society, 1 Birdcage Walk, London SWlH 9JJ. June 1973 (date to be announced) at the Institute of Sound and Vibration Research, Universsity of Southampton, a meeting on “Noise from prime movers”: four sessions on the sources of noise of machine elements, turbine engines, reciprocating engines, and electrical and hydraulic prime movers. Details from Professor T. Priede, I.S.V.R., University of Southampton, Southampton SO9 5NH. 6 July 1973, at Chelsea College, London, a meeting on “Visco-elasticity in acoustics”, joint with the Acoustics Group, Institute of Physics and the Society of Environmental i
ii
BRITISH ACOUSTICAL
SOCIETY
Engineers : discussion of the role played by visco-elasticity in acoustical phenomena with particular reference to the damping of sound in structural materials. Details from Dr R. W. B. Stephens, Chelsea College, Pulton Place, London S.W.6. A notice is published before each meeting showing the detailed programme, names of speakers, registration fees, etc. This is available from the meeting organizer or the Secretary of the Society. A registration fee is charged for all meetings to cover the cost of organization and refreshments. There is a differential between the fee for members and that for non-members. Summaries of the papers to be given are available at the meetings, and these are subsequently embodied in the Proceedings of Society, issued to all members of the British Acoustical Society free. Papers are not published in full by the Society but are considered for publication in the Journal of Sound and Vibration which also publishes reports on each meeting. Details of membership of the Society are available from the Secretary. 2.
NOISE ADVISORY
COUNCIL
The Council has just given favourable welcome to the official “Code of Practice for Reducing the Exposure of Employed Persons to Noise”, prepared by the sub-department of the Department of Employment’s Industrial Health Advisory Committee and published by H.M. Stationery Office. It has itself published a report on “Traffic Noise: the vehicle regulations and their enforcement”, price 5Op from H.M. Stationery Office. 3. PROCEEDINGS STRUCTURAL
OF THE B.A.S. MEETING ON “APPLICATIONS
OF EXPERIMENTAL
AND THEORETICAL
DYNAMICS”
These proceedings, of the B.A.S. meeting which was recently held at the Institute of Sound and Vibration Research, the University of Southampton, are available bound in (paper) book form from the I.S.V.R. at f6 each. Applications should be made direct to the Institute. 4.
PROCEEDINGS
OF A SYMPOSIUM
ON NON-LINEAR
DYNAMICS
All the papers which were presented at the Symposium which was recently held at Loughborough University of Technology have been bound and are available from the Department of Transport Technology at Loughborough University of Technology, at f4.50 each (surface postage). Applications should be made direct to the Department. 5.
BRITISH ACOUSTICAL
SOCIETY SPRING
MEETING
1972 :
LOUGHBOROUGH
Plenary Session
The Spring Meeting this year was held at Loughborough University on 5-7 April. The attendance of 110 was rather smaller than the previous year because only two areas were covered instead of the three of the first Spring Meeting. The two subjects, Aerodynamic Noise Sources in Industry and Ultrasonics in Industry, did however attract lively audiences as will be seen from the detailed reports below. The plenary session was held on Thursday afternoon, mainly to award the Rayleigh Gold Medal to Professor S. S. Stevens and the British Acoustical Society Silver Medal to Dr C. L. Morfey. The presentations were made by the President, Professor D. G. Tucker and were followed by two very interesting lectures by the recipients of the medals. Details of these lectures have already been included in Journal of Sound and Vibration. The afternoon was rounded off by a stimulating and provocative lecture by Professor Cohn Cherry entitled “Conversation and mood - an experimental approach”.
BRITISH ACOUSTICAL SOCIETY
.. 111
This plenary session was followed in the evening by the Annual Dinner of the Society which proved a very successful and enjoyable evening. J. W. R. GRIFFITHS Aerodynamic Noise Sources in Industry
Noise sources in which the noise is generated by aerodynamic mechanisms occur extensively throughout industry. Despite this situation, however, industrial aerodynamic noise sources have yet to be afforded the attention given to the related phenomenon in the transportation field. To partially rectify this situation the Society organized as part of the 1972 Spring Meeting, a session on “Aerodynamic Noise Sources in Industry”. Fifteen papers in all were presented in three sessions, each of five papers followed by a discussion period. It is of interest to note that thirteen of these papers were presented by authors directly involved with this type of industrial noise source. The other two papers were by authors in universities involved with contract work for industry. The introductory session under the chairmanship of T. Smith (C. A. Parsons), commenced with a paper on acoustic fatigue of structures followed by a paper on community response to industrial noise, both important aspects of industrial aerodynamic noise. In the opening paper Dr L. Yeh (English Electric/ AEI Turbine Generators Ltd.) described the evolution of an empirical method for predicting the life expectancy of gas circuit components for nuclear reactors. These components have to withstand without failure, in-service noise levels in excess of 160 dB for periods of up to twenty years. Although much lower, the noise levels discussed by P. Sutton (Esso Petroleum) in his paper on community response to industrial noise, could just as effectively result in the closure of plant. In this paper the results obtained by using the two existing methods for rating industrial noise (BS4142 and IS0 R/1996) were compared. It was concluded that of the two the British Standard, BS4142 provides the more accurate prediction. Following these two introductory papers, the session continued with two papers on mdustrial gas turbine noise. C. W. Freeman (Rolls-Royce (1971) Ltd.) in his paper discussed the noise characteristics of gas turbines and the manufacturer’s method of reducing the noise from this type of source. Messrs. Hickmann and Percy (Industrial Acoustics Co. Ltd.) in the paper following described the design and installation of the noise reduction treatment applied to 8 x 15 MW gas turbine generator sets located in a power station in a residential area of London. The over-riding criterion in this case was to avoid community response which the installation has since satisfied. In the last paper in the session R. M. Taylor provided details of the design and performance of the silencers his company evolved to reduce the noise produced by two-double-acting reciprocating compressors. In addition to noise in the audio-range the two compressors produced high pressure pulsations at the compressor shaft speed of 250 rpm (4.16 Hz). The existence of this infrasonic component was not appreciated initially and after some unforeseen difficulties was satisfactorily suppressed by incorporating a Helmholtz resonator into each exhaust duct. General discussion on these five papers completed the first session. The second session chaired by G. Berry (AIRO), was devoted entirely to control valve noise. Opening the session D. Headon (Gas Council ERS) presented the attitude of a major user of control valves to the problem of valve noise, indicating the areas of this subject in which there is a general dearth of knowledge and/or a conflict of opinions. His paper was followed by three others by authors representing valve manufacturers: A. Nelson and P. Smagghe (Masoneilan Ltd.), B. M. Williams (GEC-Elliott Control Valves) and J. Hall (Lincoln Valves). These three papers presented each of the manufacturers methods for predicting and/or reducing the noise produced by their products. Following these in the final paper of the session Dr P. 0. A. L. Davies and D. J. Small (ISVR) described and interpreted the results of their experimental investigation of valve noise characteristics, a
iv
BRITISH ACOUSTICAL SOCIETY
paper often at variance with the previous three. During the discussion period the important point emerged that the noise levels associated with a control valve depend a great deal on the pipework into which it is fitted. The normal accepted methods for predicting valve noise, which are derived empirically, can often give erroneous results when applied in practice. This arises due to the pipework, into which the valve was fitted for the derivation of the test data, acting as an acoustic band-pass filter. Unless these characteristics are reproduced in the pipcwork in the final location then the predicted noise levels will be in error. The final session chaired by Dr M. V. Lowson (Loughborough University), contained a miscellany of papers, the first of which, by J. B. Erskine (ICI Billingham), dealt with the calculation and control of noise from pressure venting systems. The author presented the approach of an operator of large chemical plant to the problem of vent noise, describing empirical methods derived for predicting its parameters and also for reducing it. E. G. Spalding (Delta-P International), in the paper following, described the design, construction and performance of silencers for high pressure vents, which his company manufactures. These two papers made an interesting comparison. Three authors, Drs Leventhall, Palmer and Roberts (Chelsea College) were responsible for the next paper on noise sources in oil and gas combustion processes. Dr Leventhall presented the paper which described the investigation at Chelsea College into the noise produced by industrial gas and oil burners. Switching to a completely different subject W. Waddington and J. B. Erskine (ICI Billingham) presented a paper on flow induced noise and vibration in a transverse heat exchanger. When operating, this fundamentally passive item of plant generated a pure tone which produced vigorous community response in addition to excessive vibration levels on the heat exchanger shell. The pure tone was eventually traced to the coincidence of the vortex shedding frequency of the tubes with the fundamental transverse acoustic resonance of the heat exchanger shell. Eventually the pure tone was successfully suppressed by inserting thin plates into the tube banks to detune the heat exchanger resonance. The final paper of the session, by R. J. Davies (Acoustic Technology Ltd.), reviewed the noise of airfin coolers. This item of plant is used extensively in the petrochemical industry and consists of a large bank of finned tubing, force-cooled by a large diameter axial flow fan mounted underneath. Work to date has resulted in the derivation of empirical methods for predicting the noise of and also of reducing the noise from these coolers. As with the previous sessions a general discussion followed the technical papers, after which the chairman proposed a vote of thanks to T. Smith, the session organiser, who after thanking the delegates and authors for attending, declared the meeting closed. T. SMITH Ultrasonics in Industry
Research and industrial applications of ultrasonics are frequently done by different people in different places and communication between them is essential. However, in practice, opportunities for such communication in general are not frequent and even less in the form of personal contact and discussion, creating a need for meetings of this kind. Answering this need the Society selected “Ultrasonics in Industry” as one of the sections of its Spring Meeting in 1972. In three sessions sixteen papers were presented, two of which were given by authors from abroad: one from the U.S.A. and one from Poland. There was a good balance between academic activity and industry, half of the papers being from universities and half from industry or industrial research centres. Most of the work covered was in connection with non-destructive testing and various measurements related to it; however, two papers were devoted to high power applications. The first session was started off by A. E. Crawford (H. Tinsley & Co. Ltd.) surveying the latest developments on high power ultrasonic transducers. This was followed by J. L. Bello and R. W. B. Stephens (Imperial
BRITISH ACOUSTICAL SOCIETY
V
College, Chelsea College) talking about various aspects of ultrasonic welding. One of the novelties was the study of the power required to form a good weld under different conditions, clarifying the adverse effects of both too low and too high power on the strength of the weld. After these two papers on high power ultrasonics followed two on acoustic holography. P. C. Calvert (Bristol Polytechnic) reported on his work done previously at Loughborough University of Technology using the Pohlman cell for recording the ultrasonic hologram. He found this acousto-optical image converter to be simple and cheap with the additional advantage of having a very wide angle of acceptance, but its poor sensitivity imposed limitations in practice. R. Kumar and A. Lafferty (Imperial College) also used the Pohlman cell for photographing the hologram. Their aim was to investigate the sound field within hollow cylinders, applying holographic techniques. High temperature objects are always difficult to study ultrasonically and J. D. Lavender (Steel Casting Research Association) and P. J. Emerson (British Cast Iron Research Association) fused their steel stand-off bars to their castings under test. By looking at the attenuation they were able to find out in time if the quality of a batch of castings was deteriorating, so that a lot of wastage could be saved. D. R. Peck and E. R. Dobbs (Lancaster University) presented their results on generating and receiving ultrasound electromagnetically, i.e. without contact or any couplant. This method is applicable to the testing of high temperature metal objects, but unfortunately its sensitivity is very limited. H. G. Tattersall (N.D.T. Centre, U.K.A.E.A., Harwell) described his work on ultrasonic scatter in various emulsions; his interesting results will help in the understanding of other types of scattering systems. P. D. Hanstead and R. C. Wyatt (C.E.G.B., Portishead) have developed a unique ultrasonic visualisation technique for N.D.T. giving an instantly visible real 3D image (not an illusion!) of defects in an object. D. Cook (British Rail, Derby) measured the depth of propagating cracks of test pieces on the fatigue testing machine, using ultrasonic surface waves. G. L. Wilson (Pennsylvania State University, U.S.A.) reported on his technique for measuring the bulk loss factor of small solid specimens by immersing them into a container full of water and observing the decay time. The expanding field of stress wave emissions was reviewed by R. W. B. Stephens (Chelsea College). Commercial flaw detecting probes are satisfactory as long as regarding only simple everyday flaw detection, but before using them for laboratory measurements they must be checked thoroughly. M. G. Silk and B. H. Lidington (N.D.T. Centre, U.K.A.E.A., Harwell) checked a large number of commercial probes and presented many results worth remembering. K. R. Whittington (Tube Investments Ltd.) described the recent progression of his arrangement of electronically focussed arrays for testing steel tubing at high speed. C. R. Theumer (British Rail, Derby) talked about a multiple probe array developed by BR specifically for testing rails and making use of the mode conversion of waves at the boundary of a defect. P. J. Highmore (Loughborough University of Technology) investigated the wave propagation through a multilayered medium, in practice consisting of thin sheets of steel and plastic sandwiched together, showing a very low frequency resonance of a low Q and surprisingly no upper harmonics. The final paper was given by Z. Jagodzinski (University of Gdansk, Poland) on the graphical analysis and radiation efficiency of ultrasonic transducers, covering both the magnetostrictive and the piezoelectric type. Virtually all the lectures were followed by lively and stimulating discussions and some additional general discussion time was also available before each meeting was brought to a close. J. SZILARD