Annual report 1998-1999
Every year from 1963 to 2010, the Institute of Sound and Vibration Research published its Annual Report. These are the chapters on ISVR Consultancy Services and the Automotive Design Advisory Unit for the year May 1998 - April 1999.
ISVR Consultancy Services
Manager Mr R A Davis
ISVR Consultancy Services (ICS) is a self-funding advisory unit which carries out short- and medium-term consultancy and research for a wide range of public- and private-sector clients. The Unit operates on a commercial basis, with full-time engineering and support staff and an extensive pool of measurement equipment for site and laboratory investigations. It maintains close links with ISVR Research Groups, and manages the ISVR's main test chambers, comprising anechoic and reverberation rooms.
The Unit generated a trading surplus in 1998-99 and staff numbers have increased with the recruitment of two engineers, Reuben Peckham and Brian Dennis.
Projects are client-confidential. The following review illustrates the range of work undertaken and identifies some general technical and business trends within the consultancy activity.
Many projects involve the assessment of noise from proposed industrial or leisure-related developments affecting nearby residential areas. A number of such assessments have been carried out in the vicinity of sites to be used for mineral extraction or associated uses such as asphalt manufacture, landfill or waste recycling. Other projects include the prediction and assessment of noise from night clubs, a chicken farm and a vehicle repair operation.
Other investigations are concerned with proposed new residential developments on sites close to existing noise sources. Government policy increasingly favours the development of urban 'brown field' sites for housing. These sites often present specific noise problems because of their proximity to roads, railways or noisy industry. A number of such projects have been undertaken on behalf of developers and local planning authorities. Evidence on noise has been presented at local Public Inquiries.
A number of environmental noise problems have been investigated. These most often concern industrial noise affecting residential areas at night. Many problems involve impulsive or tonal components which are often 'under-valued' (in terms of incidence of complaints) by the application of British Standard BS 4142:1997.
The Unit is advising on the noise control design of an on-shore gas compression station in Norway. A major source of environmental noise from this installation is predicted to be breakout of noise from compressors and control valves through pipe walls and from vessels. Pipe radiated noise is often important for large process works but is difficult to predict with confidence. For this project, a volume velocity transducer and associated software have been developed and supplied to the design contractor. This device permits direct measurement of noise emission from pipes and other surfaces in the presence of high levels of background noise from other sources, and provides a practicable alternative to surface vibration measurements. The system will be used to obtain data from compressors during tests at vendors' premises, and to measure pipework noise during commissioning. The information gained will enable prediction methods to be validated and enhanced.
Structural dynamics and computational acoustics
The main activity in the area of computational acoustics has centred on two research projects associated with the continuing drive to reduce noise pollution around airports. These major long-term contracts are administered through ISVR and carried out by ICS staff seconded to the Department.
In the first project ISVR are partners in the European-funded RAIN (Reduction of Airframe and Installation Noise) project, with responsibility for producing a mathematical model of the aerodynamic noise from aircraft landing gear. This is now a significant noise source for aircraft on approach. This work has involved the reduction and analysis of noise data acquired in the DNW wind tunnel on full scale landing gear and the prediction of flyover noise data from Airbus aircraft.
The second project involves mathematical modelling of sound propagating in lined ducts in order to optimise the attenuation of aero-engine noise. This work is being done in collaboration with the ISVR Fluids and Acoustics Research Group and Rolls Royce.
Other activities include the ongoing sales and consultancy work associated with the AutoSEA software, with some significant work for DERA on shipboard noise sources which draws on ISVR's expertise developed during recent research funded by the Marine Technology Directorate. A three day introductory course on the practical applications of Statistical Energy Analysis was organised in September. It is planned to repeat this course in future years.
Communications and electro-acoustics
A programme of experimental work was carried out for an electronics manufacturer to develop and test a new telephone handset for use by aircraft passengers. The original design required modifications to the casing around the noise-cancelling microphone, and acoustic treatment within the casing to minimise transmission from earpiece to microphone in order to meet the desired specifications.
An assessment of the public address system in a large safety-critical process building was undertaken. RASTI measurements indicated that the main cause of poor speech intelligibility was the excessive reverberation times, rather then the relatively high background noise level. The function of the building did not permit the addition of sound absorbent materials to reduce reverberation. A solution based on modifications to the loudspeaker density, coverage and positioning was devised.
Noise at work - hearing conservation - personal injury claims
Reports have been prepared in connection with a number of personal injury claims alleging noise-induced hearing loss.
Assessments of noise exposure in connection with the Noise at Work Regulations have been carried out for a range of occupations, including foundry workers, crane drivers, motor-cyclists, police firearms instructors and air traffic controllers. The assessment of noise exposure from headsets and 'in-ear' communications devices is an expanding area of business: reliable techniques using an acoustic manikin have been developed for such assessments.
Laboratory testing and experimental work
ICS operates and manages the main ISVR test chambers, which are in regular use for product testing and development as well as for undergraduate and postgraduate research.
High intensity testing of aerospace components is a major element of the test programme. These components include antennae for communications satellites and external stores for military aircraft. Levels of up to 165 dB can be achieved using a WAS 3000 compressed air driver unit. The flexibility of the facility will be greatly enhanced during 1999 with the installation of new air compressors.
Numerous components have been tested to determine Sound Power Levels, using reverberant or anechoic test methods. Some determinations have also been carried out on site, in some cases using sound intensity techniques. Equipment submitted for test includes cellular telephone base stations, ventilation and air-conditioning units, computer peripherals and domestic 'white goods'. In some cases, development work to reduce noise levels has been undertaken.
The reverberation chambers permit measurements of sound transmission loss of panels to be performed to BS 2750 (ISO 140) and sound absorption coefficients to BS EN 20354 (ISO 354). A number of such test have been carried out on highway noise barriers, wall and partition constructions, and acoustic ceiling materials.
Other 'ad hoc' tests include the measurement of the output levels, frequency spectrum and directivity (but not the effectiveness) of an ultrasonic cat scarer (though no cats were spotted in the test chamber during tests).
Measurements have been made at a number of sites to establish vibration environments prior to the installation of vibration-sensitive industrial and medical equipment for micro-machining, microscopy and imaging.
Work for the Department of Trade and Industry, to assist in setting safe noise limits for children's toys, was described in the 1997-98 Annual Report. Further support has been provided to the EN working group responsible for toy safety standards. Assistance has been provided to a local authority Trading Standards Department, to measure noise from a wide variety of sample toys in accordance with the newly published part-standard on toy safety (BS EN 71-1:1998), and to demonstrate the necessary measurement procedures to enable them to carry out their own screening measurements in future.
ICS were appointed as acoustic consultants to advise on acoustic aspects of the design of a large 'call centre' for a major financial institution. This type of building and activity presents specific acoustical problems. Relatively high 'activity' noise levels are considered desirable to maintain staff involvement, but must not compromise speech intelligibility during telephone discussions. Solutions involve some distributed absorptive treatment and careful selection of headsets and layout of work stations.
There is increasing work in the marine industry. Projects have been completed on workboats, mainly to reduce noise levels in wheelhouses, and on luxury motor yachts where low machinery noise levels in the accommodation are a design priority. Increasing use is being made of SEA techniques to predict structure-borne noise and to optimise the design of accommodation linings and structural treatments.
Contributions were made to a European Space Agency (ESA) design manual concerning the acoustic environment within manned spacecraft. This covered the control of noise from spacecraft life support systems and from experimental apparatus.
ICS has been retained to carry out investigations and to present evidence to the Bloody Sunday Inquiry, which is concerned with the events in Londonderry in 1972. Work is being carried out in conjunction with ISVR Research staff. The main objectives are to advise on the likelihood that witnesses could have reliably identified particular types of firearms from their sounds, whether other sounds could be confused with firearms, and whether it is possible to identify particular sound signatures on the sound tracks of contemporary television news recordings. This has involved making recordings of various firearms under various conditions, characterising the sounds, and applying advanced correlation techniques to enable sound signatures to be objectively compared. The inquiry is scheduled to re-open in September 1999.
Publicity and Information
The Unit has its own web site, http://www.isvr.co.uk/ , which contains technical information, recent publications and other material. This site attracts regular visitors and has generated a significant number of enquiries for new work.
*Bagshaw, M. and Lower, M.C., Abstract on: Hearing loss in flight crew of a major international airline - the cause and solution, Aviation Space and Environmental Medicine, 69(3), 1998, 215
Peckham, M.R., A mathematical model of the neck-head-helmet system, Proceedings of the United Kingdom Group on Human Response to Vibration, organised by the Health and Safety Executive, Buxton, 16-18 September, 1998, unpaginated, 11pp
Ratcliffe, K. *Shack, R. *Turner, S., Garsington Opera Festival, Acoustics Bulletin, 23(5), 1998, 31-34
Smith, M.G. and *Chow, L.C., Prediction Method for Aerodynamic Noise from Aircraft Landing Gear, Proceedings of 4th AIAA/CEAS Aeroacoustics Conference, Toulouse,2, 1998, 153-61
* - Not working in ISVR
ISVR Automotive Design Advisory Unit
Manager: Mr J D Dixon
The general turmoil within the Automotive industry has continued throughout the year with many major OEM's . combining their research and development efforts and the less dynamic organisations struggling to remain within this increasingly competitive market place. The drive to survive has resulted in an urgency within the industry that demands short term tangible research deliverables and thus the 'blue sky' projects (seemingly the most appropriate for Universities) are becoming increasingly harder to initiate. This situation has been reflected in the Unit's activities during the past year with a large proportion of effort being given to specific short term problem solving projects together with studies into cost saving. Although this line of study is no less challenging, it lacks the freedom to carry out the peripheral investigations which are often the source of new lines of research.
Trading was difficult for the first few months of the year, due to the continuation of the various problems within the market place seen throughout the previous year. However, the past nine months have seen a far healthier trading situation with a worthwhile operating surplus being achieved during this period.
Due to the confidential nature of much of the Units activities, publications and recognition awards are somewhat rare. It was therefore pleasing that Mr John Dixon was invited to present a paper at Euronoise 98 and Mr Dave Rhodes was awarded the prestigious Henry Ford Technology Award for his development of the Drive-by Analysis methodology and associated software. Mr Tony Rose, a technician at Chilworth for the past eight years, retired in April. The Unit will miss his wealth of experience and his "... everything is possible" attitude.
Summary of Activities
Base engine studies continue to be a major part of the experimental activities with the bias this year being more towards direct injection turbo charged diesel engines. Two of the running engine projects have been validation and correlation exercises on two very different modelling studies. In both cases the aim of the projects was to predict the radiated noise of the engines. In one approach every forcing and response component was modelled fundamentally, in the finest of detail; the other approach was to simplify every measured noise generation relationship and then recompose the engine noise by means of a flexible empirical model. Both methods have proved to be most useful for achieving insight into the noise generation mechanisms of an engine, as well as valuable tools for evaluating design modifications.
As an example of the various cost saving studies, a comprehensive investigation has been carried out into the effect on refinement of down grading the material quality of an engine's crankshaft. For many years the dynamics of the crankshaft have been viewed as a principal controlling factor of an engine's refinement, and this study is allowing some of the long held theories to be put to the test.
Various production variability studies have been carried out ranging from exhaust system response sensitivity due to turbocharger excitation through to cylinder block response sensitivity due to chain tooth-pass frequency excitation. Contrary to recent publications on this subject, the production variability in many components can be designed to be surprisingly small especially in the case of die-cast aluminium structures. Press steel spot welded fabrications, however, remain as variable as ever, especially in terms of phase response.
With many of the primary noise sources present within a modern diesel engine being successfully controlled, the fuel injection system noise is now often dominant at low speeds, especially with the continued trend towards ever higher injection pressures. A major study into the fundamental noise generation mechanisms of fuel injection systems has been recently carried out, and appropriate models created to provide guidance during the development stage.
Although most manufacturers are satisfactorily meeting the currently imposed exterior noise legislations, there is still considerable activity within the Unit to understand more completely the various aspects of the drive-by test in an attempt to identify ways to meet the legislation, but with less cost and weight penalties. A comprehensive power unit exterior noise path analysis for a family saloon has been carried out using an Engine Noise Simulator, and the attenuating properties of the principle vehicle components and apertures have been characterised.
A number of marine propulsion projects have been carried out on diesel powered craft in the range between 15 and 20 metres. In general the engine installations appear to be well engineered; however, poor transmission layouts and unfortunately dimensioned exhaust systems have been a common failing. Although such work is unlikely to form a significant proportion of Unit activities, the automotive skills within the ADAU have been shown to be of considerable relevance to the Marine industry.
The past year has been both busy and diverse for those in the analytical team. Engine FE studies have continued with the most comprehensive engine model creation and validation to date nearing completion. But perhaps the most exciting area of recent activity is in vehicle modelling. The ADAU automatic optimiser routine has been configured to optimise the design of a truck chassis to minimise the low frequency noise within the cab. Although originally there was some scepticism regarding this approach, the chassis design generated by the optimiser shows considerable logic in its detail and the hardware validation is awaited with interest.
New statistical energy methodologies continue to be developed for studying vehicle body noise and vibration. A technique for greatly reducing the number of measurements required for vehicle model creation is showing promise, thus addressing the criticism often levelled at experimental SEA of it being excessively labour and time intensive. Another potentially exciting development in energy methods is the possibility of creating an adequately accurate model from the very limited data held within a vehicle concept model. Although the ongoing studies have identified areas of potential modelling weakness, it is believed that generic characteristics may be utilised to support such ill conditioned sections of the model.
A further new use for the ADAU optimiser has been for minimising gear tooth clearance changes due to differential expansion of a multi material engine structure. The application under study was an underslung, gear driven, Lanchester balancer module attached to an aluminium ladder frame which in turn was attached to a cast iron cylinder block.
The past year has seen considerable hardware development for numerous customers. A servo fuel metering device that allowed an engine to be run on different fuels in its different cylinders was conceived and developed. A simple device for measuring the temperature of intake valves on a running engine has also been developed and, although only intended to last for 25 hours, the device continues to perform perfectly after over 800 hours of testing.
A full remote control system has been developed for driving a vehicle through various specific crash scenarios. What initially appeared to be a relatively straightforward task, evolved into a major exercise in servo development and electronic risk management.
After around five years of intermittent development, two omni-directional sound sources (one low frequency and one high frequency) are close to their final design. The ever present trade-offs between power linearity and omni-directionality has resulted in numerous design iterations, but the current specifications are now believed to be close to optimal. The various engine noise simulators developed by the Unit have been heavily used throughout the world over the past ten years. To cope with new test requirements and lack of availability of spare parts, a new generation of simulators is currently being developed.
With the award winning exterior noise software development nearing completion, attention has now been directed towards developing similar software for interior noise path analysis. Although similar in concept, the interior noise package has the added complication of a mixture of bandwidths in order to accommodate the order related structure-borne content and the broad band airborne component.
The ADAU has been heavily involved in four automotive short courses in the past year, two given at the University and two given to individual industrial organisations. Both internal and external training and education are seen as clear areas of opportunity for the Unit.
Dixon, J., Is the silent vehicle an unnecessary dream?, Proceeding of Euro Noise 98, Munchen, 1998
Dixon, J. and *Phillips, A.V., Power unit low frequency airborne noise, IMechE Transactions of European Conference on Vehicle Noise and Vibration, London, 1998, 71-75
*Robinson, I., *Walsh, S.J. and Stimpson, G., Vehicle Accessory Tonal Noise - Experimental Determination and Subjective Assessment, Proceedings of lnterNoise 98, 16-18 November, 1998, 1049-1052
*Robinson, I., *Walsh, S.J. and Stimpson, G., An investigation of vehicle accessory noise using the principle of acoustic reciprocity, Proceedings of the Institute of Acoustics, Cranfield University, 20(1), 1998, 57-64
* - Not working in ISVR
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