Annual report 1997-1998

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 1997 - April 1998.

 

ISVR Consultancy Services

Manager Mr R A Davis

Manager's Statement

ISVR Consultancy Services (ICS) is a self-funding advisory unit which carries out short- and medium term consultancy and applied research projects for a wide range of clients in both the public and private sectors. The unit operates on a commercial basis, with full-time engineering and support staff, and is a Founder Member of the Association of Noise Consultants (ANC). The Unit maintains close links with ISVR Research Groups, and a number of projects are undertaken in collaboration with academic and research staff.

Summary of Activities

Consultancy projects are client-confidential. However, the following general descriptions of projects in progress during 1997-98 illustrate the range of work undertaken.

Environmental Noise

There has been a continued growth in demand for environmental noise assessment studies, in connection with new developments or in cases of alleged noise nuisance. On many occasions, these projects lead to an appearance in Court or at Public Inquiry.

Projects included the assessment of noise and vibration from the proposed extension to the Welsh Highland (Festiniog) Railway, and the presentation of evidence on behalf of the proprietors of the Garsington Opera Festival who were being prosecuted for non-compliance with noise limits in a planning consent. Other industrial premises and operations investigated have included drop forges, foundries, asphalt and waste recycling plants.

A number of studies have concerned the assessment of the suitability for residential development of sites which are exposed to noise or vibration from transport or industry. Noise levels are assessed against guidance in the government policy document PPG24 'Planning and Noise'. Some deficiencies and ambiguities in this guidance have been identified: these are a matter of current debate amongst planning authorities, consultants and others.

A two-year project to investigate environmental noise and vibration problems from forges and foundries in the Black Country area of the West Midlands commenced in early 1998. This project (The Black Country Project) is supported by European Regional Development funding and by industry groups, trades unions and local authorities. These traditional industries are in many cases located close to housing. Noise and vibration problems are restricting the activities of many companies and, in some cases, threatening their viability with consequent adverse effects on local investment and employment. This project is intended to provide assistance by identifying cost-effective methods of dealing with the most common noise and vibration sources in these industries.

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Noise and vibration control engineering

A number of projects have involved the practical application of noise and vibration control techniques to industrial processes and machinery and to consumer appliances. The Unit has been retained by a leading supplier of acoustical packages for gas-turbine powered generator and compressor sets to provide design support. Design studies have been carried out to define noise reduction strategies for machinery used in the food and pharmaceuticals industries. Other projects include the prediction of noise breakout from a large waste heat boiler to be installed in a major new combined heat-and-power (CHP) plant, and the investigation of ground-borne vibration from a press shop at a car body plant.

The Unit is acting as noise consultant on a number of marine projects. Projects completed in 1997 include the J-class yacht 'Velsheda', which has been rebuilt to the highest luxury standards in a Southampton yard.

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Structural Dynamics and Computational Acoustics

ICS, in conjunction with the Structural Dynamics Research Group, is continuing to develop advanced techniques for the prediction of noise and vibration. Sales of the AutoSEA design software, which uses statistical energy analysis (SEA) methods, are continuing in association with a second UK agent, Topexpress. An SEA model of a section of an offshore platform was developed for a Norwegian consortium as an illustration of the applicability of SEA to the prediction of structure-borne noise.

Two major projects have been carried out on vibration and noise in buildings from nearby rail systems. A study for the proposed Croydon Tram Link combined experimental data with analytical modelling to predict vibration and noise levels within properties close to the track. A study for London Underground, to predict re-radiated noise in buildings over a new line, has used boundary element software developed by Professor Petyt. This project was carried out in collaboration with W S Atkins.

ICS is a partner, with Airbus Industrie and other European groups, in a BRITE-EURAM research contract which will develop techniques for modelling airframe-generated noise from large passenger aircraft.

There is continued collaboration with the University of the South Bank to develop practical applications for the FAME software, which uses ray-tracing techniques to predict complex sound fields within buildings.

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Test and Experimental Work

ICS operates and manages the main ISVR test chambers, including the recently refurbished large anechoic chamber, which is increasingly used for product testing as well as for undergraduate and postgraduate research. Work is in progress to convert two small anechoic chambers into a single chamber which will provide a vital additional facility for research.

High intensity testing of aerospace components continues to be a regular element of testing work. The test facility uses Ling EPT-94B and Wyle WAS-3000 compressed air drivers which can produce acoustic powers up to 30 000 watts and test sound pressure levels up to 165 dB. Building modifications have been carried out to provide additional preparation space and improved access to the reverberation chambers, mainly to enable large spacecraft antenna dishes to be handled more efficiently.

Laboratory tests to determine sound power levels have been performed on equipment such as shipboard machinery, computer peripherals, air-conditioning units and cellular telephone base stations, using reverberant and hemi-anechoic test methods. There is increased interest in the use of intensity methods for determining sound power levels in situ, using the methods of ISO 9614, particularly where equipment can only be operated over a range of conditions on a test rig at the manufacturer's premises.

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Speech, Communications and Electroacoustics

The Unit has wide expertise in the assessment of speech intelligibility, audibility of warning signals, and in the design and development of electroacoustic systems. A wide range of projects in this field were completed or started during the year.

Two investigations were carried out to prepare evidence in criminal cases, in one case for a police force and in another for solicitors acting for a defendant. These involved measurements at crime scenes to assess whether voices and other sounds might have been heard, understood or identified in other parts of the buildings concerned.

In contrast, noise measurements were carried out under a racing driver's helmet, during high-speed testing, to assess the performance of the speech communication system used by a leading Formula One motor racing team. The objective is to develop means of improving audibility by overcoming problems of unfavourable speech-to-noise ratios. Improvements using alternative hardware and adaptive noise cancellation are under review.

Hardware development activities include providing assistance to a manufacturer in the design, development and electroacoustic testing of telephone handsets which will be installed at each seat in future passenger aircraft, and the assessment of the feasibility of modifying the design of respirator masks used by military personnel to improve the speech intelligibility of the wearers in face-to-face communication.

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Personal injury claims, hearing conservation

The Unit is regularly instructed by solicitors in connection with employee claims for noise-induced hearing loss. Most of these claims relate to alleged long-term exposure to noise in manufacturing industries, although many relate to noise from communications or test signals through headsets. These require specialised measurement methods using an acoustic manikin or miniature microphones. Interesting inspections in connection with claims for noise-induced hearing loss include a nine hour trip on a sludge vessel down the River Thames, to assess the noise exposure of engine room personnel, and a visit to a 'paint ball war games' venue to measure the noise from a pyrotechnic device alleged to have caused traumatic hearing loss in a participant.

A number of assessments of workplace noise have been completed, to meet the requirements of The Noise at Work Regulations 1989 and to assist employers in developing hearing conservation policies and procedures. A survey of flight crew noise exposures, including noise from headsets, has been completed for an airline flying mainly European and domestic routes. This follows a similar assessment carried out for British Airways, referred to in previous Annual Reports. A comprehensive survey of noise levels and work patterns has been carried out in a large UK metal refinery.

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Other activities and developments

A project for the Department of Trade and Industry on noise from toys and the effects on children's hearing has been completed. Future CEN and ISO standards on toy safety will include noise limits, and one objective of the study was to inform the committees concerned about appropriate limits and test methods. Noise limits were derived on the basis of published information on play behaviour and assessment of other commonplace noises to which a child might be exposed. A review of current or proposed toy noise standards or regulations from around the world was undertaken. Noise levels from about 200 toys of various types were measured: approximately 15% produced noise levels higher than the proposed limits. The full report is available on request from the DTI.

'Bespoke' short courses have been provided for engineers in the petrochemical plant design and contracting industries. Staff from the Unit have lectured on other ISVR short courses and to undergraduate and postgraduate groups.

Technical information sheets are available on request covering most consultancy activities. These are also on the ICS web site, which can be found at https://www.isvr.co.uk/ . Information on the Black Country Forge and Foundry Project can be found at https://www.isvr.co.uk/bcffp/index.htm

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Automotive Design Advisory Unit

Manager: Mr J D Dixon

Manager's Statement

The past year has again seen much change in the field of automotive NVH (Noise, Vibration and Harshness). The move to devolving much of the Research and Development responsibility from the major manufacturers to their first-tier suppliers continues, which has resulted in the Unit (as well as other members of the ISVR) being increasingly asked to provide specific training courses for these suppliers in order to help them achieve the necessary technical standard.

For very different reasons, training is also being increasingly requested by the major manufacturers who, although highly competent technically, are now looking for robust short cuts in their development processes. Many of the CAD procedures developed in recent years are highly sophisticated, but they often fail to give designers the quick answers they require. The ADAU is therefore being increasingly asked to provide training and associated procedural development with the aim of simplifying and accelerating the design process.

It is therefore ironic, with all the recent training provision opportunities available to the ADAU, that we have lost one of our staff members to the teaching profession. Martin Hughes left the Unit in September 1997 to retrain as a secondary school science teacher. During his ten years with the Unit, Martin was involved with many successful projects, but one of his greatest achievements was to develop the Engine Noise Simulation technique (The 'Wooden Engine') from a concept through to sellable hardware.

Trading has been difficult throughout the year, principally as a result of major changes and volatility in the Automotive market as a whole. The financial problems in the Far East have resulted in Korean contracts being prematurely halted, and any further major work from Asia seems unlikely in the near future. In the West, the concerns are different, with numerous major company take-overs having changed the supplier support requirements almost overnight. Three of our regular customers have acquired new owners in the past six months and, with inherited in-house expertise, it is unlikely that they will need external NVH research support in the short term.

Summary of Activities

Experimental studies

The four semi-anechoic engine test chambers at Chilworth continue to be heavily utilized, mainly for car-sized petrol and direct-injection diesel engines. Much of the work involves gaining an understanding of generic noise issues, with chain and belt drive systems still being a major area of investigation.

A number of studies have been carried out into the refinement of ancillaries. In general, suppliers are attempting to gain greater performance from their components at lower cost and weight, which often results in basic low-noise design guidelines being contravened. To improve power output, alternators are being run at increasingly higher belt ratios, and studies have shown that at high engine speeds broadband alternator noise can rise to within 2 dB of base engine noise. Novel solutions to high alternator noise levels have recently been demonstrated, along with the setting of noise quality targets for alternator whistle. Another ancillary suffering from compromising design pressures is the air compressor. To save weight and cost, multi-cylinder compressors are being increasingly replaced by single-cylinder units up to quite large applications. This results in a general increase in compressor noise and increased potential for vibration generation. Studies have been carried out to create simple empirical models of compressor noise generation, which will allow designs to be optimized at the concept stage.

Experimental combustion excitation simulation (The 'Banger' Rig) has been very active, with eleven engines studied in the past year. One of the popular uses for the 'Banger' rig is as a means of validating finite-element (FE) models in a controlled yet representative manner. The rig has also been used to evaluate cost-saving structural modifications to a current production petrol engine.

There has been a diversity of vehicle projects, ranging from an in-depth investigation into the noise characteristic of medium-sized commercial trucks to a comparative study of the transmission loss characteristics of luxury cars.

Analytical studies

The analytical studies continue to be centred around FE modelling of engine structures, both for optimizing existing designs and for comparative studies of alternative concepts. A recent investigation into the forcing of such engine models clearly demonstrated the effectiveness of simplified loading, with results comparing very favourably with the far more complex loading incorporating full oil-film representation.

The in-house optimizer is primarily used for engine structure studies, but has also been used for a non-automotive application, namely to maximize the fundamental resonance frequency of a transmitter aerial. It is believed that this highly-developed optimization process has vast potential in many other areas which are as yet untapped.

The empirical models for predicting engine noise as pioneered by the ISVR in the early 1970s are seeing renewed interest. Although the models are now considerably more detailed, they still maintain the simplistic approach that allows rapid evaluation of design parameters. A recent gasoline direct-injection, four-stroke model has
proved most useful in demonstrating the refinement issues inherent in this currently fashionable combustion cycle.

Software development

There has been an increasing trend to deliver the findings of large studies in the form of dedicated software. Impressive Windows-based packages for predicting drive-by noise, base engine noise and engine balance have all been developed during the year as a means of conveniently conveying the findings of specific projects. Windows-based software for automating a handheld point mobility meter has also been delivered.

Training and process development

In the past year the ADAU has had a major involvement in five short courses with an automotive slant. Although there continues to be a demand for courses dedicated to NVH techniques and methods, there is increasing interest in NVH awareness courses designed for non-specialist engineers.

The Unit has also led specific process development and training for individual companies which involves on-the-job training, mainly in analytical areas. The ISVR's recently acquired Video Conference facility has allowed such training to be efficiently carried out throughout the world.

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