Annual report 1999-2000

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 1999 - April 2000.


ISVR Consultancy Services

Manager Dr A J Bullmore

Manager's Statement

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 the ISVR Research Groups, and manages the ISVR's main test chambers, comprising anechoic and reverberation rooms and acoustic high intensity facilities.

The Unit has undergone a number of important changes during the year. In October Mrs Pam Dawson, the Unit Secretary, retired after 16 years of loyal service. A party was held for her at which many former staff who had worked with Pam returned to express their appreciation of her contribution. In December, Mr Reuben Peckham left the Unit to take up a position with another firm of acoustic consultants.

Another significant change has been in the Unit's business objectives and management structure. A new management team has been set up comprising Dr A J Bullmore (General Manager), Mr R A Davis (Technical Manager), and Mr M G Smith (Deputy Manager). To support the Unit, which now employs a total of nine engineers, Mrs H E Smith has also been appointed Unit Administrative Secretary and PA to the managers.

The new management structure has resulted in the development of a strategic marketing effort in a number of major sectors. The added value of ICS as a consultancy unit that sets it apart from most other acoustic consultancies lies in its links with the rest of the ISVR, and in the expertise and facilities thereof. To emphasise this benefit a new brochure and associated marketing material have been produced. The aim of this material has been to promote the ISVR's consultancy services as a complete package, breaking down the barriers between fundamental research and practical applied solutions to allow clients access to the ISVR's complete range of expertise. This approach is proving highly successful, with several new large scale projects having already been secured for the forthcoming financial year.

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.

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Summary of Activities

Environmental noise

Most significant advances over the year have been made in the field of environmental noise. Through the actions of both the UK Government and the European Commission, environmental noise has re-emerged as one of the primary considerations in general acoustics. The 1996 EU Green Paper on future noise policy concluded that 60% of the population of the EU is exposed to unacceptably high levels of noise in their home environments, and that action must be taken to improve the situation. Consequently, a number of working groups were set up by the EU to look at the problem of environmental noise. The membership of these groups includes the ISVR's representation through Dr I H Flindell of the Human Sciences Group who is co-chair of one of the working groups.

As a result of the deliberations of these working groups, it is likely that the EU will shortly issue a directive requiring all local authorities responsible for centres of population greater than 50,000 to produce a noise map of their area. Noise maps must be accompanied by a strategic noise action plan to reduce the general level of noise to which residents are exposed. The activities of noise mapping and strategic planning for reduced environmental noise have been identified as areas in which the ISVR should increase its involvement through the consultancy activity of ICS, both because of ICS's long established experience in environmental noise and the potential research spin-offs for the ISVR. Marketing efforts in this area, and close collaboration with the Human Sciences Group, have thus far proved highly successful. ICS will be looking to appoint at least one additional engineer in the near future to assist in the work already secured.

ICS also managed a highly successful multi-disciplinary feasibility study investigating the effect of night-time aircraft flyover noise on sleep disturbance. This project, which was technically managed by Dr Flindell, involved a collaboration with the DERA Centre for Human Sciences, the National Physical Laboratory and MVA, who undertook the social survey aspects of the work. This project demonstrated the effectiveness of laboratory-based sleep disturbance tests. It is hoped a full scale investigation will follow.

Work is continuing on the EU-funded project to define cost-effective means of reducing noise from forges and foundries. This project is based in the West Midlands and work is now well-advanced on demonstration projects at three sites. One major project involves uprating the sound insulation of a large forge shop by over-cladding, new doors, and the installation of a simple ventilation system to eliminate openings. The outcomes of the projects will be published in early 2001.

As in previous years, there is a growing demand for providing assessments of noise climates on proposed sites for new housing. There is great interest in sites which have previously been disregarded: next to busy roads, railways or industrial premises. Assessments generally involve extended monitoring periods of at least 24 hours, to enable daytime and night-time noise levels to be defined in accordance with Planning Policy Guidance PPG 24. Noise impacts can be minimised by careful site layout and the use of suitably located barriers in the form of walls or fences. In some cases, additional protection to individual rooms is required, by the use of uprated glazing with acoustic ventilator units.

Alongside the larger scale environmental noise projects, ICS has continued to service numerous smaller scale jobs. 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, assessment and control of noise from pubs and night clubs.

Other investigations concerned proposed 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. Work has also been undertaken in assessing the impact of noise from new road schemes on existing housing. This work has primarily been undertaken to investigate claims made under Part 1 of the Land Compensation Act. This Act compensates for a reduction in property value resulting from, amongst other physical factors, increased noise. The problem arises because many claim properties lie 500 metres or more from the new road, and at such distances received A-weighted traffic noise levels can vary by 15dB or more, due to meteorological effects alone. Much effort has been expended on establishing the dependence of received noise levels at large distances from roads on specific meteorological parameters. The ultimate objective of this work is to provide a consistent and defendable approach to establishing noise levels in respect of compensation claims.

A number of other 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 application of British Standard BS 4142:1997.

Vibration also continues to be a problem, in particular in the community. Disturbance due to equipment operating in commercial premises under apartments has been investigated, and dynamic tests have been carried out in a new multi-storey hotel. Modal response data was acquired to assess whether activity in the public area would cause disturbance in bedrooms.

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Computational acoustics and structural dynamics

The main activity in the area of computational acoustics has continued to centre on two research projects associated with the drive to reduce noise pollution around airports. These major long-term contracts are administered through the ISVR and carried out by ICS staff seconded to the Department. In the first, the 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 generated by 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 a wind tunnel on full scale landing gear, and the prediction of flyover noise of Airbus aircraft. The second project involves mathematical modelling of sound propagation in lined ducts in order to optimise the attenuation of aero-engine noise. This work is being carried out in collaboration with the ISVR Fluid Dynamics and Acoustics Research Group and Rolls-Royce plc.

Other activities include the ongoing sales and consultancy work associated with the AutoSEA (Statistical Energy Analysis) software, with some significant work for DERA on shipboard noise sources, which draws on the ISVR's expertise developed during recent research funded by the Marine Technology Directorate. The ISVR was also successful in securing an 18 month contract to apply SEA techniques to the refinement of the noise and vibration characteristics of a high speed boat. This work has also involved the application of Finite Element techniques to optimise mounting arrangements of power plant, including hull modifications.

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Communications and hearing conservation

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 police firearms instructors and television studio technicians. Noise exposure for fire-fighters has also been assessed, with particular reference to noise from communication systems and alarms from personal safety equipment. Although the 'Kemar' head and torso simulator has been used by ICS for over 10 years to measure noise levels and exposures of people who use headsets at work, the publication of the TUC/RNID report 'Indecent Exposure' has increased the demand for this specialist expertise.

This year, ICS has undertaken the measurement and assessment of noise exposures of agents in several telephone call centres, mainly help desks and insurance companies, and of operators in the control rooms of various police forces. Measurements were also taken of the noise output from headsets used by telephone switchboard operators, headsets and stethoscopes used by interview tape transcribers, the D-types 'earhangers' or earpieces which are becoming popular with many police forces for use with personal radios, and covert inductive earpieces used for undercover police work.

A study was undertaken of the noise exposures of flight-deck crew for a major airline, in which recordings were made of the noise on 12 sectors or flights in two (long) days. This is the third airline for which measurements of both headset output and cockpit noise during scheduled flights have been made.

A comparison of the noise attenuation of flying helmets fitted with Active Noise Reduction systems from two different manufacturers has been made. The objective was to determine which system gave the greater hearing protection when used in small helicopters, such as those used by police air support and air ambulance services.

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Architectural acoustics

Specialist projects over the year have included the acoustic design of telephone call centres including one housing 800 operators in a single area, a science exploration centre, a planetarium, auditoria, remedial treatment of night-clubs, recording studio complexes and the improved acoustic design of lightweight and modular buildings. This specialist work has been undertaken in parallel with many smaller scale projects including the on-site testing of party walls and floors in houses and flats to assess compliance with the Building Regulations. This work has been supported by the laboratory testing of architectural elements for both sound insulation and sound absorption properties.

Photograph of Call Centre

Enhancement of the acoustic properties of a call centre for 800 workers

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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 and other aircraft components. Levels of up to 165 dB can be achieved using a WAS 3000 compressed air driver unit. The flexibility of the facility has been greatly enhanced during 1999 with the installation of new air compressors. Further work is planned in the forthcoming year to increase the sound insulation of the test facility so that higher acoustic levels can be achieved without break-out noise affecting other activities within the ISVR, and also to allow out-of-hours operation to maximise the use of the facility.

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 measurement. Equipment submitted for test includes cellular telephone base stations, ventilation and air-conditioning units, computer peripherals and domestic 'white goods'. An increasingly large part of the ISVR's test programme is now associated with development work to reduce the noise levels of various products.

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 tests have been carried out on highway noise barriers, wall and partition constructions, and acoustic ceiling materials.

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.

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Other projects

ICS staff continue to act as expert witnesses for in various national inquiries. Assistance has been provided to the ISVR in the design and development of a new paediatric test room for the South of England Cochlear Implant Centre. Other work has been carried out for confectionery manufacturers, clients with flow rigs, and packaging companies, in order to enhance their production and product.

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ISVR Automotive Design Advisory Unit

Manager: Mr J D Dixon

Manager's Statement

The automotive industry has seen yet another year of significant change, with numerous manufacturers being involved in mergers, take-overs and sell-offs. Although such developments may provide a brighter overall future for the companies involved, it causes considerable upheaval at the lower levels, including their Research and Development activities. Many suppliers are living in the world of acquisition, with a firm trend being seen towards fewer and larger suppliers. Some first-tier suppliers are now manufacturing more components for a particular vehicle than the Original Equipment Manufacturer (OEM) to whom they supply. This somewhat surprising situation should, in time, result in an increasing Research and Development budget being spent by the suppliers to counteract the falling Research and Development resources being spent by the OEMs.

All this turmoil in the industry is clearly a result of the need to take cost out of the vehicle in order to remain competitive. This cost reduction, or 'thrifting', of vehicles is becoming perhaps the most important issue in the industry. But, however important cost reduction may be, no sign of product cheapness must be seen, and all other features of the vehicle must either improve or at the least stay the same. Luckily for the automotive activities within ISVR, many avenues of thrifting potentially impinge upon the refinement of the vehicle, and so the NVH cost trade-off is currently very much of concern to the OEMs and their suppliers.

Despite this continued upheaval within the automotive industry, the Automotive Design Advisory Unit (ADAU) has had a relatively stable year, with a gently rising order book, a slight increase in customer base and a modest increase in reserves recorded in the end of year figures.

The turnover of staff within the ADAU is low, and therefore it is always a big occasion when someone leaves. Bruce Appleton left the Unit in July to take up a career in the Health and Safety Executive in his birthplace of Hull. Bruce joined the Unit over twelve years ago, fairly soon after graduating from the ISVR. Although very able in most areas of automotive work, he specialised in duct acoustics and soon became the Unit's expert on intake and exhaust systems. He became known by a major manufacturer as 'Bruce the Moose' for his work on a major cross-vehicle-range problem of induction air instability (which produced a Moose-like noise). Bruces's open exhaust noise studies and his midnight vehicle transmission loss measurements in Chilworth laboratories car park will not be missed by either the Science Park or guests in Chilworth Manor. However, his solid knowledge of acoustics, his robust experimental procedures and his often novel viewpoint will be greatly missed by all staff and students who have had the pleasure to work with him.

 

Summary of Activities

Experimental Studies - Powertrains

The four semi-anechoic engine test chambers continue to be heavily utilised and the once-threatened wind down of running engine work in preference to analysis seems ever further away. Reversing the trend of last year, the majority of the test bed studies have been on petrol engines, especially of the large V type configuration.

The long term study of the fundamentals of chain noise generation has continued. It has become clear that at least four different mechanisms can be responsible for the generation of tooth pass frequency noise plus further mechanisms for the broad band (wash). Although simple models have been proposed for some of the individual mechanisms, no complete model has yet been constructed. It is hoped that such system modelling will be attempted in the near future in collaboration with a major chain supplier.

The focus of the Unit's gear noise studies has predominantly moved from the front-end gear sets of medium-to-large size truck engines, to the 2nd order balancer drive systems of small high speed petrol and diesel car engines. Although many of the noise generation mechanisms are common between these two applications, the detail of the forcing and the design constraints are often different. A high speed gear noise rig has been designed and commissioned. The variable speed rig has provision for varying the input speed torsional fluctuations, the gear clearance and the bulk oil temperature. To date, three different gear set designs have been evaluated and a number of clear parametric trends have emerged.

As with gear noise, the fuel injection noise studies have also moved from large diesel truck engines to small direct injection car petrol engines. Although the operations of the injectors are very different for these two applications, the problems are very similar. For performance and good emissions, injectors need to open and close very rapidly resulting in high levels of jerk and very rapid impact velocities, both of which are undesirable for low noise. Simple models of the excitation mechanisms clearly show that for the current injection concepts, a clear trade-off between noise and performance is inevitable. It would appear that the only practical way to 'silent' injection will be the development of a totally novel way of injecting the fuel without the need for pintle valve operation.

Main bearing cross bolting remains a debatable subject in relation to its effect on engine NVH. Although perhaps there is no one definitive statement regarding the benefits or penalties of such a feature, a recent study on a light weight V8 engine designed for cross bolting was most illuminating. A customer's Finite Element study was paralleled with a 'Banger rig' study carried out by the Unit. It was found that quite significant casting changes to the crankcase gave only marginal improvements in the engine's combustion attenuation. However, the simple removal of the main bearing cross ties increased the noise dramatically. Conversely, previous studies where cross bolting was introduced on an engine of a deep skirt design have shown little improvement, and sometimes even an increase in noise. Perhaps the encouraging aspect of this apparent contradiction is that it appears that these effects can be modelled, even with relatively simple concept models.

A major study into the mechanical excitation of a range of V8 engines is currently underway, where each of the major sources (ie piston slap, valve gear, front end ancillary drive, etc) are quantified for both the customer's engines and an agreed target engine. Although the project is not yet complete, very clear trends and differences between the engines are emerging. Although not surprising, perhaps the most worrying finding is the high level of noise generated by the ancillaries on all the engines tested to date.

Experimental Studies - Vehicles

The major part of both interior and exterior vehicle noise at (legal) motorway speeds is due to tyre noise. Therefore, understanding tyre noise and developing procedures for its measurement have been a significant Unit activity for many years. Although there are considerable complications with the apparent non-linear effects of the road-tyre interaction, a robust airborne tyre noise path analysis technique has been developed. One somewhat surprising finding from this study is the high levels of tyre noise entering the vehicle through the door skins.

Assorted support activities have been provided for a number of trim suppliers. These studies have ranged from simple quantification of trim performance through to validation of complete vehicle SEA models.

Some vehicle refinement problems never seem to die; perhaps one of the best examples is axle whine from rear wheel drive vehicles. The history of axle whine studies in the 1SVR goes back to the '60s, and although the problem remains the same, a new twist arises each time. A recent study showed that the very intrusive pinion whine heard in a vehicle at around 85 kph was brought on by the second bending mode of the prop shaft sitting over a resonance of one of the major transmission paths. Dimensional changes to the prop shaft significantly reduced the levels of whine.

Although the majority of recent vehicle studies have been carried out on passenger cars or light commercial vehicles, there are still ongoing design projects on heavy goods vehicles. Manufacturers of commercial vehicles value the NVH overview that can be given by the Unit at the initial design stage as well as the specific design input (mainly in the form of analysis) for both the cab and the chassis.

The marine activities of the Unit continue, albeit at a relatively minor level. Projects have ranged from investigating luxury yacht engine failure through to the prediction of machinery foundation mobility for a new vessel under construction. Bearing in mind the location of the University and the collective skills within the faculty, it is believed marine work should be more proactively sought.

Analytical Studies

The analytical group based on the campus has had a very busy year. Although they have completed projects on both vehicles and a ship machinery installation, their main area of activity has remained the design of engine structures. One structural optimisation of a European car engine has been completed, whilst another optimisation on a North American truck engine is currently underway. In both cases the finite element models and force developments were supplied by the customer. However, the North American customer's analytical team had been trained by the ADAU over previous years. It was found that the models and forcing conditions developed under the guidance of the ADAU were of a markedly higher quality.

After a number of years avoiding major engine model construction tasks (preferring to add value to customers own models), the analytical team were recently persuaded to model a complete prototype engine including all covers. The North American customer now has a very high quality model to aid new engine development. It is envisaged that the Unit will soon use the model for structural optimisation purposes.

Instrumentation Development

After all the development effort put into the high frequency omni-directional sound source, it is gratifying that a number of the units have now been produced to the same design. Ironically, the low frequency sound source that took even greater development effort has not been met with the same popularity. A one-off experimental 8 channel white noise signal generator was developed to allow a customer to study the effect of vehicle noise path coherence using one of the standard ADAU developed Engine Noise Simulators (ENS). Upgrading of customers ENS units to the new ADAU specification has continued throughout the year. It is hoped that this new specification of electronics will remain maintainable for at least the next fifteen years.

Software Development

A vehicle interior noise path analysis package being developed for a customer is nearing completion. The Windows based modelling architecture allows the user to construct a vehicle model by specifying the sources and paths.

A simple solid body engine vibration prediction package has been developed for a customer who wished to be able to predict the best place to locate his component on an engine to minimise durability issues. This however was not as simple as first envisaged.

The past year has seen an increase in requests to support previously delivered software; most tasks are to convert DOS routines into Windows format.

Training

The vehicle and engine noise short courses, now run by the Unit, were over subscribed this year. This suggests that there is still a need by the industry for the broad brush knowledge transfer ably delivered by the ISVR.

A number of informal, one-day, educational visits have been made to various customers. In general, the instruction is targeted at their specific product; but often the broader picture has to be presented, to allow the NVH performance of their component to be placed in context.

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