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Annual report 2001-2002

[] Every year the Institute of Sound and Vibration Research publishes an Annual Report. These are the entries for ISVR Consultancy Services and the Automotive Design Advisory Unit covering the year May 2001 - April 2002, before the two groups combined.

 


ISVR Consultancy Services

Manager: Mr S J C Dyne

Manager's Statement

ISVR Consultancy Services 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 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 the ISVR Research Groups, and a number of projects are undertaken in collaboration with academic and research staff.  The Unit website at www.isvr.co.uk includes details of the full range of services and facilities available.

There have been a number of staff changes in the reporting period.  Mr Christos Karatsovis has joined the unit expanding expertise in environmental noise and vibroacoustics and Mrs Diane Farrenden has become unit secretary. Brian Dennis has moved on to another acoustic consultancy and former Technical Manager, Bob Davis, has officially retired but continues to support unit activities in a new role as Associate Consultant.

Summary of Activities

Consultancy projects are client-confidential.  However, the following outline descriptions of projects in progress during 2000-2001 illustrate the range of work undertaken and the general direction of consultancy activities.  During the period there were nearly 200 enquiries logged, with over 28% becoming actual projects.

Environmental Noise

A significant achievement has been the completion of our Black Country Forge and Foundry Project sponsored by the EU. Traditional metal working industries are important to the economy of the 'Black Country' area in the West Midlands. Many forges and foundries are located here, and many of these companies are small or medium sized businesses. However, forges and foundries are often situated close to residential areas. Much of their work is inherently noisy, and the noise is often impulsive and distinctive. The cost of noise control or of restricting working hours constrains development of these businesses and in some cases threatens their survival. Alleviation of community noise problems significantly improves the long-term prospects of foundries and forges with obvious benefits for employment and the local economy.  The project was directed towards the study of noise emission from foundries and forges and the development of practicable, effective means of noise control within the budgets of small companies. The final report was published early in 2002 as a handbook directed towards forge and foundry owners and managers, although it may also be useful to Environmental Health Officers, to others involved in noise assessment and control, and to residents who are bothered by noise from a forge or foundry.  Although some of the information relates specifically to forges and foundries, the same principles apply to most other industries, and the handbook has wide application. The handbook "Reducing Noise from Forges and Foundries" has also been published in full on our website.

Demand for environmental noise assessment studies continues to grow in connection with new developments and in cases of alleged noise nuisance.  In many cases, these projects lead to an appearance in Court or at Public Inquiry. 

Projects included the assessment of noise likely to result from various commercial and industrial developments such as mineral extraction and waste disposal sites including, in some cases, assessment of the impact of noise on wildlife as well as people.  The public inquiry into the proposed container terminal on Southampton Water is still in progress and noise issues are expected to be heard in September of this year. The unit is working with academic staff in the Dynamics group on an assessment of the level of groundborne noise likely to arise in the proposed Heathrow Terminal 5 from the underground railways feeding the terminal.

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 generally assessed using standards set out in Planning Policy Guidance document PPG 24.

Litigation Work

In addition to the public inquiry activity referred to above, a number of investigations have been carried out to prepare evidence in connection with criminal cases, where questions were raised about 'earwitness' testimony or the ability of witnesses to hear or recognise specific sounds.  In many other cases the unit has undertaken analysis of recordings made during alleged criminal activity, often with the aim of enhancing the audibility of recorded events or speech, and frequently involving transcription work.  Further audio enhancement and transcription work has been carried out in civil cases under instructions from solicitors, increasingly as a 'joint expert' representing both sides in a case.

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Noise and Vibration Control Engineering

The unit has worked on a significant number of diverse projects involving the practical application of noise and vibration control techniques to industrial processes, machinery and consumer appliances. A project on the acoustic design aspects of a new high-speed gas turbine-powered luxury motor yacht is continuing. Other areas of activity include an investigation of excessive noise and vibration in the exhaust stack of a power station in Macau, China, calculations of low frequency noise from a diesel power station stack, ground-borne noise from water pumping stations and estimates of shock noise from a fuel testing rig.

 

Structural Dynamics, Noise Control and Computational Acoustics

Aero-acoustics projects this year have included the modelling of noise from wings and landing gears for Airbus UK to provide a comprehensive airframe noise model for the design of new aircraft. This work continues under the SILENCER project with the Unit involved in several tasks on low noise design of landing gears and modelling of interaction effects between gears and flaps. On-going work on ray acoustics methods for Rolls Royce has also continued with the codes now being used to design new liner configurations for testing under the SILENCER project.

The long term relationship with Vibro-Acoustic Sciences Inc in the marketing and use of the AutoSEA2 software has changed significantly this year and the Unit now provides mainly a customer training service in SEA methods and a capacity for consultancy projects. This is a useful change of role since it focuses on the technical strengths of the Unit. The expectation is that we should be able to significantly expand the value of AuoSEA2 related consultancy we do over the coming years, with a further boost anticipated when a mid-frequency combined SEA/FE package is released in the near future.

As always in the acoustic consultancy field there has been a wide mix of other projects including noise control on water pumping stations, power stations and wind turbines, design and testing of absorptive materials and lightweight building materials and the design of a fire alarm. These projects provide a valuable and varied source interest and income.

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Test and Experimental Work

ISVR Consultancy Services operates and manages the main the ISVR test chambers, including the large anechoic chamber, which is increasingly used for product testing as well as for undergraduate and postgraduate research. 

High intensity testing of aerospace components continues to be a major element of testing work.  The valves in the chambers have been replaced recently to improve feedback control. This has increased slightly the maximum sound pressure level capability of the facility. The progressive wave tube facility, located in the P E Doak Aeroacoustics Laboratory, has been used for major test programmes for composite aircraft fuselage components at sound pressure levels of up to 165 dB.

Laboratory tests to determine sound power levels have been performed on equipment such as shipboard machinery, computer peripherals, air-conditioning units, cellular telephone base stations and domestic 'white goods', using reverberant and hemi-anechoic test methods.

The Unit was also tasked with an unusually demanding noise measurement project, measuring the background noise levels inside the brand new acoustic test chambers at the National Physical Laboratory (NPL), for John Laing Construction. The measurements in the free-field room were the most involved. The maximum noise levels in this room were specified in one-third octave bands from 100 Hz to 10 kHz, and noise levels below -20 dB were specified in each of the one-third octave bands from 400 Hz upwards.

Photograph of a brass microphone enclosure

Photograph of low-noise microphone inside the microphone enclosure


Microphone enclosure and low-noise microphone used
to measure extremely low noise levels

We used a low-noise microphone and a custom-made noise-excluding microphone enclosure. By measuring the noise levels with the microphone in the room we obtained measurements of the ambient acoustic noise in the room contaminated with the self noise of the instrumentation. By placing the microphone inside the enclosure we measured the self-noise of the instrumentation separately. By subtracting the self noise from the total noise we derived the ambient acoustic noise. Though not a new technique it is rare that the method is used to measure such low levels. Considerable care was taken with the measurements, a number of precautions were taken to ensure that the instrumentation was stable, and the method was pilot tested in our own anechoic room at Southampton before the NPL room was completed. By replicating the measurements over and over and applying a statistical analysis we demonstrated that the noise levels in the new NPL room met the requirement easily, and our estimates of the actual noise levels in the room suggest levels are around -30 dB or lower in the middle and high frequency bands.

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Noise at Work, Communications, Hearing Conservation and Personal Injury Claims

The year saw a continued rise in the assessment of noise exposures from headsets particularly for Call Centre agents. ISVR Consultancy Services assessed noise exposures in 12 call centres in London, Bristol, Plymouth, Cheltenham, Swindon, Northampton, Merseyside, Sunderland and Middlesbrough. Clients included two mobile phone network operators, a building society, a bank, a credit card company and UCAS, the University and Colleges Admission Service.

One of the call centres was experiencing a number of "acoustic shock" incidents, loud noise interference during calls, and had audio recordings of the incidents. Our investigations, replaying looped recordings into the call centre equipment, demonstrated that the agents' turrets were limiting the gain for loud signals. Although the interference sounds were loud and unpleasant noise exposures, even at maximum volume settings would have been well below the action levels of the Noise at Work Regulations.

In a similar vein ISVR Consultancy Services investigated an incident in a Fire Brigade control room in which an operator had taken a 999 call from a payphone. The telephone was unfortunately positioned immediately below a fire alarm sounder, and the operator was exposed the sound of the fire alarm through her headset for the duration of the call. By recreating the original occurrence we again found that the sound levels of the fire alarm from the headset were not excessive.

Laboratory work on headsets has included the testing and evaluation of headphone limiters used by radio operators. This work was undertaken to provide information for a number of personal injury claims for hearing damage. ISVR Consultancy Services measured the performance of the limiters used with various types of headphone and compared the sound levels with the equipment's specification and the action levels of the Noise at Work Regulations. We have also measured the output of radio earpieces to enable the manufacturer to attenuate their output to safe levels when used with specific types of personal radio.

Further personal injury claim investigations has included:

  • the measurement and assessment of the ultrasonic output of a dog deterrent which had been held close to a person's ear
  • an assessment of the likely noise levels and exposures of a former police firearms officer, and assessment of the effectiveness of hearing protection provided, from about 1980 onwards
  • measurement of the sound levels from emergency vehicle sirens at close range to determine the sound level experienced by a garage worker who was working under a vehicle when a colleague sounded the siren sounded. The siren in this case was mounted in the engine compartment.

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ISVR Automotive Design Advisory Unit

Manager: Mr J D Dixon

 

Unit Development

Accommodation

After nearly 30 years of split site working, the Unit has at last come under one roof. The final stage of this move took place in December 2001 when the Analytical and Computational team left the Highfield Campus to set up their computer system in newly acquired space at the Chilworth Laboratory. The move was far less traumatic than had been anticipated and their operation suffered minimal disruption. Although the day-to-day benefits of being on one site are clearly improving the efficiency of the Unit, there is the danger that the ADAU will become even more distanced from the main department: positive moves to prevent this occurring must be made.

Staffing

This year has seen the retirement of the three most senior members of the ADAU, all of whom were instrumental in setting up the Unit in 1972. Jeff Baker, who retired at the end of May 2001, pioneered much of the early research into noise quality issues associated with crankshaft dynamics; his 2 bar/deg combustion rise rate criterion is still used by many throughout the industry. Yanis Erotokritos, who, over the past 25 years, developed the Unit's powerful Finite Element and optimisation capability, retired at the end of February 2002. George Bazeley, who retired at the end of March 2002, designed, built and evaluated numerous prototype engines and components for customers throughout the world. The vast knowledge and expertise of these three engineers will be greatly missed. The Unit's Finite Element team has been strengthened by the arrival of Kengo Koshimizu who has joined the Unit for 18 months on secondment from Komatsu in Japan.

Trading

In line with just about all of the automotive industry, trading continues to be difficult. Customer numbers remain high, but the spend per customer has fallen, especially by the large multi-national manufactures. Specialist equipment sales have been very buoyant, but sponsorship for large research projects has become increasingly hard to find.


Summary of Activities

Powertrains

As in recent years the majority of the powertrain studies have focused more upon individual components rather than the total engine and transmission. Drive system noise of gears and chains continues to be studied. The dedicated chain noise rig has undergone considerable development throughout the year and is now able to apply a controlled load across the test span. Initial studies into the effect of lubrication and static tension have been carried out and plausible results have been recorded. Early attempts to model some of these observations have confirmed the belief that a number of different mechanisms of noise generation are present even with the simplest of chain systems.

A fundamental study has been undertaken into the sound quality aspects of a twin camshaft, toothed belt drive system. The excitation mechanisms of a simple drive system with both steady drive and load are usually fairly easy to understand. However, when installed on an engine, with a fluctuating drive, a fluctuating load and a resonant supporting structure, the noise generation and subsequent sound quality issues are far from simple. An understanding of some of the associated sound quality issues has been achieved, but considerable effort is still required to develop a comprehensive model of belt noise generation.

Turbochargers have been the subject for a number of studies, as both noise sources and attenuators. Although the unit has acquired considerable expertise with regard to noise generated at once-per-revolution and blade passage frequencies, this year, for the first time, both sub-synchronous and banded, speed-related noise mechanisms have been investigated, with satisfactory outcomes. For many years it has been recognised that both the turbine and the compressor of a turbocharger unit can provide significant attenuation to exhaust and intake noise respectively. In collaboration with members of the Fluid Dynamics and Acoustics Group a fundamental study has been carried out into the attenuation afforded by the compressor. A fairly accurate model has been developed for one particular installation, and now efforts must be put into improving the generic robustness of this model such that other configurations and installations may be considered.

As diesel fuel injection systems continue to work at increasingly higher pressures, so the challenge to control their noise becomes ever harder. A recent study suggests that to avoid subjective issues due to injector impacts, serious consideration must now be given to the design of the injector clamping arrangement as well as the surrounding cylinder head geometry.

The Banger Rig continues to earn its keep as a convenient means of model validation and base-lining of the structural attenuation performance of engine blocks. The now very large database on structures reveals some interesting historical trends with structural response having become spectrally smoother and generally convergent on a mass controlled asymptote.

The hybrid modelling approach to engine noise proposed by ADAU some two years ago is at last being considered by the industry as a possible way forward. A combination of the power of finite element methods (for studying the structural detail) with the robustness of empirical and lumped-parameter methods for handling such elements as forcing functions, oil films, damping, etc, provides a quick, effective and easily implemented approach.

The Unit's ongoing intake and exhaust noise studies had an interesting variation this year with the need to considerably improve the spark arresting capabilities of an exhaust silencer. A totally new swirl-inducing geometry was conceived and developed such that the spark arresting performance of the final prototype far exceeded the design targets: the acoustic attenuation of the new silencer also measurably improved.

Marine activities continue to increase; however, most projects involve gearbox or exhaust concerns rather than base engine noise.

Vehicles

Tyre noise studies have continued throughout the year with the emphasis still on improving the methods by which it is measured. As the accuracy of measurement of the source noise and its transmission through the vehicle improve, so various anomalies are surfacing. Although test-to-test variability is now small, and the effect of weather conditions can be largely accommodated, there is evidence that a particular tyre can have a 'bad day' when its source noise (and corresponding interior noise) can change measurably for, as yet, unexplainable reasons.

A new method for rapidly determining the source contributions to vehicle interior noise is showing great promise. When fully developed the technique should allow the balance between the primary sources to be determined within an hour with minimal instrumentation.

Power unit component studies are increasingly being carried out in the operating vehicle. This year a number of cars have been driving around Hampshire laden with instrumentation. A major study into the potential refinement benefits of crankshaft bending dampers has been recently carried out using solely road testing. Although the instrumentation is necessarily more complex than in the test cell, the benefits of real vehicle conditions are considerable.

Instrumentation

In the past year a further nine high frequency sound sources have been sold, six of which were to overseas customers. A Mark 2 low frequency sound source has been developed and delivered to the customer, who is most enthusiastic about its increase in power output. Both the high and low frequency sources continue to use in-neck pressure as an approximate monitor of volume velocity, but for a particular customer alternative methods are being investigated.

A high quality, low cost, multi-channel acquisition system has been developed based upon a low budget recording studio interface for which software has been written to provide calibration and the functionality required for scientific and engineering applications. Although developed for a specific project, this new system is showing great potential as an additional mainstream data acquisition system.

Software Development

As the vehicle noise modelling techniques developed in recent years by the Unit continue to spread throughout the industry, so the software support has become a growing activity. Suggestions for improvements and expansions to the packages are always being received, and if resources can be found customer-led development will continue.

Training

Even in such hard times, the Engine and Vehicle short courses still appear to be popular, although last year the engine course attracted smaller numbers than in recent years. Fortunately, the situation looks as though it will be reversed this year with the engine course already close to capacity. The Unit was responsible for running the week long Exhaust and Intake MSc Module which proved to be very popular as a short course with 12 participants.
 

Low frequency sound source

The low frequency sound source


Archive of our Annual Reports from other years
 

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For further information contact

Stuart Dyne or John Dixon
ISVR Consulting,
University of Southampton,
Highfield,
Southampton,
SO17 1BJ,
United Kingdom

Telephone:  023 8059 2162 (+44 23 8059 2162 from outside the UK),
Fax:  023 8059 2728 (+44 23 8059 2728 from outside the UK)
or e-mail: consultancy@isvr.co.uk


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