Annual report 2000-2001
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 2000 - April 2001.
ISVR Consultancy Services
Manager Mr S J C Dyne
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 is at www.isvr.co.uk.
There have been a number of staff changes in the reporting period. Mr Dave Rawlinson has returned to the fold after 16 years outside the ISVR. Mr Neil Pinder has retired after 29 years with the Unit. The former manager, Dr Andrew Bullmore has moved on to another acoustic consultancy, and Mrs Hilary Smith, the Unit Secretary, who also acted as secretary to the Editor of the Annual Report, has moved to a new post in the Engineering Enterprise Office within the university. Their contributions to ISVR Consultancy Services are much appreciated.
Mr Stuart Dyne, formerly head of the ISVR Shock Analysis Laboratory, has been appointed to the post of Manager.
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 350 enquiries logged, with over 35% becoming actual projects.
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. 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 increased activity at a military firing range in Cumbria and from various commercial and industrial developments including supermarkets and mineral extraction sites including, in some cases, assessment of the impact of noise on wildlife as well as people. A major project concerning a proposed container terminal on Southampton Water is in progress.
Extensive surveys were carried out along the route of a new motorway in the Midlands to establish pre-scheme noise levels. These measurements were also used to evaluate and validate a range of recently-available noise mapping software. An EU Directive will require local authorities responsible for major conurbations to produce and maintain noise maps to serve as benchmarks for planning purposes. This development is likely to offer significant business opportunities to software companies and consultants. However, further work is required to define the virtues and limitations of noise mapping, and to develop guidance on how noise maps can be used within the planning process.
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.
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 the ability of witnesses to hear or recognise specific sounds. One of these concerned a widely-publicised murder investigation. 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. Several unit staff attended an expert witness training course as the volume of work in this demanding role has increased.
Noise and Vibration Control Engineering
As usual, there has been a significant number of diverse projects involving the practical application of noise and vibration control techniques to industrial processes and machinery and to consumer appliances. The list includes a number of marine projects ranging from the noise control design for a new high-speed gas turbine-powered luxury motor yacht to a vibration problem on an undersea oil production system. Other areas of activity include 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 and Computational Acoustics
This category has also seen a wide range of studies, with a significant number concerning the useful effects of sound and vibration. Prominent amongst these have been some very palatable projects for the food industry: a study of the effect of vibration on the flow properties of liquid chocolate and some specialised acoustical problems for vending machine manufacturers. Other projects involving the useful application of sound and vibration have been follow-on mathematical modelling studies for the manufacturer of a mass-flow meter and the manufacturer a fluid flow meter.
In other areas of computational acoustics there has been continued activity on existing long term projects including duct acoustics modelling under the auspices of the Rolls Royce UTC, the modelling of aerodynamic noise generation from aircraft under the EU-funded RAIN project, and the modelling of noise and vibration transmission problems using Statistical Energy Analysis (SEA). The SEA activity, deriving mainly from sales and consultancy associated with the AutoSEA package, has been particularly profitable this year. A substantial number of projects have involved the application of modal analysis methods, including a particularly intensive experimental program for a UK-based manufacturer aimed at understanding vibration problems in a circuit board printing machine.
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 progressive wave tunnel facility, located in the P E Doak Aeroacoustics Laboratory, has been refurbished to reduce the transfer of noise to other rooms in the building so as to permit unrestricted operation at high sound pressure levels. The facility has been used for major test programmes for composite aircraft fuselage components at SPLs of around 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. An increasingly large part of the Unit's testing is now associated with development work to reduce the noise levels of a variety of products. One project has concerned the development of a novel type of attenuated ventilator unit for use in housing or hotels affected by high levels of external noise.
There is an increasing demand for testing of airborne and impact sound insulation between dwellings. It is clear that the minimum insulation standards required by the current Building Regulations (for England and Wales), as set out in Document E of the Regulations, do not satisfy the expectations of many people moving into new homes. The government agency responsible has published proposals for new Regulations as a Consultation Draft, although there is a general view (not necessarily shared by builders and developers) that the proposed changes are not adequate to provide the considerable improvement in sound insulation standards which is clearly required.
Noise at Work, Communications, Hearing Conservation and Personal Injury Claims
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 was completed or started during the year.
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. These have included, for example, a food processing factory, bar staff in a London club, a credit card manufacturer, and print rooms, including one on a cruise ship. One particular survey was carried out just before Christmas in a turkey processing plant: the ISVR Consultant suffered a slight loss of appetite over the festive season! Peak noise levels from small arms, handguns and pyrotechnic devices were measured at the training establishment of a large city police force. The results were assessed in relation to the Action Levels of the Noise at Work Regulations; a number of firearms instructors were making compensation claims against the force for hearing injury leading to premature retirement. In a related job, hearing protector attenuation was determined for a sample of earmuffs used by police instructors and officers undergoing firearms training.
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. In one example, the noise level of a fire alarm system was assessed in a hospital in respect of a hearing injury claim by a fire-fighter. The officer was observing a simulated evacuation of patients form a ward and suffered tinnitus after a considerable time spent close to the alarm sounders.
Measurements were carried out for several police services. These measurements were of noise levels and exposures from the headsets used by control room and switchboard operators, covert and overt earpieces used with personal radios, earpieces in motorcycle helmets, and headsets used by staff transcribing recorded interviews. In each case a manikin was used to compare noise exposures with the Action Levels of the Noise at Work Regulations to verify compliance. Similar measurements of headset output were carried out for the control room of a fire and rescue service and in a number of call centres for building societies, an insurance company and a directory service.
Further noise measurements for a fire and rescue service included various items of equipment used by fire-fighters including pumps, an aerial ladder platform, positive pressure ventilation fans, generators and compressors, radios, distress signal units. Noise within vehicles on the road, with and without sirens, was also measured. This work, and the control room measurements described above, formed part of a comprehensive safety audit carried out by the Hampshire Fire and Rescue Service, and our reports were available on their website for the benefit of other brigades.
A medical equipment manufacturer commissioned a worldwide review of current workplace noise exposure regulations, and of likely future changes which might arise. It is clear that there is pressure to introduce lower exposure limits in the light of recent discussions concerning the EU Physical Agents (Noise) Directive and a report sponsored by the World Health Organization.
Bullmore A.J., Noise: Planning Issues and Legislation, Proceedings of the Institute of Mechanical Engineers Conference on Noise Legislation, London, 1999
Bullmore A.J., Meteorological effects on outdoor noise propagation over large distances, Proceedings of the Institute of Physics Conference on Environmental Noise, London, 1999
Smith, M.G. and *Lewis, D.N., Noise reduction in a cyclone separation system - A Case Study, Institute of Acoustics Industrial Noise Group, Stratford-upon-Avon, November 2000, 22(5), 87-94
* Not working in ISVR
Automotive Design Advisory Unit
Manager: Mr J D Dixon
Overview of Market Trends
The current policy within the automotive industry of placing development responsibility upon those in the supplier chain is beginning to be questioned by a number of Original Equipment Manufacturers (OEMs). Understandably, most suppliers are becoming increasingly focused on delivery to a specific programme at the lowest cost and as a result, the more long term research into vehicle NVH, previously carried out by the OEMs, is no longer being quite so actively pursued. This development delegation policy is also having the secondary effect of slowly reducing the refinement skill levels within many OEMs who, possibly wrongly, assume this skill and knowledge base has seamlessly transferred to the supplier chain. These two issues have been clearly identified in many parts of the industry and a general feeling is that engineering skills and advanced research needs to return to OEMs.
Although this is clearly not an easy policy to introduce rapidly due to specific skill shortages and general tight budgets, this general intention bodes well for the Automotive Design Advisory Unit (ADAU). With its flexible facilities and working practices, the Unit is in an ideal position to efficiently support the OEMs in both their research and training needs. Although such OEM research and training support is on the increase, supplier sponsored projects currently make up the major share of the Units activities.
In August 2000, Matt Parker, (an ISVR graduate and former ADAU summer placement), joined the Unit as a Junior Engineer. Matt's youthful enthusiasm is proving to be a great asset to the Unit, and already, with just minor supervision, he is competently servicing a number of projects.
Summary of Activities
Experimental Studies - Powertrains
The majority of the powertrain studies carried out over the past year have focused upon individual components rather than the total engine and transmission.
The projects have ranged from understanding the dynamics of various moving components through to in-depth studies into the fundamental parameters controlling
the radiation from non-structural covers. Many of the projects have had a healthy balance between experimental and analytical approaches, ensuring that
the four semi-anechoic engine test chambers, as well as the silicon graphics workstations, are fully employed.
Drive system noise of gears and chains continues to be actively studied. Much of the gear noise research is focused on the particular application of 2nd order balancer drive systems for small high speed car engines. Four very different design concepts have now been evaluated, and design guidelines for low noise systems are beginning to emerge. The increasing occurrence of chain noise problems in small engines has led to the recent commissioning of a dedicated chain noise rig. The rig has been designed to allow the sensitivity of most design parameters (for example, tension span, phase, etc) to be studied in a controlled manner. Results from this rig are keenly anticipated.
The imminent change to 42 volt vehicle systems brings with it a number of NVH-related opportunities. The resulting drastic increase in electrical capacity negates early energy consumption criticism of full active vibration control systems, and therefore research in this field carried out a number of years ago is being revisited. Perhaps even more exciting is the potential freedom that the higher voltage system may bring to I.C. engine design. No longer will the base engine structure need to be compromised to accommodate the menagerie of (often noisy) front end ancillaries, and therefore significant reductions in base engine noise should hopefully be seen. The larger generator-starters can of course bring with them their own problems and therefore investigations into both low noise rear end drives and novel multimass 'flywheels' are currently being carried out.
Studies using the Banger rig have taken a slightly different slant this year with the rig being used principally for evaluating the weight and cost saving of various modifications to engine block structures. One further use was to study the isolation characteristics of a particular valve cover gasket design. A number of other valve cover projects have also been carried out in recent months. Most of the studies, both experimental and analytical, have been generic investigations into shape, material properties and isolation methods, and some novel solutions have been forthcoming.
The noise-from-mean-surface-vibration technique has for many years been used by the Unit for evaluating powertrain noise radiation both experimentally and analytically. In many cases simplistic approximations for radiation efficiency are perfectly adequate; however, if absolute predictions of noise radiation from a surface are required, then more accurate values for its radiation efficiency are necessary. An effort has therefore been made in the past year to enlarge the Unit's database of radiation efficiencies for various designs of covers.
In order to reduce both vehicle assembly times and the number of multi-pin connectors required, many manufacturers are attempting to mount as much engine electronics as possible on the engine rather than the vehicle. Clearly, such a policy results in the electronics having to survive in a far more aggressive environment in terms of vibration amplitude. Studies have been carried out in an attempt to develop design guidelines for such electronic modules in terms of mounting location, isolation and module casing design.
Experimental Studies - Vehicles
One method for reducing energy flow into a vehicle cab or body shell is to reduce the point mobility at the various forcing locations, for example, engine mounts, chassis mounts, etc. Using a detailed finite element approach, the cab of a commercial vehicle has been successfully optimised in the local areas around the chassis mounts resulting in substantial reductions in respective point mobility. This local optimisation (rather than a full cab optimisation) clearly can save considerable development time, and thus looks an attractive development process.
Finite element methods have also been used to develop intake air-cleaner boxes where the natural frequencies of their panels are targeted well above the respective engines 4th order frequency range (above ~ 450 Hz). Such studies have required the development of orthotropic elements to accommodate the directional material properties of the composites used in the production of such components.
A number of studies have been carried out into the cost and weight reduction of vehicle trim packs. Bulkhead trim evaluation has been carried out on full sized vehicle bulkheads which have been installed in the large transmission loss suit in the Rayleigh Building. Wheel arch trim and other smaller components have been evaluated using simple transmission loss cabins. In many cases, cost and weight can be taken out of trim products without causing major deterioration of their vibro-acoustic performance.
Efficient methods for the measurement of tyre noise, both in terms of source and transmission, continue to be developed. A convenient technique for tyre noise transmission loss measurement has been developed which uses a flat plate like tyre noise source simulator, sandwiched between the stationary tyre and the road surface. By combining the transfer functions generated by this method with their respective on road sound pressure measurements around the tyre patch, estimations of the tyre noise spectral contribution to both interior and exterior noise can now be made with a high degree of confidence.
An increasing area of activity within the Unit is that of producing design guideline documents for ensuring good vehicle refinement. The vast knowledge base within the ISVR allows comprehensive design manuals to be compiled for specific vehicle types. Although the NVH of most vehicle concepts can be developed to a satisfactory level, the cost and weight penalties may well be high. However, with a fundamental understanding of the parameters effecting vehicle refinement, good NVH potential can be designed in at the concept stage, thus eliminating the need for expensive and heavy palliative treatment.
The recently developed high frequency omni-directional sound source is becoming increasingly used throughout the automotive industry. With three new devices (plus one upgrade) being delivered this year and numerous further enquiries from around the world, it would appear that this could be an expanding area of the Unit's business. It is also most gratifying that current owners of these devices regularly contact the Unit to enthusiastically describe 'new' uses they have found for their sound sources.
Instrumenting rotating shafts is becoming a fairly routine task for the Unit. However, a recent project to characterise the isolation performance of a novel crankshaft pulley design removed any complacency. Using a combination of lasers, optical probes and magnetic probes a set of plausible data was eventually obtained; however the task was anything but routine.
Software is continually being developed to support our Finite Element activities. Although new elements are occasionally required, the major effort is nearly always focused on customising the ADAU's optimiser for a particular project. As with any automatic process, success is highly dependent upon the instructions given, and so understanding what is required, and then creating precise objective functions for the optimiser, is seen as a major value added area of our F.E. activities.
Vehicle noise prediction modelling has continued strongly throughout the year and the all-encompassing mixed bandwidth, interior noise prediction package created over the past two years for a major manufacturer has now been transferred to a full Windows format and is being introduced to the companies NVH teams both in Europe and North America. A full vehicle exterior noise prediction model has just been completed for a major exhaust manufacturer. The model allows the customer's in-house tailpipe predictions to be placed in a generic virtual vehicle and any major driveby issues to be identified before any metal is cut.
Both the vehicle and the engine short courses run by the Unit in September continue to be popular with the industry as again they were over subscribed. The recent policy of accommodating all of the delegates in the same hotel appears to be a great success, and not an insignificant part of the course appears to be given in the bar during the evenings. The ADAU has also had considerable involvement with the Automotive Refinement MSc as well as specific customer courses given both at the University and on their own premises.
Dixon, J.D., Baker, J.M and *Challen, B., A hybrid method for modelling engine noise, Proceedings of the Institution of Mechanical Engineers, C577/036/2000, 2000, 107-123
*Bowden, D.R., *Derry, S.L. and Dixon, J., NVH characteristics of air-assisted direct injected (DI) spark ignition four-stroke engines, Institution of Mechanical Engineers, Proceedings of European Conference on Vehicle Noise and Vibration 2000, London, C577/011 /2000, 2000, 65-79
* - Not working in ISVR
Archive of our Annual Reports from other years