Annual report 1995-1996
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 1995 - April 1996.
ISVR Consultancy Services
Manager Mr R A Davis
ISVR Consultancy Services (ICS) provides a wide range of consultancy services, mainly to commercial and industrial clients and local and national government agencies, but also to private individuals. The policy is to maintain a flexible approach to market conditions, whilst concentrating on the development of business in those areas in which the ISVR Research Groups are active. The fostering of closer links between consultancy and research activities continues to be an important objective.
The Unit generated an operating surplus in the 1994-95 financial year, and prospects for 1995-96 are satisfactory, although trading conditions, particularly in the industrial sector, remain difficult.
Summary of Activities
The Unit's projects are client-confidential, but the following general descriptions illustrate the wide range of work being undertaken.
Environmental noise and vibration
A number of environmental noise assessments have been carried out, in connection with planning applications or in cases of alleged noise nuisance from industrial premises or leisure activities. Unit staff are regularly involved in presenting evidence at Planning Inquiries and in Court. Projects have included the assessment of noise from minerals developments, a concrete products plant, a foundry and drop-forge, an airfield used by a parachuting club, and nightclubs and public houses.
There has been an increase in the number of reported problems of inadequate sound insulation between dwellings. Several surveys have been performed on behalf of Housing Associations. In most cases, it has been found that walls or floors did not achieve the minimum standards of sound insulation required by the Building Regulations. These deficiencies were generally caused by poor workmanship. A number of remedial schemes, specified by the Unit, have been implemented and in all cases produced an outcome satisfactory to the residents.
A number of sites, subjected to noise and vibration from road and rail traffic, have been surveyed to assess their suitability for development for residential development. Most Planning Authorities are requiring developers to provide information on site conditions, in accordance with the Noise Exposure Categories in PPG24 Planning and Noise.
Laboratory testing and measurement services
A major refurbishment of the large anechoic chamber was completed in January 1996. The chamber is now fully re-commissioned and considerably enhances the quality of the test facilities for research and consultancy. The bare chamber is approximately 9 m × 9 m × 7 m with a usable volume of 7 m × 7 m × 5 m between the wedges and is one of the largest in the UK.
There has also been further investment in the High-Intensity Facility, which provides the capability of generating sound pressure levels in excess of 160 dB for aerospace component certification testing. Extended programmes of high-intensity testing, of up to 70 hours duration, were carried out on C130 Hercules wing components, on behalf of clients in the UK and Australia. Acceptance tests were also performed on a number of spacecraft payload components, mainly communications antennae.
The Unit is able to carry out laboratory measurements of sound reduction index to BS 2750 (ISO 140) and of sound absorption coefficient to BS EN 20354 (ISO 354). Measurements of sound reduction index were performed on a number of components, including sections of a gas-turbine acoustic enclosure, a series of composite honeycomb-cored panels, and experimental motorway noise barriers. Absorption coefficients were measured for a number of designs of concert-hall seating.
An investigation was undertaken for a manufacturer of industrial pumps to investigate repeated failures of rolling element bearings. An array of strain gauges on the bearing housing was used to determine the dynamic deflections of the housing during on-load operation.
Measurements were made to establish the flyover noise levels of a large piston-engined aircraft to establish the potential for noise-certification. An investigation was carried out in a small executive jet to determine the level of cabin noise, and to identify the principal noise sources.
Development tests were carried out on aircraft cockpit voice recorder microphones to improve the microphone housing design. The systems were type-tested to ensure compliance with EUROCAE performance specifications.
The survey of noise exposures of flight-deck crew in a range of civil aircraft, including Concorde, was completed. Expressed in terms of an effective daily personal noise exposure (LEP,d) levels in some cases were 85 dB(A) or more, the main contribution being from communications headsets. Chosen headset output is influenced by the ambient noise level which is generally in the range 70 dB(A) to 80 dB(A) on the flight deck at cruise. A number of commercially available headsets incorporating active noise reduction were evaluated in flight. Some of these headsets were effective, and permitted lower communications signal levels to be used. A paper on this investigation will be presented at Internoise '96.
An extensive survey of noise exposures of road tanker drivers has been carried out for a major oil company. Measurements of daily personal noise exposure were performed using body-worn integrating meters with logging facility. Examination of the output data, together with independent measurements and observations, revealed several sources of systematic and random variation, related to position and driving conditions. A revised measurement protocol was developed for the company to use for their own noise surveys.
Further measurements were carried out for the Home Office (PSDB), in conjunction with Hampshire Constabulary, on noise levels under motorcycle helmets. These tests were performed using a BMW motorcycle in the 7 ft × 5 ft wind tunnel. A number of prototype helmets incorporating active noise control were evaluated. The results of this work will be presented at Internoise '96.
Unit staff are regularly engaged as expert witnesses in cases of alleged noise-induced hearing loss of employees in a wide range of industries, from coke manufacture to pig-farming. Particular expertise has been developed in the investigation of noise exposures received through headsets.
Structural dynamics and computational acoustics
Steady progress has been made in the sales and support of the AutoSEA acoustic prediction software, for which the Unit is the UK agent. The package, based on statistical energy analysis (SEA), has proven application in the design and development of road and rail vehicles, ships and aircraft, to reduce interior noise levels and improve noise quality. Other applications include the design of domestic appliances and industrial machinery. The package is in use by several major companies in these fields, with the Unit providing training, support and consultancy. Close liaison is maintained with the ISVR research Groups which are active in experimental and theoretical SEA studies.
The Unit has been appointed by the Marine Technology Directorate (MTD) to coordinate a programme of research and practical applications studies to develop the use of Statistical Energy Analysis techniques in the marine industry. The specific applications being appraised are design methods to minimize fatigue failures in piping systems, and the prediction of noise in craft such as workboats and small ferries.
Several projects were undertaken on behalf of the European Space Agency. These included:
- An experimental investigation of the response to acoustic excitation of spacecraft equipment-mounting panels, to establish the influence of the loading of the panel by attached equipment.
- A study of the effects of the addition of discrete masses on the sound transmission loss of a launcher fairing. This was an extension of an earlier study into the passive sound transmission loss of sandwich-wall cylinders.
- A theoretical study, in association with the Department of Aeronautics and Astronautics, to investigate the application of dynamic stiffness modelling methods to the prediction of spacecraft equipment vibration response. Further contributions were also made to an updated edition of the ESA Structural Acoustic Design Manual.
A three-day course on noise control for engineers in the process industries was held at the Chilworth Conference Centre. It is proposed to expand the range and frequency of post-experience courses.
Ratcliffe, K. Amplified music within residential buildings. Proceedings of the Institute of Acoustics, 17(5), 1995, 191-5.
Automotive Design Advisory Unit
Manager: Mr J D Dixon
With the mainstream automotive industries continuing to arm themselves with ever more sophisticated NVH facilities and analytical tools, the nature of the work carried out by the Automotive Design Advisory Unit is slowly changing. The once regular routine testing is now giving way to contracts requiring original thought. The majority of the Unit's activities are either in developing new measurement techniques or else solving specific product concerns.
Although conceiving a measurement or analytical technique to satisfy a requirement may in itself be far from straightforward, the greatest effort is often in the associated implementation and procedural development. Over the past year the Unit has spent much time refining measurement methodologies into robust packages and, where appropriate, helping to introduce them into the respective organizations. Even after the successful launch of a technique, support is often requested for an appreciable period for customer education. It is gratifying to see that many of the total vehicle measurement and analytical concepts pioneered by the Unit in the late 1980's are now becoming recognized as everyday methodologies throughout the industry.
Its size and working flexibility makes the Unit ideal for product trouble shooting where a practical solution to either an engine or a vehicle problem has to be rapidly found. Throughout the year the already interesting collection of research vehicles at the laboratory has been joined by vehicles from around the world, ranging from a 7.5 kW scooter to a 310 kW tractor unit. A slight diversion from the mainstream automotive industry was a study into a durability issue on a 25 kW outboard motor. This project involved considerable testing in the newly-recommissioned outboard motor test facility at the Chilworth Laboratories, together with a finite-element stress analysis of the offending component.
Although graduates from the ISVR have probably never had such good job prospects in the automotive industry as at present, the complaint is still heard from prospective employers that students have increasingly less practical ability. In an attempt to remedy this deficiency, a pilot training scheme has been initiated, whereby an undergraduate, Mr S C Scott, has taken a year out from his MEng studies and joined the Unit as a Temporary Assistant Engineer. As the year nears its end, it is already clear that the student has gained in practical experience whilst the Unit has also gained from his computational skills and ideas around the laboratory.
Healthy trading figures were achieved, showing a modest increase in turnover on last year. The planned increase of in-house research has meant a corresponding increase in running expenses. However, the knowledge generated by this research, together with a substantial order book, gives promise of yet another successful year ahead.
Summary of Services Provided
The past year has been a record for vehicle and running-engine experiments. All four test chambers at Chilworth as well as the Unit's chamber in the Rayleigh Building are currently on active projects. To satisfy demand, use of a second chamber in the Rayleigh Building has been made available by the Vehicle Dynamics Group; moreover, engine tests are being carried out for the first time in the Priede Laboratory at Chilworth.
The vehicle facilities have been equally active, with the Priede Laboratory often accommodating two projects at one time and both chassis dynamometers in regular use, principally on intake and exhaust system development. Early in the year, a free-field exhaust shell-noise rig was commissioned which, in addition to facilitating the study of system shell radiation, also enables the vehicle transfer functions for interior and exterior noise to be determined.
Design and manufacture
A low-frequency sound source has been developed with the help of the Fluid Dynamics and Acoustics Group. The device has been designed to provide sufficient energy at low frequencies to allow measurement of in-vehicle structural/acoustic transfer functions. By using a single small microphone housed in the neck of the source, a good approximation of volume velocity may be monitored, in real time.
A portable point mobility meter has been developed and manufactured for the Structural Dynamics Group to aid in their research programme into the generation and radiation of tyre noise.
Development of the automotive structural optimization package has continued, and its services are regularly sought. With the almost universal adoption of automatic meshing of finite-element models, there is a natural move within the automotive industry towards increasingly complex, but not necessarily better, models. This has resulted in an escalation of computation time but less flexibility in model modification. Effort is therefore being directed towards the automatic generation of optimum models.
The Unit participated in a number of departmental activities, including lecturing on internal and external short courses organized by the Vehicle Dynamics Group and project supervision for MSc courses.
Erotokritos, N.R., Dixon, J. and Lalor, N. Using computer models to design quiet engines. Proceedings of the 3rd International ATA Conference on Vehicle Comfort and Ergonomics, Bologna, 1995, paper 95A1004.