Annual report 2006
|Every year the Institute of Sound and Vibration Research
publishes an Annual Report. This is the entry for ISVR Consulting
covering the year January to December 2006.
ISVR Consulting has continued to provide services to industry and the public sector in a wide range of aspects of acoustics, noise and vibration. In a change from our general review of all our projects for the annual report we describe some of the more interesting projects for the reporting year.
Prediction of the Groundborne Noise from a Proposed Underground Metro System
ISVR Consulting is developing groundborne noise and vibration predictions for a new underground system in a major European city. The proposed system will be constructed during the next 6 years. The track will run in twin tunnels at a maximum depth of 28 metres. The route will follow a main road through the city and will pass a number of sensitive and historic buildings including: a university, a hospital, prestigious hotels and a concert hall.
The project has involved site visits to survey the route and to carry out baseline vibration measurements. Preliminary predictions of the vibration levels in the vicinity of the route and the benefits of different track types have been carried out using the in-house prediction methods developed by Dr Chris Jones from the Dynamics Group, ISVR. The prime contractor is currently undertaking seismic survey work to provide details of important parameters that are required for the final vibration predictions which are expected to be completed in 2007.
EPSRC Project to Review the Requirements for an Instrument for Soundscape Recognition.
The unit has started work on a three-year research programme investigating the measurement of soundscapes. We are working in partnership with the University of York and Newcastle University on the development of a network sensor system for measurement and discrimination of sounds in a variety of environments.
The parameters that are used to characterise a sound field are necessarily governed by what it is practical to measure. Predominantly environmental sound is characterised by the A-weighted sound pressure level at a point and has remained so since the earliest sound level meters. Consequently most legislative controls and guidance are expressed in terms of the A-weighted levels. However, advances in technology mean that it may be possible for a sound level meter to discriminate between and localise sound sources so it becomes possible to characterise a sound field in terms of the relative contributions of different sources. This is a significant departure from existing sound level meters which can provide a detailed analysis of the characteristics of the sound at a location but are unable to provide information directly on the source contributing at that location. /p>
Such a meter would have a significant potential impact on planning guidance. It would be possible to identify “positive” sound sources, such as natural sounds (e.g. waterfalls or bird song) and potentially rare, but loud, sources (such as overflying aircraft) which may make a small contribution to the average levels but which are a source of great annoyance.
A meter capable of identifying the sound source has the potential to revolutionise the assessment of the noise impact of both the existing and planned environments. It would make a significant contribution towards an improved environment and enhanced quality of life, especially within urban locations.
The Ototoxicity of Styrene: a Review of Occupational Investigations
The objective of this study was to review a number of occupational investigations of the exposure/effect relation between inhaled styrene vapour and hearing loss. There is concern that workers’ hearing may be impaired by exposure to styrene, as used in industries making plastics and fibreglass reinforced products.
Seven occupational studies dealing with the ototoxicity of styrene were examined. Factors assessed included: the experimental design and number of subjects within exposure groups, measurement of the styrene-in-air concentration, confirmation of the styrene exposure by blood or urine analysis, determination of the hearing threshold levels for the exposure and control groups, and measurement of any occupational noise in the subjects’ workplaces. Consideration was also given to statistical relations between high-frequency hearing loss and lifetime exposure indices for styrene and noise.
The results are equivocal. Four investigations failed to find any effect of styrene on hearing thresholds. In contrast, other investigations claimed to have demonstrated styrene-induced hearing loss in industrial populations, with synergism between styrene and noise. However, these reports exhibited shortcomings in experimental design and data analysis.
Considering the body of evidence as a whole, hearing deficits due to occupational exposure to styrene at low concentrations have not been demonstrated by scientifically reliable argument. There is some suggestion of an association between styrene exposure, occupational noise, and hearing dysfunction. Further studies in humans are necessary to clarify this question.
The Acoustic Excitation of Building Components
A new area of work for the unit is wind tunnel testing of components to be installed on buildings to assess them as a potential source of wind noise. If structures such as louvre screens or other regular architectural features are excited into resonance the consequences can be costly, so testing to identify problems before installation is recommended.
The test typically comprises a measurement of noise and vibration on the component over a range of wind speeds and angles of incidence to the flow. The aim is identify conditions where the vortex shedding frequencies of the component in the flow occur at the same frequency as the natural vibrational or acoustic modes of the structure. This can create a feedback mechanism that generates high levels of noise and vibration.
Because there are many vortex shedding mechanisms, many natural frequencies, and a number of potential feedback mechanisms, calculating the interactions that will cause problems is difficult leading to the need for testing.
Remedial action in the cases where a problem is identified can sometimes be very simple, as is often the case in this type of resonance. The key requirement is to understand the mechanism.
Diesel Engine Noise Impulsiveness
Over the last few years the diesel engine has undergone a substantial increase in popularity within the passenger car market. One of the major unresolved issues is the very impulsive nature of the sound of the diesel engine, especially at idle and low speeds. A significant pilot study into the characteristics and propagation of this noise has been carried out over the last year. It is believed that the attenuation of the diesel noise from the engine bay to the passenger compartment not only gives a level reduction but can also influence the perception of impulsiveness. The ultimate goal is to quantify this process such that it can be suitably engineered during the design of a vehicle.
Two key issues have been investigated. It is desirable that the impulsive nature of the sound can be adequately represented by a series of engine-related orders to engineer the sound quality using existing frequency domain modelling methods. Recorded engine noise has been decomposed into the order domain and then existing ISVR auralisation software has been used to synthesise engine sound based only on a summation of orders. This has proved successful.
A second crucial requirement is the measurement of transfer functions between combustion forcing (pressure) in each individual cylinder and the driver's ear. It is hypothesised that differences in these individual transfer functions may play a key role in defining and hence controlling the sound perceived by the driver.
For many years ISVR has made use of its unique "Banger Rig" which allows a controlled explosion to be produced in any cylinder of a non-running engine. This method has seen a very significant resurgence in the last few years and has now been extended to allow transfer functions to be measured directly to the driver's ear location. This was carried out using an enhanced version of the in-house EngWaves software.
Summation of individual cylinder sound contributions derived from measured running cylinder pressures and these transfer functions has allowed the combustion noise contribution at the driver's ear to be successfully synthesised.
It is now planned to develop these concepts into a readily exploitable engineering methodology.
Attenuation of slat trailing edge noise using slat gap acoustic
Control of Noise Sources on Aircraft Landing Gear Bogies
Prediction of low noise aircraft landing gears and comparison with
Acoustic measurement of boundary layer flow parameters
Attenuation of slat trailing edge noise using acoustic liners
Design and Testing of Low Noise Landing Gears
Directivity and sound power radiated by a source under a boundary
The ototoxicity of styrene: a review of occupational investigations
Reducing noise from an oil refinery catalytic distillation column
Measuring the noise in a hot exhaust stack
* Authors not from ISVR
Archive of our Annual Reports from other
For further information contactStuart Dyne ISVR Consulting,
University of Southampton,
Telephone: 023 8059 2162 (+44 23 8059 2162 from outside the UK),
Copyright © 2007 ISVR Consulting, University of Southampton.
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