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Details of Grant 

EPSRC Reference: GR/S87126/01
Title: Aerocoustic Inverse Method (AIM) for Quiet Automative Design
Principal Investigator: Wright, Dr MC
Other Investigators:
Nelson, Professor P
Researcher Co-Investigators:
Dr G Dewar
Project Partners:
Department: Inst of Sound and Vibration Research
Organisation: University of Southampton
Scheme: Standard Research (Pre-FEC)
Starts: 01 January 2004 Ends: 31 May 2004 Value (£): 17,267
EPSRC Research Topic Classifications:
EPSRC Industrial Sector Classifications:
Transport Systems and Vehicles
Related Grants:
Panel History:  
Summary on Grant Application Form
Wind noise is a major problem for car designers, mainly because efforts to reduce engine noise have been so successful. We know that the shape of the car is important, as is the positioning of wing-mirrors and so on, but it still takes a certain amount of trial and error to make a good, quiet design the satisfies all other requirements at the same time. This requires expensive wind-tunnel tests with scale model cars. These are usually solid and made of clay so that they can be modified easily, but this makes it impossible to measure the interior noise and quite hard to measure the noise on the surface. An alternative that several companies are looking into is to make an array of microphones to record the sound radiated by the car model whit it's in the wind tunnel. This forms a sort of 'acoustic telescope' which, when correctly processed by computer, can give a colour image of the car showing 'hot spots' where the noise is generated. The difficulty is in doing the processing, there are a couple of ways of doing this, called 'beamforming' and 'acoustic holography', but both of them have difficulties with resolution. When we look at things we can resolve tremendous amour of detail because the wavelength of light is much, much smaller than the things we're looking at. This isn't necessarily true with sound waves, at low frequencies the wavelength can be longer than the thing that's making the sound.This proposal is to try a new way or processing the microphone signals to produce a better image. The previous methods are equally applicable to noise from any source, but the noise produced when air flows past something solid has distinct characteristics governed by a rather esoteric branch o mathematics which has been studied in depth over the last fifty years, mainly due to attempts to reduce aircraft noise. At the speed a car goes the relevant equations become simpler, and we have found a way to build them into the microphone processing algorithm. This should produce a sharper better defined image of the noise sources which should allow a quicker design process leading to quieter cars.In a previous project we had the opportunity to make some recordings in a wind tunnel in Germany. We put a wooden box, about the size of a cornflake packet, into an air jet and simultaneously recorded the signals from an array of 128 microphones placed to one side. We also used microphones embedded in the surface of the box to measure what the real surface noise sources were. In this piece of work we intend to process the recorded array signals according to the new technique and compare the results with the surface measurements, and with the competing techniques.
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Organisation Website: http://www.soton.ac.uk