Identification of Complex Noise Sources Using the HELS Method

Abstract

In this paper, the Helmholtz Equation Least Squares (HELS) method (Wang and Wu, 1997; Wu and Wang, 1998; Wu and Yu, 1998; Wu, 2000) is used to reconstruct the radiated acoustic pressure fields from a replicated vehicle front end. To simulate sound radiation from a real vehicle, an engine noise simulator (ENS) is installed inside the front end at the location of the engine. The white noise emitted from the ENS is measured by a microphone. For convenience, measurements are taken over finite planar surfaces above, in front, and alongside of the structure. These measured data are taken as input to the HELS formulation to reconstruct the acoustic pressures on the top, front, and side surfaces of the vehicle. The reconstructed acoustic pressures are then compared with measured ones at the same locations. Also shown are comparisons of the reconstructed and measured acoustic pressure spectra at various locations on the surface. Results show that satisfactory reconstruction can be obtained based on relatively few measurements taken in the field. Experiments indicate that the accuracy of reconstruction can be further improved by taking more measurements over a conformal surface around the structure at closer range. However, planar measurements are easier to implement in practice, while conformal measurements often requires a programmed robot arm which may make the reconstruction process more costly. In any event, the HELS method has proven to be effective in reconstructing the radiated acoustic pressure field from a non-spherical source in the low-to-mid frequency and may become potentially a viable noise diagnostic tool for the practicing engineers.