Synthesis of Drive-by Noise Based on Numerically Evaluated Source-Receiver Transfer Functions Employing the FMBEM

Prediction of the drive-by noise level in the early design stage of an automotive vehicle is feasible if the source signatures and source-receiver transfer functions may be determined from simulations based on the available CAD/CAE models. This paper reports on the performance of a drive-by noise synthesis procedure in which the transfer functions are numerically evaluated by employing the Fast Multipole Boundary Element Method (FMBEM). The proposed synthesis procedure first computes the steady-state receiver contributions of the sources as appearing from a number of vehicle positions along the drive path. In a second step, these contributions are then combined into a single transient signal from a moving vehicle for each source-receiver pair by means of a travel time correction. The determination of the multiple source-receiver transfer functions is by far the most computationally intensive part in the procedure, and an FMBEM configuration is presented that is optimized for predicting the drive-by noise source pressure levels (SPLs). The introduced approximations result in an overall reduction in accuracy of about 1 dB while reducing the computation time to 25-30 hours on a modern desktop PC for a frequency range up to 2.2 kHz. To coarsen the frequency resolution, a frequency domain interpolation approach is discussed that yields good results in reconstructing the impulse response functions. The accuracy of the transfer functions is studied by comparison of twelve simulated transfer functions with measured ones for a Dodge Neon vehicle, showing a deviation of 3-5 dB for most sources. The resulting drive-by noise levels are presented and discussed for the tires, exhaust and intake. The developed synthesis procedure allows for the prediction of the drive-by noise level on the basis of CAD/CAE models with a satisfactory accuracy and within a feasible evaluation time.