Visualization of Sound Transmission Into a Vehicle Passenger Compartment

The paper examines the effectiveness of the Helmholtz equation least-squares (HELS) method (Wu and Yu, J. Acoust. Soc. Am., Vol. 104, 2054–2060, 1998; Wu, J. Acoust. Soc. Am., Vol. 107, 2511–2522, 2000) in visualizing the areas that are prone to noise transmission into a full-size vehicle passenger compartment due to exterior excitations such as the engine and turbulent flow. To simulate sound transmission, harmonic excitations are assumed to act on arbitrarily selected vehicle interior surfaces. The surface acoustic pressures are calculated using the boundary element method (BEM) based Helmholtz integral equation. A fine mesh for the interior cavity is generated so as to yield as accurate as possible the acoustic pressure distributions as benchmark using the BEM codes. The radiated acoustic pressures inside the vehicle compartment are calculated and taken as the input to the HELS formulation. Once the HELS formulation is established, the acoustic pressure anywhere including the vehicle interior surface is reconstructed. The normal component of the surface velocity can be reconstructed in a similar manner. Consequently, the normal component of the time-averaged acoustic intensity and acoustic energy flow inside a vehicle passenger compartment can be visualized. This three-dimensional acoustic image can provide valuable insight into vehicle interior noise reduction. The reconstructed acoustic pressures are compared with the benchmark values evaluated at the same locations. The effect of the measurement locations on the accuracy of reconstruction is investigated.