Volume 119, Issue 6, June 2006
Index of content:
- NOISE: ITS EFFECTS AND CONTROL 
119(2006); http://dx.doi.org/10.1121/1.2200140View Description Hide Description
Air-pumping noise from a car tire is investigated with a hybrid technique composed of three stages: (1) small-scale air-pumping noise generation process is modeled as a piston-like movement of the base-side of the tire groove and then numerically simulated; (2) the flow properties in the tire groove are used as air-pumping sources and noise propagation is simulated with emphasis placed on scattering process with full tire/road geometry; (3) the far-field acoustic pressure is predicted from a Kirchhoff integral method by using unsteady flow data in space and time which is provided by the computational fluid dynamics(CFD) calculation of full tire-road domain. The comparison of predicted results shows that the nonlinearity of the air-pumping noise generation mechanism affects not only noise characteristics in frequency domain but also in the directivity pattern. It seems that this approach can overcome the weakness of the acoustic monopole theory which stems from the usual assumption of a small amplitude acoustic waveequation while using nonlinear governing equation for the CFD calculation. Furthermore, through the use of a computational domain which covers tire and road surface, the geometric effects on air-pumping noise generation and propagation are taken into account in the source modeling process.
A linearized Euler finite-difference time-domain sound propagation model with terrain-following coordinates119(2006); http://dx.doi.org/10.1121/1.2200139View Description Hide Description
The equations of a linearized Euler finite-difference time-domainmodel for sound propagation through an inhomogeneous and moving atmosphere above absorbing ground are adapted to terrain-following coordinates. With the transformed numerical grid the effect of gentle orography is fully considered and the shortcomings of the representation of the orography by blocked-out grid cells in an untransformed grid are avoided. Comparisons with an analytical method to predict the interference patterns of a monochromic sound field above an idealized hill with rigid ground show good agreement. Further applications include absorbing ground and wind. A three-dimensional application also is discussed.