Abstract
AbstractThe Phenomenon of the sound field generated by a moving sound source hasbeen investigated in the present work with two-part subject. The first part is to establishthe mathematical model and the corresponding numerical scheme; the second part is toemploy the established numerical scheme in practical acoustic problems. In order toestablish the mathematical model, a novel governing equation is derived and it can beviewed as a modified Ffowcs Williams-Hawkings equation (FW-H-equation). Themajor characteristic of the novel governing equation is to include the interior and theexterior domain. In addition, the acoustic position vector, the quality describes therelations about the distance and the direction between the observer and the soundsource, is represented for applying to the condition of the sound source moving withvariable speed. As to the solution of the governing equation, it is expressed in the formof the Surface Integral Formula (SIF) by convoluting the free-space Green’s function intime domain. Then, this SIF is used to numerical implementation in the concept of theBoundary Element Method in time domain (BEMTD).After establishing the numerical scheme and verifying the correctness of thecalculating results, two acoustic problems were investigated for revealing the ability ofthe numerical scheme. The first case considers that a moving line source with variablespeed. This case reveals that the restriction of the constant speed is released in theestablished numerical scheme. For the simulation results, it shows that the effect of thevariable speed not only influenced the variation rate of the frequency modulation, i.e.,Doppler effect, but also the time about the maximum acoustic pressure being observed.In addition, the rate of the amplitude variation is shaper than that in the constant speedcase when the line source is approaching to the observer point. The second caseinvestigates the binaural hearing perceived by a moving sound source. Forunderstanding the weighting of the eventful cues about perceiving the direction and thespeed of the moving sound source, the sound pressure at the entrance of the external earcanal was calculated by the established numerical scheme. Furthermore, the HilbertHuang transformation (HHT) is used to find the instantaneous frequencies of acousticsignal. Results show that the Interaural Level Difference (ILD) and the frequenciesshifting are eventful than Interaural Time Difference (ITD). The perceived loudnesslevel will be larger in the motional case than that found in the stationary case. Theseengineering problems are shown that the acoustic properties are different forcomparing with the sound field generated by a moving sound source and that by astationary sound source. As to the analytical methodology developed in the presentwork, it turns out that it indeed can be used to simulate and analyze these acousticproblems whenever the sound source moves or not. Furthermore, some meaningfulphenomenon relating to these problems then can be observed through discussing thecalculating results.