Sound field of a fast moving source in a horizontally stratified medium above an impedance plane.

Abstract

A continuous source motion model is developed for computing the sound fields of a uniformly moving monopole source in a horizontally stratified atmosphere. The numerical model is based on the Lorentz transformation and the one-dimensional fast field formulation. The global matrix method and a bounded Green’s function solution expressed in the wavenumber domain is used in the numerical implementation. The solution is then expressed in the Lorentz frame. A transformation is performed to map the spatial Lorentz frame quantities into a reception time history in the stationary frame. Numerical results for an elevated source in a downward refracting atmosphere demonstrates the importance of a continuous source motion model especially at high Mach numbers in the presence of sound speed gradients where the pseudo-stationary source approximation becomes questionable. Coupled with the convective effects of continuous source motion and a frequency dependent ground impedance model, the resulting sound fields are significantly different from those predicted due to a pseudo-stationary source. Fluctuations on the order of 20 dB are predicted in the interference pattern in the far-field. A shift of the interference onset time to lower values is predicted when the source Mach number and/or sound speed gradient is increased.