This paper investigates the pressure time history of a monopole source moving uniformly above an impedance ground. The classical Lorentz transform converts the problem of a uniformly moving source into an equivalent problem of a stationary source in the Lorentz frame. A modified Lorentz transform is proposed which facilitates the numerical analysis in a horizontally stratified medium while allowing a height-dependent density and sound speed profile to be incorporated in the analysis. A set of the Lorentz frame governing equations has been obtained that allows implementation of a Fast Field Program (FFP) in the Lorentz frame. A global matrix formulation is developed by adapting the stationary source method to the moving frame. Further refinements yield an improved representation of the global matrix that can be expressed in a tri-diagonal form. It can subsequently be inverted with much greater efficiency than the original penta-diagonal matrix. A three-dimensional FFP can be applied to obtain the pressure time-histories at various sideline distances simultaneously. The numerical results are compared against a ray tracing algorithm. Unlike the ray theory approach, the wave-based FFP formulation can lead to more accurate predictions since wave phenomena such as interference and diffraction are included.
展开▼
