Sound propagation in low-Mach-number layered moving medium

A three-dimensional sound propagation model in low Mach number moving media has been established based on the Gaussian beam tracing and the wave equation for high-frequency sound wave in a moving media with low Mach number. The model has been applied to horizontally layered medium in shallow and deep water. The simulation results show that ocean currents can qualitatively and quantitatively change the sound propagation mode. In shallow water, the sound speed gradient is greater than the flow velocity gradient, which results in the difference of convergence zone position of the upstream and downstream increasing with the propagation range, and the arrival structure of rays changing significantly. In deep water, the flow velocity gradient is greater than the sound speed gradient, causing the surface duct to disappear in the downstream direction, resulting in a difference of more than 10 dB in the propagation loss of the upstream and downstream. In addition, there is three-dimensional sound propagation effects in the horizontally layered environments caused by the currents. Therefore, while the flow velocity gradient is comparable to or greater than the sound speed gradient, the impact of ocean currents on sound propagation cannot be ignored.