Waveshape distortion of high frequency acoustic waves in gas media

Molecular dynamics simulation of soundwave propagation in a simple fluid

A molecular dynamics (MD) simulation was performed to study the propagation of soundwaves in a fluid. Soundwaves are generated by a sinusoidally oscillating wall and annihilated by a locally applied Langevin thermostat near the opposite wall. The waveform changes from sinusoidal to sawtooth with increasing wave amplitude. For low-frequency sounds, the simulation results show a very good agreement with Burgers's equation without any fitting parameters. In contrast, for high-frequency sounds, significant deviations are obtained because of acoustic streaming. The speed of sound can be directly determined from the Fourier transform of a waveform with high accuracy. Although obtaining the attenuation rate directly from the simulation results is difficult because of the nonlinear effects of the wave amplitude, it can be estimated via Burgers's equation. The results demonstrate that MD simulations are a useful tool for the quantitative analysis of soundwaves.