Molecular Dynamics Simulation of Soundwave Propagation in a Simple Fluid

TL;DR

This study uses molecular dynamics simulations to analyze soundwave propagation in a fluid, revealing how waveform shape and frequency affect sound speed and attenuation, and demonstrating MD's utility in acoustic analysis.

Contribution

The paper introduces a method to simulate and analyze soundwave behavior in fluids using molecular dynamics, including waveform transformation and comparison with Burgers equation.

Findings

Waveform changes from sinusoidal to sawtooth with amplitude increase

Good agreement with Burgers equation for low-frequency sounds

High-frequency sounds show deviations due to acoustic streaming

Abstract

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 very good agreement with Burgers equation without any fitting parameters. In contrast, for highfrequency 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 equation. The results demonstrate that MD simulations are a useful tool for the quantitative analysis of soundwaves.