Molecular Relaxation Simulations in Nonlinear Acoustics using Direct Simulation Monte Carlo

The direct simulation Monte Carlo (DSMC) method describes gas dynamics through direct physical modeling of particle motions and collisions. DSMC is based on the kinetic theory of gas dynamics, where representative particles are followed as they move and collide with other particles. DSMC provides a useful tool for capturing all physical properties of interest for nonlinear acoustic problems, such as dispersion, attenuation, absorption, harmonic generation and nonequilibrium effects. The validity of DSMC for the entire range of Knudsen numbers (Kn), where Kn is defined as the mean free path divided by the wavelength, allows for the exploration of sound propagation at low Kn (low frequency, atmospheric conditions) as well as sound propagation at high Kn (high frequency, dilute gases, or in microdevices). For low Kn, nonlinear effects play an important role in waveform evolution. For high Kn, nonequilibrium effects are strong and increased absorption cancels out nonlinearity effects.