Molecular dynamics approach for a sonoluminescing bubble

Abstract

Up to now the numerical calculations for the converging shock or compression wave model of sonoluminescence have been based primarily on continuum methods. Here an alternative approach by molecular dynamics simulation is shown to be feasible with today’s computer memory and speed. Both approaches are compared. Results of the simulations are presented for the scaling behavior with the number of particles, for different boundary conditions (spherical and ellipsoidal bubbles) and for one and more species in the bubble. The dependence of the light intensity and pulse duration on the sphericity of the bubble is discussed. [Work supported by the Graduiertenkolleg Stroemungsinstabilitäten und Turbulenz.]

Molecular dynamics simulations of cavitation bubble collapse and sonoluminescence

“…Similar calculations with more than a million hard sphere particles in a bubble collapsed at a Mach number of about 1.5 confirm the strong increase in temperature towards the centre of the collapsed bubble in this kind of gas ( [32], figure 21). Moreover, a comparison with a continuum mechanics calculation based on Euler's equations showed reasonable agreement [33][34][35][36]. The differences (a steep shock for the Euler equations and the singularity at the bubble centre) can be explained by the dissipation missing in the Euler equations but being naturally included in the MD calculations.…”

“…The hybrid method was extended by Metten et al [33][34][35][36][47][48][49] through the coupling of the bubble interior, which is modelled by MD with hard spheres, with the continuum Rayleigh-Plesset (RP) equation for the surrounding liquid. The coupling of the two fluid parts is effected by determining the MD gas pressure inside the bubble and applying the boundary pressure as input gas pressure to the RP equation (RP-MD model).…”