Molecular Dynamic simulation on hydrodynamic instability of interface due to convergence shock and vortex dynamics

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We have investigated nonlinear evolution of hydrodynamic instabilities, such as the Richtmyer-Meshkov instability(RMI) and the Rayleigh-Taylor instability(RTI) induced by converging shock, with the use of Molecular Dynamic(MD) simulations. We have developed a new MD code for macroscopic hydrodynamic simulations and nonlinear theories for a study of vortex dynamics with density jump at an interface. Main results can be summarized as follows.1.Large scale Molecular Dynamic simulation codeWe have developed a new large scale MD simulation code with a suitable potential barrier for converging shock drive. The code was parallelized for many computers connected through a computer network, such as SUPER SINET. A new dynamic domain composition method was developed, in which computational domains are dynamically reconstructed according computational environment. The scalability of the method was proofed with the use of 720 computers and also super-computers connected through the SUPER SINET.2.Nonlinear evolution of the Richtmyer-Meshkov instability.With the use of the MD simulations existence of Mach shock and Mach stem were examined. Nonlinear stability of a rippled shock in converging geometry was also investigated. Nonlinear evolution of RMI was also studied in a cylindrical geometry for the first time, in which unstable interface is strongly deformed due to reflected shocks. A fully nonlinear theory was developed for vortex dynamics of an interface with density difference. We have shown dependence of nonlinear growth of bubble and spike and double spiral structures on density jumps and initial vorticity.3.Nonlinear evolution of the Rayleigh-Taylor instabilityWe have shown that anomalous diffusion occurs due to the vorticity in the spiral in RTI with the use of MD simulations. We have also developed a nonlinear theory in which asymptotic nonlinear growth of a bubble and its curvature were obtained as a function of density difference.