THE ROBUSTNESS ASSESSMENT FOR EVENT DRIVEN MOLECULAR DYNAMICS BY CALCULATING SPEED OF SOUND

Abstract

Event-driven molecular dynamics (EDMD) is a special application of Molecular Dynamics (MD) derived from kinetic theory of gases. While classical solution of Navier-Stokes equations fails at high Knudsen (Kn) number flows, EDMD is valid on entire regime. Interaction potentials are considered discrete and exist only at the moment of impact. Hence, molecule trajectories are linear. Unlike the classical MD, this helps to simulate bigger systems. Molecular interactions, interaction times and partners can be predicted deterministically. Diatomic and polyatomic molecules are handled by an implemented energy relaxation scheme. Calculation of possible event times and determination of the earliest are the most timeconsuming steps of the simulation. In order to improve computational speed, a cell partitioning methodology and a priority queue structure are implemented in this study. The effect of the implementations on the performance is investigated and optimum simulation parameters are determined; when using PQ, number of cells must be greater than the number of molecules for maximum computational speed. Robustness assessments for the implementations are conducted with a realworld problem. Extreme density difference in confined geometries has vast usage in engineering and is also a good example of stress test because of its complex nature. This paper addresses the calculation of sound speed in a shock tube filled with a diatomic gas by using EDMD simulations. The robustness is validated since the results agrees perfectly with the theoretical values.