分子動力学シミュレーションのための新しい外部境界条件の開発 : 周期殻境界条件

抄録

This paper proposes a new outer boundary condition called the "periodic-shell boundary condition" which is used for molecular dynamics simulations on a flow around a body. The present boundary condition is devised to diminish the influences of the limitedness of simulation regions by making molecules inside regions interact with imaginary molecules outside which are replicas of actual molecules existing near boundary surfaces. In using this condition we need no information such as temperature, densities, and averaged velocities at boundaries, which is in contrast with the case of ordinal uniform-flow conditions where such information is indispensable. To clarify the availability of the present boundary condition we have carried out simulations of a rarefied gas flow past a circular cylinder. The results of simulations show that the periodic-shell boundary condition significantly diminishes the distortions of the flow fields compared with conventional conditions such as uniform-flow and free-outflow conditions. Such improvements enable us to use smaller simulation regions and lead to a dramatic decrease in computation times.