Effect of boundary conditions on diffusion in two-dimensional granular gases - art. no. 011301

We analyze the influence of boundary conditions on numerical simulations of the diffusive properties of a two-dimensional granular gas. We show in par ticular that periodic boundary conditions introduce unphysical correlations in time that cause the coefficient of diffusion to be strongly dependent o n the system size. On the other hand, in large enough systems with hard wal ls at the boundaries, diffusion is found to be independent of the system si ze. We compare the results obtained in this case with Langevin theory for a n elastic gas. Good agreement is found. We then calculate the relaxation ti me and the influence of the mass for a particle of radius R-s in a sea of p articles of radius R-b. As granular gases are dissipative, we also study th e influence of an external random force on the diffusion process in a force d dissipative system. In particular, we analyze differences in the mean-squ are velocity and displacement between the elastic and inelastic cases.