Scaling behavior of granular particles in a vibrating box

Using numerical and analytic methods, we study the behavior of granular particles contained in a vibrating box. We measure, by molecular dynamics (MD) simulation, several quantities which characterize the system. These quantities — the density and the granular temperature fields, and the vertical expansion — obey scaling in the variable x = Af. Here, A and f are the amplitude and the frequency of the vibration. The behavior of these quantities is qualitatively different for small and large values of x. We also study the system using Navier-Stokes type equations developed by Haff. We develope a boundary condition for moving boundaries, and solve for the density and the temperature fields of the steady state in the quasi-incompressible limit, where the average separation between the particles is much smaller than the average diameter of the particles. The fields obtained from Haffʹs equations show the same scaling as those from the simulation. Also, the origin of the scaling can be easily understood. The behavior of the fields from the theory is consistent with the simulation data for small x, but they deviate significantly for large x. We argue that the deviation is due to the breakdown of the quasi-incompressibility condition at large x.