Surface properties and the flow of granular material in a two-dimensional rotating-drum model.

Monodisperse and 1:1 bidisperse disk assemblies have been studied by a very efficient numerical algorithm for a nearly half-filled two-dimensional rotating drum. The model simulates a limiting case of granular systems emphasizing geometrical factors during spatial organization of the filling. The analysis of geometrical properties of the free slope gives insight into one of the size segregation mechanisms which is active in this model. Segregation occurs for all ratios of the disk radii. Statistical analysis of the surface flow of large disks shows finite-size scaling. Almost perfect temporal periodicity has been observed in monodisperse fillings, while the spatial disorder induced by bidispersity destroys this periodic behavior.