Coarsening dynamics in a vibrofluidized compartmentalized granulas gas

Coarsening is studied in a vertically driven, initially uniformly distributed granular gas within a container divided into many connected compartments. The clustering is experimentally observed to occur in a two-stage process: first, the particles cluster in a few of the compartments. Subsequently, the clusters collapse one by one, at ever increasing timescales, until eventually only one large cluster remains. We find the same series of events in molecular dynamics simulations. To quantitatively account for the coarsening, we apply a flux model. It reveals the self-similar features of the process and allows us to calculate the mean lifetime of the competing clusters. The size of the surviving clusters is found to grow anomalously slowly as [log(t)]1/2