The dynamics of sandpiles: The competing roles of grains and clusters

The competing roles of grains and clusters in the dynamics of a driven sandpile are investigated via two models. First, we present a coupled-map lattice model of a slowly rotating sandpile: we find that our inclusion of parameters to represent grain reorganisation and inertia leads to a rich diversity of behaviour, which we interpret via a simple model of grains and voids. Next, we present a set of coupled nonlinear stochastic equations which model the interactions between immobile clusters and mobile grains; in particular, we are able to model the effect of rotation via the inclusion of a ‘tilt’ term. We find that these nonlinearities are relevant and we present the new and nontrivial exponents we obtain in a number of different cases.