Granular ratchet

This is a dynamical simulation of a vertically vibrated layer of granular material (the system is two-dimensional) driven by a base with a sawtooth profile. The underlying model consists of disklike particles whose collisions are inelastic (the computational techniques are the same as in molecular dynamics). The simulation region is horizontally periodic.

The unexpected phenomenon that can be observed in this simulation is the appearance of stratified horizontal flow; the flow rate varies with height within the granular layer and oppositely directed flows can occur at different levels. By altering the parameters it is possible to change the detailed nature of the flow. The arrows show the mean velocities at different heights in the layer, averaged over the duration of the run (they may fluctuate wildly at first). These averages are reset when the run is restarted or when the frequency is changed.

The controls available to the user are start/stop and restart buttons, and sliders used to set the vibration frequency, the number of timesteps between display updates (a larger value produces a faster but less smooth animation), the layer thickness and the number of sawteeth.