Horizontal size segregation in a vibrating granular layer

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. Grains can escape over the barriers at either end of the base and also through the opening on the right side. 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 vertically periodic, and grains leaving through the bottom are reinjected at the top with an inward-directed velocity.

After a sufficiently large number of cycles (typically 300) segregation will start to become apparent, with the larger (red) grains moving towards the left. This demonstrates that (at least in the simulations) vertical vibration is able to produce horizontal size segregation, a totally unexpected phenomenon whose existence has yet to be investigated experimentally.

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

(c)   D. Rapaport