Physics of Granular Media

Granular material, like sand or powders, present many intriguing phenomena like heap formation under vibration, size segregation and the emission of density waves. These collective effects have eluded description in terms of continuum descriptions up to now. We show how the granular medium can be modelled by a packing of elastic spheres and simulated via Molecular Dynamics. Dissipation of energy and shear friction at collisions are included. The onset of fluidization can be determined and is in good agreement with experiments. Various types of rheology can be identified for flow down an inclined chute. Flowing through a pipe a slugging instability can produce density waves. On a vibrating plate the material can form convection cells due to walls or amplitude modulations. Velocity profiles on conveyor belts and outflowing containers are measured. A movie of the simulations gives a better understanding of the dynamics.