A piston is compressing with a certain force onto an assembly of granular materials. No gravity is acting. The Material is very soft, so there are oscillations.

We have a hopper, filled with particles. Additional to the repulsive forces due to collisions we have cohesive forces. You can find more information in this publications.

The walls of the hopper are not as steep as in the other examples. The flow ends when an arch forms spontaneously and the hopper is blocked.

A very tiny simulation. 36 balls are being thrown into a container. The rolling of the particles leads to a final configuration, which is virtually flat. 

Not quite a hopper, but a hole in the floor.

A Poster on stress propagation in sand beds.

• What is the pressure distribution below sandpiles? → DIP
• How can I get information from the inside ?
• What can be stated about continuum theories now ?

We are interested in the stress distribution in static granular matter. Experiments have found a minimum of the vertical normal stress beneath the apex of a sandpile. Because of the indeterminacy of static friction force even in the simplest sandpile and the ensuing absence of a constitutive relation between stress and strain (Hooke's law) there is no closed set of equations. Continuum theories, trying to describe the dip, have to make assumptions on the existence of constitutive relations among the components of the stress tensor itself.

The problem of granular materials is not alone a problem of material properties, but also a problem of structures. To examine these  interesting systems, one uses molecular dynamics simulations. The objective of the work presented here was to have a program which can run on cheap high-end shared memory workstations. Therefore we have developed  a fast thread-based simulation of polygonal particles.

We investigate the stresses and pressures under a 2-dimensional heap using a simulation of convex polygonal particles. Former Experiments and simulations on granular cones strongly suggest that for cones no generic pressure distribution exists but that the pressure and stress distribution is highly sensitive to the size distribution of the grains and the building history of the heap.