Bulk Material Handling and Processing - Numerical Techniques and Simulation of Granular Material

When we drop a pebble into the sand on a beach, the pebble does not bounce very much, but sticks in the hole it has made. When we pluck the pebble out, some sand may flow back into the hole, but the indentation largely remains. This simple observation illustrates two unique properties of granular materials. The first property is that the contact between the grains is dissipative. The thousands of grain-to-grain contacts dissipate kinetic energy rapidly. While the material of each grain is relatively elastic, the relative motions between the grains dissipate the energy so that the overall behavior is inelastic. The fact that the sand does not flow back to fill the hole completely illustrates the common occurrence in nature of granular arrangements which are local minima but which are far from the global minimum energy state. The dent in the sand remains, although lower energy states are available, because thermal vibrations are insufficient to drive the particles to the lowest Energy State. These two properties make the behavior of granular systems unique. While they exhibit some or the properties associated with the gaseous, liquid and solid states of matter, the granular state cannot be characterized by any one of them alone. Here we discuss the research in discrete element methods (DEM) that capture the contacts between individual particles in an explicit manner. In contrast to continuum methods that smear out the individual particles into a smooth plenum, the discrete element method captures the individual geometry and dynamics of each particle, including the dissipative effects of contact friction.