SIMULATIONS OF GRANULAR MEDIA
H. J. Herrmann, Matthias Müller · 2000
Introduction Many rather astonishing phenomena are known to occur when granular materials like sand or powders move. [1 4] Examples are the so-called \\Brazil nut" segregation, [5 8] heap formation under vibration, [9 11] density waves emitted from outlets [12] and 1/f noise in the power spectra of local forces. [13] All these eects originate in the ability of granular materials to form a hybrid state between a uid and a solid: When the density exceeds a certain value, the critical dilatancy, [14;15] it is resistant to shear, like solids, while below this density it will \\uidify". This uidi ed state can be rather complex, specially in the presence of density uctuations and density gradients. In order to formalize and quantify the complicated rheology of granular media various attempts have been made. Continuum equations of motion, a kinetic theory [3;16] , and thermodynamic formulations [17 19] have been proposed. But many of the above mentioned eects, such as si