Sound propagation in dense, frictional granular materials

The understanding of the sound propagation mechanisms (dispersion, scattering, power-spectra, etc.) inside dense granular matter is still a challenge. Using discrete element simulations we examine the effect of interparticle forces like friction and thus also the role of rotations. A small perturbation is created on one side of a dense, static packing of grains and then examined during propagation and when arriving at the opposite side. The perturbations can be applied to longitudinal, shear or rotational degrees of freedom in order to select the respective modes of information propagation. In order to bridge the gap between the particle "micro"-method and the "macroscopic" continuum theory, we use a micro-macro approach for finding relations between the wave speeds and the components of the stiffness tensor.