Mechanic waves in sand, 3d simulations

The sound propagation mechanisms inside dense granular matter are challenging the attempts to describe it because of the discrete nature of the material. Phenomenona like dissipation, scattering, and dispersion are hard to predict based on the material state and/or properties and vice-versa. We propose here a simulation method using dynamic discrete elements in order to get more insight in this problem. The idea is to examine a small perturbation created on one side of a dense, static packing of grains, during its propagation and when it arrives at the opposite side. A pertinent choice for the boundary conditions allows us to apply longitudinal or shear perturbations in order to select the respective modes of information propagation. Moreover the rotational degree of freedom permits to observe the role of rotations in the wave propagation. The propagation of rotational energy in itself is studied as well. The control on the inter-particle forces like contact potential, cohesion and friction make it possible to observe the effect of these micro-parameters on the macro-behavior at the wave scale. Simulations performed on different types of packings - regular and random poly-disperse-already show the consequences of anisotropy and allow its characterization. The goal of this study is a better understanding of the numerous sound propagation mechanisms in granular materials.