Density relaxation is the phenomenon in which granular solids undergo an increase in bulk density as a result of properly applied external loads.  The ability of particulate solids to experience density changes is an inherent property that is not well-understood, and thus it remains a critical impediment in developing predictive models of flowing bulk materials.  In this talk, the results of Monte Carlo (MC) and Discrete Element (DM) models of the density relaxation process are discussed, in which a vessel filled with uniform spherical particles is subjected to discrete taps.

Both stochastic (MC) and deterministic (DE) models reveal the same dynamical process responsible for density relaxation, namely, the upward progression of organized layers induced by the floor of the vessel as the taps evolve.  Furthermore, results suggest that the evolution of bulk density is highly dependent on the microstructure and contact network.  Compelling evidence is also found of a tap amplitude that optimizes the evolution of packing density.