Numerical model for granular compaction under vertical tapping

A simple numerical model is used to simulate the effect of vertical taps on a packing of monodisperse hard spheres. Our results are in good agreement with an experimental work done in Chicago and with other previous models, especially concerning the dynamics of the compaction, the influence of the excitation strength on the compaction efficiency, and some aging effects. The principal asset of the model is that it allows a local analysis of the packings. Vertical and transverse density profiles are used, as well as size and volume distributions of the pores. An interesting result concerns the appearance of a vertical gradient in the density profiles during compaction. Furthermore, the volume distribution of the pores suggests that the smallest pores, ranging in size between tetrahedral and octahedral sites, are not strongly affected by the tapping process, in contrast to the largest pores which are more sensitive to the compaction of the packing.