Molecular dynamics studies of granular flow through an aperture

Molecular dynamics methods are used to study two-dimensional gravity-driven granular flow through a horizontal aperture. Two distinct approaches to modeling the granular particles are studied. (a) Circular particles subject to a strongly repulsive short-range interaction, together with normal and tangential frictional damping forces. (b) Rigid nonconvex particles, each consisting of disks arranged as an equilateral triangle, suitably spaced to provide a tangible indentation along each edge; the same repulsive interactions between disks in different grains and normal frictional damping forces are incorporated, but transverse damping is omitted, with the model relying on grain shape to resist sliding motion. In order to allow accurate measurements under steady-state conditions, a continuous-feed approach is adopted, in which grains exiting through the hole are returned to the top of the material in the container. For both models the output flow is measured as a function of aperture size, and the observed behavior is compared with previous theoretical and experimental results. Tests of the degree to which the models reproduce the depth independence of the flow are reported, and the influence of the container width and the nature of the walls are studied. The depth dependence of the pressure, the local stress distribution, and the particle flow patterns are also examined.