CONTINUOUS POTENTIAL DISCRETE PARTICLE SIMULATIONS OF STRESS AND VELOCITY-FIELDS IN HOPPERS - TRANSITION FROM FLUID TO GRANULAR FLOW

A number of numerical hopper discharge experiments were conducted usin g a novel simulation technique in which the individual circular disc p articles are allowed to fill a two-dimensional hopper under gravity an d are subsequently discharged through a central slot orifice. The nove l aspect of the present technique is the incorporation of a continuous potential interaction for frictional granular flows which ensures the stability of contact mechanical force algorithms over much larger tim e steps than were hitherto possible. This is achieved by allowing soft er interactions which vary on the same scale as the nominal particle s ize rather than the micro-contact scale used in the majority of previo us literature. The resulting technique allows the filling and discharg e events to be simulated over a sufficiently long time scale. The cont inuous potential confers on the particles an ''excluded volume'' which prevents excessive overlap. In addition, the effects of frictional fo rces are introduced via a tangential displacement vs force model simil ar to that developed by Mindlin for contacts of perfectly elastic sphe res, but scaled to the normal potential interaction. Transition from f luid-like to granular flow is simulated by increasing the friction coe fficient from zero. During both the filling and discharge stages of th e simulation, the radial and tangential components of particle velocit ies are damped by a force proportional to the relative particle veloci ties. The effects of material head in the hopper, the outlet size and the hopper half-angle were investigated to predict material discharge rates as well as the wall stress profiles during both filling and disc harge. The effects of the ratio of the interparticle and wall friction coefficients on the prevailing flow and stress fields were also inves tigated in both ''mass-flow'' and ''funnel-flow'' hoppers. Encouraging agreement was found between the simulation and experimental flow beha viour.