COMPUTER-SIMULATIONS OF CRITICAL, NONSTATIONARY GRANULAR FLOW-THROUGHA HOPPER

Computer simulations based upon molecular dynamics techniques are used to study the case of a granular material consisting of non-spherical particles flowing through a collimating hopper. In these simulations w e identify four generic flow regimes which depend upon the rate at whi ch material flows into the hopper: (A) The outflow rate is steady and relatively unaffected even when there are large fluctuations in the in flow rate; (B) the outflow is steady, but the hopper can clog given su fficiently large fluctuations in the inflow rate; (C) the outflow vari es with time and the mean time to clogging is nonzero, hence, even in the absence of fluctuations the hopper will eventually clog; and (D) T he outflow is unsteady and the hopper is always clogged. Region C defi nes the critical flow regime, with flow exponent, beta = 1. This expon ent may be universal, but our present simulations can reach no definit e conclusion on this point.