Discrete Element Method Based Simulation of Pebble Bed Test Reactor

摘要

Discrete Element Method (DEM) is a numerical approach used to compute the motion of a large number of particles1. The calculations performed in DEM alternate between the application of Newton's second law of motion to individual particles and a force-displacement law at each contact. The main principle behind DEM is that the time steps taken are so small that disturbances cannot propagate beyond each particle's immediate neighbors. Hence, at all times the resultant force acting on any particle is determined exclusively by its interaction with neighboring particles. The resulting force acting on each particle is used to find the acceleration, velocity and displacement of individual particles. The forces corresponding to new displacements are determined using force-displacement laws (constitutive equations). The whole cycle is repeated again and again throughout a time period. The numerical calculation scheme used in DEM is explicit and hence the stability is ensured by choosing time steps as a fraction of a critical time step.