COHERENT VORTEX STRUCTURES IN DEFORMING GRANULAR-MATERIALS

Discrete element models are used to investigate the formation of coher ent structures within a deforming granular material. The numerical mod els predict the formation of coherent vortex-like structures, even whe n the boundary deformations introduce zero vorticity. We name these st ructures circulation cells because the particles instantaneously trans late and rotate as a rigid body about a common centre. They occur for all the particle shapes and material properties tested. The size of th ese coherent structures range from approximately 20 to 600 particles, with the largest structures being limited by the test boundaries. Circ ulation cells are seen to play an important role in granular deformati ons including the formation of shear bands. (C) 1997 by John Wiley & S ons, Ltd.