FLOW OF FRACTURED ICE THROUGH WEDGE-SHAPED CHANNELS - SMOOTHED PARTICLE HYDRODYNAMICS AND DISCRETE-ELEMENT SIMULATIONS

Computer simulations of the wind driven motion of fractured ice in a w edge-shaped channel are presented. Two numerical approaches were used. One is a discrete-element method, in which the ice blocks (or flees) are simulated as random-sized disks floating on the water surface, dri ven by the wind force and interacting with each other through normal a nd friction forces. This approach is based on 'granular-dynamic' techn iques that have been used in recent years to simulate particulate flow s. The second approach is smoothed particle hydrodynamics (SPH), which is used here to solve continuum equations for flow of fractured ice. SPH is a Lagrangian approach in which the continuum flow is modelled b y using point particles. Field properties such as velocity and stress are evaluated at the particle positions and no finite differences or g rids are necessary. The cases studied involve unsteady flows of the fr actured ice through wedge-shaped channels. The rheology used in the co ntinuum model is based on the Mohr-Coulomb yield criterion and the ass umption of coincidence of principal axes of stress and strain rate. Co mparisons are made between the results obtained from the discrete-elem ent method and from SPH. We focused on testing: (a) the appropriatenes s of the assumptions made in the development of the continuum model, n amely the stress states described in terms of the Mohr-Coulomb yield c riterion and the assumption of coaxiality; and (b) the ability of SPH to handle the problem of moving boundaries. The unsteady flows studied in the present work exhibit moving free boundaries that deform during the flow. Two main problems are found when one uses finite difference methods on fixed Eulerian grids; (1) moving boundaries cannot be clea rly defined due to problems of artificial diffusion, and (2) setting t he boundary conditions on the moving boundary can be a very difficult task. We show that by using SPH, one can avoid these problems. (C) 199 8 Elsevier Science Ltd. All rights reserved.