Visualization Of Marginal Ice Zone Dynamics

Abstract

Ice floe dynamics in marginal ice zones are simulated using a discrete element model. The ice floes are modelled as random sized, inelastic circular discs floating on the water surface. Contact conditions are represented by a constant restitution and friction coefficients. The ice floes are driven by a uniform wind field. The simulations predict ice floe displacements, rotations, compaction and pressures. This paper focuses on animation and visualization of the simulation output. INTRODUCTION Marginal Ice Zones (MIZ) are broken ice fields which often form at the edge of the polar ice pack, next to open ocean. They form as a result of several processes that take place at the pack ice edge including the incidence of waves and increase of temperatures. A MIZ typically extends over a width of the order of 100 km, and consists of distinct floes with diameters varying from a few meters to several kilometres. Discussions of the morphology and behaviour of MIZ were given by Wadhams [1] and [2], and Lepparanta and Hibler [3]. Models of MIZ dynamics have been developed using a viscous-plastic rheology by Lepparanta and Hibler [4], and a cavitating fluid analogy by Flato and Hibler [5]. The discrete nature of the ice floes has also prompted the use of continuum models of flowing granular materials to treat MIZ (e.g. Shen et al. [6] and Lu et al. [7]). The discrete element approach is used here to simulate MIZ dynamics. This approach has been used to model a variety of problems in Transactions on Information and Communications Technologies vol 5, © 1993 WIT Press, www.witpress.com, ISSN 1743-3517 364 Visualization and Intelligent Design soil and rock mechanics, flow of granular materials, and ice-structure interaction. Some of recent papers on this subject were compiled by Mustoe [8], The present study examines the response of an assembly of ice floes to wind drag, water drag and Coriolis force. Interaction forces between the floes are calculated from an inelastic contact model. The simulation predicts the spatial and temporal distributions of ice velocities, concentrations, trajectories and pressures. Animation of the numerical simulations played an essential role throughout this study. It provided an effective means for debugging and verification of the model. Also with the very large amount of information generated by the simulations, animation was necessary for illustrating the salient trends of MIZ behaviour. The present simulations are based on a model developed by Savage [9]. The following sections briefly discuss the discrete element model of the floes, the equations of motion of individual floes, and the boundary conditions. Presentation of a simulation run follows with emphasis on the animation approach and visualization of the results. DISCRETE MODEL OF ICE FLOES Contact model The ice cover is modelled as an assembly of circular, random sized, inelastic discs. At the contact between two discs, linear loading and unloading springs are used to calculate the normal force as illustrated in Figure 1. The normal force per unit length is given by