ARCTIC SEA ICE: LARGE-SCALE FRACTURE MECHANICS

Abstract eng:
The ice pack covering northern seas is composed of a mixture of thick ridged and rafted ice, undeformed ice, and open water. Existing ice-ocean models of the Arctic ice pack are large-scale Eulerian continuum models that use a plastic yield surface to characterize the constitutive behavior of the pack. An alternative is to adopt a discontinuous Lagrangian approach and explicitly model ice parcels and the interactions between them. We have constructed a granular sea ice model that consists of thousands of discrete polygonal floes 5-10 km in width. At the beginning of a simulation the ice floes completely fill the Arctic basin and are frozen together. Wind driven deformation of the pack creates relative motion between floes that stretches the viscous-elastic joints between adjacent floes. The stress at each point along the frozen joints is defined by a constitutive model that follows linear loading and unloading paths. After unloading the joint is broken at that point. Fractures propagate along joints forming crack patterns in the model ice pack. The crack patterns define large plates 10-100 km in width that are aggregates of many individual floes. Subsequent deformation occurs along slip lines defined by the crack patterns. Since the usual state of the ice pack is a state of failure, an interesting situation is created in which the initial wind-driven deformation defines the conditions under which subsequent deformation occurs. Simulation results are used to characterize the formation of the aggregate under a divergent deformation state and the dependence of the average area of the aggregate floes on tensile strength, the wind stress gradient, and the size of the individual floes.

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