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A Maxwell-Elasto-Brittle model for the drift and deformation of sea ice

Presented by: 
Veronique Dansereau
Friday 8th December 2017 - 09:00 to 10:00
INI Seminar Room 1
In recent years, the viscous hypothesis and other underlying physical assumptions of the viscous-plastic (VP) rheology widely used in current climate and operational models have been revisited and found to be inconsistent with the observed mechanical behaviour of sea ice. Other studies have suggested that while the VP model can represent the mean global drift of sea ice with a certain level of accuracy, it fails at reproducing some key observed properties of sea ice deformation. We developed a new mechanical model, named Maxwell-Elasto-Brittle, as an alternative to the VP rheology in the view of accurately reproducing the drift and deformation of the ice cover in continuum sea ice models. The model builds on a damage mechanics framework used for ice and rocks. A viscous-like relaxation term is added to a linear-elastic constitutive relationship together with an effective viscosity that evolves with the local level of damage of the material, like its elastic modulus. This framework allows the internal stress to dissipate in large, permanent deformations along faults, or leads, once the material is highly damaged, while reproducing the small deformations associated with the fracturing process and retaining the memory of elastic deformations over relatively low damage areas. A healing mechanism counterbalances the effects of damaging over large time scales.

Idealized simulations have confirmed that the Maxwell-EB model reproduces the important characteristics of sea ice mechanics revealed by the analyses of available ice buoy and satellite data: the anisotropy of the deformation, the strain localization and intermittency, as well as the associated scaling laws. Sensitivity analyses show that the model, with few independent variables, can represent a large range of mechanical behaviours, with both the persistence of creeping leads and the activation of new leads with different shapes and orientations. Realistic simulations will be presented, in particular, simulations of the flow of ice through Nares Strait. These will demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a common phenomenon within numerous channels of the Arctic. In agreement with observations, the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features, defining floes, and the eventual opening of polynyas downstream of the Strait are all represented.
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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons