Session B.pdf - Clarkson University

frozen lead ice controls the ice dynamics through its strength (Coon et al., 1992).
The architecture for a new large-scale anisotropic constitutive law intended for use in a
sea-ice dynamics model has been presented by Coon et al. (1992, 1998). This architecture
accounts directly for refrozen lead systems in pack ice strength with an anisotropic
failure surface. This constitutive law has sub-scale simulation that allows for the inclusion
of phenomena such as ridging, rafting, buckling, and fractures on the behavior of
the ice. The oriented thickness distribution for sea ice presented here is intended to
complete the architecture set forth by Coon et al. (1998). Pritchard (1998) demonstrated
the behavior of an anisotropic elastic-plastic constitutive law with examples using
an idealized deformation history. Therefore, in this paper, we will describe the formulation
of the model and not its implementation.
In order to account for lead and ridge orientation for pack ice, Coon et al. (1992, 1998)
introduces two types of ice:
• Isotropic ice is consolidated multi-year and thick first-year ice. Much of it is the
jointed ice described above; isotropic ice is assumed rigid in this paper.
• Oriented ice includes open water, new ice, nilas, young ice, first-year ice, rafted ice,
and ridged ice that occurs in long, narrow features. These features are assumed linear
for (grid, element, or cell) scales of 5 to 100 km. All pack ice deformations are
assumed to occur in the oriented ice. In addition, the linearity assumption implies
that a shearing deformation of a lead does not cause rafting or ridging of the oriented
ice and does not cause any failure of the isotropic ice.
ICE-THICKNESS REDISTRIBUTION
Subfreezing temperatures will cause oriented ice to form in leads, and ice deformations
will cause a distribution of ice thickness within these leads. The distribution of ice
thickness at each lead orientation can be described much as Thorndike et al. (1975) described
the distribution of ice thickness, and Pritchard (1998) described the distribution
of ice thickness in an anisotropic model. Figure 1 illustrates how to characterize these
ice-thickness distributions, assuming isotropic ice has one ice-thickness category and
oriented ice has four ice-thickness categories in two lead systems. The thickest oriented
ice category may be thicker than the isotropic ice.
Isotropic ice
∆ G ∆G
01
M0
∆ G 11
∆ G 21
∆ G 31
Oriented ice
θ
2
∆ G 02
θ 1
∆ G 12
∆G 22
∆ G 32
Fig. 1. Ice thickness distribution includes ice in each slip-line direction and the isotropic ice
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