The Effects of Non-Normal Flow Rules on Fracture Angles in
Viscous-Plastic Sea Ice Models
Abstract
High-resolution viscous-plastic (VP) sea ice models reproduce the narrow
deformations lines observed in the Arctic sea ice, called the Linear
Kinematic Features (LKFs). Recent studies showed that standard VP models
overestimate the intersection angles between the LKFs when compared to
observations. We investigate fracture angles in a uniaxial compression
test and two different VP rheology. The first one uses an elliptical
yield curve and a normal flow rule. In contrast, the second rheology
uses a different elliptical plastic potential that creates a non-normal
flow rule. Results show that the non-normality of the flow rule changes
the angles of fracture. This new rheology can create fracture angles as
low as 22º when the rheology with normal flow rule is limited to angles
above 30º. A newly adapted theory – based on one developed from
granular material observations – predicts the modeled fracture angles
accurately. Using a non-normal flow rule takes longer to solve
numerically, but allow reductions of the fracture angle to values within
the range of satellite observations and decouples the angle of fracture
from the shape of the yield curve.