6.6. Flow law

Several options for the flow law of polycrystalline ice are available. They can be selected by the parameter FLOW_LAW in the run-specs headers:

• 1: Glen’s flow law (Glen [19], Nye [49]) with stress exponent \(n=3\).

• 2: Goldsby-Kohlstedt [21, 22] flow law with stress exponent \(n=1.8\) and grain-size exponent \(p=1.4\). Average grain size defined by the parameter GR_SIZE.

• 3: Flow law by Durham et al. [16] with stress exponent \(n=4\).

• 4: Polynomial flow law by Smith and Morland [58] (summarized by Greve and Blatter [30], Section 4.3.3).

For the cases FLOW_LAW = 1, 2 or 3, the additional parameter FIN_VISC allows choosing between the unmodified flow law with an infinite-viscosity limit for low strain rates (FIN_VISC = 1), or using a regularized flow law with a finite-viscosity limit (FIN_VISC = 2). The latter is defined by a non-vanishing residual stress \(\sigma_0\) (parameter SIGMA_RES; see Greve and Blatter [30], Section 4.3.2).

Note

The rate factor \(A(T')\) must fit the flow law unit- and value-wise. It is defined in the physical-parameter files as a list for integer temperature values (between which linear interpolation is applied).