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 [51]) with stress exponent \(n=3\).2
: Goldsby-Kohlstedt [22, 23] flow law with stress exponent \(n=1.8\) and grain-size exponent \(p=1.4\). Average grain size defined by the parameterGR_SIZE
.3
: Flow law by Durham et al. [16] with stress exponent \(n=4\).4
: Polynomial flow law by Smith and Morland [60] (summarized by Greve and Blatter [31], 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 [31], Section 4.3.2).
Note
The rate factor \(A(T')\) must fit the flow law unit- and value-wise. It is defined as a list for integer temperature values, to be read from a file specified in the run-specs header (parameter RF_KAPPA_C_FILE
). Between integer temperatures, linear interpolation is applied.