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The file USF_Sliding.f90 contains two user functions to apply non-linear friction at the base of glacier.
The first user function (Sliding_Weertman) is a non-linear Weertman-type friction law and is described here. The second user function (Friction_Coulomb) is a non-linear water pressure dependant friction law, as proposed by Schoof (2005) and Gagliardini et al. (2007), and is presented in this page.
The required keywords in the SIF file for this user function are:
!!! Bedrock Boundary Condition Boundary Condition 1 Target Boundaries = 1 Normal-Tangential Velocity = Logical True Flow Force BC = Logical True Velocity 1 = Real 0.0 Slip Coefficient 2 = Variable Coordinate 1 Real Procedure "./USF_Sliding" "Friction_Coulomb" Slip Coefficient 3 = Variable Coordinate 1 Real Procedure "./USF_Sliding" "Friction_Coulomb" !! Parameters needed for the Coulomb Friction Law Friction Law Sliding Coefficient = Real 4.1613e5 Friction Law Post-Peak Exponent = Real 1.0 !(q=1) Friction Law Maximum Value = Real 1.0 !(C=1) Friction Law PowerLaw Exponent = Real 3.0 !(m = n = 3 Glen's law) Friction Law Linear Velocity = Real 0.01 !(=1m/a dans un premier temps) End
An example of the usage of the user function Friction_Weertman TODO
When this friction law is used, it can be cited using the following reference:
Gagliardini O., D. Cohen, P. Råback and T. Zwinger, 2007. Finite-Element Modeling of Subglacial Cavities and Related Friction Law. J. of Geophys. Res., Earth Surface, 112, F02027.