• USF Fortran File: USF_Sliding.f90
• USF Name: Sliding_Weertman
• Required Input Variable(s): A Flow Solution in Flow Solution Name, Normal Vector

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 in this page. 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 here.

The friction law in Weertman_Sliding is of the form:

The Slip Coefficient in Elmer is then given as

When , in the previous equation is replaced by (linearisation for small velocity).

The parameters to be given are:

• Weertman Friction Coefficient →
• Weertman Exponent →
• Weertman Linear Velocity →

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 "ElmerIceUSF" "Sliding_Weertman"
  Slip Coefficient 3 =  Variable Coordinate 1
    Real Procedure "ElmerIceUSF" "Sliding_Weertman"
    
  Weertman Friction Coefficient = Real 2.412579e-2        
  Weertman Exponent = Real $1.0/3.0
  Weertman Linear Velocity = Real 0.00001

End

An example of the usage of the user function Sliding_Weertman TODO