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userfunctions:coulomb [2012/11/15 02:29]
gag
userfunctions:coulomb [2015/12/02 12:24] (current)
gag [General Description]
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 ==== General Informations ==== ==== General Informations ====
-  * **USF Fortran File:​** ​//USF_Sliding.f90// +  * **USF Fortran File:​** ​''​USF_Sliding.f90''​ 
-  * **USF Name:​** ​//Friction_Coulomb// +  * **USF Name:​** ​''​Friction_Coulomb''​ 
-  * **Required Input Variable(s):​** A //Flow Solution// in //Flow Solution Name////Normal Vector////Stress//+  * **Required Input Variable(s):​** A ''​Flow Solution'' ​in ''​Flow Solution Name''​''​Normal Vector''​''​Stress''​ or the ''​Effective Pressure''​ variable.
  
  
 ==== General Description ==== ==== General Description ====
-The file //USF_Sliding.f90// contains ​two user functions to apply non-linear friction at the base of glacier.  ​+The file ''​USF_Sliding.f90'' ​contains ​three 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 [[:​userfunctions:​weertman|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 first user function (''​Sliding_Weertman''​) is a non-linear Weertman-type friction law and is described [[:​userfunctions:​weertman|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 third user function (''​Sliding_Budd''​) is described [[:​userfunctions:​budd|here]] and is from Budd et al 1984 (Annals of Glaciology 5, page 29-36)
   ​   ​
  
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 The //Slip Coefficient//​ in Elmer is then given as\\ The //Slip Coefficient//​ in Elmer is then given as\\
 <​m> ​ C.N {[{ {chi . {u_b}^{-n} }/ {(1 + a . chi^q)} }]}^{1/​n} ​ </​m>​\\ <​m> ​ C.N {[{ {chi . {u_b}^{-n} }/ {(1 + a . chi^q)} }]}^{1/​n} ​ </​m>​\\
-When  <​m>​u_b < u_{t0}</​m>, ​$u_bin the previous is replaced by <​m>​u_{t0}</​m>​.+When  <​m>​u_b < u_{t0}</​m>, ​<m>u_b</​m> ​in the previous ​equation ​is replaced by <​m>​u_{t0}</​m>​.
  
  
 The parameters to be given are:\\ The parameters to be given are:\\
-  * Friction Law Sliding Coefficient ​     -> <​m>​A_s</​m>​ +  * ''​Friction Law Sliding Coefficient'' ​     -> <​m>​A_s</​m>​ 
-  * Friction Law Post-Peak Exponent ​      -> <m>q >= 1</​m>​ +  * ''​Friction Law Post-Peak Exponent'' ​      -> <m>q >= 1</​m>​ 
-  * Friction Law Maximum Value            -> <​m>​C</​m>​ ~ max bed slope +  * ''​Friction Law Maximum Value'' ​           -> <​m>​C</​m>​ ~ max bed slope 
-  * Friction Law Exponent ​       -> m = (n Glen's law) +  * ''​Friction Law Exponent'' ​      -> m = (n Glen's law) 
-  * Friction Law Linear Velocity -> <​m>​u_{t0}</​m> ​       +  * ''​Friction Law Linear Velocity'' ​-> <​m>​u_{t0}</​m> ​  
 + 
 +The effective pressure is defined as <m>N = -sigma_{nn} -p_w</​m>, ​ where <​m>​sigma_{nn}</​m>​ is the normal Cauchy stress and <​m>​p_w</​m>​ the water pressure. If a variable ''​Effective Pressure''​ exists, it is used to evaluate directly <​m>​N</​m>​. Else, the normal Cauchy stress is estimated from the stress computed at previous timestep. The water pressure is prescribed as an ''​External Pressure''​ (Negative - Compressive convention, and therefore '​External Pressure'​ should be equal to the opposite of the water pressure in the sif).  
 +      ​
    
  
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   Normal-Tangential Velocity = Logical True   Normal-Tangential Velocity = Logical True
   Flow Force BC = Logical True   Flow Force BC = Logical True
 +   
 +  !! Water pressure given through the Stokes '​External Pressure'​ parameter  
 +  !! (Negative = Compressive) 
 +  External Pressure = Equals Water Pressure 
 +   
   Velocity 1 = Real 0.0   Velocity 1 = Real 0.0
   ​   ​
   Slip Coefficient 2 =  Variable Coordinate 1   Slip Coefficient 2 =  Variable Coordinate 1
-    Real Procedure "./​USF_Sliding" "​Friction_Coulomb"​+    Real Procedure "ElmerIceUSF" "​Friction_Coulomb"​
   Slip Coefficient 3 =  Variable Coordinate 1   Slip Coefficient 3 =  Variable Coordinate 1
-    Real Procedure "./​USF_Sliding" "​Friction_Coulomb"​+    Real Procedure "ElmerIceUSF" "​Friction_Coulomb"​
     ​     ​
   !! Parameters needed for the Coulomb Friction Law   !! Parameters needed for the Coulomb Friction Law
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   Friction Law Maximum Value = Real 1.0            !(C=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 PowerLaw Exponent = Real 3.0        !(m = n = 3 Glen's law) 
-  Friction Law Linear Velocity = Real 0.01         !(=1m/a dans un premier temps)+  Friction Law Linear Velocity = Real 0.01         
 End End
 </​code>​ </​code>​
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 ==== Examples ==== ==== Examples ====
-An example ​of the usage of the user function ​//Friction_Weertman// TODO +The Coulomb friction law is tested in ''​[ELMER_TRUNK]/​elmerice/​Tests/​Friction_Coulomb''​ with a direct input of the effective pressure and ''​[ELMER_TRUNK]/elmerice/Tests/Friction_Coulomb_Pw''​ with the effective pressure computed from the stress and a prescribed water pressure.  ​
  
  
userfunctions/coulomb.1352946542.txt.gz · Last modified: 2012/11/15 02:29 by gag
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