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userfunctions:coulomb [Elmer/Ice Wiki]

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userfunctions:coulomb [2014/01/07 08:44]
gag [SIF contents]
userfunctions:coulomb [2015/11/26 15:50]
gag [Examples]
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   * **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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   * ''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. Hereat time t+dt, the normal Cauchy stress is estimated from the stress computed at time t. The water pressure is prescribed as an ''External Pressure'' (Negative - Compressive convention, and therefore the water pressure is the opposite of the 'External Pressure'). +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'' existsit 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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 ==== Examples ==== ==== Examples ====
-An example of the usage of the user function //Friction_Coulomb// 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.txt ยท Last modified: 2015/12/02 12:24 by gag
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