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userfunctions:coulomb [2014/01/07 08:44] gag [SIF contents] |
userfunctions:coulomb [2015/12/02 12:24] (current) gag [General Description] |
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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. Here, at 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'' 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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==== 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. |