added compute_strain_rate_and_derivative to ConstViscPrefactors

geodynamics · Aug 15, 2020 · c865b8e · c865b8e
1 parent a097196
commit c865b8e
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diff --git a/include/aspect/material_model/rheology/constant_viscosity_prefactors.h b/include/aspect/material_model/rheology/constant_viscosity_prefactors.h
@@ -67,6 +67,15 @@ namespace aspect
           compute_viscosity (const double base_viscosity,
                              const unsigned int composition_index) const;
 
+          /**
+          * Compute the strain rate and first stress derivative
+          * as a function of stress.
+          */
+          std::pair<double, double>
+          compute_strain_rate_and_derivative (const double stress,
+                                              const double viscosity,
+                                              const unsigned int composition_index) const;
+
         private:
           /**
            * The constant viscosity prefactors, which are read in

diff --git a/source/material_model/rheology/constant_viscosity_prefactors.cc b/source/material_model/rheology/constant_viscosity_prefactors.cc
@@ -48,6 +48,18 @@ namespace aspect
 
 
 
+      template <int dim>
+      std::pair<double, double>
+      ConstantViscosityPrefactors<dim>::compute_strain_rate_and_derivative (const double stress,
+                                                                            const double viscosity,
+                                                                            const unsigned int composition_index) const
+      {
+        const double eta = viscosity * constant_viscosity_prefactors[composition_index];
+        return std::make_pair(0.5*stress/eta, 0.5/eta);
+      }
+
+
+
       template <int dim>
       void
       ConstantViscosityPrefactors<dim>::declare_parameters (ParameterHandler &prm)