compositional_viscosity_prefactors.h

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// ------------------------------------------------------
//
// SPDX-License-Identifier: GPL-2.0-or-later
//
// SPDX-FileCopyrightText: Copyright (C) 2024-2026 by the ASPECT authors.
//
// This file is part of ASPECT.
//
// Detailed license information governing the source code and
// contributions can be found in the folder LICENSES and in
// LICENSE and CONTRIBUTING.md at the top level directory.
//
// ------------------------------------------------------

#ifndef _aspect_material_model_rheology_compositional_viscosity_prefactors_h
#define _aspect_material_model_rheology_compositional_viscosity_prefactors_h

#include <aspect/global.h>
#include <aspect/material_model/interface.h>
#include <aspect/simulator_access.h>

namespace aspect
{
  namespace MaterialModel
  {
    namespace Rheology
    {
      template <int dim>
      class CompositionalViscosityPrefactors : public ::aspect::SimulatorAccess<dim>
      {
        public:
          CompositionalViscosityPrefactors();

          static
          void
          declare_parameters (ParameterHandler &prm);

          void
          parse_parameters (ParameterHandler &prm);

          // The flow laws that can be
          // currently modified.
          enum ModifiedFlowLaws
          {
            diffusion,
            dislocation
          } modified_flow_laws;

          double
          compute_viscosity (const MaterialModel::MaterialModelInputs<dim> &in,
                             const double base_viscosity,
                             const unsigned int composition_index,
                             const unsigned int q,
                             const ModifiedFlowLaws &modified_flow_laws) const;

        private:
          enum ViscosityPrefactorScheme
          {
            none,
            hk04_olivine_hydration,
            interface_weakening,
          };
          ViscosityPrefactorScheme viscosity_prefactor_scheme;

          // Initialize variables for the water fugacity calculation, from HK04
          std::vector<double> diffusion_water_fugacity_exponents;
          std::vector<double> dislocation_water_fugacity_exponents;
          std::vector<double> minimum_mass_fraction_water_for_dry_creep;

          // Variables for the interface weakening scheme
          std::vector<std::string> weakening_field_names;
          std::vector<double> interface_weakening_factors;
          double interface_weakening_threshold;

          // From Hirth & Kohlstedt 2004, equation 6
          const double A_H2O = 2.6e-5; // 1/Pa
          const double activation_energy_H2O = 40e3; // J/mol/K
          const double activation_volume_H2O = 10e-6; // m^3/mol

          // We calculate the molar mass of olivine using the molar mass of fayalite (0.20379 kg/mol)
          // and the molar mass of forsterite (0.140693 kg/mol), and a mole fraction of 90% forsterite
          // in olivine.
          const double molar_mass_olivine = 0.1470027; // kg/mol
          const double molar_mass_H2O = 0.01801528; // kg/mol
      };
    }
  }
}
#endif