divergence_penalty_operator.h

/*  ______________________________________________________________________
 *
 *  ExaDG - High-Order Discontinuous Galerkin for the Exa-Scale
 *
 *  Copyright (C) 2021 by the ExaDG authors
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program. If not, see <https://www.gnu.org/licenses/>.
 *  ______________________________________________________________________
 */
 
#ifndef EXADG_INCOMPRESSIBLE_NAVIER_STOKES_SPATIAL_DISCRETIZATION_OPERATORS_DIVERGENCE_PENALTY_OPERATOR_H_
#define EXADG_INCOMPRESSIBLE_NAVIER_STOKES_SPATIAL_DISCRETIZATION_OPERATORS_DIVERGENCE_PENALTY_OPERATOR_H_
 
// ExaDG
#include <exadg/grid/calculate_characteristic_element_length.h>
#include <exadg/incompressible_navier_stokes/user_interface/parameters.h>
#include <exadg/matrix_free/integrators.h>
#include <exadg/operators/integrator_flags.h>
#include <exadg/operators/mapping_flags.h>
 
namespace ExaDG
{
namespace IncNS
{
/*
 *  Divergence penalty operator:
 *
 *    ( div(v_h) , tau_div * div(u_h) )_Omega^e
 *
 *  where
 *
 *   v_h : test function
 *   u_h : solution
 *   tau_div: divergence penalty factor
 *
 *            use convective term:  tau_div_conv = K * ||U||_mean * h_eff
 *
 *                                  where h_eff = h / (k_u+1) with a characteristic
 *                                  element length h derived from the element volume V_e
 *
 *            use viscous term:     tau_div_viscous = K * nu
 *
 *            use both terms:       tau_div = tau_div_conv + tau_div_viscous
 *
 */
 
namespace Operators
{
struct DivergencePenaltyKernelData
{
  DivergencePenaltyKernelData()
    : type_penalty_parameter(TypePenaltyParameter::ConvectiveTerm),
      viscosity(0.0),
      degree(1),
      penalty_factor(1.0)
  {
  }
 
  // type of penalty parameter (viscous and/or convective terms)
  TypePenaltyParameter type_penalty_parameter;
 
  // viscosity, needed for computation of penalty factor
  double viscosity;
 
  // degree of finite element shape functions
  unsigned int degree;
 
  // the penalty term can be scaled by 'penalty_factor'
  double penalty_factor;
};
 
template<int dim, typename Number>
class DivergencePenaltyKernel
{
private:
  typedef CellIntegrator<dim, dim, Number> IntegratorCell;
 
  typedef dealii::LinearAlgebra::distributed::Vector<Number> VectorType;
 
  typedef dealii::VectorizedArray<Number> scalar;
 
public:
  DivergencePenaltyKernel()
    : matrix_free(nullptr), dof_index(0), quad_index(0), array_penalty_parameter(0)
  {
  }
 
  void
  reinit(dealii::MatrixFree<dim, Number> const & matrix_free,
         unsigned int const                      dof_index,
         unsigned int const                      quad_index,
         DivergencePenaltyKernelData const &     data)
  {
    this->matrix_free = &matrix_free;
 
    this->dof_index  = dof_index;
    this->quad_index = quad_index;
 
    this->data = data;
 
    unsigned int n_cells = matrix_free.n_cell_batches() + matrix_free.n_ghost_cell_batches();
    array_penalty_parameter.resize(n_cells);
  }
 
  DivergencePenaltyKernelData
  get_data()
  {
    return this->data;
  }
 
  IntegratorFlags
  get_integrator_flags() const
  {
    IntegratorFlags flags;
 
    flags.cell_evaluate  = dealii::EvaluationFlags::gradients;
    flags.cell_integrate = dealii::EvaluationFlags::gradients;
 
    // no face integrals
 
    return flags;
  }
 
  static MappingFlags
  get_mapping_flags()
  {
    MappingFlags flags;
 
    flags.cells = dealii::update_JxW_values | dealii::update_gradients;
 
    // no face integrals
 
    return flags;
  }
 
  void
  calculate_penalty_parameter(VectorType const & velocity)
  {
    velocity.update_ghost_values();
 
    IntegratorCell integrator(*matrix_free, dof_index, quad_index);
 
    dealii::AlignedVector<scalar> JxW_values(integrator.n_q_points);
 
    ElementType const element_type =
      get_element_type(matrix_free->get_dof_handler(dof_index).get_triangulation());
 
    unsigned int n_cells = matrix_free->n_cell_batches() + matrix_free->n_ghost_cell_batches();
    for(unsigned int cell = 0; cell < n_cells; ++cell)
    {
      scalar tau_convective = dealii::make_vectorized_array<Number>(0.0);
      scalar tau_viscous    = dealii::make_vectorized_array<Number>(data.viscosity);
 
      if(data.type_penalty_parameter == TypePenaltyParameter::ConvectiveTerm or
         data.type_penalty_parameter == TypePenaltyParameter::ViscousAndConvectiveTerms)
      {
        integrator.reinit(cell);
        integrator.read_dof_values(velocity);
        integrator.evaluate(dealii::EvaluationFlags::values);
 
        scalar volume      = dealii::make_vectorized_array<Number>(0.0);
        scalar norm_U_mean = dealii::make_vectorized_array<Number>(0.0);
        for(unsigned int q = 0; q < integrator.n_q_points; ++q)
        {
          volume += integrator.JxW(q);
          norm_U_mean += integrator.JxW(q) * integrator.get_value(q).norm();
        }
        norm_U_mean /= volume;
 
        scalar h     = calculate_characteristic_element_length(volume, dim, element_type);
        scalar h_eff = calculate_high_order_element_length(h, data.degree, true);
 
        tau_convective = norm_U_mean * h_eff;
      }
 
      if(data.type_penalty_parameter == TypePenaltyParameter::ConvectiveTerm)
      {
        array_penalty_parameter[cell] = data.penalty_factor * tau_convective;
      }
      else if(data.type_penalty_parameter == TypePenaltyParameter::ViscousTerm)
      {
        array_penalty_parameter[cell] = data.penalty_factor * tau_viscous;
      }
      else if(data.type_penalty_parameter == TypePenaltyParameter::ViscousAndConvectiveTerms)
      {
        array_penalty_parameter[cell] = data.penalty_factor * (tau_convective + tau_viscous);
      }
    }
 
    velocity.zero_out_ghost_values();
  }
 
  void
  reinit_cell(IntegratorCell & integrator) const
  {
    tau = integrator.read_cell_data(array_penalty_parameter);
  }
 
  /*
   * Volume flux, i.e., the term occurring in the volume integral
   */
  inline DEAL_II_ALWAYS_INLINE //
    scalar
    get_volume_flux(IntegratorCell const & integrator, unsigned int const q) const
  {
    return tau * integrator.get_divergence(q);
  }
 
private:
  dealii::MatrixFree<dim, Number> const * matrix_free;
 
  unsigned int dof_index;
  unsigned int quad_index;
 
  DivergencePenaltyKernelData data;
 
  dealii::AlignedVector<scalar> array_penalty_parameter;
 
  mutable scalar tau;
};
 
} // namespace Operators
 
struct DivergencePenaltyData
{
  DivergencePenaltyData() : dof_index(0), quad_index(0)
  {
  }
 
  unsigned int dof_index;
  unsigned int quad_index;
};
 
template<int dim, typename Number>
class DivergencePenaltyOperator
{
private:
  typedef DivergencePenaltyOperator<dim, Number> This;
 
  typedef dealii::LinearAlgebra::distributed::Vector<Number> VectorType;
 
  typedef std::pair<unsigned int, unsigned int> Range;
 
  typedef CellIntegrator<dim, dim, Number> IntegratorCell;
 
  typedef Operators::DivergencePenaltyKernel<dim, Number> Kernel;
 
public:
  DivergencePenaltyOperator();
 
  void
  initialize(dealii::MatrixFree<dim, Number> const & matrix_free,
             DivergencePenaltyData const &           data,
             std::shared_ptr<Kernel> const           kernel);
 
  void
  update(VectorType const & velocity);
 
  void
  apply(VectorType & dst, VectorType const & src) const;
 
  void
  apply_add(VectorType & dst, VectorType const & src) const;
 
private:
  void
  cell_loop(dealii::MatrixFree<dim, Number> const & matrix_free,
            VectorType &                            dst,
            VectorType const &                      src,
            Range const &                           range) const;
 
  void
  do_cell_integral(IntegratorCell & integrator) const;
 
  dealii::MatrixFree<dim, Number> const * matrix_free;
 
  DivergencePenaltyData data;
 
  std::shared_ptr<Operators::DivergencePenaltyKernel<dim, Number>> kernel;
};
 
} // namespace IncNS
} // namespace ExaDG
 
#endif /* EXADG_INCOMPRESSIBLE_NAVIER_STOKES_SPATIAL_DISCRETIZATION_OPERATORS_DIVERGENCE_PENALTY_OPERATOR_H_ \
        */