source_term_calculator.h

/*  ______________________________________________________________________
 *
 *  ExaDG - High-Order Discontinuous Galerkin for the Exa-Scale
 *
 *  Copyright (C) 2025 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_AERO_ACOUSTIC_CALCULATORS_SOURCE_TERM_CALCULATOR_H_
#define EXADG_AERO_ACOUSTIC_CALCULATORS_SOURCE_TERM_CALCULATOR_H_
 
// ExaDG
#include <exadg/matrix_free/integrators.h>
#include <exadg/utilities/lazy_ptr.h>
 
namespace ExaDG
{
namespace AeroAcoustic
{
template<int dim>
struct SourceTermCalculatorData
{
  unsigned int dof_index_pressure;
  unsigned int dof_index_velocity;
  unsigned int quad_index;
 
  // density of the underlying fluid.
  double density;
 
  // speed of sound of the fluid.
  double speed_of_sound;
 
  // use material or partial temporal derivative of pressure as source term.
  bool consider_convection;
 
  // function if blend in is required.
  bool                                                  blend_in;
  std::shared_ptr<Utilities::SpatialAwareFunction<dim>> blend_in_function;
};

template<int dim, typename Number>
class SourceTermCalculator
{
  using This       = SourceTermCalculator<dim, Number>;
  using VectorType = dealii::LinearAlgebra::distributed::Vector<Number>;
 
  using CellIntegratorScalar = CellIntegrator<dim, 1, Number>;
  using CellIntegratorVector = CellIntegrator<dim, dim, Number>;
 
  using scalar = dealii::VectorizedArray<Number>;
  using qpoint = dealii::Point<dim, dealii::VectorizedArray<Number>>;
 
public:
  SourceTermCalculator() : matrix_free(nullptr), time(std::numeric_limits<double>::min())
  {
  }
 
  void
  setup(dealii::MatrixFree<dim, Number> const & matrix_free_in,
        SourceTermCalculatorData<dim> const &   data_in)
  {
    matrix_free = &matrix_free_in;
    data        = data_in;
  }
 
  void
  evaluate_integrate(VectorType &            dst,
                     dealii::Function<dim> & analytical_source_term,
                     double const            evaluation_time)
  {
    time = evaluation_time;
 
    dst.zero_out_ghost_values();
 
    analytical_source_term.set_time(time);
 
    matrix_free->cell_loop(&This::compute_source_term, this, dst, analytical_source_term, true);
  }
 
 
  void
  evaluate_integrate(VectorType &       dst,
                     VectorType const & velocity_cfd_in,
                     VectorType const & pressure_cfd_in,
                     VectorType const & pressure_cfd_time_derivative_in,
                     double const       evaluation_time)
  {
    time = evaluation_time;
 
    dst.zero_out_ghost_values();
 
    if(data.consider_convection)
    {
      velocity_cfd.reset(velocity_cfd_in);
      velocity_cfd->update_ghost_values();
 
      pressure_cfd.reset(pressure_cfd_in);
      pressure_cfd->update_ghost_values();
    }
 
    matrix_free->cell_loop(
      &This::compute_source_term, this, dst, pressure_cfd_time_derivative_in, true);
  }
 
private:
  void
  compute_source_term(dealii::MatrixFree<dim, Number> const &       matrix_free_in,
                      VectorType &                                  dst,
                      VectorType const &                            dp_cfd_dt,
                      std::pair<unsigned int, unsigned int> const & cell_range) const
  {
    CellIntegratorScalar dpdt(matrix_free_in, data.dof_index_pressure, data.quad_index);
    CellIntegratorScalar p(matrix_free_in, data.dof_index_pressure, data.quad_index);
    CellIntegratorVector u(matrix_free_in, data.dof_index_velocity, data.quad_index);
 
    auto get_scaling_factor = get_scaling_function();
 
    Number const m_rho_c2 =
      static_cast<Number>(-data.density / (data.speed_of_sound * data.speed_of_sound));
 
    for(unsigned int cell = cell_range.first; cell < cell_range.second; ++cell)
    {
      dpdt.reinit(cell);
      dpdt.gather_evaluate(dp_cfd_dt, dealii::EvaluationFlags::values);
 
      if(data.consider_convection)
      {
        p.reinit(cell);
        p.gather_evaluate(*pressure_cfd, dealii::EvaluationFlags::gradients);
        u.reinit(cell);
        u.gather_evaluate(*velocity_cfd, dealii::EvaluationFlags::values);
 
        for(unsigned int q = 0; q < dpdt.n_q_points; ++q)
        {
          scalar flux = m_rho_c2 * (dpdt.get_value(q) + u.get_value(q) * p.get_gradient(q));
 
          if(data.blend_in)
            flux *= get_scaling_factor(dpdt.quadrature_point(q));
 
          dpdt.submit_value(flux, q);
        }
      }
      else
      {
        for(unsigned int q = 0; q < dpdt.n_q_points; ++q)
        {
          scalar flux = m_rho_c2 * dpdt.get_value(q);
 
          if(data.blend_in)
            flux *= get_scaling_factor(dpdt.quadrature_point(q));
 
          dpdt.submit_value(flux, q);
        }
      }
 
      dpdt.integrate_scatter(dealii::EvaluationFlags::values, dst);
    }
  }
 
  void
  compute_source_term(dealii::MatrixFree<dim, Number> const &       matrix_free_in,
                      VectorType &                                  dst,
                      dealii::Function<dim> const &                 analytical_source_term,
                      std::pair<unsigned int, unsigned int> const & cell_range) const
  {
    CellIntegratorScalar dpdt(matrix_free_in, data.dof_index_pressure, data.quad_index);
 
    auto get_scaling_factor = get_scaling_function();
 
    for(unsigned int cell = cell_range.first; cell < cell_range.second; ++cell)
    {
      dpdt.reinit(cell);
 
      for(unsigned int q = 0; q < dpdt.n_q_points; ++q)
      {
        scalar flux = FunctionEvaluator<0, dim, Number>::value(analytical_source_term,
                                                               dpdt.quadrature_point(q));
 
        if(data.blend_in)
          flux *= get_scaling_factor(dpdt.quadrature_point(q));
 
        dpdt.submit_value(flux, q);
      }
 
      dpdt.integrate_scatter(dealii::EvaluationFlags::values, dst);
    }
  }
 
  std::function<scalar(qpoint const &)>
  get_scaling_function() const
  {
    // In case we blend in the source term, we check if the scaling is space dependent. Only in that
    // case we have to evaluate the function in every equadrature point. Otherwise the scaling
    // is purely temporal and constant during this function.
    if(data.blend_in)
    {
      AssertThrow(data.blend_in_function != nullptr,
                  dealii::ExcMessage("No blend-in function provided."));
    }
 
    bool const space_dependent_scaling =
      data.blend_in_function != nullptr ? data.blend_in_function->varies_in_space(time) : false;
    Number const pure_temporal_scaling_factor =
      (not space_dependent_scaling) ? data.blend_in_function->compute_time_factor(time) : 1.0;
 
    if(space_dependent_scaling)
    {
      return [&](qpoint const & q) {
        return FunctionEvaluator<0, dim, Number>::value(*data.blend_in_function, q, time);
      };
    }
    else
    {
      // capture scaling factor by copy
      return
        [pure_temporal_scaling_factor](qpoint const &) { return pure_temporal_scaling_factor; };
    }
  }
 
 
  dealii::MatrixFree<dim, Number> const * matrix_free;
 
  SourceTermCalculatorData<dim> data;
 
  lazy_ptr<VectorType> velocity_cfd;
  lazy_ptr<VectorType> pressure_cfd;
 
  double time;
};
 
} // namespace AeroAcoustic
} // namespace ExaDG
 
#endif /*EXADG_AERO_ACOUSTIC_CALCULATORS_SOURCE_TERM_CALCULATOR_H_*/