Op_Diff_DG_base.cpp

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#include <Modele_turbulence_scal_base.h>
#include <Echange_externe_impose.h>
#include <Op_Diff_DG_base.h>
#include <Check_espace_virtuel.h>
#include <Domaine_Cl_DG.h>
#include <Champ_Elem_DG.h>
#include <Champ_Fonc_P0_base.h>
#include <Schema_Temps_base.h>
#include <Domaine_DG.h>
#include <Champ_Uniforme.h>
#include <communications.h>
#include <Probleme_base.h>
#include <EcrFicPartage.h>
#include <Milieu_base.h>
#include <TRUSTTrav.h>
#include <SFichier.h>
 
Implemente_base(Op_Diff_DG_base, "Op_Diff_DG_base", Operateur_Diff_base);
 
Sortie& Op_Diff_DG_base::printOn(Sortie& s) const { return s << que_suis_je(); }
 
Entree& Op_Diff_DG_base::readOn(Entree& s) { return s; }
 
/**
 * @brief Computes the maximum stable explicit time step for the diffusion operator.
 *
 * @details Two branches are handled depending on whether a variable density field is present:
 *
 * - **Constant density** (standard branch): The criterion is
 *     dt = h_min^2 / (2 * dim * alpha_max),
 *   where h_min is the minimum mesh size and alpha_max is the maximum diffusivity over all elements.
 *   This estimate is conservative: if the maximum diffusivity and the minimum mesh size are not
 *   co-located, the time step will be underestimated.
 *   Additionally, if a Robin boundary condition (Echange_externe_impose) is present, the Biot number
 *     Bi = h_imp_max * sqrt(h_min^2) / lambda_max
 *   is computed. If Bi > 1, alpha_max is scaled by the same factor, further tightening the criterion.
 *
 * - **Variable density** (rho field present): A per-element time step is computed as
 *     dt = 0.5 * rho / (nu * h),   for VDF-like elements (exactly 2*dim faces),
 *     dt = rho * h^2 / (2 * dim * nu),  for general elements,
 *   and the global minimum is taken across all elements and MPI processes.
 *
 * @return The minimum stable time step across all elements and MPI processes.
 */
double Op_Diff_DG_base::calculer_dt_stab() const
{
  update_nu();
  const Domaine& mon_dom = le_dom_dg_->domaine();
  double dt_stab = DMAXFLOAT;
 
  const int nb_elem = mon_dom.nb_elem();
 
  if (!has_champ_masse_volumique())
    {
      // "Standard" method for computing the time step
      // This estimate is very conservative: if the maximum diffusivity
      // is not co-located with the minimum delta_h_squared,
      // the time step will be underestimated.
      const Champ_base& champ_diffusivite = diffusivite_pour_pas_de_temps();
      const DoubleVect& valeurs_diffusivite = champ_diffusivite.valeurs();
      double alpha_max = local_max_vect(valeurs_diffusivite);
 
      // Detect if a heat flux is imposed on a boundary through Paroi_echange_externe_impose keyword
      double h_imp_max = -1, h_imp_temp = -2;
 
      const Domaine_Cl_DG& le_dom_cl_dg = la_zcl_dg_.valeur();
      for (int i = 0; i < le_dom_cl_dg.nb_cond_lim(); i++)
        {
          // loop on boundaries
          const Cond_lim_base& la_cl = le_dom_cl_dg.les_conditions_limites(i).valeur();
 
          if (sub_type(Echange_externe_impose, la_cl))
            {
              const Echange_externe_impose& la_cl_int = ref_cast(Echange_externe_impose, la_cl);
              const Champ_front_base& le_ch_front = ref_cast(Champ_front_base, la_cl_int.h_imp());
              const DoubleVect& tab = le_ch_front.valeurs();
              if (tab.size() != 0)
                {
                  h_imp_temp = local_max_vect(tab); // get h_imp from datafile
                  h_imp_temp = std::fabs(h_imp_temp); // we should take the absolute value since it can be negative!
                  h_imp_max = (h_imp_temp > h_imp_max) ? h_imp_temp : h_imp_max; // Should we take the max if more than one bc has h_imp ?
                }
            }
        } // End loop on boundaries
      h_imp_max = Process::mp_max(h_imp_max);
 
      if (alpha_max != 0.0 && nb_elem != 0)
        {
          double min_delta_h_carre = le_dom_dg_->carre_pas_du_maillage();
          if (h_imp_max > 0.0)  //a heat flux is imposed on a boundary condition
            {
              // get the thermal conductivity
              const Equation_base& mon_eqn = le_dom_cl_dg.equation();
              const Milieu_base& mon_milieu = mon_eqn.milieu();
              const DoubleVect& tab_lambda = mon_milieu.conductivite().valeurs();
              double max_conductivity = local_max_vect(tab_lambda);
 
              // compute Biot number given by Bi = L*h/lambda.
              double Bi = h_imp_max * sqrt(min_delta_h_carre) / max_conductivity;
              // if Bi>1, replace conductivity by h_imp*h in diffusivity. We are very conservative since h_imp_max is not necessarily located where max_conductivity is.
              if (Bi > 1.0)
                alpha_max *= h_imp_max * sqrt(min_delta_h_carre) / max_conductivity;
            }
          dt_stab = min_delta_h_carre / (2. * dimension * alpha_max);
        }
 
    }
  else
    {
      const int deux_dim = 2 * Objet_U::dimension;
      const Champ_base& champ_diffu = diffusivite();
      const DoubleTab& valeurs_diffu = champ_diffu.valeurs();
      const Champ_base& champ_rho = get_champ_masse_volumique();
      const DoubleTab& valeurs_rho = champ_rho.valeurs();
 
      assert(sub_type(Champ_Elem_DG, champ_rho));
      assert(sub_type(Champ_Fonc_P0_base, champ_diffu));
      // assert(valeurs_rho.size_array()== mon_dom.les_elems().dimension_tot(0));
      // Champ_Elem_DG: field at elements and faces
      // Variable density field.
      const IntTab& e_f = le_dom_dg_->elem_faces();
      for (int elem = 0; elem < nb_elem; elem++)
        {
          const double diffu = valeurs_diffu(elem);
          const double rho = valeurs_rho(elem);
          double dt;
          if (e_f.dimension(1) == deux_dim || e_f(elem, deux_dim) == -1)
            {
              // VDF-type cell (deux_dim faces on the element)
              // ToDo: implement for the case has_champ_masse_volumique()==false
              double h = 0;
              for (int f = 0; f < deux_dim; f++)
                {
                  int face = e_f(elem, f);
                  const double d = le_dom_dg_->volumes(elem) / le_dom_dg_->face_surfaces(face);
                  h += 0.5 / (d * d); // multiply by 0.5 because each face is counted twice
                }
              // See Op_Diff_VDF_Elem_base::calculer_dt_stab():
              dt = 0.5 * rho / ((diffu + DMINFLOAT) * h);
            }
          else
            {
              dt = le_dom_dg_->carre_pas_maille(elem) * rho / (deux_dim * (diffu + DMINFLOAT));
            }
          if (dt < dt_stab)
            dt_stab = dt;
        }
    }
 
  dt_stab = Process::mp_min(dt_stab);
  return dt_stab;
}
 
int Op_Diff_DG_base::impr(Sortie& os) const
{
  return 1;
}
 
/**
 * @brief Associates the operator with a DG domain and its boundary conditions.
 */
void Op_Diff_DG_base::associer(const Domaine_dis_base& domaine_dis, const Domaine_Cl_dis_base& zcl, const Champ_Inc_base&)
{
  le_dom_dg_ = ref_cast(Domaine_DG, domaine_dis);
  la_zcl_dg_ = ref_cast(Domaine_Cl_DG, zcl);
}
 
/**
 * @brief Computes the diffusion operator applied to inco and stores the result in resu.
 * @details Initializes resu to zero then delegates to ajouter(), which adds the diffusive
 *          contribution. This follows the standard TRUST operator pattern where calculer()
 *          resets the result before calling ajouter().
 * @param inco  The input field (e.g., temperature, velocity component).
 * @param resu  The output field, zeroed then filled with the diffusion contribution.
 * @return A reference to resu.
 */
DoubleTab& Op_Diff_DG_base::calculer(const DoubleTab& inco, DoubleTab& resu) const
{
  resu = 0.;
  return ajouter(inco, resu);
}
 
/**
 * @brief Finalizes the operator setup after all associations have been made.
 * @details Calls the parent completer(), then allocates and initializes the effective
 *          diffusivity table nu_. The number of components is set to 2 for the
 *          Transport_K_Epsilon equation (one per turbulent quantity), or to the
 *          line size of the diffusivity field for all other equations.
 *          The nu_a_jour_ flag is reset to 0 to force a recomputation on the first use.
 */
void Op_Diff_DG_base::completer()
{
  Operateur_base::completer();
  nu_.resize(0, equation().que_suis_je() == "Transport_K_Epsilon" ? 2 : diffusivite().valeurs().line_size());
  le_dom_dg_->domaine().creer_tableau_elements(nu_);
  nu_a_jour_ = 0;
}
 
/**
 * @brief Updates the cached effective diffusivity field nu_ by combining molecular and turbulent contributions.
 *
 * @details This method is a no-op if nu_a_jour_ is already set. Otherwise, it fills nu_ as follows:
 *
 *  1. **Molecular diffusivity** (all equations except Transport_K_Epsilon):
 *     - If the diffusivity has no metadata vector (i.e., it is spatially uniform), nu_ is filled
 *       by broadcasting the uniform value to all elements, treating both arrays as flat 1D vectors.
 *     - Otherwise (spatially variable diffusivity), nu_ is directly injected from the diffusivity array,
 *       after asserting that both share the same parallel metadata vector.
 *
 *  2. Not usable for now: **Turbulent diffusivity** (if has_diffusivite_turbulente() is true):
 *     @warning This branch is currently unreachable: it starts with a throw statement,
 *              indicating that turbulent diffusivity is not yet supported for DG operators.
 *     - For Transport_K_Epsilon, nu_(i,j) = nu_molecular(i) + nu_turb(i,j) for j in {0,1}.
 *     - For other equations, nu_turb is added to nu_ element-wise, handling the uniform case
 *       (no metadata vector) and the variable case separately.
 *
 *  After the update, nu_a_jour_ is set to 1 to prevent redundant recomputations.
 */
void Op_Diff_DG_base::update_nu() const
{
  if (nu_a_jour_) return; // already computed
 
  int i, j;
 
  const DoubleTab& diffu = diffusivite().valeurs();
  if (equation().que_suis_je() != "Transport_K_Epsilon")
    {
      if (!diffu.get_md_vector())
        {
          // uniform diffusivity
          int n = nu_.dimension_tot(0), nb_comp = nu_.line_size();
          // Arrays viewed as one-dimensional:
          const DoubleVect& arr_diffu = diffu;
          DoubleVect& arr_nu = nu_;
          for (i = 0; i < n; i++)
            for (j = 0; j < nb_comp; j++)
              arr_nu[i * nb_comp + j] = arr_diffu[j];
        }
      else
        {
          assert(nu_.get_md_vector() == diffu.get_md_vector());
          assert_espace_virtuel_vect(diffu);
          nu_.inject_array(diffu);
        }
    }
 
  /* ajout de la diffusivite turbulente si elle existe */
  if (has_diffusivite_turbulente())
    {
      throw;
 
      const DoubleTab& diffu_turb = diffusivite_turbulente().valeurs();
      if (equation().que_suis_je() == "Transport_K_Epsilon")
        {
          bool nu_uniforme = sub_type(Champ_Uniforme, diffusivite());
          double val_nu = diffu(0, 0);
          for (i = 0; i < diffu_turb.dimension(0); i++)
            for (j = 0; j < 2; j++)
              {
                if (!nu_uniforme)
                  val_nu = diffu(i, 0);
                nu_(i, j) = val_nu + diffu_turb(i, j);
              }
        }
      else
        {
          if (!diffu_turb.get_md_vector())
            {
              // uniform diffusivity
              int n = nu_.dimension_tot(0), nb_comp = nu_.line_size();
              // Arrays viewed as one-dimensional:
              const DoubleVect& arr_diffu_turb = diffu_turb;
              DoubleVect& arr_nu = nu_;
              for (i = 0; i < n; i++)
                for (j = 0; j < nb_comp; j++)
                  arr_nu[i * nb_comp + j] += arr_diffu_turb[j];
            }
          else
            {
              assert(nu_.get_md_vector() == diffu_turb.get_md_vector());
              assert_espace_virtuel_vect(diffu_turb);
              nu_ += diffu_turb;
            }
        }
    }
 
  nu_a_jour_ = 1;
}