geometry_step.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2022 - 2026 by the ryujin authors
//
 
#pragma once
 
#include <ryujin/base/compile_time_options.h>
#include <ryujin/geometries/geometry_common_includes.h>
 
namespace ryujin
{
  namespace GridGenerator
  {
    template <int dim, template <int, int> class Triangulation>
    void step(Triangulation<dim, dim> &,
              const double /*length*/,
              const double /*height*/,
              const double /*step_position*/,
              const double /*step_height*/)
    {
      AssertThrow(false, dealii::ExcNotImplemented());
      __builtin_trap();
    }
 
 
#ifndef DOXYGEN
    template <template <int, int> class Triangulation>
    void step(Triangulation<2, 2> &triangulation,
              const double length,
              const double height,
              const double step_position,
              const double step_height)
    {
      using namespace dealii;
 
      dealii::Triangulation<2, 2> tria1, tria2, tria3;
      tria3.set_mesh_smoothing(triangulation.get_mesh_smoothing());
 
      GridGenerator::subdivided_hyper_rectangle(
          tria1, {15, 4}, Point<2>(0., step_height), Point<2>(length, height));
 
      GridGenerator::subdivided_hyper_rectangle(
          tria2,
          {3, 1},
          Point<2>(0., 0.),
          Point<2>(step_position, step_height));
 
      GridGenerator::merge_triangulations(tria1, tria2, tria3);
      triangulation.copy_triangulation(tria3);
 
      /*
       * Set boundary ids:
       */
 
      for (auto cell : triangulation.active_cell_iterators()) {
        for (auto f : cell->face_indices()) {
          const auto face = cell->face(f);
 
          if (!face->at_boundary())
            continue;
 
          /*
           * We want slip boundary conditions (i.e. indicator 1) at top
           * and bottom of the rectangle. On the left we set inflow
           * conditions (i.e. indicator 2), and we do nothing on the right
           * side (i.e. indicator 0).
           */
 
          const auto center = face->center();
 
          if (center[0] > 0. + 1.e-6 && center[0] < length - 1.e-6)
            face->set_boundary_id(Boundary::slip);
 
          if (center[0] < 0. + 1.e-06)
            face->set_boundary_id(Boundary::dirichlet);
        }
      }
 
      /*
       * Refine four times and round off corner with radius 0.0125:
       */
 
      triangulation.refine_global(4);
 
      Point<2> point(step_position + 0.0125, step_height - 0.0125);
      triangulation.set_manifold(1, SphericalManifold<2>(point));
 
      for (auto cell : triangulation.active_cell_iterators())
        for (unsigned int v : cell->vertex_indices()) {
          double distance =
              (cell->vertex(v) - Point<2>(step_position, step_height)).norm();
          if (distance < 1.e-6) {
            for (auto f : cell->face_indices()) {
              const auto face = cell->face(f);
              if (face->at_boundary())
                face->set_manifold_id(1);
              cell->set_manifold_id(1); // temporarily for second loop
            }
          }
        }
 
      for (auto cell : triangulation.active_cell_iterators()) {
        if (cell->manifold_id() != 1)
          continue;
 
        cell->set_manifold_id(0); // reset manifold id again
 
        for (unsigned int v : cell->vertex_indices()) {
          auto &vertex = cell->vertex(v);
 
          if (std::abs(vertex[0] - step_position) < 1.e-6 &&
              vertex[1] > step_height - 1.e-6)
            vertex[0] = step_position + 0.0125 * (1 - std::sqrt(1. / 2.));
 
          if (std::abs(vertex[1] - step_height) < 1.e-6 &&
              vertex[0] < step_position + 0.005)
            vertex[1] = step_height - 0.0125 * (1 - std::sqrt(1. / 2.));
        }
      }
    }
#endif
  } // namespace GridGenerator
 
 
  namespace Geometries
  {
    template <int dim>
    class Step : public Geometry<dim>
    {
    public:
      Step(const std::string &subsection)
          : Geometry<dim>("step", subsection)
      {
        length_ = 3.;
        this->add_parameter(
            "length", length_, "length of computational domain");
 
        height_ = 1.;
        this->add_parameter(
            "height", height_, "height of computational domain");
 
        step_position_ = 0.6;
        this->add_parameter(
            "step position", step_position_, "x position of step");
 
        step_height_ = 0.2;
        this->add_parameter("step height", step_height_, "height of step");
      }
 
      void create_coarse_triangulation(
          dealii::Triangulation<dim> &triangulation) const final
      {
        GridGenerator::step(
            triangulation, length_, height_, step_position_, step_height_);
      }
 
    private:
      double length_;
      double height_;
      double step_position_;
      double step_height_;
    };
  } // namespace Geometries
 
} // namespace ryujin