Dear all,
attached is a minimal example which demonstrates that the function
"extract_surface_mesh()" in the GridGenerator namespace
does not extract refined cells.
That is, it seems to work only for globally refined meshes.
There is a comment in the implementation of this function:
// Create boundary mesh and mapping
// from only level(0) cells of the volume mesh.
Since the documentation states nothing about the usage of this function for
adaptively
refined meshes (like it is done in flatten_triangulation, for instance),
I am not sure whether this is desired behavior or not.
In my case, I probably do not need the full power of this function.
All I want to do is to "copy" the solution values on a surface of the
volume mesh
to a surface mesh, and to associate a DoFHandler object to the surface mesh
that allows me to do further postprocessing.
So I do not care about the boundary and manifold id as well
as the return type, however, my volume mesh may contain hanging nodes.
Best regards,
Simon
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#include <deal.II/grid/tria.h>
#include <deal.II/grid/grid_generator.h>
#include <deal.II/grid/grid_out.h>
#include <deal.II/grid/grid_tools.h>
#include <deal.II/base/geometry_info.h>
#include <set>
using namespace dealii;
int main()
{
Triangulation<3> tria, triaTmp;
dealii::Point<3> center;
double radius = 2.5;
unsigned int boundaryID = 2;
GridGenerator::hyper_cube_with_cylindrical_hole(triaTmp,
radius,
7.5,
2.0,
1,
false);
triaTmp.refine_global(2);
// symmetry in global Z
std::set<typename dealii::Triangulation<3>::active_cell_iterator> cellsToRemove;
for (const auto &cell : triaTmp.active_cell_iterators())
if ( cell->center()[2] > 1.0)
cellsToRemove.insert(cell);
dealii::GridGenerator::create_triangulation_with_removed_cells(triaTmp,
cellsToRemove,
tria);
// one local refinement along hole
for (const auto &cell : tria.active_cell_iterators())
for (unsigned int f = 0; f < dealii::GeometryInfo<3>::faces_per_cell; ++f)
{
dealii::Point<3> faceCenter(cell->face(f)->center());
faceCenter[2] = 0.0;
if ((std::abs(center.distance(faceCenter)) < radius))
cell->set_refine_flag();
}
tria.execute_coarsening_and_refinement();
// set boundary ID for surface mesh
for (const auto &cell : tria.active_cell_iterators())
for (unsigned int f = 0; f < dealii::GeometryInfo<3>::faces_per_cell; ++f)
if(std::abs(cell->face(f)->center()[2]) < 1e-5 && cell->face(f)->at_boundary())
cell->face(f)->set_boundary_id(boundaryID);
// extract surface mesh
dealii::Triangulation<2, 3> tria2d;
dealii::GridGenerator::extract_boundary_mesh<dealii::Triangulation, 3, 3>(
tria,
tria2d,
std::set<dealii::types::boundary_id>{boundaryID});
// output the volume mesh
std::ofstream file("tria.vtk");
dealii::GridOut gridOut;
dealii::GridOutFlags::Vtk vtkFlags(true, true, true, false);
gridOut.set_flags(vtkFlags);
gridOut.write_vtk(tria, file);
// and the surface mesh
std::ofstream file2d("tria2d.vtk");
gridOut.write_vtk(tria2d, file2d);
return 0;
}
