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gassmoeller merged 1 commit into from
Feb 3, 2026
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Improve mesh diffusion code documentation #6843

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99 changes: 67 additions & 32 deletions source/mesh_deformation/diffusion.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -132,35 +132,62 @@ namespace aspect
const std::set<types::boundary_id> tangential_velocity_boundary_indicators =
this->get_boundary_velocity_manager().get_tangential_boundary_velocity_indicators();

// The list of all tangential mesh deformation boundary indicators.
std::set<types::boundary_id> tmp_tangential_boundaries, tmp2_tangential_boundaries, all_tangential_boundaries;
std::set_union(tangential_velocity_boundary_indicators.begin(),tangential_velocity_boundary_indicators.end(),
additional_tangential_mesh_boundary_indicators.begin(),additional_tangential_mesh_boundary_indicators.end(),
std::inserter(tmp_tangential_boundaries, tmp_tangential_boundaries.end()));
std::set_union(tmp_tangential_boundaries.begin(),tmp_tangential_boundaries.end(),
periodic_boundary_indicators.begin(),periodic_boundary_indicators.end(),
std::inserter(tmp2_tangential_boundaries, tmp2_tangential_boundaries.end()));
// Tangential Stokes velocity boundaries can also be mesh deformation boundaries,
// so correct for that.
std::set_difference(tmp2_tangential_boundaries.begin(),tmp2_tangential_boundaries.end(),
boundary_ids.begin(),boundary_ids.end(),
std::inserter(all_tangential_boundaries, all_tangential_boundaries.end()));

// The list of mesh deformation boundary indicators of boundaries that are allowed to move either
// tangentially or in all directions.
std::set<types::boundary_id> all_deformable_boundaries;
std::set_union(all_tangential_boundaries.begin(),all_tangential_boundaries.end(),
boundary_ids.begin(),boundary_ids.end(),
std::inserter(all_deformable_boundaries, all_deformable_boundaries.end()));

// The list of mesh deformation boundary indicators of boundaries that are not allowed to move.
std::set<types::boundary_id> all_fixed_boundaries;
std::set_difference(all_boundaries.begin(),all_boundaries.end(),
all_deformable_boundaries.begin(),all_deformable_boundaries.end(),
std::inserter(all_fixed_boundaries, all_fixed_boundaries.end()));

// Make the no flux boundary constraints
for (const types::boundary_id &boundary_id : all_fixed_boundaries)
// Here we start to construct the list of all
// tangential mesh deformation boundary indicators.
std::set<types::boundary_id> tangential_stokes_and_mesh_boundaries;
std::set<types::boundary_id> tangential_stokes_and_mesh_and_periodic_boundaries;
std::set<types::boundary_id> all_tangential_mesh_deformation_boundaries;

// tangential_stokes_and_mesh_boundaries contains both the tangential Stokes velocity boundaries
// and the additional tangential mesh boundaries.
std::set_union(tangential_velocity_boundary_indicators.begin(),
tangential_velocity_boundary_indicators.end(),
additional_tangential_mesh_boundary_indicators.begin(),
additional_tangential_mesh_boundary_indicators.end(),
std::inserter(tangential_stokes_and_mesh_boundaries,
tangential_stokes_and_mesh_boundaries.end()));

// tangential_stokes_and_mesh_and_periodic_boundaries contains also the periodic boundaries.
std::set_union(tangential_stokes_and_mesh_boundaries.begin(),
tangential_stokes_and_mesh_boundaries.end(),
periodic_boundary_indicators.begin(),
periodic_boundary_indicators.end(),
std::inserter(tangential_stokes_and_mesh_and_periodic_boundaries,
tangential_stokes_and_mesh_and_periodic_boundaries.end()));

// The set of tangential_velocity_boundary_indicators might already contain the
// diffusion boundaries (i.e. those boundaries contained in the set boundary_ids).
// These are not boundaries on which the mesh deforms tangentially,
// so we here create a new set containing only tangential_mesh_deformation_boundaries
std::set_difference(tangential_stokes_and_mesh_and_periodic_boundaries.begin(),
tangential_stokes_and_mesh_and_periodic_boundaries.end(),
boundary_ids.begin(),
boundary_ids.end(),
std::inserter(all_tangential_mesh_deformation_boundaries,
all_tangential_mesh_deformation_boundaries.end()));

// We now add the diffusion boundaries to the list of tangential mesh deformation boundaries
// to create a set of all boundaries on which the mesh is allowed to deform in some way.
std::set<types::boundary_id> all_deformable_mesh_boundaries;
std::set_union(all_tangential_mesh_deformation_boundaries.begin(),
all_tangential_mesh_deformation_boundaries.end(),
boundary_ids.begin(),
boundary_ids.end(),
std::inserter(all_deformable_mesh_boundaries,
all_deformable_mesh_boundaries.end()));

// Finally, we get the set of all fixed mesh boundaries by
// subtracting the deformable mesh boundaries from all boundaries.
std::set<types::boundary_id> all_fixed_mesh_boundaries;
std::set_difference(all_boundaries.begin(),
all_boundaries.end(),
all_deformable_mesh_boundaries.begin(),
all_deformable_mesh_boundaries.end(),
std::inserter(all_fixed_mesh_boundaries,
all_fixed_mesh_boundaries.end()));

// Make the no flux boundary constraints for boundaries on which the mesh is fixed
for (const types::boundary_id &boundary_id : all_fixed_mesh_boundaries)
{
VectorTools::interpolate_boundary_values (this->get_mapping(),
mesh_deformation_dof_handler,
Expand All @@ -169,12 +196,20 @@ namespace aspect
matrix_constraints);
}

// Make the no normal flux boundary constraints
// Make the no normal flux boundary constraints for boundaries on which the mesh is
// allowed to move tangentially. We can use the manifold information to
// compute the normal vector because these boundaries do not move normal to themselves.
VectorTools::compute_no_normal_flux_constraints (mesh_deformation_dof_handler,
/* first_vector_component= */
0,
all_tangential_boundaries,
matrix_constraints, this->get_mapping());
all_tangential_mesh_deformation_boundaries,
matrix_constraints,
this->get_mapping(),
/* use_manifold_for_normal= */
true);

// Note that we do not apply any constraints on the mesh of the diffusing boundaries
// listed in boundary_ids. Their displacement is governed by the diffusion equation.

matrix_constraints.close();

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