Feature Curved meshes

Feature - Curved meshes

t8code has the functionality to read in a mesh file along with the geometry file used to generate the mesh. With this parallel read in, we can generate curved adaptive meshes, as we call them. The curved adaptive meshes then are refined along the original geometry. This is shown in the following figure.

Requirements

To use this feature, we have to fulfill some requirements:

1. t8code has to be linked to OpenCASCADE. This is done via the configure option --with-occ.
2. The used mesh has to be written in the Gmsh's .msh 4.X format. Moreover, the parametric export option from Gmsh has to be enabled.
3. The geometry file has to be written in OpenCASCADE's .brep format.
4. The mesh has to be hex-only.

Generating a geometry

Generally, we can use every Software, which supports the .brep file format: FreeCAD, Gmsh, TiGL (all based on OpenCASCADE) to name a few. But we can also use OpenCASCADE itself.

Note: If you are using Gmsh for the generation of geometries, make sure to export the geometry into a .brep file and import it again before meshing. Gmsh has an internal geometry indexing system based on the order of geometry generation. In the resulting .brep file, the geometries have different indices than in Gmsh itself. This can result in different .msh files in which the mesh nodes are attributed to the wrong geometries. By reloading the .brep file into Gmsh, Gmsh adapts the indexing of the .brep file.

Henceforth, we are going to generate a geometry and mesh with Gmsh. For this, we use the scripting language .geo from Gmsh. If we take a look at the t8_features_curved_meshes_generate_cmesh.geo file in the tutorials directory, we can see how the geometry and mesh are created.
After the two-dimensional definition of the NACA geometry, it is extruded and meshed hex-only. Note, that the .brep file is reloaded before the meshing, as discussed before.