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Mesh Refinement

Erase Elements

FEM

Description

The FEM MeshGroup command enables the user to create groups of Vertices, Edges, Surfaces and elements. It is useful in case of using FreeCAD as a pre-processor to export an organized and labeled mesh. The mesh is then usable by external solver codes, where mesh groups can be used more readily to set boundary conditions and attribute solver related properties. It is possible to use the FreeCAD mesh group object name or the label as the group name on export of the mesh. If the label is chosen, the user has to be mindful if special characters are used. If the mesh export format does not allow special character its fallback is to use the mesh group object name.

FEM MeshGroup therefore enables FreeCAD to be used with external solvers (or viewers such as ParaView) when they are not yet implemented with their own case-writing routine within FreeCAD.

Usage

1. To enable the command a Mesh From Shape by Gmsh must be provided first.
2. Select the Mesh object in the Tree View.
3. There are several ways to invoke the command:
   • Press the Mesh Group button.
   • Select the Mesh → Mesh Group option from the menu.
4. Select whether the group is named or labeled
   • If Name is selected, the name of the MeshGroup is used when exporting the mesh.
   • If Label is selected, the specified label name will be used when exporting the mesh.
5. Click the Add button and select the geometrical entity (solid, face, edge or vertex). More such objects can be added but they have to be of the same type. The mesh group will consist of underlying mesh entities. introduced in 1.1: To remove objects from the selection, press the Remove button.
6. Click the OK button.

   Result: You now should see a new FEMMeshGroup object under the FEMMeshGMSH object in your active analysis container.

7. Double-click on the FEMMeshGMSH parent object in your Model Tree and press Apply to force a mesh recalculation / relabeling.
8. Close the task.

Notes

• After the mesh has been created, you can change the label property using the Property View.
• After you change a property, you must reopen the Gmsh dialog again and click the Apply button (you can leave the dialog open while changing properties).
• You can create as many different mesh groups as needed.
• By default, mesh groups can only be exported to .med, .unv, .xdmf (without DataGroups Of Nodes) and YAML/JSON formats. To be able to export them to the .inp format, one needs to enable the Export group data option in INP export preferences.
  • Setting the Which mesh elements to export to Highest or FEM ensures that lower order elements not used for analysis (e.g. shells in the case of analysis with solids) won't be exported.
  • To export node sets to this format, the DataGroups Of Nodes property of the Gmsh mesh object must be set to true.
• To check if a group was properly exported, you can open the generated file in any text editor and search for the group's name.

Mesh Refinement

Erase Elements

FEM