Using The 3D Tetrahedron Element

Pre-Processing

For pre-processing, you may use the meshing software 'Gmsh' (Geuzaine & Remacle, 2022):

• The Gmsh software can be found here.
• A sample Gmsh input file, which will create tetrahedral mesh within a hexahedral bounding box, can be found here.
  • The program will output a .msh file.
  • Note that this .msh file cannot be directly used as an input in MPM: it must be converted.
  • When converting, note that the Gmsh nodal numbering convention is to start at 1, while the MPM convention is to start at 0.
• A sample Gmsh output conversion program, compatible with tetrahedral mesh within a hexahedral bounding box and the input file mentioned above, can be found here.
  • The conversion program will take a Gmsh output file and convert it to MPM input files.
  • Note that the .msh must be saved to a .csv before using the converter.
  • The following MPM input files will be created:
    • Mesh file (eg. mesh.txt).
    • Entity file (eg. entity_sets.json). Creates a nodal set for each surface of the mesh bounding box.
    • Velocity constraints file (eg. velocity_constraints.txt). Requires inputs of the desired velocity per direction, and per surface of the bounding box.

References

• Geuzaine, C., & Remacle, J. F. (2022). Gmsh (4.9.5) [Computer software]. https://gmsh.info/

Limitations

• The 3D tetrahedron is currently not compatible with MPI.
• Some boundary conditions may not be compatible with the 3D tetrahedron. For details, please see this page.