CAD shape to tetrahedral FEA mesh

Drive a CAD shape through gmsh to obtain a tetrahedral mesh suitable for finite-element analysis, then bring the volumetric result back into PyVista as an pyvista.UnstructuredGrid.

This imports a real STEP part, the NIST AM Bench 2022 LPBF bridge specimen (public domain, https://doi.org/10.18434/mds2-2607), directly into gmsh via gmsh.model.occ.importShapes, the canonical way to move from CAD to FEA, and meshes the volume tetrahedrally.

import gmsh
import pandas as pd
import pyvista as pv

import pyvista_cad
from pyvista_cad.examples import downloads

Import the real STEP into gmsh’s OCC kernel and mesh the volume.

gmsh.initialize()
try:
    gmsh.model.add('part_fea')
    gmsh.model.occ.importShapes(downloads.step_part_path())
    gmsh.model.occ.synchronize()

    gmsh.option.setNumber('Mesh.MeshSizeMax', 2.0)
    gmsh.option.setNumber('Mesh.MeshSizeMin', 0.5)
    gmsh.model.mesh.generate(3)
    grid = pyvista_cad.from_gmsh('part_fea')
finally:
    gmsh.finalize()

# gmsh returns a mixed grid (vertex, line, triangle, tet). For a
# volumetric FEA mesh we only keep VTK_TETRA (cell type 10).
VTK_TETRA = 10
grid = grid.extract_cells(grid.celltypes == VTK_TETRA)
grid

UnstructuredGrid (0x7f6fa8111120)
  N Cells:    6470
  N Points:   2041
  X Bounds:   0.000e+00, 7.500e+01
  Y Bounds:   -2.446e-13, 5.000e+00
  Z Bounds:   0.000e+00, 1.225e+01
  N Arrays:   3

UnstructuredGrid 2,041 points 6,470 cells 377 KiB

Bounds⧉X [0.000e+00, 7.500e+01]Y [-2.446e-13, 5.000e+00]Z [0.000e+00, 1.225e+01]

• Point Data: (1)
  • vtkOriginalPointIds⧉
    scalar
    int64
    [0.000e+00, 2.040e+03]
• Cell Data: (1)
  • vtkOriginalCellIds⧉
    scalar
    int64
    [4.456e+03, 1.092e+04]
• Field Data: (1)
  • cad.source_format⧉
    (1,)
    <U4

Quality check: a healthy tet mesh has no zero-volume elements.

vols = grid.compute_cell_sizes(length=False, area=False, volume=True)['Volume']

pd.DataFrame(
    {
        'metric': ['min', 'mean', 'max'],
        'tet_volume': [vols.min(), vols.mean(), vols.max()],
    }
)

	metric	tet_volume
0	min	0.005826
1	mean	0.551671
2	max	3.264683

Slice through the part to expose the tet interior.

bnds = grid.bounds
clip = grid.clip(normal='x', crinkle=True)
clip['Z'] = clip.points[:, 2]

pl = pv.Plotter()
pl.add_mesh(grid, color='lightgray', opacity=0.15)
pl.add_mesh(clip, scalars='Z', cmap='inferno', show_edges=True, edge_color='black')
pl.show()

Static Scene

Interactive Scene