Element types

CalculiX names its elements by a numeric code in the second field of each element record. This reader maps fourteen of them onto VTK cell types, which is every type CalculiX’s own frd.c writes plus the two experimental pyramids.

Each mesh below was solved by CalculiX from a one-element deck in tests/fixtures/generated/src.

from pathlib import Path

import pyvista as pv

import pyvista_frd

The table the reader works from.

for code, name in sorted(pyvista_frd.ELEMENT_TYPE_NAMES.items()):
    print(f'  {code:3d}  {name}')

 1  HE8
 2  PE6
 3  TE4
 4  HE20
 5  PE15
 6  TE10
 7  TR3
 8  TR6
 9  QU4
10  QU8
11  BE2
12  BE3
15  PY5
16  PY13

One solved fixture per type, drawn together. The FRD files here are genuine CalculiX output; the decks that produced them are this repository’s.

Twelve of the fourteen appear. CalculiX 2.22 answers C3D5 is an unknown element type and stops, so there is no solver-written pyramid to draw – the PY5 and PY13 fixtures this package is tested against are hand-written.

root = Path('../../tests/fixtures/generated').resolve()
files = sorted(root.glob('*.frd'))

columns = 4
rows = -(-len(files) // columns)
pl = pv.Plotter(shape=(rows, columns), window_size=(900, 200 * rows))
for index, path in enumerate(files):
    mesh = pyvista_frd.read(path)
    pl.subplot(index // columns, index % columns)
    pl.add_text(path.stem, font_size=8)
    pl.add_mesh(mesh, show_edges=True, color='#c4a484', line_width=2)
    pl.add_points(mesh.points, color='crimson', point_size=8, render_points_as_spheres=True)
pl.show()

An element the reader does not recognise, or one whose record holds the wrong number of nodes, is reported rather than silently dropped. pyvista.InvalidMeshWarning is raised at construction naming the line it was found on, and the rest of the file still reads.

The wedge is worth a note of its own. VTK changed the node order of a linear wedge at 9.7, so the correct connectivity depends on which VTK the cells are destined for. The Python layer reads that from the installed VTK; a C++ caller has to say which convention it wants, because there is nothing to detect it from.

print('VTK', pv.vtk_version_info)
mesh = pyvista_frd.read(root / 'wedge6.frd')
print('wedge6 cell type:', mesh.celltypes, '->', pv.CellType(mesh.celltypes[0]).name)

VTK (9, 6, 2)
wedge6 cell type: [13] -> WEDGE