OpenRadioss animation files (<run>A001, A002, …)

The animation files an OpenRadioss (or Radioss) run writes, one per output time: the model as it is at that time and the results the run was asked to animate (/ANIM in the engine deck). Each file is one state, so a run's files together are a transient sequence. The starter deck that defines the model is read by radioss.

Format name	radioss_anim
File names	a stem, then A and three or more digits (crashA001, crashA042); also recognised by content, the magic number 0x542C
Read / Write	✓ / —
Extra dependencies	—

Reading

import meshioplusplus

state = meshioplusplus.read("crashA010")                  # or meshioplusplus.radioss_anim.read(...)
for time, mesh in meshioplusplus.read_sequence("crashA*"):
    ...                                                    # every state, in time order

meshioplusplus convert 'crashA*' crash.vtkhdf              # the whole run as one time series

read takes no options. Both engines (the C++ core and the pure-Python reference) read the same meshes. The state's time is field_data["meshio:time"] and read_metadata(...).time_values, so a sequence over a run's files takes each file's own time rather than the number in its name.

The file

A big-endian binary file with the magic 0x542C: the time, three titles and ten flags, then

Section	When	Holds
2-D	always	the nodes (coordinates, nodal scalars and vectors) and the 4-node facets of shells, with element scalars and 2-D tensors
3-D	flag 3	8-node bricks with element scalars and tensors
1-D	flag 4	2-node elements (beams, springs, rigid-body links) with element scalars and force/moment sets
masses, ids	flags 1, 2	element and nodal masses; node and element ids
hierarchy	flag 5	each part's subset, material and property; subset, material and property names
time history	flag 6	the nodes and elements saved for time history (skipped)
SPH	flag 8	particles with scalars and tensors

The layout is the one OpenRadioss's anim_to_vtk converter reads (MIT); no code is copied. Older layouts (another magic number) are refused.

The mesh

• Points are the state's coordinates (the deformed shape), as 64-bit floats.
• Cells, in the file's family order: 1-D elements as line, facets as quad (or triangle when a node repeats), bricks as hexahedron or the tetra, pyramid or wedge a brick with repeated nodes stands for (as the starter reader collapses them), SPH particles as vertex. One block per type, in order of first appearance.
• Point data: every nodal scalar and vector under its name (Velocity, Displacement, Contact Forces…), radioss:node_id and radioss:mass when the file has them.
• Cell data: every element scalar under its name, the union over the families, NaN on the cells of a family that does not have it (a 2-D and a 3-D Plastic Strain are one array). Tensors have six components xx yy zz xy yz zx; a 2-D tensor's zz, yz and zx are NaN. A 1-D force/moment set has nine components, NaN off the 1-D cells. radioss:part, and radioss:alive (1 while the element exists, 0 once it is deleted), always; radioss:element_id, radioss:mass, radioss:material, radioss:property when every family has them.
• Regions: each part is a cell region named by its title (tag = part id). A 1-D and a 2-D part may share an id.

anim_to_vtk writes a facet's alive flag, 0xFF, as its "erosion status" 0 and the bricks' 1 as 1; meshio++ reads every non-zero flag as alive. anim_to_vtk also places a 3-D tensor's fifth and sixth values at xz and yz, where its own reading code documents them as yz and zx; meshio++ keeps the file's order.

Validation

The fixtures under tests/python/meshes/radioss_anim/ are written by tools/gen_radioss_anim_fixtures.py (two states of a small model with every section), and anim_to_vtk/ holds what anim_to_vtk makes of them; the tests compare every array with it. Outside the repository both engines were also run on three animation files OpenRadioss wrote (Kitware's openradioss-to-vtkhdf test data, bricks, shells, beams and SPH): they agree with each other and with anim_to_vtk to its printed precision.