026-G08 HEX20 CalculiX Rescue¶
Decision boundary¶
This document records a targeted correction to the external verification
deck. It does not change QF Solver numerical behavior and does not close or
promote 026-G08.
Root cause¶
The C3D20 element continuation line generated by
calculix_buckling_025.py started with an empty comma field. CalculiX accepted
the process invocation but stopped before producing a buckling factor. The
same node mapping and model passed the existing HEX20 static correlation,
which isolated the issue to the buckling deck writer.
The fix writes the remaining node numbers directly on the continuation line
and is covered by tests/unit/test_calculix_buckling_025.py. No formulation,
geometric stiffness, eigenproblem or QF Solver buckling implementation was
changed.
Controlled evidence¶
The machine-readable evidence is
qualification/0_2_6/g08_hex20_calculix_rescue_evidence.json.
| Mesh | QF factor | CalculiX factor | Relative difference | Replays |
|---|---|---|---|---|
| 1 HEX20 cell | 12.50453659 | 12.71666 | 1.696% | 2 |
| 2 HEX20 cells | 10.98539335 | 11.21546 | 2.094% | 2 |
The existing 10% correlation screen was declared before execution and was
reused unchanged. Both levels pass that bounded numerical comparison, and
both replays reproduce the CalculiX factor within 1e-12 absolute difference.
Mode comparison¶
CalculiX first-mode vectors were read from the final FRD displacement block and compared with QF's first mode. The arbitrary eigenvector sign was aligned before reporting the cosine and MAC:
| Mesh | Raw cosine | Sign-aligned cosine | MAC |
|---|---|---|---|
| 1 HEX20 cell | -0.935479009 | 0.935479009 | 0.875120975 |
| 2 HEX20 cells | -0.890656829 | 0.890656829 | 0.793269586 |
The G08 contract does not define an external MAC acceptance threshold for this case, so these values are diagnostic evidence, not an invented PASS criterion.
Scope and limitations¶
C3D20is compared with the same QF HEX20 mesh factory, connectivity mapping, material and nodal dead-load pattern.- The study covers the first linearized tangent-instability factor and first mode only.
- It is numerical external correlation, not physical validation.
- The historical G08 Owner decision remains
PASS_WITH_LIMITATIONS. - HEX20 mesh sensitivity remains bounded evidence; no universal high-order convergence claim is made.
- No independent high-order analytical oracle or comparable Code_Aster route is added.
- No post-buckling or multi-mode qualification is claimed.