Structures · ANSA Python API · 2024–25

Scripting hex meshes in ANSA

A camshaft comes in as STEP. The script maps the shells, fills hex, caps NASTRAN aspect at 2.3, and writes three CDB decks. One object. Three sizes. A log you can actually read.

Aerospace Structures (AS244AI) EL · with Akula Uday Kiran, Movva Sai Lalitha Devi, and Tejas L. Guide: Dr. Benjamin Rohit.

98.9%hexahedra
5.97 s3 mm batch
0.83–1.0Jacobian
3 / 5 / 7mm sizes

Clicking through ANSA for every CAD revision is how you lose an afternoon. This wraps the Python API so the same camshaft (two lobes + shaft) gets a mapped block mesh, a volume hex fill, and a .cdb at 3, 5, and 7 mm in one run.

The class is MeshProcessor. It pulls PSHELL 1/2 (lobe and shaft faces: 18 + 4) and PSOLID 3/4/5 (lob1, lob2, shaft1), maps the shells, remeshes the volumes with quality criterion 3 / target 2 / max aspect 2.3, logs every step, exports.

CAD model of the two-lobe camshaft — The part: two cam lobes on a shaft. Imported as STEP (`CAM_SHAFT.STEP` / `Assem1.STEP`).

Batch times from the log

One script, three sizes, NASTRAN deck, ANSYS CDB out. Logged 1 July 2025:

Size	3.0 mm	5.0 mm	7.0 mm
Mesh + export	5.97 s	2.89 s	2.48 s
CDB size	18.85 MB	4.89 MB	1.90 MB

That is the point of the API: minutes of GUI work become a few seconds you can re-run when the STEP changes.

Element counts (Assem1 cam)

Screenshots from the three mapped volumes:

	3 mm	5 mm	7 mm
Hexas	62,309	14,612	4,920
Pentas	1,762	744	432
Solid total	64,071	15,356	5,352
Hex share	97.3%	95.2%	91.9%
Shell quads / trias	16,428 / 228	6,016 / 144	3,168 / 104

A later CAM_SHAFT deck used for the quality overlay sits at 29,020 hex / 29,352 solids = 98.9% hexahedra, 9,630 quads and 24 trias on the skin. That is the number the report quotes as “>98% hex.”

Mapped hex mesh at 3 mm on the camshaft — 3 mm. 64,071 solids, 62,309 hex.

Mapped hex mesh at 5 mm — 5 mm. 15,356 solids, 14,612 hex.

Mapped hex mesh at 7 mm — 7 mm. 5,352 solids, 4,920 hex. Coarser, still structured.

Quality envelopes

ANSA QGRAPH, NASTRAN aspect, FLUENT skew, ANSA Jacobian. From the report tables:

Check	Size 5 (shell / vol)	Size 7	Bar
Aspect ratio	1.02–1.65 / 1.03–1.85	1.02–1.65	ideal < 3
Jacobian	0.825–1.00 / 0.977–1.00	0.825–1.00	> 0.7
Skewness	0.003–0.477	0.003–0.477	< 0.5
Warpage	0.003–0.430	0.003–0.430	< 0.5

Size 3 solids Jacobian 0.835–1.00 (shells down to 0.717 near high curvature). No inverted elements. The conclusion in the report is the one on the homepage card: aspect under 2, Jacobian 0.83–1.0, skewness under 0.5, hex dominant.

Jacobian plot for 3 mm mesh — Jacobian, 3 mm. Solids 0.835–1.0; most of the volume is dark blue (~1).

Aspect ratio plot for 7 mm mesh — Aspect ratio, 7 mm. Solids 1.02–1.65. Red only on a few lobe-face elements.

Jacobian plot for 7 mm mesh — Jacobian, 7 mm. Same 0.83–1.0 envelope as the finer decks.

ANSA quality criteria overlay on the camshaft mesh — Quality overlay on CAM_SHAFT: 29,020 hex, 332 penta, Qcheck 1.23. Skewness criterion on.

How the script is built

Object-oriented on purpose so the same object can run three sizes. File I/O, entity collection, and meshing are split (FileManager, EntityManager, MeshManager) in the UML we drew for the report. The live script still talks to ansa.base / ansa.mesh / constants.NASTRAN.

UML of ANSAMeshingWorkflow and managers — Workflow: load STEP → shells → map blocks → solids → remesh volumes → export. Suggested split vs a single `main()`.

Logging is file-based with timestamps so a failed size does not erase the successful ones. Export is ANSYS CDB so the deck can go straight into a structural run.

This is an EL report for Aerospace Structures, not a production mesher for every CAD family. The geometry is a camshaft. The win is: same Python object, three densities, quality that actually hits the NASTRAN/ANSA bars, and a log you can read when it does not.

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