forked from 1b-agent/fieldcraft-upstream
jyvikoandClaude Opus 5.5
94fdbf0fca
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo
81 lines
5.2 KiB
Markdown
81 lines
5.2 KiB
Markdown
---
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name: fieldcraft-meshing
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description: Agentic hex meshing (AHM) in FieldCraft — read the part, plan partitions, and build a structured all-hex (or hex-dominant) mesh an analyst would accept. Use before any mesh.* command on a part that matters, and whenever a mesh comes back with fans, slivers or a low scaled Jacobian.
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---
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# Agentic hex meshing (AHM)
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You mesh like an experienced analyst: you look first, plan the blocks, and only then call a mesher.
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A mesh is judged by its worst elements, not its count. A fast mesh with fans, slivers or collapsed
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corners is a failed mesh, even when every element is "valid".
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## 1. Look before you mesh (always)
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Before the first mesh command:
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1. `inspect_model` / `geometry.bodies`: bodies, volumes, bounding boxes, faces, holes, fillets.
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2. Take screenshots from the principal views and an iso view. Name, in words, what the part is.
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3. **Symmetry.** Test it geometrically (mirror the bounding box and the key faces). If the part (and
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the loads you will apply) are symmetric, mesh one half or quarter only and mirror the mesh
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(`mesh.mirror`). Never mesh a symmetric part whole.
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4. **Primary vs secondary features.**
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- Primary: what carries the physics and sets the topology — the main body, walls, bosses,
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the load path, thin directions, the direction a section is swept along.
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- Secondary: small fillets, chamfers, logos, small holes far from the region of interest.
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Start the block structure from the primary features. Secondary features are fitted into it
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(or defeatured), never allowed to drive it.
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5. **Where to split.** Before meshing, list the cuts: planes or curved surfaces that turn every
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region into a six-sided block or a sweepable prism. Say why each cut is there.
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## 2. Plan the blocks (the rules)
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- **Never make sharp corners.** No element angle near 0° or 180°. Where a block would have a
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corner angle far from 90°, cut differently or add a block (an O-grid) so every corner in the mesh
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is close to 90°.
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- **Partitions must never create skewed, tapered or high-aspect-ratio hex.** Check every cell you
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create: if it is a wedge, a sliver or a long thin strip relative to the element size, the cut is
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wrong. Move or remove it.
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- **Butterfly (O-grid) around curved parts.** Around a hole, a boss, a cylinder or a fillet, cut a
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square block around it and an O-grid ring between the square and the curve, so element lines run
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radially and the corners of the square sit at 45° on the curve. Never let a mesh fan into a hole
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or pinch at a tangency.
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- **Split and merge to make it square.** When a region is far from a square (an L, a long strip
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with a bump), split it into pieces and merge pieces again so each final cell is closer to a cube.
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Aim for cells with aspect ratio near 1 at the target size.
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- **Curved splits are allowed.** A cut does not have to be a plane: use a cylindrical or offset
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surface (a ring around a boss, an offset of a fillet) when a plane would create slivers.
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- **Never cut along an existing face** (a plane coincident with a face within tolerance leaves
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micrometre slivers, #384) and never through the axis of a small hole (degenerate tessellation at the
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hole edge). Offset the cut to just outside the feature instead.
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- **Keep cuts consistent across touching bodies** so their meshes can match, or tie them
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deliberately (`interaction.tie`; linear faces only today).
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## 3. Mesh
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- Mesh each cell with the structured method that fits (`mesh.hex.generate` extrude/sweep/revolve/
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mapped; `mesh.cells` for partitioned parts; `mesh.hex.blocks` when every cell is a block).
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- Use edge seeds (`mesh.seed.edge`) so counts match across shared edges and so there are enough
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elements through thin walls (at least 2–3 through a wall for bending, 1 for pure conduction only).
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- Tet (`tet10` preferred for stress) only for cells that are not worth blocking, and only where
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they are far from the region of interest.
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## 4. Verify (every time, before solving)
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1. `mesh.quality`: all valid; scaled Jacobian min ≥ 0.3 (≥ 0.5 in the region of interest);
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edge ratio max ≤ 10; no element below these is acceptable without a stated reason.
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**Isolated spikes** (a few bad elements in an otherwise good mesh) are fixed last, with
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`mesh.node.relax {"around_element": <worst>}` (or `center` + `radius`): nodes there relax, surface
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nodes sliding on their faces, nothing inverting. It is a final touch, never a substitute for a
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better block plan: many bad elements mean the cuts are wrong (§2). Pass `"reapply": true` (or
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run `mesh.node.relax.apply {field}`) so the relaxation follows a later remesh.
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2. Look at it: screenshots of each body and a section. Fans, pinches, wedges, slivers → back to §2.
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3. Volume: `mesh.quality` volume equals the geometry volume (a mismatch means orphan or missing
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cells, #385).
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4. `mesh.check.duplicates`: no cracks or free edges inside a body.
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5. After solving, refine once and compare the quantity of interest (convergence).
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## 5. Report
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State: symmetry used, primary features, every cut and why, method per cell, element counts,
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quality numbers, and anything you defeatured. If the plan failed, say which rule failed and the
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next cut you will try — don't silently fall back to a worse mesh.
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