OneCAD-Simulation/docs/architecture.md

Architecture

ModelCraft turns geometry into finite element models, writes them for the solvers engineers already use, and solves linear problems itself.

SolidCraft B-rep ──tessellate──▶ boundary surface ──▶ volume mesh ──▶ FE model ──▶ Abaqus .inp
 (solidcraft-kernel)           (welded, watertight,   tet (Delaunay)   materials,     Nastran .bdf
                                face-tagged)          hex (core goal)  sections,      LS-DYNA .k
                                                                       BCs, loads,  ──▶ own linear
                                                                       steps            solver

Crates and layers

cargo xtask layers enforces the table in xtask/src/layers.rs: a crate may depend only on crates in strictly lower layers.

Layer	Crate	Role	Status
L0	modelcraft-model	Solver-neutral FE model: nodes, elements by label; materials, sections, sets, BCs, loads and steps as they land. Knows no file format.	started
L1	modelcraft-geometry	The only door to SolidCraft: opens .solidcraft designs (rebuilt from their timeline, bodies with persistent face names), B-rep bodies, measures, tessellation into a face-tagged SurfaceMesh; face-tagged 3MF files read into the same type without the kernel (docs/formats/tagged-mesh.md). No SolidCraft type in its API.	started
L1	modelcraft-mesh	Surface preparation (weld, watertightness, feature edges), robust predicates, Delaunay tetrahedralization and refinement, Voronoi-based optimization, hex meshing, quality metrics.	started
L1	modelcraft-solver	Element formulations, assembly, sparse linear static and modal solution.	planned
L1	modelcraft-decks	Abaqus input, Nastran bulk data and LS-DYNA keyword readers and writers, to and from model.	planned
L1	modelcraft-render	Display data without a GPU dependency: the visible faces, element edges and nodes of a model, the orbit camera, a CPU rasterizer for headless snapshots; contour maps later.	started
L2	modelcraft-doc	The document: geometry, mesh, model, results, history.	planned
L3	modelcraft-io	.modelcraft files, result files.	planned
L4	modelcraft-engine	Commands (CommandSpec), Session::execute with rollback and the panic guard, scripts.	started
L5	modelcraft-ui-egui, modelcraft-mcp	Desktop UI (egui + wgpu viewport, model tree, commands, status bar) and control channel requests (docs/control-protocol.md); MCP server.	ui started
testkit	modelcraft-testkit	Test tooling, a dev-dependency only: the meshing test corpus (tests/corpus/*/recipe.json, analytic shapes) and its runner (cargo xtask corpus).	started
apps	modelcraft, modelcraft-cli, modelcraft-web	Desktop, command line, browser.	desktop, cli started

Rules beyond the layer order:

• Nothing below L5 uses egui, eframe, winit, wgpu or rfd.
• Only modelcraft-geometry uses solidcraft-*, pinned by rev in the workspace Cargo.toml. SolidCraft's [patch.crates-io] (its fixed truck crates) does not reach dependents, so the workspace repeats it from the same rev; bump both together. The same goes for SolidCraft's patched egui-wgpu (MSAA clamped to what the device supports, 1x on OpenGL adapters, so the desktop app's 4x never fails pipeline validation at start).
• Everything below the apps builds for wasm32-unknown-unknown.
• modelcraft-geometry's non-default scripts feature builds designs from SolidCraft command scripts (script_design, through solidcraft-engine) for the test corpus; the library opens designs without it.

Meshing pipeline

1. Boundary surface. SolidCraft tessellates each body; every triangle carries its B-rep face, so feature edges and face-based loads and BCs survive meshing. Faces of an opened design also carry SolidCraft's persistent names (F2:side:l4, from the feature and sketch curve that made them), so a load on a named face follows it when the design is edited and opened again. Bodies of components are placed in the world through their occurrences (one body per placement), as SolidCraft displays and exports them.
2. Surface preparation (modelcraft-mesh::surface, mesh.surface.check). Weld the tessellation's per-face vertex copies (at twice SolidCraft's linear tolerance), check the surface is closed, manifold, consistently and outwardly oriented (voids inwards) and free of self-intersections (exact triangle–triangle tests), and find feature edges (face boundaries, sharp dihedral angles). Defects come back located by triangle, vertex and position.
3. Tetrahedral meshing. Bowyer–Watson Delaunay on Shewchuk's adaptive predicates (symbolic perturbation for degeneracies), boundary recovery by the robust constrained Delaunay method of Diazzi et al. 2023 (implicit Steiner points on indirect predicates, gift-wrapping fallback), so every boundary triangle and its B-rep face tag survives. Then constrained Delaunay refinement to a size field, ODT smoothing interleaved as in Tournois et al. 2009, and the Klingner–Shewchuk 2007 improvement schedule against slivers.
4. Hexahedral meshing (the core). Octree/grid dual all-hex first, the one family that meshes any input validly (Livesu et al. 2021 dual schemes, Pitzalis et al. 2021 refinement, Gao et al. 2019 feature projection and padding, Garanzha et al. 2021 untangling). Then hex-dominant by tet recombination (Pellerin et al. 2018), then polycube (DualCube labelling) for blocky parts; frame-field/integer-grid-map methods stay research. Validity uses a certified trilinear Jacobian check (Marschner et al. 2020), not corner Jacobians alone.
5. Structured hex and face meshing. Faces get all-quad meshes on shared, prescribed edge nodes (modelcraft-mesh::quad): transfinite interpolation for four-sided faces (Gordon and Hall 1973), and for free faces a half-resolution constrained Delaunay triangulation, recombination (Lee and Lo 1994) and one uniform split that lands on the boundary nodes, then smoothing and untangling; every quad is checked with exact predicates. One SizeField trait (modelcraft-mesh::size) sets interior sizes and edge divisions, with even counts per loop. Mapped and swept hex build on these face meshes.
6. Quality. Scaled Jacobian, aspect ratio, dihedral angles; every generated mesh is checked for positive Jacobians and conserved volume before it reaches the model.

Commands

Every user-visible action is a CommandSpec in crates/engine/src/cmd/<area>.rs with a JSON form. Session::execute clones the model, runs the command under catch_unwind, and restores the model on an error or a panic; commands that changed the model are journalled, so the journal replays as a script.

Test corpus

Meshers are measured on our own parts (docs/adr/0001-libraries.md, test geometry). Each part is a SolidCraft command script in tests/corpus/<name>/recipe.json (the file solidcraft-cli run takes, plus a corpus object with its categories and, when it has one, its closed-form volume) with a one-line README.md; analytic shapes (sphere, torus, cylinder, thick-walled pipe, plate with a hole) are generated in code. modelcraft-testkit runs a recipe in SolidCraft's engine, saves the design and opens it through open_design, the path a person's design takes, so no geometry is stored. cargo xtask corpus (a release build of the testkit's corpus binary) builds every part, tessellates it and runs each stage of modelcraft_testkit::runner, writing docs/meshing/corpus.md. A mesher joins by implementing runner::Stage (its columns, and a run over the part's tessellated surfaces) and adding itself to runner::stages().