freecad-automation-fem-chain-workflow

name	freecad-automation-fem-chain-workflow
description	Sub-skill of freecad-automation: CalculiX FEM analysis chain — geometry creation via gmsh, INP export, ccx solve, and result extraction.
version	2.0.0
category	engineering
type	reference
scripts_exempt	true

FEM Chain Workflow (CalculiX)

Overview

End-to-end structural FEM pipeline: gmsh geometry → INP file → CalculiX solve → stress/displacement extraction.

Pipeline Steps

1. Create geometry — gmsh OCC kernel (plate-with-hole, STEP import, etc.)
2. Define analysis — material, BCs, loads → INP file via INPWriter
3. Solve — CalculiX ccx subprocess
4. Extract results — parse .frd (nodal fields) and .dat (reactions)

Quick Start: Plate-with-Hole Validation

from digitalmodel.solvers.calculix.fem_chain import FEMChain

chain = FEMChain()
result = chain.run_plate_validation(sigma_applied=100.0)
print(f"Kt = {result['kt']:.3f}")  # ~3.0 within 5%

Custom Analysis

from pathlib import Path
from digitalmodel.solvers.calculix.fem_chain import FEMChain

chain = FEMChain(work_dir=Path("/tmp/my_fem"))

# 1. Create geometry (quarter-symmetry plate with hole)
stats = chain.create_plate_with_hole(
    plate_w=200.0, plate_h=200.0, hole_r=10.0,
    thickness=1.0, element_size=5.0,
)

# 2. Setup analysis
chain.setup_analysis(
    material={"name": "STEEL", "E": 210000.0, "nu": 0.3},
    loads=[{
        "type": "cload", "node_set": "LOAD",
        "dof": 1, "magnitude": 100.0, "direction": (1, 0, 0),
    }],
    boundary_conditions=[
        {"node_set": "SYM_X", "dof_start": 1, "dof_end": 1},
        {"node_set": "SYM_Y", "dof_start": 2, "dof_end": 2},
        {"node_set": "FIX_Z", "dof_start": 3, "dof_end": 3},
    ],
)

# 3. Solve
status = chain.solve()
assert status[]


results = chain.extract_results()
()
()

Key Classes

Class	Module	Purpose
FEMChain	solvers.calculix.fem_chain	End-to-end orchestrator
INPWriter	solvers.calculix.inp_writer	Mesh → INP file conversion
CalculiXResultParser	solvers.calculix.result_parser	.frd/.dat parsing
GMSHMeshGenerator	solvers.gmsh_meshing.mesh_generator	STEP import + meshing

Prerequisites

• gmsh Python package (pip install gmsh)
• ccx binary on PATH (CalculiX solver)
• Check availability: from digitalmodel.solvers.calculix.fem_chain import is_calculix_available

Node Sets (Plate-with-Hole)

Set	Description
SYM_X	Nodes on x=0 symmetry plane
SYM_Y	Nodes on y=0 symmetry plane
FIX_Z	Nodes on z=0 face (out-of-plane constraint)
LOAD	Nodes on far edge (x=W/2) for applied traction

Validated Results

• Plate-with-hole Kt within 5% of theoretical 3.0 (d/W < 0.3)
• Quarter-symmetry model with W/d > 5