freecad-automation-parametric-hull-workflow

name	freecad-automation-parametric-hull-workflow
description	Sub-skill of freecad-automation: Parametric hull generation workflow — HullProfile definition, NURBS surface creation, STEP export, and manifold validation.
version	2.0.0
category	engineering
type	reference
scripts_exempt	true

Parametric Hull Workflow

Overview

Generate hull geometry from naval architecture parameters using the HullProfile → FreeCADHullGenerator → ManifoldChecker pipeline.

Pipeline Steps

1. Define HullProfile — stations with (z, y) waterline offsets
2. Generate NURBS surface — FreeCADHullGenerator interpolates stations
3. Validate geometry — ManifoldChecker verifies watertight + no self-intersection
4. Export STEP — solid body for downstream FEM or CAD use (requires FreeCAD)

Code Example

from digitalmodel.hydrodynamics.hull_library.profile_schema import (
    HullProfile, HullStation, HullType,
)
from digitalmodel.visualization.design_tools.freecad_hull import FreeCADHullGenerator
from digitalmodel.visualization.design_tools.manifold_check import ManifoldChecker

# 1. Define hull
stations = [
    HullStation(x_position=x, waterline_offsets=[(0, y), (10, y)])
    for x, y in [(0, 0), (25, 8), (50, 10), (75, 8), (100, 0)]
]
profile = HullProfile(
    name="example", hull_type=HullType.SHIP,
    stations=stations, length_bp=100, beam=20, draft=8, depth=10,
    source="example",
)

# 2. Generate surface
gen = FreeCADHullGenerator(profile)
surface = gen.generate_nurbs_surface()
# surface["surface_type"] = "freecad" or "scipy"

# 3. Validate
checker = ManifoldChecker(surface["surface_points"])
result = checker.run_all_checks()
assert result["pass"]  # watertight + no self-intersection + consistent normals

# 4. Export (FreeCAD only)
gen.export_step(Path("hull.step"))

Key Classes

Class	Module	Purpose
HullProfile	hydrodynamics.hull_library.profile_schema	Hull definition with stations
HullStation	same	Single cross-section (z, y) offsets
FreeCADHullGenerator	visualization.design_tools.freecad_hull	NURBS surface + STEP export
ManifoldChecker	visualization.design_tools.manifold_check	Geometry validation

Conventions

• Keel-up: z=0 at keel, z=draft at waterline, z=depth at deck
• Half-breadth: y is distance from centreline (starboard side)
• Stations sorted by x_position (aft perpendicular = 0)
• Without FreeCAD: scipy-mode NURBS grid (numpy array) — no STEP export