"""Feed STEP-derived leaf stiffness into a reduced-order impact contact.""" import argparse import hashlib import json import math import subprocess import sys from pathlib import Path ROOT = Path(__file__).resolve().parent def measure(step: Path, setup: dict) -> dict: import cadquery as cq import gmsh from OCP.BRepGProp import BRepGProp from OCP.GProp import GProp_GProps shape = cq.importers.importStep(str(step)).val() if shape.ShapeType() != "Solid" or not shape.isValid() or len(shape.Solids()) != 1: raise ValueError(f"Expected one valid solid: {step}") props = GProp_GProps() BRepGProp.VolumeProperties_s(shape.wrapped, props) if props.Mass() <= 0: raise ValueError("Leaf volume must be positive") pad0 = cq.Solid.makeBox(10, 20, 10, cq.Vector(0, -10, -5)) pad1 = cq.Solid.makeBox(10, 20, 10, cq.Vector(90, -10, -5)) slabs = [cq.Solid.makeBox(10, 20, 20, cq.Vector(x, -10, -10)) for x in (0, 90)] envelope = cq.Solid.makeBox(100, 20, 14, cq.Vector(0, -10, -7)) pads = (pad0, pad1) pad_overlap = sum(pad.intersect(shape).Volume() for pad in pads) slab_overlap = sum(slab.intersect(shape).Volume() for slab in slabs) result = { "step_sha256": hashlib.sha256(step.read_bytes()).hexdigest(), "volume_mm3": props.Mass(), "mass_kg": props.Mass() * setup["material_density_kg_m3"] * 1e-9, "end_pad_missing_mm3": max(0.0, sum(p.Volume() for p in pads) - pad_overlap), "end_pad_excess_mm3": max(0.0, slab_overlap - pad_overlap), "envelope_excess_mm3": max(0.0, shape.Volume() - shape.intersect(envelope).Volume()), "meshes": {}, } gmsh.initialize() try: gmsh.option.setNumber("General.Terminal", 0) gmsh.model.add("leaf") gmsh.model.occ.importShapes(str(step)) gmsh.model.occ.synchronize() if len(gmsh.model.getEntities(3)) != 1: raise ValueError("STEP import must produce one volume") for size in setup["mesh_sizes_mm"]: gmsh.model.mesh.clear() gmsh.option.setNumber("Mesh.CharacteristicLengthMin", size) gmsh.option.setNumber("Mesh.CharacteristicLengthMax", size) gmsh.option.setNumber("Mesh.Algorithm3D", 1) gmsh.model.mesh.generate(3) tags, coordinates, _ = gmsh.model.mesh.getNodes() nodes = {str(int(tag)): [coordinates[3 * i + axis] / 1000 for axis in range(3)] for i, tag in enumerate(tags)} types, _, element_nodes = gmsh.model.mesh.getElements(3) tets = [] for kind, connectivity in zip(types, element_nodes): if kind != 4: raise ValueError(f"Expected first-order tetrahedra, got {kind}") tets.extend([[int(value) for value in connectivity[i:i + 4]] for i in range(0, len(connectivity), 4)]) if not nodes or not tets: raise ValueError("Gmsh produced an empty mesh") result["meshes"][str(size)] = {"nodes": nodes, "tets": tets} finally: gmsh.finalize() return result def dynamics(meshes: dict, setup: dict) -> dict: import pychrono as ch import pychrono.fea as fea results = {} for size, data in meshes.items(): system = ch.ChSystemSMC() system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) system.SetSolver(ch.ChSolverSparseLU()) mesh = fea.ChMesh() material = fea.ChContinuumElastic() material.SetYoungModulus(setup["young_modulus_Pa"]) material.SetPoissonRatio(setup["poisson_ratio"]) material.SetDensity(setup["material_density_kg_m3"]) center_region = [(key, point) for key, point in data["nodes"].items() if 0.045 <= point[0] <= 0.055] if not center_region: raise ValueError("Mesh is missing the center load patch") top = max(point[2] for _, point in center_region) load_ids = [key for key, point in center_region if abs(point[2] - top) < 1e-8] fixed_ids = [key for key, point in data["nodes"].items() if abs(point[0]) < 1e-8 or abs(point[0] - 0.1) < 1e-8] if len(load_ids) < 4 or len(fixed_ids) < 8: raise ValueError("Mesh is missing a mount or center load face") nodes = {} for key, point in data["nodes"].items(): node = fea.ChNodeFEAxyz(ch.ChVector3d(*point)) if key in fixed_ids: node.SetFixed(True) if key in load_ids: node.SetForce(ch.ChVector3d( 0, 0, setup["fea_probe_force_N"] / len(load_ids))) mesh.AddNode(node) nodes[int(key)] = node for a, b, c, d in data["tets"]: element = fea.ChElementTetraCorot_4() element.SetNodes(nodes[a], nodes[b], nodes[c], nodes[d]) element.SetMaterial(material) mesh.AddElement(element) system.Add(mesh) system.DoStaticLinear() deflections = [data["nodes"][key][2] - nodes[int(key)].GetPos().z for key in load_ids] mean_deflection = sum(deflections) / len(deflections) if not math.isfinite(mean_deflection) or mean_deflection <= 0: raise ValueError("Invalid leaf deflection") stiffness = abs(setup["fea_probe_force_N"]) / mean_deflection impact = simulate_impact(stiffness, setup) results[size] = { "center_probe_deflection_m": mean_deflection, "effective_spring_stiffness_N_m": stiffness, "impact": impact, "node_count": len(nodes), "tetrahedron_count": len(data["tets"]), "clamped_node_count": len(fixed_ids), "loaded_node_count": len(load_ids), } return results def simulate_impact(stiffness: float, setup: dict) -> dict: import pychrono as ch ch.ChCollisionModel.SetDefaultSuggestedEnvelope(1e-6) ch.ChCollisionModel.SetDefaultSuggestedMargin(1e-6) system = ch.ChSystemSMC() system.UseMaterialProperties(False) system.SetCollisionSystemType(ch.ChCollisionSystem.Type_BULLET) system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) material = ch.ChContactMaterialSMC() material.SetFriction(0) contact_stiffness = stiffness / math.sqrt(setup["reference_compression_m"]) material.SetKn(contact_stiffness) material.SetGn(2 * setup["contact_damping_ratio"] * math.sqrt(contact_stiffness * setup["impactor_mass_kg"])) floor = ch.ChBodyEasyBox(0.3, 0.01, 0.3, 1000, False, True, material) floor.SetPos(ch.ChVector3d(0, -0.01, 0)) floor.SetFixed(True) system.Add(floor) radius = setup["impactor_radius_m"] mass = setup["impactor_mass_kg"] ball = ch.ChBodyEasySphere( radius, mass / (4 * math.pi * radius ** 3 / 3), False, True, material) ball.SetPos(ch.ChVector3d(0, setup["impactor_initial_center_y_m"], 0)) ball.SetLinVel(ch.ChVector3d(0, -setup["impactor_initial_speed_m_s"], 0)) system.Add(ball) dt = setup["impact_time_step_s"] steps = round(setup["impact_duration_s"] / dt) if dt <= 0 or abs(steps * dt - setup["impact_duration_s"]) > 1e-12: raise ValueError("Invalid impact duration or time step") peak_force = 0.0 stroke = 0.0 contact_steps = 0 rebound_speed = None for _ in range(steps): system.DoStepDynamics(dt) force = ball.GetContactForce().Length() peak_force = max(peak_force, force) stroke = max(stroke, radius - ball.GetPos().y) if force > 1e-7: contact_steps += 1 if (contact_steps and rebound_speed is None and ball.GetPos().y > radius + 0.0001 and ball.GetLinVel().y > 0): rebound_speed = ball.GetLinVel().y if not all(math.isfinite(x) for x in (peak_force, stroke)): raise ValueError("Nonfinite impact response") return {"peak_force_N": peak_force, "maximum_stroke_m": stroke, "rebound_speed_m_s": rebound_speed, "contact_steps": contact_steps} def invoke(python: str, phase: str, payload: dict) -> dict: run = subprocess.run([python, str(Path(__file__).resolve()), "--phase", phase], input=json.dumps(payload), text=True, capture_output=True) if run.returncode: raise RuntimeError(f"{phase} failed:\n{run.stderr[-1600:]}") return json.loads(run.stdout) def main() -> None: parser = argparse.ArgumentParser() parser.add_argument("--cad-python", default=sys.executable) parser.add_argument("--physics-python", default=sys.executable) parser.add_argument("--phase", choices=("measure", "dynamics")) args = parser.parse_args() if args.phase: payload = json.load(sys.stdin) result = (measure(Path(payload["step"]), payload["setup"]) if args.phase == "measure" else dynamics(payload["meshes"], payload["setup"])) print(json.dumps(result)) return setup = json.loads((ROOT / "setup.json").read_text()) results = {} for name in ("before", "after"): properties = invoke(args.cad_python, "measure", { "step": str(ROOT / f"{name}.step"), "setup": setup, }) meshes = properties.pop("meshes") results[name] = { "step_properties": properties, "simulation_result": invoke(args.physics_python, "dynamics", { "meshes": meshes, "setup": setup, }), } before = results["before"] after = results["after"] bp, ap = before["step_properties"], after["step_properties"] bs, gs = before["simulation_result"], after["simulation_result"] sizes = [str(size) for size in setup["mesh_sizes_mm"]] baseline = [bs[size]["impact"]["peak_force_N"] for size in sizes] candidate = [gs[size]["impact"]["peak_force_N"] for size in sizes] reductions = [1 - a / b for a, b in zip(candidate, baseline)] bk = [bs[size]["effective_spring_stiffness_N_m"] for size in sizes] gk = [gs[size]["effective_spring_stiffness_N_m"] for size in sizes] checks = { "baseline_impact_measurable": min(baseline) >= setup["minimum_baseline_peak_force_N"], "peak_force_reduced_both_meshes": min(reductions) >= setup["required_relative_peak_force_reduction"], "stroke_and_rebound_limited": all( gs[size]["impact"]["maximum_stroke_m"] <= setup["maximum_impact_stroke_m"] and gs[size]["impact"]["rebound_speed_m_s"] is not None and setup["minimum_rebound_speed_m_s"] <= gs[size]["impact"]["rebound_speed_m_s"] <= setup["maximum_rebound_speed_m_s"] for size in sizes), "contact_observed": all( bs[size]["impact"]["contact_steps"] > 0 and gs[size]["impact"]["contact_steps"] > 0 for size in sizes), "mesh_response_stable": all( abs(values[1] / values[0] - 1) <= setup["maximum_relative_mesh_stiffness_change"] for values in (bk, gk)) and max(reductions) - min(reductions) <= setup["maximum_mesh_improvement_spread"], "mass_fixed": abs(ap["mass_kg"] / bp["mass_kg"] - 1) <= setup["maximum_relative_mass_change"], "end_pads_fixed": ap["end_pad_missing_mm3"] <= setup["maximum_end_pad_missing_mm3"] and ap["end_pad_excess_mm3"] <= setup["maximum_end_pad_excess_mm3"], "envelope_fixed": ap["envelope_excess_mm3"] <= setup["maximum_envelope_excess_mm3"], } after["comparison_to_before"] = { "relative_peak_force_reductions": reductions, "checks": checks, "passed": all(checks.values()), } for name, result in results.items(): (ROOT / f"{name}.results.json").write_text(json.dumps(result, indent=2) + "\n") print(f"Impact peak force: {baseline} -> {candidate} N") print(f"Task passed: {all(checks.values())}") if not all(checks.values()): raise SystemExit(1) if __name__ == "__main__": main()