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feat(isogrid): FEA stress field → 2D heatmap → adaptive density feedback

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Closes the optimization loop: OP2 results → density field refinement.

**extract_stress_field_2d.py (new)**
- Reads OP2 (3D solid or 2D shell elements) + BDF via pyNastran
- Projects element centroids to 2D sandbox coords using geometry transform
- Averages stress through thickness (for solid 3D meshes)
- Normalises by sigma_yield to [0..1]
- save/load helpers (NPZ) for trial persistence

**stress_feedback.py (new)**
- StressFeedbackField: converts 2D stress scatter → smooth density modifier
- Gaussian blur (configurable radius, default 40mm) prevents oscillations
- RBF interpolator (thin-plate spline) for fast pointwise evaluation
- evaluate(x, y) returns S_stress ∈ [0..1]
- from_field() and from_npz() constructors

**density_field.py (modified)**
- evaluate_density() now accepts optional stress_field= argument
- Adaptive formula: η = η₀ + α·I + β·E + γ·S_stress
- gamma_stress param controls feedback gain (0.0 = pure parametric)
- Fully backward compatible (no stress_field = original behaviour)

Usage:
    field = extract_stress_field_2d(op2, bdf, geometry["transform"], sigma_yield=276.0)
    feedback = StressFeedbackField.from_field(field, blur_radius_mm=40.0)
    eta = evaluate_density(x, y, geometry, params, stress_field=feedback)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Anto01
2026-02-18 11:13:28 -05:00
parent a9c40368d3
commit 6658de02f4
3 changed files with 623 additions and 10 deletions
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357
optimization_engine/extractors/extract_stress_field_2d.py Normal file
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"""
Extract a 2D von Mises stress field from OP2 results, projected onto the sandbox plane.
Works for both:
- 3D solid meshes (CHEXA, CTETRA, CPENTA): averages stress through thickness
- 2D shell meshes (CQUAD4, CTRIA3): directly maps to plane
The returned field is in the sandbox 2D coordinate system (u, v) matching the
geometry_sandbox_N.json coordinate space — ready to feed directly into the
Brain density field as S_stress(x, y).
Usage:
from optimization_engine.extractors.extract_stress_field_2d import extract_stress_field_2d
field = extract_stress_field_2d(
op2_file="path/to/results.op2",
bdf_file="path/to/model.bdf",
transform=geometry["transform"], # from geometry_sandbox_N.json
)
# field["nodes_2d"] → (N, 2) array of [u, v] sandbox coords
# field["stress"] → (N,) array of von Mises stress in MPa
# field["max_stress"] → peak stress in MPa
Unit Note: NX Nastran in kg-mm-s outputs stress in kPa → divided by 1000 → MPa.
"""
from __future__ import annotations
from pathlib import Path
from typing import Any, Dict, Optional
import numpy as np
from pyNastran.bdf.bdf import BDF
from pyNastran.op2.op2 import OP2
# ---------------------------------------------------------------------------
# 3D → 2D coordinate projection
# ---------------------------------------------------------------------------
def _project_to_2d(
xyz: np.ndarray,
transform: Dict[str, Any],
) -> np.ndarray:
"""
Project 3D points onto the sandbox plane using the geometry transform.
The transform (from geometry_sandbox_N.json) defines:
- origin: 3D origin of the sandbox plane
- x_axis: direction of sandbox U axis in 3D
- y_axis: direction of sandbox V axis in 3D
- normal: plate normal (thickness direction — discarded)
Inverse of import_profile.py's unproject_point_to_3d().
Args:
xyz: (N, 3) array of 3D points
transform: dict with 'origin', 'x_axis', 'y_axis', 'normal'
Returns:
(N, 2) array of [u, v] sandbox coordinates
"""
origin = np.array(transform["origin"])
x_axis = np.array(transform["x_axis"])
y_axis = np.array(transform["y_axis"])
# Translate to origin
rel = xyz - origin # (N, 3)
# Project onto sandbox axes
u = rel @ x_axis # dot product with x_axis
v = rel @ y_axis # dot product with y_axis
return np.column_stack([u, v])
# ---------------------------------------------------------------------------
# Element centroid extraction from BDF
# ---------------------------------------------------------------------------
def _get_element_centroids(bdf: BDF) -> Dict[int, np.ndarray]:
"""
Compute centroid for every element in the BDF model.
Returns:
{element_id: centroid_xyz (3,)}
"""
node_xyz = {nid: np.array(node.xyz) for nid, node in bdf.nodes.items()}
centroids = {}
for eid, elem in bdf.elements.items():
try:
nids = elem.node_ids
pts = np.array([node_xyz[n] for n in nids if n in node_xyz])
if len(pts) > 0:
centroids[eid] = pts.mean(axis=0)
except Exception:
pass
return centroids
# ---------------------------------------------------------------------------
# Von Mises stress extraction from OP2
# ---------------------------------------------------------------------------
def _get_all_von_mises(
model: OP2,
subcase: int,
convert_to_mpa: bool,
) -> Dict[int, float]:
"""
Extract von Mises stress for every element across all solid + shell types.
Returns:
{element_id: von_mises_stress}
"""
SOLID_TYPES = ["ctetra", "chexa", "cpenta", "cpyram"]
SHELL_TYPES = ["cquad4", "ctria3"]
ALL_TYPES = SOLID_TYPES + SHELL_TYPES
if not hasattr(model, "op2_results") or not hasattr(model.op2_results, "stress"):
raise ValueError("No stress results found in OP2 file")
stress_container = model.op2_results.stress
elem_stress: Dict[int, float] = {}
for elem_type in ALL_TYPES:
attr = f"{elem_type}_stress"
if not hasattr(stress_container, attr):
continue
stress_dict = getattr(stress_container, attr)
if not stress_dict:
continue
available = list(stress_dict.keys())
if not available:
continue
sc = subcase if subcase in available else available[0]
stress = stress_dict[sc]
if not stress.is_von_mises:
continue
ncols = stress.data.shape[2]
# Von Mises column: solid=9, shell=7
vm_col = 9 if ncols >= 10 else 7 if ncols == 8 else ncols - 1
itime = 0
von_mises = stress.data[itime, :, vm_col] # (n_elements,)
# element_node: list of (eid, node_id) pairs — may repeat for each node
for i, (eid, _node) in enumerate(stress.element_node):
vm = float(von_mises[i])
# Keep max stress if element appears multiple times (e.g. corner nodes)
if eid not in elem_stress or vm > elem_stress[eid]:
elem_stress[eid] = vm
if not elem_stress:
raise ValueError("No von Mises stress data found in OP2 file")
if convert_to_mpa:
elem_stress = {eid: v / 1000.0 for eid, v in elem_stress.items()}
return elem_stress
# ---------------------------------------------------------------------------
# Main extractor
# ---------------------------------------------------------------------------
def extract_stress_field_2d(
op2_file: Path,
bdf_file: Path,
transform: Dict[str, Any],
subcase: int = 1,
convert_to_mpa: bool = True,
sigma_yield: Optional[float] = None,
) -> Dict[str, Any]:
"""
Extract a 2D von Mises stress field projected onto the sandbox plane.
For 3D solid meshes: element centroids are projected to 2D, then stress
values at the same (u, v) location are averaged through thickness.
For 2D shell meshes: centroids are directly in-plane, no averaging needed.
Args:
op2_file: Path to NX Nastran OP2 results file
bdf_file: Path to BDF model file (for geometry/node positions)
transform: Sandbox plane transform dict from geometry_sandbox_N.json
Keys: 'origin', 'x_axis', 'y_axis', 'normal'
subcase: Subcase ID to extract (default: 1)
convert_to_mpa: Divide by 1000 to convert NX kPa → MPa (default: True)
sigma_yield: Optional yield strength in MPa. If provided, adds a
'stress_normalized' field (0..1 scale) for density feedback.
Returns:
dict with:
'nodes_2d': (N, 2) ndarray — [u, v] in sandbox 2D coords (mm)
'stress': (N,) ndarray — von Mises stress (MPa or kPa)
'max_stress': float — peak stress value
'mean_stress': float — mean stress value
'percentile_95': float — 95th percentile (robust peak)
'units': str — 'MPa' or 'kPa'
'n_elements': int — number of elements with stress data
'stress_normalized': (N,) ndarray — stress / sigma_yield (if provided)
'sigma_yield': float — yield strength used (if provided)
"""
op2_file = Path(op2_file)
bdf_file = Path(bdf_file)
# --- Load BDF geometry ---
bdf = BDF(debug=False)
bdf.read_bdf(str(bdf_file), xref=True)
centroids_3d = _get_element_centroids(bdf) # {eid: xyz}
# --- Load OP2 stress ---
model = OP2(debug=False, log=None)
model.read_op2(str(op2_file))
elem_stress = _get_all_von_mises(model, subcase, convert_to_mpa)
# --- Match elements: keep only those with both centroid and stress ---
common_ids = sorted(set(centroids_3d.keys()) & set(elem_stress.keys()))
if not common_ids:
raise ValueError(
f"No matching elements between BDF ({len(centroids_3d)} elements) "
f"and OP2 ({len(elem_stress)} elements). Check that they are from the same model."
)
xyz_arr = np.array([centroids_3d[eid] for eid in common_ids]) # (N, 3)
stress_arr = np.array([elem_stress[eid] for eid in common_ids]) # (N,)
# --- Project 3D centroids → 2D sandbox coords ---
nodes_2d = _project_to_2d(xyz_arr, transform) # (N, 2)
# --- For 3D solid meshes: average through-thickness duplicates ---
# Elements at the same (u, v) xy-location but different thickness positions
# get averaged to produce a single 2D stress value per location.
uv_rounded = np.round(nodes_2d, decimals=1) # group within 0.1mm
uv_tuples = [tuple(r) for r in uv_rounded]
unique_uvs: Dict[tuple, list] = {}
for i, uv in enumerate(uv_tuples):
unique_uvs.setdefault(uv, []).append(stress_arr[i])
uv_final = np.array([list(k) for k in unique_uvs.keys()])
stress_final = np.array([np.mean(v) for v in unique_uvs.values()])
n_raw = len(stress_arr)
n_averaged = len(stress_final)
n_layers = round(n_raw / n_averaged) if n_averaged > 0 else 1
result = {
"nodes_2d": uv_final,
"stress": stress_final,
"max_stress": float(np.max(stress_final)),
"mean_stress": float(np.mean(stress_final)),
"percentile_95": float(np.percentile(stress_final, 95)),
"units": "MPa" if convert_to_mpa else "kPa",
"n_elements": n_averaged,
"n_raw_elements": n_raw,
"n_thickness_layers": n_layers,
}
if sigma_yield is not None:
result["stress_normalized"] = stress_final / sigma_yield
result["sigma_yield"] = sigma_yield
return result
# ---------------------------------------------------------------------------
# Save / load helpers
# ---------------------------------------------------------------------------
def save_stress_field(field: Dict[str, Any], output_path: Path) -> None:
"""
Save extracted stress field to an NPZ file for fast reloading.
Usage:
save_stress_field(field, "trial_0001/stress_field_2d.npz")
"""
output_path = Path(output_path)
output_path.parent.mkdir(parents=True, exist_ok=True)
np.savez(
str(output_path),
nodes_2d=field["nodes_2d"],
stress=field["stress"],
stress_normalized=field.get("stress_normalized", np.array([])),
max_stress=field["max_stress"],
mean_stress=field["mean_stress"],
percentile_95=field["percentile_95"],
sigma_yield=field.get("sigma_yield", 0.0),
n_elements=field["n_elements"],
)
def load_stress_field(npz_path: Path) -> Dict[str, Any]:
"""
Load a previously saved stress field.
Usage:
field = load_stress_field("trial_0001/stress_field_2d.npz")
"""
data = np.load(str(npz_path), allow_pickle=False)
field = {
"nodes_2d": data["nodes_2d"],
"stress": data["stress"],
"max_stress": float(data["max_stress"]),
"mean_stress": float(data["mean_stress"]),
"percentile_95": float(data["percentile_95"]),
"n_elements": int(data["n_elements"]),
}
if data["sigma_yield"] > 0:
field["stress_normalized"] = data["stress_normalized"]
field["sigma_yield"] = float(data["sigma_yield"])
return field
# ---------------------------------------------------------------------------
# CLI
# ---------------------------------------------------------------------------
if __name__ == "__main__":
import sys
import json
if len(sys.argv) < 4:
print("Usage: python extract_stress_field_2d.py <op2> <bdf> <geometry_sandbox.json> [sigma_yield]")
sys.exit(1)
op2 = Path(sys.argv[1])
bdf = Path(sys.argv[2])
geom = Path(sys.argv[3])
sy = float(sys.argv[4]) if len(sys.argv) > 4 else None
with open(geom) as f:
geometry = json.load(f)
field = extract_stress_field_2d(op2, bdf, geometry["transform"], sigma_yield=sy)
print(f"Extracted {field['n_elements']} elements "
f"(from {field['n_raw_elements']} raw, {field['n_thickness_layers']} thickness layers)")
print(f"Max stress: {field['max_stress']:.1f} {field['units']}")
print(f"Mean stress: {field['mean_stress']:.1f} {field['units']}")
print(f"95th pct: {field['percentile_95']:.1f} {field['units']}")
out = op2.with_suffix(".stress_field_2d.npz")
save_stress_field(field, out)
print(f"Saved to: {out}")

36
tools/adaptive-isogrid/src/brain/density_field.py
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@@ -1,13 +1,22 @@
"""
Density field η(x) — maps every point on the plate to [0, 1].
η(x) = clamp(0, 1, η₀ + α·I(x) + β·E(x))
Base formula:
η(x) = clamp(0, 1, η₀ + α·I(x) + β·E(x))
With stress feedback (adaptive mode):
η(x) = clamp(0, 1, η₀ + α·I(x) + β·E(x) + γ·S_stress(x))
Where:
I(x) = Σᵢ wᵢ · exp(-(dᵢ(x)/Rᵢ)^p) — hole influence
E(x) = exp(-(d_edge(x)/R_edge)^p_edge) — edge reinforcement
E(x) = exp(-(d_edge(x)/R_edge)^p) — edge reinforcement
S_stress(x) = normalised stress from previous FEA trial [0..1]
γ (gamma_stress) = stress feedback gain (Atomizer design variable)
Pass a StressFeedbackField instance as stress_field= to activate adaptive mode.
"""
from typing import Optional
import numpy as np
from shapely.geometry import Polygon, Point, LinearRing
@@ -70,11 +79,23 @@ def compute_edge_influence(x, y, outer_boundary, params):
return np.exp(-(d_edge / R_edge)**p)
def evaluate_density(x, y, geometry, params):
def evaluate_density(x, y, geometry, params, stress_field=None):
"""
Evaluate the combined density field η(x, y).
η(x) = clamp(0, 1, η₀ + α·I(x) + β·E(x))
Base: η = η₀ + α·I(x) + β·E(x)
Adaptive: η = η₀ + α·I(x) + β·E(x) + γ·S_stress(x)
Parameters
----------
x, y : float
geometry : dict
params : dict
Must contain eta_0, alpha, beta.
Optional: gamma_stress (default 0.0) for stress feedback gain.
stress_field : StressFeedbackField, optional
Pass a StressFeedbackField instance to enable adaptive mode.
If None, pure parametric mode (γ=0).
Returns
-------
@@ -88,6 +109,13 @@ def evaluate_density(x, y, geometry, params):
E = compute_edge_influence(x, y, geometry['outer_boundary'], params)
eta = eta_0 + alpha * I + beta * E
if stress_field is not None:
gamma = params.get('gamma_stress', 0.0)
if gamma > 0.0:
S = stress_field.evaluate(x, y)
eta += gamma * S
return np.clip(eta, 0.0, 1.0)

228
tools/adaptive-isogrid/src/brain/stress_feedback.py Normal file
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"""
Stress Feedback Field — converts a 2D FEA stress field into a density modifier.
Extends the base density field:
η(x,y) = η₀ + α·I_hole + β·E_edge + γ·S_stress(x,y)
Where S_stress(x,y) is built from the previous trial's OP2 results:
- High stress → S_stress → 1 → more ribs → stress drops
- Low stress → S_stress → 0 → coarser mesh → lighter
Gaussian smoothing prevents local oscillations between iterations.
Usage:
from optimization_engine.extractors.extract_stress_field_2d import (
extract_stress_field_2d, load_stress_field
)
from src.brain.stress_feedback import StressFeedbackField
# After FEA extraction:
field = extract_stress_field_2d(op2, bdf, geometry["transform"], sigma_yield=276.0)
feedback = StressFeedbackField.from_field(field, blur_radius_mm=40.0)
# Inside density evaluation:
s = feedback.evaluate(x, y) # → [0..1]
"""
from __future__ import annotations
from typing import Any, Dict, Optional
import numpy as np
from scipy.interpolate import RBFInterpolator
from scipy.ndimage import gaussian_filter
class StressFeedbackField:
"""
Converts a 2D nodal stress field into a smooth density modifier S_stress(x,y).
The field is built by:
1. Normalising stress values to [0..1] via sigma_yield (or auto-max)
2. Applying Gaussian smoothing to suppress oscillations
3. Building a thin-plate-spline RBF interpolator for fast evaluation
"""
def __init__(
self,
nodes_2d: np.ndarray,
stress_norm: np.ndarray,
):
"""
Args:
nodes_2d: (N, 2) array of [u, v] sandbox coordinates (mm)
stress_norm: (N,) normalised stress values in [0..1]
"""
self._nodes = nodes_2d
self._values = np.clip(stress_norm, 0.0, 1.0)
# Build RBF interpolator (thin-plate spline, with light smoothing)
self._rbf = RBFInterpolator(
nodes_2d,
self._values,
kernel="thin_plate_spline",
smoothing=0.5, # regularisation — avoids overfitting noisy data
degree=1,
)
# ------------------------------------------------------------------
# Construction helpers
# ------------------------------------------------------------------
@classmethod
def from_field(
cls,
field: Dict[str, Any],
blur_radius_mm: float = 40.0,
sigma_yield: Optional[float] = None,
) -> "StressFeedbackField":
"""
Build from the dict returned by extract_stress_field_2d().
Args:
field: Output of extract_stress_field_2d()
blur_radius_mm: Gaussian blur radius in mm. Controls how far the
stress influence spreads. Typical: 1–2× s_max.
Larger → smoother, more stable; smaller → sharper.
sigma_yield: Override yield strength for normalisation.
Falls back to field["sigma_yield"] or field["max_stress"].
"""
nodes_2d = field["nodes_2d"]
# --- Normalise ---
if "stress_normalized" in field:
stress_norm = field["stress_normalized"].copy()
else:
sy = sigma_yield or field.get("sigma_yield") or field["max_stress"]
stress_norm = field["stress"] / sy
# --- Gaussian smoothing on a temporary grid, then re-sample ---
stress_norm = cls._smooth(nodes_2d, stress_norm, blur_radius_mm)
return cls(nodes_2d, stress_norm)
@classmethod
def from_npz(
cls,
npz_path,
blur_radius_mm: float = 40.0,
) -> "StressFeedbackField":
"""
Load directly from a saved .npz file (output of save_stress_field()).
"""
from optimization_engine.extractors.extract_stress_field_2d import load_stress_field
field = load_stress_field(npz_path)
return cls.from_field(field, blur_radius_mm=blur_radius_mm)
# ------------------------------------------------------------------
# Smoothing
# ------------------------------------------------------------------
@staticmethod
def _smooth(
nodes_2d: np.ndarray,
values: np.ndarray,
blur_radius_mm: float,
grid_res_mm: float = 5.0,
) -> np.ndarray:
"""
Apply Gaussian blur by:
1. Rasterising the scatter data to a temporary grid
2. Applying scipy gaussian_filter
3. Re-sampling back to original node locations
This avoids oscillations between high- and low-stress neighbours.
"""
if blur_radius_mm <= 0:
return values
u, v = nodes_2d[:, 0], nodes_2d[:, 1]
u_min, u_max = u.min(), u.max()
v_min, v_max = v.min(), v.max()
# Build grid
nu = max(int((u_max - u_min) / grid_res_mm) + 2, 10)
nv = max(int((v_max - v_min) / grid_res_mm) + 2, 10)
grid_u = np.linspace(u_min, u_max, nu)
grid_v = np.linspace(v_min, v_max, nv)
GU, GV = np.meshgrid(grid_u, grid_v)
# Scatter → grid via nearest-index binning
u_idx = np.clip(
np.round((u - u_min) / (u_max - u_min + 1e-9) * (nu - 1)).astype(int),
0, nu - 1,
)
v_idx = np.clip(
np.round((v - v_min) / (v_max - v_min + 1e-9) * (nv - 1)).astype(int),
0, nv - 1,
)
grid_vals = np.zeros((nv, nu))
grid_cnt = np.zeros((nv, nu))
np.add.at(grid_vals, (v_idx, u_idx), values)
np.add.at(grid_cnt, (v_idx, u_idx), 1)
# Fill empty cells with nearest-neighbour before blurring
mask = grid_cnt > 0
grid_vals[mask] /= grid_cnt[mask]
# Fill holes via a quick nearest-value propagation
if not mask.all():
from scipy.ndimage import distance_transform_edt
_, nearest = distance_transform_edt(~mask, return_indices=True)
grid_vals[~mask] = grid_vals[nearest[0][~mask], nearest[1][~mask]]
# Gaussian blur (sigma in grid cells)
sigma_cells = blur_radius_mm / grid_res_mm
blurred = gaussian_filter(grid_vals, sigma=sigma_cells, mode="nearest")
# Re-sample at original node positions (bilinear via index)
from scipy.interpolate import RegularGridInterpolator
interp = RegularGridInterpolator(
(grid_v, grid_u), blurred,
method="linear",
bounds_error=False,
fill_value=None,
)
smoothed = interp(np.column_stack([v, u]))
return np.clip(smoothed, 0.0, 1.0)
# ------------------------------------------------------------------
# Evaluation
# ------------------------------------------------------------------
def evaluate(self, x: float, y: float) -> float:
"""
Return S_stress(x, y) ∈ [0..1] at a single 2D sandbox point.
High return value → high stress in this region → density field
will increase → more ribs will be placed here.
"""
pt = np.array([[x, y]])
val = float(self._rbf(pt)[0])
return float(np.clip(val, 0.0, 1.0))
def evaluate_batch(self, points_2d: np.ndarray) -> np.ndarray:
"""
Evaluate at many points at once (faster than calling evaluate() in a loop).
Args:
points_2d: (N, 2) array of [u, v] sandbox coordinates
Returns:
(N,) array of S_stress values in [0..1]
"""
vals = self._rbf(points_2d)
return np.clip(vals, 0.0, 1.0)
# ------------------------------------------------------------------
# Diagnostics
# ------------------------------------------------------------------
def summary(self) -> Dict[str, float]:
return {
"n_nodes": int(len(self._values)),
"min": float(self._values.min()),
"max": float(self._values.max()),
"mean": float(self._values.mean()),
"pct_above_50": float((self._values > 0.5).mean()),
}