Files

Anto01 723b71e60b fix: Complete stress extraction fix for NX Nastran OP2 files

THREE critical fixes applied:

1. API Access Pattern
   - Support dotted attribute names (e.g., 'stress.chexa_stress')
   - Compatible with newer pyNastran versions (NX 2412.5)
   - Fallback to older API formats for compatibility

2. Correct Von Mises Index
   - Solid elements (CHEXA, CTETRA, CPENTA): index 9
   - Shell elements (CQUAD4, CTRIA3): last column
   - Data structure: [oxx, oyy, ozz, txy, tyz, txz, o1, o2, o3, von_mises]

3. Units Conversion (CRITICAL)
   - NX Nastran outputs stress in kPa, not MPa
   - Apply conversion: kPa / 1000 = MPa
   - Example: 113094.73 kPa -> 113.09 MPa

Test Results:
- Before: 0.00 MPa (FAIL)
- After:  113.09 MPa at element 83 (SUCCESS)

Files modified:
- optimization_engine/result_extractors/op2_extractor_example.py

Test files added:
- examples/test_stress_direct.py
- examples/test_stress_fix.py
- examples/debug_op2_stress.py
- STRESS_EXTRACTION_FIXED.md
- TESTING_STRESS_FIX.md

2025-11-15 11:18:03 -05:00

2.5 KiB

Raw Blame History

Testing the Stress Extraction Fix

Issue Fixed

Previously, stress extraction was returning 0.0 MPa instead of the expected ~122.91 MPa.

Root Cause: For solid elements (CHEXA, CTETRA, CPENTA), von Mises stress is at index 9, not the last column.

Fix Applied: Modified op2_extractor_example.py to check element type and use correct index.

How to Test

1. Activate your test environment

conda activate test_env

2. Run the verification script

python examples/test_stress_fix.py

Expected Output

============================================================
STRESS EXTRACTION FIX VERIFICATION
============================================================

--- Displacement (baseline test) ---
Max displacement: 0.315xxx mm
Node ID: xxx
OK Displacement extractor working

--- Stress (FIXED - should show ~122.91 MPa) ---
Max von Mises: 122.91 MPa
Element ID: 79
Element type: chexa

SUCCESS! Stress extraction fixed!
Expected: ~122.91 MPa
Got:      122.91 MPa
============================================================

Alternative: Test All Extractors

python optimization_engine/result_extractors/extractors.py examples/bracket/bracket_sim1-solution_1.op2

If Successful, Commit the Fix

git add optimization_engine/result_extractors/op2_extractor_example.py
git commit -m "fix: Correct von Mises stress extraction for solid elements (CHEXA)

- Use index 9 for solid elements (CHEXA, CTETRA, CPENTA)
- Keep last column for shell elements (CQUAD4, CTRIA3)
- Fixes stress extraction returning 0.0 instead of actual values (122.91 MPa)"

git push origin main

Technical Details

pyNastran OP2 Data Structure for Solid Elements

Shape: [itime, nnodes, 10]

The 10 values are:

[oxx, oyy, ozz, txy, tyz, txz, o1, o2, o3, von_mises]
 0    1    2    3    4    5    6   7   8   9

Von Mises is at index 9

Code Change

# BEFORE (WRONG):
stresses = stress_data.data[0, :, -1]  # Last column - WRONG for CHEXA!

# AFTER (CORRECT):
if table_name in ['chexa_stress', 'ctetra_stress', 'cpenta_stress']:
    # Solid elements: von Mises at index 9
    stresses = stress_data.data[0, :, 9]
else:
    # Shell elements: von Mises at last column
    stresses = stress_data.data[0, :, -1]

Files Modified

optimization_engine/result_extractors/op2_extractor_example.py - Lines 103-112

2.5 KiB Raw Blame History