# Optimization Engine

Core optimization engine for Atomizer structural optimization projects.

## Overview

The optimization engine provides NX Nastran integration, result extraction, and optimization orchestration. Originally developed for the SAT3 mirror project, now generalized for multiple projects including Hydrotech Beam.

## NX Integration (`nx/`)

### Supported NX Versions

| Version | Status | Notes |
|---------|--------|-------|
| NX 2412 | ⚠️ Legacy | Original development version |
| **DesigncenterNX 2512** | ✅ Current | Siemens rebranded NX to "DesigncenterNX". Install path: `C:\Program Files\Siemens\DesigncenterNX2512` |

> **Important:** Siemens rebranded NX to "DesigncenterNX" starting with version 2512. The install directory, executable paths, and search paths all use the new name. Solver configuration must specify `2512` and include `DesigncenterNX` in search paths.

### Key Files

| File | Purpose |
|------|---------|
| `solver.py` | NX solver interface — manages NX session, expression updates, solve execution |
| `solve_simulation.py` | NX journal script — runs inside NXOpen Python, handles simple + assembly workflows |
| `solve_simulation_simple.py` | Simplified journal for single-part (simple) workflow |
| `updater.py` | Expression updater — writes `.exp` files, handles unit types |
| `export_expressions.py` | Export expressions from NX model |
| `import_expressions.py` | Import expressions into NX model |
| `session_manager.py` | NX session lifecycle management |
| `model_cleanup.py` | Model cleanup utilities |
| `mesh_converter.py` | Mesh format conversion |

### Path Resolution — CRITICAL on Windows

**`Path.absolute()` on Windows does NOT resolve `..` components.** Use `Path.resolve()` everywhere.

```python
# WRONG — NX cannot follow ".." in paths
path = Path("../../models/Beam_sim1.sim").absolute()
# → C:\...\studies\01_doe_landscape\..\..\models\Beam_sim1.sim  ← BROKEN

# CORRECT — fully resolved path
path = Path("../../models/Beam_sim1.sim").resolve()
# → C:\...\projects\hydrotech-beam\models\Beam_sim1.sim  ← WORKS
```

This applies to ALL paths passed to NX journals, including:
- `.sim` file path
- `.exp` file path
- Model directory path
- Output file paths

### NX File References — In-Place Solving Required

NX `.sim` files store **absolute internal references** to `.fem` and `.prt` files. Copying model files to different directories breaks these references (`Parts.Open` returns `None`).

**Solution:** Always solve on master model files in-place. Use backup/restore for isolation between optimization trials:

1. Backup master model files before trial
2. Write expressions, rebuild, solve in original location
3. Archive outputs (OP2, F06) to trial-specific folder
4. Restore master from backup

### Expression Units

When writing `.exp` files for NX:
- Length design variables: unit = `MilliMeter`
- Integer expressions (e.g., `hole_count`): unit = `Constant`
- **Critical:** Using wrong unit silently corrupts the model

### Workflow Types

**Simple workflow** (single-part, e.g., Hydrotech Beam):
```
Beam.prt → Beam_fem1_i.prt → Beam_fem1.fem → Beam_sim1.sim
```

**Assembly FEM workflow** (multi-part, e.g., SAT3 mirror):
```
Multiple .prt → .afm → .sim (node merge, label conflicts)
```

The journal auto-detects workflow type by checking for `.afm` files.

## Result Extraction

### pyNastran Compatibility

pyNastran warns "nx version 2512 not supported" but **reads OP2 files correctly**. Safe to ignore the warning.

**Unit note:** pyNastran returns stress in kPa for NX models using kg-mm-s unit system. Divide by 1000 for MPa.

### Mass Extraction

Mass is extracted via NX expression `p173` (or project-specific expression). The journal writes the value to a temp file (`_temp_mass.txt`) after solve, which Python reads.

## Dependencies

- Python 3.10+
- pyNastran (OP2 parsing)
- NXOpen Python API (on Windows solver node)
- Optuna (optimization orchestration)
- scipy, numpy, pandas

## Projects Using This Engine

| Project | Status | NX Version | Workflow |
|---------|--------|------------|----------|
| Hydrotech Beam | Active (DOE Phase 1) | DesigncenterNX 2512 | Simple |
| SAT3 Mirror | Legacy reference | NX 2412 | Assembly FEM |

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*Last updated: 2026-02-11*