# Study: 01_doe_landscape — Hydrotech Beam

> See [../../README.md](../../README.md) for project overview.

## Purpose

Map the design space of the Hydrotech sandwich I-beam to identify feasible regions, characterize variable sensitivities, and prepare data for Phase 2 (TPE optimization). This is Phase 1 of the two-phase strategy (DEC-HB-002).

## Quick Facts

| Item | Value |
|------|-------|
| **Objective** | Minimize mass (kg) |
| **Constraints** | Tip displacement ≤ 10 mm, Von Mises stress ≤ 130 MPa |
| **Design variables** | 4 (3 continuous + 1 integer) |
| **Algorithm** | Phase 1: LHS DoE (50 trials + 1 baseline) |
| **Total budget** | 51 evaluations |
| **Constraint handling** | Deb's feasibility rules (Optuna constraint interface) |
| **Status** | ✅ Pipeline operational — first results obtained 2026-02-11 |
| **Solver** | DesigncenterNX 2512 (NX Nastran SOL 101) |
| **Solve time** | ~12 s/trial (~10 min for full DOE) |
| **First results** | Displacement=17.93mm, Stress=111.9MPa |

## Design Variables (confirmed via NX binary introspection)

| ID | NX Expression | Range | Type | Baseline | Unit |
|----|--------------|-------|------|----------|------|
| DV1 | `beam_half_core_thickness` | 10–40 | Continuous | 25.162 | mm |
| DV2 | `beam_face_thickness` | 10–40 | Continuous | 21.504 | mm |
| DV3 | `holes_diameter` | 150–450 | Continuous | 300 | mm |
| DV4 | `hole_count` | 5–15 | Integer | 10 | — |

## Usage

### Prerequisites

```bash
pip install -r requirements.txt
```

Requires: Python 3.10+, optuna, scipy, numpy, pandas.

### Development Run (stub solver)

```bash
# From the study directory:
cd projects/hydrotech-beam/studies/01_doe_landscape/

# Run with synthetic results (for pipeline testing):
python run_doe.py --backend stub

# With verbose logging:
python run_doe.py --backend stub -v

# Custom study name:
python run_doe.py --backend stub --study-name my_test_run
```

### Production Run (NXOpen on Windows)

```bash
# On dalidou (Windows node with DesigncenterNX 2512):
cd C:\Users\antoi\Atomizer\projects\hydrotech-beam\studies\01_doe_landscape
conda activate atomizer
python run_doe.py --backend nxopen --model-dir "../../models"
```

> ⚠️ `--model-dir` can be relative — the code resolves it with `Path.resolve()`. NX requires fully resolved paths (no `..` components).

### Resume Interrupted Study

```bash
python run_doe.py --backend stub --resume --study-name hydrotech_beam_doe_phase1
```

### CLI Options

| Flag | Default | Description |
|------|---------|-------------|
| `--backend` | `stub` | `stub` (testing) or `nxopen` (real NX) |
| `--model-dir` | — | Path to NX model files (required for `nxopen`) |
| `--study-name` | `hydrotech_beam_doe_phase1` | Optuna study name |
| `--n-samples` | 50 | Number of LHS sample points |
| `--seed` | 42 | Random seed for reproducibility |
| `--results-dir` | `results/` | Output directory |
| `--resume` | false | Resume existing study |
| `--clean` | false | Delete Optuna DB and start fresh (history DB preserved) |
| `-v` | false | Verbose (DEBUG) logging |

## Files

| File | Description |
|------|-------------|
| `run_doe.py` | Main entry point — orchestrates the DoE study |
| `sampling.py` | LHS generation with stratified integer sampling |
| `geometric_checks.py` | Pre-flight geometric feasibility filter |
| `nx_interface.py` | AtomizerNXSolver wrapping optimization_engine |
| `iteration_manager.py` | Smart retention — last 10 + best 3 with full data |
| `requirements.txt` | Python dependencies |
| `OPTIMIZATION_STRATEGY.md` | Full strategy document |
| `results/` | Output directory (CSV, JSON, Optuna DB) |
| `iterations/` | Per-trial archived outputs |

## Output Files

After a study run, `results/` will contain:

| File | Description |
|------|-------------|
| `doe_results.csv` | All trials — DVs, objectives, constraints, status |
| `doe_summary.json` | Study metadata, statistics, best feasible design |
| `optuna_study.db` | SQLite database (Optuna persistence, resume support) |
| `history.db` | **Persistent** SQLite — all DVs, results, feasibility (survives `--clean`) |
| `history.csv` | CSV mirror of history DB |

### Iteration Folders

Each trial produces `iterations/iterNNN/` containing:

| File | Description |
|------|-------------|
| `params.json` | Design variable values for this trial |
| `params.exp` | NX expression file used for this trial |
| `results.json` | Extracted results (mass, displacement, stress, feasibility) |
| `*.op2` | Nastran binary results (for post-processing) |
| `*.f06` | Nastran text output (for debugging) |

**Smart retention policy** (runs every 5 iterations):
- Keep last 10 iterations with full data
- Keep best 3 feasible iterations with full data
- Strip model files from all others, keep solver outputs

## Architecture

```
run_doe.py
  ├── sampling.py              Generate 50 LHS + 1 baseline
  │     └── scipy.stats.qmc.LatinHypercube
  ├── geometric_checks.py      Pre-flight feasibility filter
  │     ├── Hole overlap:  span/(n-1) - d ≥ 30mm
  │     └── Web clearance: 500 - 2·face - d > 0
  ├── nx_interface.py          AtomizerNXSolver (wraps optimization_engine)
  │     ├── NXStubSolver       → synthetic results (development)
  │     └── AtomizerNXSolver   → real DesigncenterNX 2512 SOL 101 (production)
  ├── iteration_manager.py     Smart retention (last 10 + best 3)
  ├── Optuna study
  │     ├── SQLite storage (resume support)
  │     ├── Enqueued trials (deterministic LHS)
  │     └── Deb's feasibility rules (constraint interface)
  └── history.db               Persistent history (append-only, survives --clean)
```

## Pipeline per Trial

```
Trial N
  │
  ├── 1. Suggest DVs (from enqueued LHS point)
  │
  ├── 2. Geometric pre-check
  │     ├── FAIL → record as infeasible, skip NX
  │     └── PASS ↓
  │
  ├── 3. Restore master model from backup
  │
  ├── 4. NX evaluation (IN-PLACE in models/ directory)
  │     ├── Write .exp file with trial DVs
  │     ├── Open .sim (loads model chain)
  │     ├── Import expressions, rebuild geometry
  │     ├── Update FEM (remesh)
  │     ├── Solve SOL 101 (~12s)
  │     └── Extract: mass (p173 → _temp_mass.txt), displacement, stress (via OP2)
  │
  ├── 5. Archive outputs to iterations/iterNNN/
  │     └── params.json, params.exp, results.json, OP2, F06
  │
  ├── 6. Record results + constraint violations
  │
  ├── 7. Log to Optuna DB + history.db + CSV
  │
  └── 8. Smart retention check (every 5 iterations)
```

## Phase 1 → Phase 2 Gate Criteria

Before proceeding to Phase 2 (TPE optimization), these checks must pass:

| Check | Threshold | Action if FAIL |
|-------|-----------|----------------|
| Feasible points found | ≥ 5 | Expand bounds or relax constraints (escalate to CEO) |
| NX solve success rate | ≥ 80% | Investigate failures, fix model, re-run |
| No systematic crashes at bounds | Visual check | Tighten bounds away from failure region |

## Key Design Decisions

- **Baseline as Trial 0** — LAC lesson: always validate baseline first
- **Pre-flight geometric filter** — catches infeasible geometry before NX (saves compute, avoids crashes)
- **Stratified integer sampling** — ensures all 11 hole_count levels (5-15) are covered
- **Deb's feasibility rules** — no penalty weight tuning; feasible always beats infeasible
- **SQLite persistence** — study can be interrupted and resumed
- **No surrogates** — LAC lesson: direct FEA via TPE beats surrogate + L-BFGS

## NX Integration Notes

**Solver:** DesigncenterNX 2512 (Siemens rebrand of NX). Install: `C:\Program Files\Siemens\DesigncenterNX2512`.

The `nx_interface.py` module provides:
- **`NXStubSolver`** — synthetic results from simplified beam mechanics (for pipeline testing)
- **`AtomizerNXSolver`** — wraps `optimization_engine` NXSolver for real DesigncenterNX 2512 solves

Expression names are exact from binary introspection. Critical: `beam_lenght` has a typo in NX (no 'h') — use exact spelling.

### Outputs extracted from NX:
| Output | Source | Unit | Notes |
|--------|--------|------|-------|
| Mass | Expression `p173` → `_temp_mass.txt` | kg | Journal extracts after solve |
| Tip displacement | OP2 parse via pyNastran | mm | Max Tz at free end |
| Max VM stress | OP2 parse via pyNastran | MPa | ⚠️ pyNastran returns kPa — divide by 1000 |

### Critical Lessons Learned (2026-02-11)
1. **Path resolution:** Use `Path.resolve()` NOT `Path.absolute()` on Windows. `.absolute()` doesn't resolve `..` components — NX can't follow them.
2. **File references:** NX `.sim` files have absolute internal refs to `.fem`/`.prt`. Never copy model files to iteration folders — solve in-place with backup/restore.
3. **NX version:** Must match exactly. Model files from 2512 won't load in 2412 ("Part file is from a newer version").
4. **pyNastran:** Warns about unsupported NX version 2512 but works fine. Safe to ignore.

## References

- [OPTIMIZATION_STRATEGY.md](./OPTIMIZATION_STRATEGY.md) — Full strategy document
- [../../BREAKDOWN.md](../../BREAKDOWN.md) — Tech Lead's technical analysis
- [../../DECISIONS.md](../../DECISIONS.md) — Decision log
- [../../CONTEXT.md](../../CONTEXT.md) — Project context & expression map

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*Code: 🏗️ Study Builder (Technical Lead) | Strategy: ⚡ Optimizer Agent | Updated: 2026-02-11*