README.md

---
pretty_name: "Automotive Underbody Panel Impact Dataset"
license: mit
tags:
  - 3d
  - timeseries
  - finite-element-analysis
  - impact-mechanics
  - graph-neural-networks
viewer: false
---

# Automotive Underbody Panel Impact Dataset

**Version:** 1.1.1  
**Data type:** finite-element simulation trajectories  
**Task:** impact-conditioned displacement and shell von Mises effective-stress field prediction

The Automotive Underbody Panel Impact Dataset contains independent impact simulations
on three automotive structural geometries. Each geometry has 500
Latin-hypercube-sampled impact conditions. Every case stores 17 aligned states
of the full three-dimensional nodal displacement field and shell-element
von Mises effective stress.

The dataset supports research on graph neural operators, mesh-based surrogate
models, spatiotemporal field prediction, peak-event prediction, and
simulation-based design screening.

Detailed generation documentation is provided in:

- `metadata/SIMULATION_PROTOCOL.md` for units, the impactor, boundary/contact
  conditions, and solver/output settings;
- `metadata/LHS_DESIGN.md` for parameter definitions, design bounds, and the
  geometry-specific constrained-LHS construction;
- `metadata/TEMPORAL_SAMPLING.md` for the 17-state reduction and the discrete
  peak-time definition.

## Dataset summary

| Geometry | Cases | Nodes | Directed graph edges | Shell elements | Displacement | von Mises effective stress |
|---|---:|---:|---:|---:|---|---|
| `floorfrontdriver` | 500 | 7,408 | 29,572 | 7,374 | `[7408,17,3]` | `[7374,17]` |
| `floorfrontR` | 500 | 12,011 | 48,138 | 12,055 | `[12011,17,3]` | `[12055,17]` |
| `trunkfloor` | 500 | 14,440 | 58,074 | 14,589 | `[14440,17,3]` | `[14589,17]` |

The three geometries are independent datasets. Equal case identifiers across
geometries do **not** denote paired physical simulations.

## Conditions and units

The simulations use the tonne--mm--s--N consistent unit system. Coordinates
and displacements are in mm, time is in s, velocity is in mm/s, mass is in
tonne, density is in tonne/mm^3, and stress and Young's modulus are in MPa.

| Symbol | Released field | Definition | Design domain | Unit |
|---|---|---|---|---|
| p | `impact_xyz` | centroid of the selected eligible panel shell | geometry-dependent discrete candidate set | mm |
| v | `velocity_xyz` | initial rigid-impactor translational velocity | derived from speed and angles | mm/s |
| s | `impact_speed` | velocity magnitude | [1732.05, 5196.15] | mm/s |
| mu | `mass_ratio` | common scale factor for reference impactor mass and density | [0.75, 1.25] | dimensionless |
| theta | `theta_deg` | polar angle measured from global +Z | [0, 15] | degree |
| phi | `phi_deg` | azimuth in global XY, from +X toward +Y | [0, 360] | degree |
| E | `material_young_mpa` | rigid-impactor Young's modulus | {70000, 110000, 210000} | MPa |
| nu | `material_poisson` | rigid-impactor Poisson ratio | {0.33, 0.34, 0.30} | dimensionless |

The velocity is constructed as
`v = s [sin(theta) cos(phi), sin(theta) sin(phi), cos(theta)]`.
The mass-ratio convention is
`impactor_mass = 0.01 tonne * mu` and
`impactor_density = 5.205e-5 tonne/mm^3 * mu`.

Impact positions are not sampled as three independent continuous coordinates.
Eligible positions are shell-element centroids at least 80 mm from the
topological outer boundary. Two LHS coordinates are mapped in normalized XY to
the nearest unused eligible centroid; the released Z coordinate is the actual
centroid height.

## Constrained-LHS design

Each design uses seven normalized coordinates: position X, position Y, speed,
mass ratio, theta, phi, and material class. Candidate designs are generated by
Latin hypercube sampling, and the design with the largest normalized minimum
pairwise distance among 128 trials is retained. Material is a balanced
three-level categorical coordinate.

`floorfrontR` and `trunkfloor` use independent single-batch designs with seeds
20260728 and 20260723, respectively. `floorfrontdriver` is a staged design:
cases 001--100 use seed 20260721, cases 101--200 are a complementary nested
extension using seed 20260722, and cases 201--500 form an independent
augmentation using seed 20260722. The geometries share parameter bounds and
simulation rules but do not share paired physical conditions.

## Impactor and simulation setup

The impactor is a rigid spherical shell with radius 12.5 mm and an initial
5.0-mm gap from the target centroid along the direction opposite to travel. It
uses shell ELFORM 2, shear factor 0.833333, three through-thickness integration
points, thickness 0.1 mm, and `*MAT_RIGID`. The material class changes only the
rigid impactor's E and nu; mass ratio changes only its density and nominal
mass.

All nodes on the panel's topological outer boundary are constrained in all six
degrees of freedom. Impactor--panel interaction uses
`*CONTACT_AUTOMATIC_SURFACE_TO_SURFACE_ID` with static and dynamic friction
coefficients of 0.15. A body acceleration of 9810 mm/s^2 is applied in global
+Z. Simulations end at 0.03 s. They were run with LS-DYNA SMP single precision
R12 through ANSYS v221 `lsdyna_sp.exe` using `ncpu=8` and `memory=400m`.

The panel material definitions and shell sections remain those of the cited
upstream Version 3 model; their full keyword cards are not redistributed in
this compact release.

## Stress definition

The `effective_stress` field is the shell-element von Mises equivalent stress
exported from LS-PrePost. The LS-PrePost `etime 9` component corresponds to
`Effective Stress (v-m), ip#max`: for each shell element and retained state,
the stored scalar is the maximum von Mises stress over all through-thickness
integration points. The maximizing integration-point index is not retained.
Stress values are in MPa, and the tensor shape is `[Ne, 17]`.

## Repository structure

```text
underbody-impact-data/
├── data/
│   ├── floorfrontdriver/cases_001_100.zip ... cases_401_500.zip
│   ├── floorfrontR/cases_001_100.zip ... cases_401_500.zip
│   └── trunkfloor/cases_001_100.zip ... cases_401_500.zip
├── meshes/
├── metadata/
├── generation_evidence/
├── scripts/
├── manifest.csv
├── checksums.sha256
├── DATASHEET.md
└── schema.json
```

Each ZIP member is stored as `cases/caseNNN.pt`. The files are PyTorch-serialized
plain dictionaries. `manifest.csv` records the byte size and SHA-256 digest of
every case.

## Download

```python
from huggingface_hub import snapshot_download

dataset_root = snapshot_download(
    repo_id="structmeshdata/underbody-impact-data",
    repo_type="dataset",
    revision="v1.1.1",
)
```

## Loading a case

PyTorch 2.6 or newer is recommended. The loader uses `weights_only=True` and
reads cases directly from ZIP shards:

```bash
python scripts/load_case.py \
  --dataset-root . \
  --geometry floorfrontdriver \
  --case case001
```

```python
from pathlib import Path
import sys

sys.path.insert(0, str(Path("scripts").resolve()))
from load_case import load_case, load_mesh

case = load_case(Path("."), "floorfrontdriver", "case001")
mesh = load_mesh(Path("."), "floorfrontdriver")
print(case["disp"].shape)
print(case["effective_stress"].shape)
```

## Validation

```bash
python scripts/validate_dataset.py --dataset-root . --verify-checksums
```

The validator checks the case schema, tensor shapes, finite values, aligned
time arrays, split coverage, mesh connectivity, archive membership, and
SHA-256 digests.

## Fixed split and peak-event task

The fixed split is 400 train / 50 validation / 50 test cases per geometry with
seed 12345. Normalization statistics must be computed from the training cases
only.

For peak-event prediction, the supplied script selects the state containing the
global maximum valid nodal displacement magnitude and uses the von Mises
effective-stress field from that same state.

## Temporal sampling

The solver writes D3PLOT output at a nominal interval of 0.0002 s. Compact
conversion retains every tenth raw state and appends the final state. Every
released case therefore uses indices `[0, 10, 20, ..., 150, 151]`; the first
16 retained states have a nominal 0.002-s spacing, while the appended terminal
state can be very close to index 150. Exact floating-point times are stored in
each case and should be used instead of reconstructing them from the nominal
interval.

The peak time `t*` is discrete: it is the argmax of nodal displacement magnitude
over valid nodes and the 17 retained states only. It is not a continuous-time
solver maximum. Stress at the same selected retained state is used as the
paired peak-event stress target.

## Data-version note

The included `floorfrontR` data passed the release quality audit. Files from
earlier internal builds must not be mixed with this release; see
`metadata/floorfrontR_DATA_NOTE.md`.

## Limitations

- The fields are numerical simulation results, not physical crash-test measurements.
- The dataset covers three fixed meshes and their documented sampled conditions.
- It does not establish generalization to arbitrary vehicle geometries or real tests.
- Public test labels reproduce the fixed paper protocol but are not a hidden benchmark.
- The exact LS-DYNA R12 sub-build is not retained for every case.
- The recorded `impactor_mass` is the generator-defined nominal mass; users
  requiring an independently recomputed solver mass should inspect an original
  solver `MATSUM` output.
- Peak-event time is quantized to the released 17-state temporal grid.

## License

This repository is released under the MIT License. Third-party names and source
model provenance are documented in `THIRD_PARTY_NOTICES.md`.

## Citation

Please cite the versioned Hugging Face repository for release `v1.1.1`:
https://huggingface.co/datasets/structmeshdata/underbody-impact-data/tree/v1.1.1.
Citation metadata is also provided in `CITATION.cff`.