# Geometry Troubleshooting

This page covers problems that are not resolved by the standard preparation workflow - isotropic remeshing and baseline cleanup - described in {doc}`Geometry Preparation <geometry-preparation>`. Use this as a reference when a specific issue persists or when simulation results near a surface are unexpected.

## Large holes

As noted in the preparation guide, small holes and open surfaces are generally harmless in AeroSim. Problems arise when a hole is large enough that IBM points are missing from a significant portion of the surface. This can happen when triangles are lost during CAD export or format conversion, and may result in the solver not fully enforcing the boundary condition in that region.

```{figure} /_static/img/references/torus_hole.png
:align: center

Example of a geometry with a hole.
```

To close holes in MeshLab:

1. Go to `Filters` > `Remeshing, Simplification and Reconstruction` > `Close Holes`.
2. The default values are sufficient for most cases.
3. Press `Apply`.

```{figure} /_static/img/references/close_holes.png
:align: center

Close Holes dialog.
```

```{figure} /_static/img/references/torus_hole_closed.png
:align: center

Geometry with the hole closed. Newly generated triangles are shown selected.
```

```{warning}
If the geometry has intentionally open regions (e.g. an inlet face or an explicitly modeled opening), verify those areas have not been closed unintentionally.
```

## Persistent low-quality triangles after remeshing

Isotropic remeshing resolves most triangle quality issues. In some cases, however, specific regions - particularly sharp corners or edges from CAD models - may retain poor triangles because the remesher cannot fully recover the original shape there.

If the aspect ratio inspection (described in the preparation guide) still highlights faces after remeshing:

- Try running `Isotropic Explicit Remeshing` again with a smaller `Target Length` in the affected region, using `Remesh only selected faces`.
- If the issue is concentrated at sharp edges, consider slightly softening those edges in the source CAD model before exporting to STL, as very sharp features are inherently difficult to triangulate uniformly.

```{note}
Sharp corners and edges can also be deliberately left at a coarser resolution if they are not in the primary region of interest. IBM can tolerate some local variation in point spacing without significantly affecting global results.
```