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Geometry & units

STEP vs STL, watertight solids, declaring length units.

SimScale, Fusion, and Ansys all start with geometry prep. Wrong scale or a non-manifold STL will not “average out” in the solve.

STEP (preferred)

  • Upload .step / .stp from your CAD system.
  • You tag whole B-rep faces for Support, Load, Preserve, and Obstacle — same idea as selecting faces in Fusion or SolidWorks Simulation.
  • Multi-solid STEP lists each body for whole-body preserve / keep-out; adjacent preserves can auto-tie so assemblies share load paths.

STL (allowed, with caveats)

  • Tessellated triangles — fine for quick checks, weaker for curved supports/loads.
  • Prefer a watertight, manifold mesh (no holes, non-manifold edges, or inverted normals) — the same checks your slicer cares about.
  • Tagging uses mesh paint / planar patches — less precise than STEP. Study shows a face-mapping notice for STL.

Length units (critical)

Declare mm / cm / m / in to match how the file was modeled. The solver scales to meters. A part drawn in inches but labeled mm will see loads and voxels off by ~25× — results look “solved” and still be nonsense.

Default in Study is millimeters (most CAD exports).

declared mm — true sizesame file read as inches — ~25× off
The same file read in mm (true size) vs inches — everything downstream scales ~25×, and the solve still 'succeeds'.

What to fix before upload

  • One primary solid for Body-bound topology (or use multi-body tools intentionally).
  • Remove decorative micro-features that only inflate mesh cost.
  • Keep bolt holes and mating pads as clean faces you can Preserve.

Next: Supports & loads.

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