Theory
The curvature rule sizes elements in proportion to the local radius of curvature, and the growth rule propagates small surface elements into the volume. On a model with very small radii, either rule could request elements far smaller than the wavelength requires; this multiplies the number of unknowns without improving the acoustic result. The minimum is a floor under both rules, equation (1). The program passes it to Gmsh as Mesh.MeshSizeMin and also applies it in its own size callback (Gmsh reference manual, 2025).
On auto, the minimum is a fixed fraction of the maximum, so it follows the frequency and the temperature in the same way. Geometry smaller than the minimum is still represented in the mesh; only the size the rules may request is limited.
Equations
| where | meaning | unit |
|---|---|---|
| Minimum element size | m | |
| Maximum element size (on auto: for the smallest sound speed of the model) | m | |
| Element size at a point | m |
Default and rule
- Default
- auto: maximum element size / 20Computed by the program
- Rule
Auto = maximum / 20. Example: = 68.6 mm gives = 3.43 mm.
- Source
The divisor 20 is the program's default; it is not derived from a published rule and has not been compared with other values. The Gmsh option is described in the Gmsh manual (Gmsh reference manual, 2025).
Valid range 0 < h_min < h_max
Values
Above 0, at most 10 m and below the maximum element size (checked when the setting is saved). Displayed and entered in mm.
Too large
A minimum close to the maximum disables most of the curvature refinement: curved walls and port rims become faceted. The model fidelity check compares each meshed face area with its CAD area (warning at 0.5 % for ports, 1 % for walls).
Not quantified
The effect of the divisor on the transmission loss has not been quantified.