[Tobi]

Hey together,

in the attachment you find a simple meshing example and I am trying to figure out how to remove these bad cells during the snap procedure. I know that I can move my backgroundmesh to get rid of these cells but I do not want to do it in this way. A look into the snappyHexMeshDict and the mesh quality controls is promising with 3 parameters:

//- Minimum pyramid volume. Is absolute volume of cell pyramid.
//  Set to a sensible fraction of the smallest cell volume expected.
//  Set to very negative number (e.g. -1E30) to disable.
minVol 1e-13;


//- Volume ratio of neighbouring cells (0 -> 1)
minVolRatio 0.01;



//- if >0 : preserve cells with all points on the surface if the
//  resulting volume after snapping (by approximation) is larger than
//  minVolCollapseRatio times old volume (i.e. not collapsed to flat cell).
//  If <0 : delete always.
//minVolCollapseRatio 0.1;

The first one is recognized by snappyHex mesh (I can see it in the output) but all bad cells remain. The last parameter (minvolCollapseRatio) is not working with negative or even values up to 0.9. And the parameter (minVolRatio) is also not working.

Hence, there are several questions:

• Why we have these parameters if they do not influence the result
• Does anybody know if minVolRatio or minVolCollapseRatio is working

Thanks in advance,
Tobi

[gcampana]

Dear Tobi,

Did you ever find out what was happening?

Best regards,

Guillén

[Tobi]

Hi, never investigate further.

[Tobi]

Let me check if the case still work's with the crap things. Since it is a long time ago and I got way more knowledge, maybe it's now straight forward to me

I guess one point was, that some of the mesh quality parameters are uses within the castellated part. Hence, snapping makes cells crazy but there is no removing adding algorithm. Thus, we move the mesh to its surface but if the quality parameters are not satisfied, we move it back to its origin position to reach a more or less valid mesh.

[Tobi]

Out of the box, one could use topoSet to select different cells (or checkMesh to create cellSets) and remove the cells via subsetMesh.

[gcampana]

Thank you for your prompt response!

I am struglling with "strange" cells (highlighted cell on snapped2.png) at a patch.

This low quality cell comes from an isolated face that is assigned to the patch at the castellated phase (castellated.png, white triangles represent the STL surface).

This cells totally break the add layer process. I do not want to use explicitFeatureSnap as it also messes with addLayers.

I thought that some of the parameters that you pointed out could manage this issue but I am not being able to solve it.

Do you have any suggestions?

Thank you for your help!