SimScale CAE Forum

Meshing make a box around the cad part

I try to make a flow simulator for a marine reef skimmer, but when make the meshing, there will be make a “mesh box” around the CAD modell. I use the HexMesh internal flow type.
It’s look like, as the SimScal change the direction of meshing.
Anybody has idea what I make wrong?

I hide some side of the box:

Best Regards,


Hi Tibi @tribor,

the short answer: To fix this fast without working on your CAD model, you could go with the full, manual “snappyHexMesh” mesh operation, which might be a bit more work but in the end you’ll also have more control over the mesh. Find the a general description for it in the documentation where the important part to have the mesh inside the model and not around it in this article. Basically you’ll need to set this box around the reef skimmer and the material point location yourself.

The longer answer: This HexMesher starts with a cartesian box around your model, meshes the entire box and then removes the cells that are on the other side of where you put the Material Point. In the automatic version, this box as well as the material point location is determined automatically based on a specific algorithm. However we’ve seen similar situations, when there were some “spurious” wires somewhere in the CAD model or the CAD model was not properly closed. Here the box seems unusually big and obviously the wrong side was meshed. This suggest that there might be some spurious features in that model. Any chance you could share it with me? That way we could dig deeper.

To understand the material point concept, check out these images from the documentation:

  • Material point inside the model

  • Material point outside the model

Hope that helps!