SimScale CAE Forum

Meshing Problem

I am using Hex-Dominant Automatic (CFD Only) meshing and the result is an external mesh rather than internal. I have using this for several weeks and it always created an internal mesh. Starting yesterday, it is now creating an external mesh which is clearly not correct. I don’t believe I am doing anything different this time.

Here is the project.

https://www.simscale.com/workbench?publiclink=d3e1abdb-d5e2-4eb6-9c7b-ffc9f7af4f81

Unfortunately, I have now used up a lot of core hours trying to figure out what has gone wrong.

Update - If I choose parametric CFD, I notice that the default material point is outside of the geometry. I think the issue with the Automatic is that the default material point is not inside the object which it always should be for that type of mesh.

Hi @mas985,

if you remove all your Entities from Surfaces with layers the Hex-dominant automatic option works perfectly fine. This issue will be reported.

Cheers,

Jousef

Ok but it used to work fine with the Surfaces with layers set. What changed?

Also, shouldn’t that be set since these are surfaces where the water flows along and more resolution is needed in those locations?

Thanks

Hi @mas985,

You are right, yes. Will come back to you as soon as I know more about that issue.

In the meantime you can work with the parametric option as you mentioned.

Best,

Jousef

Hi again @mas985,

reported this and the issue will be resolved as soon as possible. Thank you for reaching out to us ! :+1:

Will let you know when everything works fine again.

When using the parametric option just make sure you add refinements for the layers manually.

Best,

Jousef

OK so I was able to create the mesh with the parametric option but there was one odd thing about the results. Last week, when the automatic option was working, I set the fineness to level 3 - Moderate. Now when I used the parametric option, I created a refinement for all surfaces for level 3. However, the parametric mesh is much much finer than the automatic mesh. Does the fineness level mean different things for the two options?

Here is the mesh properties for the automatic option:

Nodes 919271
1D elements (edges) 0
2D elements (faces) 2519901
3D elements (volumes) 804417

And here it is for the parametric option (with same fineness):

Nodes 4269830
1D elements (edges) 0
2D elements (faces) 11804329
3D elements (volumes) 3775290

Hey @mas985,

maybe this documentation page might help you a little bit in understanding how the refinement in parametric works: SnappyHexMesh - Main Settings

Let me know if that helps or if you need some more information. As mentioned by you the levels are (as can be seen in your results) not identical.

Best,

Jousef

Thanks, I had read that before but it really doesn’t explain the relationship between that option and the automatic option. In other words, I would like to know how the parametric setup would have to be in order to match the automatic setup.

Hi @mas985,

I will come back to you as soon as I have found the settings that fit to the automatic meshing.

Best,

Jousef

Hi @mas985,

some feedback about your question: So it is a bit complicated to get the exact same parametric and automatic meshes, since the base mesh box of the mesh is determined based on the fineness settings.

I will tag my colleague @jprobst here. He might give you some useful information and maybe something like a rule of thumb that you can work with.

Cheers!

Jousef

Thanks for the response. It isn’t terribly important but it would be nice just to get a high level view of how the automatic settings are determined. Clearly, the resolution numbers between the two do not appear linked (i.e. 3<>3 for both). But any clarification would help.

Hi @mas985.

Thank you very much for your feedback and I agree that this should be somehow described in the documentation. Will do so as soon as I have time! :slight_smile:

Thanks again and have a nice weekend!

Jousef

Regarding my original post regarding the problem of the automatic meshing, I am now experiencing the same problem with the Parametric Mesh. Even though the surface is water tight and the mesh point is inside the solid body, the mesh is created on the outside of the body.

The new project has two geometries. The first meshed fine but the second which had a slight modification to the geometry, meshed outside the object even though the settings were identical.

https://www.simscale.com/workbench?publiclink=823c0e01-2fee-4369-8ec0-628a18242d7a

Hi @mas985,

could you please send me your CAD model via email? I will send you my mail address (check your messages).

Cheers,

Jousef