SimScale CAE Forum

Issue with "Background Mesh Box"


I am trying to run a simple wind tunnel Incompressible cfd
my geometry imports fine, and i set the simulation up with hex dom external
it automatically generates a background mesh box, i wish to change the size of the
“background mesh box”, i select it and change a value, when i save it, it reverts back to the original size and generates a new box. no matter what i do i cannot change the automatically generated size of the background mesh box?


I am suspecting that the user interface has been changed lately since I also have similar issues and since I have had no issues in the past concerning changing BMB sizes…

@jousefm can you check into this?


Will check and get back to you guys!




The same problem with me


We are investigating this. Sorry for any inconvenience @skamel!

Keeping you up-to-date!



The same happening with me. After entering the dimensions of BMB as i click on the workspace to see the visuals of BMB it creates a new BMB.
Looking for solution.


We are still looking into it Hamza! I will post updates here once I receive more information from my colleagues.

Thanks for your patience and sorry for any lost productivity so far!



There seems to be a similar issue with material point, instead of moving the pre-existing one it creates a new point


@ScottySpoon Thank you for making this post, I’m new to SimScale and I was thinking that I was doing something wrong or I’m too stupid to follow the CFD tutorials ahaha.


Thanks for confirming this message @qwerty12345 & @nvalenti!

The engineers are working on this :slight_smile: I will (as previously mentioned) keep you up-to-date once I have an update on this.

Thanks a lot and feel free to check out the SimWiki in the meantime :slight_smile:




Hi everyone, i just recently checked out with the BMB issue and it’s seems like the issue is resolved.
@jousefm thank you for your support.
Happy Simulating.


May not be completely fixed yet, material point ‘Geometry Primitive’ is missing in ‘Hex-Dominat (for CFD)’ external meshing…

Material Point is still there for ‘Hex-Dominat parametric (for CFD)’

Unless it was mean’t to be this way, in an effort to have the UI automatically put your Material Point between the BMB and the object (if so, it should at least show use where it has assumed the MP to be before we generate a mesh to see if it got the MP correctly positioned for ‘Hex-dominat (for CFD)’ external meshes)

I see a likelihood of many confused existing users appearing on this one :wink:


@DaleKramer I agree with your point on the Hex-dominant ( CFD) external mesh, but i think that you should not have to know about the material point location as this type of algorithm is solely created for the external meshes. It’s fine unless you encounter any problem while meshing.

Well, the issue with Hex-dominant parametric (CFD) regarding BMB and MP is solved. It no longer creating the new BMB or MP when clicking on the work space for having the visuals of created BMB or MP.


My point is that if the UI can now determine what volume to mesh without specifying an MP for one type of mesh algorithm, then why not have it set the MP for all types (when I started SimScale it was confusing to me that I had to even set an MP since it was easy for me to see what I wanted meshed, based on Meshing Mode).

Now we have it both ways depending on Algorithm, that is where I think the confusion will surface…


@DaleKramer thanks for the question. I’m happy to clarify.

Afaik the Hex-dominant automatic meshing mode automatically chooses the MP position to be outside of the model and inside of the BMB. We just recently finally got to hiding the MP in External meshing mode, but already when it was still showing in the UI, the position you specified it to be at was ignored, using the automated positioning instead. (Don’t nail me down on that, but that’s how it works afaik)

So essentially we just hid something that was not used in the first place.

And the reason why the parametric meshing algorithm doesn’t use the same automation simply is that in case you run into issues with the automatic mesher, there is still a completely manual backup that you can use instead.

Hope I could clarify the question.



Thanks Sebastian, I hope when you are satisfied your MP algorithm has proven itself that the MP will disappear completely from our vocabulary :slight_smile: