Problem with material assignment in single region simulation

I am beginner here on SimScale and I need a little bit of your help in my first simulation attempts.
I tried to simulate a tank whose content will be mixed with an injector and I have problem because I can not start the simulation run. I provided object geometry as .igs file exported from AutoCad, edited it with SimScale CAD Mode, created fluid regions, set up boundary conditions and meshed whole object successfully. When I try to run simulation I see the alert: β€œIn single region simulations, only the fluid region can be assigned to a material. Please review your material assignments, making sure that only the flow volume region is assigned.”
I assume that problem is with two fluid regions, but both of them have the same medium (water) and the same conditions. When I tried to sum them in one region, it lost some of the faces and elements. Thus I could not set up my boundary conditions in the new geometry and do further steps.
Could you please help me in my problem? How can I create one flow region keeping all of the faces from existing ones? Maybe there are other methods and settings which I should use? Do I have to delete walls of tank and pipes (I tried it but it is still two soild bodies in the simulation)?
I will be very grateful for any help and support :slight_smile:

Here is the link to my project: SimScale Login

Hello @mik222 ,

You are correct, the problem is due to a couple of volumes being assigned to materials. Incompressible simulations are single phase/single volume analyses, so you can only have a single flow region volume.


  • Delete the β€œ65” and β€œ68” volumes. They represent walls and should not be in the final CAD model. This is possible in CAD mode with a β€œDelete body” operation
  • For the flow regions, if I understood what you are looking to do correctly, you would need to run a β€œBoolean > Subtract” operation, using the pipe as a β€œTool” and the main tank as a β€œTarget”. You can also discard the tools in this operation, since you need a single flow region for the analysis.

The result should be a single volume for the flow region of the tank, containing a negative representation of the duct system. This way you will still be able to define boundary conditions to the appropriate faces.



Hello @RicardoParis ,
Thank you very much for your help and suggestions given. I have created a new project on the copy of the first one and tried to achieve some effects with substract operation. However, even if I managed to get a single flow region as a result, I had a lack of one velocity inlet and one pressure outlet. In my opinion I would need to keep faces 13@Flow region (pressure outlet) and 103@Flow region (velocity inlet). I have also modified my CAD model in AutoCad, but maybe I am still doing in somehow wrong? Is it possible to unify all three regions in one and keep all the faces that I need?
I will be very grateful for any further help and information.

Link to new version of my project: SimScale Login