Hello,
I’m new and have been working with SimScale for a while and I need some help.
I created a 3D model in Revit - simple 4 walls, floor and 2 pipes.
I made an internal air space.
→ I assigned a material to the internal air
→ I assigned the air supply to the pipe
→ I assigned the discharge to the other pipe
→ I set all the other parts as “wall”
but now I honestly don’t know how to proceed to make the simulation successful.
https://ctrlv.cz/WwYQ
https://ctrlv.cz/ug82
Hi @Luksajetop10, thanks for posting on the forum and welcome to the SimScale Community 
These prompts usually appears when users are trying to run an Incompressible study with solid bodies other than the flow region in the simulation. Please note that Incompressible analysis is not concerned with any sort of Fluid-Solid Interaction, e.g., thermal interaction.
Therefore, please make sure that you only have one solid body, i.e. the flow region, in your project before moving on with the simulation. This tutorial is usually very helpful in showing a workflow to do that: Aerodynamic Flow Behavior Around a Vehicle Tutorial | SimScale. By searching for the project in your profile (I assume it’s this one), I see that this is exactly what’s happening.
You can Edit your model within SimScale and exclude every solid part except for the flow region and the ducts. Then, you can merge the remaining solids using a Boolean Union operation. I think you’d greatly benefit from running some of our introductory Thermal Analysis tutorials before going to your own sim!
Caveat: If you’re going for some sort of thermal study, the ideal solver would be Conjugate Heat Transfer, not Incompressible.
Cheers
Igor