Difficulty selecting only "Faces" for Wall Boundary Condition with 27 Solid Bodies

Hi everyone,

I am working on an incompressible wind simulation of a 3D city model (SAAO site in Cape Town). My geometry is a STEP file consisting of 27 Solid Bodies (26 buildings and 1 terrain volume) with a total of 5,896 faces.

I am trying to assign all building and terrain surfaces to a Wall boundary condition. However, I am running into a persistent issue where I cannot select the faces without the selection also grabbing the Volumes (Solid Bodies).

When a Volume is accidentally included in the assignment list, I receive the error: “The physics cannot be taken into account as the simulation setup is not valid… Missing material or advanced concepts were detected for the following entities.”

My current workflow:

  1. I have used Facet Split on the terrain to access the triangles.

  2. I have tried toggling the Face Selection filter on and the Volume Selection filter off.

  3. Despite the filter, the assignment list in the Boundary Condition panel still shows the parent Solid Bodies (Open CASCADE STEP translator entities) instead of just the face IDs.

Questions:

  1. Is there a way to “Lock” Volume selection so that a box-select (Ctrl+A) only picks up the 5,896 faces?

  2. If the terrain is a solid “chunk” (skirted), do I need to extract the top surface specifically to avoid assigning the internal “solid” to the Wall condition?

  3. Is there a “Select all exposed faces” shortcut that ignores internal solid volumes?

Project Link: [SAAO: wind and heat]

Thanks for the help!