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

Using SimScale CAD & Meshing
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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.

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Update: I have updated the .step file to include a surface + solid terrain (skirted with a bottom cap). However, I am now hitting several validation errors that prevent the simulation from starting.

Current Errors:

  1. Invalid Boundary Condition (Wall 3): SimScale reports that Wall 3 is assigned to bodies without a material assignment (e.g., Open CASCADE STEP translator 7.8 1.1, 1.3, etc.).

  2. Missing Pressure BC: “The simulation does not contain at least one pressure boundary condition… Mass balance will be difficult to enforce.”

The Problem: Even when I use the Face Selection filter, the assignment list for “Wall 3” continues to populate with the parent Solid Body names (Open CASCADE STEP translator...) rather than individual Face IDs.

Refined Questions for the Team:

  1. How can I get SimScale to only accept the 5,000+ faces into the Wall 3 assignment without it grabbing the parent volumes?

  2. Why are the bodies appearing in the Wall 3 list if the “Volume Selection” toggle is turned off?

  3. Since I am doing a pedestrian comfort study at the SAAO site, should the “Terrain Solid” be assigned to the Wall 3 condition as a whole, or must I extract only the top faces?

  4. Should I just ignore these and Generate the Mesh?

Thank you.

Further update: The challenge was the Flow Volume and the restriction region (for pedestrian analysis). I originally did this by creating a primitive Box –from the toolbar but its actually established with a Refinements then Refinement regions' should be set to Cartesian Box with the Geometry Primatives –the option just below– defining the area (be sure to set the name).

Some other challenges exist but that a different and separate post. So this is solved.

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