How to Import Mesh and solid bodys together

Using SimScale CAD & Meshing
1

Hello everyone,

I am currently working on an aerodynamic project and have encountered an issue when importing my geometry into SimScale.

I created an assembly in Autodesk Inventor (.iam) consisting of a BMW M4 reference model and a rear spoiler that I designed myself. The spoiler was positioned and aligned relative to the vehicle using assembly constraints and reference planes.

After completing the assembly, I exported the entire project as a STEP file and uploaded it to SimScale. However, when the geometry is imported, only the spoiler is visible. The vehicle itself does not appear.

Some additional information:

  • The spoiler is a solid body created directly in Inventor.

  • The vehicle is not a native CAD solid. It was imported as a mesh model and is displayed in Inventor as a mesh body (triangulated geometry).

  • Within the Inventor assembly, the vehicle is listed as a mesh and not as a standard solid body.

  • I also noticed that under the “Third Party” section in the assembly browser there is an entry with my project name ending in “.htm”.

My questions are:

  1. Is SimScale unable to import mesh bodies that are included in a STEP assembly?

  2. Do I need to convert the vehicle mesh into a solid or surface body before exporting?

  3. Is there a recommended workflow for combining a mesh vehicle model with a CAD solid spoiler for CFD simulations in SimScale?

  4. Could the “.htm” third-party reference be related to the missing geometry during export?

My goal is to simulate the airflow around the complete vehicle and spoiler assembly, so I would like both components to be imported correctly into SimScale.

Any advice or recommended workflow would be greatly appreciated.

Thank you very much for your help.

3

Hi,

I’m afraid that having both solids and meshed parts in the same geometry is not supported, the geometry needs to be exported from the CAD tool as all solids or all meshes (.stl). All solids is usually best, if possible.

Have you considered using some of the models in the Public Projects section? Public Simulation Projects Library | SimScale...

4

Thank you for your fast reply. If I import everything as .STL Mesh, does it affect the simulation in its accuracy and repeatability?

6

Stl files are officially supported and, if they are high quality, it should be Ok. I personally do not like stl files because they are very difficult to interact with and edit.

7

Hi Ricardo, It would be great if you could help me another time. I finally got the car from mesh to solid body with different CAD Softwares like FreeCAD and Inventor and wanted to import it into simscale a second ago but when I do it nothing happens and Simscale says there was a problem with the upload. What could be the reason for that? Could it be the size of the STEP-File? It has 5,36MB. I would really appreciate it if you can help me further. Thanks!

9

From your description it sounds like you ended up with a step file that contains a geometry with thousands of faces (1 face for each triangle of the stl surface mesh), is that so?

This is probably going to be worse than stl due to the number of faces. The best option would be to create the whole car with solid parts only (like this). But if an stl was exported at some point, it’s best to just use a stl file instead of re-creating a solid out of the stl, because the thousands of triangles are not going to be very optimal to mesh.

10

Hi Ricardo, I am sorry I need to disturbe you again. I finally was able to import everything as one Step-file but while setting up my simulation area I got the error that there would be gaps in my own constructed modell. I just checked my older simulations and the 3D-Modell in Inventor but I haven´t changed anything at the geometry since then and in Inventor I don´t have any gaps. The only change is that I have a different reference modell infront of it. How can I fix that? Because to my knowledge I can´t close a geometry that isn´t open and in the past it did work every time without any issues. Would be great if you could give me some tipps. Thanks!

12

Suggestion: try to create a flow region in your CAD tool before bringing the CAD model to SimScale (create a solid box, run a boolean/subtract operation removing the car parts from the box, delete the car parts, export the model from the CAD tool, import to SimScale).

If you can create the flow region in CAD then that already solves the problem. If it fails, the CAD tool may give you more insights about what could be causing trouble.

13

Hi Ricardo, thanks for the tipp. I just tried to delete some roundings and it works now, don´t know what the problem was but it works. When I create my simulation area with a bounding box and want to boolean subtract my model from the box it is loading forever. I just stopped the time and for 20 minutes it said performinng operation. Is that normal if the model is bigger and more complex? Or is there another way to create a Incompressible Simulation?

14

Hi, thanks for the update - my suggestion remains the same.

15

Dear Simscale Support Team,

I am reaching out to you again regarding an ongoing issue I am experiencing with the Boolean subtraction operation in Simscale, and I would like to provide a detailed summary of all the steps I have taken so far in order to find the most efficient solution together.

Background and initial issue:

When attempting to subtract my geometry from the flow region (simulation box) using the boolean subttract function, the operation get´s stuck on performing operation indefinitely,e ven after 20 minutes without producing any result.

Steps taken based on your previous advice:

Following your earliest suggestion to pre-process the geometry in a CAD tool before importing it to Simscale (create a solid box, run a boolean subtract removing car parts from the box, delete the car parts and then import into Simscale.) I contacted the Autodesk Inventor Support team and forwarded them the exact instructions provided by your team. After thoroughly checking my geometry for errors, the Inventor Support Team concluded that Inventor is not well suited for this type of operation. Although they provided a workaround, they explicitly stated that the result would most likely be faulty or fail entirely. Theyy recommended that I contact your Support Team again because your are better equipped to handle this kind of task.

Current Geometry Details:

My geometry consists of 22 solid bodies ins total including mounting parts etc.

Attemted workarounds:

I have already attemted to simplify the geometry using [Wrap] or [Simplify] functions in Simscale. While this allowed the boolean subtraction to proceed, parts of my geometry were missing in the result, making it unusable for my CFD simulations.

Even when placing only 50% of the geometry within the flow region, the operation either produces errors or loads indefinitely when using the original file.

Latest error message (16/06/26):

In my most recent attempt, I followed these exact steps:

  1. Created a External flow Volume generously surrounding my geometry
  2. Applied boolean subtraction with the flow region box as the base and my entire geometry as target bodies.
  3. Set Tool bodies to [Discard tool bodies]

The operation returned the following error message:

Subtraction result empty. Subtract operation has an empty result. Please select overlapping bodies for the operation.

I will put a screenshot from the error message below the text. If you need any more Screenshots or information please don´t hesitate to ask. I´ll gladly provide them to you.

Best Regards, Tim

Screenshot 2026-06-16 222922
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