Making watertight objects

Hello all. I’m fairly new to CFD and CAD with only some slight experience with solidworks in the past. I am trying to analyse airflow around a part of downtown Vancouver for a grade 10 project. I found the model on the sketchup warehouse and imported it to AutoCAD. Unfortunately most of the buildings are not watertight and either are missing a base or have holes in the side of them. Is there any quick solution to this? Thickening all the walls and surfaces came to my mind but the times I have never found success in doing this (I have no idea how to use AutoCAD). Any sort of help would be greatly appreciated. I can email the model file as I do not know how to attach it in a thread.


Hi @MichaelYTZ, have you tried OnShape? It is a Cloud-based CAD tool, and we are partners. This means with your SimScale account, you can directly import models from OnShape. Here are more details about the collaborations. Hope this helps! Cheers!

Unfortunately, I don’t believe you can import .skp files to Onshape. You might try converting it to an STL ( which can then be uploaded to SimScale - I’ve never tried this but it could work as opposed to trying to fix the holes using AutoCAD.

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@MichaelYTZ - If you want to share the geometry with me, I can show you how to fix it up. Sketchup can export to Onshape via the Collada format or by using the STL export extension. I also have solidworks and autocad, so I can show you how to fix it in any of these tools… Let me know how I can help!

Hi Jim,

Sorry for the late response, I’ve been away for the summer. I’ve completed the project already but it would be nice to know how to fix it for future reference. Is there an email that I can email the model to you at?



Sure thing, Mike. You can email me at

Hi guys!

Just wanted to add that Autodesk Fusion 360 (which is free under certain circumstances) also has some tools to get that job done.

However it does need to be in an STL, OBJ, IGS or STEP.

If you have it as STL follow these steps

  1. Open Fusion.
  2. In the model tab under the create section dropdown menu click “Create Mesh”
  3. The mesh environment opens, click the first icon form the ribbon bar “Insert Mesh”.
  4. Browse to the file hit okay and hit okay
  5. Under modify click “make closed mesh” and click your mesh. Hit okay and Voila its closed.
  6. Export to step or STL or even use the SimScale add-in to upload it directly.

Really recommend Fusion. Its very intuitive and easy to use. Workflow is way faster than “normal” CAD like Solidworks or Solid Edge. Plus they constantly add features.

No i’m not affiliated :smile:

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