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What CAD software do you use to define STL surfaces?

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Old   March 21, 2016, 02:34
Default What CAD software do you use to define STL surfaces?
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Florian Nguyen
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Hello to everybody,

I want to use OpenFOAM on a complex geometry in which I need to define many patches. From the posts that I read on this forum, SnappyHexMesh seems to require STL files forming a closed surface. In many tutorials that I followed these STL files contained surfaces, but my CAD software (AutoDesk Inventor) refuses to export surfaces to that format (which is normal, since STL was not thought for that purpose).

A solution that I found was to export my parts in STEP format with Inventor, and then convert them, one by one, to STL using Salome. However, because of this, some gaps appear in the STL files and the overall STL geometry is no longer waterproof (I used surfaceCheck to make sure of that). Obviously, SnappyHexMesh doesn't give me the expected output.

Could you advise me on what CAD software I can use, or give me a method to have STL files that are consistent with one another ? Is it possible to use STLs of solid parts instead of surfaces and still define patches easily ?

If some of you guys are curious, you can have a look at me STL files to understand my problem.

Any help would be deeply appreciated ! Thank you

Florian
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File Type: gz STLgeometry.tar.gz (4.8 KB, 3 views)
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Old   April 5, 2016, 08:54
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Alejandro García Soto
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You could try Blender.

It can import CAD geometry and export stl.

I think you have to activate an addon to do that, but is provided with the software anyway.
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Old   April 5, 2016, 09:54
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Florian Nguyen
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Hi Alejandro,

Thanks for your answer. I know that Blender is a great tool when it comes to editing CAD files, but I was wondering if anybody here was able to avoid this "CAD mesh editing" step and was able to directly generate a set of patches forming a closed volume directly from their CAD software. Designing directly in Blender is of course possible, but I find it to be far less convenient than with conventional CAD software.

Not having to manually edit one's geometry when it is supposed to be clean in the CAD design phase will make me save a lot of time.

I think I am getting closer to find a solution, and this might be very useful for many OpenFOAM new and veteran users, so I will share as soon as I can confirm that my method works.

If you have other suggestions, I am still listening !
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Old   April 6, 2016, 03:20
Default What CAD software do you use to define STL surfaces?
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Derek Mitchell
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I use freecad .16 to create the geometry in the gui or programmatically and then produce the stl
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Old   April 6, 2016, 04:41
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Florian Nguyen
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And with FreeCad you're able to define patches that form an overall watertight surface? Especially for circular shapes? I did try to use it a while ago, but I had difficulty defining complex geometries. I guess I didn't spend enough time trying to master it...
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Old   April 8, 2016, 04:06
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Derek Mitchell
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cylinders, ellipsiods spheres ... yep its all there in FreeCAD

I create the basic shapes as entries in a spreadsheet, use the spreadsheet to generate a script that creates the shapes and the operations, then tweak around in the GUI and use another script to generate the STL files. I'm using this for a CHTmultiregion problem with 13 regions and 20+ additional geometries for things like fvOptions and baffles. it includes geometries like the intersections between ellipses and ellipses and the ellipses and boxes and well the inverse of everything to realise the air region.
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Old   April 8, 2016, 04:35
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Florian Nguyen
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Thank you ! I'll go have a closer look.

Alternatively, Fusion 360 (by AutoDesk) can also be used. The surfaces remain consistent even when placed in separate STL files, and I was able to use SHM successfully using this method. One has to be careful when exporting the different surfaces, though.
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