Volume sweep and export to a usable CAD format for subsequent analysis.

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szam619

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Jan 13, 2021, 3:21:38 PM1/13/21
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Dear Onur,

First, a big thanks from my work group at my university (RWTH Aachen, Germany) for creating this pure Python package. It has been fun to work with so far, and the codes are quite robust.
I am working with it for the modelling of a single layer textile weave structure for the final export to a CAD format directly usable by an FEA software. So far, I have managed to construct a weave structure through interpolation, and to construct yarns through the sweeping of cross-sections along these interpolated curves. 
In the process, I modified the existing "sweeping" function in your library to return the new location of the swept cross-section after it has been translated to the next evaluated point of the curve. Then I iteratively use this sweeping along each of the evaluated points as vectors to construct the complete surface/volume along the curve. 
Now there are two key problems I have been facing at the moment:
  1. Export of created volume - I am not an expert on the CAD file architectures, but I understand from your documentation that so far we only have the exchange type ".vmesh" to export the created volumes. I have been unable to use this exported file in general CAD viewers/manipulators (ParaView, Abaqus, Solidworks, etc.). If you, or someone here can advise on the above, I would be really thankful. 
  2. Export of ".stl" surface - I have been able to export and view the ".stl" surface, but it just takes too much time (~5 minutes) to export just a single body of scale ~5 mm. I might be doing something inefficient there (including limitations of my laptop during the work-from-home ordeal), but advices are welcome while I try to fix the problem myself.
I understand that you are working on the possibilities to export to ".iges" and ".stp" files as well, and it would be amazing to have that soon for my project. Then again, it would be amazing for quite a good number of the users here I suppose. 

Regards
Saurabh Sharma

Onur Bingol

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Jan 14, 2021, 3:53:21 AM1/14/21
to nurbs-python
Hi Saurabh,

Thanks for your email. I am glad you and your research group liked geomdl.

Sorry for the confusion about the "vmesh" file format. "mesh" and "vmesh" file formats are custom formats for the in-house libraries that I used during grad school. I am aware that there is actually an official "vmesh" format, but geomdl does not support that one.

To speed up the stl export, you may decrease the sample size (via sample_size property of the Surface class) or increase the vertex_spacing value of the exchange.export_stl function.


Currently, there is no STEP support (I have a long-term plan to support it, though). However, there is an option to convert geomdl JSON output to 3dm (OpenNURBS/Rhino file): https://github.com/orbingol/rw3dm

I haven't implemented volume import/export for .3dm, I couldn't find a good example to understand how OpenNURBS stores the volume data. I've tried to use On_NurbsCage class, but it somehow didn't work. It has been some time since I last tried to extract volumes from a .3dm file, so I can't remember what the problem was. However, I'd like to try again if I can find a .3dm NURBS volume and also some tips on the data structure.

If you have access to Rhino, you could convert the data into different file formats after using rw3dm.

Thanks,
Onur




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