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stability of geometry creation

Posted Feb 4, 2013, 10:03 a.m. EST Geometry Version 4.3a 5 Replies

GuRu@BFI
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Suppose that the geometry is not simple enough to be represented by regular geometry primitives.
Then, there are two chooses:
1- use of parametric surfaces (possible as external function)
2- use of import geomerty (i.e. STL file which is externally created)

use of parametric surfaces are in my case relatively slow. So I concentrated on STL import.
I externally create STL file (a surface defined by triangles). I can convert it to a solid in comsol. But I cannot use this solid in difference or union operation later on in a stable manner. I almost always get a domain decomposition error.

In general, even for standard models, one needs to play with the relative repair tolerances to get to desired final geometry (which is not practical it is an automated model). If the geometry creation fail, all automated model fails.

Did anyone of you had similar problems? Any solution suggestions?
Does comsol have any plan to improve the stability of geometry creation?

regards,
dr.ing.- yalcin kaymak
5 Replies Last Post Feb 6, 2013, 3:19 p.m. EST
Josh Thomas Certified Consultant
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Posted: 1 decade ago Feb 5, 2013, 10:01 a.m. EST
Yalcin-

Building geometry within COMSOL is always going to be the most stable, but if you do need to import there are some best practices.

My experience is similar to yours for importing STL files. Since STL is not actually solid geometry rather surfaces (like you pointed out) there is a conversion to solid operation that is needed. This conversion doesn't always work for complex geometries and even if it does you may not be able to operate on the geometry further downstream.

If you need to import, I would recommend generating your solids in a 3rd party CAD or Direct Modeler software and then importing in Parasolid format or the native file type. With the CAD Import Module, COMSOL can run on a Parasolid kernel which is very stable and robust for importing as well as performing future modifications within COMSOL. If your file is a Parasolid format, then no conversion is needed which means less errors.

Also, stay away from IGES format if possible.

Best regards,
Josh Thomas
AltaSim Technologies

Yalcin- Building geometry within COMSOL is always going to be the most stable, but if you do need to import there are some best practices. My experience is similar to yours for importing STL files. Since STL is not actually solid geometry rather surfaces (like you pointed out) there is a conversion to solid operation that is needed. This conversion doesn't always work for complex geometries and even if it does you may not be able to operate on the geometry further downstream. If you need to import, I would recommend generating your solids in a 3rd party CAD or Direct Modeler software and then importing in Parasolid format or the native file type. With the CAD Import Module, COMSOL can run on a Parasolid kernel which is very stable and robust for importing as well as performing future modifications within COMSOL. If your file is a Parasolid format, then no conversion is needed which means less errors. Also, stay away from IGES format if possible. Best regards, Josh Thomas AltaSim Technologies
GuRu@BFI
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Posted: 1 decade ago Feb 6, 2013, 11:49 a.m. EST
Thanks Josh for your valuable comments. What does that mean "Parasolid format or the native file type". Are there any open source or free tools to create a geometry parasolid format? Basically I have a surface triangulation as starting point. Can I convert this triangulation (ie STL file) to a parasolid format using a command line function. Ultimately, I want to perform an optimization (probably, will need to compute ~100 different STL files).

OK. I have read about parasolid kernel. So I need a tool to generate my parasolid file from my stl file. and additinally I need a comsol cad import module. What is the best ways (softwares) to create the parasolid file. are there any opensource tools?
Thanks Josh for your valuable comments. What does that mean "Parasolid format or the native file type". Are there any open source or free tools to create a geometry parasolid format? Basically I have a surface triangulation as starting point. Can I convert this triangulation (ie STL file) to a parasolid format using a command line function. Ultimately, I want to perform an optimization (probably, will need to compute ~100 different STL files). OK. I have read about parasolid kernel. So I need a tool to generate my parasolid file from my stl file. and additinally I need a comsol cad import module. What is the best ways (softwares) to create the parasolid file. are there any opensource tools?
GuRu@BFI
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Posted: 1 decade ago Feb 6, 2013, 12:17 p.m. EST
?
?
Josh Thomas Certified Consultant
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Posted: 1 decade ago Feb 6, 2013, 12:49 p.m. EST
Yalcin-

There are a number of tools on the market but I am not aware of any that are open source. A simple internet search on Direct Model Modeler Software will identify a number of options.

Regards,
Josh
Yalcin- There are a number of tools on the market but I am not aware of any that are open source. A simple internet search on Direct Model Modeler Software will identify a number of options. Regards, Josh
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 6, 2013, 3:19 p.m. EST
Hi

Parasolid is a propretary kernel, but the STEP format should be open source, I believe. Both are true 3D topology valid formats, while STL and DXF (even DWG) are not really good for geoemtry transfer, as the format is too floppy (or rather there are too many floppy implementations. Its like HGL it was more a txt plotter command language, originally

--
Good luck
Ivar
Hi Parasolid is a propretary kernel, but the STEP format should be open source, I believe. Both are true 3D topology valid formats, while STL and DXF (even DWG) are not really good for geoemtry transfer, as the format is too floppy (or rather there are too many floppy implementations. Its like HGL it was more a txt plotter command language, originally -- Good luck Ivar

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