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problem with the CAD imported model, can anyone help?

[ Edited ]

Dears, I took couple of days to model this structure with autocad, it's a real solid model. I exported the model as sat and imported to femap. I guess it was a quite complicate model to solve, so I integrate all components to one complete solid model and then use automatic middle surface generate function to simplify the model, everything looks good, what I can say is that the automatic function is perfect, you don't even do any input, just click the mouse, so easy.


After that, I choose material and automatically assign the thickness, then mesh the middle surface model as usual. Everything looks quite good. But when I tried to do the analysis, several fatal error message appeared. I tried many times to figure out what happened, it seems something wrong with during meshing, but I could not find the solution.


I am a newbie to femap and also have not many experience with fea, before I done few simple excesiss and never met such kind of error. Can anybody help me to see what happened and how to solve this problem. It may take time, appreciate indeed. The femap file is very big, more than 100Mb and could not upload here, I attached the autocad exported file here. Thanks again.



this is the sat model exported from autocad.

Accepted by topic author Gerry
‎02-22-2017 10:37 AM

Re: problem with the CAD imported model, can anyone help?

You have some very thin bodies in this model relative to the overall mesh size you used.  For a solid tetrahedral mesh with mid-side nodes, you would need a mesh size about 60 percent (60 %) of the thinest wall in order to get at least two (2) elements thickness through those sections.


What happened with your model is that you exceeded the NX Nastran limits for aspect ratio (ratio of the longest element edge to the smallest element edge on a single element) that caused NX Nastran to fail.

For a model of this type, you should consider using a combination of Shell and Beam elements or Shell and Solid elements with the shell elements in the thinest wall parts.

Best Regards,
Chip Fricke
Principal Applications Engineer - Femap Product Development

Re: problem with the CAD imported model, can anyone help?

Many thank buddy, althrough I may not capable to solve this issue by myself at this moment, but your really give me a direction, it's a valuable experience to a newbie. thanks again.