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Element Quality check for TET 10

Hi everybody,

 

when using the defined element quality check of Siemens NX 11, I get problems when solving the written solution with NX Nastran.

 

In the case of TET 4 elements, the internal element quality check works without problems. Elements with error are recognized and a calculation process can not be performed for a model with incorrect elements.

 

 I have problems doing the same with TET 10 elements. An internal network check detects, for example, incorrect elements, but the calculation process can still be carried out in most cases. Is there a possibility to create meshes or to check that the calculations can always be carried out?

 

Thanks for your help.

 

Best regards

 

Werner

1 REPLY
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Accepted by topic author Werner
‎03-15-2017 09:26 AM

Re: Element Quality check for TET 10

Werner,

 

What do you mean by "internal network check"? Is this referring to an element quality check done by NX? If so, do you get the incorrect elements warning just after meshing or as part of your own use of the Element Quality Checks command?

 

The element quality checks in NX are solver specific. Development of the checks performed by the command included review of solver documentation to see how each solver computes element quality. So, the checks vary according to the solver you are using.

 

For NX Nastran, the NX Nastran development team provided routines that match exactly the element quality checks done there. So, the pre-processing check in NX should match the check done in NX Nastran if you are using the same thresholds. For NX Nastran parabolic tetrahedron elements, you mainly need to be concerned about 2 things:

 

1. Aspect ratio greater than 100

2. Jacobian values less than zero

 

Edge point length ratio is another check that can lead to failures, but that tends to be rare.

 

I get the sense that you received a false negative regarding element quality. The pre-processor told you there were bad elements, but the solver used them anyway with no issue. Since I don't know where you are getting this warning, or the thresholds being used, I'm not so concerned about the warning. I've ignored mesh quality warnings from the mesher in the past because I realized that the mesher wasn't using the worst case thresholds. Honestly I don't exactly know what thresholds the meshers use when reporting failing elements. They are supposed to use the settings defined at the time in the element quality checks command.

 

My best advice to you is to check your parabolic tetrahedron meshes with the above thresholds. If your mesh passes those checks, you are very likely to get an NX Nastran solve to pass the element quality phase.

 

Regards,

Mark

 

Mark Lamping

Simulation Product Management

Simulation and Test Solutions

 

Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

 

mark.lamping@siemens.com

www.siemens.com/plm