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bad polygon body shape and mesh in FEM

[ Edited ]

Hi,

 

Is there a reason why the bodies in FEM file looks bad compared to part file? In modelling the bodies look fine when I use update display. Gets bad when going from modelling to FEM. When meshing you can clearly see that this will generate bad mesh. How to avvoid this?

 

Edit: I am using glue mesh mathing in FEM file.

 

Edit2: I have tried to recreate bodies in FEM file many times, but that does not help. I have feeling that mesh mating is making big problems!

 

I am using NX10.

 

 

I have attached picture below showing the body with and without mesh.

 

 

5 REPLIES

Re: bad polygon body shape and mesh in FEM

Polygon bodies in the FEM are tesselated bodies. You are seeing differences due to the coarse nature of the polygon body tesselation and the refined nature of your mesh. Further, NX meshing will infer node locations on edges that are interpreted as analytical (i.e. circles, conics). You should try using the option to project nodes to CAD to get a better approximation of the CAD in the mesh. Another option is to use high resolution polygon bodies. In NX 10, both of these options are found in the Meshing Preferences dialog.

 

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

Re: bad polygon body shape and mesh in FEM

Hi. Thanks for reply.

 

I tried to mesh the body without using glue mesh mating. Then the mesh were perfect without any defects. For me it looks like the mesh mating is making problems? If I can not use mesh mating, I have to use glue in SIM file. I would like not to use glue in SIM file because this typically increase the local stiffness. I am preparing model for fatigue analysis and I need the nodes to be coincident with out any glued interfaces in the areas of interest.

 

I have recently found out there is way to merge the nodes together in FEM file, but then I got problems with mesh not associative to geometry. Is there a tutorials for how to merge the mesh together without using glue of mesh mating?

 

Thomas

Re: bad polygon body shape and mesh in FEM

Could you provide the part and the .fem of an example that contains the problem mentioned above? 

Re: bad polygon body shape and mesh in FEM

[ Edited ]

Hi,

 

No sorry. I will see if I can prepare a different model to share with the samme problem. Other problem is that the FEM file is approx. 100MB in size. Not sure if its possible to upload this size here.

 

Thomas

Re: bad polygon body shape and mesh in FEM

Hi Thomas,

I do not know if you solved your problem, but may be this can help.

I made the experience that mostly bodies with cylinder faces and "large circumference ratios" will provoke FEM meshes of lower quality due to the approximation with polygon bodies. Faces are no cicular but splitting the body into multiple sub bodies on part level mostly improves the mesh quality. We have also problems after stitching with those bodies. It can drives one mad.

But one thing I realized in my years with NX: The more one works accurately on part level the more one gets good or even better results in meshing. All actions with extending polygone bodies reduce quality of mesh afterwards.

Mesh mating is no problem.

 

Best wishes, Michael