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Only part of hand-meshed model is used in simulation

8 REPLIES 8
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Message 1 of 9
bjorn_fallqvist
591 Views, 8 Replies

Only part of hand-meshed model is used in simulation

I have a problem with my Algor model; I have hand-meshed four solid parts to act as contact surfaces for other parts of the model, but in the simulation, only three quarters of these are used. I don't think it's going to be a problem, but I'm very curious as to why this happens?

 

I have attached images in the pre-processor and analysis itself. The model is, except for the contact brick element part, only beam elements and a truss element. Could it be related to the contact settings for some reason?

 

Thanks,

Björn

 

 

8 REPLIES 8
Message 2 of 9
S.LI
in reply to: bjorn_fallqvist

Hi, Björn,

 

What's the meaning of "only three quarters of these are used"? It looks like this in post-processor, or acts like this in processor?

 

To handle hand-draw mesh sometimes is more complicated than CAD mesh.

 

Thanks. 

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Message 3 of 9

Hi,

 

What I mean is that even though I have drawn a "box" of brick elements (as shown in the preprocessor picture), there is one sector of this part that is not used in the solving of the problem (post-processing picture).

Message 4 of 9
xli
Alumni
in reply to: bjorn_fallqvist

Björn,

 

If the missing part is manually made part, you might have missed all interior lines. So in preprocessing model what you see is only the external surface of the part. But missing interior lines (may due to copying etc. modeling error) make none of brick elements in that part is complicated. So no element is actually made.  It looked whole part is missing in post-processed model.

 

You may need to check how that part is made. 

 

regards,

 

-xli

Message 5 of 9

Hi Bjorn,

 

I see what you mean from the images you attached, but it is not clear whether the missing elements are on the same part number as the elements shown, or if they are on a different part number. So, here's a variety of things to check.

 

  1. Are they missing or hidden? Go to "Inquire > Model Statistics" to see if the proper number of elements are in the part.
  2. If the missing elements are reflected in the number of elements listed in the Model Statistics, right-click in the Results canvas and choose "Show all elements".
  3. If the missing elements are not in the Model Statistics, then one of these may be the problem:
  • The lines in the FEA Editor are not drawn properly to create elements.
  • The missing elements are on a new part number, most likely one number higher than the first analysis. If surface to surface contact is included in the analysis and the analysis was performed before adding the new part, then the Results thinks the new part is contact elements and therefore does not show them. In the FEA Editor, change the new part to a different part number (preferably higher than the part number used for contact elements in the previous analysis.)

No other thoughts come to mind at the moment. If these suggestions do not fix the problem, you may need to post the archive.

 



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


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Message 6 of 9

Hi John

 

The elements are missing, not just hidden. I've ensured that the lines are all in the same parts, and I can't find anything wrong with the part at all. I just created it using "copy/join" with selected lines.

 

Unfortunately I don't think I'm allowed to post the archive file, so I will need to look into it some more.

Message 7 of 9
xli
Alumni
in reply to: bjorn_fallqvist

Björn,

 

When you say the manual drawn part is copied/pasted from existing part (CAD), I think the problem is likely as my previously guessed: missing the interior lines. I attached a simple 2x2 brick case to explain what is external and interior lines. The red line is the internal line. You can see if it is missing, none of four bricks will make complete drawn and eventually they won't make brick elements.

 

In FEA editor, it actually only shows external lines for a CAD part. So you could have copied only external lines to the manual part. And that could cause your problem. Let us know if this is your problem. Other than this scenario, I only can image you may have some odd tolerance problem. Thanks.lines.png

 

-xli

Message 8 of 9
bjorn_fallqvist
in reply to: xli

Hi, Xli

 

I made the entire part from scratch. When I said I used existing lines to copy, they were lines which I made by the "draw lines" tool. I have also investigated if there seems to be any discrepancies inside the block, but I can't find anything.

 

Maybe it's some kind of tolerance bug (I'm using the 2012 Beta) as you said.

Message 9 of 9
xli
Alumni
in reply to: bjorn_fallqvist

Björn,

 

I just sort of reproduced your problem following the guess I had in previous email. As I said in default the CAD meshed part only shown its external mesh lines. If you just copied by selecting whole part to another part actually those interior lines are potentially all missing and resulting a no element made part eventually. The fix is turning on internal mesh option before you copy the CAD part. Then you will get all lines.

 

OK, as you said, your whole element part is sketched by hand. Then you need to be careful of following problems:

 

Make sure every drawing is use that "lock" symbol which connect new drawn line "exact" (snap) to existing lines. Otherwise two lines potentially are not snaped together, if every drawn element possible having one or more such lines, you may end up no element too. In such case, you may go to Draw:modify:"global snap" to snap all possible "broken" lines. That function sometimes work :-). Before glonal snap, make sure "set search tolerance" using a tolerance close to the minimum lines but just slightly smaller. And I assumed you are using the new Ribbon UI. If not, that global snap and setting tolerance is under Geometry:Utilities:

 

The other potential problem is in the drawing you have some extra lines, longer line cross over the mesh etc. Program would ignore them, but some case those illegal lines can cause problem. Drawing a FEA mesh by hands is always tough, it can drag you back 20 years :-). Let us know you findings.

 

-xli

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