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konradl
Posts: 12
Registered: ‎03-03-2011

Meshing problem - Bolted Joint - Holes not watertight

1313 Views, 5 Replies
03-27-2012 06:35 AM

I have tried to mesh my crane model for quite some time now. I have made a smaller version with just one flange and just a part of the top part and the leg part (which works perfectly), but i need to make a big version now and i have a hard time getting a good mesh.

 

First i use the Bolt command and place bolts in all the holes on both flanges (54 mm head and nut diameter, 36 mm bolt diameter, 750 000 N axial force preload, 12 spokes). Then i set Surface Contact between the flanges.

The problem arises when i try to mesh it. Just pushing the mesh button generates numerous water tight-problems in the bolt holes. And half of the Bolts generated by the Bolt command failes, it says something about the bolt head diameter being smaller than the hole diameter (which is not true at all since the holes are 38 mm). I was kinda hoping that it would have to connect the mesh edges to the spokes of the generated bolts, leading to a fine mesh around each hole automatically, since i chose 12 spokes. But i was wrong i guess. :smileyhappy:

Most often the water tight problems are located in the bolt holes on the leg parts, so i just set a finer mesh on those two parts. It still does 6 retries but successfully meshes the parts, the problem is that the mesh is so fine that it bogs down the computer, i can't imagine the time it would take to try to do a analysis on such a fine mesh.

 

So i begin again (i havn't been able to find a way to clear an allready generated mesh so i just close ASIM down and delete the files).

 

I figure that all i need is fine mesh around the holes, so i load the model, mesh it at 100%, accept the not-watertight-errors, use the Rectangle Select tool together with Select Vertices and select all the vertices in the flanges, then i apply Refinement Points to the selected nodes. Since the holes are 38 mm diam i have tried to set node size to 20, 15 and 10 mm. But when i do this the Meshing takes AGES to complete for some reason, so i cancel it (meshing shouldn't take 5+ minutes, at least not for such a simple model like this).

 

I just want a rough mesh everywhere except around the flanges, i just can't figure out how to do it correctly in this big model.

 

I have attached the model as a .DWG if you would like to try to mesh it. :smileyhappy:

 

 

This is what i get, it looks kinda ok, i would like to have less detailed mesh on the top part, but i guess i can live with that. This is meshed model has several not-water-tight-problems, and they are pretty much random each time i mesh. :/

Crane.png

 

 

 

 

Thank you! :smileyhappy:

Konrad Lindblad
Mechanical Engineering
Royal Institute of Technology
Sweden
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INACTIVE_AstroJohn
Posts: 492
Registered: ‎03-25-2010

Re: Meshing problem - Bolted Joint - Holes not watertight

03-27-2012 08:57 AM in reply to: konradl

Hi Konrad,

 

Try to turn off the option "Mesh > Mesh > Use VCAD". This should fix the problem with the bolts distorting the holes.

 

You do not need to delete the existing mesh before changing the mesh parameters. Just make the changes and mesh the model.

Sincerely,
John Holtz, P.E.
Senior User Experience Designer, Simulation
Autodesk, Inc.

Current version of Mechanical & Multiphysics: 2013 SP1 (2013.01.00.0012 28-Jun-2012)
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Contributor
konradl
Posts: 12
Registered: ‎03-03-2011

Re: Meshing problem - Bolted Joint - Holes not watertight

03-28-2012 01:57 AM in reply to: INACTIVE_AstroJohn

Hi John,

 

disabling VCAD solved the not-water-tight problem, but meshing at 100% it had to retry 6 times for each part, making the mesh really fine. And when i try to run the simulation i get an error stating: The Model contains errors due to geometry problems. Do you wish to view those errors?

 

This is what it shows when i click Yes:

 

fem2esh - Make esh file from fem file for a specified design scenario
Version 2012.01.00.0017-W64/X64 15-Jun-2011
Copyright (c) 2011, Autodesk, Inc. All rights reserved.

  Version of fem2esh.exe          : 2012.01000017
  Version of dcx1-win-x64.dll     : 2012.01000017
  Version of femapi-win-x64.dll   : 2012.01000017
  Version of agsdb_ar-win-x64.dll : 2012.01000017
  Version of tsx2tsy.exe          : 2012.01000017

  Input Model     : C:\Users\ladmin\Desktop\FEM\Full Simulation\Full2.ds_data\1\ds
  Input File      : C:\Users\ladmin\Desktop\FEM\Full Simulation\Full2.fem
  Output File     : C:\Users\ladmin\Desktop\FEM\Full Simulation\Full2.ds_data\1\ds.mod\group.esh
  Log File        : C:\Users\ladmin\Desktop\FEM\Full Simulation\Full2.ds_data\1\ds.mod\group.ldx
  Design scenario : 1
  Analysis type   : Linear Stress
  Start time      : 2012/03/28-10:48:53  

  --- Get 4 active element parts in range [1, 4] from fem file
  --- 60 enabled L&C groups are defined
  --- Get 355801 points defined in range [1, 360561] from fem file
  Calling the Surface Topology Generator (tsx2tsy)...
  tsx2tsy: re-made part surface contact/bonding data (duration=2 sec.)
  --- No mid-side node required
  Set up FEM points and B.C. by connected elements...

  In working on FEM file or outputting ESH file
  Terminal Error: FEM2ESH#63, FEMAPI#1
    NO_3D_ELEMENT: please check meshing phase
2012/03/28-10:48:55

 

(I have tried setting the contact to Bonded between the parts but it still doesn't work.)

 

 

Any ideas?

This is what it looks like right now:

 

Crane3.png

 

Crane4.png

Konrad Lindblad
Mechanical Engineering
Royal Institute of Technology
Sweden
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Employee
INACTIVE_AstroJohn
Posts: 492
Registered: ‎03-25-2010

Re: Meshing problem - Bolted Joint - Holes not watertight

03-28-2012 06:44 AM in reply to: konradl

Regarding the error message, it is implying that some part is set to be brick elements, but the mesh is not appropriate for 3D bricks. So two ideas that come to mind are:

  1. Check the mesh results and confirm that the parts were solid meshed. ("Mesh > Mesh > View Mesh Results") The solid mesh is normally created when you use either "Check Model" or "Run Simulation". If it was not created, you can start the solid mesh manually by selecting the parts to mesh, right-click >
  2. Check the element type for each part to make sure that is set correctly.

 

Regarding the retries, you could try the following:

  1. Reduce the number of retries, perhaps even to 0. I have seen a few cases where the software does retries even though it is not absolutely necessary. ("Mesh > Mesh > 3D Mesh Settings > Options > Surface > Number of retries")
  2. If you disable all retries, be sure to set the mesh size to something reasonable.

 

Sincerely,
John Holtz, P.E.
Senior User Experience Designer, Simulation
Autodesk, Inc.

Current version of Mechanical & Multiphysics: 2013 SP1 (2013.01.00.0012 28-Jun-2012)
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New Member
joshua.parks
Posts: 1
Registered: ‎05-06-2013

Re: Meshing problem - Bolted Joint - Holes not watertight

05-06-2013 05:08 AM in reply to: INACTIVE_AstroJohn

Hello John,

 

I'm having a similar error, and I was hoping you could tell me how you were able to identify the problem is having brick elements just by looking at the error? 

 

I ask becuase I'm writing our FEA standard at my company, and I have a seciton I'm building up of FEA errors (what they are and how to handle them).  I assume there's a syntax that tells you that this problem is brick elements, but I was hoping you could elaborate. 

 

To give you a flavor, the specific error we recieved the other day was this:

 

Terminal Error:  FEM2ESH#63. 

NO_3D_ELEMENT:  please check meshing phase 27

 

It looks very similar to the error reported above, so again, I was hoping you could break down the syntax for me so I could explain it in our standard.

 

Thanks

 

 

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Valued Mentor
AstroJohnPE
Posts: 494
Registered: ‎08-30-2012

Re: Meshing problem - Bolted Joint - Holes not watertight

05-07-2013 05:53 PM in reply to: joshua.parks

The way that Simulation Mechanical works is the pre-processor (the FEA Editor tab) only operates on lines. The solvers (when you click the Run Simulation command) cannot do anything with the lines themselves, so there is an intermediate step that converts the FEA Editor’s lines into elements that the solver (and the Results tab) can work with. This is what happens if you use “Analysis > Analysis > Check Model” or during the “verifying geometry” step of running the simulation.

 

So, your error message (in the file DS.LDD if I remember correctly) occurs during this intermediate step. The only thing in the error message that makes sense to me is “No 3D element”, meaning that the software was trying to convert the lines into 3D elements (brick, 3D, or tetrahedron elements). If the part number that caused the failure was 63 or 27, that would explain the two numbers that appear in the message. Otherwise, the rest of the error message is only intelligible to the developers at Autodesk.

 

I am looking forward to reading your book when you are done. :smileyhappy:

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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