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Message 1 of 7
drpalo
2095 Views, 6 Replies

Watertight warning

Currently working on a file & getting a lot of watertight problems. I always try to check layer 2, view bad CAD features & make sure multimatched/unmatched features are 0. Obviously there are things I'm missing if all these areas look good & I'm still having watertight problems. I'm assuming the only way to check for watertight problems is to solid mesh the model. It's frustrating that the only way to find this out is after it's been running all weekend, you come in monday morning, stop it & then it tells you it's not watertight. Looking at the attached file, I can't make everything beams, I have to have some CAD geometry. Any element/meshing tips for this specific situation and also element/meshing tips in general will be greatly appreciated.

 

Thanks.

Autodesk Product Design Suite 2016
Dell Precision T5610
HP Z800 Workstation
6 REPLIES 6
Message 2 of 7
xli
Alumni
in reply to: drpalo

 

Here are some ideas in general. From the figure attached, to model such structure with many thin parts, the best way is using plate/shell mesh or plate & solid combined model. Using plate/shell kind of element type will fit the structue's true geometry and avoid water-tight problems.

 

And we have a few meshers to choose for plate/shell (midplane mesher and SURFACE MESHER, ...). Although if you need to combine with solid parts you have to make sure the connection between shell and solid right. A few options you may use also. And as other people suggested, using tet mesh for the solid part may get fast and easy too. 

 

My best wish!

 

-xli

Message 3 of 7
drpalo
in reply to: xli

With a plate element you designate the thickness under the element definition correct? So I would need seperate parts for all of my CAD geometry. Right now the whole structure is one solid CAD part. I thought it would be so much easier to analyze that way. So as it sits, my only option is a brick or tet element correct?

Autodesk Product Design Suite 2016
Dell Precision T5610
HP Z800 Workstation
Message 4 of 7
xli
Alumni
in reply to: drpalo

I see your point: not like modifying any CAD geometry for FEA model abstraction. The midplane mesher would take 3D CAD geometry and mesh the shell/plate element on their middle plane. You may want to try this setting: pcik those element parts as plate and change the mesher to midplane in mesh UI. Then let's see what problem will follow.

 

-xli

Message 5 of 7
robinsmk
in reply to: xli

i have gone through the same problems. The issue I face here is that i tried thin cross section meshing option. Is it a good approach for bending? or should go with plate/ shell. When going with plate elements, am getting un realistic results. 

 

 

Message 6 of 7
S.LI
in reply to: robinsmk

To simulate thin sheets with solid elements (tet or brick) could result in locking for bending problems.

Shell/plate is helpful here, and for solid elements to enable mid-side nodes is also helpful.

 

 

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Message 7 of 7
robinsmk
in reply to: S.LI

thank you. But I have not seen a good explanation about Bricks and wedges (layered mesh of thin parts) . is it a good  alternative for plate elements? 

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