FEM of a simple table over two legs.

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GAZ082
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FEM of a simple table over two legs.

Post by GAZ082 »

Hi there. I have a table, with two legs. How can I FEM the table which is over the legs? Please note the table is not fused with the legs but just sits on top. The table should bend and the both ends over the legs should raise a bit.

Tried to create a part for the table, two more for the legs, set the base face of the legs as locked, no luck.


Any tip is welcomed! Thanks!
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chrisb
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Re: FEM of a simple table over two legs.

Post by chrisb »

Moved to FEM forum.
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NewJoker
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Re: FEM of a simple table over two legs.

Post by NewJoker »

You have to mesh those parts separately and connect them somehow. Either using tie constraint (perfect bonding) or contact (more realistic if the parts aren't glued but not so easy to model due to convergence issues). I would start by modeling this as a single part or applying tie constraint and then try with contact.

Consider using shell elements for this model, it's quite thin-walled.
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Re: FEM of a simple table over two legs.

Post by johnwang »

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NewJoker
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Re: FEM of a simple table over two legs.

Post by NewJoker »

But first you will have to use BooleanFragments tool because multiple mesh analysis is not supported.
GAZ082
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Re: FEM of a simple table over two legs.

Post by GAZ082 »

Thanks for the tips guys, will try with the tie constraint which adds minimal modification to my workflow. I'm rather new to FC and still haven't gone deep with meshes.
GAZ082
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Re: FEM of a simple table over two legs.

Post by GAZ082 »

NewJoker wrote: Sat Sep 18, 2021 8:36 am You have to mesh those parts separately and connect them somehow. Either using tie constraint (perfect bonding) or contact (more realistic if the parts aren't glued but not so easy to model due to convergence issues). I would start by modeling this as a single part or applying tie constraint and then try with contact.

Consider using shell elements for this model, it's quite thin-walled.
Hi NewJoker,

Used BooleanFragments in the model, and meshed it. Then Tied the parts. Generated the inp file, ran Calculix and throw an error: "

Code: Select all

13:49:18  FEM: No nodes found in Frd file.
13:49:18  Problem on frd file import. No nodes found in frd file.
13:49:18  FEM: No result object in active Analysis.
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NewJoker
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Re: FEM of a simple table over two legs.

Post by NewJoker »

Actually, tie constraint is not needed in this case because there's no gap between the surfaces (that's how it currently works in FreeCAD). So you can delete them and the analysis will complete. I would just refine the mesh, it shouldn't be so coarse.
GAZ082
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Re: FEM of a simple table over two legs.

Post by GAZ082 »

Mmmh, not quiet what i expected. The mesh is still a single body, the corners of the table should be lifting a bit from the legs. I even applied the force not on the whole table but in a surface on the center to make the effect more noticeable, no luck:

Image

Cant attach the sample, looks like the denser G Mesh is making the file larger, above the forum's attachment limit.
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NewJoker
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Re: FEM of a simple table over two legs.

Post by NewJoker »

The mesh will be continuous unless you separate the parts by some distance and define contact (this limitation is described for example here: https://forum.freecadweb.org/viewtopic.php?f=18&t=62307). But that would probably cause convergence issues. I'm afraid that it will be hard to achieve such an effect (tabletop pulling away from the legs) in FreeCAD. You might need another CalculiX preprocessor for that.

Btw. you can utilize symmetry here to simplify the model and make it easier to apply more sophisticated boundary conditions.
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