"contact" beam mesh

[coasterchris]

Hi,

Here's a question regarding a beam meshtype.
I'm trying to simulate the maximum displacement and stress of an arch shaped structure to be able to define the best way and place of stiffening the structure with tension lines.

The thing being, that because of the shape, the archway tends to deflect into an opposing part.

The question is, is there a possibility to make a "contact set" type interaction between the two parts, like what can be done with a solid mesh.
My guess is that this won’t be possible, seeing as the fundamentals of the meshtype don’t make it possible to recognise touching of parts seeing as it has no "faces".

Hopefully someone could give me a hand with this one.

Model:

http://files.engineering.com/getfile.aspx?folder=558b385a-8e3a-4761-b4da-19c4f0ed4124&file=arch.bmp

Beam mesh:

http://files.engineering.com/getfil...a7b-41b5-ae9c-c0f4b83b6162&file=Beam_arch.bmp

 

[GregLocock]

Even if you could, it would slow the model down a lot.

However I'd have thought that pretzeling is exactly one of the failure modes you are trying to prevent, soartificially suppressing it seems iunproductive.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kellnerp]

GregLock

The model is not pretzeling. That's the scaling on displacements you are seeing. The biggest deflection is .05mm.

CoasterChris

One of the things experienced FEA analysts do is use symmetry. Place boundary conditions that mimic the other side.

Contact occurs between nodes even when using surface to surface contact. The element only knows what is going on at the nodes and when surface to surface contact is used the software internally creates forces on the nodes involved in contact.

Are those really beam elements or is it just a solid mesh of a bunch of tubes?

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[GregLocock]

" the archway tends to deflect into an opposing part"

sure sounds like pretzeling to me.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kellnerp]

Look at the scale and the displacements. Yeah it is moving towards it. But I rather doubt there is contact. Let's ask the OP to plot it with a scale of 1 and look at the displacement only in the direction where they may contact. Bet you'll see a different picture then.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[GregLocock]

Well if it is just a visual artefact then there is no contact to suppress, is there?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kellnerp]

Greg,

Look at the plot. My guess is that this is a roller-coaster support. Don't know what gives me that thought, maybe the OP's handle. So that tube may stand ten or more feet in the air. If you look carefully at the very top in the displaced plot the two sides are not attached to each other. This wouldn't be so in the actual application because whatever applies loads to these towers would hold them together. Yet the two triangular sections at the top are embedded in each other, but the legend on the right says they only moved .0007in.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[GregLocock]

Sure. but if the contacts are just near the top they'll have no effect on the displacement further down.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kellnerp]

Not contacts, just displacement boundary conditions at the very top. This structure holds something up and that something is going to hold the columns apart in a very rigid manner. We still need the OP to plot the displacement at a scale of 1.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[coasterchris]

Thanks again for your kind replies.