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determination of initial gap between contact tips

Posted Sep 18, 2016, 10:37 a.m. EDT Structural Mechanics Version 5.0 6 Replies

Zeng Chao
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Hi,

I encountered a contact problem. The upper geometry is solid domain and the lower component is also solid domain, otherwise the intermediate component is fluid domain. The assembly of this geometry is " "union fluid-solid parts" and then "form assembly". The premise is that, I think, the contact problem is involved, "form assembly" is needed, fluid-solid interface should be de-doubled, first "union fluid-solid parts" is implemented.
If initially I set a tiny gap between contact tips, the first study step for solid mechanics module doesn't converge, even though I made various trials. But if I touch the contact tips in initial stage, it works well. But I didn't know the accuracy of this choice, whether it is reasonable or not.
Does anyone would interpret the difference for this difference and suggest one method for that?

Thanks in advance,

Zeng
6 Replies Last Post Sep 21, 2016, 5:45 p.m. EDT
Henrik Sönnerlind COMSOL Employee

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Posted: 8 years ago Sep 19, 2016, 4:59 a.m. EDT
Hi,

Note that an assembly is not a necessary prerequisite for a contact analysis. It only mandatory if the contacting parts are adjacent in the initial configuration (to avoid that they automatically form a union).

Regards,
Henrik
Hi, Note that an assembly is not a necessary prerequisite for a contact analysis. It only mandatory if the contacting parts are adjacent in the initial configuration (to avoid that they automatically form a union). Regards, Henrik
Zeng Chao
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Posted: 8 years ago Sep 19, 2016, 11:23 a.m. EDT
Dear Henrik,

Thanks for your comments. If the contacting pair will be always in contact with each other, but the compressive stress and contact area are time-varying. Is it reasonable to "form union" at geometry setup? And how about the setup of initial gap between them, connection or tiny gap?

Thanks,

Zeng
Dear Henrik, Thanks for your comments. If the contacting pair will be always in contact with each other, but the compressive stress and contact area are time-varying. Is it reasonable to "form union" at geometry setup? And how about the setup of initial gap between them, connection or tiny gap? Thanks, Zeng
Henrik Sönnerlind COMSOL Employee

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Posted: 8 years ago Sep 19, 2016, 2:18 p.m. EDT
Hi,

If they are always in contact, then you would in principle need an assembly to avoid that the get 'welded' in the sense that the shear forces will be unlimited.

If forming an assembly is a problem, then you can make a small slit in the geometry so that Union can be used, and then use the Offset option in the Contact node to control the (mathematical) distance. Using offset is also a good way to control the initial gap, irrespective of whether Assembly or Union is used.

Regards,
Henrik
Hi, If they are always in contact, then you would in principle need an assembly to avoid that the get 'welded' in the sense that the shear forces will be unlimited. If forming an assembly is a problem, then you can make a small slit in the geometry so that Union can be used, and then use the Offset option in the Contact node to control the (mathematical) distance. Using offset is also a good way to control the initial gap, irrespective of whether Assembly or Union is used. Regards, Henrik
Zeng Chao
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Posted: 8 years ago Sep 20, 2016, 12:32 p.m. EDT
I followed your advice and set the contact offset. The radius of adjacent sphere is R, the initial gap between them is set to a=0.01*R, then "form union" is used to assemble geometry. In Structural mechanics module, both destination contact offset and source contact offset are set to 0.01*a. I think it's really small compared to the radius of sphere. But when I run only structural mechanics, It still didn't converge. In segregation solver plot, contact pressure converge well, otherwise displacement suspend at 10^-2 a long iteration.
I didn't figure out the problem of this divergence. Is the value of contact offset reasonable in my setting?

I followed your advice and set the contact offset. The radius of adjacent sphere is R, the initial gap between them is set to a=0.01*R, then "form union" is used to assemble geometry. In Structural mechanics module, both destination contact offset and source contact offset are set to 0.01*a. I think it's really small compared to the radius of sphere. But when I run only structural mechanics, It still didn't converge. In segregation solver plot, contact pressure converge well, otherwise displacement suspend at 10^-2 a long iteration. I didn't figure out the problem of this divergence. Is the value of contact offset reasonable in my setting?
Zeng Chao
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Posted: 8 years ago Sep 21, 2016, 12:42 p.m. EDT
Does anyone give me more clue on it? Even the contact offset are set, the contact of adjacent sphere didn't converge.
Does anyone give me more clue on it? Even the contact offset are set, the contact of adjacent sphere didn't converge.
Zeng Chao
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Posted: 8 years ago Sep 21, 2016, 5:45 p.m. EDT
I posted the error plot in the attachment. Does anyone give any advice about it?
I posted the error plot in the attachment. Does anyone give any advice about it?

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