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Limiting simulation volume/area or displacement for mechanical model
Posted Feb 11, 2013, 10:33 a.m. EST Structural Mechanics Version 4.3a 1 Reply
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Hey,
while doing a buckling study of an optical fiber I tried including a fixed box around the fiber to constrain the movement of the fiber within this box. Sadly this increases the required simulation time a lot so I replaced the box with 'beams' that would effectively constrain the fiber between the beams.
When converging (the model seems quite unstable for certain parameter values) I noticed that, eventhough I specified contact pairs between the fiber and the inner boundaries of the constraining beams, the simulation tends to give me a result where the fiber ignores the beams and buckles in another direction.
It seems the fiber ignored it's contact pairs with the beams and somehow went through them.
So I was wondering if there is a way to limit the displacement/deformation of an object, in a 3D stationary mechanical model.
If this "box-approach" is the only way to do this: is there a way to either reduce the simulation time by telling COMSOL that you're not interested at all in what happens with the objects that form this constraining box, or make sure the contact pairs are respected during a deformation.
thanks
Evert
while doing a buckling study of an optical fiber I tried including a fixed box around the fiber to constrain the movement of the fiber within this box. Sadly this increases the required simulation time a lot so I replaced the box with 'beams' that would effectively constrain the fiber between the beams.
When converging (the model seems quite unstable for certain parameter values) I noticed that, eventhough I specified contact pairs between the fiber and the inner boundaries of the constraining beams, the simulation tends to give me a result where the fiber ignores the beams and buckles in another direction.
It seems the fiber ignored it's contact pairs with the beams and somehow went through them.
So I was wondering if there is a way to limit the displacement/deformation of an object, in a 3D stationary mechanical model.
If this "box-approach" is the only way to do this: is there a way to either reduce the simulation time by telling COMSOL that you're not interested at all in what happens with the objects that form this constraining box, or make sure the contact pairs are respected during a deformation.
thanks
Evert
1 Reply Last Post Feb 12, 2013, 3:07 p.m. EST
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Posted:
1 decade ago
Hi Evert,
The default search method for contact is “Fast”. I found in some cases this leads to contact being missed, and to avoid that I switch to “Direct” search. You can change that from the Advanced Tab defining the Contact Pair.
I’m not sure I understand what you mean by limiting displacement/deformation but I believe there is no feature to specify an upper limit on the displacement during an iteration (which would be useful for some nonlinear problems). However, the relatively new “Double Dogleg” solver that is now the default algorithm for contact problems is based on a trust region method. Trust region methods in general limit the maximum displacement during a solver iteration. That limit only applies per iteration though, so overall you can still get large displacements.
Nagi Elabbasi
Veryst Engineering
The default search method for contact is “Fast”. I found in some cases this leads to contact being missed, and to avoid that I switch to “Direct” search. You can change that from the Advanced Tab defining the Contact Pair.
I’m not sure I understand what you mean by limiting displacement/deformation but I believe there is no feature to specify an upper limit on the displacement during an iteration (which would be useful for some nonlinear problems). However, the relatively new “Double Dogleg” solver that is now the default algorithm for contact problems is based on a trust region method. Trust region methods in general limit the maximum displacement during a solver iteration. That limit only applies per iteration though, so overall you can still get large displacements.
Nagi Elabbasi
Veryst Engineering