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Solid Mechanics-Rigid Connection

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Hi all, I am also new to COMSOL and just trying to recreate a classic example, found by Bleich of the displacement of a ship superstructure.
I just want to add a boundary condition that says the displacement on one face in plate 1 is equal to the displacement on the face of plate 2 that is contact with plate 1. Basically, I want to fuse the plates together so that their displacements are equal. Is that possible?
I've tried using Rigid Connector, but it wasn't converging. Do I need to explore contact or pairs options?
Thanks,
Sam


4 Replies Last Post 25.04.2011, 23:46 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 25.04.2011, 04:10 GMT-4
Hi

if you two plates are in contact (common boundary, and you use the default "union" geometry "Finish" mode, then you have by default "continuity of the displacements between both items.

Rigid Connector is a tricky one, be sure you really understand what it's doing, it's not only adding nice BC possibilities such as torque/moment loads but it also makes the Boundary fully stiff, that is not always the desired effect

Another issue, try to avoid Point and Edge loads in 3D, as these re singularities and destroy the useful stress analysis and use only distributed loads (Domain = volume i.e. gravity or volume forces or Boundary = surfaces loads i.e. distributed pressure or total Force => pressure = average force/Area applied

But you might want to do a periodic (or anti-periodic link, from what I suspect of your model), then I would rather use pairs, or coupling variables, check the doc

Finally, an advice, update to latest patch (# 3 by today) as there are a few internal formula issues in the old one you use

--
Good luck
Ivar
Hi if you two plates are in contact (common boundary, and you use the default "union" geometry "Finish" mode, then you have by default "continuity of the displacements between both items. Rigid Connector is a tricky one, be sure you really understand what it's doing, it's not only adding nice BC possibilities such as torque/moment loads but it also makes the Boundary fully stiff, that is not always the desired effect Another issue, try to avoid Point and Edge loads in 3D, as these re singularities and destroy the useful stress analysis and use only distributed loads (Domain = volume i.e. gravity or volume forces or Boundary = surfaces loads i.e. distributed pressure or total Force => pressure = average force/Area applied But you might want to do a periodic (or anti-periodic link, from what I suspect of your model), then I would rather use pairs, or coupling variables, check the doc Finally, an advice, update to latest patch (# 3 by today) as there are a few internal formula issues in the old one you use -- Good luck Ivar

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Posted: 1 decade ago 25.04.2011, 17:08 GMT-4
Thanks for the response.
I use the the Rigid Connector because I want to restrict the motion of the plates along certain axes (x,y) but not the z axis. Is there a way I can do this without using the RC?
Thanks for the response. I use the the Rigid Connector because I want to restrict the motion of the plates along certain axes (x,y) but not the z axis. Is there a way I can do this without using the RC?

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 25.04.2011, 17:22 GMT-4
Hi

yes the prescribed displacement is there for that, one of the nice things with the RBC is the access to the rotation angle in a quaternion formulation hence, also valid for large angles

--
Good luck
Ivar
Hi yes the prescribed displacement is there for that, one of the nice things with the RBC is the access to the rotation angle in a quaternion formulation hence, also valid for large angles -- Good luck Ivar

Nagi Elabbasi Facebook Reality Labs

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Posted: 1 decade ago 25.04.2011, 23:46 GMT-4
You can “fuse” two surfaces such that their displacement is the same in X, Y but not Z, by defining a Boundary Similarity Model Coupling. Define one surface as the Source and the other surface as the Destination. If we call this coupling operator bndsim1, then you add a prescribed displacement on the Destination surface with u=bndsim1(u), v=bndsim1(v), and leave the Z direction free.

Nagi Elabbasi
Veryst Engineering
You can “fuse” two surfaces such that their displacement is the same in X, Y but not Z, by defining a Boundary Similarity Model Coupling. Define one surface as the Source and the other surface as the Destination. If we call this coupling operator bndsim1, then you add a prescribed displacement on the Destination surface with u=bndsim1(u), v=bndsim1(v), and leave the Z direction free. Nagi Elabbasi Veryst Engineering

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