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Strange Problem within Structural Mechanics time dependent study

Posted Jan 16, 2012, 7:15 p.m. EST Structural Mechanics Version 4.2a 4 Replies

Roy Martin
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I am looking for some feedback on the attached model.

The attached 2d model is of a simple lever swinging under its own weight. Lever starts horizontal and its weight should start it to pivot down. This model was the first step to make sure I set things up correct before adding more complexity.

However, the model below has the linkage grow as it swings down. I.e. the linkage expands in size as it swings down under its own weight. I'm stumped as to why this is happening. So if someone could point out what is happening, I would greatly appreciate it.

Thanks,

Roy Martin

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4 Replies Last Post Jan 17, 2012, 7:25 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 17, 2012, 2:54 a.m. EST
Hi

indeed slightly astonishing, in fact the ending point remains at x=1, so as you have not selected "large deformations" (include geometric non-linearities), in the solver settings I believe this is "on purpose", or by equations (but large deformations does not change it either)

But then with "large deformations" the solver is not happy, so one need far more subtle tweaking with the solver settings and probably you need an ALE around your fixation circle, to allow the mesh to rotate with the part

Also in this case I would propose to split the bar and use a structured mesh with 3-5 elements in the thickness, this will allow to limit the ALE just to the rotating tip, but then I get grow of stress on the rotating bar I/F

FEM is not really set-up "as is" for "multibody" ;)

--
Good luck
Ivar
Hi indeed slightly astonishing, in fact the ending point remains at x=1, so as you have not selected "large deformations" (include geometric non-linearities), in the solver settings I believe this is "on purpose", or by equations (but large deformations does not change it either) But then with "large deformations" the solver is not happy, so one need far more subtle tweaking with the solver settings and probably you need an ALE around your fixation circle, to allow the mesh to rotate with the part Also in this case I would propose to split the bar and use a structured mesh with 3-5 elements in the thickness, this will allow to limit the ALE just to the rotating tip, but then I get grow of stress on the rotating bar I/F FEM is not really set-up "as is" for "multibody" ;) -- Good luck Ivar
Roy Martin
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Posted: 1 decade ago Jan 17, 2012, 6:56 p.m. EST
So, how would you model a pendulum? i.e. have a pinned condition at one end of the lever?
So, how would you model a pendulum? i.e. have a pinned condition at one end of the lever?
Roy Martin
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Posted: 1 decade ago Jan 17, 2012, 6:58 p.m. EST
ahh, never mind, I notice the physical pendulum model in the model exchange. I'll give that a try...
ahh, never mind, I notice the physical pendulum model in the model exchange. I'll give that a try...
Roy Martin
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Posted: 1 decade ago Jan 17, 2012, 7:25 p.m. EST
or not, seems the pendulum model was made in an old version...

So how would you model a simply pendulum in comsol?
or not, seems the pendulum model was made in an old version... So how would you model a simply pendulum in comsol?

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