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physical pendulum model

Posted Nov 29, 2011, 7:53 a.m. EST Studies & Solvers, Structural Mechanics Version 3.5a 3 Replies

Yadu Krishnan
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Hi all
I was trying to find the motion of a physical pendulum and I checked the sample 2D model ( www.comsol.com/community/exchange/2/ ). It has a Rayleigh damping, but when I remove the damping the solution does not converge but trying with a damping constant very very feeble the solution does converge.
What must be the problem if it is simulated without damping.?
3 Replies Last Post Dec 1, 2011, 8:48 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 30, 2011, 11:09 a.m. EST
Hi

have you tried a eigenfrequency analysis, this gives you the frequencies, even without damping
but an oscillating system without any damping would easily diverge by integrating small numerical round-off errors

--
Good luck
Ivar
Hi have you tried a eigenfrequency analysis, this gives you the frequencies, even without damping but an oscillating system without any damping would easily diverge by integrating small numerical round-off errors -- Good luck Ivar
Yadu Krishnan
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Posted: 1 decade ago Dec 1, 2011, 6:53 a.m. EST
Hi
Thanks for your reply.
I tried to extrude the 2d geometry and make a 3d pendulum. Included solid stress strain (transient ) and moving mesh (transient). I gave the same initial values of velocity. But when I solve it , the pendulum moves to a particular amplitude and then stops. Even if decrease or increase the time or velocity the pendulum moves the same distance. The solution takes very less time compared to the 2d geometry. How to get a 3d model pendulum.
Hi Thanks for your reply. I tried to extrude the 2d geometry and make a 3d pendulum. Included solid stress strain (transient ) and moving mesh (transient). I gave the same initial values of velocity. But when I solve it , the pendulum moves to a particular amplitude and then stops. Even if decrease or increase the time or velocity the pendulum moves the same distance. The solution takes very less time compared to the 2d geometry. How to get a 3d model pendulum.
Yadu Krishnan
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Posted: 1 decade ago Dec 1, 2011, 8:48 a.m. EST
Hi
Thanks for your reply.
I tried to extrude the 2d geometry and made a 3d pendulum, included solid stress strain (transient ) and moving mesh (transient). I gave the same initial values of velocity. But, when I solve it , the pendulum moves to a particular amplitude and then stops. Even if we decrease or increase the time or velocity, the pendulum moves the same distance. The solution takes very less time compared to the 2d geometry. How to get a 3d model pendulum ??
Hi Thanks for your reply. I tried to extrude the 2d geometry and made a 3d pendulum, included solid stress strain (transient ) and moving mesh (transient). I gave the same initial values of velocity. But, when I solve it , the pendulum moves to a particular amplitude and then stops. Even if we decrease or increase the time or velocity, the pendulum moves the same distance. The solution takes very less time compared to the 2d geometry. How to get a 3d model pendulum ??

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