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simulation of eddy current damper

Posted May 16, 2012, 1:59 a.m. EDT Low-Frequency Electromagnetics, Structural Mechanics Version 4.2a 5 Replies

Mohit Sharma
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hi all
i am working on eddy current damper....in which beam (cantilever type) vibrations (free) are to be damped...the material of beam is aluminium....i have simulated the two electromagnets..but i am not able to simulate the beam vibration with initial conditions @t=0 displacement of free end is 0.003m and velocity =0. i have used the eigen frequency study but the tip displacement is very large as per our initial condition....when i used the time dependent study it gives an error of singular matrix...and one thing more should i use the moving mesh for beam...

plz help

i've attached the model...

Thanks and regards
Mohit

Attachments:

5 Replies Last Post May 18, 2012, 12:21 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 16, 2012, 11:07 a.m. EDT
Hi

an eigenfrequency solver does only give frequency and mode shapes, but the absolute values of the displacements are arbitrary, they can only be used for comparison between modes. YOu have different ways of normalising the eigenfrquencies too, w.r.t. rms value, all to 1, mass participation factor ...

For any damping like you do you need to define a displacement with a velocity (or via an acceleration). The eddy curreents come from the velocity term coupling in to the EM equations

--
Good luck
Ivar
Hi an eigenfrequency solver does only give frequency and mode shapes, but the absolute values of the displacements are arbitrary, they can only be used for comparison between modes. YOu have different ways of normalising the eigenfrquencies too, w.r.t. rms value, all to 1, mass participation factor ... For any damping like you do you need to define a displacement with a velocity (or via an acceleration). The eddy curreents come from the velocity term coupling in to the EM equations -- Good luck Ivar
Mohit Sharma
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Posted: 1 decade ago May 16, 2012, 3:06 p.m. EDT
thanks for your response..sir when i am trying to introduce the velocity term into model via lorentz term,it shows the beam is not applicable for this case...is there another way to introduce the velocity term into the model...and also i have given the velocity and displacement as variables....plz tell me how to couple velocity term into the EM equations....

Thanks and regards
Mohit
thanks for your response..sir when i am trying to introduce the velocity term into model via lorentz term,it shows the beam is not applicable for this case...is there another way to introduce the velocity term into the model...and also i have given the velocity and displacement as variables....plz tell me how to couple velocity term into the EM equations.... Thanks and regards Mohit
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 16, 2012, 4:47 p.m. EDT
Hi

indeed you have a few pecularities in your model. You are using MEF but you have no material using the V dependent variable as your all domains are defined in the Amper law node (and not ampere law and current conservation node) uncheck the Al beam and you can define a Lorentz veocity domain condition as for that you need the current and the voltage variable.
Then your infinite elements should be a thin shell around your "air" domain, not the full air domain, check the doc and a few model library examples

--
Good luck
Ivar
Hi indeed you have a few pecularities in your model. You are using MEF but you have no material using the V dependent variable as your all domains are defined in the Amper law node (and not ampere law and current conservation node) uncheck the Al beam and you can define a Lorentz veocity domain condition as for that you need the current and the voltage variable. Then your infinite elements should be a thin shell around your "air" domain, not the full air domain, check the doc and a few model library examples -- Good luck Ivar
Mohit Sharma
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Posted: 1 decade ago May 18, 2012, 2:04 a.m. EDT
hello.
i' ve tried to remove peculiarities within my but my model is not working as per my expectations....the amplitude of tip displacement should die out with the passage of time....but it is not happening...i think some thing is wrong with my model....i am attaching the model plz have a look at this......

i am also interested in showing graphically (qualitatively and quantitatively) the diffusion of magnetic flux into cantilever beam....

thanks and regards
mohit
hello. i' ve tried to remove peculiarities within my but my model is not working as per my expectations....the amplitude of tip displacement should die out with the passage of time....but it is not happening...i think some thing is wrong with my model....i am attaching the model plz have a look at this...... i am also interested in showing graphically (qualitatively and quantitatively) the diffusion of magnetic flux into cantilever beam.... thanks and regards mohit

Attachments:

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 18, 2012, 12:21 p.m. EDT
Hi

But why should it damp out ? you have an enforced oscillation continuous there it will never die out like that.

You should rather run a stationary to enforce a given displacement, then releas it for the ime series

--
Good luck
Ivar
Hi But why should it damp out ? you have an enforced oscillation continuous there it will never die out like that. You should rather run a stationary to enforce a given displacement, then releas it for the ime series -- Good luck Ivar

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