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Beam excited by a shaker

Posted May 9, 2013, 2:03 p.m. EDT Acoustics & Vibrations, Studies & Solvers, Structural Mechanics 2 Replies

Fabrizio Magi
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Hi All,

I aim to model a simple beam excited by a shaker. I am using the Solid Mechanics.
I would like to know how big is the displacement of a particular mode (eg first flexural) when I excite the beam in resonance.

I found the eigenfrequencies using the study step EIGENFREQUENCY. Let's talk about just one of them, eg 100Hz

now I would like to excite the beam with this frequency I have just found. How to do that?

What I tried to do was to use the study step FREQUENCY DOMAIN choosing the frequencies 100Hz and to compute it.

I have this error:

Failed to find a solution.
The relative residual (0.25) is greater than the relative tolerance (0.001).
Returned solution is not converged.

I can imagine it is for the reason that using a stationary solver, without damping, at resonance it can't converge. but, in this case, how can I do? Is it wrong to use he stationary? What abut the frequency dmain as study step rather than FREQUENCY DOMAIN MODAL?

Thanks in advance

Fabrizio
2 Replies Last Post Feb 16, 2014, 9:50 p.m. EST
COMSOL Moderator

Hello Fabrizio Magi

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Nicolas Tsagarakis
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Posted: 1 decade ago Feb 16, 2014, 7:51 a.m. EST
Hi Fabrizio,

You should use Frequency Domain Study instead of Frequency Domain Modal Study, and you have to define a kind of load for the excitation.

Although it's a bit of an old matter, I 'd be glad to learn more about it. Hope someone will reopen it.

Regards,
Nicolas T.
Hi Fabrizio, You should use Frequency Domain Study instead of Frequency Domain Modal Study, and you have to define a kind of load for the excitation. Although it's a bit of an old matter, I 'd be glad to learn more about it. Hope someone will reopen it. Regards, Nicolas T.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Feb 16, 2014, 9:50 p.m. EST
When you excite a structure with a harmonic force exactly at one of its natural frequencies with no damping you get infinite displacement magnitude. For this type of loading damping becomes very important and you should include it in the analysis.

Nagi Elabbasi
Veryst Engineering
When you excite a structure with a harmonic force exactly at one of its natural frequencies with no damping you get infinite displacement magnitude. For this type of loading damping becomes very important and you should include it in the analysis. Nagi Elabbasi Veryst Engineering

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