resonance frequencies and harmonics

[Vegas125]

Hello,

if a system has got a basic resonance frequency, it's also supposed to swing in the harmonic frequencies, belonging to the basic resonance frequency, if excited, and these harmonic frequencies are supposed to be whole-number multiples of the first frequency(for example: 2..4..8...12...etc.)?
Should FEM simulations with nonlinear geometry also yield whole-number-multiples of eigenfrequencies? In my calculations the multiples don't seem to be whole-numbers.

 

[electricpete]

I agree with Mike (as I'm sure everyone does), linear systems can definitely have resonances. The complex proportionality constant
H(w) = Output(w)/Input(w) may be very large at resonance (w=w_resonant), but it's a constant (in the sense that it doesn't change over time and doesn't depend on magnitude of the input).



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(2B)+(2B)' ?

 

[izax1]

I think all should be clear when we are talking linear systems. But it seems that there are some confusion as to non-linear systems. And I get a little confused myself. I owe electricpete an answer to my post on the 19. I mean to say that you will not get harmonics in a non-linear system. And we can argue that you will not get resonances either, but you can see amplifications from a linear input to a non-linear system. Maybe it is not correct to call that resonnance???

 

[electricpete]

I mean to say that you will not get harmonics in a non-linear system

Thanks. I mistakenly thought from your context that you had mistyped a word. (still looks like that from the context to me).

I agree with FE.

The frequencies present on output of non-linear system do not necessarily match those present on input. And in particular it is not uncommmon for sinusoidal input to result in output which includes harmonics of the input frequency (for example sinusoidal unbalance force causes harmonics of running speed in vibration spectrum).

Note, this is different than having resonant frequencies which occur in exact multiples of the first resonant frequency.

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(2B)+(2B)' ?

 

[electricpete]

Sorry, I left out a word:
(for example sinusoidal unbalance force in presence of looseness, which is a non-linearity) causes harmonics of running speed in vibration spectrum).



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(2B)+(2B)' ?

 

[izax1]

Well, I think we are on the same track then. Sorry for not being more presise in my context.