Harmonics And Modes
Harmonics And Modes
(OP)
What is the exact meaning of (harmonics) in a vibrational system, and what are the modes?
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RE: Harmonics And Modes
modes are the different ways a system can oscillate... e.g. a rope held by the ends.
this is the 1st mode (2 nodes):
)
This is the 2nd mode (3 nodes):
)
(
and so on and so forth...
HTH
saludos.
a.
RE: Harmonics And Modes
I am not actually positive that I am right in all this, but could be some good food for thought, or lead you to the answer that you really want.
PS
RE: Harmonics And Modes
RE: Harmonics And Modes
"Harmonics" means "multiples" (of a given frequency).
You can have an impact once per revolution which will give time domain impacts at once per revolution and frequency spectrum with components at 1x running speed, 2x running speed, 3x running speed etc... which are harmonics of running speed.
You could have a bearing defect which will give rise to harmonics of the bearing fault frequency.
Nothing in the term harmonics has anything to do with resonance. In general a machine resonance which is excited will not be accompanied by harmonics of that resonance in the vibration spectrum.
Modes - I think these might roughly describe the different shapes and associated frequencies that the system can vibrate at without excitation. (This term is related to resonance).
RE: Harmonics And Modes
But Harmonics due to VFDs are electrical harmonics resulted because of frequent swithcing of power supply.
Electricpete! the experiment we did during our studies (rising and lowering water column to detect harmonics) is based on resonance only.
Regards,
RE: Harmonics And Modes
If I have given the impression that I disagree with that then I apologize.
My point was that the term "harmonic" has a much broader meaning and application which can be completely unrelated to resonance. In the case of rotating machinery monitoring, harmonics in a spectrum most often arise from repetitive impacts. The fundamental frequency is the impact frequency, not any resonant frequency. I have never heard of a case in rotating machine diagnostics where two different harmonically-related resonances were both important.
I don't know what the original poster had in mind... that's why I asked for clarification.
RE: Harmonics And Modes
at the frequency(s)of the rubbing components but this "hard" rub case may have 1X harmonics running all the way to near zero frequency as well as to very high frequencies. I'm not sure whether rubbing events produce "true" 1X rotationally-ordered harmonics or just spread out from the contact response frequency in which case the rotationally-spaced peaks could actually be be rotationally-unordered if the contact response frequency is
not rotationally ordered.