How to identify the natural frequency for the phase/magnitude?
How to identify the natural frequency for the phase/magnitude?
(OP)
I did a bump test. In the magnitude chart in FRF, there are few peaks, but none of them corresponds to +90degree in the phase chart, but there is one points to -90 degree.
Can I say the peaks are natural frequency anyways? please help
Can I say the peaks are natural frequency anyways? please help





RE: How to identify the natural frequency for the phase/magnitude?
RE: How to identify the natural frequency for the phase/magnitude?
If the driving point has the highest response then you may have problems with technique or setup or analysis.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: How to identify the natural frequency for the phase/magnitude?
RE: How to identify the natural frequency for the phase/magnitude?
Hard to narrow itdown much. Can you upload your reciprocity test?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: How to identify the natural frequency for the phase/magnitude?
I'm understanding right:
driving point impedance = response / excitation....at location of excitation
other impedance = response / excitation.... at other location
Then, why would be be suprised to see driving point impedance > other impedance... i.e. max response at the location of the excitation ?
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(2B)+(2B)' ?
RE: How to identify the natural frequency for the phase/magnitude?
Thanks.
RE: How to identify the natural frequency for the phase/magnitude?
RE: How to identify the natural frequency for the phase/magnitude?
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RE: How to identify the natural frequency for the phase/magnitude?
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RE: How to identify the natural frequency for the phase/magnitude?
One abrupt phase increase at 420hz occurs at location where a zero is very evident from the magnitude. That's exactly what we'd expect (assuming convention that positive phase angle corresponds to response leading excitation)
Another phase change one as 220hz doesn't make any sense to me.
I'm trying to think of what a linearly decreasing phase means. One thing that comes to mind from Fourier theory is a time delay (delay a signal by T0 by multiplying it by exp(-i*T0).
At any rate, the change in phase does not seem related to the peaks in magnitude as I would expect (would expect relatively distinct decreases in phase at locations of the peaks). Maybe this linear phase increase obscures the underlying behavior somehow.
Just my rambles fwiw (not being a big modal analysis guy myself). If Greg or others have some rambles, I'm sure they'll be worth more.
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(2B)+(2B)' ?
RE: How to identify the natural frequency for the phase/magnitude?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: How to identify the natural frequency for the phase/magnitude?
Just wanted to tell what I got. For the test mentioned above, the reciprocity was so bad and not consistent at all. I moved the test points from "the bad spot" to more rigid spot, and it gave me very good results. No issue any more.
I am thinking "the bad spot". Those area are filled with epoxy material and not consistent at all. I guess the reason might be not only the high damping but also the non-consistent filling or say non-linear problem.
Again, thanks Greg
RE: How to identify the natural frequency for the phase/magnitude?
RE: How to identify the natural frequency for the phase/magnitude?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?