GMarsh
Mechanical
- Sep 30, 2011
- 123
Hi,
I am doing experimental modal analysis of a cylindrical casing. I have 64 FRFs. I have curve fitted dominant modes and obtained a synthesised FRF. Now when I see the animation of mode shapes corresponding to each of the frequencies in FRF, I am finding a not-so-significant (amplitude wise) mode in FRF is having the highest vibration amplitude on relative scale.
To explain in detail a bit, I have nearly 65 modes in frequency range 1200 - 15000 Hz. As expected the initial bending modes are showing greater magnitude in FRF. But when I see mode shapes, a small mode at 4900 Hz is vibrating heavily. This is validated through experiment as well. In operational condition, 4900 Hz and its harmonics clearly stand out in FFT of vibration signal.
How to identify the strength of a mode from FRF ? And is it possible that a low amplitude mode in FRF has heavy vibrating amplitude in mode shape.
I am attaching the file with FRFs and mode shape.
Thank you in advance for your time and help.
Rgds
Geoff
I am doing experimental modal analysis of a cylindrical casing. I have 64 FRFs. I have curve fitted dominant modes and obtained a synthesised FRF. Now when I see the animation of mode shapes corresponding to each of the frequencies in FRF, I am finding a not-so-significant (amplitude wise) mode in FRF is having the highest vibration amplitude on relative scale.
To explain in detail a bit, I have nearly 65 modes in frequency range 1200 - 15000 Hz. As expected the initial bending modes are showing greater magnitude in FRF. But when I see mode shapes, a small mode at 4900 Hz is vibrating heavily. This is validated through experiment as well. In operational condition, 4900 Hz and its harmonics clearly stand out in FFT of vibration signal.
How to identify the strength of a mode from FRF ? And is it possible that a low amplitude mode in FRF has heavy vibrating amplitude in mode shape.
I am attaching the file with FRFs and mode shape.
Thank you in advance for your time and help.
Rgds
Geoff
