FRF analysis

Dp12

Hi,

I am performing FRF analysis of an overhang part mounted on engine.

From testing, I requested following  vibration data at mounting and at tip-

1) G vs RPM (sweep up) - from this I got to know at which RPM, G value is maximum due to resonance.

2)FFT data (G vs Freq)  at that single RPM where G was maximum while sweep up.

 

Now, my query is ...from FFt data, my maximum G value at particular frequency is less than 1G .

But from sweep up data (G vs RPM), if I check G value at that RPM , then it is more than 3G.

So, Now For FRF analysis in CAE, which G value I should take for excitation input (from FFT or from sweep up).

 

How to correlate max. displacement and acceleration plotted at tip in CAE with testing. 

 

Thanks in advance.

Rahul Rajan_21763

You can refer to below link for the paper presented in Altair technical conference for FRA Correlation Analysis.

https://altairatc.com/india/bangalore/technical-presentations/OSA-12-FRA_Correlation_Analysis_for_Hammering_Test_Autoliv.pdf

 

Comping to understanding the test procedure and replicating that in the model becomes more of domain related activity and we will not be able to suggest more on that.   
 

Dp12

Thanks for sharing the paper.

 

But that was done with defined load as excitation.

My query is different.

What excitation (g value) should I use in CAE for FRF analysis of an overhang part - 

Example If I found acceleration peak of 2 G at 1500 RPM   in engine sweep up data ( acceleration vs RPM -idle to full throttle).

My engine is 4 cyl - 4 stroke then engine resonance freq is (1500/60)*2 = 50Hz

then when I again run the engine at 1500RPM (50 Hz), and get FFT data - Acceleration vs Frequencies.

So, at 1500 RPM, there are various acceleration peaks at 50 Hz and its harmonic. But its acceleration values are 0.7 G or 0.5 G.

 

So, for FRF analysis in CAE, which G value I should take - 2 G or 0.7 G??

 

Thanks in advance