Learning Forum

[deepesh.p.gurdasani]

If I do MSUP for various analysis like random vibration:

1) I extract just 6-7 modes and ratio of efetive to total mass in all three directions is far less than 0.80 and the frequency till 7 modes comes from 2 to 10 Hz.

2) Now, I attach this modal to random vibration analysis and give PSD data from 2 to 6 Hz.

Now as my PSD data itself lies below 10 Hz. (This mode already being extracted in first 6-7 modes in modal), do I have to extract more modes for getting ratio of effective to total mass as 0.80 ? 

 

Thanks in advance 

 

[Ankush Choudhary]

Please check out the below link.

/courses/index.php/courses/intro-to-modal-based-methods/lessons/summary-28/

[deepesh.p.gurdasani]

I do understand that 1.5 times the frequency (here 6 * 1.5 = 9 Hz), the modes should be extracted in the direction of excitation or expected response but even after this, if the ratio of effective mass to total mass is far less than 0.9, then is it ok? 

 

[Ankush Choudhary]

Yes, it's fine.