Spectrum analysis of unbalanced rotating rotor

[Tung Jian Seng]

Homework Statement

Hi guys, I have done a lab experiment about unbalanced rotating rotor.
In the first part of the experiment, the rotor was run in a balanced condition at different frequencies (40, 50 and 60 Hz). The spectrum of acceleration vs frequency for each frequency was recorded.
In the second part of the experiment, the rotor was run in unbalanced condition where screws are added on the rotor as the unbalanced mass. The results are recorded in 3 different frequencies (40, 50 and 60 Hz)

For the balanced case, I can observe that the acceleration decreases with the increasing frequency but I can't find the reason why does this happens?

For the unbalanced case, I can see that the acceleration increases with the increasing frequency. I would like to ask what does the increasing acceleration indicates?
And why do people choose to analyze the acceleration spectrum instead of velocity and displacement?
How does the acceleration can be related to vibration analysis?

These are my douts on this experiment. It would be much appreciated if anyone could help me out with this.

Thank you in advance.

Relevant Equations

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Spectrum of acceleration vs frequency

Results of balanced condition

Results of unbalanced condition

 

[Baluncore]

I assume the shaft is driven by a 4 pole induction motor, which explains the rate of rotation, the fundamental frequency, and the small slip.

How many and how are the unbalance screws arranged in the disk?
What is meant by 2, 4 or 6 screws, in what geometric positions ?