raphatss
Mechanical
- Jan 24, 2011
- 6
Hello guys,
I have some questions about the damped unbalanced response analysis that api requires for centrifugal compressors.
The rotor of this compressor has 7 impellers between the bearings (no overhung impellers).
Api says that, for conical modes an unbalance shall be added at the location of maximum displacement nearest to each journal bearing.
To calculate the unbalance to be added we use the equation U = 6350 (W/N);
Where U is the unbalance in g.mm, N is the speed and W is the journal static load (kg) or, for bending modes where the maximum deflection occurs at the shaft ends, the overhung mass.
Now, for the second mode of this rotor, the first maximum deflection is at the shaft end and the second maximum deflection is between the bearings.
So, to calculate the first unbalance to be added at the shaft end I should use the overhung mass and for the second unbalance (between bearings) I should use the static load on the nearest bearing. Is that right?
The other question is about the third mode unbalances weights.
For the same rotor, on the third mode, the first peak is at the at the first shaft end, the second peak is between the bearings, and the third at the second shaft end.
Do I have to use three unbalance weights for the third mode?
If yes, what values for W should I use (1 - first overhung mass, 2 - static load at nearest bearing and 3 - second overhung mass)?
And what would be the position to place than? 1 - 0°, 2 - 180° and 3 - 0°.
Thanks in advance!
I have some questions about the damped unbalanced response analysis that api requires for centrifugal compressors.
The rotor of this compressor has 7 impellers between the bearings (no overhung impellers).
Api says that, for conical modes an unbalance shall be added at the location of maximum displacement nearest to each journal bearing.
To calculate the unbalance to be added we use the equation U = 6350 (W/N);
Where U is the unbalance in g.mm, N is the speed and W is the journal static load (kg) or, for bending modes where the maximum deflection occurs at the shaft ends, the overhung mass.
Now, for the second mode of this rotor, the first maximum deflection is at the shaft end and the second maximum deflection is between the bearings.
So, to calculate the first unbalance to be added at the shaft end I should use the overhung mass and for the second unbalance (between bearings) I should use the static load on the nearest bearing. Is that right?
The other question is about the third mode unbalances weights.
For the same rotor, on the third mode, the first peak is at the at the first shaft end, the second peak is between the bearings, and the third at the second shaft end.
Do I have to use three unbalance weights for the third mode?
If yes, what values for W should I use (1 - first overhung mass, 2 - static load at nearest bearing and 3 - second overhung mass)?
And what would be the position to place than? 1 - 0°, 2 - 180° and 3 - 0°.
Thanks in advance!
