Have a question I need some help with...
When doing a modal analysis on a vertical pump, there is no water in the columns or the bowl assembly when the pump is not running. Just to clarify, we will be instrumenting this pump both above and below grade. The water will be drained from the sump the pump takes suction from during the Modal analysis portion. An ODS will be performed following the modal.
This lack of water will effect the stiffness and the damping of the components, not to mention it may shift the frequencies of the resonance(s) identified by an unknown amount.
With the ODS being done while the pump is running and filled with water, you should be able to see the mode shape of the components (ie; column) if they are at resonance which will be beneficial and will help narrow down how much of a change there may have been. I am thinking that we would also be able to look at the spectrums collected during the ODS (and the frequency range of the resonance identified) in log scale to then help determine the amount they (NF's) may have shifted with the water now in the pump and the associated changes in frequency/damping.
How do you account for these unknown values of change when you are entering the modal in ME' Scope and with the conclusion? How do you know how much of a shift you may see in the resonant frequencies given this situation? I am curious how people have handled this in the past.
Please let me know.... I would appreciate any help I can get on this topic as I have an upcoming project that this will be an issue with.
Thanks so much,