Vibration Analysis Of A Motor-flexible Coupling-Rotor System Subject To Misalignment And Unbalance, Part II: Experimental Validation

Abstract

Experimental studies were performed on a rotordynamic test apparatus to verify the theoretical model of shaft misalignment and rotor unbalance. A self-designed simplified flexible coupling and a commercial helical coupling were used in the experiments. The rotor shaft displacements were measured under the different misalignment and unbalance conditions. The measured and predicted frequency spectra were obtained. The theoretical predictions are in good agreement with the experimental measurements. Both the measured and predicted spectra show that unbalance and misalignment can be characterized primarily by one and two times shaft running speed, respectively. However, misalignment effects at times may not be apparent because the forcing frequency of misalignment (2 × shaft running speed) is not close enough to one of the system natural frequencies to excite the system appreciably. Therefore, in some cases the misalignment response is hidden and does not show up in the vibration spectrum. On the other hand, if 2 × shaft running speed is at or close to one of the system natural frequencies, the misalignment effect can be amplified and a high frequency density level at 2 × shaft running speed is pronounced in the frequency spectrum.