VIBRATION ANALYSIS OF A MOTOR FLEXIBLE COUPLING ROTOR SYSTEM SUBJECT TO MISALIGNMENT AND UNBALANCE .2. EXPERIMENTAL VALIDATION

Experimental studies were performed on a rotordynamic test apparatus t o verify the theoretical model of shaft misalignment and rotor unbalan ce. A self-designed simplified flexible coupling and a commercial heli cal coupling were used in the experiments. The rotor shaft displacemen ts were measured under the different misalignment and unbalance condit ions. The measured and predicted frequency spectra were obtained. The theoretical predictions are in good agreement with the experimental me asurements. Both the measured and predicted spectra show that unbalanc e and misalignment can be characterized primarily by one and two times shaft running speed, respectively. However, misalignment effects at t imes may not be apparent because the forcing frequency of misalignment (2 x shaft running speed) is not close enough to one of the system na tural 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 x 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 x sha ft running speed is pronounced in the frequency spectrum.