Vibration Analysis of Misaligned Shaft-ball Bearing System

Experimental studies were performed on a rotor dynamic test apparatus to predict the vibration spectrum for shaft misalignment. A self-designed simplified 3 pin type flexible coupling was used in the experiments. The rotor shaft accelerations were measured using dual channel vibration analyzer (ADASH) under the misalignment condition. The experimental and numerical (ANSYS) frequency spectra were obtained. The experimental predictions are in agreement with the ANSYS results. Both the measured and ANSYS results spectra shows that misalignment can be characterized primarily by 2X (two times) shaft running speed. However, misalignment 2X is not close enough to one of the system natural frequencies to excite the system appreciably. Therefore, there are cases where the misalignment response is hidden and does not show up in the vibration spectrum. On the other hand, if 2x shaft running speed is at or close to one of the system natural frequencies, the misalignment effect can be amplified and the speed is pronounced in the frequency spectrum.