No abstract

A simplified mathematical model has been developed based on Jeffcott rotor to investigate the dynamic behavior of cracked . shaft. Analysis has indicated the existance of unstable zones. of operation at the vicinity of which rotor response is largely magnified. In general rotor response due to unbalance forces contain vibrations at 1/rev and 2/rev components while gravity excited vibration is characterized by 3/rev harmonics as well. The measured response curve of the rotor shows an increased shaft deflection at all speeds. Also a subcritical peak is detected. Comparing the analytical results with experimental measurements indicates that the mathematical model is very realistic.

The effect of partial rotor-to-stator rubbing is studied both experimentally and analytically. The measured vibration signal is distorted showing a flattenned portion of the waveform.' Spectral analysis indicated that light rubbing induced vibration is characterized by harmonics at frequencies equal to 1/rev., 2/rev. and 3/rev. Severe rubbing is identified by a spectrum containing subharmonics at 1/3, 2/3 of the rotational frequency. The synchronous component is generally attenuated as a result of rubbing introduced friction. Because of the stiffening effect of rubbing on the rotor, the resonance frequency is further delayed. The results obtained analytically show good qualitative agreement with the experimentally obtained ones. ••