The dynamic response of a multi-disk rotor system with coupling misalignment is investigated theoretically and experimentally, considering the nonlinear oil film force. The rotor is simplified to a lumped mass model and the governing equations are derived considering the gyroscopic effect. The reacting forces and moments caused by misalignment are treated as excitations to the rotor system. The unbalanced responses of the system with/without misalignment are calculated using a numerical integration method and comparisons made. Spectrum cascades are utilized to obtain the overall view of the response characteristics during the starting up of the rotor. The modified Bode plot is used to trend the amplitude variation of different frequency components. The study indicates that coupling misalignment can cause 2 X, 3 X, 4 X, and other multiple frequency responses. The amplitude of the 2 X vibration could be larger than that of the 1 X one, depending on the misalignment level. Also, the amplitude of 2 X vibration decreases with the increment of the distance between the measuring points and the coupling. Theoretical analysis also reveals that oil whip will happen when the rotating speed exceeds twice the first critical speed of the rotor system. It is suggested that coupling misalignment could suppress the vibration of the rotor and delay the occurrence of oil whip. The experimental and theoretical results agree well with each other, which verify the model adopted and analytical procedure in this study.
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Wan et al. (2012) studied this question.
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