Dynamic analysis of an unbalanced rotor-water pump-bearing system considering varying compliance effect and localized defects on bearing races

A multi-degree of freedom (DOF) dynamic model is developed using the transfer matrix method to obtain the vibration response of an unbalanced rotor-coaxial water pump bearing system due to varying compliance and localized race defects of the bearing. In this model, the bending flexibility and masses of the rotor and bearing housing are taken into consideration. The two rolling element rows of the water pump bearing are modeled as a series of springs and dampers, and the anisotropic bearing stiffness and damping changing with the rotational speed are analyzed. The varying compliance and the localized race defect are both modeled as periodic excitations, on which the influences of the unbalanced forces in the rotor are considered. By using the vibration model, the discrete frequency spectra of vibration responses caused by the varying compliance and localized race defects of the two rolling element rows are predicted. The results show that for the varying compliance or a race defect of an individual rolling element rows, there are a series of additional components in the frequency spectrum in addition to the peaks at the harmonics of characteristic frequency due to the effect of the rotor unbalance. The response amplitude due to varying compliance of the roller row is found to be quite high in comparison to that due to varying compliance of the ball row because the axial load carried by the ball row uniforms the contact load distribution among balls and then reduces the varying compliance excitation.