Nonlinearity measure based assessment method for pedestal looseness of bearing-rotor systems

In this paper, nonlinearity measure based assessment method is proposed for the pedestal looseness of bearing-rotor systems under constant rotational speeds. A nonlinear mathematical model is developed for a bearing-rotor system which including the effect of pedestal looseness. Also, piecewise-linear stiffness, damping force, and nonlinear elastic force are considered in the model. These parameters depend on the position of pedestal looseness. Nonlinearity measure is used to quantify the degree for nonlinear behaviors of the bearing-rotor systems with different looseness clearances. A linear model is obtained by linearizing the nonlinear terms via the Taylor expansion from the static equilibrium position. Moreover, the dynamic behaviors predicted by the linear model are compared to the predictions of the nonlinear model. Then, nonlinearity can be quantified by evaluating the difference between linear and nonlinear models. The fourth order Runge-Kutta method was used to calculate the dynamic responses. The trend of nonlinearity degree is obtained by nonlinear fitting method under different looseness clearances. The performance of the proposed approach is validated numerically and experimentally. The relationship between for looseness clearances and nonlinearity degree can be used to assess the pedestal looseness in rotor systems.