Abstract
In this paper, a nonlinearity evaluation is proposed in order to identify the rub‐impact in rotor systems with pedestal looseness. Nonlinear mathematical models have been established for bearing‐rotor systems with single pedestal looseness and pedestal looseness coupled with rub‐impact. Piecewise linear stiffness and damping are considered regarding the position of pedestal looseness, while radial impact forces are defined using the Colulomb type of frictional relationship during rub‐impact. The nonlinearity evaluation is employed to quantify the nonlinearity of the dynamics of bearing‐rotor systems, which are calculated at different looseness clearances. The experiments for rotor systems with pure pedestal looseness and pedestal looseness coupled with rub‐impact are conducted respectively to collect the vibration signals on different looseness clearances. Two different curves are obtained using the nonlinear fitting method for the values of nonlinearity evaluation. The rub‐impact within rotor systems with pedestal looseness can then be identified by comparing the curves that denote the trend of nonlinearity evaluation for the measured vibration responses.
Highlights
Pedestal looseness is a common issue in rotating machinery. e excessive vibration caused by pedestal looseness often results in a secondary phenomenon, rub-impact [1]
Nonlinear mathematical models are established for rotor systems with single pedestal looseness as well as pedestal looseness coupled with rub-impact. e elastic force and the rubbing force are considered in regards to the position of pedestal looseness and rubbing. en, the severity of the nonlinearity of the rotor systems is quantified using a nonlinearity evaluation. e definition of nonlinearity measure is introduced and a special case is used to quantify the nonlinearity of dynamics. e dynamics of rotor systems with pedestal looseness coupled with rub-impact is analyzed by integration using the adaptive fourth-order Runge–Kutta method for the mathematical models
Two kinds of experiments are conducted for the rotor system with pure pedestal looseness and with pedestal looseness coupled with rub-impact. e trend curves with the increasing looseness clearances show that the rubimpact will have important in uences on the nonlinearity degrees of the dynamics, which can be used to identify the existence of rub-impact in rotor systems with pure pedestal looseness
Summary
Pedestal looseness is a common issue in rotating machinery. e excessive vibration caused by pedestal looseness often results in a secondary phenomenon, rub-impact [1]. Using signal-based methods alone, it is difficult to identify rub-impact from rotor systems with pedestal looseness in rotating machinery. When rub-impact occurs in rotor systems with pedestal looseness, the nonlinear rubbing forces with a piecewise linear form of stiffness are considered in the system [29, 30]. Erefore, a nonlinearity evaluation has the capacity to identify the variation of nonlinearity severity on the dynamics of the rotor systems. A nonlinearity evaluation is proposed to identify the rub-impact in rotor systems with pedestal looseness. E dynamics of rotor systems with pedestal looseness coupled with rub-impact is analyzed by integration using the adaptive fourth-order Runge–Kutta method for the mathematical models. En, rub-impact can be identified from the rotor systems with pedestal looseness by comparing the curves that denote the trend of the nonlinearity evaluation Two curves are obtained by nonlinear fitting method for the values of nonlinearity measures on different looseness clearances. en, rub-impact can be identified from the rotor systems with pedestal looseness by comparing the curves that denote the trend of the nonlinearity evaluation
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