Research On Identification Of Nonlinear Behavior And Fault Of Rub-impact In Rotors

Chaos theory developed in the late half of 20th century gives a new approach for the research on nonlinear dynamical system. The researches on strong nonlinear behavior such as chaos in complex mechanical system and application of chaos theory in machinery fault diagnosis are of significance to design, operation, diagnosis and maintenance of complex mechanical system.With the increase of machinery operating speed and wide application of various new-style material in high-speed machinery, nonlinear problem of mechanical system which may cause abnormal state even fault directly or indirectly becomes more and more obvious. Theoretical and experimental studies focusing on this problem are very important. Particularly, it is more important to study the prediction of nonlinear behavior and chaotic behavior, early detection of operating state and signal/information processing method based on chaos theory. Under this circumstance, this dissertation suggests two research aspects, namely experimental study on complex nonlinear behavior underlying rotor system with stator-rotor rub and deep study on identification method and early diagnosis of rotor fault based on chaos theory.Subsequently, this dissertation mainly includes, observation and identification of chaotic phenomena from rub-impact rotor rig, analysis and prediction for nonlinear behavior of rotor rub-impact based on nonlinear signal processing, early detection and recognition of rub-impact fault based on nonlinear theory and chaos theory. The detailed contents and innovative work include,1. Nonlinear behavior and characteristic rule of rub-impact rotor are deeply and systematically studied.(1) Combined with quantitative and qualitative analysis, solutions of vibration response of sharp rub-impact rotor are obtained by the improved sharp rub-impact model of rotor. Test rig of sharp rub-impact rotor is designed and meticulous experiment has been accomplished. Characteristic Rile of vibration response is obtained in various cases of rub-impact. The result that the 1/3X,2/3X sub-harmonic components (X denotes operating frequency component) occur in inception of rub-impact in the case of sharp rub-impact under certain condition, is obtained via theoretical and experimental analysis.(2) Dynamics model of Jeffcott nonlinear rotor with eccentric between stator and rotor is built based on rub-impact force. Numerical simulation demonstrates that local rub-impact has sub-harmonic phenomena and bifurcation phenomena. The rub-impact rotor response includes quasi-periodic or chaotic vibration when severe unbalance, small damping and high rotating speed. Based on the result of numerical analysis, rotor test rig about local rub-impact is designedand built. Experimental research has been done within broad range of rotating speed. A very rich and complicated vibration phenomenon including not only periodic (synchronous and non-synchronous) components but also quasiperiodic and chaotic motions, is observed. The observed result is qualitatively consistent with that of simulation.(3) Phase space reconstruction analysis method based on observed time series is used to analyze and identify nonlinear dynamics of rotor system. The evidence with statistical meaning representing strong nonlinear behavior is obtained.The results show that sub-harmonic phenomena produced by local rub-impact provide mechanism and evidence for the early diagnosis of this fault. Vibration response characteristics of rub-impact rotor obtained by theoretical and experimental analysis are of significance to prediction of rub-impact.2. Phase space reconstruction technology and characteristic indices algorithms, which show the wide prospects of engineering application, are presented to In order to distinguish dynamical behavior underlying observed time series from rub-impact rotor.(1) In the case of short data set, to select embedding space parameters as fast and exact as possible, the improved across displacement method for selecting time delay and the relative gain ratio of fal...