Research On Dynamic Characteristics And Fault Feature Extraction Of Damaged Rotor Systems

With the development of science & technology and modern industry, rotating machinery is taking more and more important part in many fields such as power system, transportation, national defense and chemical industry, etc., consequently, the study of the dynamics of rotating machinery receives more and more recognition. A complicated machine system may vibrate violently due to nonlinearity that inherently exists in the system and multi-kind of faults, catastrophic disasters may occur if the vibration is violent enough, which can cause the machine to destroy and the operators to death. So it signifies much to study the nonlinear dynamics of rotor systems with faults or malfunctions and the technology to diagnosis the faults. Researchers all over the world made much study in these fields and made great progress.The dissertation takes the project, Vibrating Test System of Large Scale Air-compressor Rotor, conducted by the Shenyang Blower (Group) Ltd. Corp and Northeastern University, as the background and Test Rotor-Bearing System is regard as the research subject. Firstly, "1+3 Synthesis Design Method for Product-Oriented generalized mass" presented by professor Bangchun Wen is used to design and check the test rotor-bearing system and some dynamic parameters are determined. Subsequently, the dynamic characteristics of multi-disk over-hung rotor-bearing system with rub-impact fault, crack fault and the coupling fault with crack and rub-impact are studied by nonlinear finite element method and some faults of rotor-bearing system are simulated by small-size rotor test rig. The time-frequency features of the various fault vibration signals collected by experiment are extracted in detail. Finally, the chaotic characteristics of response time series of rub-impact rotor system are researched. The main research contents are as follows:(1) "1+3 Synthesis Design Method for Product-Oriented generalized mass" presented by professor Bangchun Wen is used to design the test rotor-bearing system. Firstly, the function optimization design of the test rotor-bearing system is performed, subsequently, the dynamic optimization design of the test rotor-bearing is performed and the rub-impact system of the test rotor-bearing system is designed by intelligent optimization method. Lastly, the visual optimization of the test rotor-bearing system is carried out.(2) Introduce the principal theory of modern contact mechanics and the nonlinear finite element method for solving the contact problems, the dynamic characteristics of rotor system are studied by nonlinear finite element method under three kinds of rub-impact conditions, namely the single rub-impact, local arc-shaped rub-impact and the annular rub-impact. And the effects of the clearance between rotor and stator, stiffness of stator, the position of rub-impact and the eccentricity are investigated. The results show that the single rub-impact mainly arouses impact and the frequency components are mainly high-level double frequency; local arc-shaped rub-impact mainly arouses impact and rubbing, the frequency components include low frequency components and high frequency components and the lower frequency components appear with the broadening of rub-impact arc-shaped region; the annular rub-impact mainly arouses rubbing and continuous spectrum appears in the amplitude spectrum.(3) The rotor crack fault is studied by nonlinear finite element method and the effects of crack depth and position are investigated. The results show that shallow crack has little effect on dynamic characteristics of rotor system. When the crack propagates radius depth, the system dynamic characteristics will greatly change. When the crack position keeps away from impeller, the amplitude of 2X is secondary to that of 1X(X denotes rotating frequency). When the crack position is close to impeller, the amplitude of 5X is secondary to that of 1X. The frequency components caused by crack are mainly regular high frequency components.(4) Finally, the coupling fault with crack and rub-impact is studied by nonlinear finite element method. The research results show that the rub-impact aggravates and backward whirl can be clearly seen from the trajectory. For arc-shaped rub-impact and annular rub-impact, the continuous spectra all appear and the 5X frequency component is comparatively obvious.(5) The dynamic characteristics of rotor-system with rotor-stator rub-impact, rotor crack, coupling fault with crack and rub-impact and coupling fault with oil-film instability and bearing rub-impact are studied by experiments. The fault features of the collected vibration signals are extracted by spectrum cascade, reassigned wavelet scalogram, amplitude spectrum and trajectory.The results show that frequency components are mainly high-level double frequency for the single rub-impact. The arisen frequency component is higher, the rub-impact degree is more serious. The local arc-shaped rub-impact research shows that the frequency components are mainly low frequency components and the frequency is lower the rub-impact is more serious when rub-impact occurs before the critical speed. Low frequency and high frequency components all exist, high frequency components are main in slight rub-impact stage and irreducible low frequency and color noise components appear in serious rub-impact stage.(6) The research result for coupling fault with crack and rub-impact shows that the frequency components are mainly X/2 harmonic series in slight rub-impact stage, X/4 harmonic series appear when rub-impact aggravates and continuous spectra appear in amplitude spectra plot when rub-impact becomes serious. The wavelet-decomposed signals are analyzed by reassigned wavelet scalogram, which can effectively extract the impact components caused by rub-impact. The analyzed results show that rub-impact appear once in a rotation period and one times slight rub-impact and next times serious rub-impact appear alternately.(7) The coupling fault with oil-film instability and bearing rub-impact is studied. The results show that the frequency components are mainly high-level doubling frequency components when rub-impact appears before oil-film instability; the slight bearing rub-impact caused by oil-film instability will arouse the combination frequency components of rotating frequency and oil whirl frequency and the combination frequency components are few; the serious bearing rub-impact will caused many combination frequency components; the appearance of the lower combination frequency component suggests that oil whip appears and at this time rub-impact is also most serious.(8) Chaotic characteristics of rub-impact rotor system response time series are studied. Firstly, Surrogate data method is used to carry out nonlinear identification of experimental and simulation data of rub-impact rotor system, subsequently, the nonlinear parameters, such as maximal Lyapunov exponent, correlation dimension, complexity, approximate entropy and chaotic degree, are computed. The results show that the nonlinear parameters of serious rub-impact are greater than these of slight rub-impact; correlation dimension is most sensitive for rub-impact degree, approximate entropy is secondary to complexity is tertiary and maximal Lyapunov exponent is most insensitive.(9) The experiment data of coupling fault with crack and rub-impact in three different rub-impact stages are analyzed by chaotic exponent. The results show that the chaotic exponents are approximate in 14s-15s and 17s～18s and they are all in slight rub-impact stage; the chaotic exponent is maximum in 18s～19s,which shows that rub-impact is most serious.