Crack Rotor Fault Diagnosis Method Based On Nonlinear Output Frequency Resopnse Function

This paper is supported by the National Natural Science Foundation of China (50775208,51075372), the Mechanical Equipment Health Maintenance Foundation of Hunan Province Key Laboratory (200904) and the Natural Science Foundation of Henan Education Department (2008C460003), introduces Nonlinear output frequency response function (NOFRF) to the system identification of crack fault, deeply studies the nonlinear identification method of crack rotor fault based on NOFRF and does some simulations. Some preferable innovative achievements are obtained in this paper. The primary contents of this article involve the followings:The first chapter discusses the significance of proposing and studying on this thesis, summarizes the research status of non-linear system identification, as well as its application in fault diagnosis, and presents a nonlinear method of fault detection and diagnosis of the crack fault and research status at home and abroad, At last the primary contents and innovation points of this paper are presented.The second chapter introduces the definition and algorithms of frequency response functions, on this basis, and introduces the frequency response functions of linear systems to the nonlinear systems, the NOFRF theory and identification algorithm are introduced detailedly, The process of fault diagnosis based on the NOFRF model is given clearly. The content of this chapter is the basic theory of the whole paper.The third chapter discusses the calculation of crack shaft stiffness, the vibration of cracked rotor system shows a strong nonlinear vibration, and crack reduces the stiffness of the rotor, a slant crack can also cause the mutual coupling stiffness. This chapter introduces several different crack model firstly, then based on the fracture mechanics, the crack stiffness is calculated in detail, and it analyzes the change of crack rotor stiffness with the change of the crack position, crack depth and other parameters, in particular, the coupling stiffness of the slant crack shaft is analysed in-depth, a reasonable explanation that multi-frequency couplings occur on the transverse and axial response of the slant crack rotor is gived.The fourth chapter discusses the basic theory and algorithms of the nonlinear output frequency response functions(NOFRF). Nonlinear output frequency response functions is proposed based on the generalized frequency response function, and it is the expandition of the Volterra series and also reflects the system functional characteristic, and could reflects the functional characteristic of the nonlinear systems, it can be obtained through the identification of the system's input and output, the great advantage is a one-dimensional representation, it's easier to be understanded. On this basis, the nonlinear output frequency response function (NOFRF) is introduced to the fault diagnosis of rotor crack in this paper, a new method for diagnosing rotor crack based on the NOFRF is proposed. The NOFRF values identified explain the generation of system high frequency clearly; Comparing the NOFRF values of systems with different positions and depths can obtain the relationships between the NOFRF values and crack parameters, and can find the parameter sensitive to the crack diagnosis; Detecting the sensitive parameter, combined with the frequency domain analysis, can achieve the fault detection and diagnosis of cracks. Experimental results demonstrate the effectiveness of the method.The fifth chapter introduces nonlinear output frequency response functions to the slant-cracked fault identification. A slant crack causes the stiffness coupling of each direction, this paper solves the dynamic equation of rotor system under the four directions'load conditions of horizontal and vertical forces, axial force and torque, and analyzes the dynamic characteristics of rotor system inclined cracks axial and transverse vibration, this paper also obtains the NOFRF model of the slant crack rotor system. It analyzes the NOFRF kernel values with the change of crack angle, and researches the nonlinear output frequency response functions of different systems including a normal rotor, a transerve crack rotor and a slant crack rotor. At last, the crack fault feature information is derived. Experimental results show that NOFRF values can not only reflect the crack's exist, also can reflect the direction of crack.The sixth chapter summarizes the research results, the nonlinear system identification and future application in the rotating machine fault detection and diagnosis are prospected.