| This dissertation was supported by the National Natural Science Foundation of China(No.51075372,50775208,51265039), Science and Technology Projects of Education Department of Jiangxi Province, China(No. GJJ12405) and the Open Fund of Key Laboratory of Machanical Equipment Health of Hunan Province (201204). A rotor system with two cracks is taken as an example in this paper, the nonlinear output frequency response function (NOFRF) is introduced to fault diagnosis of rotor system with two cracks, a fault diagnosis method of cracked rotor based on nonlinear output frequency response function (NOFRF) is proposed. The NOFRF characteristic of a rotor with two transverse cracks is studied by simulation research and experimental validation, some useful innovation results are obtained. The research contents in this dissertation are mainly as follows1. The topic and research significance of this subject is discussed, the methods of nonlinear system identification and the domestic and foreign research situation on the crack fault identification of rotor system are discussed, the research situation and achievements of nonlinear output frequency response function are stated, the main content and innovation of this paper is given based on this.2. The stiffness matrix of a shaft with two open transverse cracks under the action of two mutually perpendicular shear is derived based on the concepts of fracture mechanics and strain energy release rate method. The effect of crack depth, crack angle and slenderness ratio on the stiffness of the cracked shaft is discussed. For a shaft with two breathing transverse cracks, the breathing behavior of two transverse cracks along with the stable rotation of the shaft was simulated by using stress intensity factor, the effect of crack depth, crack angle on the breathing process of two cracks and the time-varying stiffness of the cracked shaft in a steady rotating period is discussed.3. The dynamics model of a rotor system with two open transverse cracks is built and the dynamic equation of this model is solved. The effect of crack depth, crack angle on the nonlinear output frequency response function (NOFRF) is analyzed. The research results show that the NOFRF values are very sensitive to different crack angle and different crack depth, the sensitivity of NOFRF values to the crack fault can be used o detect rotor crack fault when the rotor crack fault can not be identified effectively using traditional method of analyzing the pattern characteristic. The values of G2(j2ωF) and G4 (j2ωF) first increase and then decrease with the increase of the crack angle, the values of G3(jωF)and G3(j3ωF)will increase with the increase of the open crack depth and the change of G3(j3ωF) is most obvious. These valuable conclusions can be provided as the main references on fault diagnosis of a rotor system with two full open cracks. Finally the effectiveness of the proposed method are verified through a experimental research.4. The dynamics model of a rotor system with an open and a breathing crack is built and the dynamic equation of this model is solved by Runge kutta method. The nonlinear output frequency response function (NOFRF) values of this rotor system under different crack angle and different crack depth is obtained. The research results show that the values of G2 (j2ωF) will increase with the increase of the crack angle and achieve the minimum when the crack angle is 90°. The values of G3(jωF) and G4(j4ωF) are very sensitive to the change of right side open crack depth and increase with the increase of this crack depth. Compared with the rotor system with two full open cracks, G2(j2ωF) is the only decision basis for the change of crack angle and the decision basis for the change of crack depth changes from G3(jωF) and G3(j3coF)to G3(jωoF) and G4(j4ωF). Finally, the above conclusions are verified through the experimental study.5. The dynamics model of a rotor system with two breathing crack is built and the dynamic equation of this model is solved by Runge kutta method. The nonlinear output frequency response function (NOFRF) values of this rotor system under different crack angle and different crack depth is obtained. The research results show that the values of G2(j2coF) and G4(j2ωF) are very sensitive to the change of crack angle, both values will achieve the maximum when the angle is 90° at the minimum and achieve the maximum when crack angle is 180°, this rules can be used to reflect the change situation of the crack angle. The values of G3(jωF), G3(j3ωF) and G4 (j4ωF) will increase with the increase of the right breathing crack depth. Compared with the rotor system with an open and a breathing crack, the decision basis for the change of crack angle changes from G2(j2coF) and G2(j2coF)to G4(j2coF) and the decision basis for the change of crack depth changes from G3 (jωF) and G4 (j4coF) to G3 (jωF) G3(j3ωF) and G4 (j4ωF).Finally, the above conclusions are verified through the experimental study.6. A comprehensive summary about this paper is made and the research work which is necessary to focus on furtherly are summarized and prospected. |
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