Dynamic Characteristics Of The Rotor System With A Slant Crack On The Shaft

Crack is one of classic malfunctions in the rotor system. From the 1970s, many researchers began to study the dynamic behaviors of the rotor with a transverse crack on the shaft. In practice, there are many kinds of cracks which could occur in a rotor system. The slant crack, which is often found in the rotor with the operating torque, is one of them. Based on the theoretical and experimental researches, this dissertation investigates the dynamic behaviors of a slant-cracked rotor system, and presents characteristic frequencies used to detect the slant crack on the shaft of a rotor system through comparing with the dynamic behaviors of a transverse-cracked rotor system.Since a crack mainly affects the stiffness of a rotor system, the dissertation discusses firstly how to obtain the stiffness of a cracked rotor and develops two new methods: neutral equilibrium method and SIF=0 method. After comparing these two methods with traditional method and experimental stiffness curve in a reference, it is found that the stiffness obtained by SIF=0 method is the most similar to the experimental stiffness, and this method is preferable to obtain the stiffness of a cracked rotor. Stiffnesses in two bending directions, torsional direction and axial direction of a slant-cracked rotor system and a transverse-cracked one are obtained by SIF=0 method. The analysis demonstrates that for a cracked rotor system, a slant crack can lead to coupling stiffnesses of bending-tension, bending-torsion and torsion-tension, however, a transverse crack only can lead to bending-tension coupling stiffnesses.Runge-Kutta numerical method is used to solve four motion equations of a slant-cracked rotor system and a transverse-cracked one. In order to thoroughly investigate the dynamic behaviors of the cracked rotor system, different kinds of conditions are considered. There are many useful conclusions achieved. The most important conclusions among them include that under the same conditions, the transversal natural frequency of the slant-cracked rotor system is greater than that of the transverse-cracked one; in the transversal responses of the slant-cracked rotor system, the amplitudes of combined frequencies between rotating speed and torsional excitation frequency are far larger than those in the transversal responses of the transverse-cracked rotor; in the axial response of the slant-cracked rotor system, the amplitude of torsional excitation frequency is far larger than that in the axial response of the transverse-cracked rotor. Nonlinear analysis about the transversal responses of the slant-cracked rotor system is conducted and the changing parameters are rotating speed, crack depth and eccentricity. The results show that the routes into and out of chaotic vibrations include break of quasi-periodic torus and intermittency.The last part of the dissertation is experimental researches about the transversal responses of the slant-cracked rotor system and the transverse-cracked one with or without torsional excitation. The results of experiments are identical to the above two conclusions and demonstrate that the combined frequencies in the transversal responses can be used to discriminate between a slant crack and a transverse crack on the shaft of a rotor system.