A model-based dynamic characteristics analysis of a coupled multi-crack rotor system

The model-based method plays an essential role in crack detection of rotor systems. To improve the reliability and accuracy of model-based method in rotor crack detection, this paper proposes a coupled multi-crack rotor model by considering the coupling effect between cracks under complex excitations as an additional flexibility. The systemic stiffness matrix is derived based on the Timoshenko beam theory and fracture mechanics, in which a detailed description of the coupling mechanism between cracks is presented. The systemic stiffness variation with rotation angles and the effects of crack orientation angles, unbalance orientation angles, and crack depths on dynamic characteristics of the coupled multi-crack rotor are analysed at 1/3 and 1/2 subcritical speeds. The complex nonlinearity induced by the coupling effect between cracks is responsible for the dynamic differences between the coupled and uncoupled models of a multi-crack rotor. The magnitudes of most of 2X and 3X components (X is the rotating frequency of rotor system) of the coupled rotor model are nearly twice as those of the uncoupled model. The prominent super-harmonic components and orbits' morphological features of the coupled multi-crack rotor model are shown to be suitable for early crack detection and crack parameter identification. The theoretical findings of the proposed coupled model show an excellent agreement with the experimental results. This work can give confidence in the applications of the model-based method in health monitoring and multi-crack detection for actual rotors.