The Study Of The Model-based Methods For Crack Identification In Rotor Systems In Time Domain And Frequency Domain

As a kind of faults on rotors, the crack has been studied and researched widely in several decades. The monitoring and diagnosis of cracked rotors are considered great importance. In the present thesis, two on-line identification methods for cracked rotors are researched.Firstly, the finite element model of the rotor system and the identification software are introduced. The stiffness of the cracked element is calculated by Strain Energy Release Rate method. Assembling the time-vary stiffness matrix of the cracked element, the whole stiffness matrix is obtained. The crack identification software is developed by Visual C++6.0and Visual FORTRAN6.5and it consists of three parts:pre-processing, calculating and after processing.Presently, the model-based method in time domain is studied. The measured residuals of the responses between the uncracked rotor and the cracked rotor are obtained. Then the residuals of the whole system are calculated. The identification of the crack is taken into account by equivalent loads using the finite element model. Finally the method is verified by the data calculated via the model. The location and the type of the crack could be identified by such method. In addition, for the rotor which has two transverse cracks, the angle between two cracks referring to the axial direction could also be identified.The second identification method utilizes the model-based method in frequency domain. Combining with the finite element model of the rotor and harmonic components of the frequency responses measured from several nodes, equivalent loads are calculated. Simulation results show that the location of the transverse crack can be identified efficiently by the method.Finally, those identification methods are verified by experiments. The result reveals that those methods perform well under experimental circumstances.