Dynamic behavior of cracked rotor subjected to multisine excitation

It is widely known that a developing shaft crack manifests itself in the appearance of nonlinear effects resulting in higher harmonics in a vibration spectrum. However, such symptoms are characteristic not only for developing shaft cracks but also for other malfunctions such as a shaft bow, a coupling misalignment, etc. That is why novel shaft crack detection methods introduce a specially designed diagnostic force applied to the shaft in order to amplify the particular symptoms of the crack. Most often a simple harmonic force is used for such purposes, yet the results may not be reliable. The present paper analyzes the possible application of the multisine excitation technique for an early shaft crack detection problem. This technique was previously used for identification problems where the influence of nonlinear distortions on the linear system behavior was to be evaluated and measured. In the present paper the multisine technique is adopted for the detection of a shaft crack in a rotor. The possibility to evaluate the crack depth is also verified. The approach is illustrated with the numerical results of the flexible rotating shaft modeled with the rigid finite element method. In order to assess the effectiveness of the proposed method the numerical results obtained for the uncracked and cracked rotors are compared. The robustness of the method to additional disturbances is checked by introducing some noise to the system. The results demonstrate a potential of the presented method to detect the shaft cracks and to evaluate their severity. Possible problems of the practical implementation of the method are briefly discussed. (C) 2013 Elsevier Ltd. All rights reserved.