Identification of multiple faults in rotor systems

Many papers are available in literature about the identification of faults in rotor systems. However they generally deal with a fault only, usually an unbalance. Instead, in real machines, the case of multiple faults is quite common: the simultaneous presence of a bow (due to several different causes) and an unbalance or a coupling misalignment occurs often in rotor systems. In this paper a model based identification method for multiple faults is presented. The method requires the definition of the models of the elements that compose the system, i.e. the rotor, the bearings and the foundation, as well as the models of the faults, which can be represented by harmonic components of equivalent force or moment systems. The identification of multiple faults is made by a least square fitting approach in the frequency domain, by means of the minimization of a multidimensional residual between the vibrations in some measuring planes on the machine and the calculated vibrations due to the acting faults. Some numerical applications are reported for two simultaneous faults and some experimental results obtained on a test rig are used to validate the identification procedure. Accuracy and limits of the proposed procedure has been evaluated.