Abstract: A new quantitative diagnosing method for rotor system is proposed, in which the super-harmonic response of the rubbing rotor system is used for rubbing location and rubbing force identification. The harmonic balance theory is applied to study the dynamic of the rubbing rotor system, and it’s revealed that the ratio of the super-harmonic frequency responses of any two nodes in the rubbing rotor system is equal to the ratio of the corresponding elements in the frequency response matrix of the pre-fault rotor system. The new model based rubbing identification method and the procedures are presented by utilizing this relationship: using the residual responses between the responses of the fault system and that of the pre-fault system, and by combining the dynamic model of the rotor system, the rubbing location can be obtained; then the rubbing forces can be obtained by using the harmonic components of the rubbing rotor responses. In order to test the efficiency of the presented detection method, numerical simulations are carried out and the effects by the supporting stiffness and noise are analyzed, and experiments based on a rotor test rig are also carried out. Using this method, the rubbing location and rubbing forces can be identified by using measured vibration responses of only two nodes in one operation speed, so it’s easy to apply in real rotating machinery.

Key words: Harmonic component, Quantitative diagnosis, Rotor system, Rubbing