Identification of Crack and Internal Damping Parameters Using Full Spectrum Responses from a Jeffcott Rotor Incorporated with an Active Magnetic Bearing

Abstract

In smart rotor technology the active magnetic bearing plays a vital role in controlling vibration for safe and efficient running of high speed machineries, and for its condition monitoring or system identification. Researchers mostly investigated the dynamics of cracked rotors independent of the internal damping. Nevertheless, the internal damping is also influenced by the presence of crack in a rotating system because of rubbing of crack fronts during its opening and closing throughout the shaft whirling. The present work deals with the identification of rotor dynamic parameters in the cracked Jeffcott rotor considering both external and internal damping through a model based technique. The active control of vibration that is caused due to the transverse crack, unbalance and internal damping can be done by using the magnetic bearing. Numerical rotor responses and AMB currents are investigated using the full spectrum tool, which can reveal directional nature of the vibration signature in frequency domain. The response and current harmonics due to the excitation force of crack function, which is found from full spectrum analysis, are input to the proposed identification algorithm. It estimates the additive crack stiffness, unbalance in rotor, external damping, internal damping and AMB parameters such as the force-displacement and force-current coefficients. For different noise levels in responses and currents the proposed identification algorithm is tested for validating its robustness against measurement noise.