Finite element modelling, analysis and identification using novel trial misalignment approach in an unbalanced and misaligned flexible rotor system levitated by active magnetic bearings

This paper investigates the finite element modelling, analysis and identification of a fully-levitated flexible rotor with faults using active magnetic bearings (AMBs). For simultaneous estimation of the rotor residual unbalance and AMB residual misalignment (combination of parallel and angular), a novel trial misalignment approach has been proposed. Additionally, the force–displacement and force-current stiffness coefficients of AMBs are identified. This novel work is similar to the idea of trial unbalance in the rotor balancing. An unbalanced flexible shaft with multiple discs levitated by multiple misaligned AMBs has been mathematically modelled utilizing finite element method based on Timoshenko beam theory. To overcome the practical difficulty in measuring responses, the dynamic reduction scheme has been implemented to eliminate the transverse rotational degrees of freedom from the system model, which are further utilized in development of the identification algorithm. To numerically illustrate the reliability and robustness of the proposed algorithm, the algorithm is tested against the measurement noise in responses and rotor modelling errors.