Quantification of Dynamic Parameters of Flexible Rotor Partially Levitated on Active Magnetic Bearing

Abstract

An unavoidable fault that generally present in the rotor system is residual unbalance, and plenty of research has been carried out to develop off-line balancing techniques in the past. But, as present industrial need is moving towards a very high speed (supercritical) and light weight drivelines, it is important to use on-line balancing techniques instead of off-line balancing. Therefore, present work is focused on the on-linebalancing of a rotor system by estimating the distributed unbalance parameters with the help of active magnetic bearings (AMBs). The flexible rotor model having helicallydistributed unbalances along its length and supported by two conventional bearing at both ends is well thought-out here for the analysis. Two active magnetic bearings are considered to generate controlling force for suppressing the unbalance. Then, an equivalent discretized modelis formulated by utilizing seven numberof mass-less thin discs having an eccentricity equivalent to distributed unbalance in theflexible rotor.The finite element approachhas been used to obtain a unified model. In the present work, an identification algorithm has been developed to estimate unbalance parameters in addition with dynamic parameters of bearings i.e. conventional as well as AMBs. Equation of motion of the system hasbeen derived by considering only linear DOFs at bearing locations as generalized coordinates. Displacement at various nodes as well as current signals at AMB locations are calculated by using MATLAB Simulink. Since the present proposed algorithm requires frequency domain data to estimate unknown parameters, the time domain signal obtained from Simulink has been transformed into frequency domain by using Fast Fourier Transformation (FFT). The proposed algorithm is developed on the premise of the least-squares fit method in the frequency domain. Fourth order Runge-Kutta solver is used during numerical simulation. Gyroscopic effect has been neglected in the present work.