The Impact of Design Deviations on Dynamic Characteristics of a Flexible Multispan Rotor on Complete Electromagnetic Suspension

Abstract

The paper presents a study of dynamics of rotors on complete electromagnetic suspension, a characteristic feature of which is a relatively low stiffness of the support system. The experience of balancing the rotors of this type shows that deviations of geometrical parameters, although the latter are within design tolerance limits, may have a significant impact on the rotor dynamics. The analysis of the impact of design deviations caused by the nonorthogonality of the disk plane of the axial active magnetic bearings (AMBs) to the rotation axis and noncoaxiality of the rotor shafting in the elastic clutch section on the dynamics of the flexible multispan rotors was made. The model of the dynamics of the rotor was refined considering the above deviations. The resulting model of the dynamics of a rotor on the complete electromagnetic suspension comprises a mechanical model, models of forces of different physical nature, and a model of the AMB control system. The model takes into consideration the effects of forces in the radial and axial active magnetic bearings, imbalance, gyroscopic forces, the force of gravity, and the frequency-independent inner damping; it also describes circulation impacts and tension forces caused by electromagnetic interactions in the generator and exciter as well as gas-dynamic forces in turbines, compressors, and labyrinth seals of their shafts. It is shown in the paper that the considered design deviations caused by nonorthogonality of the disk plane of the axial AMB to the rotation axis and noncoaxiality of the rotor shafting in the elastic clutch section lead to amplitude- constant harmonic influences on the rotor, whose frequency coincides with the rotational speed of the rotor. The verification of the refined computer model was conducted on a scale-modeling test bench for the vertical flexible rotor of a high-temperature gas-cooled reactor. The testing of the model demonstrated qualitative identity of the numerical and experimental results that describe the rotor dynamics in the running- down mode. The proposed mathematical model of the flexible rotor allows for enhancing the precision of the method for identification of unknown parameters, in particular, the residual imbalance, based on solving the inverse dynamics problem.