Modelling and Dynamic Analysis of Rotor-AMBs System with Shrink Fit Assembly

Rotor-active magnetic bearings (rotor-AMBs) systems nowadays have been widely used in fluid machinery and the shrink fit assembly is widely applied in the rotor. However, when the shrink fit is tight enough, additional external perturbation could be introduced when rotor is levitated. The mechanism of this additional perturbation should be assessed to ensure stable operation of the machine. The effect of the shrink fit interface contact is equated to an additional stiffness matrix by massless spring units, whose certain contact stiffness is uniformly distributed over the interface. Particularly, we consider that there is partial separation in the contact interface due to the AMBs supporting and a novel additional stiffness matrix related to contact status is proposed by calculating the real-time contact area. The contact stiffness is calculated by microscopic contact model based on fractal theory. Finally, numerical simulation shows that the interface contact influences the system robustness and the unstable mode is excited. The increase of interference and contact length both will increase the amplitude of the rotor response. Moreover, the influence and order of the vibration are quantitatively validated by the experiments.