Dynamic simulation of a flexible rotor during drop on retainer bearings

Active magnetic bearings (AMBs) present a technology which has many advantages compared to traditional bearing concepts. However, they require retainer bearings in order to prevent damages in the event of a system failure. In the drop-down when the rotor falls from the magnetic field on the retainer bearings, the design of the retainer bearings has a significant influence on the dynamic behavior of the rotor. In this study, the dynamics of an active magnetic bearing supported rotor during the drop on retainer bearings is studied employing a detailed simulation model. The retainer bearings are modeled using an accurate ball bearing model which takes into account damping and stiffness properties, oil film, inertia of rolling elements and friction between races and rolling elements. The model of a flexible rotor system accounts for unbalances as well as stiffness and damping properties of the support. In this study, the flexibility of the rotor is described using the finite element approach with the component mode synthesis. This study sheds light on the effects of a number of modes used in the component mode synthesis on the accuracy of simulated responses during the drop-down. In addition, the effect of different friction models on the behavior of the rotor is examined.