Rotor Drop Analyses and Auxiliary Bearing System Optimization for AMB Supported Rotor - Part I: Analysis Method

For rotors supported with active magnetic bearings (AMBs), the auxiliary bearing system (AUX) is needed to avoid potential severe internal damaging due to AMB loss power or overload. The evolution of auxiliary systems has been required by the American Petroleum Institute (API) using analytical or experimental methods. In part I of this paper, a detailed rotor drop transient analysis method including flexible shaft, rolling element bearing components, as well as flexible/damped supporting structures is given. Part 2 gives the experimental validation of the method with a test rig and model optimization. A finite element based flexible rotor model is used to indicate the shaft motion before the drop (operating conditions) and during the rotor drop event. Un-lubricated Hertzian contact models are used for the shaft and inner races, for balls and races. To avoid heavy time consumption, two different methods, which calculate the ball bearing contact loads, are discussed and the simulation results are compared. These models are applied to predict shaft-race-ball displacements and angular speeds, contact loads and ball bearing stresses during the drop for auxiliary bearings. This method also can be used to design and optimize the auxiliary bearing system as presented in the 2nd part of this paper, based upon the experimental testing results and validation.