Numerical Analysis on the Nonlinear Hysteresis Phenomenon Associated with Instability of a Steam Turbine Rotor-Bearing System

The finite element method with a nonlinear film force model is applied to investigate the dynamic response and instability of a steam turbine rotor-bearing system. The nonlinear governing equations of motion with a large number DOF are solved by employing the Newmark method. The Budiansky-Roth criterion is developed to determine the threshold speed of the instability of rotor-bearing system during run-up and run down. The simulations manifest there are two different threshold speeds of the instability during run-up and run-down, which is referred to as hysteresis phenomenon associated with the instability of rotor-bearing system. The effects rotor damping on the dynamic response and instability of the steam turbine rotor-bearing system are numerically examined. It is shown that the location and width of the hysteresis loop are greatly influenced by rotor damping.