Establishment of nonlinear dynamic model for prediction of rotordynamic instability of steam turbine rotor-bearing system caused by partial admission

A nonlinear dynamic model is developed for a rotor-bearing system with radial steam force due to partial admission, taking into account the prediction of subsynchronous instability of a steam turbine. The optimum schemes are obtained by comparing the rotor responses subjected to maximal radial steam forces in different partial admission schemes. It is found through comparison that the instability of a rotor-bearing system is directly related to the direction of the radial steam force in the partial admission scheme.