Investigation And Optimal Design Of Generator Support-bearing-rotor Dynamical Systems

The analysis of the dynamic characteristics for the generator rotor system plays an essential role in the pre-engineering and post-maintenance of the generator units,which determines the safety and economy of the them.Therefore,it is of great significance to accurately establish the dynamical model of the generator rotor system.Most of the research on the generator rotor system failed to consider the stiffness of the foundation or only utilized the empirical values.In addition,the dynamical characteristics of the multicurvature elliptical bearing supporting the generator rotor,the nonlinear dynamics of the multi-curvature elliptical bearing-rotor system and optimal design of the rotor system have not been investigated.This paper mainly addressed these four issues.The dynamical model of the generator support subsystem and the whole rotor system were established and experimentally verified.Based on the mathematical models,the nonlinear dynamical characteristics of the generator bearing-rotor system are analyzed and the bearing-rotor system was optimized as well.The main research and conclusions of this dissertation are listed in the following contents:(1)The finite element models of generator bearing pedestals were established and modified according to the experimental results.And the finite element models were also verified.Accordingly,the dynamical stiffness characteristics of the bearing pedestals are obtained.The numerical calculation model of multi-curvature elliptical bearing with discontinuous property is developed by combining finite difference method and finite volume method.The oil film stiffness and oil film damping characteristics of multi-curvature elliptical bearings are analyzed as well.(2)The complex structure of generator rotor was simplified and the corresponding finite element models were established and validated by the experimental results of the rotor static deformation tests.Integrating the influence of the generator support subsystem on the rotor system,the complete dynamical model of the generator support-bearing-rotor system was developed.The critical speeds and the unbalanced responses of the generator rotor system were investigated using the dynamical models.The experimental studies of the rotor system of the generator were carried out to obtain the critical speeds and the unbalanced response characteristics of the rotor system,the results of which verified the correctness of the generator rotor dynamics system.Considering the nonlinearity of oil film force of multi-curvature elliptical bearing,a weakly coupled nonlinear dynamical model of oil film-rotor system was established.The nonlinear characteristics of multi-curvature elliptical bearing-rotor system was analyzed.The traditional elliptical bearing-rotor system under different unbalanced excitations were studied and compared with that of multi-curvature elliptical bearing-rotor system,which demonstrated the superiority of the multicurvature elliptical bearings.(3)The influence of various design parameters of multi-curvature elliptical bearing on oil film stiffness and damping was determined.The sensitivity of the natural frequencies and logarithmic decrement rate of the rotor system with regard to the system parameters was analyzed as well.Utilizing the dynamic characteristics of the rotor system including critical speed,logarithmic decrement rate at rated speed and unbalanced responses as optimal targets,the optimization functions were formulated and were solved through genetic algorithm.The optimal oil film stiffness and damping are obtained under different optimization targets.Subsequently,the final values of oil film stiffness and damping were chosen by thorough consideration of the influence of oil film stiffness and damping on the three kinds of dynamical characteristics.According to the optimal values of oil film stiffness and damping,the geometrical parameters of the corresponding multi-curvature elliptical bearing were given and validated by substituting them into the rotor system,the results of which illustrated the effectiveness of the optimization design method.In summary,the results of this research can provide useful theoretical guidance for modeling,analyzing and optimizing the generator rotor systems.