Study On Modeling And Behaviors Of Rotor-Bearing-Seal System Dynamics

Rotor dynamics is being studied prosperously at home and abroad. A great many of researchers and technicians are engaged in this field, and plenty of valuable references are published. Nowadays, more and more people are paying much attention to the nonlinear rotor dynamics of large rotating machinery, and it is found out that the rotor dynamic behaviors are affected heavily by the nonlinear factors, which especially include the oil-film forces in journal bearings and the fluid excited forces in gas seals.This thesis focuses on a better dynamic model of complicated rotor system and an efficient algorithm involved. Considering most relevant researches take the Jeffcott rotor or rigid rotor as research objects, comparatively, high-order industrial rotor system with local nonlinearity is studied here. This thesis studies on several aspects, such as, the model and algorithm of nonlinear oil-film forces and their Jacobian matrices in journal bearings, the model and algorithm of gas seals dynamics, and the model and algorithm of rotor dynamics of complicated rotor-bearing-seal system. Some achievements are acquired in current research from theory and practice, and conclusions that are reached here may be beneficial to the engineering applications in stability of rotor motion.In detail, there are the following contents and achievements in current research.(1) It is summarized that the history and appearance of bearing lubricating dynamics, seal dynamics, and rotor dynamics. Meanwhile, the relevant analytic methods and their applied ranges are also illuminated systematically.(2) A kind of new model with an efficient algorithm is put forth to solve the nonlinear oil-film forces and their Jacobian matrices of journal bearings together. Based on a one-dimensional variational inequality of the Reynolds equation, the oil-film forces and their Jacobian matrices are solved synchronously and rapidly. Meanwhile, according to the special characteristics of coefficient matrix within the algebraic equation with regard to the oil-film pressure, its formation is decomposed into an assembly of a term of the journal motion and some invariable matrices. Theseinvariable matrices can be calculated in advance, and they don't need to take part in the iterating process of nonlinear dynamics. That is an improvement of traditional models.(3) A two-control-volume dimensionless model and relevant algorithm of labyrinth gas seal are put forward to be an improvement of the traditional calculative model. We deduce the governing equations in a matrix form, and present a relevant algorithm that is based on the perturbation method. We can find that the nondimensional process and the matrixing make current model more concise, the substance clearer, and the approach simpler.(4) A kind of model of rotor-bearing-seal system dynamics is set up integrally in this thesis. Within this model, a new modal order-reduction method is presented, which takes the influence of nonlinear forces into account in the process of modal transformation, which makes the determination of the transformation matrix more reasonable and accurate. Meanwhile, the shooting method is introduced to acquire the periodic responses whose stability is determined by the Floquet theory. The Runge-Kutta integral method is introduced in solving the long-term responses in order to obtain the nonwandering sets of solution, which are used then to draw figures to analyze.(5) The relevant program of current algorithm is developed. With this program, for the first time, we analyze the rotor dynamics of an industrial centrifugal compressor with oil-film and gas seals forces together. Further, we investigate the linear and nonlinear dynamic behaviors comparatively, and analyze how the parameters of bearings influence the rotor dynamic characteristics. Comparing of consideration the gas seals or not, we are finding that the gas seals cannot be neglected about the rotor dynamic stability of certain high-pressure compressors. These analyses reveal that the fluid excited forces in gas seals play a key role in rotor dynamic stability sometimes.