Nonlinear Dynamical Behaviors And Control Of A Journal Bearing-Flexible Rotor System

Rotating machinery plays a very important role in machinery, power, communication, aerospace, space technology and so on. It is also one of main equipments in national economy. Along with the rapid development of production, science and technology, research on some problems of nonlinear dynamical behaviors of a rotor system has evolved to be a top point in related fields nowadays. Based on this background, the method removing abnormal behaviors consisting in the flexible rotor-short journal bearing system is studied in this paper, and some useful results are got.During the operation of rotating machinery, serious accidents often happen. In fact, the irregular behaviors of machinery are mainly caused by its nonlinear vibrations So, the normal operation of system can be obtained if its complicated motions such as chaos are converted into simple synchronous periodic motions by small perturbations. Based on this idea, the displace feedback terms are introduced into the system directly in this thesis, instead of solving the unsteady periodic target orbit in traditional feedback control method. Then, the nonlinear dynamical behaviors of the controlled flexible rotor-short journal bearing system are studied by using numerical simulations.The motion characteristics and the control effects are analyzed by phase diagram, bifurcation diagram and Poincare maps. Researches show the results agree with the imagination. Furthermore, the approach adopted is easy to be used in experiment, for it only needs a small feedback-gain (less than 0.5), and only two variables are required to be controlled.Firstly, the analytical formula of the unsteady oil film force of the short journal bearing, is cited in this thesis. In addition, the methods for the research of the motion characteristics of system are introduced.Secondly, based on the theories above, the dynamical model of the short journal bearing-flexible rotor system is established, and the motion differential equation of the system is solved by using the Runge-kutta method, then, the diagrams about uncontrolled system are plotted by numerical simulations. Results show the various forms of periodic, quasi-periodic and chaotic motions.Thirdly, two displace-feedback terms are added to the model mentioned, the motion characteristics of the short journal bearing-flexible rotor system are investigated under the consideration of control, and its motion differential equation is solved by the Runge-Kutta method, then, the diagrams about controlled system are plotted by numerical simulations. Results show this control method can transform chaotic, quasi-periodic and multiple periodic motions into synchronous periodic motions.Finally, the results we've obtained are summarized in the end of this thesis. Also some creativities as well as existing problems are pointed out.