Optimum Design Research Of Nonliner Rotor-Bearing System Stability Performance

Rotor-bearing system is the main part of the all kinds of rotational machinery that is widely used in many engineering fields such as mechanism, power, aviation and spaceflight. With the rapid advances of engineering and technology, the designs of rotor-bearing system are increasingly developing towards to high speed and flexibility. Meanwhile, many phenomena such as chaotic and quasi-period movement that are not interpreted by linear theory appear and bring a lot of serious accidents. This task comes from National Nature Foundation. Based on this ground, this paper studies the some nonlinear dynamic problems existing in bearing-rotor system. The results give some theoretical basis to designs of the rotor-bearing system.First, the nonlinear dynamic behaviors of rotor-bearing system are extensively investigated in some models of nonlinear rotor-bearing system. The result shows that when the rotational speed, mass eccentric and a synthesizing parameter of the system change, there exists such nonlinear dynamical phenomena as chaos and quasi-period movement. Through analyzing the characteristic point, the paper analyzes precisely the character of the system.Then based on the theory and methods of the stability of the rotor-bearing system in the nonlinear dynamics, Floquet theory and the shooting method are chosen to obtain the bifurcation patterns of periodic motions and their stability. Meanwhile, the period-doubling route to chaos is also illustrated. The results show that the rotor-bearing system have three bifurcations: saddle-node bifurcation, doubling bifurcation, Hopf bifurcation.In the end, using the rotor structure optimal design method based on genetic algorithms, rotor-bearing system structure are designed to maximize the instable speed of the rotor. Compared with a series of original parameters, the instable speed of the rotor has improved a lot. By analyzing the bifurcations pictures, the bifurcate point of the pictures is moving towards the point of high speed of the rotor. That shows that the stability of rotor-bearing system has been improved. By using GA we can get a series of optimal parameters quickly. That proves the method is advanced and effective.