Nonlinear Dynamic Analysis Of Bearing-Rotor System Lubricated With Non-Newtonian Fluid

With the development of science and technology, more and more countries pay attention to the high-speed and high-precision machine tool, which is a symbol of national scientific and technological progress. The machine tool requires the spindle not only keeps high speed operation stably, but also has tiny radial runout and rotary errors. Considering various nonlinear factors when the spindle operates at high speed, such as nonlinear liquid film force, air force, sealing force etc, this is very important to analyze nonlinear dynamics characteristics of the spindle system. The spindle system can be attributed to a class of bearing-rotor system. Among above factors, the influence of nonlinear liquid film force is the most outstanding. Therefore, there is necessary to study nonlinear dynamic of the bearing-rotor system which under the action of the nonlinear liquid film force.In practical applications, people add some additives in lubricants to improve lubrication characteristics. So lubricants should be no longer seen as Newtonian fluid simply, but considered as non-Newtonian fluid. For the moment, the research of nonlinear dynamic behavior of bearing-rotor system more limited to Newtonian fluid lubrication, but less in non-Newtonian fluid lubrication. This paper uses the basic theory of nonlinear dynamics and research methods to study nonlinear dynamic characteristics of bearing-rotor system supported by two couple-stress fluid film journal bearings with nonlinear suspension. Paper work mainly points to the following aspects:1. The research progress of high-precision spindle of machine tool, and the research status of water lubrication technology and couple-stress fluid are reviewed. And also the related concepts and common research methods of nonlinear dynamic are reviewed.2. Deduced the model of couple-stress fluid film force, and on this basis, established differential equation of bearing-rotor system with nonlinear suspension.3. Used numerical method to calculate the bifurcation diagram, time process diagram, phase diagram, Poincare mapping diagram and spectrum diagram of the system. And the results showed that the non-linear suspension system can inhibit the system bifurcation and the molecular characteristics length of couple-stress fluid has significant effect on nonlinear dynamic behavior of the system. With the increase of molecular characteristics length, the system critical speed will reduce so as the vibration amplitude.4. Analyzed the influence of lubricant viscosity, spindle stiffness and radius clearance on the system dynamics characteristics. The results showed that lubricant viscosity, spindle stiffness and radius clearance have obvious effect on nonlinear dynamics characteristics of the system.Through this study, we will have a certain understanding on nonlinear dynamics characteristics of bearing-rotor system under couple-stress fluid lubrication. The results provide some basis for the design of spindle system.