Research On The Dynamic Characteristics Of Rolling Element Bearings And The Dynamic Model Of Bearing Rotor System

Rolling element bearing-rotor systems are widely used in industry. Their dynamic characteristics depend on bearings to some extent. The key of studying rolling element bearing-rotor systems lies in calculating bearing stiffness and damping accurately and understanding the influences of bearing structure stiffness on whole system. In past studies on rolling element bearing stiffness and damping, the influences of bearing material and lubrication film on stiffness and damping are not considered simultaneously. Therefore bearings are usually simplified to be a point on the shaft with radial stiffness and damping coefficient. According to the simplification, the computational accuracy for studying real rolling element bearing-rotor system decreased and the studies on bearing-rotor system is difficult to be acknowledged.In this dissertation, ball bearing, cylindrical roller bearing and tapered roller bearing are studied respectively and the concept of overall stiffness is proposed for the first time. Analytical model for calculating overall stiffness of rolling element bearing is established through stress EHL analysis, and the new model includes the influences of both lubrication and elastic deformation of roller and raceways. By use of the model, the influences of roller length, roller diameter, roller number, radial load and rotating speed on bearing overall stiffness are studied in detail and significant results are obtained and discussed. The concept of overall damping is also proposed for the first time. A new model for calculating the overall damping of rolling element bearing is established through analysis on load, deformation and implementation of Reynolds equation. By use of the new model, the influences of rolling element bearing structure on bearing overall stiffness are studied and some significant results are obtained and discussed. Also, by using the new stiffness and damping model, Jeffcott and chain-linked cantilever rotor supported by rolling element bearing are studied. The influences of bearing structure (roller length and roller diameter etc.) and working conditions (rotating speed and radial load etc.) on the critical speed and unbalanced response of Jeffcott rotor, and the influences of roller length of cylindrical, cantilever length, and bearing distance on dynamic characteristics of chain-linked bearing-rotor system are studied and discussed.By structure and mechanics analysis on cylindrical roller bearing, tapered roller bearing and ball bearing, the bearing-structure-stiffness model is proposed for rotor vibration dynamics analysis, new state vector relationships between ends of rolling element bearing are obtained, and the relationships are applied in the whole transfer matrix of the bearing-rotor system to built a new transfer matrix and vibration equations. A real bearing-rotor example is studied by using the new method, influences of rolling element bearing structure on modal shape, critical speed and unbalanced response are studied, and results show that the influences of rolling element bearing structure (especially cylindrical roller bearing and tapered roller bearing) on rotor dynamic modal shapes are significant, the influences of bearing structure on critical speed are faint, bearing structure reduce the unbalanced respond amplitude of the system, especially for cylindrical roller bearing supported rotor.Utilizing the new calculating models of stiffness, damping, bearing structure stiffness and the new transfer matrix, the dynamic characteristics of a nuclear air blower is studied. The influences of bearing structure on modal shape, critical speed and unbalanced response of the blower are calculated by use of the new transfer method. FEM is also used to calculate the same example to verify the new transfer method. Calculating results by use of FEM and by use of the new transfer method are quite close to each other. It indicates that the new stiffness model, damping model, bearing structure stiffness and the new transfer method established in this paper are quite credible.The new calculating models of stiffness and damping of rolling element bearings in this paper are more accurate than before, what is more, these models are easier for practical application. The established rolling element bearing structure stiffness model and the new transfer method also increase the accuracy of the dynamic chacteristics of the rolling element bearing rotor system. The research conclusions obtained in this dissertation will be very helpful for the further application and studies of rolling element bearing and its supported rotor.