| Rotor dynamics is a sub-discipline of modern mechanics, focusing on research and analysis about the high-speed rotating dynamic characteristics, which has an advantaged engineering application background. These years, with the development of science and technology, the role of rotating machinery has been becoming more and more essential, accounting for the development directions towards high-speed, heavy load, light type and automation. On the other hand, faults and trouble manifested in the operation are attracting more and more concern. In the study of rotor dynamics, the importance of calculation and analysis can’t be neglected, which lays a foundation of the discussion about characteristics of rotor dynamics and analysis on various dynamic phenomena of rotor system.Meanwhile, it also contributes to optimizing rotor system design and solving relevant engineering problems.The research significance of this dissertation can be listed as follows. Firstly, verify the accuracy of modeling methods for various kinds of rotor model and make a theoretical analysis. Secondly, make a comparative analysis on versatility characteristics of rotor system with different parameters, considering sorts of factors affecting the stability. Thirdly, provide theoretical and technical support for optimal rotating machinery design, reliability and efficiency enhancement, vibration reduction as well as life extension. Among the known faults of rotor-bearing system, film instability is a common form of mechanical failure, which is characterized by sudden and destructiveness. Assume that the system is only affected by unbalanced force with fixed rotating frequency; it will present the periodic movement. When film instability occurs, however, rotor system will allow a greater low-frequency vibration beyond that, which will then undermine the original periodic motion, and result in non-coordinated precession, so that the shaft produces a large alternating stress which causes severe vibration of the rotor, and thus induces other failures directly related to the safety prevention and reliable operation of machine set. Therefore, study on the instability law of nonlinear rotor-bearing system and complicated nonlinear dynamic characteristics have a crucial significance to enhance motion stability of rotating machinery.Firstly, we establish mathematic expressions of the analytical model for continuous rotor system, based on Timoshenko simply-supported beam element theory, by which directly reach the integral dynamics equation. And then, we build finite element model of rotor system based on Timoshenko beam element theory, and form the integral dynamic equation through the matrix combination. After that, we make a finite element model simulation of the rotor based on Timoshenko beam element with the help of ANSYS software. Then we use numerical methods to analyze the natural characteristics of the rotating rotor system, verify the accuracy of the analytical model, and discuss the impact of the Gyroscopic Effect on the natural frequencies of each dimension in the system.Secondly, we transform the simply-supported at both ends of the shaft into elastic support, and draw Campbell diagram of the various speeds in the absence of the exciting force. In addition, considering unbalanced force caused by mass eccentricity and using NewMark-β solving linear differential equation, we cross-validate the accuracy by analyzing the Campbell diagram and harmonic response curve. We also make a comparative analysis of amplitudes at different nodes of the shaft under different offset positions, as well as of the effect on precession characteristic and critical speed caused by different moments of inertia, with the aim of providing theoretical support for subsequent model improvement.Finally, we replace the elastic support with nonlinear oil film force to establish an analytical model of the single disk rotor-sliding bearing system. By taking this system as the research object, the main research directions cover potential problems existed in the sliding bearing rotor system during the process of the high-speed rotating, such as film unstable vibration etc. Moreover, we analyze law of instability of the rotor system and its nonlinear characteristics under different conditions, by drawing chart of axes track, time-domain response diagram, three-dimensional frequency spectrum graph, bifurcation diagrams and Poincare sectional view. With those information, comparative analysis is made according to the effects on motion characteristics and nonlinear law of the system,which are created by variance of film thickness, eccentricity radius and gyroscopic effect. |
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