| Journal centre motion trajectory is a comprehensive behavior of journal bearing working condition. Journal centre trajectory analysis can be used to ascertain index repeatability and the least oil film thickness that to judge stability of rotor and rationality of the bearing design parameters. Directed towards complex stress state of journal bearing, the transient and periodical feature of nonlinear journal centre trajectory is studied in this dissertation, which is significant to precision and stableness control of rotating machinery.In the first place, the non-linear analysis model of journal centre trajectory is establish, which based on equivalence of neck journal inertial force, non-linear oil film force and dynamic load. Synchronously, based on linearization technique of oil film force the linear model that journal center whirl around its static equilibrium position is established for conveniently analyze.Secondly, an algorithmic method is proposed that locate the center position of journal centre trajectory. The following is the procedure, first solve the Reynolds equation of transient bearing center position according to initial conditions, resultant force of oil film can be got by integral of oil film force distribution, then acceleration of journal centre can be got by solve move equation, the next calculate parameters of next position by using Euler method, iteration in this method until acquire a completed journal centre trajectory.Thirdly, instantaneous characteristic of journal centre trajectory, maximum oil film force and minimum depth of oil film under step, square wave pulse, sinusoidal pulse and triangular pulse transient load are calculated separately, variation of main parameters is analyzed and also the influence to these parameters caused by different types of loads. Transient load applied to steady working journal bearing will cause the main parameters significantly changed. Step and square wave pulse load fluctuate considerable in time domain such as sinusoidal pulse and triangular pulse signals influence journal centre trajectory and main parameters notably. Owing to action time of impulse load is finite the shaft center will go back to its equilibrium position that the load applied before, on the other side step load will cause the shaft center transit to another equilibrium position.The cyclophysis of journal centre trajectory under unbalanced rotating load is investigated. Linear analysis and non-linear analysis of journal centre trajectory that affected by small disequilibrium load are compared, and both journal centre trajectory center position error and displacement amplitude error are studied. Under the condition of disequilibrium load is small, it can be taken as small disturbance, that non-linear analysis of journal centre trajectory can be taken placed by linear analysis, and the error between these two methods is small.When the load increased, the center of journal centre trajectory departs its equilibrium position and moves towards to journal center, and whirling displacement increases nonlinearly to the load, and the error between methods of Linear analysis and non-linear analysis will increase too. Spectral analysis is carried out to journal centre trajectory characteristic and dynamic oil film force, results show that shaft center displacement and oil film force not only contain the fundamental frequency component, but also second-harmonic generation and upper, and fundamental frequency force will increase linearly to the unbalanced load.Based on spectral features of nonlinear journal centre trajectory and oil film force, an idea of quasi-linear analysis method of journal centre trajectory under large disequilibrium load is proposed, which expresses the fundamental frequency part of oil film force as linear function of displacement and velocity, identify stiffness coefficient and damping coefficient of the bearing by LMS method, and then use these coefficient to analysis journal centre trajectory. The error between non-linear and quasi-linear analysis is calculated, results show that the latter can meet engineering demands and its computer time is much less.Finally, according to application of noncircular locus, method of shaping elliptic locus is investigated. The computational modeling of desired trajectories is established, and the control force is calculated that used to force the journal center to move along desired locus when the journal is rotating, the error between desired trajectory and test trajectory is worked out. After analysis the wave pattern, it can be concluded that the force needed to form a circle locus surpasses that to form an ellipse, besides the error is smaller to shape a circle than an ellipse. The ability of resist disturbance of backward precession is stronger than forward precession, even in the condition of critical whirl the locus of backward precession can reproduce desired trajectory accurately.Transient and periodical characteristic of nonlinear journal centre trajectory are investigated minutely in this dissertation, that to exposit inherent law of variation of it, these all lay the foundation for precision realization of rotating machinery, stableness control and acquiring desired trajectory.It is to be remarked that both the establishment of nonlinear journal centre trajectory calculating model and the proposing of its computing method are not concerned with concrete bearing structure, so all these methods can be used to all types of journal bearings such as hydrostatic bearing and hybrid bearing.This project is supported by National Natural Science Foundation of China (No.50275089,51075242)...
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