| In recent years,with the increasing pressure of environmental protection,gas turbine is more and more widely used in the field of power generation.However,the rotor mostly used in gas turbine is rod fastening rotor.This rotor structure causes the rotor system to contain various non-linear factors,which makes it possible to produce different dynamic behavior between the rod fastening rotor and the turbine rotor in the process of operation.Under the action of alternating load,the rotor of gas turbine may produce cracks,which may lead to the hidden danger of safety in the operation of the rotor system of gas turbine.Because of the particularity of the rod fastening rotor structure,the traditional linear vibration theory has some limitations in dealing with its dynamics problems.Therefore,it has certain theoretical significance and practical value to study the nonlinear dynamic characteristics of the pull rod rotor.In this paper,according to the rotor dynamics theory,the rotor structure of the gas turbine is used for reference,the lumped mass model of the three disk rod fastening rotor considering the nonlinear contact between the disks is established,and the equations of motion are solved by the Runge-Kutta method,and the bifurcation diagram is used.The influence of different system parameters on the nonlinear dynamic characteristics of rotor system is studied by means of chaos theory,which provides some theoretical support for revealing the dynamic characteristics of tension rod rotor system and understanding the influence of crack fault on rotor dynamics.The main contents of this paper are as follows:(1)In the rotor modeling,the three-disk circumferential rod fastening rotor is used as the research object,and the nonlinear contact between the disk and the rotor wheel is considered.The nonlinear motion equations of two kinds of rod fastening rotors with rigid support and journal bearing support are established and the time domain response signals of the system are calculated by the fourth order Runge-Kutta method.(2)On the basis of the contact stiffness between the wheels and the time-varying stiffness of the crack axis,a nonlinear differential equation of motion for the bending vibration of the rotor with open and close cracks is established by taking the three-disc rod fastening rotor with rigid support as the object.Numerical analysis method is used to solve the problem.The effects of rotation speed,crack depth,crack inclination angle and eccentricity on the response of the system are analyzed by using the spectrum waterfall diagram and amplitude frequency curve.The results show that sub-harmonic resonance occurs around the critical speed of 1/2 and 1/3 order during the increase of the speed of the cracked rod fastening rotor.Besides the fundamental frequency component,the spectrum waterfall of the cracked rod fastening rotor also contains 2 times frequency component.The analysis results can provide theoretical guidance for understanding the response characteristics of cracked rotor system and developing fault diagnosis of cracked rotor system.(3)On the basis of nonlinear oil film force,a dynamic model of a three-disc rod fastening rotor-bearing system with crack failure is established,and the fourth order Runge-Kutta is used to solve the model.The effects of rotation speed,crack depth,crack inclination angle and eccentricity on the response of the system are analyzed by using bifurcation diagram,three-dimensional spectrum diagram,time-history graph,spectrum diagram,Poincare section diagram,axis trajectory diagram,etc.The results show that the system has rich nonlinear dynamic behaviors such as multi-period,chaos and so on.When the cracks are serious,the rotational speed of the system entering bifurcation will increase and the nonlinear and instability of the system will increase.The increase of unbalanced force caused by eccentricity will simplify the nonlinear behavior of the system and make the system unsteady lag. |
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