| Hydro-generator unit has the advantages of clean and environmental protection,convenient start-up and shutdown.It plays an important role in regulating the power grid and maintaining the safe and stable operation of the power grid.The complex non-linear dynamic behavior of hydropower plant and unit under the influence of electromagnetic,mechanical and hydraulic vibration sources has always been the focus and difficulty of research.However,for a long time,the vibration problems of unit and unit have been studied separately,ignoring the coupling effect between the two.For the coupled system,the previous research used the modal method to establish the dynamic equation for analysis,but in recent years,the research mostly used the complete finite element method.However,the modal method mainly solves the linear problems,but it can not accurately deal with the nonlinear problems;the complete finite element method has the advantages of accurate modeling,but for the complex structural model such as hydropower station,its discrete degree of freedom is large,the calculation is complex and time-consuming problems are particularly prominent.Therefore,in order to study the non-linear vibration characteristics of unit and foundation structure in the coupling system and improve the calculation efficiency,a simplified dynamic model of unit shaft-foundation coupling system is proposed and established in this paper.The non-linear dynamic behavior of the system is analyzed in depth.The non-linear dynamic characteristics of the system under random foundation excitations with different frequencies and strengths are studied.In addition,an optimization modeling method for foundation subsystem based on dynamic response is proposed,and the influence of changes in foundation parameters on the operation state of the system is studied.The main contents and achievements are as follows:(1)A simplified model of unit shaft-foundation coupling system was proposed and established.Considering the influence of non-linear forces such as electromagnetic force,sealing force and oil film force,the non-linear kinematic equations of the coupling system were derived by Lagrange equation method.(2)The system motion equation is solved by numerical method.The dynamic characteristics of coupling system and classical shaft system are compared and analyzed by combining bifurcation diagram,axle center trajectory diagram,Poincare mapping diagram,spectrum diagram and time history diagram.The results show that the coupling action of foundation can significantly affect the dynamic behavior of unit shafting.(3)The influence of external excitation on system vibration is studied by applying random external excitation of different frequencies and strengths to the foundation structure.The results show that the low frequency random external excitation will significantly affect the stability of system motion,while the medium and high frequency excitation is not obvious;the increase of random external excitation intensity also has a greater impact on the system motion state.When the external excitation is strong,the system cannot maintain the stable motion state.(4)A response-based equivalent model establishment method for foundation optimization is proposed and an optimization model of foundation subsystem is established.Compared with the model based on modal characteristics,the accuracy of the optimization model at low frequency region is slightly reduced,but the calculation accuracy in medium and high frequency region is significantly improved,which has a wider band application range.(5)The non-linear dynamic behavior of the system under different parameters is studied by changing the stiffness and damping parameters of the foundation subsystem.The results show that when the frequency of rotation is low,the change of the foundation parameters has little influence on the system.When the frequency of rotation is increased to the rated speed,the change of the foundation parameters will have a great influence on the motion state of the system. |
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