Nonlinear Vibration And Dimension Reduction Modelling Method Study Of Whole Aeroengine

The modeling method and nonlinear vibration research of aero-engine are important engineering science problems in aeroengine field.Modeling and analysis of high dimensional aeroengine dynamics is always a difficult problem in engineering.Solid element model can fully reflect the structural characteristics.The three-dimensional finite element model based on commercial finite element software has been used in many modeling studies of the whole aeroengine,but it is only applicable to the dynamic characteristics calculation of linear rotor system.The nonlinear factors brought by the support and connection of aeroengine structure cannot be considered comprehensively and the typical nonlinear vibration phenomenon cannot be analyzed in the solid whole machine model.Single-disk rotor model is used for nonlinear theoretical analysis at most of the existing researches.A few nonlinear dynamic models of the whole aeroengine based on one-dimensional beam elements have been verified on some simple testers.However,it is difficult to guide practical engineering design because these models can not accurately reflect engine structure characteristics.In this paper,a high dimensional dynamic model of the aeroengine was established,which can reflect the structural characteristics of the aero-engine.Local nonlinear modeling method,nonlinear substructure modeling method and nonlinear vibration analysis method of whole aeroengine were developed.The coupling vibration mechanism of the whole aeroengine system under the action of nonlinear Hertz contact force of rolling bearing,nonlinear oil film force of squeezed oil film damper,nonlinear joint force and nonlinear rubbing force was studied.Firstly,a contact force model of discontinuous rotor curvic coupling was proposed based on the nonlinear relationship between the interface displacement deformation and the restoring force to solve the local nonlinear representation problem of aeroengine structure.Based on the bearing force and oil film force models,a nonlinear double rotor model with support was established.i.A nonlinear contact force model was established according to the nonlinear relationship between the displacement and the contact interface.Considering the influence of the number of curvic coupling,a nonlinear model of curvic coupling was proposed.The contact force model proposed in this paper was verified via the pretightening force loss.ii.Support nonlinearities of rolling bearings and squeezed oil film dampers were established in the dual rotor model.Bearing clearance,number of ball bearings,outer ring stiffness,oil film thickness,oil film width,oil film radius and oil viscosity were considered comprehensively.The bearing nonlinear dynamic model was established,and the accuracy of the support nonlinear model was verified by the variable stiffness vibration of the rolling bearing and the damping effect of the squeezed oil film damper in the dual rotor model.The curvic coupling contact force model and support force model established in this paper provide a basis for the research of nonlinear dimensionality reduction methods of aeroengines with local nonlinearity.Secondly,a nonlinear substructure analysis method was proposed based on the component modal synthesis method and interface connection relation to solve the modeling analysis problem of nonlinear dimension reduction of high-dimensional complex structures.i.Based on the high-dimensional solid finite element model of each sub-structure of the rotor,virtual nodes are established in the corresponding area of the loading position,and massless beams were used to connect the virtual nodes and their corresponding area solid elements.The virtual nodes acted by loads were taken as the reserved nodes in physical space,and the dimensional-reduction mass matrix,stiffness matrix and gyro matrix were extracted by modal synthesis method for each substructure of the rotor.ii.The connection relation between each substructure was constructed by using generalized spring combined with the nonlinear contact force of curvic coupling proposed in this paper.The connection relation was applied to the virtual node corresponding to the interface region of the substructure.iii.Nonlinear supporting force was applied to the corresponding node at the journal,and unbalanced force was applied to the corresponding disk retaining node.The nonlinear vibration response of the discontinuous rotor was solved by the fourth-order Runge-Kutta method.iv.The rotational response of the gas generator rotor with curvic coupling connection nonlinearity and support nonlinearity was tested to complete the verification of the nonlinear substructure analysis method.Furthermore,a nonlinear vibration analysis method of high-dimensional aeroengine considering nonlinear support and nonlinear connection was proposed based on nonlinear substructure analysis method to solve the problem of nonlinear vibration analysis of highdimensional aeroengine.The method was verified by vibration test of the whole machine.Taking a typical twin-rotor turboshaft engine as the research object,the dynamics model of the whole machine for dimensionality reduction was established.The vibration characteristics of linear engine were studied,and the coupling effects of sharing support structure and casing structure on rotor dynamic characteristics were analyzed.The key points of engine critical speed design were proposed by analyzing the influence law of coupling critical speed.ii.Vibration response analysis was carried out for rolling bearing-whole machine,rolling bearing-squeezed oil film damper-whole machine and rolling bearing-squeezed oil film damper-nonlinear connection-whole machine respectively.Typical nonlinear phenomena such as parametric resonance,combined resonance,uncoordinated precession response,jump and bistable were studied.The important design parameters causing these nonlinear behaviors were studied regularly,which provided reference and guidance for engine vibration design.Finally,based on dimension reduction method and nonlinear vibration analysis method,a modeling and analysis method of vibration dimension reduction of high-dimensional engine with rubbing fault was proposed to solve the problem of coupling vibration analysis of bearingconnection-rub multi-nonlinear whole machine.A more complex aero-engine with blades was studied.Nonlinear connections and supports between substructures were further considered with the dimension reduction modeling method.The dynamic equation of substructure was constructed by adding nonlinear interfacial force and nonlinear rubbing force.The nonlinear dynamic equation of rub-impact was further constructed by the support relation between the structure of the whole machine,and the nonlinear vibration response of rub-impact was studied by numerical method.The bifurcation mechanism of the whole machine under the coupling effect of the nonlinearity of blade casing rubbing and structure was studied.The influence of rubbing,support,connection and coupling on the motion mode of the whole machine was discussed respectively.The motion law of rubbing fault of high dimensional machine was analyzed,which provided the basis for the vibration clearance design of the whole machine.