| The metal flexible hose is an important compensation device in a pipeline system,which is mainly composed of metal bellows,metal braided mesh sleeve,and joints.Because the metal flexible hose has good flexibility,it is often used for the connection between pipes and can compensate for the displacement deviation of the pipeline system under special circumstances.With further research on the metal flexible hose,it is found that metal flexible hose has other functions such as noise reduction and vibration isolation in addition to displacement compensation,so the metal flexible hose is widely used in the pipeline systems.With the improvement of vibration and noise requirements of the pipeline system in the nuclear power industry,chemical industry,and other industries,the structural design,dynamic performance,and other aspects of metal flexible hoses are put forward higher requirements.However,at present,the theoretical research on metal flexible hose mainly focuses on metal bellows,while the theoretical research on the metal braided mesh sleeve and the metal flexible hose is very inadequate.In this paper,DN25 metal flexible hose is taken as the research object,and the following research work is carried out on the equivalent model and numerical simulation of metal flexible hose,stiffness and damping model,dynamic response analysis of metal flexible hose,and vibration reduction mechanism.(1)The geometric modeling method of the flexible metal hose is studied.In this paper,a geometric modeling method based on the generalized rose curve for the metal braided mesh sleeve is proposed,and an equivalent model of the metal hose is established based on the equivalent axial stiffness of the metal mesh sleeve.The modeling accuracy of the flexible metal hose is improved by solving the problem of the metal mesh sleeve.The accuracy of the flexible metal hose model was verified,and the reliability of the model was improved by crosscomparison with the metal hose numerical calculation and axial tensile test.(2)The axial stiffness and bending stiffness models of flexible metal hose are proposed.The axial stiffness model of metal bellows was established based on the beam element method.Based on the 1:1 braided element structure,the axial stiffness model of the metal braided mesh sleeve was established based on the energy method.The deformation mechanism of the metal mesh sleeve was studied.The axial stiffness of the metal mesh sleeve was characterized by Taylor series expansion in view of the nonlinear phenomenon caused by friction damping between metal wires and contact coupling stiffness caused by contact with bellows.Finally,the metal bellows and metal mesh sleeves are coupled in parallel to form the flexible metal hose axial stiffness model.The reliability of the axial model is verified by experiments,and the influence of different structural parameters on the axial stiffness of the flexible metal hose is discussed.According to the characteristics of the bending direction displacement of flexible metal hose,the bending stiffness calculation formula of flexible metal hose was established based on EJMA bending stiffness calculation formula,and the reliability of the bending stiffness model of the flexible metal hose was verified by comparing it with the finite element results.(3)The flexible metal hose damping model is proposed.The hysteresis damping is used to replace the structural damping in the flexible metal hose,and the characteristics of the axial and bending hysteresis curves of the flexible metal hose are summarized by analyzing the experimental data of the axial and bending hysteresis curves of the flexible metal hose: the axial hysteresis curve of the flexible metal hose has the characteristics of asymmetry and stiffness hardening,and the bending hysteresis curve of the flexible metal hose has the characteristics of symmetry.Based on the Bouc-Wen hysteresis model,a modified Bouc-Wen hysteresis model is proposed.By adjusting the parameters of the model,the model can describe the axial and bending hysteresis curves of the flexible metal hoses respectively.Aiming at the phenomenon that the parameters of the Bouc-Wen model of metal hose are not easy to determine,a "twostep identification method" for bouc-wen parameter identification is proposed based on the experimental data.For the linear region of the Bouc-Wen curve,the least square method is used to fit the parameters.Particle swarm optimization(PSO)is used to identify the parameters in the hysteresis region.This identification method not only solves the problem of traditional nonlinear convergence,but also solves the problem of single data of the traditional limit cycle method and provides an identification method for establishing the hysteresis model of the flexible metal hose accurately.(4)Based on the stiffness and damping models of the flexible metal hose,the single-DOF axial and bending dynamic models of the flexible metal hose were proposed.The equivalent linearization method is used to simplify the dynamic equation of the flexible metal hose.For the damping,the equivalent linearization damping of the model is obtained based on the energy conservation principle and the energy dissipation calculation method of the Bouc-Wen model.For stiffness,the linear stiffness of the flexible metal hose under small-displacement movement is selected for equivalence.The complex nonlinear dynamics equation was simplified to the linearization equation,and the response curve of the flexible metal hose system was obtained by frequency sweep.By comparing with the experimental data,it was found that the equivalent linearization model could meet the calculation requirements at low frequencies.(5)The vibration damping characteristics of the flexible metal hose are studied.The vibration isolation test of metal hose with different metal bellows structures and different metal mesh layers shows that the size of bellows mainly affects the stiffness of the flexible metal hose.The larger the size of the bellows,the harder the stiffness is,and the worse the vibration damping effect is.The number of layers of metal mesh sleeves can increase the vibration damping effect of the flexible metal hose,but when the number of layers increases to a certain extent,the stiffness of the flexible metal hose will increase,and the vibration damping effect will decrease instead of rising.The bending vibration reduction effect of the flexible metal hose is far better than that of axial vibration reduction because the bending stiffness of the flexible metal hose is far less than the axial stiffness.In axial vibration reduction,the vibration reduction effect of a long flexible metal hose is not necessarily better than that of a short flexible metal hose,because a long flexible metal hose will bring bending stiffness due to natural bending,and in bending vibration,the long flexible metal hose vibration reduction effect is better than short flexible metal hose vibration reduction effect.(6)This paper presents a two-step optimization method for flexible metal hose parameter design.According to the vibration reduction characteristics of the flexible metal hose,a twostep optimization method is used to optimize the axial stiffness of the flexible metal hose.Firstly,the structural optimization of DN25 metal bellows is carried out based on a genetic algorithm,with the axial stiffness as the objective function and the thickness,wave radius,and wave height as the independent variables.On the basis of determining the best size of the metal bellows,the metal mesh set in the metal hose is optimized.Taking the axial stiffness and equivalent stress of metal hose as the optimization objective,and the equivalent diameter of metal mesh sleeve as the optimization independent variable,after determining the optimal equivalent diameter of metal mesh sleeve,the number and diameter of the wire in metal mesh sleeve are determined according to the calculation formula of the flexible metal hose bursting pressure.It provides engineering design guidance for metal mesh sleeves so that the optimized metal hose can not only provide a better vibration reduction effect but also meet the working pressure requirements of the flexible metal hose. |
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