| The pipeline hoop is a standard component in aeroengines,and its main function is to fix the pipelines on the casing parts or connect various pipelines.It can be seen that the analysis and design of pipeline system with hoops must be carried out scientifically especially on the important equipment such as aeroengines,and the basis of these analyses is to obtain relatively accurate mechanical parameters of hoops under dynamic load.At the same time,the hoop in areoengines is typically composed of a metal belt and mental rubber.Since the metal rubber contains viscoelastic damping material and the viscoelastic material is frequency dependent,the mechanical parameters of the hoop obtained by statics may be different from the real state.Therefore,in this study,a method was developed by using the measured vibration data to obtain the mechanical parameters of the hoop inversely.This approach is called the inverse method.Based on the above problems,this paper carried out the research on the inverse identification of mechanical characteristics of a pipeline hoop in the aeroengine under dynamic load,which includes the following four parts:(1)Based on the measured frequency response functions(FRFs),the inverse method for identifying support stiffness and damping was adopted and the influence of preload was discussed.A dynamic model of the pipe-hoop system was built with the finite element method,and the formulas for solving the FRF were provided.On the premise of selecting initial values reasonably,an inverse identification algorithm based on sensitivity analysis was proposed.A case study was performed,and the support stiffness and damping of the hoop were identified using the proposed method.The rationality of the results was verified.Finally,the values of support stiffness and damping of the pipeline hoop under different preloads of the bolts were identified and the influence of preload was also discussed.Results indicated that the support stiffness and damping of the hoop exhibited frequency-dependent characteristics,and the stiffness and damping values in horizontal and vertical directions are different.(2)An inverse method for identifying the support stiffness and damping was proposed,which was based on the measured sweep response.The dynamical equation for solving vibration response of pipeline system was deduced by the developed finite element method.Then on the basis of response surface method,the polynomial fitting of stiffness and damping about frequency and corresponding response was carried out by the matching calculation,and the simple genetic algorithm was used for optimization.Finally,a case study was carried,and the support stiffness and damping with frequency-dependent characteristic were identified by the proposed method.By including identified values into the analysis model,the reliability of the identified results was proved by comparing the predicted and measured responses in the frequency domain.(3)The mechanical parameters of the hoop such as elastic modulus and material damping were identified,which was based on ANSYS optimization and measured frequency sweep response.First,an integral finite element model of the pipeline system was established and vibration response analysis were carried out under specific preload.Then the optimization tools and methods were determined by a simplified finite element model,which were applicable to this study.The random tool and zero order method were used to identify the mechanical parameters of the hoop.Finally,the elastic modulus and material damping of a typical pipe hoop were identified by the proposed method.The identification results were substituted into the three-dimensional finite element model,and the rationality of the identification results and methods was validated by comparing the calculated and measured frequency responses.In addition,the identification results show that the material damping of the hoop is frequency dependent.(4)ANSYS optimization module was used to study the elastic modulus and material damping on the basis of simplified hoop modeling based on virtual materials.Mechanical parameters were obtained based on the established integral finite element model of the pipehoop system,and then a new three-dimensional finite element model based on virtual material was established by isotropic virtual material method.Then,an inverse method for identifying the elastic modulus and material damping of the hoop(including metal rubber and metal clamps)was determined based on the random tool and zero order method.Finally,the pipe-hoop system was performed as an example and the rationality of the identification results was verified.It is necessary to obtain mechanical parameters of pipeline hoops in the aeroengine pipeline system accurately under dynamic load during dynamic modeling and vibration reduction analysis.In this paper,the inverse identification method was used to determine the mecnanical parameters of the hoop unaer aynamic ioad,wnicn can provide support for the dynamic modeling of aeroengine system and also provide reference for the inverse identification of other values. |
