The Vibration Properties Analyzation And Damage Detection For The Complex Multi-span Pipe Conveying Fluid

The hydraulic piping system is one of the key airborne systems in the aircraft,the vibration properties of the piping systm are complex and the damages occur frequently with the development of the hydraulic system towards the direction of high pressure and high work-to-weight ratio.Therefore,the accurate prediction of the vibration and the damages detection technology is the key to ensure the safe operation of the airbone systems.This thesis aims to study the vibration characteristics and the damage detection technology of the multi-span pipe conveying fluid with the multiple accessories and complex boundary condition,and focuses on breaking through the solution method to analyze the vibration properties,exploring its vibration properties and damage detection technology.This thesis focuses on the key scientific issues of dynamics modeling and the solution methods for the multi-span pipe conveying fluid with multiple accessories and complex boundary condition,its damage mechanism and the dmage detection methods,etc.The research of the thesis includes the following contents:(1)To the best knowledge of the author,there is no work to study the multi-span pipe conveying fluid with multiple accessories and complex boundary condition.Therefore,the unified modeling and soluting method for the cascaded pipeline are given in present study.Then,the mechanism of the influence of fluid parameters(fluid pressure/flow velocity)on the vibration properties of the pipeline is investigated.It is found that the mode shapes of the pipeline within the critical flow velocity and critical pressure range are almost unaffected by the flow velocity and pressure changes.The interference factors of the mode shapes based damage detection are elimated by this discovery.To address the issue of cumbersome unified calculation of the vibration response of the pipeline under the harmonic and random excitation,the pseudo excitation method is employed to unify the calculations.What's more,the FFT based Transfer Matrix Method(TMM)is proposed to calculate the vibration response in the time domain to circumvent the cumbersome calculation in the modal superposition method.(2)To improve the numerical instability in analyzing the high-frequency vibration properties of the long-span pipeline for the conventional TMM,an improved TMM is proposed in this paper.Compaered with the improved TMM in the literature,the dimension of the global matrix is still 4 × 4.(3)Firstly,a simplified clamp looseness model is presented in this thesis,the vibration properties of the pipeline under the clamp looseness are studied based on this model.It is found that the strain mode shapes at the position of looseness are so different from the ones of healthy condition,and the differences increase with respect the degree of clamp,which provides the guidance for detect the position and relative degrees of the looseness.Then,to reduce the measurement points and the time needed for fitting,the tansimissibility based method is employed to calculate the mode shapes in the proposed operational modal analysis method.Finally,the corresponding experiments are conducted to validate all the discoveries and the poposed clamp looseness detection methods.In order to monitor the clamp directly,an FBG based smart clamp in present study.The smart clamp can address the limitations of the FBG based smart bolt and smart casher.The properties and the application of the smart clamp are studied with corresponding experiments.This smart clamp opens a new path to detect the clamp looseness.(4)The vibration properties of the pipe under different crack depth are analyzed in present study.It is found that the modal strain is more sensitive to the local crack and the distortion of the modal strain occurs on the crack.The degree of the disortation incrases with respect to the crack depth.Meanwhile,the region of the disortation for the crack is more localized when compared with the clamp looseness.The fingdings provide the guidance for the carack detection and the distinguition between the crack damage and calmp looseness.To address the issue that the conventional modal strain based damage indicator cannot distinguish the cracks whose modal strains cannot distinguishable,the enhance modal strain damage indicator considering the weights of the variation of the ratio of the natural frequencies is proposed.The corresponding experiments have proved that the findings and the poposed damage indicator are effective to detect the crack.The anti-noise performance of the proposed method is also studied.(5)Based on the research of the damage detection mentioned above,a condition monitoring system for the hydraulic piping system in the aircraft utilizing the C#language and MATLAB language is developed and designed.Meanwhile,a supervised classifier for the the clamp looseness detection under the multi-harmonic excitation is developed.The operational strain shape under the exciting frequency is proposed to be the featrure of the clamp looseness.The classification accuracies for the operational strain shape(OSS)and multiscale sample entropy(MSE)are compared,the experiment shows that the classification accuracy of the OSS is far higher than the MSE.The functional experiment for the condition monitoring system and the clamp looseness online detection are conduted,the experimental results show that the condition monitoring system can detect the clamp loosness accurately.