Fault Diagnosis Research Of Aircraft Hydraulic Pipeline With Circumferential Crack Under Cyclic Pressure Impact Load

In the aircraft hydraulic pipeline system,the cyclic hydraulic impact is one of the main incentives to cause leakage,and the number of times of cyclic pressure impact is also the main index to evaluate its life.Defects often occur on the surface of aircraft hydraulic pipes during manufacturing,assembly and service.Under the action of cyclic hydraulic impact load,cracks will gradually form at the defect location,and then expand to form penetrating cracks,which may lead to leakage fault of pipeline system and flight accidents in serious cases.Therefore,the dynamic analysis of cracked hydraulic pipeline and leakage fault diagnosis become the important content and direction of aircraft hydraulic system reliability research.Based on this point,the dynamic analysis and leakage fault diagnosis of aircraft hydraulic pipeline with circumferential cracks are carried out in this paper.The main research contents are as follows:(1)Based on Newton's method,the fluid-solid interaction vibration equation of aircraft hydraulic pipeline is established with fixed-end constrained straight pipeline as the research object.And based on Euler-Bernoulli beam theory,the transverse bending vibration modal function and frequency equation of aircraft hydraulic straight pipeline under fixed support constraint are established.The frequency equation is solved by using MATLAB software,and the first two eigenvalues of pipeline are obtained,which lays a theoretical foundation for the follow-up work.(2)The modal function of cracked pipeline is constructed by adding a third-order polynomial to the modal function of fixed-support constrained pipeline.On this basis,the Galerkin method is used to discretize the fluid-solid interaction vibration equation of pipeline and simplify it to a low-order differential equation group of pipeline vibration.The differential equation group of pipeline vibration is solved by programming with MATLAB software,The variation of crack position,crack circumferential angle,mass ratio and fluid velocity on the dynamic characteristics of the pipeline is obtained.(3)The basic principle of detecting pipeline leakage fault by negative pressure wave method is elaborated in detail;the simulation model is established by AMEsim software to simulate and analyze the leakage fault of annular cracked aircraft hydraulic pipeline under cyclic pressure impact load;according to the simulation analysis results of pressure signal in pipeline,five kinds of wavelet functions in Daubechies wavelet system are used to decompose the signals respectively;Compared with the decomposition results of five kinds of wavelet functions,the optimal decomposition results are selected to locate the singular points in the signal,which lays a theoretical and methodological foundation for the follow-up experimental research.(4)Based on the hydraulic pipeline test bench,pipeline leakage experiments under cyclic pressure impact load were carried out.According to the pipeline pressure signal collected by the sensor,the optimal wavelet function is used to decompose the pressure signal and capture the position of singular points in the pressure signal.On this basis,the leakage position of pipeline is located based on the principle of negative pressure wave location.