Research On Influencing Factors Of Aircraft Hydraulic Pipeline Structure Vibration

Aircraft hydraulic pipeline structure services in complex vibration environment,and the pipeline structure is not only subject to the pipe wall vibration under the random excitation of the engine,but also the pipeline fluid-solid coupling vibration under the excitation of the pump source fluid.The former is mostly due to the basic machine body vibration caused by the diversified spatial layout of the pipeline structure,restraint conditions,and complex vibration coupling between the pipeline bodies.The latter is due to the fluid-solid coupling vibration caused by the pulsating flow output of the aircraft hydraulic plunger pump,the actual pipeline itself is in a vibration environment under multi-source excitation such as random vibration and flow pulsation.It will not only cause damage to the pipe wall,but also cause fretting wear of the supporting structure,resulting in a decrease in the supporting rigidity of the original pipeline structure,and making the pipeline structure failure.This paper takes a real aircraft hydraulic pipeline structure as the research object.ANSYS Workbench finite element analysis software is used to obtain the vibration response of the pipeline structure under the single excitation of engine random vibration and plunger pump fluid pulsation based on related theories such as mechanical vibration,pipeline fluid-solid coupling,and computational fluid dynamics.Comprehensively considering the coupling effect of the two,screening and verifying the stress limit under common excitation.On this basis,this paper carries out technical research on the influence factors of aircraft hydraulic pipeline structure from four aspects,pipeline structure support parameters,conduit parameters,pipeline boundary constraints and pipeline conditions.The main work and research content are as follows.(1)The research discussed the simplified reconstruction technology from the original CATIA model of the aircraft hydraulic pipeline structure to the three-dimensional solid model,and on the basis of this model,the vibration characteristic response analysis was carried out using ANSYS Workbench software.Based on the principles and methods of model simplification,the main key supports of the pipeline structure including single-hole pipe clamps with wall plates,135° three-way joints with flange structure and two right-angle joints are simplified.The Solid Works as modeling software was used to extract the shape,size and assembly parameter positioning information of the key component model,reconstruction,establishment and assembly to obtain a complete simplified 3D solid model of the pipeline structure.The static analysis of prestressed modal in the pipeline structure was carried out,and the vibration shape and frequency of the main order of the pipeline structure were obtained,which laid the foundation for the subsequent simulation analysis.(2)Analyzed and compared the stress response of the pipeline structure under the random excitation of the body and the pump source fluid pulsation excitation,and superimposed the stress response of the pipeline structure at the same position and the same point under the two excitations,and comprehensively analyzed and verified the pipeline structure Whether to meet the strength design requirements.The fluid model is equivalent by using the equivalent mass method,and the first four dangerous points of the 3paradigm equivalent stress value under the random excitation in different materials are screened.Based on this,the paradigm equivalent stress occurrence location and stress peak of the four materials under the excitation of fluid pulsation is obtained.the results show that random vibration hazards mainly occur on pipe clamp bolts,three-way joints and supports such as brackets,and the pulsating stress response to the stress on the overall conduit path is larger than the supports such as pipe clamps,brackets,joints,etc.and the impact of the pulsating fluid at the joint causes a greater stress response.Through comprehensive screening,the stress limits of the eight dangerous points under the four materials are obtained.Compared with the yield limit check of the materials,they all meet the strength requirements and no strength damage will occur.(3)The vibration of the pipeline structure under different factors is studied from four aspects: Support parameters,conduit parameters,boundary constraints,and pipeline conditions.First,by adjusting the support position of the straight pipe section where the support is located,it is found that it has a greater impact on the surrounding parts of the pipe section.By changing the thickness of the horizontal plate and the thickness of the side plate of the original L-shaped bracket,a comprehensive comparison found that an appropriate increase in the thickness of the side plate can greatly reduce the random vibration response of the pipeline structure.The theoretical calculation of the wall thickness of the analysis model of the pipe found that it meets the minimum wall thickness design requirements.A simple calculation example is used to compare the theoretical calculation with the simulation results,and the stress distribution on the end of the pipe was analyzed to verify the rationality of the simulation.By changing the damping parameters of the pipeline material and the pipeline structure,the analysis shows that selecting a stronger pipe and a reasonable increase in the damping ratio can effectively reduce the vibration response of the pipeline structure.Secondly,by changing the restraint method of the pipe end,the results show that the pipe end is connected with the adjacent hard pipe,and the constraint of fixed or hinged pipe end is close to the actual situation,while the free boundary constraint will lead to large vibration displacement error,and when the pipe end is far from the next support and the pipe section where it is deformed,it should be based on the real support layout of the aircraft hydraulic pipeline structure to consider setting constraints.Finally,Through the fluid-solid coupling transient response analysis of the pipeline structure under different environmental conditions during ground test and flight test operation,it is found that the pipeline near the pump source is more likely to produce greater stress response and bend the introduction of joints is the main cause of stress concentration.