Simulation Analysis And Fatigue Life Prediction Of Aircraft Hydraulic Piping Structure In Complex Vibration Environment

As an important part of the aircraft,the hydraulic system is adapted to the needs of the rapid development of the aerospace industry.It tends to develop in the direction of high pressure and complexity.The vibration caused by it also increases the problem of pipeline damage.Therefore,it is necessary to analyze and study the vibration response and fatigue life of the pipeline structure to improve the safety and reliability of the aircraft hydraulic pipeline structure.At present,most of the analysis of the vibration characteristics of the aircraft hydraulic pipeline structure considers a single pipeline structure under the excitation of a single vibration source,and there is no fatigue life prediction for it under a complex vibration environment.In view of this,This paper takes a section of double-pump parallel pipeline structure as the research object,comprehensively analyzes its vibration characteristics under the coexistence of random vibration excitation and hydraulic oil pulsation excitation,and proposes a fatigue life prediction method for aircraft hydraulic pipeline structure under complex vibration environment,and calculate the fatigue life of the double-pump parallel pipeline structure.The main content of this article is as follows:(1)The modal simulation analysis methods of aircraft hydraulic pipelines are compared and studied.For the L-shaped pipeline structure,the fluid-structure coupling method and the equivalent mass method modal simulation analysis were performed respectively,and the simulation solution and the theoretical solution were compared and analyzed to verify the effectiveness of the aircraft hydraulic pipeline modal analysis simulation method;The fluidstructure coupling method modal simulation analysis of the dual-pump parallel pipeline structure is studied,and its natural frequency and vibration shape diagram are obtained,which provides reference and technical support for the design of aircraft hydraulic pipelines and vibration control;The modal simulation analysis of the equivalent mass method of the double-pump parallel pipeline structure is studied,and the results are compared with the modal simulation analysis results of the fluid-structure coupling method.It is verified that the modal of the equivalent mass method is extracted during the random vibration response simulation analysis.(2)The dynamic response simulation analysis and strength check of the aircraft hydraulic pipeline under random vibration excitation are carried out.The modal superposition method is used to simulate and analyze the random vibration of the dual-pump parallel pipeline structure with the engine power spectrum excitation in three directions in space at the same time.Then,according to the response results,the dangerous points with the highest stress corresponding to different materials are screened out,which provides a basis for the subsequent screening of the comprehensive dangerous points of the hydraulic pipeline structure under the complex vibration environment and the fatigue life prediction.Finally,the strength of the aircraft hydraulic pipeline structure was checked according to the 3σ Von Mises stress value of the dangerous point,and the results show that the strength of the piping structure damage does not occur.(3)The simulation analysis and strength analysis of the pressure pulsation response of the aircraft hydraulic pipeline are carried out.First,the Bernoulli equation of the reducing pipe is derived,and taking a tapered pipe as an example,the outlet pressure is calculated through the deduced Bernoulli equation of the tapered pipe and the outlet velocity is calculated at the same time.The calculation results are compared with the simulation analysis results obtained by the ANSYS Mechanical and ANSYS CFX co-simulation method,which verifies the feasibility and reliability of the ANSYS Mechanical and ANSYS CFX co-simulation method.Then,according to the dynamic response results of the dual-pump parallel hydraulic pipeline structure under the excitation of hydraulic oil pulsation,the dangerous points of the pipeline structure are screened out,which provides a basis for the subsequent screening of the dangerous points in the complex vibration environment and the fatigue life prediction.Finally,the strength of the aircraft hydraulic pipeline structure was checked according to the magnitude of the Von Mises stress peak at the dangerous point,and the results showed that the pipeline structure would not undergo strength damage.(4)A method for predicting the fatigue life of aircraft hydraulic pipeline structure under the coexistence of random vibration excitation and hydraulic oil pulsation excitation is proposed.First,based on the results of the selected dangerous points of the dual-pump parallel pipeline structure under the excitation of a single vibration source,the dangerous points under the excitation of random vibration and hydraulic oil pressure pulsation are screened out.Secondly,according to the stress response of the hydraulic oil pulsation excitation at the dangerous point,the average stress is corrected by Goodman formula and the fatigue damage of the pipeline structure is calculated according to the corrected stress amplitude.Then according to the random vibration excitation response at the dangerous point,the frequency domain-time domain method is used to simulate the equivalent Von Mises stress time history,and the fatigue damage of the pipeline structure is calculated based on this.Finally,the fatigue life of the pipeline structure was calculated according to the proposed life prediction method under the co-excitation of random vibration and hydraulic oil pulsation,and the fatigue life of the pipeline structure was compared with that of the aircraft to confirm the safety of the pipeline structure.