Vibration Analysis And Resonance Fatigue Test Of The Aircraft Hydraulic Pipeline

The aircraft hydraulic pipeline system is an important part of aircraft system, while its strength problems caused by vibration fatigue are always puzzling the hydraulic system designers and accident analysis personnels. With the development of the aircraft hydraulic system, these problems become more and more prominent. These problems may lead to fatigue destructions of the aircraft hydraulic pipelines, even huge economic losses or life casualties, which have certainly put foward a high request for the aircraft hydraulic system design. So it is essential in theoretic and engineering to study vibration characteristics and resonance fatigue testing of aircraft hydraulic system, improve design approach for safety and fatigue reliability.Previous researches on theoretic calculation and finite element simulation technology of pipeline system vibration has achieved great progress. However, the research on vibration of aircraft hydraulic pipe system in our country is mainly focus on the derivation of pipeline mathematical model and the finite element simulation of simple pipelines, so there are still certain gaps from the engineering application. Therefore, based on the practical project, it can provide an important theoretic guidance for vibration fatigue test to carry out the numerical analysis and finite element simulation on vibration caused by fluid-structure interaction for a typical aircraft hydraulic pipeline.Now, the research on vibration fatigue of pipelines is still in its infancy, and there are few universal methods and specifications for vibration fatigue test. In order to obtain the changing regularity of resonance fatigue life of pipes under sinusoidal excitations, it is needed to develop some test methods of vibration fatigue under sinusoidal excitations. Therefore, it is of the great importance to research on vibration fatigue test of the typical aircraft hydraulic pipeline.In this paper, numerical analysis and finite element simulation on the fluid-structure interaction of hydraulic pipeline systerm are studied. Moreover, the vibration characteristics analysis and resonance fatigue test of the typical aircraft hydraulic pipeline are studied. The main works can be described as follows:1. The mathematical model of the fluid-structure interaction vibration based on the transfer matrix method is presented, and the basic vibration equations of pipe and fluid are given.Then the point transfer matrix, the field transfer matrix and the overall transfer matrix are deduced respectively. The mathematical model of the fluid-structure interaction vibration based on transfer matrix is solved. The simulation results demonstrate the effectiveness of the transfer matrix method(TMM).2. According to the basic theory of Fluid-structure interaction(FSI) Method and Equivalent Mass(EM) Method, the modal analysis and finite element simulation technology are studied. The accuracy of FSI and EM methods are verified by comparing the results of simple pipes with the theoretical results, laying the foundation for the vibration characteristic analysis of the typical aircraft hydraulic pipeline.3. The geometry model and finite element model of typical aircraft hydraulic pipeline are simplified. The modal analysis of the typical pipeline is carried out through EM method, and the harmonic frequency of displacement excitation is determined based on the results.Then the transient analysis of the typical pipeline is carried out through FSI method, and the vibration fracture characteristic is determined according to the stress and acceleration response. Moreover, the monitoring points and load spectrum for fatigue test are provided.4. The vibration fatigue test system is designed with a short pipe in the actual hydraulic pipeline system as the objects of experiments. According to the test load spectrum, vibration fatigue test is performed, and the testing method and procedure are proposed. From the experimental data, the failure characteristics of pipeline fatigue can be obtained and the accuracy of simulation is verified. The strain life curves and acceleration fatigue curves of pipelines can provide the first-hand information for structure design, strength check and life prediction of typical aircraft hydraulic pipelines.