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In order to decrease the vibration of aircraft hydraulic pipeline, the vibration control techniques are studied from two aspects, i.e. suppression of the vibrating source and installation of dynamic vibration absorber. In this paper, the methods of increasing the length of the tubular joint and reduce the number of elbow are adopted to suppress the vibrating source, and a dynamic vibration absorber is developed to absorb the vibration of the main system. A finite element model of a real pipeline is established using ANSYS software and the exciting force is deduced under the pressure pulsation to study the response characteristics of the pipeline system. The results show that the designed pipe vibration can be reduced effectively after applying above methods. Introduction The hydraulic piping system [1][2] is an important part of the aircraft. Pipeline failure is becoming a prominent problem in military aircrafts. Excessive vibration might result in the oil leakage from the pipe joint, fatigue fracture, wearing of pipe wall, as well as the bursting of pipe wall. Oil leakage from the pipe joint has become the most frequent failure, which is caused by vibration for loose connection [3]. With the requirements of combat performance of modern military aircraft, the pressure of the hydraulic system has reached 21Mpa, and even 28Mpa.The pressure fluctuation caused by hydraulic piston pump has become the main excitation source of aircraft pipeline vibration [4]. According to the statistical results, the vibration fault caused by the pressure fluctuation accounted for more than 90% [5]. The greater the unevenness of pressure fluctuation, the larger the vibration force caused by pressure fluctuation. At the same time, the unreasonable pipe elbow and tube shape will cause the resonance of the pressure pulsation, which causes greater the pipeline vibration [6][7]. In order to decrease the vibration of aircraft hydraulic pipe excited by the pressure pulsation, this article studies the methods of suppressing vibration and maintain the natural frequency through modeling and simulation. Calculation and analysis methods of pressure pulsation in pipeline Before the analysis of the vibration of the hydraulic pipeline, it is necessary to carry out the corresponding analysis of the pressure pulsation. In this paper, an actual oil pipeline of a certain type of aircraft 1-166 is selected as the research object. Its pipe’s (1Cr18Ni9Ti stainless steel) outer diameter D is 18mm and inner diameter d is 16mm. The performance parameters of the pipe are as follows: the density 3 7850 / kg m ρ = , the modulus of elasticity 210 E GPa = , Poisson ratio 0.3 μ = . Then we calculate the finite element by ANSYS. During the pretreatment, we carry out the grid division of pipelines by the way of automatic mesh division and the cell edge size is 0.01m. The finite element model is shown in Fig.1. The working pressure of oil absorption pipeline is 21Mpa. The pressure pulsation amplitude is 10% of the pressure in the pipeline, that is 2.1 P Mpa ∆ = . We can obtain the component of excitation force produced by the fluctuating pressure along the pipeline direction, 407.1N. The boundary 6th International Conference on Mechatronics, Materials, Biotechnology and Environment (ICMMBE 2016) © 2016. The authors Published by Atlantis Press 142 conditions of the pipeline are shown in Fig.2. Elastic constraint are exerted at both ends of the pipe, whose support stiffness is 7 10 / k N m = . Then two exciting forces are exerted along the direction of the pipeline at both ends of the elbow. The excitation force of Pressure Pulsation is as bellow, 2 2 1 1 1 2 2 2 1 1 Δ Δ , Δ Δ 4 4 x x R S P d P R S P d P π π = = = = (1) In the type, ΔP is the fluctuating quantity of pressure in the pipeline, Δ / P P β = is the uneven pressure, 1 S and 2 S are the pipe flow area on both sides of the joint, 1 d and 2 d are the inner diameter of the pipeline on both sides of the joint [8]. Fig.1. Mesh generation of Pipeline 1-166. Fig. 2. Boundary conditions for harmonic response analysis of Pipeline 1-166. Fig. 3. Stress distribution of Pipeline 1-166 at Resonance. Fig. 4. Displacement distribution of Pipeline 1-166 at Resonance. According to the real pressure fluctuation frequency range of the aircraft, the pipeline analysis frequency is 500-1000Hz. We set 500 solving points to carry out the harmonic response analysis. According to the results, the stress and displacement distribution of the entire model at the resonance point of the frequency range can be obtained, as shown in Fig.3 and Fig.4. In these two figures we can observe that the red area has occurred in two different regions which are the weakest stress and the maximum displacement. 500 600 700 800 90

Vibration Controlling Techniques for Aircraft Hydraulic Pipe Excited by Pressure Pulsation Forces