| Pipeline system in aero-engine pipeline is mainly used for the transmission of hydraulic oil,fuel oil,lubricating oil,air and other media,which is an important part of the accessory device of the aero-engine.In recent years,there have been many aircraft failures and accidents caused by pipeline vibration at home and abroad.With the further development of aviation hydraulic system to high-pressure,the vibration of pipeline system will be more prominent,which is essential for the engineering.Therefore,it is of great significance to study the vibration mechanism and control of hydraulic pipeline.In this paper,typical pipline systems in aero-engines are studied,including L-type,U-type and Z-type,and finite element(FE)models of pipeline systems with clamps are constructed based on Matlab software to analyze the dynamic behavior of different pipeline types under different excitation types.The main contents in this paper are listed as follows:(1)Timoshenko beam element is derived based on Hamilton principle,and the dynamic model of L-type pipeline is established by FE method,and the elbow part of the L-type pipeline is modeled by means of multiple straight beams with different angles.Firstly,the proposed model is verified by the ANSYS and the modal test under free conditions.On this basis,the bilinear stiffness model of single clamp is established.Then the dynamics model of L-type pipeline system with single clamp is established by coupling the pipeline and the clamp.And the proposed model is further verified by ANSYS software and modal test under constrained conditions.On the basis of the dynamic model of the empty pipeline system,considering the influence of non-viscous and incompressible fluid,the dynamic model of the fluid-conveying pipeline system is established,and the influence of the velocity and pressure on the natural characteristics of the pipeline system is analyzed.(2)The equivalent viscous damping coefficient of the single clamp is determined by the complex stiffness method,and the influence of damping is considered on the basis of the bilinear stiffness of the single clamp.Dynamic simulation and experimental verification under the simple harmonic excitation,shock excitation and random excitation are performed.The simulation results are in good agreement with the experimental results,and the basic harmonic excitation test shows that the bilinear stiffness of the single clamp will lead to the appearance of multi-harmonic frequency in the amplitude spectrums,which can describe the real constraint conditions of the pipeline system with single clamp.(3)The multi-clamp pipeline systems based on FE method are established including the U-type pipeline system with three clamps and the Z-type pipeline system with three clamps.Firstly,the established model is verified by the modal test.On this basis,the difference and relation between section modeling and integral modeling are analyzed.In order to simplify the modeling of the pipeline system with multiple single clamps and improve the calculation efficiency.The natural characteristics under different tightening torques and the response characteristics of the pipeline system are also studied respectively,which are verified by the modal test and the basic excitation experiment.(4)Some linear stiffness and angular stiffness of the double clamp are obtained by experimental test.And the stiffness of the double clamp which could not be measured by stiffness test device is identified by genetic algorithm corribined with.modal test Considering the width of the double clamp,the double clamp is discretized equivalently into several linear spings.And dynamic model of the pipeline system with single and double clamps is established.Then the proposed model is verified by the hammering test and vibration experiment.The modal strain energy is proposed to quantify the vibration coupling degree of the pipelines. |
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