Vibration Analyses Of Aero Hydraulic Pipeline System Under Multi-excitations And Its Constrained Layer Damping Technology

The hydraulic pipeline system,connecting the hydraulic pump to actuator,is one of the most important part in aircraft system for controling rudder and landing gear etc.Many types of aircraft are suffering from the excessive pipeline vibration damage duo to higher fluid pressure and lighter aircraft weight in China,which has a great impact on the safety and reliability of the aircraft.It is an urgent need and great challenging to solve the vibration problem of the aero hydraulic pipeline system.However,the vibration mechanism of hydraulic pipeline is very complex.On the one hand,the vibration coupling mechanism is complex duo to the long pipeline,muti elastic supports and the limited spatial layout by aircraft.On the other hand,the high fluid pressure pulsation by pump may easily result in serious vibration with large amplitude or mechanical resonance.There are still many challenges for the coupling vibration of pipeline,the complex vibration response of pipeline under multi-excitations,and the investigation on the vibration control technology of pipeline system.Therefore,for a typical hydraulic pipeline,it is of great important significance to carry out the modeling method for the pipeline system with long distance and muti elastic supports,the characteristics of the fluid pressure pulsation by pump and the base excition by airframe,the vibration behaviour of pipeline under the multi-excitations,and the vibration and dampling analysis of the pipeline with constrained layer damping(CLD)treatment.In this paper,the vibration characteristics of hydraulic pipeline system under the multi-excitations,the vibration and dampling behaviours of the pipeline with constrained layer damping treatment were investigated via the analytical method.numerical solution and experiments.The main obtained results are listed as follows:A model reduction method for the vibration analysis of hydraulic pipeline with long distance and multi elastic supports is proposed.An efficient solution procedure for the reduction model of pipeline is developed based on component mode synthesis.A pipeline with four elastic supports is investigated as a numerical example to validate the present approach.The natural frequencies,mode shapes and dynamic responses of the reduced model and are consistent with the full FEM model.The obtained results indicate that the current approach can reduce the computational cost significantly with sufficient accuracy,which is convenient and efficient to deal with the vibration of hydraulic pipeline.The mechanism of fluid pressure pulsation is investisgted based on the structure characteristics of hydraulic pump.The test method of pressure pulsation is obtained by the piezoelectric pressure sensor placed at the outlet of the pump.The characteristics of fluid pressure pulsation are investigated based on the spectrum analysis.A numerical coupling MOC-FEM approach is presented to solve the fluid-structure interaction for hydraulic pipeline.Based on the measured fluid pressure data,the hydraulic equations are solved by the method of characteristics(MOC)and the vibration equations of pipeline are solved by the finite element method(FEM)combined with the Newmark algorithm.The numerical results are compared with the experimental results,which verify the effectiveness of the proposed method.The results shows that the hydraulic pipeline system has the multiple harmonic peaks under the pressure pulsation,which leads to serious vibration of the pipeline.The base excitation characteristics are investisgted based on aircraft load spectrum,namely the airframe random excitation superposition the unbalance harmonic excitation of aeroengine rotor.The pseudo excitation method is presented to solve the vibration response of pipeline under random excitation.The results show that the pipeline has multi resonances under random excitation superposition harmonic excitation.The complex vibration characteristics of hydraulic pipeline system are investigated under fluid pressure pulsation and airframe base excitation.The present paper reveals the beat vibration phenomenon when the fluid pressure pulsation frequencies are close to the base excitation frequency.Moreover,the conditions of the dangerous beat vibration for hydraulic pipeline system are discussed.In order to effectively suppress the vibration of pipeline under multi-excitations,the constrained layer damping technique is presented.The developed nonlinear finite element method is employed to derive the motion equations of the CLD pipeline.The influence of the support stiffness,the thickness and the elasticity modulus of viscoelastic layer,and the constraining layer parameters are all considered.The numerical and experimental results show that the CLD technique can obviously control the pipeline vibration,resonance and the beat vibration,which can serve as an efficient tool for the vibration control of pipeline in engineering field.According to the present paper,a model reduction method for the vibration analysis of hydraulic pipeline with long distance and multi elastic supports is proposed.The beat vibration characteristics of pipeline under multi-excitations are discovered.The influence of constrained layer damping parameters for the vibration control of pipeline is defined.The findings of the present paper may serve as an efficient tool for the vibration analysis and design of hydraulic pipeline in aircraft.