Research On The Active-passive Compounded Periodic Strut Of Main Gearbox For Helicopter Cabin Noise Reduction

The noise in the helicopter cabin is very serious.How to reduce the noise level in the helicopter cabin has become a problem that can not be ignored in the process of helicopter development.Based on the background of reducing the broadband noise control in the cabin caused by the meshing vibration of helicopter main reducer gears,this paper studies the vibration reduction and control characteristics of an active/passive composite main reducer periodic brace by means of vibration control.The main research contents include the following parts:(1)A periodic brace scheme of active/passive composite main reducer embedded with piezoelectric elements is proposed.Based on the spectral element method and transfer matrix method,the dynamic analysis model of the periodic brace is established.According to the boundary conditions,the vibration transmission characteristics of the brace are obtained,and the active control method of feedforward differential control is proposed,which provides a theoretical basis for the subsequent design of the periodic brace.(2)Based on MATLAB,the simulation and the influence rule of parameters are studied.The variation of band gap and rigidity of strut structure with material properties,structure size and number of unit periods is obtained by simulation.At the same time,the influence of structural damping and control voltage on the band gap of strut structure is analyzed by numerical simulation of finite element software,which provides technical preparation for subsequent sample periodic strut design.(3)The sample periodic brace is developed,the broadband excitation test system is built,and the vibration characteristic test of the sample periodic brace is carried out.The experimental results show that when the control voltage is not applied,the composite main damping period brace exhibits good broadband vibration reduction characteristics after 500 Hz.Compared with the common main damping rod,the vibration attenuation can reach 45 d B.When the active control is applied,the starting frequency of the vibration band gap can move forward 210 Hz,and the attenuation in the resistance band range increases about 10 d B.The effectiveness of active/passive composite periodic struts is studied.