Research On Three-Parameter Isolator And Multidirectional Isolation System For Sensitive Airborne Equipment

In airborne space,the mechanical environment with vibration and shock is the key factor restricting the working accuracy and service life of sensitive airborne equipment.It is necessary to study the high-performance isolation device to suppress the transmission of harmful vibration.Due to the highly integrated assembly density,the installation space is more strictly limited.In consideration of simplicity and reliability,it is necessary to design an isolator with high resonant frequency by decreasing some isolation performance.Therefore,the collision caused by exceeding the installation space could be avoided.At the same time,the increase of resonance frequency often leads to the insufficiency of damping ratio and the high value of resonant amplitude.So the damping force should be great enough to prevent from strength failure.In order to accommodate the broadband vibration source,three-parameter isolator design is proposed to improve isolation performance in high frequency.Combined with the requirements of minimization and lightweight design for sensitive airborne devices,three-parameter multidirectional isolation system with large dynamic stiffness is studied by theoretical and experimental methods.The study includes:1.Isolation performance Analysis of the concentrated parameter model.Research objects include the two-parameter model with spring-damping parallel connection,the three-parameter model with secondary spring in series,and the four-parameter model with internal mass.The influence of the characteristic parameters on the transmissibility curve is analyzed.For the higher order system with more than three parameters,the solution method of the optimal damping coefficient is given.The advantages and disadvantages of various systems are summarized.Two-parameter model has a low attenuation rate,while four-parameter model has the highest attenuation rate however a larger internal mass is needed.Comparatively,three-parameter model meets the requirement of lightweight design just by connecting secondary spring.The attenuation performance of threeparameter model in high frequency is fine,and the optimal damping could be calculated to minimize the resonance peak.2.Dynamic analysis and structural design of fluid damping isolation element.A mechanical model of thin circular plate with intermediate mass is proposed as the main spring cell,which can provide greater magnitude stiffness.Moreover,the welded bellow is used as secondary spring cell and the gap-piston cavity filled with viscous oil is used as damping cell.The dynamic model of the coupling between the elastic part and the fluid region is established so as to associate the internal design parameters of the isolation element with characteristic parameters of the three-parameter model.3.Dynamic analysis of multidirectional isolation system.Based on the Substructure frequency response synthesis,an analytical model of isolation system with centroid migration is established,and vibration coupling effecting on transmissibility in multiple directions is also analyzed.By solving the energy distribution matrix,the peek indicator to evaluated coupling degree is given.In addition,the time-domain angular vibration induced by coupling is also studied,which indicates that reducing the eccentricity and increasing the dynamic stiffness could significantly suppress oscillation.4.Experimental verification and performance test for the vibration isolation system.(1)The accuracy of theoretical modeling is verified by adjusting the thickness of diaphragm spring,oil viscosity and isolated mass.(2)Eight isolation elements were assembled and tested separately,so that the resonance peak is suppressed to about 6d B and the resonance frequency is adjusted to around 120 Hz.(3)The vertical and horizontal isolation elements are assembled into a two-direction isolation component.It should be noted that the input port of the isolation element is connected with the base through a flexible hinge,which reduces the influence of stiffness coupling.(4)Four isolation assemblies constitute the whole isolation system,and vertical and horizontal transmissibility curves are subsequently measured.The vertical resonance frequency is 121 Hz,and the amplification factor is 6.3d B.The horizontal resonance performance is respectively(113Hz,6.9d B)and(117Hz,8.6d B).The high frequency attenuation rate is all close to-40 d B/ dec,and time-domain RMS is decreased by 80% among0～1024Hz bandwidth.Therefore,the isolation system has high resonance frequency,low resonance amplification factor and good high frequency vibration isolation performance.