| Complex viscoelastic boundary conditions are widely used in the structural-acoustic coupling system in the engineering field.Rubber and epoxy adhesive are used to seal the four sides of the plate with the cavity.The viscoelastic body in the boundary can absorb the vibration energy,which has great application value in the field of noise reduction.However,it is difficult to establish the dynamic model of viscoelastic boundary materials by theoretical analysis.Clarifying the Structural-acoustic coupling mechanism of viscoelastic supported plate can promote the research of structural-acoustic coupling field with complex boundary conditions and has great signification for enhancing the application level of damping material construction technology in the fields of aviation,aerospace,ships and transportation.The boundary conditions are directly related to the fundamental resonant frequency and modal damping factor of composite plate structures.With the view of engineering application,the boundary conditions of elastic plate structure are changed from simply supported,clamped and elastic supported to more complex viscoelastic supported.In this paper,the vibroacoustic characteristics of composite structures under different boundary conditions are studied to obtain excellent acoustic properties.The main research work of this paper is as follows:The sound absorption characteristics of MPP(micro-perforated plate)-PM(permeable membrane)composite structure are analyzed,and an improved experimental device for measuring the flow resistance of PM material is designed.Considering the influence of material quality,the acoustic impedance electro-acoustic equivalent circuit of MPP-PM composite structure was established,which can be generally applied to the prediction of sound absorption characteristics of such composite structures.The effect of the surface density and flow resistance of the PM material on the absorption coefficient of the composite structure under normal incidence is analyzed.The results show that adding a layer of polyurethane micro-porous PM behind the MPP can improve the sound absorption performance in the middle and low frequency band.Aiming at the coupling boundary condition between porous material and panel,the sound insulation characteristics of composite plate structure with porous material and air layer simply supported on four sides are analyzed.The wave number of sound waves propagating in porous media is calculated based on Biot theory.The theoretical model of sound insulation coefficient of composite plate structure is deduced by means of mode superposition method and Galerkin method,and the sound isolation quantity of composite plate is calculated numerically.The theoretical model is feasible after comparing the sound insulation of composite panel under simply supported obtained by theoretical model with experimental results.Finally,The influence of the main parameters such as the plate structure size,boundary conditions and the thickness of porous material on the sound insulation characteristics is analyzed.The theoretical model of vibration response of rectangular plate is derived.The influence of complex viscoelastic supported element on the vibration response of plate is analyzed.The modified beam function is used as the trial function of Rayleigh-Ritz method to ensure the fast convergence of the calculation results,which is conducive to the vibration analysis of high-order modes.By adjusting the stiffness of translation spring and rotation spring,the Rayleigh-Ritz method can be used to analyze the vibration response of plate under arbitrary boundary conditions.By comparing the natural frequency prediction of the two methods,it is proved that the analytical model and the beam function are feasible.Theoretical calculation and experimental comparison methods are used to study the sound absorption and sound insulation performance of different forms,and the sensitivity of boundary conditions and key parameters of porous materials to the acoustic characteristics of composite structures under normal incidence is discussed.At the same time,the influence of different coupling modes between porous material and panel on the acoustic performance of the structure is analyzed.The sandwich plate structure designed in this paper has the characteristics of light weight,low energy consumption,good acoustical absorption and acoustical insulation characteristics in a wide frequency band.It is not only suitable for the vibration and noise reduction in the interior of the car riding space,but also can be widely used in various vehicles and buildings,which has a certain reference value. |
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