Study On Prediction Method Of Dynamical Responses For Thin-Walled Structures Under A Combination Of Thermal And Acoustic Environmet

With the improvement of working performance,hypersonic vehicles will be exposed to an extremely combination of aerodynamic,thermal and acoustic environments during cruise or re-entry flights,which severely affect the integrity and durability of these vehicles.The researches on the dynamic and acoustic responses of thin-walled structures in thermal environments are significant to the optimal design of hypersonic vehicles.Prediction method of dynamical response for thin-walled Structures under a combination of thermal and acoustic environments is studied.Firstly,the governing equation of high-temperature composite plates and its solutions are established on the basis of the thin-plate theory and finite element method,and the influences of high temperature on the inherent characteristic of thin-walled structures are investigated from three aspects: material characteristics,warm prestress and geometrically nonlinear deformation.Secondly,based on the thermal modes and mode superposition method,the frequency response function can be obtained.Then,taking advantage of the reciprocity feature of frequency response function and Fourier transform,transfer function of thin-walled structures in wavenumber domain can be solved.Combing transfer function with the calculation method of sound pressure spectrum in wavenumber and frequency domain,and response spectrum of structures subjected to acoustic loads in wavenumber and frequency domain can be calculated,and the prediction method of dynamical response for thin-walled structures under a combination of thermal and acoustic environments is established.Meanwhile,making use of the Polynomial Chaos Expansion Method,the influences of uncertain parameters of structures on its natural characteristic and frequency response functions are studied.It is found that in the whole temperature range,the frequency decreases to the minimum values and then turns to increase as the temperature rises.The softening effect of reduced elastic modulus and thermal stresses is the major influence factor in the decreasing stage and the stiffening effect of buckling deflection plays the leading role in the increasing stage.With the temperature increasing,the modal shape interchange and change may occur.The characteristics of the linear thermal-acoustic responses of plate are determined by its thermal modes.The uncertain parameters of structures may have great influence on its natural frequencies and responses.When existing a variation coefficient of 8.75% in uncertain Young’s modulus or 5% in uncertain thickness,the response of structure may reach 6dB.