| Hypersonic vehicle will encounter noise load,thermal load,and mechanical load and other complex mechanical environment in the cruise and reentry phases.The noise load is mainly caused by the shock wave and the turbulent boundary layer,it is not only distributed in a wide frequency band,but also rich in high frequency components,which will affect the working precision and reliability of the key equipments in the aircraft.Thermal load will lead to the carrying capacity of the aircraft decreased,and have a great influence on the inherent characteristics,dynamic characteristics of the structure.The thermo-acoustic load will not only cause the severe sound and vibration response,but also may cause the initiation of crack,expansion,and lead to the panel and skin fatigue damage under rapid alternating stress.Therefore,we must pay attention on the thermal-acoustic-vibration fatigue failure in the aircraft design stage.The main contents of this dissertation are on the thermo-acoustic-vibration coupling responses and the fatigue failure of some key components.Firstly,the finite element method is used to find out how to obtain the accurate coupling loss factor(CLF)and ensure the accuracy of high frequency response.The influence of thermal effect on the low frequency,high frequency structural-acoustic responses and fatigue lives of aluminum panel are studied by the finite element method(FEM)and the statistical energy analysis(SEA),respectively.The details are as follows:1.Typical structural CLF calculation and error analysisThe finite element method is used to calculate the CLF and the numerical error is obtained by comparing its results with the those of the wave method.The influence of side length,internal loss factor(ILF),concentrated mass and boundary condition on the accuracy of CLF are studied,and some suggestions are listed for obtaining high accuracy CLF by FEM.Finally,the influence of prestress on the CLF is studied.2.The influence of thermal effect on low frequency structural-acoustic response and fatigue lifeThe influence of thermal effect on the vibration response of the panel is studied by FEM.The fatigue life of the panel is calculated by frequency domain method.We study the impact of changes of structural stiffness(elastic modulus and thermal stress)and S-N curve,caused by temperature variation,on the low-frequency fatigue life of aluminum panel.Finally,the fatigue life of the structure is studied under nonuniform temperature field.3.The influence of thermal effect on high frequency structural-acoustic response and fatigue lifeThe high-frequency structural-acoustic response and mean square stress of aircraft aluminum panel under different temperature conditions are analyzed by using SEA.The simplified stress power spectrum of the critical point is obtained by the zero moment stress spectrum method,and then high-frequency fatigue life of the panel is calculated by combining the frequency domain fatigue life methods.We study the impact of changes of structural stiffness and S-N curve,caused by temperature variation,on the high-frequency fatigue life of aluminum panel. |
PDF Full Text Request