Analysis Of Vibration Characteristics Of Thin-walled Structures Under Thermal Noise Loading

With the rapid development of high-speed aircraft,the speed of the aircraft is faster and faster.This phenomenon leads to the high temperature load caused by friction and the strong noise load caused by thrust acting on the surface of the aircraft structure,which has a great impact on its vibration characteristics.Thin-walled structures are widely used for weight-reducing aircraft,so it is very important to study the buckling characteristics of thin-walled structures under thermo-noisy loads and the vibration responses before and after buckling.Based on Von Karman’s theory of large deflection nonlinearity,the thermal buckling of thin plates,the vibration characteristics before and after thermal buckling,and the nonlinear vibration response under the combined action of thermo-noisy loads are analyzed by finite element method.Firstly,based on the basic equation of thermal buckling problem,the variational principle of thermal buckling problem of thin-walled structures is established by using the method of variational product,and the eigenvalue finite element formulation of the problem is further derived.The critical buckling temperatures and buckling configurations of each order are obtained.The effects of different boundary conditions and different aspect ratios on the critical buckling temperatures are analyzed.Then,based on the basic equations of nonlinear dynamics,the variational principle of thermal vibration of thin-walled structures is established by using the variational method,and the vibration characteristics of thin-walled structures before and after buckling are analyzed by using the finite element method.The results show that the frequency before buckling decreases with the increase of temperature,but after buckling,the frequency increases with the increase of temperature.In this paper,the cause of this phenomenon is attributed to the effect of stiffness.At the same time,it is found that with the increase of temperature,the lower order modes of the structure will be lost in turn.Besides,random noisy excitation is simulated by using finite stationary white Gaussian noise.Thermal noise of thin-walled structures is analyzed by Newmark method in time domain.The displacement time history curves and stress time history curves of the midpoint of thin plate under different boundary conditions,different temperatures and different noiselevels are obtained.It is found that when the thermal load is larger than the noisy load,the structure vibrates slightly around a certain equilibrium position;when the thermal load is equal to the noisy load,the structure undergoes intermittent jump;and when the noisy load is larger than the thermal load,the structure undergoes persistent jump.This paper explains the cause of this phenomenon from the angle of stiffness and external excitation strength of the structure.At the same time,it is also found that high temperature and strong noisy excitation can increase the displacement response and stress response significantly,which seriously affects the fatigue life of the structure.