Nonlinear Flutter And Its Suppression Of New Composite Panels In Hypersonic Airflow

New composite materials including curved fiber composite panel and tunable Poisson’s ratio honeycomb sandwich structure have excellent characteristics such as light weight,high strength,energy absorption,vibration reduction and so on.These characteristics can well meet the requirements of innovative aircraft designation,therefore have good application prospects in the aerospace field.In this thesis,taking the aircraft skin structure as the research object,the nonlinear flutter of new composite panels with non-uniform stiffness distribution in hypersonic airflow is studied.Firstly,the third-order piston theory is used to describe the hypersonic aerodynamic force of the composite panel.According to the energy variational principle method,the finite element flutter equation of the composite panel is derived,and the fourth-order Runge-Kutta method is utilized to solve the nonlinear flutter response of the panel.On the basis of verifying the correctness and convergence of the method,the influences of high-order nonlinear terms of aerodynamic force on the flutter boundary and time-domain limit cycle oscillation of the curved fiber composite panel are discussed.The results show that utilizing the third-order piston theory can increase the critical flutter dynamic pressure of the curved fiber composite panel.For symmetric lay-up laminate,the dimensionless critical flutter dynamic pressure increases along with the increase of initial and terminal ply angles.This same effect can also be obtained by increasing the end ply angle of the curve fiber in the case of asymmetric ply.Secondly,in order to simulate the boundary loosening of the composite panel,nonlinear spring supports are added to the curved fiber composite panel,and the effects of nonlinear spring coefficients on the flutter characteristics of the composite panel are investigated.The results show that by introducing nonlinear spring supports,the stiffness of the composite panel is decreased,thus having a destabilizing effect on the aeroelastic stability of the cantilever panel.Also,the best position for the springs to be deposited is on the opposite side of the clamped edge.Finally,the nonlinear energy sink(NES)is applied in order of the panel flutter suppression.The effects of the positive / zero / negative Poisson ’s ratio effect caused by the change of the internal angle of various honeycomb units on the flutter behaviors of the hypersonic sandwich panel are calculated,and the effects of NES parameters on the flutter suppression of the concave honeycomb sandwich panel are analyzed in detail.The results show that the honeycomb sandwich panel with zero Poisson’s ratio has the smallest flutter amplitude.Meanwhile,by designing the appropriate NES parameters and installation position,the better suppression of panel flutter can be achieved.The research results may provide reference value for the design of new composite panel for aircraft.