Supersonic Flutter And Control Of Laminated Structures With Complex Boundary Conditions

Flutter is a self-excited vibration phenomenon caused by the mutual coupling of the inertial force,elastic force and aerodynamicn pressure when the structure is exposed to the supersonic airflow.When flutter occurs,the aircraft structure will exhibit a large amplitude limit cycle oscillation,which will cause fatigue damage of the aircraft structure and even cause the aircraft to crash in flight.In recent years,with the rapid development of materials science,the laminated structures with light weight and high specific strength are used in the structural design of the aircraft,which directly leads to more complex for the aircraft structure.In addition,the temperature rise caused by aerodynamic heating during the flight will introduce in-plane thermal stresses and bending moments to the aircraft structure,which will seriously affects the structural aeroelastic stability.Therefore,it is of great value to investigate the aerothermoelastic characteristicss of the light weight laminated structure with complex bounday conditions.In this paper,the supersonic flutter behaviors and active vibration control of the laminated structures complex boundary conditions are studied systematically.Based on the Rayleigh-Ritz method,the supersonic flutter and thermal buckling behaviors of the laminated cylindrical shells with elastic boundary are studied.The elastic boundary are simulated by a series of distributed springs.The aerodynamic pressure acting on the structure is calculated by the piston theory.The shape functions of the cylindrical shell with elastic boundary are derived by the Rayleigh-Ritz method.The equation of motion of the structure is established using Hamilton’s principle.The influences of different types of spring stiffnesses on the flutter and thermal buckling bounds are studied.The aerothermoelastic behaviors of the cylindrical shell under different length to diameter ratios and ply angles are analyzed.After that,the aerothermoelastic behaviors of laminated panels with relaxed boundary are studied.The relaxed boundary is simulated by a set of springs,and the degree of the boundary relaxation is evaluated by adjusting the stiffness of the boundary springs.The influences of the relaxation degrees of different boundary constraints on the structural flutter and thermal buckling behaviors are studied.The natural frequencies of the panel under different elastic boundaries are obtained by experimental method,which demonstrates the rationality of elastic boundary design and the correctness of theoretical calculation.Supersonic flutter and aerothermal postbuckling behaviors of the composite lattice sandwich panels resting on elastic foundations are deeply studied.A mechanism is proposed to suppress the limit cycle oscillation and eliminate the thermal buckling of the structure by means of the Winkler–Pasternak elastic foundation.The von Kármán large deflection theory is used to simulate the structural geometric nonlinearity.The aerodynamic pressure is calculated by piston theory.The effects of the shear layer and Winkler parameters on the limit cycle oscillation and thermal buckling amplitudes of the lattice sandwich panel are studied.The supersonic flutter and thermal buckling responses of the structure with different ply angles,and radius and material properties of the trusses are calculated.The influences of several significant paremeters including ply angles,elastic foundation parameters,aerodynamic pressure and temperature change on the bifurcation and chaotic dynamic behaviors of the structure are investigated.An experiment is designed to test the natural frequencies of the lattice sandwich panel resting on elastic foundation,which verifies the correctness of the theoretical results.Supersonic flutter behaviors of the composite laminated panels with moving boundary consitions are studied,and the investigations on active flutter and aerothermal postbuckling suppressions for the piezoelectric compsoite laminated panels with moving boundaries are carried out using the displacement feedback and LQR/EKF(linear quadratic regulator and extended Kalman filter)control methods.According to the von Kármán large deflection and classical lamianted plate theories,the strain-displacement relation are established.Nonlinear dynamic equations of the structural system are established using Hamilton’s principle and the assumed mode method.The frequency-domain method is used to study the flutter bound and aerothermoelastic stability region of the structural systems,and the flutter behaviors are investigated by the time-domain method.The effects of aspect ratio and ply angle on the aerothermoelastic behaviors are studied.In displacement feedback control,the active stiffness generated by MFC(macro fiber composite)is used to suppress the flutter and aerothermal postbuckling of the structure.In LQR/EKF control algorithm,the extended Kalman filter is used to evaluate the state of the structural system,and the nonlinear effect of the system is considered.Controlled vibration responses of the structural system and the control voltages applied on the actuator under the two different controllers are compared.Nonlinear vibration characteristics and active control of composite lattice sandwich panels are studied.Three types of the sandwich panels with pyramidal,tetrahedral and Kagome cores are considered.The nonlinear free and forced vibration responses of the sandwich panels are calculated using the forth-order Runge-Kutta method.The influences of the ply angle of the laminated face sheets,the thicknesses of the lattice core and face sheets and the excitation amplitude on the nonlinear vibration behaviors of the sandwich panels are studied.The velocity feedback and H_∞ robust control methods are used to control the nonlinear vibration of the lattice sandwich panel.In the H_∞ robust analysis,the effects of the uncertainty caused by the linearization of the nonlinear system are taken into account.The mixed sensitivity method is used to solve the robust control problem.