Nonlinear Aerothermoelastic Analysis Of Structures In Supersonic Airflow

Aeroelastics is a subject concerned mainly with the coupling effects between structures and aerodynamic pressure. Flutter is a typical aeroelastic phenomenon. It is a self-excited vibration under the interaction of the aerodynamic pressure, elastic force and inertia force of the structure. After the flutter happens, the stucture in the airflow will undergo the limit cycle oscillation, and it will be damaged due to fatigue because of the long-time periodic vibration. In recent years, with the increase of the flight speed of aircraft, more and more supersonic and hypersonic aircraft are produced. The aerodynamic heating caused by such flight speed that is much higher than the sound velocity will make the aeroelastic stability of the structure worsened, which brings new challenges to the investigations of aeroelastic problems, that is, the influences of the thermal effect caused by the aerodynamic heating under the high Mach number on the aeroelastic behaviors of aircraft structures must be further considered in the analysis. Therefore, it is significant to study the aerothermoelastic characteristics of supersonic and hypersonic aircraft structures. In this paper, aerothermoelastic properties of different materials, different boundary conditions and different strctures in supersonic and hypersonic airflow s are investigated thoroughly and systematically.Aerothermoelastic characteristics of composite laminated panels and shells in supersonic airflow are investigated. Before the flutter(Pre-flutter), the deformation of the structural system is relatively small. So the flutter bound and aeroelastic stability region of the structure can be researched by the linear small deformation theory. In order to establish the equation of motion of the laminated panels and shells in supersonic airflow using the linear theory, the influences of in-plane thermal loads on the transverse deflection of the structure are taken into account. Different discretization methods(assumed mode method and finite element method) are used in the structural modeling, and the effects of the aerodynamic pressure on the structural natural mode are investigated. The variations of the aerothermoelastic properties of laminated structures with the fiber orientation are also analyzed.Aerothermoelastic behaviors of new type lattice sandwich structures are deeply investigated. The research objects include the two-dimensional corrugated and triangular grid and three-dimensional pyramidal lattice sandwich structures, and the face sheets include the isotropic and composite lamianted panels. The constitutive relations of the lattice cores are evaulated using the equivalent theory. In the analysis, the linear frequency-domain method is used to study the flutter bound and aeroelastic stability region of the structural systems, and the nonlinear post-flutter dynamical behaviors are investigated by the time-domain method. The influences of the bending stiffness and different parameters on the aerothermoelastic properties of the lattice sandwich structures are investigated. The advantages of the lattice sandwich structures in the aerothermoelastic behaviors are also analyzed.The nonlinear fluid-structure-heat interaction of composite laminated panels in hypersonic airflow are studied. In the analysis, the influences of the shock wave on the airflow parameters are considered. Meanwhile, the interaction between the aerodynamic heating and aerodynamic pressure is also taken into account to realize the analysis of the fluid-structure-heat multi-field interaction. The heat flux produced by the aerodynamic heating is calculated using the reference temperat ure method. The equation of the transient heat conduction in the laminated panel is established by the finite element method. Time-domain responses of the aerothermoelastic structural system under the fluid-structure-heat interaction are computed.The methods for the aeroelastic problems of structures with complex boundary conditions and complex structures are investigated. First of all, the aeroelastic characteristics of two- and three-dimensional flat panels with different boundary conditions are analyzed. The method of solving the partial differential equation of motion directly and the finite element method are used, and the influences of the boundary conditions on the flutter characteristics are studied. Then the vibration and aeroelastic properties of two-span thin panels are investigated. The influences of the asymmetry of the structure on the vibration response and flutter bound are analyzed. At last, the analysis method for the aeroelastic behaviors of composite laminated conical shells under different boundary conditions is studied. The calculation accuracies of different solution methods are investigated.The nonlinear flutter and aerothermal postbuckling properties of active aeroelastic structures with the piezoelectric materials in supersonic airflow are analysed by using two kinds of control algorithms(H∞ and discrete LQG control methods). In the H∞ robust analysis, the influences 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. In addition, a discrete LQG control method is proposed to study the nonlinear flutter and aerothermal postbuckling properties of the active aeroelastic structure.