Vibration and flutter analysis of stiffened composite laminated plates has been performed. The purpose of this study is to develop a finite element model and a reliable analysis code and to analyze the flutter characteristics of stiffened and unstiffened plates subject to thermal load. First order shear deformable plate and Timoshenko beam theory are used for the finite element model of skin panel and stiffeners, respectively. The von Karman nonlinear strain-displacement relation is used to account for large deflection due to thermal buckling load. The first order piston theory is used for modeling aerodynamic loads. The equation of motion is derived using principle of virtual work and can be separated into two coupled equations : static and dynamic governing equations. Newton-Raphson iteration method is used to obtain a static equilibrium shape. An iterative procedure of nonlinear complex eigenvalue analysis is used to analyze vibration and flutter problem considering geometric nonlinearity. Guyan reduction method is employed to reduce the problem size and computational time. Mode tracing procedure is applied to an efficient and accurate linear and nonlinear flutter analysis of stiffened composite panels. The procedure of linearized update mode/nonlinear time function(LUM/NTF) is applied to construct nonlinear eigenvalue problem in frequency domain analysis. The effects of thermal load, added stiffeners, and lamination angle on the flutter values of composite panels are examined. The presence of thermal load decreases the flutter values of unstiffened and stiffened panels. The flutter characteristics of stiffened panels are sensitive to the stiffening scheme, thermal load, lamination angle, and boundary conditions. The selection of proper stiffening scheme can improve the flutter characteristics of panels without increasing additional masses.
