NONLINEAR FLUTTER OF ORTHOTROPIC COMPOSITE PANEL UNDER AERODYNAMIC HEATING

The problem of nonlinear aerothermoelasticity of isotropic and specially orthotropic panels in supersonic airflow is examined. The Reissner functional is used with Hamilton's principle to derive the governing equations of motion, the constitutive relations, and the natural boundary conditions. The work done by aerodynamic forces is represented by using the ''piston'' theory for two-dimensional lifting surfaces. The aerodynamic heating effect is estimated on the basis of the adiabatic wall temperature due to the high-speed airstream. Galerkin's method is then applied to generate a set of coupled ordinary nonlinear differential equations for any number of modes. Linear flutter analysis for heated and unheated panels is carried out for the linearized six mode equations that are aerodynamically coupled. Nonlinear dynamic deflection due to the six modes is estimated for different aerodynamic pressure levels. Poincare sections are estimated for three different types of materials, and it is shown that isotropic and 90-deg orthotropic panels experience chaos whereas 0-deg orthotropic panels exhibit regular limit cycles under all possible temperature levels. The 90-deg orthotropic panels are found to exhibit flutter at lower aerodynamic pressure than the one for isotropic or 0-deg orthotropic panels. The nature of chaotic response characteristics is further examined in terms of statistical response parameters such as power spectra and probability density functions.