Increased-Order Models for the Prediction of Aeroelastic Limit Cycle Oscillations

While extensive research has been conducted on reduced-order aeroelastic modeling that starts with high-fidelity nonlinear computational schemes, an alternative increased-order approach that starts with linear schemes is presented. The alternative approach assumes that the system is essentially linear, namely can be adequately analyzed with linear models supplemented with some nonlinear components. The equations of motion are formulated as aeroservoelastic state-space models were the aeroelastic plant is linear and the nonlinearities are expressed as feedback loops. The feedback loops may be refined until adequate accuracy is obtained in comparison with experiments or high-fidelity computational fluid-dynamics and/or structural-dynamics results. The formulation approach and the solution processes are demonstrated for simulation of limit-cycle oscillations with actuator free play, aeroelastic response with nonlinear strain actuators, and for wing-store limit-cycle oscillations of a fighter aircraft with nonlinear aerodynamics.