Evaluation of time-domain damping identification methods for flutter-constrained optimization

Abstract

As engineers increasingly pursue air vehicle designs with slender, lightweight aerostructures, it has become necessary to model nonlinear aeroelastic effects earlier in the design process. As a result, high-fidelity analysis tools are required that can efficiently identify flutter within the flight envelope, and find design modifications to alleviate adverse aeroelastic behavior. To address these requirements, we have systematically evaluated automated methods to identify the damping of an aeroelastic system from a time-domain simulation. The techniques evaluated include the log decrement method, envelope function methods that use the Hilbert transformation, the half-power bandwidth method, and the matrix pencil method. The optimal approach was determined to be the matrix pencil method due to its robustness to noise and its ability to handle multi-component signals over short time simulations. Identification of the flutter boundary of the AGARD-445.6 wing is demonstrated with an automated method based on the adjoint sensitivities and the matrix pencil method. While the matrix pencil method is robust, identification of the flutter boundary using gradient-based optimization is shown to be sensitive to the initial dynamic pressure guess.