Improved Matrix Fraction Approximation of Aerodynamic Transfer Matrices

Linearized aeroelastic stability and response analyses in the state domain may require the identification of an asymptotically stable finite-state aerodynamic subsystem from available aerodynamic transfer matrices, related to structural motions and gusts. To such an aim, the paper develops an improved rational matrix approximation, combining three nonlinear least squares identification techniques with a system reduction based on a double dynamic residualization. An alternative gust formulation is also presented that, by reconstructing generalized gust forces through the use of special structural motion-like modes called gust modes, makes it possible to determine a gust response even without the usual gust-penetration model in the frequency domain. Examples are presented to demonstrate the behavior of the proposed approaches applied to sample flutter and gust/turbulence response analyses.