Nonlinear Aeroelastic/Aeroservoelastic Modeling by Block-Oriented Identification

The investigation of aeroelastic/aeroservoelastic stability through flight testing is an essential part of aircraft certification. The stability boundary prediction is especially difficult when the instability is associated with nonlinearities in the dynamics. An approach is presented for the characterization of the nonlinear dynamics by noniterative identification algorithms. Two different block-oriented nonlinear models are considered to augment existing linear models with nonlinear operators derived by analyzing experimental data. Specifically, focuse is placed on the identification of Hammerstein or Wiener block-oriented models from a N-point data record {ūk, ȳk}k = 1 of observed input–output measurements from an aeroelastic/aeroservoelastic system. Central in the identification of block-oriented models is the use of an a priori set of orthonormal bases tuned with the dynamics of the aeroelastic/aeroservoelastic system. In both cases, a method is proposed to generate the orthonormal bases that is based on the cascade of input-normal balanced state-space realizations of all-pass filters. Case studies with a simulated structurally nonlinear prototypical two-dimensional wing section and actual F/A-18 active aeroelastic wing ground vibration test data are presented.