MODAL IDENTIFICATION OF AN AEROELASTIC SYSTEM USING AN EXTENDED KARHUNEN-LOEVE DECOMPOSITION

The paper presents recent applications of an output-only technique for modal identification of systems with non-uniform mass, based on an extension of the Karhunen-Loeve Decomposition (KLD). The method is here applied to identify the aeroelastic modes of a wing with a concentrated mass in a uniform flow. First, the spatial modal shapes of the coupled system are evaluated as the eigenfunctions (eigenvectors in the numerical approach) of the so-called extended Karhunen-Loeve integral operator, whose L(2)-kernel is the time-averaged autocorrelation tensor of the elastic displacement vector of the wing in the flow (available from experiments or computer simulations), multiplied by the density function of the structure. Then, the identification of the aeroelastic modal parameters is completed by considering the projection of the elastic displacement vector onto the Karhunen-Loeve eigenfunctions. Frequency and damping associated to each aeroelastic mode are evaluated as the solution of a multi-dimensional minimization problem, based on the optimal matching of the projection with an ideal damped oscillator. The methodology is here validated on the basis of a computer simulation and different approaches are shown. The output modes are in a very good agreement with the aeroelastic modes used to build the numerical input. Frequency and damping of each. mode are also in a good agreement with the relative input values.