Modal analysis of structures with frequency dependent properties

A method is presented for obtaining a frequency dependent modal model from experimental test data. It is based on the decomposition of the system frequency response matrix in terms of real valued frequency dependent unit vectors and the complex exponentials of the phase angles between monophase excitation and response vectors. Modal parameters of normal modes are estimated from spatially filtered receptance plots using frequency domain identification algorithms. Real normal modes are directly calculated from monophase response vectors evaluated at the undamped natural frequencies, avoiding the complex-to-real conversion of the mode shapes in correlation and updating applications.