A Method for the estimate of modal parameters of time-dependent aerospace structural systems using operational data

For the Aerospace Industry the dynamic identification of a Launch Vehicle under its actual operative conditions is of great importance for assessing the numerical model of the structure and for improving the structural design. Therefore, the development of Operational Modal Analysis procedures able to track the time-dependency of the modal parameters of time-varying systems is of great interest for the aerospace applications. In this paper a method for the estimate of modal parameters of a time-dependent dynamic system that uses the Hilbert-Huang transform is proposed. First, the global time-trend of the natural frequencies is obtained by applying the Hilbert-Huang transform to subsequent time subintervals of the whole observation time. Finally, the damping ratios corresponding to the natural frequencies estimated for each time subinterval are estimated by using a standard method in operational modal analysis working in the frequency domain. The proposed method is assessed considering the numerically evaluated vibrations of a booster of a space launcher system.