An approach for identifying the dynamics of large space structures is applied to a free-free beam. In this approach the system’s order is determined on-line, along with mode shapes, using recursive lattice filters which provide a linear least square estimate of the measurement data. The mode shapes determined are orthonormal in the space of the measurements and, hence, are not the natural modes of the structure. To determine the natural modes of the structure, a method based on the fast Fourier transform is used on the outputs of the lattice filter. These natural modes are used to obtain the modal amplitude time series from the measurements. The modal time series provides the input data for an output error parameter identification scheme that identifies the autoregressive moving average (ARMA) parameters of the difference equation model of the modes. Results using this approach for experimentally identifying the dynamics of a flexible beam hardware are presented.

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