Empirical mode analysis of structural response and damping
A general method for the analysis of a time series, called the Empirical Mode Decomposition (EMD) and Hilbert Spectrum method, has recently been developed by Huang et al. This method contains two parts: the first part (EMD) decomposes any given time series data into a set of simple oscillatory functions by the repeated application of a nonlinear iterative procedure; the second part defines time-dependent amplitudes (or energies) and frequencies of the simple oscillatory functions using a Hilbert transform. In this paper, the EMD and Hilbert spectrum method is used to evaluate structural response by means of acceleration data of four different configurations of a two-dimensional welded steel frame constructed from many box beams, all filled with small viscoelastic beads. The results were compared to those of conventional methods such as modal analysis. The EMD method is also being further developed to extract damping values from experimental time series. In this approach, the damping loss factor is determined at regularly spaced frequencies associated with sampling. The method is particularly important for evaluating damping for time series data taken from an underlying physical process in which damping is dependent upon both time and frequency characteristics of the system.
