The Z-plane modal analysis (ZMODAL) algorithm is based on topological characteristics of amplitude and phase in the Z-plane of the Z-transform of damped sinusoids. Since damping is a dimension of the signal representation space, it is possible to dissociate frequency modes that are close but have different damping coefficient. The algorithm is a trade-off between optimum utilization of information and CPU time. A suboptimal algorithm with a N In N growth is proposed, with the suboptimality compensated by a greater record length and a higher sampling frequency. In fact, ZMODAL is particularly suitable for high modal densities and populations, and appreciable record lengths. Like the Ibrahim Tine Domain (ITD) algorithm, it is based on free decay responses and does not call for force inputs. It accepts high-side-lobe-rejection spectral windows, which increase cross-modal rejection thus ensuring excellent results. The paper includes a description of the appropriate domain of utilization of these spectral windows and proposes a new method for quantitative evaluation of real mode-shape accuracy based on the phase output. The algorithm has been tested for different experimental results and computer-generated signals, and shows good agreement with ITD results.
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