IDENTIFICATION OF TRUE STATE-VARIABLE DECOMPOSITION MODES FROM MODAL COORDINATE DATA

摘要

The recently developed state-variable modal decomposition method provides a quick and efficient way to estimate modal parameters from data for a multi-degree-of-freedom vibratory system without having the need to measure inputs. Associated with the decomposition method are the state-variable modal coordinates (SVMC), which can be used to determine the quality of decomposition. In present work, a systematic way is established to distinguish a true mode from a spurious one from features of the modal coordinates. In an approach similar, in principle, to the modal assurance criterion (MAC) for assessing mode shapes, a value is directly obtained by comparing the fast Fourier transform (FFT) of the impulse response of the modal coordinate, to the sampled ideal frequency response generated by the modal parameters obtained from the decomposition. Also, the norm of the difference between the FFT magnitude of the SVMC impulse response and the sampled identified ideal frequency response is used to distinguish the true modes. Various case studies using combinations of frequency and damping values are obtained in numerically simulated results. Actual modes are also distinguished from the spurious modes using test data from a uniform thin beam.