Identification of Modal Parameters for Close-Mode Structures with Output-Only Data

A time domain method to directly separate system modes from spurious modes for close-mode structure with output-only data is presented in the paper. The time series analysis is often adopted for identifying structural dynamic characteristics in time domain with output-only data. However, the problems caused by spurious mode contradict its application to close-mode structures. According to the equivalent relationship between system equation of motion and state equation of output vector, the backward differential model of the correlation function is formulated with output-only data. Based on the location relationship between the unit circle and the eigen-values on the complex plane, a method to determine the system modes is proposed. The system modal parameters are then calculated by the system eigen-values and eigen-vectors of the characteristic matrix of the backward differential model. To verify the validity of the proposed method, numerical simulations of the Kabe's mass-spring model, which is a typical close-mode system, have been carried out with output-only data. The results indicate the feasibility of using the present method in the modal identification for close-mode structures with output-only data.