عنوان مقاله [English]
In this paper an enhanced method for extraction of modal parameters (frequencies and damping ratios) of a structure from stationary or non-stationary measurement dynamic responses recorded by a sensor is presented. Surely one of the simplest methods in area of ambient modal identification (operational modal analysis) is autoregressive method. Major problem in autoregressive method is that for identification of m modes of a structure at least m sensors is needed. Besides, this method like other similar methods in this area such as frequency domain decomposition and stochastic subspace identification, is appropriate for extraction of modal parameters from stationary measured dynamic structural responses. To address these issues, in this study, the Hilbert vibration decomposition method which is a simple method for time-varying vibration decomposition based on the Hilbert transform, is adopted to improve the performance of the autoregressive method for extraction of frequencies and damping ratios of a structure from stationary or non-stationary responses recorded by a sensor. The efficiency and performance of the newly- enhanced method is investigated through two numerical examples and a verification example. The first numerical example deals with a single degree of freedom system subjected to a non-stationary force and the second one presents a two degree of freedom structure excited by a stationary force. Finally, using the proposed method the frequencies and damping ratios of a support tower of the segmental bridge via an experimental test are obtained. The results indicated that the proposed method adequately estimates the frequencies and damping ratios of a structure from stationary and non-stationary responses recorded by only one sensor. Moreover, it is found that this method outperforms the other relevant methods which dealing with the non-stationary responses. Consequently, the enhanced method is strongly recommended for extraction of the frequencies and damping ratios of the structures from stationary or non-stationary responses especially when dynamic response of the structure is non-stationary and measured using only one sensor.