摘要(英) |
In the past, Fourier Transform (FT) was mostly used in the field of structural health monitoring as the analysis method to convert the structural response signals excited by seismic forces from the time domain to the frequency domain. However, Fourier Transform uses time-invariant bases to expand the signal which is only suitable for processing linear and stationary signals, and the characteristics of instantaneous signal fluctuations cannot be obtained. In order to deal with nonlinear and non-stationary signals such as seismic forces and structure responses, more sophisticated methods are needed for analysis.
Hilbert-Huang Transform (HHT) is a relatively new time-frequency analysis technique featuring with two characteristics of posteriori base and adaptive base, which is suitable for the analysis of nonlinear and non-stationary signals. This conversion can express the original signal as an energy distribution in time-frequency domain, so as to further observe the dynamic characteristics of the structure over time. HHT SHM is a method based on Hilbert-Huang Transform and integrates some numerical analysis methods. Through the time-frequency domain amplification function (T.F.AF) and the modal temporal variation curve (MTVC), we can find out the modal parameters that can represent the dynamic information of the structure.
In this study, bilinear materials are used to simulate the weakening of structures by changing the elastic modulus. The simulation can be divided into "elastic slope reduction", "yield stress reduction" and "plastic slope reduction ". Through the finite element software ABAQUS, a research model is established. We then apply seismic forces on the base for analysis and obtain the acceleration data of the base and the roof. To proceed, the acceleration signal is converted into a time-frequency spectrum by HHT SHM method, and the modal vibration characteristics can be extracted from the spectrum. Finally, we discuss the impact of altering elastic modulus on the modal parameters, and summarize the trend in order to interpret the modal parameters measured in actual cases in the future. |
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