Folding-line-envelope-based Empirical Mode Decomposition And Its Applications

Hilbert-Huang transform (HHT) is a new processing method for non-stationary signal, which comprises Empirical Mode Decomposition (EMD) and Hilbert Spectral Analysis (HSA). After its introduction, HHT method has found its applications in the fields of the study of engineering properties of ground motion and structural system identification, ect. And it is just the method of HHT and its applications that the studies in this paper are centered around.As the study of the HHT method itself, aiming at the problem confronted by the traditional EMD method when processing long-period signals, a more efficient folding-line-envelope (FLE) based EMD method is proposed in this paper. By the function with definite analytical expression, the mathematical significance of the results obtained by the proposed method is demonstrated, and the characteristics of waveforms and spectra of the intrinsic mode function (IMF) resulted from decomposing the seismic wave by the method are also discussed.In order to validate in depth the physical significance of the results obtained by the proposed method, the FLE-based EMD is applied in analyzing the dynamic responses of linear time-invariant and linear time-variant single-degree-of-freedom (SDOF) systems, whose dynamic properties are identified meanwhile. The results show that, under the regular input, the FLE-based EMD can decompose the stationary part and the transient part from the system dynamic response, where the stationary part can provide the information on the spectral properties of input and the transient one can provide the information on the dynamic properties of system. This study not only demonstrates deeply the physical significance of the results obtained by applying the FLE-based EMD in the basic structural dynamic issues, but also offers to some extent the foundation for the in-depth application of this method in the field of structural system identification.At last, as the application of the FLE-based EMD in the study of the engineering properties of ground motion, the method is used to analyze the near-fault seismograms recorded in the Chi-Chi, Taiwan, earthquake in 1999, which contain velocity pulses. And the acceleration pulses are identified, whose contributions to the engineering properties of near-fault pulse-like ground motions are discussed using the response spectra.