Analysis Of Time-frequency Characteristics Of Seismicity Based On WPT And Simulation Of Ground Motion Field

The time-frequency characteristics of ground motion are constantly changing with time and frequency,showing obvious non-stationary characteristics,which will have a significant impact on the results of structural response analysis.Therefore,it is a problem that structural response analysis must face for how to understand the time-frequency non-stationary characteristics of ground motion and how to consider this characteristic in ground motion time-history simulation.Wavelet packet transform is a more efficient time-frequency analysis method,which not only can focus the time domain and frequency domain features simultaneously,but also further split the high-frequency part of the signal,which makes up for the poor resolution of the wavelet transform in the high frequency range.Based on the theory of wavelet packet transform,this thesis studies the non-stationary characteristics of ground motion,the spatial correlation analysis of ground motion time history,the ground motion simulation of ground motion,and the simulation of space-related ground motion field.The main contents and conclusions are as follows:(1)Based on wavelet packet transform theory,this thesis establishes a time-varying power spectrum estimation method which is based on wavelet packet transform.The MATLAB platform is used to program to realize the estimation of time-varying spectrum.The method can not only analyze the time-frequency characteristics of the ground motion time history on the three-dimensional level of frequency-time-amplitude,but also obtain more accurate details in the high frequency band.At the same time,the correctness test can be carried out by comparing the relationship between the time-varying power spectrum and the Fourier spectrum and the corresponding energy accumulation curve relationship.(2)Based on the measured records of Taiwan's SMART-1 ground motion array,the MATLAB platform is used to program the spatial correlation study.In the aspect of frequency domain correlation,the correlation analysis of the spectrum based on wavelet packet transform can obtain the frequency domain coherence coefficients of two different distances in space.In the time domain,comparing the time of the time-varying power spectrum excellent frequency band,we can get the time-domain time-shift length function corresponding to different distances,which provides a basis for spatial correlation ground motion field simulation.(3)Based on the orthogonal characteristics of wavelet baseband,a new seismic wave simulation method is established by reconstructing wavelet packet.Based on the method,the program is programmed in MATLAB environment,which realize ground motion acceleration time history simulation based on the given target power spectrum,and the correctness of the method is verified by examples.(4)Based on the historical time history of the input ground motion,this thesis adjusts the sub-signal which is obtained by decomposing wavelet packet,and then obtains the ground motion time history by reconstructing wavelet packet.The method is extended to the multi-point correlation process,and the spatial coherence coefficient and time-shift function obtained in the previous thesis are used to simulate the ground motion time history,which can realize the simulation of the space-related ground motion field.The analysis of the example shows that the simulated ground motion field has a given spatial correlation property and retains the characteristics of the ground motion history record.