Instantaneous Frequency Estimation Of Time-Varying Structures Based On Generalized S-Transform Reassignment

The dynamic response signals of bridge structures vary with time due to the influence of load,environment,human factors and etc.The accurate identification of dynamic characteristics plays an important role in the finite element modeling,fine analysis of the stressed state,structural model modification,health monitoring,wind resistance and seismic design of the bridge.The transient frequencies can reflect the characteristics of the transient components of the signal well.In this paper,based on the existing signal processing methods,an improved S transform and spectrum rearrangement technique is used to identify the transient frequencies of the time-varying structure.The main work of this thesis is as follows:Firstly,the existing time-frequency analysis methods are introduced.The advantages of S-transform are illustrated by comparison.It shows that S-transform is more suitable for analyzing non-stationary signals.The window width of S-transform is inversely proportional to the frequency,and the variation trend of the window cannot be changed.The expression of Gauss function cannot be used directly in computer because the Gauss kernel has infinite support and must be truncated to introduce a discontinuity at the boundary of a finite window,which may lead to errors in subsequent analysis and cannot be particularly accurate in signal parameter identification.Here,the fixed window function of S-transform is replaced by the elastic window tight support kernel function,and then the parameters of window function are optimized by time-frequency centralization criterion.The purpose is to improve the time-frequency resolution and applicability of S-transform,make the calculation simpler,and optimize the parameters of the kernel function by using optimization criterion,so as to make the time-frequency energy aggregation better.Because the time resolution and frequency resolution cannot reach the maximum at the same time,the focus of time-frequency is limited.The time-frequency curve in time-frequency diagram is generally wider,and a blurred time-frequency diagram is obtained.In order to get a better relationship between time and frequency,the time-frequency reassignment method is introduced in time-frequency analysis to improve the time-frequency clustering and effectively resist noise interference.Then the signal ridge is extracted by dynamic programming method to estimate the instantaneous frequency.In dynamic programming method,the energy is maximized by adding penalty function under smooth constraints.It improves the accuracy of instantaneous frequency identification.Through the experiment of cable structure with time-varying stiffness,the instantaneous frequency is identified by the extraction method,and compared with the results of wavelet transform,the proposed method is more accurate and effective.