| The influence of wind-induced vibration on structural response of long-span bridges can not be ignored,and the characteristics of wind load have a direct impact on structural vibration.Wind loads have obvious non-stationary characteristics,that is,they change with time and frequency.The traditional Fourier transform method can not study the time-frequency local characteristics of wind loads.A new method is proposed to analyze the time-frequency non-stationary characteristics of wind loads from a three-dimensional perspective.At the same time,in order to meet the needs of structural dynamic response analysis,non-stationary wind speed time series samples were simulated.Wavelet Packet Transform(WPT)is an effective signal processing method,which can provide time-frequency local characteristics.It overcomes the shortcomings of the previous Fourier Transform methods that can not analyze both time-domain and frequency-domain,and also makes up for the problem of insufficient resolution of the wavelet method in frequency-domain.Based on the theory of wavelet packet transform,the time-frequency non-stationary characteristics of wind loads and the simulation of wind loads are studied in this paper.The main contents and conclusions are as follows:(1)Based on the theory of wavelet packet transform and the physical meaning of time-varying power spectrum,a method for estimating time-varying power spectrum was proposed.Programming was carried out on the platform of MATLAB to study the time-frequency characteristics of wind loads from the three-dimensional perspective of "time-frequency-amplitude",and compared with the results based on Fourier transform method,the correctness of this method was verified from two aspects: energy accumulation in time domain and power spectral density function in frequency domain.(2)Based on the given target spectrum,an algorithm of non-stationary fluctuating wind speed time series simulation was proposed by using inverse wavelet packet transform theory.Programming was carried out on the platform of MATLAB,and the sequence of simulation wind speed was obtained,and the correctness test was carried out.The example shows that the simulation spectrum is in good agreement with the target spectrum.(3)In order to retain some unknown characteristics of the wind speed time series signal,a method of simulation and adjustment of the non-stationary fluctuating wind speed time series was proposed based on the given historical time series.The simulation of thenon-stationary fluctuating wind speed time series was realized by programming on the platform of MATLAB,and the correctness of the simulation results were verified.(4)On the basis of single-point simulation,the simulation of spatial correlation wind field based on inverse wavelet packet transform was realized,and the correctness of the simulation of spatial correlation of wind field was verified from two aspects of power spectral density function and correlation function curve.(5)Based on the East Tower Suspension Bridge in Shenyang,the whole bridge was modeled and analyzed by Midas-civil finite element software.The validity of the model was proved by comparing the pulsation test with the modal analysis.Using the above method,the fluctuating wind speed time series of different grades were simulated and loaded on the suspension bridge model,and the time-history analysis was carried out.The displacement variation range of key parts of bridge structure under different levels of wind load was studied,which can provide reference for construction monitoring and health monitoring. |
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