Turbulent Characteristics Of Nonstationary Typhoon Winds In A Coherence Structure Viewpoint

It is capable of causing significant pecuniary losses together with heavy casualties yearly,so it is important to analyze fluctuating wind load of structures in the typhoon affected area,and those structures usually include tall buildings,large-span spatial structures,etc.Coherent structure and of fluctuating wind characteristics is an important intermediate parameter in wind load calculation,and the coherent structure of fluctuating wind is the key factor to accurately estimate the wind load and wind-induced response.This dissertation will establish coherent structure based on field measured data in the near ground typhoon field,systematic analysis the characteristics of coherent structure and its impact on the,turbulence intermittency,Gaussian property,peak factor and gust factor simultaneously.The dataset was selected based on the following quality control procedures: The anemometers were calibrated according to the clauses of “Near Surface Meteorological Observation Regulations in China”;Wind data segments were eliminated in case of instrument mechanical failures or voltage irregularities.the wind observation system has been improved,which comprises two movable wind observing towers,and the main purpose of this improvement is to enable them to work steadily and continuously for a long time in typhoon environment.Typhoon and normal wind have been measured with this observation system,fluctuating wind characteristics of typhoon and normal wind have been comparatively analyzed.Based on the data of the Typhoon hagupit and normal wind,the extraction of coherent structure and the characteristic analysis of the coherent structure are carried out,and the effects of the coherent structure on some turbulence characteristics are analyzed.In order to extract the multi-scale coherent structure and analyze the effect of coherent structure on turbulence characteristics,a discrete wavelet transform method is introduced.By analyzing the characteristics of the coherent structure,a wavelet coefficients spectrum analysis method is proposed,which combines the high resolution of the continuous wavelet large scale and the highest frequency resolution of AR model(autoregressive model),and obtains the regularity of the short and interval occurrence of the coherent structure.Finally,the correlation coefficients of coherent structures are analyzed.The effects of intermittent turbulence,Gaussian property,gust Factor and peak factor,it is concluded that the coherent structure is the essential cause of turbulence intermittent,and the coherent structure influences the turbulence intermittently by influencing the turbulence Gauss,and the correlation coefficient after the coherent structure are extracted from turbulence.Peak factor and gust factor declined.The precise estimation of the evolutionary power spectral density of a nonstationary typhoon wind procedure is a very interesting task.the wavelet-based procedure for estimating evolutionary power spectral density of non-stationary stochastic oscillatory processes and its application to field measured typhoon processes.This paper presents a methodology based in discrete wavelet transform(DWT)and multiresolution analysis to estimate the evolutionary power spectral density(EPSD)of nonstationary random processes.First,the nonstationary random process is described as the sum of two terms: a nonstationary mean and the product of a nonstationary variance and a stationary random process.Then,the methodology involves a double DWT: one is used to estimate the nonstationary mean and the second is used to estimate the nonstationary variance and the PSD of the stationary process.At last,the evolutionary power spectral density is determined.The proposed methodology showed an outstanding performance in the estimation of the EPSD of the speed of the winds produced by typhoon Hagupit,which passed through SE China on September 24 th 2008.Some features of the proposed methodology include its simple theoretical foundation,straightforward application,low computational burden and good performance with different mother wavelets.