Experimental Study On Nonstationary Characteristics Of Urban Boundary Layer Wind Field

With the gradual increase of the height of modern buildings,wind load has become one of the main control loads,making wind field characteristics become a hot research topic in the field of wind resistance of super high-rise buildings and long-span structures.At present,field measurement,wind tunnel test and numerical simulation have been widely used in the study of wind field characteristics in a certain area,among which the most effective method is to use the field wind observation data of the area to analyze,and get the appropriate model and parameters.Studies have shown that the wind speed series of typhoons show obvious non-stationary characteristics.At present,most of the specifications are based on the stationary wind speed model,which is different from the existing research.Therefore,non-stationary wind field should be studied.It is of great significance to study the non-stationary characteristics of typhoon measured in urban areas for the improvement of wind resistance theory of high-rise buildings and long-span buildings.For extreme wind environments such as strong/typhoon,the extraction of time-varying mean wind is an important step in constructing non-stationary wind speed model to calculate wind characteristic parameters.In this paper,the wind speed data of Beijing 325 m meteorological tower at three heights under sandstorm weather is taken as the background,and the time-varying mean wind is extracted based on the wavelet transform technology.The stability of the fluctuating wind is tested by the round check method.The wind field characteristics of boundary layer strong winds in urban areas are studied by using non-stationary wind speed model at different time intervals.Based on three measured typhoons at a height of30 m in the suburbs of Wenzhou,the time-varying mean values were extracted by VMD(Variational Mode)parameter optimization based on genetic algorithm,and the non-stationary wind field characteristics near the ground of the city under typhoon action were studied.Based on the wavelet packet transform,the time-varying mean wind was extracted from three measured typhoons at 150 m height in Xiamen,and the characteristics of non-stationary wind field in the ultra-high altitude of the city were analyzed.Through the analysis of the samples,it is found that the measured wind speed under the sandstorm weather and the urban wind speed under the typhoon show strong non-stationarity.Based on non-stationary wind speed model,it is concluded that turbulence characteristics of turbulent flow characteristics and stable model have obvious difference,for dust samples of wind speed and wind speed samples typhoon evolution power spectral analysis,found the evolution power spectrum shows the characteristics of obvious temporal changes,the traditional wind speed model is difficult to accurately describe the measured wind field characteristics of the non-stationary wind.The research results provide scientific basis and important data for wind resistance design of large scale civil engineering structures.