Study On Fractal Characteristics Of Wind Field And Wind Pressure On A Building

With the improvement in the domestic economic level,the development of science and technology and the demand for material conditions,there has been more and more high,large,thin and long flexible structure.The effect of wind load on the structure becomes more and more obvious,which plays a decisive role in the design load,and puts forward higher requirements and challenges on the safety and stability of the engineering structure.Structural wind engineering research has received more and more attention.Fractal theory is one of the most important parts of nonlinear science.It is a popular subject in natural science research because it can qualitatively or quantitatively analyze irregular geometries and complex phenomena and it is also helpful to reveal the dynamics of a complex system.Thus,it's widely used in many disciplines.However,the literature on the research of fractal theory in wind engineering is still rare.Based on the existing research,this paper studies the fractal characteristics of wind speed and wind pressure on a building surface.The field test,wind tunnel test and numerical simulation are the 3 most commonly used methods in the wind engineering,but they also have their own advantages and disadvantages.The 3 methods are all used in this paper.They are the main source of the data.As the wind tunnel test has the characteristics of a controllable condition,repeated test and high precision,it is used more often.Firstly,wind fields of terrain category B,C and D were simulated in the wind tunnel,and wind speed samples were obtained at different heights.The box dimensions of wind speeds in different wind fields are analyzed,and the Jonckheere-Terpstra test is used;relations of box dimensions of wind speed to turbulence intensities and power spectra of wind speed were analyzed.It is found that box dimension of wind speed is affected by the terrain categories,and is also related to turbulence intensity and the energy distribution of power spectra of wind speed.Secondly,the wind speed samples of terrain category A are obtained in the field test.Based on 3 empirical power spectra,the wind speed under different turbulence was simulated by using the harmonic superposition method with FFT technique and the box dimensions of wind speed simulated and wind speeds obtained from field test and wind tunnel test were analyzed respectively.The results show that the box dimension of wind speed simulated is different from that of field measured.With the increase of the turbulence intensity,the box dimension of wind speed simulated doesn't change obviously,which is not consistent with the change of box dimension of wind speed obtained in wind tunnel test.Finally,wind fields of terrain category A,B and C were simulated in the wind tunnel,and wind pressure samples on a low-rise building were obtained.Based on fractal theory,relations of box dimensions of wind pressure to wind pressure coefficients of variation and power spectra of wind pressure coefficients were analyzed.The results show that box dimension of wind pressure is affected by the terrain categories and is also related to the location of test tap.Further analysis shows that changes in wind pressure coefficient of variation and power spectrum of wind pressure coefficient will cause the change of the box dimension of wind pressure.