Experimental Research On Wind Sand Flow And Nonlinear Dynamical Characteristics Of Bed Load Motion

This dissertation first reports the effects of the turbulence intensity on the structures of wind-sand currents by simulating the boundaries in actual atmospheric turbulences. In the experimental simulation processes, two approaches, i.e., minaret and rough elements, were adopted, and the turbulence intensity served as a variable. The structures of the wind-sand currents were measured at two turbulence degrees, indicating that the turbulence degree significantly impacts the transport quantity of sand and this effect increases with the wind velocity and height. The increment of the turbulence on the earth's surface can make more sand particles leave the surface and jump to higher space. Also, we believe that one reason that causes the difference between the wind-sand currents on Gobi and sand surface is due to the different turbulence degrees in both cases, and the turbulence degree should be considered when designing sand-defence projects.Then, the study of the dust emission perpendicular to the sand surface is meaningful for understanding the formation mechanisms of wind-sand currents and dust storms. In this paper, the dust emission rate was measured using the Particle Image Velocimetry technique in a wind tunnel. The velocity of sand grains was calculated the cross-correlation arithmetic based on the PTV technique, and then the displacement was obtained from the time relation from both, imagines. Based on the above calculation, the number of sand grains moving up from the sand surface could be achieved, and it was found that the dust emission rate varies linearly with the square of the friction speed from the analysis using the method of least squares and the corresponding formula was obtained. The analysis of the distribution of the grain size indicates that the grain size varies following the normal distribution. As the friction speed increased of the impact of the large particles will be larger.Finally, the differential equation of collective creeping in stratum of the bed was founded based on the force analysis of sand particles. And from the characteristic of the equation, non-linear dynamic features of the differential equation were discussed. Found that the entraining and creeping velocity of the sand are controlled by the non-linear dynamic characteristic parameters of the equation and corresponding to the different non-linear states, respectively. The non-linear dynamic characteristic parameters of creeping depend on the entraining Shields parameters and Reynold number of sand. The non-linear dynamic characteristic parameters are complex function of Shields parameters and Reynold number, and the relationship between them was given.