【作者】 李晖；

【导师】 黄宁；

【作者基本信息】 兰州大学 ， 工程力学， 2009， 硕士

【摘要】 本学位论文主要研究了风沙流的风洞实验和蠕移运动。首先探讨了湍流对输沙风沙流结构的影响,并通过改变湍流度的大小研究了湍流度对风沙流结构的影响。实验测量了两种湍流度下的风沙流结构,结果表明湍流度对输沙量的变化有一定影响,且会随着风速和高度的增大而增强。结果还表明地表湍流度的提高会使更多的沙粒离开床面而跃移到更高的位置,并认为湍流度的不同是造成戈壁与沙面上风沙流结构的不同的原因之一。其次,利用PIV测量技术在风洞中测量床面起沙率。利用PIV技术的互相关算法计算出颗粒的速度,然后通过两幅图像的时间关系得出位移,从而得到沙面起动的沙粒个数。使用最小二乘法得出平坦沙面的起沙率与摩阻速度的相应公式。同时还分析了平坦沙面起动的颗粒粒径分布情况,结果表明粒径是按照正态分布的,随着摩阻速度的增大会使更多粒径大的颗粒起动。最后,从沙粒受力出发,建立了床面层内蠕移集体运动的微分方程,进而从微分方程特性出发,探讨了蠕移运动过程的非线性动力学特征.发现沙粒的起动、蠕移运动的速度均受蠕移运动过程的非线性动力特征参数所控制,它们分别对应于蠕移运动过程中不同的非线性状态:而蠕移运动过程的非线性动力特征参数又取决于沙粒起动Shields参数和颗粒Reynold数,是两者的复杂函数.给出了沙粒的起动和蠕移沙粒的运动速度与shields参数和雷诺数的关系。更多还原

【Abstract】 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.更多还原