【作者】 辛涛；

【导师】 武建军；

【作者基本信息】 兰州大学 ， 工程力学， 2012， 硕士

【摘要】 在风沙二相流中,颗粒在风场的作用下脱离床面起动的机理是重要的研究课题。颗粒脱离地表起动标志着地表风蚀的开始,风蚀是造成干旱半干旱沙漠地区土地退化的主要驱动力之一,起动风速又是影响风蚀的关键因素。因此,沙粒的起动风速一直受到研究者的高度关注本学位论文的主要研究内容如下：1.本文首先建立沙粒受力平衡方程,根据沙粒起动这一物理过程的突变特性,运用非线性科学中的突变理论建立了颗粒起动的尖点突变模型,通过理论推导验证了沙粒在受重力、拖曳力、升力及电场力时的起动可以用非线性尖点突变模型来刻画,并采用数值计算加以验证。本文在验证了尖点突变模型对沙粒起动建模可行性的基础上,主要讨论了电场力对沙粒起动的影响。计算结果也与实验及其他理论模型结果一致的,表明弱电场情况下电场力对沙粒起动的影响很小,在计算分析时可以忽略,强电场情况下,电场力对起动风速影响较大,故不能忽略。2.实验观察到,风沙颗粒在风场作用下,起动之前,并非静止不动而是来回振动或摆动。而这种振动是由风场的脉动所引起的。但是由于以上都为实验观测结论,并没有理论模型加以支持。所以本文从沙粒的受力出发,建立了颗粒在风场作用下的微分动力学方程,并以正弦函数模拟风场脉动。首先,求解常微分方程的初值问题,得到无脉动时颗粒的临界起动风速,并且调整脉动强度,求解不同脉动强度对颗粒起动平均风速的影响。结果表明当风场的脉动强度越强,颗粒的临界起动平均风速就越小。其次,针对颗粒在风场作用下来回振动这一物理现象,本文通过建立非线性非自治系统模型并求解,对颗粒的周期运动,倍周期分岔,准周期运动,混沌等动力学特性进行了研究。并给出了激励参数不同时,床面颗粒不同的运动形态。更多还原

【Abstract】 In the two-phase flow of sand blown, the mechanism of particles starting from the surface of bed under the effect of wind field is an important research subject. Particles starting from the earth’s surface indicating the beginning of wind erosion, wind erosion is one of the main powers which causing the land degradation in arid and semiarid areas, while the threshold wind velocities of particles is a key factor which may influences wind erosion. Therefore, threshold wind velocities of particles has been pay high attention by researchers. The main contents of this thesis are as follows:l.This thesis derived mechanical equilibrium equations of particles firstly, according to the mutation characteristics of process of particles starting from the surface of bed, using catastrophe theory in nonlinear science set Cusp Catastrophic Model on that process, through theoretical derivation verified that particles starting with effects of gravity、drag force、saffman force and electric field force can be described by Cusp Catastrophic Model and then verified this conclusion using numerical calculation. After verifying the feasibility of process of particles starting with Cusp Catastrophic Model, we mainly discussed the electric field force effect on that process. The calculated result is in accordance with experiment and other theory model results. It demonstrated that under the conditions of weak electric field, the electric field force has a low effect on process of particles starting, so it can be neglected when computational analysis. While under the conditions of strong electric field, electric field force has a high effect on threshold wind velocities, so it can not be neglected.2. We observed that in the wind field effect before particles starting from the surface of bed,the particles is shaking instead of holding still. This kind of shaking is caused by fluctuating wind field. However, this conclusion is obtained from experimental observation and there is no theory model can support the conclusion. Therefore, we begin from force analysis of particles, established the differential dynamic equation of particles effected by the wind field and imitated the fluctuation as a sine function. Firstly, solving the initial boundary value of differential equation in order to get the threshold wind velocities of particles when there is no fluctuation, and then adjusting fluctuation intensity, getting the influence of different fluctuation intensity to get the threshold wind velocities of particles. The conclusion is that when the fluctuation intensity of wind field is stronger the of main value of threshold wind velocities will become slower. Secondly, aiming at the physical phenomenon that vibration of particles in fluctuating wind field, after setting the Nonlinear non-autonomous system model, we studied the dynamic characteristics of periodic vibration, period-doubling bifurcation, QPO, chaos and so on. And provided different movement form of particles on the bed under different incentive parameters.更多还原