【作者】 宋玉江；

【导师】 武建军；

【作者基本信息】 兰州大学 ， 工程力学， 2010， 硕士

【摘要】 在过去的几十年里,许多学者对风沙的产生机制做了卓有成效的研究,但对于起动机理并没有一个统一的认识。而目前的研究则主要集中在沙粒起动的影响因素上,比如,在自然界中,影响沙粒起动的因素很多,除了沙粒密度、沙粒的大小外,其实沙床的含水率,沙地的地势(坡度)对起沙也有很重要的影响。因此,本文基于这两方面对起沙进行了研究,从而对于风沙危害的防止及风沙两相流理论的完善有一定的意义。在起动摩阻风速与含水率的研究中,本文采用Bagnold建立的起动风速模型,推导了沙粒起动摩阻风速与沙粒含水率的函数关系,得到了一个含有经验系数C的推导公式。利用这个推导公式,进一步得出：沙粒起动摩阻风速随着含水率的增大而增大,但是,在含水量低于0.5%时,增大效果非常明显,而高于0.5%时,增大效果则不明显；而且沙粒起动摩阻风速并不一定随着沙粒粒径的增大而增大,而是存在一个极值,当沙粒粒径小于这个极值时,沙粒起动摩阻风速随着沙粒粒径的增大而减小,而大于此极值时,沙粒起动摩阻风速随着沙粒粒径的增大而增大。在坡面非均匀沙的起动风速研究中,本文考虑了床面颗粒之间的相互荫暴影响,引入了暴露度、等效粒径和床面阻力等概念来研究坡面非均匀风沙的起动条件,推导了坡面上非均匀沙的起动公式。最后将坡面起动公式化为平坦床面上的起动公式,并应用文献中所列各沙的起动风速实测结果对公式中的系数进行了确定,计算出的起动风速与实验数据之间的相关系数为0.823,说明在天然风沙起动研究中采用暴露度、等效粒径和床面阻力来反映风沙不均匀性对起动的影响是合理的。更多还原

【Abstract】 Many researches have been done in the forming mechanism of incipient sand movements in the past decades and no agreement has been reached on their causes. Current studies mostly focus on some factors leading to sand movements such as the density and size of the sands. This thesis will explore two other influencing factors—the moisture content of sand bed and the gradient of sand hill, aiming to contribute to the prevention of sand movement and the wind-sand flow theory.Adopting Bagnold’s threshold wind velocity model, this thesis has got a functional relation between threshold friction velocity and moisture content, and induced an equation with the empirical coefficient C. This equation indicates that threshold friction velocity increases with the rise of moisture content. The increase is obvious when the moisture content is less than 0.5%, and not obvious when the moisture content is more than 0.5%. In addition, threshold friction velocity does not always increase with the rise of the sand diameter and there is an extremum of the sand diameter. The velocity decreases with the increase of the sand diameter when the diameter is less than the extremum and increases with the increase of the sand diameter when it is more than the extremum.This thesis studies the conditions of incipient non-uniform sand movement on slopes with exposure degree, equivalent grain size and flow resistance, taking the mutual hiding-exposing action between sands into consideration. An equation has been induced about the incipient non-uniform sand movement on slopes, which is then turned into one on plat lands. Threshold wind velocities in the previous studies have been applied to test the coefficient of the equation. The correlational coefficient between threshold wind velocity and the empirical data is 0.823, indicating that it is reasonable to reflect the effect of non-uniformity on incipient sand movement with exposure degree, equivalent grain size and flow resistance taken into account.更多还原