推移质运动基本规律研究

发布时间：2019-06-17 10:50

【摘要】：推移质运动是河流动力学研究的基础,以科学的方法对其进行研究已逾百年,由于该领域涉及内容较为宽广且极为复杂,取得公认的研究成果不多。围绕推移质运动基本规律,本文从四个方面对其进行研究:⑴归纳提出了表层沙摩擦角的物理概念,通过试验论证了泥沙休止角与表层沙摩擦角之间的区别,论述了非均匀沙休止角随分选系数的变化规律,初步探讨了偏度系数与峰度系数对非均匀沙休止角的影响,针对非均匀沙休止角及表层沙摩擦角的工程应用,提出了非均匀沙的最优化级配设计方面的建议。⑵针对泥沙起动条件,同时考虑了水流紊动特性和泥沙颗粒排列的随机性对泥沙起动的影响,利用泥沙滚动起动模型计算得出泥沙起动条件并不是一个确定值,而是随机分布在一个区间内;针对泥沙起动概率,从面积比、数量比和时间比三个角度重新阐述了Einstein(1950)泥沙起动概率的物理图景,推求了一个新的泥沙起动概率计算模型,并从水流上举力分布、起动概率积分区域及泥沙颗粒受力三个方面论证了Einstein(1950)起动概率模型的合理性。⑶在改进Engelund(1976)推移质公式的基础上,推求了一个推移质平衡输沙率公式,新公式兼具确定性和随机性研究方法的优点,能够较好地兼顾低强度输沙和高强度输沙计算的问题;开展了382组次的均匀推移质平衡输沙试验,利用经典的推移质输沙率数据和本文试验数据检验了多家推移质公式的性能,结果表明本文公式具有较好的适用性。⑷开展了2种非均匀沙的多组次粗化试验,实时记录了粗化过程中的推移质输沙量、测量了推移质分时段级配和粗化层级配,并利用新研发的三维地形仪测量、重构了粗化层表面形态。数据表明,首次粗化与再次粗化过程中,推移质输沙率及级配具有显著不同的变化特征,并且粗颗粒比例占优床沙的粗化过程中还存在输沙率陡增及输沙级配变粗的“二次粗化”现象;高强度水流冲刷下,粗颗粒比例占优床沙的粗化层形态呈沙波状,而粗细颗粒比例相当床沙的粗化层形态呈凹槽状;在床沙级配和阶梯冲刷水流中最大一级流量相同的条件下,推移质输沙总量、粗化层级配及床面冲刷深度与水流的冲刷模式基本无关,即上述三要素在不同阶梯水流冲刷下的结果基本相同。
[Abstract]:Bed load movement is the basis of river dynamics research, which has been studied by scientific method for more than a hundred years. Because of the wide and complex contents involved in this field, few recognized research results have been obtained. Based on the basic law of push mass movement, this paper studies it from four aspects: (1) the physical concept of surface sand friction angle is summarized, the difference between sediment rest angle and surface sand friction angle is demonstrated by experiments, the variation law of non-uniform sand rest angle with separation coefficient is discussed, and the influence of skewness coefficient and kurtosis coefficient on non-uniform sand friction angle is discussed. In view of the engineering application of non-uniform sand stop angle and surface sand friction angle, some suggestions on the optimal gradation design of non-uniform sand are put forward. 2 according to the sediment starting condition, considering the influence of the turbulent characteristics of flow and the randomness of sediment particle arrangement on sediment starting, the sediment starting condition is not a definite value, but is randomly distributed in an interval by using the sediment rolling starting model. Aiming at the starting probability of sediment, the physical picture of Einstein (1950) sediment starting probability is reexpounded from three angles of area ratio, quantity ratio and time ratio, and a new calculation model of sediment starting probability is deduced, and the rationality of Einstein (1950) starting probability model is demonstrated from three aspects: the distribution of lifting force on water flow, the integral area of starting probability and the force acting on sediment particles. 3 on the basis of improving Engelund (1976) bed load formula, A formula of bed load equilibrium sediment transport rate is deduced. The new formula has the advantages of both deterministic and stochastic research methods, and can give good consideration to the calculation of low intensity sediment transport and high intensity sediment transport. The equilibrium sediment transport test of 382 groups of uniform bed load is carried out, and the performance of several load transfer formulas is tested by using the classical bed load transport rate data and the test data in this paper. the results show that the formula has good applicability. 4 the multi-group coarsening experiments of two kinds of non-uniform sand are carried out, the bed load transport volume in the process of coarsening is recorded in real time, and the gradation and coarsening grade distribution of bed load are measured. The surface morphology of coarsening layer is reconstructed by using the newly developed three-dimensional topographic instrument. The data show that the bed load transport rate and gradation have significantly different characteristics in the process of first coarsening and re-coarsening, and the "secondary coarsening" phenomenon of the sharp increase of sediment transport rate and the thickening of sediment transport gradation exists in the process of coarsening the proportion of coarse particles to the dominant bed sand. Under the erosion of high intensity flow, the coarse layer with the proportion of coarse particles and fine particles is in the shape of sand wave, while the coarse layer with the proportion of coarse and fine particles is in the shape of grooves. Under the condition that the maximum flow rate of bed sediment gradation and ladder scour flow is the same, the total amount of bed load sediment transport, coarsening gradation and bed surface scour depth have nothing to do with the scour model of water flow, that is to say, the results of the above three elements under different stepped flow scour are basically the same.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TV142.2

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