【作者】 渠庚；

【导师】 张小峰；

【作者基本信息】 武汉大学 ， 水力学及河流动力学， 2014， 博士

【摘要】 含植物河流是自然生态的重要组成部分。由于影响因素众多,水沙运动规律相对复杂,含植物河流水沙运动特性是河流泥沙动力学中的难点问题之一。本文在资料收集的基础上,对含植物水流问题的国内外研究现状进行系统的总结,并采用三种仿真柔性植物进行了含植物明渠水沙运动规律的室内水槽试验；首先分不同区域(植物带上游、植物带和植物带下游)研究了无草、淹没型、非淹没型柔性植物水流阻力特性规律,继而对含不同植物明渠水动力运动特性进行深入探讨；最后对含不同植物明渠泥沙运动进行详细分析。全文主要研究以下三个方面的问题：1.含植物明渠水流阻力特性研究利用水槽试验研究了无草、淹没型、非淹没型柔性植物水流阻力特性的变化规律,分析了含植物明渠沿程水面比降和阻力系数的变化特性。得到各植物阻力系数变化与尼库拉兹曲线基本相似,紊流范围内同样可划分为紊流光滑区、紊流过渡区、紊流粗糙区；统计各植物经不同水流冲击倒伏后的冠顶高度,分析了植物粗糙度、水流雷诺数和阻力系数之间的关系,并对各植物的水流阻力系数分区进行回归分析,得到各植物水流阻力的分区经验表达式,该方法能较好地应用于含植物明渠水流阻力系数的推求。2.含植物明渠水动力特性试验研究利用水槽试验研究了含不同植物明渠水动力特性,试验结果表明,对于淹没植物,在植物的冠顶上方一定区域水流流速变化与无草情况下基本相似,但非淹没植物的水流纵向流速在水深方向呈“S”型分布,并呈明显的分层现象；水流紊动强度随植物形态、沿程分布和距边壁位置变化而表现出不同特性；-(uv+uv)/u2*是表征水流变化的重要因子,有植物情况下,其与植物形态和沿程分布等因素密切相关,并随植物形态和空间分布而发生不同规律的调整。3.含植物明渠泥沙运动规律研究利用水槽试验研究了含不同植物明渠泥沙运动规律,试验结果表明：泥沙级配存在明显的分层现象,呈现“上细下粗”的基本变化规律,同种植物对细颗粒泥沙的空间分布影响较小,对中、粗颗粒泥沙的影响较大。含植物明渠较无植物明渠,床沙非均匀性减小,其中淹没型莎草减小幅度最大；对含植物明渠中水流的动量扩散系数、泥沙扩散系数和二者比值β进行较详细研究,得到了三者随植物形态和空间分布的变化特征,具体为：动量扩散系数在垂向总体呈抛物线分布,随相对水深增加先增大后减小,泥沙扩散系数总体随相对水深的增加而逐渐减少,β值变化范围为0.14-10.0,多数β值明显大于1,分析认为,试验采用轻质模型沙,有利于泥沙扩散,泥沙扩散系数较大所致。更多还原

【Abstract】 River with vegetation is an essential part of natural ecology. The characteristic of water flow and sediment transport in rivers with vegetation is a difficult issue among river dynamics problems. The research status of flow with vegetation is systematically summarized, and indoor flume tests on water and sediment transport in open channel flow with vegetation are conducted by using three artificial flexible plants (plant with no grass, submerged flexible plant, and non-submerged flexible plant). The research is divided into three aspects:1. Characteristics of flow resistance in open channel flow with different plants.Variation regularity of the flow resistance of the three plants are researched through flume tests, and the variations of one-way water surface slope and drag coefficient of open channel with the three plants are analyzed. It’s found that the variation of drag coefficient of each plant is similar with Nikuradse curve in general. Turbulent flow range c can be divided into turbulent smooth zone, turbulent transition rough zone, and turbulent drag rough zone. The crown heights of plants beat down by water impact are counted and the relationship between flow resistance coefficient and roughness for each plant is obtained accordingly. Regression analysis on the relationship verified that the method can be applied to deduce the resistance coefficient of open channel flow with plants.2. Hydrodynamic properties of open channel flow with different plants.Flume test results reveal that the flow velocity variation in a certain area above the crown top of submerged plant is similar with that of plant with no grass. The longitudinal velocity for non-submerged plant distributes in "S" shape along the depth direction with clear stratification. Turbulence intensity exhibits different characteristics with the variation of plant morphology, one-way distribution and distance to the side wall.-(uv+uv)/u2*is the important factor characterizing flow variation. It is closely associated with plant morphology and one-way distribution in the presence of plants. Moreover, it regularly adjust along with the changes of plant morphology and one-way distribution.3. Regularity of sediment transport in open channel flow with different plants.Flume test result shows that the vertical distribution of sediment concentration gradient is in positive correlation with flow turbulence intensity, and the relationship between the two is fitted. The particle size of sediment decreases upwards, presenting an obvious stratification. The impact of the same plant on the vertical distribution of fine sediment is smaller than that on coarse sediment. Plants have a stronger effect of blocking coarse sediment in open channel but have little effect of blocking fine sediment, which is similar with the variation of sediment concentration in the downstream river after the operation of the Three Gorges Project. Momentum diffusion coefficient, sediment diffusion coefficient, and β(the ratio of the former to the latter) change in vertical direction. They are all functions of spatial location (regions and relative water depth) and vary with the changes of spatial location. In general, momentum diffusion coefficient distributes in parabolic shape in vertical direction, and increases before decreases with the increase of relative water depth. Sediment diffusion coefficient gradually reduces with the increase of relative water depth in the presence of different plants. The value of β ranges from0.14to10.0, most of which is significantly larger than1. This is because lightweight model sand used in the experiment is beneficial to sediment diffusion and the sediment diffusion coefficient is large.更多还原