阻水障碍物群影响下的洪水和泥沙运动数值模拟研究

发布时间：2018-06-02 03:09

本文选题：阻水障碍物群 + 透水密度系数　；参考：《浙江大学》2014年硕士论文

【摘要】：实际情况下,洪水在演进过程中会不可避免地会遇到阻水障碍物群(如植被群和建筑群等),阻水障碍物群的存在对洪水运动和泥沙输移都有很大的影响。本文通过引入透水密度系数以考虑阻水障碍物群对洪水运动过程中水流通量的影响,建立了二维动力波洪水和泥沙运动数值模型,通过对不同情况下带有阻水障碍物群的洪水演进和泥沙运动进行模拟分析,主要研究成果和结论如下： (1)分析总结了植被群和建筑群作为阻水障碍物群在洪水运动过程中的阻力作用,植被群在单位体积上的阻力可以表示为植被群对水流的阻力会因植被自身特性(刚性,柔性,有无树叶)的不同而变化；而建筑物群在单位体积上的阻力为阻力会因建筑物分布的疏密程度以及形状尺寸的不同而变化。 (2)在二维浅水运动和泥沙输移方程的基础上引入透水密度系数以综合考虑阻水障碍物群对水流通量和泥沙输移通量的影响,从而建立一个新的基于透水密度系数法的二维动力波洪水和泥沙运动数值模型。同时,模型还考虑了水流的粘性和紊动扩散作用,以及考虑地形变化影响的水沙耦合作用。本模型采用中心迎风格式求解单元界面上的流量和动量通量,并结合对界面变量的线性重构,使其具有空间上的二阶精度。单元界面上的泥沙输移通量采用迎风格式进行求解。为保证模型的和谐性和稳定性,底床坡度项采用中心差分法离散,底床摩擦项和障碍物的阻力项用半隐式法离散。粘性和紊动扩散项,泥沙运动扩散项均采用中心差分格式处理。当库朗特数满足条件时,模型能保证计算水深在任何时刻是非负的,使得模型具有良好的稳定性。 (3)模型分别对带有不同类型阻水障碍物群的定床洪水算例进行验证分析,结果表明：透水密度系数法可以将阻水障碍物群视为一个整体考虑,配置相同的计算参数,网格划分的疏密对透水密度系数法下的模拟结果影响较小,而设定高程法受网格粗细影响十分显著。在计算精度和误差相近的范围内,相比设定高程法,透水密度系数法具有较高的计算效率,计算耗时仅为其1/50,这表明在洪水演进数值模拟中,透水密度系数法比设定高程法更具优势,这对于洪水风险评估和快速防灾决策极为重要。 (4)通过算例对考虑水沙耦合作用的洪水和泥沙运动数值模型进行验证,分析其水动力特征、泥沙运动以及河床变形特征,并利用该模型对阻水障碍物群—水生植被群影响下的洪水和泥沙运动进行计算模拟,分析探讨水生植被群的存在及其分布方式对洪水运动、泥沙输移及底床冲淤的影响。结果表明：水生植被群的存在虽能有效减小上游河床的冲刷,但由于不利于过流,会使上游水位抬高而增加洪灾风险。同时分析了不同的植被群分布方式对洪水运动和泥沙输移特性的影响,结果表明：植被区沿边岸分布、宽度减半的方式是既能减小洪灾风险又能维持生态稳定的较为有效的措施。
[Abstract]:In the actual situation, water hindrance barrier group (such as vegetation and building group) will inevitably be encountered during the process of flood evolution. The existence of water hindrance barrier group has great influence on flood movement and sediment transport. In this paper, the permeability density coefficient is introduced to consider the shadow of water barrier group on the flow flux during the flood movement. The numerical model of two dimensional dynamic wave flood and sediment movement is set up. The flood evolution and sediment movement in different cases are simulated and analyzed. The main research results and conclusions are as follows:
(1) the resistance of the vegetation group and the building group as the water hindrance barrier in the flood movement is analyzed and summarized. The resistance of the vegetation group on the unit volume can be expressed as the variation of the resistance of the vegetation group to the water flow due to the characteristics of the vegetation itself (rigid, flexible, and without leaves), and the resistance of the building group to the unit volume is the resistance of the building group. Resistance will vary depending on the degree of density and size of the building.
(2) on the basis of the two-dimensional shallow water movement and sediment transport equation, the permeability density coefficient is introduced to comprehensively consider the influence of the water barrier group on the flow flux and the sediment transport flux, thus a new numerical model of two-dimensional dynamic wave flood and sediment transport based on the permeable density coefficient method is established. This model uses the central upwind scheme to solve the flow and momentum flux on the interface, and combines the linear reconstruction of the interface variables to the two order accuracy in space. The sediment transport flux on the interface is used in the windward format. In order to ensure the harmony and stability of the model, the slope term of the bottom bed is discrete by the central difference method, the friction term of the bottom bed and the drag of the obstacle is separated by the semi implicit method. The viscous and turbulent diffusion term, the sediment movement diffusion term are all treated by the central difference scheme. When the kumatt number satisfies the condition, the model can guarantee the time to calculate the depth of water depth. Carving is nonnegative and makes the model stable.
(3) the model is verified and analyzed for the fixed bed flood calculation with different types of water obstructing obstacles. The results show that the permeable density coefficient method can consider the obstruction of water barrier as a whole consideration, with the same calculation parameters, and the density of grid partition has little influence on the simulation results under the permeable density coefficient method, and the set height is high. In the range of calculation accuracy and error, the pervious density coefficient method has a higher calculation efficiency compared with the set height method, and the time of calculation is only 1/50. This shows that the permeability density coefficient method is more advantageous than the set elevation method in flood evolution numerical simulation, which is the evaluation of flood risk. And rapid disaster prevention decisions are very important.
(4) through a numerical example, the numerical model of flood and sediment movement considering the coupling of water and sediment is verified, and its hydrodynamic characteristics, sediment movement and river bed deformation characteristics are analyzed, and the model is used to simulate the flood and sediment movement under the influence of water barrier group - aquatic vegetation group, and the existence of aquatic vegetation group is analyzed and discussed. The results show that the existence of the aquatic vegetation can effectively reduce the erosion of the upstream river bed, but the water level will be raised to increase the flood risk. The results show that the way to reduce the width of the vegetation along the shore and the width of the vegetation area is a more effective measure to reduce flood risk and maintain ecological stability.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV122;TV14

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