洪水灾害是当今社会危害经济发展和人口安全的主要自然灾害之一。受国土地貌、气候等条件影响，我国洪水灾害问题十分突出，防洪减灾始终是水利工作的主要目标之一。洪水预报作为防洪决策的重要参考，理论研究和生产应用一直是水利科学研究的重点。如何准确的模拟流域洪水传播，描述流域水文现象，是洪水预报工作的重要课题。水文模型和水力模型是洪水预报系统的核心组成。本研究分别建立分布式物理水文模型和二维水力模型，并提出新的模型理论公式，实现模型间的动态耦合。有别于串联耦合方法中两种模型相对独立计算以及边界固定引发的问题，动态耦合模型充分利用两种模型的优点，高效、准确的模拟降雨洪水在不同阶段的演进变化。基于物理水文模型的概念，研究建立了以扩散波方程为核心的分布式水文模型，可以描述降雨-下渗-坡面汇流的水循环运动；基于浅水方程，建立了二维水力模型，数值格式稳定，计算准确；以有限体积法数值计算中的特征波分析理论为基础，判断两种模型在接触边界的相互作用，实现两者的动态耦合。动态耦合方法遵循质量和动量守恒理论，可以根据流态变化自行调整计算模型和不同模型的使用区域，提高模型预测精度和计算效率。为解决耦合模型应用中两种模型计算尺度可能不一致的问题，建立自适应四叉树网格生成算法，计算效率高，可以兼容不同尺度的计算单元，准确描述地形和流场的变化。网格生成过程分别以网格编码和尺寸作为检索条件，实现全局单向检索，避免对网格的重复检查以及网格调整引起的“涟漪”效应。研究利用数值算例和物理实验对模型各项性能进行验证，检验数值格式的稳定性、计算精度；对比动态耦合模型与串联耦合模型，验证了动态耦合方法对于流场的模拟更贴近真实流动；对比模型基于四叉树网格与正交网格的计算结果，验证了自适应网格的质量能够保证计算精度；将模型应用于龙溪河流域的洪水预报中，以不同频次的设计降雨和洪水验证模型能够准确模拟小流域降雨洪水的演进情况，为防洪工作提供参考依据。
The flood disaster is one of the main natural disasters that endanger the economic development and population security. Affected by land features, climate and other conditions, China's flood disaster remains serious, flood control and disaster reduction has always been one of the main objectives of water conservancy work. Flood forecasting is an important reference for flood control decision making. How to accurately simulate flood propagation and describe hydrological phenomena is an important subject for flood forecasting. Hydrological model and hydraulic model are the core components of flood forecasting system. In this study, distributed physics-based hydrological model and two-dimensional hydraulic model were established respectively, and a new theoretical formula was proposed to achieve dynamic coupling between models. Different from the problems caused by the calculation of the two kind of models without interference and boundary fixation in the 'cascade' coupling method, the dynamic coupling model makes full use of the advantages of two kind of models to simulate the evolution of rainfall flood in different stages efficiently and accurately.Based on the concept of physical hydrological model, a distributed hydrological model with diffusion wave equation as the core was established, which can describe the water circulation movement of rainfall-infiltration and slope confluence. Based on the shallow water equation, a two-dimensional hydraulic model was established. Based on the theory of characteristic wave analysis in the numerical calculation of finite volume method, the interaction between the two models at the contact boundary was judged, and the dynamic coupling of two kind of models was realized. The dynamic coupling method follows the mass and momentum conservation theory, and can adjust the calculation model and the application area of different models according to the flow state change, so as to improve the prediction accuracy and calculation efficiency of the model.In order to solve the problem that the computational scales of the two models may be inconsistent in the application of the coupled model, an adaptive quadtree grid generation algorithm was established, which had high computational efficiency and can be compatible with computing units of different scales to accurately describe the changes of terrain and flow field. In the process of grid generation, grid coding and grid size were used as retrieval conditions to realize global one-way retrieval and avoid the "ripple" effect caused by repeated checking of grid and grid adjustment.Numerical examples and physical experiments were used to verify the performance of the coupling model, and verify the stability and accuracy of the numerical scheme. By comparing the dynamic coupling model with the 'cascade' coupling model, the simulation results showed that the dynamic coupling method was closer to the real flow. The comparison between computation results of the coupling model based on quadtree mesh and orthogonal mesh verified that the quality of adaptive mesh can guarantee the accuracy of calculation. The model was applied to the flood forecasting of longxi river basin, and the designed rainfall flood with different frequencies were used to verify that the model can accurately simulate the evolution of rainfall flood in small river basin, providing reference for flood control work.
