Construction of Flood Flows Simulation Model Based on High Resolution Upwinding Finite Difference Method

建立了基于通量差分(FDS)技术和非结构有限体积法(FVM)的一阶精度二维洪水数值模型(FUF-2DF模型)。该模型采用非结构三角网格体系，既考虑了守恒性，又考虑了FDS技术对信号的传播。建立了SA-FUF-2DF模式，该模式本质上是一个空间平均的FUF-2DF模式。FUF-2DF模型被设计成适用于存在于泛滥平原中的比网格尺寸更大的单元，如建筑物和其他，而GA-FUF-2DF模型旨在处理比网格大小更小的单元，如树木、小房子和网格中存在的其他单元。在GA-FUF-2DF模型中，元素对水流的作用力被视为反作用力。为了全面验证该模型，在存在淹没和/或未淹没的…的情况下，对二维溃坝洪水波在河道和漫滩中的传播进行了实验进行了更多的粗大结构和/或小单元。本文提出了一种获取干床条件下洪泛区洪水传播深度和表面速度的新方法：利用计算机图像分析和粒子跟踪测速仪(PTV)分别测量洪流的深度和表面速度。建立了一种新的自由面流动数值模拟模型，将一阶和二阶通量差分格式与Preissmann缝隙相结合，模拟了封闭管道中的流动，其中流动可以由自由面变为有压流，反之亦然。该模型可以模拟任意形状的等截面管道，也可以模拟有床面坡度和床面摩阻的管道。用已有的管道和矩形管道自由表面加压流动的实验数据对模型进行了验证。然后，针对一些严格的样本问题对模型进行测试。结果表明，在所考虑的所有情况下，模型都能给出非常合理的结果。对缝隙的尺寸进行了敏感性分析，得出了对自由面有压流动模拟有用的结论。实验研究了定常和非定常自由面剪切流中方形立柱所受的水动力。结果表明，在定常流动中，方柱阻力系数在B/d=3~14范围内随B/d的增大而减小，当B/d≧为14时，阻力系数不变；给出了描述CD和α以及CD和B/d之间关系的图表。在非恒定流中，表面平均速度与深度平均速度之比约为1.12。柱状一维溃坝水流的Cd值与恒定均匀流的Cd值相比，在t*&gt；70后随t*的增加非常缓慢。较少

A first-order accurate numerical model- based on Flux-Difference Splitting (FDS) technique and unstructured Finite-Volume Method(FVM) for 2D Flood Flows (FUF-2DF Model) is newly constructed. The model uses unstructured triangular grid system and Incorporates conservative properties as well as signal propagation through FDS technique. A SA- FUF-2DF Model, which is essentially a spatially averaged FUF-2DF Model, is also developed. The FUF-2DF Model is designed to be appled to such larger elements existing In a flood plain than a grid size as buildings and others, while the GA-FUF-2DF Model is designed to treat such smaller elements than a grid size as trees, small houses and others existing within a grid. In the GA-FUF-2DF Model , the forces acting from elements on a flow are evaluated as reaction forces.For comprehensive verification of the model, experiments on two-dimensional dam-break flood waves propagating in a channel as well as a floodplain in presence of submerged and/or unsubme … More rged larage structures and/or small elements are conducted. A new methods to obtain the depths and the surface velocities of flood flows propagating on a flood plain In dry-bed condition have been developed: the depths and the surface velocities of flood flows are measured by using the Image analysis by a computer and Particle Tracking Velocimetry(PTV), respectively. The model verifications against these experimental data show that the proposed model can reproduce flood flows with structures with reasonable accuracy.A new numerical model for free-surface flow simulations Is constructed; first and second-order flux-difference splitting schemes are combined with the Preissmann slot to simulate flows in a closed conduit, wherein the flow may change from free-surface to pressurized flow and vice versa. The models can simulate conduits with uniform cross-sections of arbitrary shape as well as with bed slope and bed friction. The models are verified with available experimental data on free-surface-pressurized flows for pipes and rectangular conduits. Thereafter, the models are tested against some exacting sample problems. It Is demonstrated that the models yield very reasonable results In all the cases considered. A sensitivity analysis Is performed for the size of the slot and useful conclusions are drawn from the study for the simulation of free-surface pressurized flows.Hydrodynamic force exerting on a squre pillar placed In steady or unsteady free surface shear flows were Investigated experimentally. In steady flows, It is found that the drag coefficients of a squre pillar at a given 'a decreases with B/d in the range of B/d=3〜14 and is constant when B/d≧14, and that the values of Cd in a shear flow are different from those in uniform flow. Diagrams to describe the relationships between Cd and α as well as Cd and B/d are presented. In unsteady flows, It Is found that the ratio of surface to depth-averaged velocity is about 1.12. The magnitude of Cd of the pillar 1D dam break flows Is compared with that of steady uniform flows, and increases very slowly with t* after t*>70. Less