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

基于通量差分分裂（FDS）技术和非结构有限体积法（FVM），建立了二维洪水流量的一阶精确数值模型（FUF-2DF模型）。该模型采用非结构化三角网格系统，结合了信号的保守性和FDS技术的信号传播特性。本文还建立了一个SA- FUF-2DF模型，它实质上是一个空间平均的FUF-2DF模型。FUF-2DF模型被设计用于处理洪泛区中比网格大小更大的元素，如建筑物等，而GA-FUF-2DF模型被设计用于处理比网格大小更小的元素，如树木、小房子等，这些元素存在于网格中。在GA-FUF-2DF模型中，作用于流动的各单元的力被评价为反作用力。为了对模型进行全面验证，本文还进行了二维溃坝洪波在淹没和/或未淹没河漫滩中传播的实验。本文提出了一种计算干床条件下洪水在河漫滩上传播的深度和表面速度的新方法：分别采用计算机图像分析和粒子跟踪测速法（PTV）测量洪水的深度和表面速度。模型与实验数据的对比验证表明，该模型能较好地再现具有结构的洪水流量。建立了一种新的自由表面流数值模拟模型；一阶和二阶流差分裂方案结合Preissmann槽来模拟封闭管道中的流动，其中流动可以从自由表面转变为加压流动，反之亦然。该模型可以模拟任意形状的均匀截面管道，以及考虑河床坡度和河床摩擦力的管道。用已有的管道和矩形管道自由表面加压流动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了测试。结果表明，在所有考虑的情况下，模型都能得到非常合理的结果。对狭缝的大小进行了敏感性分析，得出了对自由面加压流动模拟有用的结论。实验研究了置于定常和非定常自由表面剪切流中的方形柱所受的水动力。在定常流动条件下，方柱的阻力系数在B/d=3 ~ 14范围内随B/d的增大而减小，当B/d≧14时，方柱的阻力系数保持不变，且在剪切流动条件下的阻力系数与均匀流动条件下的阻力系数有所不同。给出了Cd与α、Cd与B/d的关系图。在非定常流动中，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Cd的大小与稳定均匀水流Cd的大小进行了比较，在t* bbb70之后，Cd随t*的增大非常缓慢。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