【作者】 周刚；

【导师】 邵学军；

【作者基本信息】 清华大学 ， 水利工程， 2009， 博士

【摘要】 河型转化过程机理研究不仅对河流动力学及河流工程学等学科的完善有重要理论意义,而且在大型水利工程运用后对下游河道演变的影响研究、以及防洪航运工程应采取的对策研究等方面也有着非常显著的实际意义。本文以改进的平面二维河流数学模型为主要研究手段,对边岸抗冲性较强和有洲滩演变的长江中游原型河道进行了实际计算,并对概化河道不同条件下的河势变化及河型转化进行了数值模拟,以分析与研究河型转化过程机理。通过在水流动量守恒方程中增加弥散应力项,考虑了弯道二次流的影响且对室内水槽实验结果进行了验证比较;提出了基于传统模型上的崩岸过程模拟技术;本模型能够模拟非均匀沙悬移质与推移质的输运过程,可以更可靠的模拟天然河道的演变趋势。对边界抗冲性较强的宜昌~枝城河段,进行了三峡枢纽运用后20年内冲淤变化的数值模拟。结果表明,该河段发生了明显的冲刷现象,但河势仍然比较稳定,不会发生河型转化。对上荆江的沙市~石首河段在三峡工程蓄水运用初期阶段(2006年~2012年)的河势变化进行了模拟预测。结果表明,该段河道普遍冲刷,洲滩变化显著,尤其以三八滩分汊段和石首河段河势变化最为剧烈,但在短期内和目前的水沙条件下,河型尚不会发生根本性的转化。通过概化河道河型转化的数值模拟,从河道平面形态、横断面变化、河床纵剖面,沿程水面线以及输沙率等方面分析不同初始比降,入口含沙量,流量和河岸抗冲性对河型转化的影响,成功模拟了不同条件下河型转化的过程。所得结果与已有的河型转化理论结果符合,且动力学依据更加完善。入口含沙量保持不变(清水)而增大γQJ(或减小河岸抗冲性、减小泥沙粒径),在概化河道下游最终形成的稳定河型属于分汊或江心洲型;若γQJ保持不变而入口含沙量增大到3.0kg/m3,在概化河道下游形成的稳定河型是游荡散乱型。实现了通过数学模型对河型转化机理的分析研究。更多还原

【Abstract】 The mechanism of channel pattern changes is an important part in the study of fluvial processes and river engineering. Fluvial processes will be substantially affected after the construction of hydropower projects on large rivers, which may lead to channel pattern changes and may have impacts on various aspects, such as flood control, navigation and water diversion, therefore the practical purpose of this study is obvious.In this thesis an improved two dimensional (2-D) mathematical model for water flow, sediment transport and bank erosion is used to simulate fluvial process and channel pattern changes in river channels of the middle Yangtze River reaches, where river banks are very resistant against bank erosion, but point bars and island bars are migrating actively. In this study, the same model was also applied to a conceptual river channel with conditions similar to that of the middle Yangtze River reaches, to study channel pattern changes and the mechanism behind such changes.The secondary flow was taken into account in the 2-D model by adding a dispersion stress term in the momentum conservation equation of water flow. Flow simulation results were compared with published curved-flume measurements in laboratory experiments. The model for bank failure calculation was also improved on the basis of the commonly used method. A non-uniform, non-equilibrium transport model for suspended load and bed load transport was used in the calculations, with better reliability in the results of fluvial processes in natural river channels.A 20-year series of fluvial processes were simulated for the 63km long Yichang - Zhicheng reach just downstream of the Three Gorges Reservoir (TGR), to study the impact of the operation of the TGR. The river banks in the area are strongly resistant to bank erosion, and simulation results demonstrate that although channel bed scours are obvious, the channel pattern will be stable and no channel patter changes will occur.A 6-year series of fluvial processes were simulated using the established model for the 102km long section from Shashi to Shishou in the upper Jingjiang Reach, which is just downstream from Zhicheng, to study possible channel pattern changes at the initial stage of the TGR operation (2006~2012). The results indicate that although wide-spread scour will occur during this period, and both point bars and island bars will migrate actively, especially more severe changes of fluvial processes are observed in the areas of Sanba Tan and Shishou, there will be no essential change in the channel pattern at the present incoming sediment conditions, at least for a short period of time.A 12 km long conceptual river reach, with bed and bank conditions similar to that of the middle Yangtze River reaches, was used to simulate the impact on channel pattern changes by various factors, such as initial channel slope, sediment supply, water discharge, and resistance to bank erosion. Simulated results were discussed, such as plan form of the river channel, longitudinal bed profile, channel cross section, water surface profile and sediment transport in the channel. The simulated results of channel patterns agree well with the classic theory of channel pattern formation. The method in this thesis provided a better way to examine the dynamics behind channel pattern changes.更多还原