水库细颗粒淤积物重力驱动机制及其流变响应研究

Observed distribution of fine-grained sediment deposits in the dam area of the typical reservoir (the TGR) differs from the previous predictions based on numerical model studies during its early filling. Field data indicate that sediment deposits in the dam area are mostly found at the bottom of the main channel, which have formed a new river bed with a flat surface that is nearly horizontal. In contrast, very little fine sediment deposition can be found on the bank slopes of the channel. Traditional simulated results demonstrated that sediment deposition spreads more evenly over the cross-section. This study is intended to explain the discrepancy between measured and previously modeled sedimentation patterns of fine-grained particles in the large reservoir by several methods. The rheological properties of the fine-grained sediment deposits will be investigated by experimental studies. The gravity-driven model of fine-grained sediment deposits will be proposed based on its mechanisms and rheological properties. Then, the 3-D model for sedimentation patterns of fine-grained particles will be developed by solving the critical numerical issues. This model can not only simulate the processes of transportation and deposition of fine-grained particles, but also predict the sedimentation patterns of fine-grained sediment deposits driving by gravity. Finally, the fine sediment transport patterns dominated by both flow and gravity will be analyzed. The results of this investigation can extend our understanding of fine sediment transport mechanisms in reservoirs.

典型水库（如：三峡）蓄水初期近坝区断面淤积形态的实际观测与传统模拟结果存在显著差异，实际观测显示细颗粒泥沙主要集中淤积在断面深槽内、且呈水平状，而传统模拟中泥沙淤积则多为沿断面呈相对均匀分布。本项目拟采用多种研究手段相结合，探讨其差异的动力学成因，揭示水库细颗粒淤积物的流变特性和流型特征，分析其影响因素及变化规律，通过引入水、淤积物、河床之间的界面受力分析，在基础层面上推导建立细颗粒淤积物重力驱动流动的数学描述方程（失稳判别、运动模式）。然后，解决细颗粒淤积物重力驱动流动三维数值模拟的关键技术，构建其动力学耦合模型，揭示不同流型运动之间的耦合效应，模型不仅可模拟传统水沙输移，亦可模拟淤积物自身的重力驱动过程，弥补传统数模无法准确预测水库细颗粒泥沙断面淤积形态的不足。随后，深入分析水流剪切、重力驱动双重作用下细颗粒淤积物的流动特性和变形响应规律。研究成果可进一步丰富水库泥沙运动相关基础理论。

典型水库蓄水初期近坝区断面淤积形态的实际观测与传统模拟结果存在显著差异，实际观测显示细颗粒泥沙主要集中淤积在断面深槽内、且呈水平状，而传统模拟中泥沙淤积则多为沿断面呈相对均匀分布。本项目采用多种研究手段相结合，探明了其差异的动力学成因，揭示了水库细颗粒淤积物的流变特性与流型特征，低密度细颗粒淤积物为宾汉型流体，淤积平衡坡降较小，当其密度大于1.25g/cm3后，流动性快速减弱；通过引入水、淤积物、床面之间的界面受力分析，构建了细颗粒淤积物失稳流动描述模式，并与水沙输移模型相耦合，建立了考虑细颗粒淤积物流动特性的水库淤积形态模拟方法，实现了水库双层异型流体运动的耦合模拟，模型不仅可模拟传统水沙输移，亦可模拟淤积物自身的重力驱动过程。以三峡水库近坝区以及小浪底水库为例，开展了典型调度方式下的水库淤积形态模拟分析，结果表明：考虑细颗粒淤积物流动特征的水库淤积形态模拟结果与实测结果吻合较好。研究成果可为水库淤积形态形成机理及其对水沙调控的响应研究提供技术支撑，具有重要的理论价值和实践意义。