CAREER: Integrated Experimental and Numerical Modeling Study of Non-uniform Sediment Transport in Meandering Channels

摘要冲积河道输沙的科学认识主要来源于直河道的实验。在弯曲河道中，泥沙与高度三维的水流相互作用，引起点坝和曲流平台的演化。迄今为止，还没有任何理论能够令人满意地解释和量化水流（平均和湍流）、泥沙粒径输移、点坝动力学和弯曲的顺序迁移之间的相互作用。在许多应用于弯曲和曲流河道的数值模型中，泥沙按粒径分型输运的公式是基于直接实验室水槽的数据，而从未对弯曲河道进行过试验。目前对曲流河道沉积物分选的认识限制了数值模型模拟河床物质级配、河床形态和弯曲平台演变的能力。为了更全面地了解曲流泥沙的运移，本项目旨在解决以下问题：水流如何影响泥沙的运移？泥沙输运与近河床平均流量的偏差有多大？泥沙荷载的空间分布是怎样的？床荷载、表面和基材的尺寸等级是什么？它们是如何与泥沙输运率相关联的？空间变化的泥沙通量如何构成点坝动力学？曲流迁移如何响应点坝的增长或衰减？实验将在几个自形成的曲流通道中进行，曲流通道的正弦值从1.25到3.7不等。分级良好的泥沙混合物将被送入这些蜿蜒的河道，以研究三维水动力流场、表面和底质的分布、不同大小的泥沙在顺流和横向上的输沙特征、顶点附近和河道交叉处的点坝和池的逐渐形成、生长和阻尼、随着河岸侵蚀和点坝的进展而形成的平台演变。实验结果将整合到一个数值模型中，以模拟实验水槽和自然河流的蜿蜒迁移过程。研究结果将有助于科学认识河流曲流，为河流修复设计提供有价值的指导。其优点不仅体现在基础研究上，而且体现在工程实践中。该项目将获得新课程所需的实验设备和计算机模型，让本科生参与研究，为女学生建立长期指导计划，为科学博物馆举办计算机动画展览，并向高中生推广。其目标是鼓励创造力和创新，在工程教学中强调计算机，提高女性在工程领域的知名度，并吸引最有才华的高中毕业生进入土木工程专业。

AbstractThe scientific knowledge on sediment transport in alluvial channels stems from experiments in straight channels. In curved channels, sediment interacts with highly three-dimensional flow and induces point bars and meandering planform evolution. To date, no theory is able to satisfactorily explain and quantify the interactions among flow (mean and turbulence), sediment transport by size fractions, point bar dynamics and the sequential migration of bends. Among many numerical models applied to curved and meandering channels, formulations for sediment transport by size fractions have been based on data from straight laboratory flumes and never tested with sinuous channels. Current understanding of sediment sorting through meandering channels limits the capability of numerical models in simulating the evolution of bed material gradation, bed morphology, and bend planform. Towards a complete understanding of sediment transport in meanders, this project aims to address the following questions: How does flow influence sediment transport? How much does sediment transport deviate from the near-bed mean flow? What are the spatial distributions of sediment load? What are the size gradations of bed load, surface, and substrate material? How do they correlate to sediment transport rate by size fraction? How does spatially varied sediment flux constitute point bar dynamics? How does meandering migration response to the growth or dampening of point bars?Experiments will be conducted in several series of self-formed meandering channels with sinuosities ranging from 1.25 to 3.7. Well-graded sediment mixtures will be fed into these sinuous channels to enable investigation of three-dimensional hydrodynamic flow field, distributions of surface and substrate material, sediment transport characteristics for different size fractions at the streamwise and lateral directions, gradual formation, growth, and dampening of point bars and pools near the apex and channel crossing, planform evolution as bank erodes and point bar progresses. The experimental results will be integrated into a numerical model to simulate the processes of meandering migrations in both experimental flumes and a natural river. The results of this research will contribute to scientific understanding of river meanders and provide valuable guidance in river restoration design. The merit is not only in basic research but also in engineering practice. The project will acquire an experimental facility and a computer model needed for new courses, engage undergraduates in research, establish a longer-standing mentoring program for women students, develop a computer animation exhibition for science museums, and outreach to high school students. The objectives are to encourage creativity and innovation, stress computing in engineering teaching, increase the visibility of women in engineering, and attract most talented high school graduates to Civil Engineering.