Mechanics of Sediment Transport in Complex Flows

项目编号：CTS 9634261项目负责人：麦克莱恩这是一项资助，用于支持在近床平均流动和湍流结构与稳定均匀流动明显不同的情况下，沉积物夹带和输运的力学研究。这将在总体目标的范围内进行，即发展预测可蚀河床上的水流和泥沙动力学以及由此产生的地形反应的能力。在稳定、均匀的水流中形成的水流特性与泥沙输运之间的现有关系，对于更复杂的水流来说，结果并不准确。这种误差的产生是由于空间和时间加速度对湍流场的影响，改变了构成河床的泥沙颗粒的升力和阻力的分布。这些影响是水流结构、沉积物输送和河床形态之间相互作用的关键部分，这些相互作用产生了广泛的可蚀河床现象，如波纹和沙丘的形成和稳定。本研究的主要目的有三个：a)将从二维床形态收集到的知识扩展到三维特征；b)确定沉积物颗粒对复杂流动的响应；c)通过使用多频率声学反向散射系统以及用于观察非常近床过程的成像光纤系统，将该信息扩展到悬浮颗粒。测量将与悬浮沉积物的平流/扩散模型相结合，以研究床上局部夹带和近床流场之间关系的本质，以及这如何影响床型的演变。

ABSTRACT Proposal Number: CTS 9634261 Principal Investigator: McLean This is a grant to support the investigation of the mechanics of sediment entrainment and transport in situations where near-bed mean flow and turbulence structure is significantly different than that of steady, uniform flows. This will be done within the context of an overall goal of developing the capability to predict the flow and sediment dynamics over an erodible bed and the resulting topographic response. Existing relations between flow characteristics and sediment transport developed in steady, uniform flows yield inaccurate results for more complex flows. This error arises through the alteration of the distributions of lift and drag forces on sediment grains making up the bed as a result of the effects of spatial and temporal accelerations on the turbulence field. These effects are a critical part of the mutual interactions between flow structure, sediment transport, and bed morphology that give rise to a wide spectrum of erodible bed phenomena, such as the formation and stability of ripples and dunes. The principle aims of this research are threefold: a) to extending the knowledge gleaned from two-dimensional bedforms to three-dimensional features b) to determine the response of a sediment particle to complex flow and c) to extend this information to suspended particles through the use of a multi-frequency acoustic backscatter system as well as with an imaging fiber optic system for observing very near-bed processes. Measurements will be combined with an advection/diffusion model for suspended sediment to investigate the nature of the relationship between local entrainment at the bed and the near-bed flow field and how this affects the evolution of the bedforms.