Mechanics of Sediment Transport in Complex Flows

摘要建议编号：CTS 9634261首席研究员：麦克莱恩这是一笔赠款，用于支持在近床平均流和湍流结构与恒定、均匀流显著不同的情况下研究泥沙卷吸和输运的力学。这将在一个总体目标的范围内进行，即发展预测可侵蚀河床上的水流和泥沙动力学以及由此产生的地形响应的能力。现有的水流特性和泥沙输运之间的关系是在恒定、均匀的水流中发展起来的，对于更复杂的水流来说，结果并不准确。这种误差是由于时空加速度对湍流场的影响，改变了构成床面的泥沙颗粒的升力和阻力分布而产生的。这些影响是水流结构、泥沙运动和河床形态之间相互作用的关键部分，这些相互作用导致了一系列可侵蚀的河床现象，如波纹和沙丘的形成和稳定。这项研究的主要目的有三个：(A)将从二维底床收集的知识推广到三维特征；(B)确定沉积物颗粒对复杂流动的响应；(C)通过使用多频声波背向散射系统以及利用用于观察非常接近底床过程的成像光纤系统，将这一信息推广到悬浮颗粒。测量将与悬浮泥沙的平流/扩散模型相结合，以调查床面局部卷吸与近床面流场之间关系的性质，以及这种关系如何影响床面形态的演变。

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.