Collaborative Research: SGER - Enhanced Sediment Transport due to Transient Wave Loads

摘要：本研究的目的是探讨瞬态波浪荷载引起的超孔隙压力增加导致泥沙流动性增强的问题。这个问题是理解风暴潮和海啸期间沉积物运输和冲刷的基础。目前，大多数输沙模型将输沙通量与盾构参数联系起来，盾构参数是平坦河床上准稳定水流中水平力与垂直力的比值。然而，在槽（峰）处存在一个向上（向下）的渗流，这可以显著改变作用在土粒上的净垂直力。此外，局部河床坡度也会影响泥沙的流动性。因此，在拟议的工作中，泥沙输运速率的基本依赖于孔隙压力梯度、颗粒密度和粒度、河床坡度和河床剪切应力将通过数值和实验模拟系统地检查。将开发一个完全耦合流体、土壤和泥沙输运模式的数值模型来预测风暴潮或海啸引起的泥沙输运和冲刷。实验室研究将在夏威夷大学水力学实验室的小水槽中进行，以确定泥沙侵蚀速率的经验关系。水槽具有透明的侧壁和透明的底部，适合于详细的流动可视化和泥沙输运动力学的测量，并配备了一个泵，可以产生不同流速的水平流。利用小水槽，可以方便快捷地配置不同的流动条件和地形配置。应该强调的是，这个实验不适合，也没有必要，对于大波浪槽（如俄勒冈州立大学的）；UH的小水槽非常适合做这套系统的、可控的实验。本文的研究对提高对瞬态波荷载增强输沙作用的认识具有重要意义，对风暴潮和海啸输沙冲刷预报具有重要意义。拟议的研究还有望改善未来的设计和改造指导方针、城市规划建议，最重要的是，改善减灾战略。为了扩大影响，调查人员将把教育和推广活动纳入研究，包括教育社区关于风暴潮和海啸的危险和灾害规划策略。

Abstract:The objective of the proposed research is to investigate the problem of enhanced sediment mobility due to buildup of excess pore pressure as a result of transient wave loads. This problem is fundamental to the understanding of sediment transport and scour during storm surge and tsunami. Currently, most sediment transport models relate the sediment flux with Shield's parameter, which is the ratio of horizontal force to vertical force in a quasi-steady flow over a flat bed. However, there is an upward (downward) seepage at the trough (crest), which can significantly alter the net vertical force acting on the soil particle. In addition, the local bed slope also affects sediment mobility. Thus, in the proposed work, the fundamental dependence of sediment transport rate on the pore pressure gradient, particle density and grain size, bed slope, and bed shear stress will be systematically examined via numerical and experimental simulations. A numerical model which fully couples the fluid, soil, and sediment transport models will be developed to predict storm surge or tsunami-induced sediment transport and scour. Laboratory studies will be conducted at the small flume in the hydraulics lab at the University of Hawaii to determine the empirical relationship for the sediment erosion rate. The flume has transparent sidewalls and transparent bottom which are suitable for detailed flow visualization and measurement of sediment transport dynamics, and is equipped with a pump that can generate horizontal flow at different flow rates. With the small flume, different flow conditions and topographical configurations can be configured easily and quickly. It should be emphasized that this experiment is not suited, and not necessary, for large wave tanks (such as the ones in OSU); the small flume at UH is perfect for this set of experiment to do systematic, controlled studies. The proposed research is fundamental to improving the understanding of enhanced sediment transport due to transient wave loads, which is critical to the prediction of storm surge and tsunami-induced sediment transport and scour. The proposed research is also expected to improve future design and retrofit guidelines, urban planning recommendations, and most importantly, disaster mitigation strategies. To broaden the impact, the investigators will incorporate into the research education and outreach activities, including educating the community about the dangers and disaster planning strategies for storm surge and tsunami.