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

文摘：该研究的目的是研究由瞬时波浪荷载引起的超孔压积聚引起的泥沙移动性增强问题。这个问题对于理解风暴潮和海啸期间的泥沙输送和冲刷是基本的。目前，大多数输沙模型都将输沙通量与Shield参数联系起来，Shield参数是平面床面上准恒定流水平力与垂直力的比值。然而，在谷顶处有向上(向下)的渗流，这会显著改变作用在土壤颗粒上的净垂直力。此外，局部河床坡度也会影响泥沙运动。因此，在拟议的工作中，将通过数值模拟和实验模拟，系统地研究泥沙输移率与孔隙压力梯度、颗粒密度和颗粒尺寸、床面坡度和床面剪应力的基本关系。将开发一个完全耦合流体、土壤和泥沙运移模型的数值模型，以预测风暴潮或海啸引发的泥沙输送和冲刷。将在夏威夷大学水力学实验室的小型水槽中进行实验室研究，以确定泥沙侵蚀速率的经验关系。该水槽具有透明的侧壁和透明的底部，适合于详细的水流可视化和泥沙运动动力学测量，并配备了可在不同流量下产生水平水流的泵。利用小型水槽，可以方便快捷地配置不同的水流条件和地形形状。应该强调的是，这项实验不适合也没有必要用于大型波槽(如俄亥俄州立大学的水槽)；UH的小水槽非常适合这套实验来进行系统的对照研究。这项研究对于加深对瞬变波浪作用下泥沙输移的理解是非常重要的，这对于风暴潮和海啸引起的泥沙输移和冲刷的预测是至关重要的。预计拟议的研究还将改进未来的设计和改造指南、城市规划建议，以及最重要的减灾战略。为了扩大影响，调查人员将在研究中纳入教育和外展活动，包括教育社区了解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.