Understanding Rip Currents: The Multi-scale Interactions of Waves, Currents and Morphology

0756271余本研究研究了冲浪带波致流的复杂动力学和水-形态动力系统的多尺度动力学，最终将对近岸环境进行更好的预测。由破碎的海浪驱动的冲浪带洋流，是近岸运输、混合和分散水、沉积物和污染物的主要媒介。这些因素强烈影响海岸侵蚀，从而影响海岸漫溢和洪水以及水质。更好地了解这些洋流的动态对沿海环境、经济和生态系统的发展和保护具有重要意义。众所周知，离岸流是危险的海滩危害，占美国冲浪区救援的80%。对激流产生机制的理论认识并不令人满意，特别是在缺乏沿岸变异性的海滩上。最近的研究主要集中在形态动力学不稳定性（流体和可侵蚀海床之间的反馈）上，而没有仔细考虑波浪和洋流之间的完全动态相互作用。这有效地模拟了由形态演化控制的慢时间尺度，抑制了水动力过程的快时间尺度。为了解决不同时间尺度的意义，PI计划通过耦合波流相互作用引起的水动力不稳定性（Yu, 2006）和形态动力学，深入研究波、流和形态之间的多尺度相互作用。研究计划将包括导致离岸流的流体动力学不稳定性的扩展线性分析，非线性发展的离岸流的数值研究，以及与慢尺度形态动力学的耦合。将通过与现有观测结果的直接和间接比较来验证模型。需要改进以开发可靠的预测工具，这对基于科学的规划、决策和缓解战略至关重要。随着全球海平面的上升增加了风暴潮发生的可能性，以及海平面上升和洪水泛滥的风险，沿海地区的演变在气候变化情景中变得更加令人担忧。计划中的研究支持了研究生项目的发展。除了培训两名研究生外，还将通过PI开发海岸工程和环境流体力学研究生课程的努力来促进研究和教育。通过PI合作者的外展项目，包括威尔明顿国家气象局、北卡罗来纳州海洋基金和北卡罗来纳大学海岸研究所，也有望产生更广泛的教育影响。

0756271 YuThis research studies the complex dynamics of surf zone wave-induced currents and the multi-scale dynamics of the hydro-morphodynamic system that will eventually lead to better predictions in the nearshore environment. Surf zone currents, driven by breaking waves, are the primary agents to transport, mix and disperse water, sediments and pollutants in the near shore. These strongly influence coastal erosion, hence coastal overtopping and flooding, and water quality. Better understanding of the dynamics of these currents is important to the development and protection of coastal environment, economy and ecosystem. Rip currents are widely known as dangerous beach hazards and account for 80% of surf zone rescues in the USA. Theoretical understanding of rip generation mechanisms has not been satisfactory, in particular on beaches lacking alongshore variability. Recent studies have mostly focused on morphodynamic instabilities (feedback between fluid and erodible seabed), not carefully considering the fully dynamical interaction between waves and currents. This effectively models only the slow time scale controlled by the morphology evolution, suppressing the faster time scale of the hydrodynamic processes. To address the significance of the various time scales, the PI plans to thoroughly investigate the multi-scale interactions among waves, currents and morphology, by coupling the hydrodynamic instability due to wave-current interaction (Yu, 2006) and the morphodynamics. The research program will include extended linear analysis of the hydrodynamics instability leading to rip currents, numerical study of the nonlinear developed rip currents, and the coupling with slow-scale morphodynamics. The modeling will be validated through direct and indirect comparisons with available observations. Improvements are needed for development of reliable predictive tools essential to science-based planning, decision-making and mitigation strategies. Coastal evolution has become even more of a concern within the climate change scenarios, as the rise of global sea levels increases the likelihood of storm surges as do the risks of overtopping and flooding. The planned research supports the development of a graduate program. In addition to training two graduate students, research and education will also be fostered through the PI's efforts to develop a graduate curriculum in Coastal Engineering and Environmental Fluid Mechanics. A broader educational impact is also expected through the outreach programs of the PI's collaborators, including the National Weather Service Wilmington, NC Sea Grant and University of North Carolina, Coastal Studies Institute.