Characterizing Current and Wave Drag over Shallow Coral Reefs

浅部珊瑚礁上的海流和波浪阻力特征

• 批准号: 1558343
• 负责人: Steven Lentz
• 金额: $ 38.2万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-04-01 至 2018-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558343&HistoricalAwards=false
• 关键词: Characterizing; Current; Wave; Drag; over

The defining hydrodynamic characteristic of coral reefs is that they are rough. Consequently, the fundamental challenge in understanding and modeling the dynamics of both currents and surface gravity waves over shallow coral reefs is characterizing drag. This research is aimed at developing more accurate circulation and wave models for coral reefs that are essential for properly interpreting observations and modeling biochemical processes over reefs. A better understanding of the hydrodynamics is also essential for making accurate assessments of the impact of climate change on coral reefs. For example, the dependence of drag coefficients on water depth clearly has implications to the impact of sea level rise on coral reefs. This study will directly benefit ongoing research on the impact of ocean acidification on the barrier reefs of Palau (western tropical Pacific) and Dongsha (South China Sea) by providing a better physical context for interpreting biochemical observations. The project will inform the thesis work of two graduate students. To advance the understanding of current and wave drag over coral reefs, this study addresses four sets of questions: 1) Do drag coefficients based on depth-average currents depend on water depth in a manner consistent with theory from open-channel flow and does this dependence account for some of the scatter in coral reef drag coefficients? 2) What is the relationship between surface gravity wave friction factors over coral reefs and orbital displacements and is it consistent with results from laboratory studies and existing theories? 3) Do wave-current interactions significantly enhance current drag and wave dissipation over coral reefs? 4) Are hydrodynamic roughness estimates for currents and surface waves similar and what is their relationship to physical roughness over coral reefs? These four sets of questions will be addressed use existing observations of current profiles, pressures, and wave characteristics from three very different coral reef systems, Palau's barrier reef, Dongsha Atoll, and three platform reefs in the Red Sea. Spatial-average drag coefficients will be estimated by integrating the momentum balance across the reefs to account for spatial (and temporal) variations in water depth and determining the drag coefficient that minimizes the residual error in the momentum balance. Wave friction factors will be estimated by integrating the wave-energy balance across the reef and minimizing the residual error. Since there are substantial spatial and temporal variations in water depth over coral reefs determining the drag coefficient dependence on water depth and providing a model for that dependence will be a significant advance in the understanding of coral reef hydrodynamics. The project will advance the understanding of wave-current interactions over coral reefs, a potentially important unresolved problem. Accounting for these factors influencing current and wave drag will allow accurate and consistent estimates of hydrodynamic roughness that can then be related to coral reef physical roughness.

珊瑚礁的定义水动力特征是它们很粗糙。因此，理解和建模电流和表面重力波在浅珊瑚礁上的动力学的基本挑战是拖动的特征。这项研究旨在为珊瑚礁开发更准确的循环和波模型，这些珊瑚礁对于正确解释观察结果和建模生化过程至关重要。对流体动力学的更好理解对于对气候变化对珊瑚礁的影响进行准确评估也至关重要。例如，阻力系数对水深的依赖性显然对海平面上升对珊瑚礁的影响有影响。这项研究将直接对海洋酸化对帕劳（西部热带太平洋）和东莎（南中国海）的障碍礁的影响进行有益于研究，从而提供了更好的物理背景来解释生化观察。该项目将为两位研究生的论文工作提供信息。为了促进对珊瑚礁的当前和波浪阻力的理解，本研究解决了四个问题：1）基于深度平均水流的阻力系数是否以与开放通道流的理论相一致的方式取决于水的深度，并且这是否依赖于珊瑚礁阻力系数中的某些散射？ 2）珊瑚礁上的表面重力波摩擦因子与轨道位移之间的关系是什么，这与实验室研究和现有理论的结果一致？ 3）波流相互作用是否显着增强了珊瑚礁上的电流阻力和波浪耗散？ 4）电流和表面波的流体动力粗糙度估计是否相似？它们与珊瑚礁的身体粗糙度有何关系？ 这四组问题将通过三个非常不同的珊瑚礁系统，Palau的Barrier Reef，Dongsha Atoll和Red Sea中的三个平台礁的现有观察结果来解决当前的概况，压力和波浪特性的现有观察结果。空间平均阻力系数将通过整合整个珊瑚礁的动量平衡来估算水深的空间（和时间）变化，并确定阻力系数，以最大程度地减少动量平衡中的残留误差。波浪摩擦因子将通过整合跨礁石的波能平衡并最大程度地减少剩余误差来估算波浪摩擦因子。 由于在珊瑚礁上，水深有很大的空间和时间变化，这些珊瑚礁决定了对水深的阻力系数依赖性并为该依赖性提供模型，这将是对珊瑚礁流体动力学的理解。该项目将促进对珊瑚礁的波流相互作用的理解，珊瑚礁是一个潜在的未解决的问题。考虑到影响电流和波浪阻力的这些因素将允许对流体动力粗糙度的准确，一致的估计，这可能与珊瑚礁的物理粗糙度有关。