Collaborative Research: Coastal Form Drag and Eddies

摘要：本研究将探讨“形式阻力”的物理特性及其对沿海地区潮汐能耗散的重要性。形式阻力是流体流过障碍物（在这种情况下是粗糙地形）时，由于压力差而产生的总阻力的一部分。形式阻力通常与产生大的、连贯的流动特征有关，如潮汐涡流和内波。因此，这项研究部分集中在控制这些漩涡和波浪产生和衰减的物理机制上。这种阻力的重要性已被视为深海中潮汐能量耗散的主要候选，而在沿海海洋中，更经典的阻力类型，即底部边界层摩擦，被认为是更重要的。然而，PIs最近对普吉特海湾三树岬潮汐流的研究表明，在普吉特海湾的那个地区，形式阻力至少是从潮汐中提取能量的主要机制的20倍。他们将继续这项工作，其总体目标是预测洋流流过任何沿海地区复杂地形时所经历的净阻力（和能量损失）。此外，pi还试图了解分层流体中倾斜涡流的动力学和耗散机制，这是潮汐耗散的关键过程。目前的研究有两个主要目标。一是对现有观测资料进行进一步分析，结合新的数值模拟和实验室实验，确定倾斜涡位涡演化机制。第二个部分是形式阻力的数值研究，目标是开发一种实用的方法(i)在复杂通道形状下的计算，以及（ii）在数值模型中的参数化。这项研究将有助于提高沿海数值环流模式的预测能力，增加我们对未解决的粗糙地形影响的理解。数值模型是重要的工具，用于对海洋的概念理解和预测实际管理决策的结果。通过这样的使用，模型精度的提高将具有普遍的科学和社会效益。本研究亦将透过两名研究生及三名本科生的参与，为教育作出贡献。

ABSTRACTOCE0425893: Collaborative Research: Coastal Form Drag and EddiesIntellectual Merit This study will explore the physics of "form drag," and its importance to the dissipation of tidal energy in coastal regions. Form drag is that part of the total drag experienced by a fluid flow that arises from pressure differences across an obstacle, in this case rough topography. Form drag is typically associated with the generation of large, coherent flow features, such as tidal eddies and internal waves. The study therefore focuses in part on the physical mechanisms governing the creation and decay of these eddies and waves. The importance of this type of drag has come to be seen as a leading candidate for the dissipation of tidal energy in the deep ocean, whereas in the coastal ocean the more classical type of drag, bottom boundary layer friction, is assumed to be of greater importance. However, the PIs' recent work on tidal flow past the Three Tree Point headland in Puget Sound, WA demonstrated that form drag was, by at least a factor of 20, the dominant mechanism extracting energy from the tides in that region of the Sound. They will continue that line of work, with the overall goal of predicting the net drag (and loss of energy) a current will experience when flowing over the complex topography of any coastal region. In addition the PIs seek to understand the dynamics and dissipation mechanisms of tilted eddies in a stratified fluid, which are key processes in tidal dissipation. The current study has two main objectives. The first is to perform further analysis of existing observations, along with new numerical simulations and lab experiments, to determine the tilted eddy potential vorticity evolution mechanisms. The second component is a numerical investigation of form drag with the goal of developing a practical method of (i) its calculation in complex channel shapes, and (ii) its parameterization in numerical models. Broader Impacts This study will help to improve the predictive skill of coastal numerical circulation models, by increasing our understanding of the effects of unresolved rough topography. Numerical models are important tools used both for conceptual understanding of the ocean and for predicting outcomes of practical management decisions. Improvements to model accuracy will have general scientific and societal benefits through such uses. This study will also contribute to education through the involvement of two graduate students and three undergraduates.