Collaborative Research: Ocean Wave Dissipation through Breaking and Bubble Generation

该项目涉及海洋表面波浪的破碎和在此过程中产生的气泡。波浪破碎是海洋表面湍流和混合的重要来源，包括海洋和大气之间气体和热量的湍流交换。波浪破碎对海上航行和船舶安全通行也是一种危害。关键问题是“海浪破裂时会损失多少能量？”这一损失的能量既是准确预报海浪的重要参数，也是规定海洋-大气交换的重要参数。最近的研究表明，在波浪破碎过程中产生的气泡的数量和大小是控制能量耗散和破碎强度的关键因素。该项目将使用现场观测和计算机模型来验证这种相关性，并应用于改进波浪预报和海-气耦合。这项拟议的工作将支持一名博士后研究人员，并对公众宣传做出具体贡献，特别是对华盛顿大学一年一度的发现日活动做出贡献，该活动覆盖了来自地区K-12学校的1万名学生。该项目的技术方法是使用配备运动传感器、湍流剖面仪和用于记录气泡的相机的自由漂流浮标来测量公开海洋中的波浪破碎。这项工作是基于最新的结果，使用表面波仪器带跟踪浮子(SWIFT)漂移器来测量破碎波下的湍流耗散率，以及基于VOF(流体体积)的欧拉-欧拉多分散双流体模型来模拟两相泡状流。以前的结果表明，在高海况期间，气泡的消散可能在总的海浪破碎消散中所占的比例越来越大。将对该项目中的测量结果进行分析，以确定气泡的时间演化，以及与单个破碎波相关的湍流和运动。这些数据将被用来测试最近的一个公式，该公式用气泡羽流体积的时间积分来衡量总消散。此外，将评估一种根据海洋表面可见泡沫斑块的面积来衡量气泡羽流深度的相关配方。对后一种公式的改进将使估计烟羽体积和远程推断消散成为可能。推导出的公式将与其他耗散估计进行比较，这些估计包括：菲利普斯破裂峰值分布、平衡风输入和湍流耗散的现场测量。拟议的工作还将审查间歇的影响和稀疏抽样的实地观测的后果。这些测量将与高分辨率的双流体模型对破碎过程的模拟进行比较。这一方法将使我们能够更全面地调查破浪情况，并评估观测结果的内在稀疏性。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project concerns the breaking of waves at the ocean surface and the bubbles generated during that process. Wave breaking is an important source of turbulence and mixing at the ocean surface, including the turbulent exchange of gasses and heat between the ocean and the atmosphere. Wave breaking is also a hazard to navigation and safe passage for vessels at sea. The key question is "how much energy is lost when waves break?". This lost energy is both an important parameter for accurate wave forecasts and for prescribing ocean-atmosphere exchange. Recent work has suggested that the quantity and size of bubbles generated during wave breaking are the key controls on the energy dissipation and thus the strength of breaking. This project will use field observations and computer models to verify this dependence, with application to improve wave forecasting and ocean-atmosphere coupling. The proposed work will support a postdoctoral researcher and contribute to public outreach with specific contributions to the annual Discovery Days event at the University of Washington, that reaches 10,000 students from regional K-12 schools.The technical approach of the project is to measure wave breaking in the open ocean with freely drifting buoys that are equipped with motion sensors, turbulence profilers, and cameras for bubble recording. The proposed work builds on recent results using the Surface Wave Instrument Float with Tracking (SWIFT) drifters to measure the turbulent dissipation rate beneath breaking waves and a VOF-based (volume of fluid) Eulerian-Eulerian polydisperse two-fluid model to simulate the two-phase bubbly flow. Previous results suggest that dissipation by bubbles may be an increasingly large fraction of the total wave breaking dissipation during high sea states. The measurements to be carried in this project will be analyzed to determine the time evolution of the bubbles, as well as the turbulence and motion associated with individual breaking waves. The data will be used to test a recent formulation that scales the total dissipation with the time integral of the bubble plume volume. Further, a related formulation that scales bubble plume depth with the area of foam patches visible at the ocean surface will be evaluated. Improvement of the latter formulation will allow estimates of plume volume and infer dissipation remotely. The formulation derived will be compared with other estimates for dissipation, which include: the Phillips breaking crest distribution, equilibrium wind input, and in situ measurements of turbulent dissipation. The proposed work will also examine the effects of intermittence and the consequences of sparsely sampled field observations. These measurements will be compared with the high resolution, two-fluid model simulations of the breaking process. This approach will enable a more complete investigation of breaking wave conditions and an assessment of the inherent sparseness of the observations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.