Collaborative Research: Ocean Wave Dissipation through Breaking and Bubble Generation

这个项目关注的是海洋表面波浪的破裂和在这个过程中产生的气泡。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。波浪破碎也对航行和海上船只的安全通行构成威胁。关键问题是“波浪破碎时损失了多少能量？”这种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，破波过程中产生的气泡的数量和大小是控制能量耗散和破波强度的关键因素。该项目将使用实地观测和计算机模型来验证这种依赖性，并应用于改进海浪预报和海洋-大气耦合。这项提议的工作将支持一名博士后研究员，并为华盛顿大学的年度发现日活动做出具体贡献，该活动将惠及来自地区K-12学校的10,000名学生。该项目的技术方法是，利用配备运动传感器、湍流剖面仪和气泡记录相机的自由漂流浮标，在开阔的海洋中测量波浪破碎。本文的工作建立在最近的研究结果的基础上，使用带有跟踪的表面波仪器浮子（SWIFT）漂浮器测量破碎波下的湍流耗散率，并采用基于vof（流体体积）的欧拉-欧拉多分散双流体模型模拟两相气泡流。以往的结果表明，在高海况时，气泡耗散在总破波耗散中所占的比例可能越来越大。在这个项目中进行的测量将被分析，以确定气泡的时间演变，以及与个别破碎波相关的湍流和运动。这些数据将用于检验最近的一个公式，该公式将总耗散与气泡羽流体积的时间积分进行换算。此外，将评估一个相关的公式，该公式将用海洋表面可见的泡沫斑块面积来衡量气泡羽流深度。后一种公式的改进将使估算羽流体积和远程推断消散成为可能。推导的公式将与其他耗散估计进行比较，这些估计包括：菲利普斯破碎峰分布、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性的影响和抽样稀少的实地观测的后果。这些测量结果将与破裂过程的高分辨率双流体模型模拟进行比较。这种方法将使破碎波条件的更完整的调查和对观测的固有稀疏性的评估成为可能。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.