Experimental Study of Two-Phase Suspended Sediment Transport in Breaking Waves

本计画旨在探讨破碎波中大尺度紊流的结构，以及这些大涡与可冲床面的相互作用。实验室实验将在一个长25米、宽0.9米、深0.75米的倾斜水槽中进行，水槽配有可编程波浪发生器。一个沉积颗粒的平床将被放置在水槽底部的凹处。一个体积三分量测速（V3 V）系统将被用来测量沉积物颗粒的速度，沉积物颗粒的位置，和流体速度同时在一个三维（3-D）的流动体积以上的可侵蚀的床溢出和暴跌波条件。两相流测量将用于了解大涡的拓扑结构，以及大涡在床面沉积物拾取过程中的作用和水柱上方悬浮沉积物的分布。智力优势：该项目将建立在首席研究员（PI）之前的工作基础上。它将解决破碎波的几个方面，仍然知之甚少，是关键的成功的数值方案，预测在碎波带和海滩转化的泥沙运输的发展。测量三维流动体积中的三分量流体速度将使研究大涡的演化以及它们如何从上层对流到底部成为可能。结合使用高速数字电影摄像机的流动显示，测量将揭示大涡的产生机制和非均匀波破碎沿着波峰的结构的影响。体积流体速度测量也将允许调查员检查底部上的大涡流的冲击。这个过程是瞬态的和三维的，其特点是大的瞬时湍流动能和剪切应力的冲击area. The颗粒位置的同时测量，颗粒速度，和流体速度超过一个可侵蚀的床使用V3 V系统是创新的，并将允许该项目的研究人员来解决三个基本问题，在破碎波泥沙输运。第一个问题涉及悬浮泥沙输运的适当的底部边界条件，具体地说，如何参数化破碎波湍流对泥沙拾取率的影响。第二个问题是大漩涡和悬浮颗粒之间的相互作用。拟议中的研究将回答这样的问题：如何密切做泥沙颗粒的瞬时速度遵循那些流体颗粒？悬沙输运和湍流输运之间是否有直接联系？泥沙分布过程能否模拟为扩散过程？第三个问题涉及破碎机类型对泥沙输运的影响。调查人员将解决以下问题：如何数量和方向的悬浮负荷运输在外部冲浪区与波浪的特性在初期破碎？与其他机制（如片状流传输）相比，这种传输模式有多重要？更广泛的影响：该项目将提供高质量的数据集，以测试和改进碎波区破碎波和沉积物输运的详细模型。这些模型将促进对破碎波如何侵蚀或存款沉积物以及如何影响滨水性质的理解。V3 V在两相流测量方面的进展也将促进其在其他研究领域的发展和应用。研究人员可以从PI的研究网站下载测量数据。该项目将通过让本科生和研究生参与实验研究来培养下一代研究人员。拟议的V3 V系统的收购将为学生提供一个国家的最先进的测量仪器进行流体力学的实验研究。两个新的实验，使用V3 V将开发为本科生和研究生班，以提高学生的流体力学原理的学习。PI还将使用该设备在涉及K-12学生的研讨会上进行流体流动现象的现场演示。这些活动的结果将吸引更多的高中生（包括美国原住民学生）攻读科学和工程学的大学学位，为本科生提供研究经验，通过支持有能力的学生进行基础研究，建立一个具有全国竞争力的研究生课程，并保持一个现代化的流体力学实验室，以继续研究和教育。

This project is to investigate the structure of large-scale turbulence in breaking waves and the interaction of these large eddies with an erodible bed. Laboratory experiments will be carried out in a 25 m-long, 0.9 m-wide and 0.75 m-deep tilting flume equipped with a programmable wave generator. A flat bed of sediment particles will be placed in a recess in the flume floor. A volumetric three-component velocimetry (V3V) system will be used to measure sediment particle velocities, sediment particle locations, and fluid velocities simultaneously in a three-dimensional (3-D) flow volume above the erodible bed under spilling and plunging wave conditions. The two-phase flow measurements will be used to understand the topology of large eddies, and the role of large eddies in the sediment pickup process at the bed and the distribution of suspended sediment over the water column.Intellectual Merit: This project will build on prior work of the principal investigator (PI). It will address several aspects of breaking waves that are still poorly understood and are critical to the development of successful numerical schemes for predicting sediment transport in the surf zone and beach transformation. Measurement of three-component fluid velocities in a 3-D flow volume will enable thestudy the evolution of large eddies and how they are convected from the upper layer to the bottom. In conjunction with flow visualization using a high-speed digital movie camera, the measurements will shed light on the generation mechanisms of large eddies and the effect on their structure of non-uniform wave breaking along the wave crest. The volumetric fluid velocity measurements will also allow the investigator to examine the impingement of large eddies on the bottom. This process is transient and three-dimensional, characterized by large instantaneous turbulent kinetic energy and shear stresses in the impingement area.The simultaneous measurement of particle location, particle velocity, and fluid velocity over an erodible bed using a V3V system is innovative and will allow the project's investigator to address three fundamental problems in sediment transport in breaking waves. The first problem relates to the appropriate bottom boundary conditions for suspended sediment transport; specifically, how to parameterize the effect of breaking wave turbulence on the sediment pick-up rate. The second problem concerns the interaction between large eddies and suspended particles. The proposed research will answer questions such as: How closely do the instantaneous velocities of sediment particles follow those of fluid particles? Is there a direct link between suspended sediment transport and turbulence transport? Can the sediment distribution process be modeled as a diffusion process? The third problem concerns the effect of breaker types on sediment transport. The investigator will address the following questions: How do the quantities and direction of suspended load transport in the outer surf zone relate to the wave characteristics at incipient breaking? How important is this mode of transport compared to other mechanisms such as sheet-flow transport?Broader Impacts: This project will provide a high quality data set to test and improve detailed models of breaking waves and sediment transport in the surf zone. Such models will advance understanding of how breaking waves erode or deposit sediments and impact water-front property. Advances in two-phase flow measurements using V3V will also stimulate their development and application in other research fields. Researchers will be able to download the measured data from PI's research website.The project will train the next generation of researchers by engaging both undergraduate and graduate students in experimental investigation. Acquisition of the proposed V3V system will provide students with a state-of-the-art measurement apparatus to conduct experimental investigation in fluid mechanics. Two new experiments using V3V will be developed for both an undergraduate and a graduate class to enhance student learning of fluid mechanics principles. The PI will also use the equipment to conduct live demonstrations of fluid flow phenomena in workshops involving K-12 students. The outcomes of these activities will be to attract more high school students (including Native American students) to pursue a college degree in science and engineering, to provide research experiences to undergraduate students, to build a nationally competitive graduate program by supporting capable students to conduct basic research, and to maintain a modern fluid mechanics laboratory for continued research and education.