Alongshore Advective Acceleration in the Surf Zone

冲浪区的近岸平流加速

• 批准号: 1332705
• 负责人: Britt Raubenheimer
• 金额: $ 76.29万
• 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: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1332705&HistoricalAwards=false
• 关键词: Alongshore; Advective; Acceleration; Surf; Zone

Overview: This project focuses on the alongshore flow variations and advective accelerations owing to surfzone bathymetric variations. Feedbacks between alongshore flow variations and surfzone morphological changes may be critical to the evolution of surfzone morphology on beaches with alongshore uniform incident waves. Determining the magnitude of the alongshore advective accelerations and flow variability resulting from surfzone features is important to developing accurate models for coastal evolution and transport of pollution. Field evidence that the advective acceleration contributes significantly to the momentum balance also may lead to new theories and models for shoreline change.Intellectual Merit: Analytical and numerical studies suggest that alongshore advective acceleration may be important to surfzone rip currents, alongshore flow meanders, dispersion, and sediment transport and morphological evolution. Recent numerical model simulations indicate that alongshore advective acceleration can be large relative to other terms in the depth- and time-averaged surfzone momentum balance on beaches with alongshore bathymetric variations as small as ten centimeters. However, field measurements have shown that alongshore flows are predicted well with simplified equations that neglect advective accelerations. Furthermore, except near strong rip currents, field observations show relatively small alongshore variations in alongshore surfzone flows. The simplified equations may reproduce observed velocities accurately because the advective acceleration term is balanced by an alongshore pressure gradient term, or because advective acceleration is accounted for by the parameterized bottom friction coefficient. It also is possible that the observation-based estimates of alongshore flow gradients are biased low because flow maxima and minima are not resolved owing to the relatively large spatial separations between in situ sensors. Alternatively, the numerical models, which are sensitive to the friction coefficient, may overpredict the advective acceleration. Densely distributed observations of wave forcing, pressure gradients, and surfzone flows will be obtained to calibrate numerical model simulations. The field measurements will be used to estimate advective acceleration and the field-tested model will be used to explore the causes of the advective accelerations in the presence of alongshore inhomogeneous surfzone bathymetry. In particular, the observations and simulations will address the following questions: Is alongshore advective acceleration important? Are model predictions of alongshore flow gradients and advective acceleration accurate? And what causes alongshore advective acceleration? By combining field observations designed to measure flow variations at the spatial scales of small surfzone bathymetric variations with numerical model simulations, the investigators will be able to address these questions about the importance and causes of alongshore advective accelerations on beaches with near uniform incident waves.Broader Impacts: The American Shore and Beach Preservation Association (ASBPA, http://www.asbpa.org) is concerned that Americans interested in coastal engineering are not able to obtain field experience. Thus, a partnership with ASBPA and interested engineering firms will be established to provide field training to undergraduates, recent graduates, and young professionals embarking on coastal careers. In particular, two programs will be offered: 2- to 3-week-long fieldwork-focused internships for young professionals currently employed in coastal consulting and engineering firms, and 6-month-long fellowships for students interested in coastal engineering careers. More than a dozen companies already have expressed interest in the internships, and have offered to support their employees to participate in the proposed program. The student fellowships would be similar to the Swashzone Fellowships previously conducted by the lead investigator, Raubenheimer, which have led to several students receiving positions in coastal engineering firms. The interns and students will work with the investigators to obtain field observations, and to improve models for nearshore processes, which in turn will improve coastal management, help protect coastal communities, and sustain coastal resources.

概述：该项目着重于由于表面测深的变化而沿岸流量变化和对流加速度。沿岸流量变化与表面形态变化之间的反馈对于海滩上的表面形态的演变至关重要，沿沿岸均匀的入射波。确定沿岸的向前加速度和由表面特征引起的流动变异性的大小对于开发沿海进化和污染运输的准确模型很重要。对流加速度对动量平衡产生重大贡献的现场证据也可能导致海岸线变化的新理论和模型。智能优点：分析和数值研究表明，沿岸的对流加速度对于沿海的融合电流，沿海流动流，沿岸流量，分散和沉积物运输和形态学进化可能很重要。最近的数值模型模拟表明，在深度和时间平均的表面动量平衡的海滩上，沿岸沿岸的沿岸的沿岸沿岸的测深量变化相对于其他术语，相对于其他术语，沿岸的对流加速度可能很大。但是，现场测量结果表明，沿岸流可以很好地预测忽略对流加速度的简化方程。此外，除了近较强的撕裂电流外，田间观测表明，沿海表面流动中的沿岸变化相对较小。简化的方程式可以准确地重现观察到的速度，因为对流加速度项通过沿岸压力梯度项平衡，或者是因为参数化的底部摩擦系数可以解释对流加速度。由于原位传感器之间的相对较大的空间分离，因此无法解析基于沿岸流动梯度的基于观测的估计值偏差。另外，对摩擦系数敏感的数值模型可能会过高预测对流加速度。将对校准数值模拟模拟的波强，压力梯度和表面流的密集分布的观测值。现场测量将用于估计对流加速度，并将使用现场测试的模型来探索在沿海沿岸不均匀的表面测深的情况下，对流加速的原因。特别是，观察和模拟将解决以下问题：沿岸对流加速度是否重要？模型对沿岸流动梯度和对流加速度的预测是否准确？什么原因导致沿岸的对流加速度？通过将旨在测量小型表面范围测深的空间尺度上的流动变化与数值模型模拟相结合，研究人员将能够解决有关在海滩上与近乎统一的事件的重要性和原因有关的重要性和原因的问题。 http://www.asbpa.org）担心对沿海工程感兴趣的美国人无法获得现场经验。因此，将建立与ASBPA和感兴趣的工程公司建立合作伙伴关系，以向本科生，最近的毕业生和年轻专业人员提供野外培训。特别是，将提供两个计划：针对目前从事沿海咨询和工程公司雇用的年轻专业人员的2到3周的专注于实地调查的实习，以及为对沿海工程职业感兴趣的学生提供6个月的奖学金。十多家公司已经对实习表示了兴趣，并提出支持其员工参加拟议计划。学生奖学金将类似于首席调查员劳本海默（Raubenheimer）先前主持的Swashzone奖学金，这导致几名学生在沿海工程公司担任职位。实习生和学生将与调查人员合作以获得现场观察，并改善近岸流程的模型，这反过来又可以改善沿海管理，有助于保护沿海社区并维持沿海资源。