The Turbulence Responsible for Horizontal Surfzone Dispersion

造成水平表面区扩散的湍流

• 批准号: 1357060
• 负责人: Matthew Spydell
• 金额: $ 23.01万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-03-15 至 2018-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1357060&HistoricalAwards=false
• 关键词: Turbulence; Responsible; Horizontal; Surfzone; Dispersion

Improved understanding of the surfzone (within a few 100 m of the shoreline) horizontal turbulence that causes material dispersion is the goal of this project. Poor water quality at many beaches poses health risks to beach goers and negatively impacts local economies. Recent research has indicated that surfzone horizontal eddies, which have length scales greater than the water depth, mix and disperse surfzone tracers such as pollution. Although dispersion by surfzone eddies is critical to the dilution, as well as the cross-shore exchange of material (including larvae), how to parameterize the surfzone eddy diffusivity in computer models is unknown. Exactly how the Eulerian properties of the turbulence (the eddy velocity, and the eddy space and time scales) are related to surfzone Lagrangian statistics (i.e. the dispersion and eddy diffusivity) is unknown. Also not completely understood is how the surfzone Eulerian eddy properties are related to the incident wave field. By analyzing existing observations and performing model experiments, the link between Eulerian eddy properties and dispersion will be illuminated.Intellectual Merit:The first objective of this study is to examine surfzone horizontal eddy properties in existing observations. As dispersion depends critically on the velocity c, eddy length L, and eddy time scales T, and in particular the parameter alpha = cT/L, surfzone values will be determined from space- and time-lagged velocity autocorrelation functions. First, they will be calculated for SandyDuck observations (Huntington Beach 2006 and Imperial Beach 2009 will also be considered to the extent possible) and observed surfzone eddy fields will then be characterized. Small values of alpha indicate that the eddy field changes very quickly in time and results in qualitatively different dispersion than if the eddies are long lived (large alpha). How the observed eddy properties depend on the incident wave field will be investigated and whether alongshore currents change the nature of the eddy field determined. Also, the dependence of surfzone eddies on cross-shore position will also be calculated. In particular, as surfzone eddies are only generated within the surfzone, whether or not the surfzone eddy field is different within and seaward of the surfzone will be examined.The second objective is to perform the same type of analysis done for the observations on wave resolving and wave averaged numerical simulations of observed (e.g. SandyDuck) conditions. Do the models reproduce the observed eddy velocities, length and time scales even though wave averaged and wave resolving velocity frequency-wavenumber spectra can differ significantly? This is an important consideration as dispersion depends on the bulk properties of the frequency-wavenumber spectra rather than its detailed shape. Model simulations will also allow the calculation of very reliable Lagrangian statistics as virtual drifters will be added to the model. Eulerian and Lagrangian eddy statistics will then be compared and the relevance of an existing theory which relates Eulerian to Lagrangian statistics, developed for isotropic homogeneous turbulence, for the surfzone will be determined. If this theory is applicable, the surfzone eddy diffusivity can then be inferred without explicit Lagrangian statistics as long as the Eulerian eddy statistics are known.Broader Impacts:At United States beaches in 2008, 7% of beach water samples exceed national health standards and there were over 20,000 closure and advisory days. Pollution from urban runoff often drains directly onto beaches and poses significant health risks to swimmers. Management decisions could benefit from better understanding of surfzone turbulence and dispersion. As part of educational outreach efforts, the PI will collaborate with I Love A Clean San Diego (ILACSD), a nonprofit environmental group, and assist them with the development of their teaching materials and education program. Additionally, the PI will provide guest presentations at selected ILACSD programs. Partnering with ILACSD is going to have a large impact as they have provided environmental education to 30,000 high school students (45% Title 1 or underserved) in total and they work closely with resource managers throughout San Diego.

该项目的目的是对导致材料分散的水平湍流（在海岸线的几100 m之内）的水平湍流的提高理解是该项目的目标。许多海滩的水质较差会给海滩游客带来健康风险，并对当地经济产生负面影响。最近的研究表明，长度尺度大于水深，混合和分散表面示踪剂（例如污染）的表面水平涡流。尽管表面涡流的分散对于稀释以及材料的跨季度交换至关重要（包括幼虫），但是如何在计算机模型中参数化表面涡流扩散率是未知的。确切地说，湍流的欧拉（Eulerian）特性（涡流速度和涡流时期和时间尺度）与表面lagrangian统计数据（即分散和涡流扩散率）有关。尚不完全理解的是表面欧拉涡流与入射波场如何相关。通过分析现有的观察和执行模型实验，将阐明欧拉涡流和分散性之间的联系。IntlectualFurecit：这项研究的第一个目的是检查现有观测值中的表面水平涡流。由于色散严重取决于速度C，涡流长度L和涡流时间尺度T，尤其是参数alpha = CT/L，因此将根据空间和时置的速度自相关功能确定表面值。首先，将对Sandyduck的观察进行计算（2006年的亨廷顿海滩和2009年帝国海滩2009年也将被考虑），然后将观察到的Surfzone涡流田将被描述。小α值表明，涡流的时间很快变化，并且与长期存在的涡流（大α）相比，质量不同。观察到的涡流如何取决于入射波场以及沿岸电流是否改变确定的涡场的性质。同样，还将计算表面涡流对跨近岸位置的依赖性。特别是，由于表面涡流仅在表面上产生，因此将检查表面涡流场是否不同，并且将检查表面的海中。第二个目标是对在波浪分辨率和波浪平均和波浪平均数字模拟（例如，（例如，砂类）条件上进行的观察结果进行相同类型的分析。即使波浪平均和波浪解析速度频率波频谱也可以显着差异，这些模型即使波浪平均和波浪解析速度频率也可以重现所观察到的涡流速度，长度和时间尺度？这是一个重要的考虑因素，因为色散取决于频率波光谱的批量特性，而不是其详细的形状。模型模拟还将允许计算非常可靠的拉格朗日统计信息，因为虚拟漂流者将添加到模型中。然后将比较Eulerian和Lagrangian Eddy统计数据，并将欧拉元素与用于各向同性均质湍流开发的现有理论的相关性，以确定Surfzone。如果适用该理论，只要知道欧拉涡流的统计数据，就可以推断出表面涡流扩散率，而无需明确的拉格朗日统计数据。Broader的影响：2008年的美国海滩，在2008年的美国海滩上，海滩水样品中有7％超过国家卫生标准，并且有20,000多个关闭和顾问的日子。城市径流的污染通常会直接流向海滩，并给游泳者带来重大健康风险。管理决策可以从更好地理解表面动荡和分散体中受益。作为教育外展工作的一部分，PI将与非营利性环境团体的“我爱圣地亚哥”（ILACSD）合作，并协助他们制定其教学材料和教育计划。此外，PI将在选定的ILACSD计划中提供来宾演讲。与ILACSD合作将产生很大的影响，因为他们为30,000名高中学生（45％的标题1或服务不足）提供了环境教育，他们与整个圣地亚哥的资源经理紧密合作。