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Transport of Non-Spherical Particles in Wavy Flows

波流中非球形颗粒的输运

基本信息

批准号：
1706586
负责人：
Jeffrey Koseff
金额：
$ 34.35万
依托单位：
Stanford University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-09-01 至 2021-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1706586&HistoricalAwards=false
关键词：
Transport Non Spherical Particles Wavy

项目摘要

Plastic debris is a growing environmental concern for the world's oceans; several million metric tons of plastic enter the oceans each year. Much of the plastic debris is present as small, irregular particles five millimeters or less in length, called "microplastics," that pose a threat to marine organisms, the environment, and human health. This research project involves extending state-of-the-art research about particle-laden flows to situations relevant to the microplastics problem. Irregular particles are being studied in wavy flows to understand how to control the transport and sorting of these microparticles in the ocean and in near-shore environments. Both laboratory experiments and modeling are being performed and tools for predicting the motion of microplastics in the ocean and the length of time particles spend near the shore are being developed. The research team is working with earth scientists, biologists, and policy makers to integrate the resulting knowledge into conservation efforts. The investigators also are closely engaged in mentoring graduate students, teaching undergraduates about the transport of marine microplastics, and creating outreach activities for high school and middle school students. This research project is identifying and classifying the mechanisms that control transport and tumbling of anisotropic particles in wavy environments and quantifying the dispersion rate and sorting of these particles based on size and shape in waves. While particle-laden flows are well studied in certain limits, the complexities of particle-laden flows involving large, anisotropic particles in surface gravity waves is complicated by the wide range of length and time scales involved. In particular, direct numerical simulations become computationally expensive, and as a result, experiments are a crucial tool. The investigators have advanced facilities for generating and quantifying wavy flows and are performing experiments and empirical modeling to characterize particle transport in these flows. The experiments will allow the researchers to address how anisotropic particles, like microplastics with their additional degrees of freedom for rotational motion relative to spherical particles, may lead to complex dynamics when coupled with waves, turbulence, and the stratification found in the ocean. A better understanding of these interactions will provide guidance regarding assumptions going into simplified models. The governing nondimensional parameters (the density ratio, wave Froude number, and Stokes number) are being varied over ranges relevant to those in the ocean. Pointwise flow characteristics and turbulence are being measured using laser Doppler anemometry; waves are being characterized via wave gauges; and the mean transport due to Stokes drift is being measured via particle tracking. Anisotropic particles, including rods, disks, and ellipsoids, are being created via 3D printing, and the dispersion of these particles is being measured by releasing a cloud of particles and then measuring the phase-averaged shape of the cloud over time and space. The results are expected to enhance our understanding of the fundamental physics governing the transport of non-spherical particles in waves and to inform the empirical modeling of microplastics in the ocean.

塑料碎片是世界海洋日益严重的环境问题;每年有数百万公吨塑料进入海洋。大部分塑料碎片都是长度小于或等于5毫米的不规则小颗粒，称为“微塑料”，对海洋生物、环境和人类健康构成威胁。该研究项目涉及将有关颗粒流动的最新研究扩展到与微塑料问题相关的情况。研究人员正在研究波浪流中的不规则颗粒，以了解如何控制这些微粒在海洋和近岸环境中的运输和分选。正在进行实验室实验和建模，并正在开发用于预测微塑料在海洋中的运动以及颗粒在海岸附近停留时间的工具。该研究小组正在与地球科学家，生物学家和政策制定者合作，将由此产生的知识整合到保护工作中。研究人员还密切参与指导研究生，向本科生讲授海洋微塑料的运输，并为高中和中学生开展外展活动。本研究项目是识别和分类控制波浪环境中各向异性颗粒的运输和翻滚的机制，并根据波浪中的尺寸和形状量化这些颗粒的分散率和分选。虽然在一定的限制下，颗粒负载的流动得到了很好的研究，但表面重力波中涉及大的各向异性颗粒的颗粒负载的流动的复杂性由于所涉及的长度和时间尺度的宽范围而变得复杂。特别是，直接数值模拟变得计算昂贵，因此，实验是一个至关重要的工具。研究人员拥有先进的设备，用于生成和量化波浪流，并正在进行实验和经验建模，以表征这些流中的颗粒传输。这些实验将使研究人员能够解决各向异性颗粒（如微塑料）相对于球形颗粒具有额外的旋转运动自由度，当与波浪，湍流和海洋中发现的分层相结合时，可能会导致复杂的动力学。更好地理解这些相互作用将为简化模型的假设提供指导。控制无量纲参数（密度比，波弗劳德数和斯托克斯数）在海洋中的相关范围内变化。使用激光多普勒风速计测量逐点流动特性和湍流;通过测波仪确定波浪的特征;通过粒子跟踪测量斯托克斯漂移引起的平均迁移。各向异性颗粒，包括棒，盘和椭球体，正在通过3D打印创建，这些颗粒的分散通过释放颗粒云，然后测量云随时间和空间的相位平均形状来测量。这些结果有望增强我们对波浪中非球形颗粒传输的基本物理学的理解，并为海洋中微塑料的经验建模提供信息。