CMG Collaborative Research: Interactions of Phytoplankton with Dissipative Vortices

CMG 合作研究：浮游植物与耗散涡旋的相互作用

• 批准号: 0724598
• 负责人: Lisa Fauci
• 金额: $ 47.14万
• 依托单位: Tulane University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0724598&HistoricalAwards=false
• 关键词: CMG; Collaborative; Research; Interactions; Phytoplankton

Intellectual merit: The aim of this project is to develop coordinated laboratory experiments and computational models to address a fundamental question in oceanography concerning magnitudes and mechanisms of turbulence effects on phytoplankton and other particles at the spatial scale of individual organisms. The importance of external energy in the form of turbulence in determining relative success of different kinds of phytoplankton dates to the seminal analysis of Munk and Riley (1952) and Margalef (1978). Margalef's "mandala" asserts that high nutrient concentrations and turbulence intensities favor dominance by diatoms, whereas low values favor non-red-tide dinoflagellates. Subsequent work has revealed a wide spectrum of turbulence effects among species of dinoflagellates, including growth stimulation. The physicochemical mechanisms that govern these effects largely remain to be determined, however.Through iteration between innovative numerical models and experiments, the investigators will close a growing gap between textbook understanding of turbulent flows and understanding of consequences for suspended organisms and particles. Models and experiments have used one-dimensional shear to assess turbulence effects at the level of single cells and chains. Effects of fluid straining on concentration fields and cell rotation have been predicted, and effects on cell growth and motion, documented. Current understanding of turbulence, however, places greater emphasis on vorticity, gradients in vorticity and vortices at dissipation scales experienced by individual phytoplankton cells. We propose to develop a framework for both numerical and analog evaluation of effects that cells experience from being in and near viscous-scale vortices, that capture effects of vorticity as well as fluid deformation, evolution of concentration fields, and fluid-structure interactions. Roles of vorticity and gradients in vorticity in determining cell motions and thereby shaping concentration fields have been underappreciated, partly because a signature feature of turbulence, i.e., vortex stretching, is impossible in the two-dimensional flows that so far have been used as theoretical models and the primary basis of analog devices.Numerical approaches will use two simplified models of small-scale vortex structure and evolution, the Burgers vortex and the Lundgren stretched-spiral vortex, giving particular attention to diffusion of vorticity within and away from both. Both decaying and equilibrium vortices will be explored. Models of cells and chains of cells will be based on shapes and flexural stiffnesses of actual cells and chains. Each will be placed successively at a range of positions within and near a vortex and will be fully coupled mechanically to the fluid. Behaviors of interest are cell and chain translation, rotation and deformation and their feedbacks to local velocity and vorticity fields that could be used by grazers to locate a cell. Also to be modeled is the diffusion of scalars (nutrients with cell as sink or metabolites with cell as source), allowing calculation of diffusive fluxes for nutrient acquisition and prediction of chemical fields used by grazers. The investigators will further take advantage of their existing models of flow around flagella to include motile dinoflagellates in the modeling and measurement scheme.Analog experiments will exploit the fact that flows near Kolmogorov scale are dominated by viscosity, just as in earlier Couette experiments, but will incorporate realistic, 3D time variation. Borrowing from a burgeoning variety of geometries used in microfluidics, the investigators will construct a variety of small devices that utilize shed vortex streets, mild jets and cavity flows to match deformation rates, vorticities and gradients in them that produce interesting effects on phytoplankton in their numerical models of vortices. These analogs will be used to test the model predictions and to pose new questions of the models.Broader impacts: Results for phytoplankton extend easily to other important phenomena such as diffusion of attractants from eggs spawned in a turbulent environment (e.g., by abalone and other benthic invertebrates) and corresponding sperm swimming capabilities. They have implications for other important encounter processes such as particle coagulation and sedimentation, hydrosol filtration, and predator-prey interactions. This new approach provides both a natural bridge from larger-scale, direct numerical simulation (DNS) models of turbulence to these individual-scale effects of turbulence and a logical path to parameterizing these effects in larger-scale fluid dynamic models.Turbulence intensity is one of the parameters most likely to be influenced by climate change, and the investigators will work closely with the Center for Ocean Sciences Education Excellence Ocean Systems (COSEE-OS) that has chosen oceans under climate change as its major focus. They will also build on their history of providing teaching and outreach materials in biomechanics at low Reynolds numbers for graduate students, undergraduates and high-school teachers. They will complement both of these efforts with professionally produced, evocative visual animations of the important phenomena that they identify for incorporation into the COSEE-OS website.

智力价值：该项目的目的是开发协调的实验室实验和计算模型，以解决海洋学中的一个基本问题，即在个体生物体的空间尺度上湍流对浮游植物和其他颗粒影响的幅度和机制。湍流形式的外部能量在决定不同种类浮游植物相对成功方面的重要性可以追溯到 Munk 和 Riley (1952) 以及 Margalef (1978) 的开创性分析。马加莱夫的“曼陀罗”断言，高营养浓度和湍流强度有利于硅藻占主导地位，而低值有利于非赤潮甲藻。随后的工作揭示了甲藻物种之间广泛的湍流效应，包括生长刺激。然而，控制这些效应的物理化学机制在很大程度上仍有待确定。通过创新数值模型和实验之间的迭代，研究人员将缩小教科书对湍流的理解与对悬浮生物和颗粒后果的理解之间日益扩大的差距。模型和实验使用一维剪切来评估单细胞和链水平的湍流效应。已经预测了流体过滤对浓度场和细胞旋转的影响，并记录了对细胞生长和运动的影响。然而，目前对湍流的理解更加强调涡度、涡度梯度以及单个浮游植物细胞所经历的耗散尺度的涡度。我们建议开发一个框架，用于对细胞在粘性尺度涡流中和附近所经历的影响进行数值和模拟评估，捕获涡量以及流体变形、浓度场演化和流体-结构相互作用的影响。涡度和涡度梯度在确定细胞运动并从而塑造浓度场方面的作用一直被低估，部分原因是湍流的标志特征，即涡旋拉伸，在迄今为止已用作理论模型和模拟设备的主要基础的二维流中是不可能的。数值方法将使用小规模涡旋结构和演化的两个简化模型， 伯格斯涡旋和龙格尔拉伸螺旋涡旋，特别注意涡量在两者内部和远离两者的扩散。将探索衰减涡流和平衡涡流。单元和单元链的模型将基于实际单元和链的形状和弯曲刚度。每个将被连续放置在涡流内和涡流附近的一系列位置，并将与流体完全机械耦合。感兴趣的行为是细胞和链的平移、旋转和变形以及它们对局部速度和涡度场的反馈，这些反馈可以被食草动物用来定位细胞。还需要模拟标量的扩散（以细胞为库的营养物或以细胞为源的代谢物），从而可以计算营养物获取的扩散通量并预测食草动物使用的化学场。研究人员将进一步利用现有的鞭毛周围流动模型，将活动的甲藻纳入建模和测量方案中。模拟实验将利用这一事实，即柯尔莫哥洛夫尺度附近的流动主要由粘度决定，就像早期的库埃特实验一样，但将结合现实的 3D 时间变化。借鉴微流体中使用的各种新兴几何形状，研究人员将构建各种小型装置，利用棚涡街、温和射流和空腔流来匹配其中的变形率、涡度和梯度，从而在涡流数值模型中对浮游植物产生有趣的影响。这些类似物将用于测试模型预测并提出模型的新问题。更广泛的影响：浮游植物的结果很容易扩展到其他重要现象，例如在湍流环境中（例如鲍鱼和其他底栖无脊椎动物）产卵的引诱剂的扩散以及相应的精子游泳能力。它们对其他重要的遭遇过程有影响，例如颗粒凝结和沉降、水溶胶过滤以及捕食者与猎物的相互作用。这种新方法既提供了从更大规模的直接数值模拟（DNS）湍流模型到这些单独尺度的湍流效应的天然桥梁，也提供了在更大规模的流体动力学模型中参数化这些效应的逻辑路径。湍流强度是最有可能受到气候变化影响的参数之一，研究人员将与海洋科学卓越教育中心海洋系统中心（COSEE-OS）密切合作，该中心已 选择气候变化下的海洋作为其主要关注点。他们还将继续为研究生、本科生和高中教师提供低雷诺数生物力学教学和推广材料。他们将通过专业制作的、令人回味的视觉动画来补充这两项工作，这些动画是他们确定要纳入 COSEE-OS 网站的重要现象。