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.

智力优点：该项目的目的是发展协调一致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，即湍流对浮游植物和其他颗粒在单个有机体的空间尺度上的影响程度和机制。外部能量以湍流的形式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）和Margalef（1978）的开创性分析。Margalef的“曼陀罗”断言，高营养浓度和湍流强度有利于硅藻的优势，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，通过创新的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个细胞和链水平的湍流效应。流体应变的浓度场和细胞旋转的影响进行了预测，细胞生长和运动的影响，记录。然而，目前对湍流的理解更多地强调涡度、涡度梯度和个体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，用于数值和模拟评估细胞在粘性尺度涡中和附近经历的影响，捕获涡度的影响以及流体变形，浓度场的演变和流体-结构相互作用。涡度和涡度梯度在确定细胞运动并由此形成浓度场方面的作用一直未得到充分重视，部分原因是湍流的一个特征，即，涡的拉伸，是不可能的，在二维流动，迄今为止一直被用作理论模型和模拟装置的主要基础。数值方法将使用两个简化模型的小尺度涡的结构和演变，伯格斯涡和Lundgren拉伸螺旋涡，特别注意涡的扩散内和远离两者。衰减和平衡涡都将被探讨。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。每一个都将被连续地放置在涡流内和涡流附近的一系列位置处，并且将完全机械地耦合到流体。感兴趣的行为是细胞和链的平移，旋转和变形，以及它们对当地速度和涡度场的反馈，这些速度和涡度场可以被食草动物用来定位细胞。还将模拟标量（营养素与细胞作为汇或代谢物与细胞作为源）的扩散，允许计算营养素的获取和预测的化学领域的食草动物的扩散通量。研究人员将进一步利用他们现有的鞭毛周围的流动模型，包括能动的腰鞭毛虫的建模和测量scheme.Analog实验将利用柯尔莫哥洛夫尺度附近的流动是由粘度主导的事实，就像在早期的Couette实验，但将纳入现实，三维时间变化。借用微流体中使用的各种几何形状，研究人员将构建各种小型设备，这些设备利用脱落的涡街，温和的射流和空腔流来匹配其中的变形率，涡度和梯度，这些变形率，涡度和梯度对浮游植物产生有趣的影响。更广泛的影响：浮游植物的结果很容易扩展到其他重要的现象，例如在湍流环境中产卵的引诱剂的扩散（例如，鲍鱼和其他底栖无脊椎动物）和相应的精子游泳能力。他们有其他重要的遭遇过程，如粒子凝聚和沉淀，水溶胶过滤，和捕食者-猎物的相互作用的影响。这种新方法提供了从大尺度湍流直接数值模拟（DNS）模型到这些湍流的个体尺度效应的自然桥梁，以及在大尺度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气候变化影响的参数之一，研究人员将与海洋科学教育卓越海洋系统中心（COSEE-OS）密切合作，该中心选择气候变化下的海洋作为其主要关注点。他们还将在为研究生、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的历史基础上再接再厉。他们将以专业制作的、令人回味的视觉动画来补充这两项努力，动画将展示他们确定纳入COSEE-OS网站的重要现象。