CMG Collaborative Research: Interactions of Phytoplankton with Dissipative Vortices

智力价值：该项目的目的是发展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，即在单个生物的空间尺度上湍流对浮游植物和其他颗粒的影响的大小和机制。湍流形式的外部能量在决定不同种类浮游植物的相对成功方面的重要性可以追溯到Munk和Riley（1952）和Margalef（1978）的种子分析。Margalef的“曼陀罗”断言，高营养浓度和湍流强度有利于硅藻的主导地位，而低值则有利于非赤潮鞭毛藻。随后的工作揭示了涡旋对鞭毛藻物种的广泛影响，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细胞和链水平上的湍流效应。预测了流体张力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多地侧重于单个浮游植物细胞所经历的涡度、涡度梯度和耗散尺度上的涡。我们建议开发一个框架，用于数值和模拟评估细胞在粘尺度涡旋内和附近所经历的影响，以捕获涡度、流体变形、浓度场的演变和流体-结构相互作用的影响。涡度和涡度梯度在决定细胞运动从而形成浓度场中的作用一直没有得到充分的认识，部分原因是湍流的一个特征，即涡拉伸，在二维流动中是不可能的，而迄今为止，二维流动已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的小尺度涡旋结构和演化模型，Burgers涡旋和Lundgren拉伸螺旋涡旋，特别关注涡旋在两者内部和外部的扩散。将探讨衰减和平衡涡旋。单元格和单元链的模型将基于实际单元格和单元链的形状和弯曲刚度。每一个都将被依次放置在漩涡内部和附近的一系列位置上，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量场的反馈，这些可以被食草动物用来定位细胞。同样要建模的是标量的扩散（以细胞为汇的营养物质或以细胞为源的代谢物），从而可以计算用于养分获取的扩散通量，并预测食草动物使用的化学场。研究人员将进一步利用他们现有的鞭毛周围流动模型，在建模和测量方案中包括运动鞭毛。模拟实验将利用这样一个事实，即接近柯尔莫哥罗夫尺度的流动是由粘度主导的，就像在早期的库埃特实验中一样，但将纳入现实的三维时间变化。从微流体中使用的各种新兴几何形状中，研究人员将构建各种小型设备，利用流道涡街，温和射流和空腔流来匹配它们的变形率，涡度和梯度，在他们的涡数值模型中对浮游植物产生有趣的影响。这些类似物将被用来测试模型的预测，并提出模型的新问题。更广泛的影响：对浮游植物的研究结果很容易扩展到其他重要现象，如在湍流环境中产卵的卵（如鲍鱼和其他底栖无脊椎动物）的引诱剂扩散和相应的精子游泳能力。它们对其他重要的相遇过程也有影响，如粒子凝固和沉淀、纯溶胶过滤和捕食者-猎物相互作用。这种新方法提供了从更大规模的直接数值模拟（DNS）湍流模型到这些个体尺度湍流效应的天然桥梁，以及在更大规模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（cosees - os）密切合作，该中心选择了气候变化下的海洋作为其主要关注点。他们还将建立在他们为研究生、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。他们将用专业制作的、令人回味的视觉动画来补充这些努力，这些动画是他们确定的重要现象，并将其纳入COSEE-OS网站。

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.