Collaborative Research: The Physical Biology of Leaves in Wind and Waves

将应用数学、数值和物理模型来揭示阔叶的形态和机械适应性，使它们能够在极端的流体环境中生存。例如，主要研究人员将确定郁金香杨叶的形状和结构如何在几乎停滞的炎热夏季增强冷却，同时减少热带风暴甚至飓风的阻力。在这个项目中开发的模型和工具也将被应用于确定在什么条件下海草的波浪运动增加了废物的清除和促进光合作用。该项目的科学成果将为选择能够在极端环境条件下生存的植物提供信息，这些极端环境条件包括低二氧化碳水平、高温或强风和海浪。这项工作的意义不仅在于深入了解自然界中植物的机械适应性。发现的物理原理可以推动柔性结构（如帆、旗和电缆）工程设计的创新。此外，本项目开发的计算工具将立即应用于其他系统，这些系统在空气和水中的柔性结构之间发生交换，包括肺部的气体交换、各种动物的气味捕获和信息素释放、肠道的营养吸收和附属物的热量损失。柔韧的植物、真菌和无根的动物被认为在强风和洪水中重新配置，以减少作用在它们身上的阻力。例如，在快速流动中，树叶卷成锥形，与类似形状和灵活性的剪纸相比，减少了颤振和阻力。在微风和水流中，树叶的扑动有利于散热和气体交换。目前尚不清楚阔叶的形状和机械结构如何导致不同的被动运动在这一范围内的流动。该项目的具体目标是确定以下机制：1)单叶在低风和气流中颤振，在强气流中卷起成减少阻力的形状；2)叶片颤振在微风和气流中增强散热和光合作用；3)一些叶子，如“不碰我”，通过电信号引发的膨胀压力变化主动重新配置。数值模拟和实验室实验的结合将使用真实和人造叶子来量化被动和主动运动以及气体和热量的浓度。本文将采用浸入边界法和无粘涡片法求解流固耦合问题。将发展一种新的浸入式边界式方法来模拟叶片作为气体或热量的源或汇。超弹性材料模型将在浸入式边界框架中开发和实施，以确定应变软化或应变硬化弹性如何影响叶片性能。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Mathematical, numerical and physical modeling will be applied to reveal the morphological and mechanical adaptations of broad leaves that allow them to survive extreme fluid environments. For example, the principal investigators will determine how the shape and structure of tulip poplar leaves enhance cooling on nearly-stagnant hot summer days while also reducing drag in tropical storm or even hurricane force winds. The models and tools developed in this project will also be applied to determine under what conditions the waving motion of seagrass augments waste removal and enhances photosynthesis. The scientific results of this project will inform the selection of plants that can survive extreme environmental conditions, including low levels of CO2, high temperatures, or strong wind and wave forces. The significance of the proposed also work extends beyond gaining insight into mechanical adaptation of plants in the natural world. The physical principals discovered could drive innovations in the engineering design of flexible structures such as sails, flags, and cables. Furthermore, the computational tools developed in this project will find immediate application in other systems where exchange occurs across flexible structures in air and water, including gas exchange in the lungs, odor capture and pheromone release in a variety of animals, nutrient uptake in the gut, and heat loss in appendages.Flexible plants, fungi, and sessile animals are thought to reconfigure in strong wind and floodwaters to reduce the drag acting upon them. In fast flows, for example, leaves roll up into cone shapes that reduce flutter and drag when compared to paper cutouts of similar shape and flexibility. In light breezes and currents, leaf flutter can be beneficial to heat dissipation and gas exchange. It is not clear how the shape and mechanical structure of broad leaves results in different passive movements across this range of flows. The specific goals of this project are to determine the mechanisms by which 1) single leaves flutter in low winds and flows and roll up into drag reducing shapes in strong flows, 2) leaf flutter enhances heat dissipation and photosynthesis in light winds and flows, and 3) some leaves, such as the touch-me-not, actively reconfigure by changes in turgor pressure initiated by electrical signaling. A combination of numerical simulations and laboratory experiments with real and artificial leaves will be used to quantify both passive and active movements as well as the concentrations of gases and heat. The fluid-structure interaction problem will be solved using the immersed boundary and inviscid vortex sheet methods. A new immersed boundary-style method for modeling the leaf as a source or sink of gases or heat will be developed. Hyperelastic material models will be developed and implemented in the immersed boundary framework to determine how strain-softening or strain-hardening elasticity affects leaf performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.