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宽叶的形态和机械适应能力，使它们能够在极端流动的环境中生存。例如，主要研究人员将确定郁金香杨树叶子的形状和结构如何在几乎停滞不前的炎热夏日加强降温，同时还可以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还将用于确定在什么条件下海草的挥动运动可以增加废物的清除和增强光合作用。该项目的科学结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水平的二氧化碳、高温或强风和海浪。拟议工作的意义还超出了洞察植物在自然界中的机械适应。所发现的物理原理可以推动帆、旗帜和电缆等柔性结构的工程设计创新。此外，该项目开发的计算工具将立即应用于其他在空气和水中通过柔性结构进行交换的系统，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件的热损失。灵活的植物、真菌和固着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，与形状和灵活性相似的剪纸相比，这种形状减少了颤振和阻力。在微风和水流中，树叶的颤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在这一流动范围内的不同被动运动。这个项目的具体目标是确定单叶在低风和气流中颤动并在强风和气流中卷曲成减阻形状的机制，2)叶片颤动在微风和气流中增强热量散失和光合作用，以及3)一些叶片，如Touch-me-Not，通过电子信号引发的膨胀压力的变化来主动重新配置。使用真实和人造树叶的数值模拟和实验室实验相结合的方法，将被用来量化被动和主动运动以及气体和热量的浓度。流固耦合问题将采用浸没边界和无粘涡片法进行求解。将开发一种新的浸没边界风格的方法，将树叶模拟为气体或热量的源或汇。将在浸没边界框架中开发和实施超弹性材料模型，以确定应变软化或应变硬化弹性如何影响树叶性能。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.