CAREER: Liminal locomotion: life at the air-water-land interface

该奖项全部或部分由2021年美国救援法案（公法117-2）资助。大多数动物都是运动专家：游泳、行走或飞行。但有一些物种具有不同寻常的能力，可以在所有这些模式下移动。要做到这一点，多模式动物必须克服在水、陆地和空气等不同物理条件下产生推力的重大功能挑战。动物是如何做出这种非凡行为的尚不清楚。本项目使用生物力学方法研究三联栖淡水昆虫——会游泳、行走和飞行的水虫、背泳者和潜水甲虫。为了将四肢和身体的超快运动以3D方式可视化，一种可以在实验室或室外使用的尖端高速视频系统正在开发中。在游泳和水下行走时，这些肢体运动带动水：通过精确跟踪水是如何运动的，研究者将计算推力并获得对这些行为的机械理解。比较三个物种可以研究不同的行为途径，以及允许它们进化的身体形状。这项研究为运动多功能性的生物学和发明生物启发的多模态机器所需的功能原理提供了见解。研究生将接受尖端技术和科学传播与推广方面的培训，帮助他们从研究生涯的开始就将公共服务融入他们的工作中。为了将推广付诸实践，研究生将与当地两个自然中心合作，与社区成员分享针对不同人口统计数据的项目的见解。为了了解一些淡水昆虫是如何实现三模运动的，高速摄像和基于激光的流速测量将结合起来，建立一个完整的、三维的运动学和流体动力学图像(1)在空中和水下行走，(2)游泳，(3)从游泳到飞行的过渡。在中间雷诺数下运行并在介质之间移动，研究物种为研究过渡流体动力学提供了机会，例如，在基于拖动的划桨的缩放中，这是一种基本且广泛的运动机制。这是第一个测量目标物种游泳产生的高分辨率流场的研究，第一个测量任何节肢动物水下行走的3D速度场，第一个量化昆虫飞行与水起飞的研究。对于从水中起飞到飞行，初步数据表明，这种行为是由表面张力和空气动力共同驱动的。这项工作将通过开发一种方法来揭示自由水面运动的一般生物力学原理，该方法允许同时对水下速度场和水上运动进行高分辨率的时间和空间测量。除了研究生培训的重要影响之外，该项目还为工程研究生创建了一个新的学习社区，这将支持公共宣传工作，不仅是为了这个项目，而且还为许多其他项目，跨越机械工程学科的广度。这些努力将作为一项关于研究生如何发展成为整体学者的教育研究的一部分进行评估。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。

This award is funded in whole or in part under the American Rescue Act of 2021 (Public Law 117-2). Most animals are movement specialists: swimmers, walkers, or flyers. But a few species have the unusual ability to move in all of these modes. To be this versatile, a multimodal animal must overcome the significant functional challenge of generating thrust in the divergent physical conditions of water, land, and air. Understanding how animals do this remarkable behavior remains unclear. This project studies trimodal freshwater insects — water boatmen, backswimmers, and diving beetles that swim, walk, and fly — using a biomechanical approach. To visualize the ultrafast motion of their limbs and bodies in 3D, a cutting-edge high-speed video system that can be used in the lab or outside is being developed. During swimming and underwater walking, those limb motions move the water: by tracking precisely how the water moves, the investigator will calculate thrust and gain a mechanical understanding of the behaviors. Comparing three species allows investigation of the different pathways by which the behaviors, and the body shapes that allow them, may have evolved. This research offers insights into the biology of movement versatility and the functional principles needed to invent bioinspired multimodal machines. Graduate students will be trained both in the cutting-edge techniques and in science communication and outreach, helping them integrate public service into their work from the beginning of their research careers. To put outreach into practice, graduate students will partner with two local nature centers to share insights with community members with projects designed to reach different demographics. To understand how some freshwater insects manage to achieve trimodal locomotion, high-speed videography and laser-based flow velocimetry will be combined to build a complete, three-dimensional picture of the kinematics and fluid dynamics of (1) walking in air and underwater, (2) swimming, and (3) the swimming-to-flying transition. Operating at intermediate Reynolds numbers and moving between mediums, the study species offer opportunities to study transitional fluid dynamics, for example, in the scaling of drag-based paddling, a fundamental and widespread locomotor mechanism. This is the first study to measure high-resolution flow fields generated by the swimming of the target species, the first to measure 3D velocity fields of underwater walking in any arthropod, and the first to quantify water takeoff in conjunction with flight in insects. For the takeoff from water to flight, preliminary data suggest that the behavior is driven by both surface tension and aerodynamic forces. This work will shed new light on the general biomechanical principles of free surface locomotion by developing a methodology that permits simultaneous high-resolution temporal and spatial measurement of underwater velocity fields and above-water kinematics. In addition to the important broader impact of graduate student training, this project creates a new learning community for engineering graduate students that will support public outreach efforts, not only for this project, but also for many others, spanning the breadth of the mechanical engineering discipline. These efforts will be assessed as part of an educational study on how graduate students develop into holistic scholars.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.