First Steps: The Dynamics and Control of Underwater Walking

动物对陆地的殖民是生命历史上最伟大的进化事件之一，但我们对这一事件的物理原理的理解是有限的。早在动物在陆地上行走之前，动物在水下行走的第一步就是在水面下进行的。这种行为形成了最终在陆地上运动的基础，但物理学显示出流体作用力(阻力、浮力)和典型步行作用力(脚底相互作用、重力)的复杂组合。对这一行为的理解受到无法有效测量施加在衬底上的力的限制。该项目将创建一个定制设计的力传感系统来记录水下行走过程中发生的微小基体力，并结合对阻力、浮力和其他流体力的测量，将提供这一行为机理的第一个完整图景。这将为行走的进化以及动物如何适应最终过渡到陆地提供重要的见解。除了为研究生提供有价值的培训外，该项目还将为科学界提供一个研究水下作用力的新工具，并为以生物为灵感的水下探险车的设计提供见解。有效的运动对最初的陆地入侵至关重要，而水下行走是在这一过渡期间扩展到陆地使用的关键行为前身。然而，水下行走的生物力学和控制知之甚少，部分原因是很难测量微小的底物反作用力。流体和底物力的组合可能会使典型的行走动力学变得难以维持，特别是由于浮力支撑和周围流体的减震效应(特别是阻力和附加质量效应)而导致的有效体重减少。该项目将研究水下行走的动力学和控制，通过使用一种新型的水下力传感系统直接测量底物反作用力，并结合流体力的测量，跨越不同的底物和环境条件。这将提供关于这些力量如何相互作用、动物如何控制这些相互作用以产生受控运动的见解，以及环境变化如何影响这些动力学，以及水下行走如何适应陆地环境。对这些动力学的有效理解可以提供对水下行走在现存物种中的使用、古代从水下行走到陆地行走的生物力学的洞察，以及对用于探索的水下行走机器人系统的控制的洞察。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。

The colonization of land by animals is one of the greatest evolutionary events in the history of life, but our understanding of the physics of this occurrence is limited. Long before animals walked on land, the first steps were taken beneath the water's surface by animals walking on submerged substrates. This behavior formed the basis for eventual movement on land, but the physics display a complex mix of fluid forces (drag, buoyancy) and typical walking forces (foot-substrate interactions, gravity). Understanding of this behavior is limited by the inability to effectively measure the forces exerted on the substrate. This project will create a custom-designed force sensing system to record the small substrate forces that occur during underwater walking, and, combined with measurements of drag, buoyancy, and other fluid forces, will provide the first complete picture of the mechanics of this behavior. This will provide crucial insights into the evolution of walking and how animals adapted to the eventual transition onto land. In addition to providing valuable training for graduate students, this project will provide the scientific community with a new tool for investigating underwater forces and provide insights for the design of biologically-inspired underwater exploration vehicles.Effective locomotion was crucial to the initial invasion of land, and underwater walking was the key behavioral predecessor that was exapted into terrestrial use during this transition. However, the biomechanics and control of underwater walking are poorly known, in part due to the difficulty of measuring small substrate reaction forces. The combination of both fluid and substrate forces could make typical walking dynamics untenable, particularly the reduced effective body weight due to buoyant support, and damping effects from the surrounding fluid (particularly drag and the added mass effect). This project will investigate the dynamics and control of underwater walking via direct measurement of substrate reaction forces using a novel underwater force sensing system, combined with measurements of fluid forces, across variable substrates and environmental conditions. This will provide insights into how these forces interact and how animals control these interactions to produce controlled locomotion, as well as how changes in environment could affect these dynamics and how underwater walking could be exapted to a terrestrial setting. Effective understanding of these dynamics could provide insight into the use of underwater walking in extant species, the biomechanics of the ancient transitions from underwater to terrestrial walking, and insight into the control of underwater walking robotic systems for exploration.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.