ERI: Free surface and flexibility effects in partially-submerged bioinspired propulsion

生物在水面上的运动通常有专门的策略。它们的运动解决了独特的限制，包括表面波、飞溅和减少空气中的力量产生，空气中的密度比水低一千倍。这些行为为水下机器人提供了独特的设计机会，应用包括水对空起飞、机动和近水面站位保持。尽管这些生物例子很普遍，但需要新的信息来了解生物启发的扑翼推进在部分水下时是如何表现的。这项工作的重点是了解水面对部分潜水推进性能的影响。除了水下机器人，这项工作还有助于解释近水面运动和水上跳跃的生物力学。这个项目将训练一支由本科生组成的跨学科团队来实践研究问题的解决。该项目还将支持为人类学和设计学本科生举办的生物灵感设计研讨会，以及为南加州女高中生举办的工程研讨会。这项工作通过实验研究了自由表面和推进器灵活性在部分淹没的生物灵感拍打过程中的作用和相互作用。具体目标是确定：(1)推进性能如何随拍打运动产生的表面扰动的大小和速度而变化。(2)自由表面在部分淹没扑动过程中的变形情况，包括柔度对表面行为的影响。(3)三维空间，包括有限宽度、跨向弯曲和表面扰动，如何影响部分潜水推进性能。综合起来，这些目标提供了对自由表面在部分潜水推进中的作用的新的理解。目标将通过测试同时拍打和垂直出水的柔性板来实现。关键变量包括拍打频率和振幅、垂直速度、平板刚度和纵横比。多轴力和扭矩测量将有助于比较推力和效率。除了基于扑动运动学的参数化之外，性能趋势还将基于表面扰动的大小和速度进行缩放。为了解释性能趋势，高速成像将可视化自由表面动力学(包括气泡和波浪的形成、飞溅和扰动的程度)，并将使用粒子图像测速仪来比较尾迹。对于不同纵横比性能不同的情况，将利用推进器形状的3D成像来解释这些观察结果。此外，该项目将有助于使用开放获取的工具进行体积流动成像，材料通过开源项目公开传播。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。

Organisms often have specialized strategies for movement at the water’s surface. Their locomotion addresses unique constraints including surface waves, splashing, and reduced force production in air, which is a thousand-fold lower density than water. These behaviors present unique design opportunities for underwater vehicles, with applications including water-to-air take-off, maneuvering, and near-surface station-holding. Despite the prevalence of these biological examples, new information is needed about how bioinspired flapping propulsion performs while partially submerged. This work focuses on understanding the influence of the water’s surface on partially submerged propulsive performance. Beyond underwater vehicles, this work also helps explain the biomechanics of near-surface locomotion and aquatic jumping. This project will train an interdisciplinary team of undergraduate students in hands-on research problem solving. The project will also support a bioinspired design workshop for undergraduate anthropology and design students and an engineering workshop for women high school students in Southern California.This work experimentally investigates the roles of and interactions between the free surface and propulsor flexibility during partially submerged bioinspired flapping. Specific objectives are to determine: (1) How propulsive performance scales with the size and speed of the surface disturbance created by the flapping motion. (2) How the free surface deforms during partially submerged flapping motions, including the effects of flexibility on the surface behaviors observed. (3) How three-dimensionality, including finite widths, spanwise bending, and surface disturbances, affects partially submerged propulsive performance. Combined, these objectives provide new understanding about the role of the free surface in partially submerged propulsion. Objectives will be addressed by testing flexible plates that are simultaneously flapping and traveling vertically out of the water. Key variables include flapping frequency and amplitude, vertical velocity, plate stiffness, and aspect ratio. Multi-axis force and torque measurements will facilitate comparisons of thrust and efficiency. Performance trends will be scaled based on the size and speed of the surface disturbance, in addition to parameterizations based on the flapping kinematics. To explain performance trends, high-speed imaging will visualize the free surface dynamics (including air cavity and wave formation, splashing, and the extents of the disturbance) and particle image velocimetry will be used to compare wakes. For cases where performance differs between aspect ratios, 3D imaging of the propulsor shape will be leveraged to explain these observations. Additionally, the project will contribute to open-access tools for volumetric flow imaging, with materials publicly disseminated through an open-source project.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.