Collaborative Research: The Roles of Inter-limb Jets and Body Angles in Metachronal Paddling

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Commercial underwater drones typically rely on a single propeller element. If this element were to fail, then the drone would be lost. In contrast, the existence of multiple propulsion elements would permit continued use upon failure of a single propeller. Natural aquatic organisms illustrate a unique opportunity to use multiple propulsion elements to generate small-scale jets. Krill, shrimp, and crayfish, all use several pairs of limbs in highly coordinated motion to swim. The animal rhythmically oscillates its limbs from the tail-to-head at low velocity, with the timing of each pair delayed relative to its neighbors. Nature?s design uses much less energy than our engineered underwater drones. Mechanical elements, such as gears and timing belts, could be used to cost effectively mimic nature?s design. However, the underlying fluid dynamics of this metachronal (sequential) paddling is not well-understood. A limited number of studies have suggested limb morphology, the precision timing of the paddling sequence, and the generation of jets in the wake of the organism all contribute to this unique propulsion mechanism. This research project examines how coordination of adjacent limbs interact with the flow past the body to generate propulsive jets in the wake. Uncovering the underlying fluid dynamic principles of metachronal paddling will enable scalability to engineered devices, allowing for efficient design of miniaturized, bio-inspired autonomous underwater drones. This research project examines how the coordinated motion of multiple oscillating paddles merge with large-scale flow past a submerged object to generate propulsive forces. A combination of experiments with both live animals and robotic models will be used. Tomographic particle image velocimetry measurements of free-swimming aquatic organisms will be used to validate flow fields predicted by physical models. Self-propelled metachronal swimming robots will be used to examine the flow for individual and collective motion of the robots. Mechanical performance with respect to body angles, swimming speeds, and neighbor distances in individual and small groups of metachronal paddling robots will be examined. A primary project outcome will be the fluid dynamics mechanism by which aquatic organisms achieve large body speeds by paddling individual limbs at low velocity. The outcomes of this research will enable engineers to design and coordinate the motion of multiple propellers on engineered devices. In addition, the research project trains undergraduate and graduate students to conduct interdisciplinary research in bioengineering. Existing mechanisms at both institutions (NSF-funded Oklahoma Louis-Stokes Alliance for Minority Participation and Georgia Tech FOCUS program) are being used to recruit under-represented students for the project, and the researchers are participating in outreach activities to high school students and their teachers.