Researcher(s)
- Prasanna Krishnamoorthy, Mechanical Engineering, University of Delaware
Faculty Mentor(s)
- Tyler Van Buren, Mechanical Engineering, University of Delaware
Abstract
Fish and aquatic mammals display efficient swimming capabilities not replicable in laboratory conditions using traditional propellers. Studying and replicating these natural unsteady propulsors can inspire underwater unmanned vehicle design as well as enhance understanding of periodic and unsteady flows. To better understand the biological swimming mechanics of fins, the hydrodynamics of a bio-inspired robot propulsor will be analyzed experimentally. This propulsor consists of a simple hydrofoil acting as a fin, connected at its leading edge to a central shaft, whose housing is connected to a motor-driven linear actuator that mimics the natural side-to-side “heaving” motion of thunniform swimmers. As this hydrofoil is heaving from its leading edge, fluid forces cause the fin to rotate and “pitch” about the central shaft. Varying fin material properties contribute to thrust generation differences. Biological fins vary in stiffness spatially and temporally, due to differences in organic tissue, morphology, and muscular contraction, optimized to maximize thrust. This project focuses on modulating fin stiffness over time by manipulating a 3D-printed beam attached to the central shaft. The bending beam acts like an adjustable torsional spring, with pins on a belt-driven slider moving along the beam to vary its stiffness. These components and the shaft assemble into a 3D-printed housing bolted to the heaving actuator. Theoretical calculations and experiments were conducted to validate the mathematical relationship between slider position, torque applied to the shaft, angular deviation of the hydrofoil, and the torsional stiffness of the beam mechanism. These relationships also enable accurate programming of the slider to match a desired stiffness function. Once the slider and heaving motors are fully programmed, the bio-inspired propulsor will be tested in fluid flows. The hydrodynamic outcome data will be analyzed to develop a swimming performance model to compare against the computational and natural models, helping further understand unsteady swimming propulsion.