"An Exploration of Fundamental Mechanisms of Swimming and Flying in Nature using High-Fidelity Numerical Simulation"

Jeff Eldredge, Department of Mechanical and Aerospace Engineering, UCLA

Most aquatic creatures and airborne insects achieve motility through the dynamic interaction of their flexible body/fins/wings with the surrounding medium. This flexibility is used to provide a spectrum of active and passive control, allowing the creature to sometimes prescribe its shape changes and at other times extract energy from the fluid. This mix is particularly important in the moderate Reynolds number regime, in which wake vortices play an important energetic role. A well-devised control strategy for a bio-inspired vehicle should — perhaps must — exploit such flexion and energy exchange; as yet, we lack sufficient understanding to develop such a strategy. In this work, I will present several two-dimensional canonical problems that distill fundamental modes of fluid/flexible body mechanics in biological systems, which are analyzed using high-fidelity numerical simulation. The simulations are based on an in-house Navier—Stokes solver: the viscous vortex particle method with coupled fluid-body dynamics. The first system consists of an articulated three-link swimmer, considered in free-swimming as well as in a passive configuration in the wake of an obstacle. The shape-change kinematics of the free swimming system are explored parametrically to find optimal gaits. When in the wake of a static obstacle, under some circumstances the passive system extracts energy from the ambient flow to propel itself forward. The second system consists of a simple model for flapping with a flexible wing. The power budgets and lift generation are investigated for different hovering kinematics and wing stiffnesses. The third problem involves an articulated jellyfish model, in which the active/passive flexibility mix is explored by designation of the individual hinges.

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