Alexandra H. Techet
Mechanical and Ocean Engineering
Massachusetts Institute of Technology
ABSTRACT
Fast starting and maneuvering in the aquatic realm typically involve the formation of distinct vortex rings that deliver an impulsive change in the animals momentum. This enables these aquatic animals to maneuver in smaller spaces than that required by conventional underwater vehicles. Unsteady flapping by both plates and foils can also generate similar impulsive forces through short burst cycles, such as a single flap cycle with a fixed amplitude (figure 1a). Fast starting, jumping and maneuvering fish also generate vortex rings (figure 1b). Through the coordinated generation of impulsive forces through vortex ring formation, both solitary and aggregate systems can improve maneuvering performance. Understanding how fish and aquatic animals maneuver can help engineers improve the maneuvering performance of underwater vehicles which often operate in chaotic environments such as the surf zone.
Modeling the wake of a maneuvering fish as a simple vortex ring, with considerations taken for added mass effects, allows for straightforward analysis. Thus, by inspecting the wake generated by a rapidly maneuvering fish one can calculate the impulse imparted on the body during the maneuver. The swimming and maneuvering of aggregate swimmers, e.g. those chained together in series or parallel, can be modeled using a series of distinct vortex rings generated by each individual in the chain, with some phase shift between each individual. Particle imaging velocimetry can be used to gain insight into the mechanisms for vortex ring formation as used in fast-starting escape responses and classical maneuvers in biological animals. Both laboratory and in situ studies using both PIV and dye visualization clearly reveal the vortex ring formation and overall impulse strength over the time of the maneuver.
BIOGRAPHICAL SKETCH
Professor Alexandra (Alex) Techet is currently an Associate Professor of Mechanical and Ocean Engineering at MIT. She received her B.S.E. in Mechanical and Aerospace Engineering in 1995 from Princeton University and PhD from the MIT/WHOI Joint Program in Oceanographic Engineering in 2001. In 2002, after a post-doc at Princeton University in the Mechanical and Aerospace Engineering Department, Prof. Techet returned to MIT as an Assistant Professor in the Dept. of Ocean Engineering. Professor TechetÕs research focuses on experimental unsteady marine hydrodynamics in several key areas, including: water entry of spheres and projectiles, flow structure interactions, unsteady bio-inspired propulsion and maneuvering, and sensing at the air/sea interface. Professor Techet was a recipient of the 2004 ONR Young Investigator Award. Her imaging work has been recognized several times by the APS Gallery of Fluid Motion and has been featured on the cover of the Journal of Fluid Mechanics.