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Tail creates double jets: shark

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Connected rings of moving water / Brooke E. Fl.. / LicenseCC-by - Attribution

Tail of a shark creates double jets by actively changing the tail's rigidity in mid swing.

"[R]esearchers have discovered that as a shark’s tail swings from side to side, it creates twice as many jets of water as other fishes’ tails, smoothing out the thrust and likely making swimming more efficient. Sharks do this by stiffening the tail midswing, a strategy that might one day be applied to underwater vehicles to improve their performance." (Pennisi 2011)
"Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation...The hydrodynamic wake consists of one set of dual-linked vortex rings produced per half tail beat. In addition, we use a simple passive shark-tail model under robotic control to show that the three-dimensional wake flows of the robotic tail differ from the active tail motion of a live shark, suggesting that active control of kinematics and tail stiffness plays a substantial role in the production of wake vortical patterns." (Flammang et al. 2011: 3670)

"As the tail crosses the midline, the radialis muscles within the tail are actively stiffening the tail against this increased hydrodynamic loading. And it is precisely at this time of maximum expected stiffness and greatest drag that the first vortex is produced (figure 3), resulting in a jet with strong lift and thrust components (table 2). The remaining vorticity is shed as the tail is cupped slightly and continues laterally until it changes direction at maximum lateral excursion" (Flammang et al. 2011: 3674)

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About the inspiring organism
Med_sharktailvortex Dogfish shark
Squalus acanthias (non Linnaeus, 1758)
Common name: Spurdog

Habitat(s): Marine Neritic, Marine Oceanic
Learn more at
Some organism data provided by: FishBase
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Threat Categories LONG_VU IUCN Red List Status: Vulnerable

Bioinspired products and application ideas

Application Ideas: Underwater transportation. Medicinal administration through blood stream. Medical robotics for micro cameras and micro surgical tools.

Industrial Sector(s) interested in this strategy: Transportation, Medical

Museum of Comparative Zoology
Brooke E. Flammang
Harvard University
Flammang BE; Lauder GV; Troolin DR; Tyson Strand T. 2011. Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure. Proc. R. Soc. B. 278: 3670–3678.
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Pennisi E. 2011. How sharks go fast. ScienceNOW [Internet],
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