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Moving efficiently through water: aquatic animals

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A sawfish / Diliff / LicenseGFDL - Gnu Free Document License

Aquatic organisms move effectively through water by maximizing propulsion efficiency.

BIOMIMICRY TAXONOMY
Summary
"It [the Froude propulsion efficiency] says that for highest efficiency, the velocity of the fluid issuing from the propulsive unit--paddle, propeller, jet, or whatever--should be as close as possible to the velocity of the craft...Clearly the way to maximize Froude propulsion efficiency consists of moving the largest possible mass-per-time (m/t) of fluid and giving it the least possible increase in speed (v2-v1). In practical terms that means maximizing S, the cross section of the propulsive flow stream."

While the Froud efficiencies "vary in quality and involve differenty underlying assumptions and simplifications, the picture that emerges is satisfyingly consistent with our expectations."

"* Moving water with undulating body, beating wing, or swinging tail beats squeezing water out of a jet, as anticipated. A squid may jet fast, but when it wants to go far, it's more likely to use its fins.

"* The same undulating devices do better than systems that move water back-wards with a paddling system, with its alternating power and recovery strokes. We'll return to this comparison between 'lift-based' and 'drag-based' propulsion in chapter 13.

"*Bigger (or at least moderate size) is better than smaller. Except for one questionable datum for a bacterial flagellum, no creature below about a centimeter in length does better than ηf = 0.5. The pernicious effects of low Reynolds number (chapter 11) cannot be denied.

"*The broad hydrozoan medusae (essentially small jellyfish) may use jet propulsion, but they do it by pushing out an especially large volume (relative to their own) through a wide aperture. So they have a much higher m and lower v2 than the other jetters, and thus evade most of the difficulty inherent in equations (7.5) and (7.6)." (Vogel 2003:142-143)
About the inspiring organism
Animalia
Animalia

Learn more at EOL.org
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist


Bioinspired products and application ideas

Application Ideas: Having a transport system that moves slowly by undulation rather than rotating helix model (propeller) could increase efficiency by at least 10%.

Industrial Sector(s) interested in this strategy: Transportation, aerospace, marine architecture and engineering

References
Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
Learn More at Google Scholar Google Scholar  

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