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Author Topic: Swiming Efficiency of Aquatic Animals Far exceeds the Propeller  (Read 228 times)

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AGelbert

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Gray's "Paradox" was nothing but human ignorance.  ;D
Fluke Forces

Dolphins prove that they rely on muscle power, rather than a trick of fluid dynamics, to race through water at high speeds.

By Dan Cossins | April 1, 2014

MIGHTY FLIPPERS: Dolphins are able to swim so rapidly by generating large amounts of power from the oscillations of their flukes.


Writing in the Journal of Experimental Biology in 1936, British zoologist James Gray made a simple calculation based on observations of a dolphin swimming alongside a ship in the Indian Ocean. The dolphin, he reported, had passed the vessel, from stern to bow, in 7 seconds. The ship was 41 meters long and it was moving at 8.5 knots. “This dolphin must therefore have been travelling at 20 knots [10.1 meters per second],” wrote Gray, who concluded, after an avalanche of more complex calculations, that dolphins couldn’t possibly have attained that speed using muscle power alone.

In an attempt to resolve the quandary, which became known as “Gray’s paradox,” he suggested that dolphins must use some trick of fluid dynamics to overcome drag, the opposing forces acting on any body moving through a fluid. And despite the fact that he’d made several erroneous assumptions, Gray’s paradox lived on, spurring others to search for the dolphin’s drag-reducing secret. During the Cold War, military researchers in the U.S. and the Soviet Union went after the mysterious mechanism in the hope that it might provide inspiration for faster, deadlier submarines and torpedoes.

Frank Fish, a biologist at West Chester University in Pennsylvania who studies the biomechanics of aquatic mammals, read such tales with interest. “To resolve the paradox was to assume that flow over the dolphin’s body is laminar, meaning that the particles all move parallel to one another and to the skin, when everything said it would be turbulent,” says Fish. “The argument brought forth ideas that the dolphin has some adaptations in the skin to smooth out the flow.”

But Fish was never convinced. Instead, he believed that dolphins’ muscular tails and flexible, wing-like flukes produce ample propulsive force to swim as fast as they do, without the need for any enigmatic hydrodynamic adaptation.

In 1993, Fish used a hydrodynamic model to show as much (J Exp Biol, 185:179-93, 1993). But the point was difficult to prove because it was impossible to directly measure the thrust produced by free-swimming dolphins. For small fish, researchers use a method called digital particle image velocimetry (DPIV). A tank is filled with water and glass microbeads, a thin layer of which is illuminated with a sheet-like laser beam. Using a high-speed video camera to film how the beads move as the fish swims through, researchers can visualize the jets and vortices its motion creates. Then, once the footage is separated into successive frames and digitized, the investigators apply an algorithm to figure out the propulsive forces generated. The problem is, says Fish, “there’s no chance anyone would let you throw in glass beads and shine laser beams at dolphins. It’s way too risky.”


WHAT A WAKE: As a dolphin swims through a bubble curtain, its powerful fluke generates vortices (picture at link) that can be filmed and analyzed using digital particle image velocimetry.


Fish was stuck. But then he met Timothy Wei at an informal hydrodynamics meeting at Princeton University in 2005. Wei, now an engineer at the University of Nebraska, had been measuring the propulsive power of Olympic swimmers by asking them to swim through a curtain of air bubbles. “It was perfect,” says Fish. The bubbles reflect light, so no lasers are required, and there is no need to worry about swallowing air bubbles. “All we needed now were the dolphins,” Fish adds. So he called up longtime friend and collaborator Terrie Williams, an animal physiologist at the University of California, Santa Cruz (UCSC), who works with two captive bottlenose dolphins named Primo and Puka. 


Primo and Puka

The team laid 6 meters of fine-pored garden-soaker hose in a straight line along the floor of a large outdoor pool at UCSC’s Long Marine Laboratory and hooked it up to a SCUBA tank of compressed air to generate bubbles. The group filmed the bubbles as Primo and Puka, after some gentle persuasion from their trainers, swam through the 2-cm-wide bubble curtain, churning up the bubbles with their flukes as they went. “The hardest thing was to get them to stop investigating the bubbles or us,” says Fish. “They’re very curious animals.”

After processing the data with DPIV software, Wei and Fish worked out that the dolphins generated up to 2,380 watts, or 3.2 horsepower, of thrust when swimming steadily at 3.4 meters per second and up to a whopping 5,400 watts, or 7.2 horsepower, when accelerating from rest (J Exp Biol, 217:252-60, 2014). Fish also calculated that “the dolphins were actually incurring a heavy drag load, suggesting they don’t have any special drag-reduction tricks.” Just as he’d thought, dolphins generate enough power to overcome their drag. “So the idea of Gray’s paradox, in which the dolphin doesn’t have enough muscle to maintain a high speed, falls apart.”

Ann Pabst, an animal physiologist at the University of North Carolina Wilmington who was not involved in the work, is impressed by the authors’ strategy. “[They] figured out a very clever method to tap into the power of DPIV . . . but to do so in a way that was safe for these protected animals,” she told The Scientist in an e-mail. “Replacing lasers and neutrally buoyant particles with sunlight and air bubbles was ingenious.” The study, says Pabst, “will be the final nail in the lid [for Gray’s paradox].”

And because it appears that dolphins incur high levels of drag, the idea that their skin holds the secret to achieving laminar flow looks like a red herring. “We should certainly stop looking for special fluid dynamics–based trickery in the flow over swimming dolphins,” says Harvard biologist George Lauder, who studies fish hydrodynamics but was not part of the study. “There is no more trickery there than is present over the body of any swimming fish.”

http://www.the-scientist.com//?articles.view/articleNo/39481/title/Fluke-Forces/
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AGelbert

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https://www.youtube.com/watch?v=aVbQ4yQG64A&feature=player_embedded
Watch lots of migrating crabs along with fish and seals on camera.
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AGelbert

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Sea Turtles Have an Internal ‘GPS’ That Uses Earth’s Magnetic Field

by TreeHugger
January 26, 2015 9:00 am

Written by Michael Graham Richard

Many animals have a talent for finding their way around the globe that any of us who gets lost doing a short trip can’t help but envy. From birds who go back and forth across continents, following the seasons, to the beautiful sea turtles that can find the specific beach where they were born years before to, in turn, lay their eggs. For decades, scientists have wondered how the turtles did it, and it seems like we might finally have an answer thanks to a study conducted at the University of North Carolina at Chapel Hill.

Photo Credit: Les_Williams / Flickr

“Sea turtles migrate across thousands of miles of ocean before returning to nest on the same stretch of coastline where they hatched, but how they do this has mystified scientists for more than fifty years,” said J. Roger Brothers of the University of North Carolina at Chapel Hill. “Our results provide evidence that turtles imprint on the unique magnetic field of their natal beach as hatchlings and then use this information to return as adults.”

To prove that this is the case, the researchers compared 19 years of data on Loggerhead Sea Turtle migration on the Eastern coast of Florida with data on naturally occurring local changes in the Earth’s magnetic field. The scientists found a strong association between the spatial distribution of turtle nests and subtle shifts in the Earth’s magnetic field.

The effect went both ways: When the magnetic fields shifted in such a way that adjacent locations along the beach moved closer, the turtles came back to nest closer together, spreading over a shorter stretch of the coast. When the magnetic signature of certain spots moved apart, the turtles spread out over a longer stretch.


Little is known about how turtles detect the geomagnetic field, but at least we can now show with a fair amount of certainty that they use it.

But why have sea turtles evolved  ::) to go nest where they themselves hatched? It’s all about finding the right conditions; soft sand, the right temperature, few predators and an easily accessible beach.
“The only way a female turtle can be sure that she is nesting in a place favorable for egg development is to nest on the same beach where she hatched,” Brothers said. “The logic of sea turtles seems to be that ‘if it worked for me, it should work for my offspring.’”

Photo Credit: Les_Williams / Flickr

And yes, I’m aware that the Global Positioning System (GPS) that we use to get around doesn’t use magnetic fields, but rather Einstein’s relativity (there’s an explanation here). Using it in the title was just short-hand for a way to navigate to your destination.
Via Journal of Current Biology, Livescience
This post originally appeared on TreeHugger.

 
Agelbert NOTE: The following comment was even more interesting than the article!  Enjoy.


Beverly S.
3:31PM PST on Jan 27, 2015

Many, if not all animals have an amazing sense of direction. I remember reading that we humans also have a "compass" in our noses, so I did a little research. Interesting!

Some years ago scientists at CALTECH (California Institute of Technology in Pasadena) discovered that humans possess a tiny, shiny crystal of magnetite in the ethmoid bone, located between your eyes, just behind the nose.  :o 



Magnetite is a magnetic mineral also possessed by homing pigeons, migratory salmon, dolphins, honeybees, and bats. Indeed, some bacteria even contain strands of magnetite that function, according to Dr. Charles Walcott of the Cornell Laboratory of Ornithology in Ithaca, New York, "as tiny compass needles, allowing them [the bacteria] to orient themselves in the earth's magnetic field and swim down to their happy home in the mud".

It seems that magnetite helps direction finding in animals and helps migratory species migrate successfully by allowing them to draw upon the earth's magnetic fields. But scientists are not sure how they do this.

In any case, when it comes to humans, according to some experts, magnetite makes the ethmoid bone sensitive to the earth's magnetic field and helps your sense of direction.
Stephen Juan, Ph.D. is an anthropologist at the University of Sydney


Read more: http://www.treehugger.com/natural-sciences/no-place-like-magnetic-home-sea-turtles-gps-earth-magnetic-field.html#ixzz3QBWvIzs4

Agelbert NOTE: Have we lost our PREVIOUS ability to follow earth's magnetic fields through "use it or lose it" SUBTRACTION of genetic material otherwise known as NATURAL SELECTION? Only your Darwinian Evolutionist knows - and they don't want to go there.  Admiting we are LESS "evolved" than we previously were is a NO NO in Darwinian circles. ;D
Leges         Sine    Moribus     Vanae   
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AGelbert

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Those babies can swim FAST! No fossil fuels required.     


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AGelbert

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A case in nature where the parent doesn't argue with its offspring;)
Pseudis paradoxa (Paradoxical Frog)


Where Does the Paradoxical Frog Get Its Name?

The paradoxical frog is a South American frog also known as the “shrinking frog” because of the enormous size of its tadpoles compared with the adult frog. The tadpoles can reach more than eight inches in length, while the adult frogs are generally only two inches long.

While an ordinary tadpole transforming into a frog will simply grow legs as its tail shrinks, the tadpoles of the paradoxical frog need to shrink their entire body to grow up.  :o

Several other species of frogs have similarly large larvae, but they all spend winter as tadpoles and need greater size to survive. Tadpoles of paradoxical frogs are not subjected to the same conditions and scientists are unsure exactly why they grow so large. 



More about frogs:

Pseudis paradoxa (Paradoxical Frog) enjoying life in some duckweed.

The paradoxical frog produces a skin secretion which could be used to help combat diabetes by stimulating insulin production.

While all frogs go through a tadpole stage, not all tadpoles live in fresh water. For example, Darwin's frog tadpoles mature while contained inside the vocal sac of their father.

The largest frog species is the Goliath frog, which can grow to over a foot long and weigh up to seven pounds.  :o

Conraua goliath (Goliath Frog)

No relationship to Jabba the Hutt is claimed. ;D

http://www.wisegeek.com/where-does-the-paradoxical-frog-gets-it-name.htm
Leges         Sine    Moribus     Vanae   
Faith,
if it has not works, is dead, being alone.

AGelbert

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SLIDESHOW: Meet the Penguins!
Celebrate Penguin Awareness Day
 
January 20th is Penguin Awareness Day and what better time to celebrate these amazing birds? Penguins delight and charm nature lovers of all ages. But, many penguin species face serious, human-caused threats. Here, you'll meet 9 penguin species and learn what they're facing


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Faith,
if it has not works, is dead, being alone.

 

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