A team of researchers has set out to calculate the power of a dolphin’s thrust by using digital video and millions of tiny bubbles.
In 1936, zoologist James Gray estimated that the drag dolphins must overcome to swim faster than 20 miles an hour. Gray said dolphins lacked the muscles to swim so fast, and yet they did. This is known as Gray’s Paradox.
Over the decades, scientists have found flaws in Gray’s work, and most biologists have rejected his theory.
“There is no paradox. The dolphins always had the muscles to do this,” said Frank Fish, professor of biology at West Chester University in Pennsylvania. “Gray was wrong.”
Researchers have now determined that dolphins produce 212 pounds of thrust.
Tim Wei an engineering professor at Rensselaer Polytechnic Institute used digital video and millions of tiny bubbles to track the complex movement of water roiled by swimmers.
“Sir Gray was certainly on to something, and it took nearly 75 years for technology to bring us to the point where we could get at the heart of his paradox,” Wei said.
Researchers analyzed footage of former Navy research dolphins swimming through bubble clouds in a tank at Long Marine Lab at the University of California Santa Cruz. They also videotaped them performing tail stands on the water
Computers track the bubbles’ movement, making the invisible flow of water visible. He has used the technique to help U.S. Olympic swimmers get the most from their stroke, and now on dolphins, too.
Gray had assumed that it was dolphins’ skin that gave them such great underwater speed, but Wei said he proved this to be untrue.
“It turns out that the answer to Gray’s Paradox had nothing to do with the dolphins’ skin,” Wei said. “Dolphins can certainly produce enough force to overcome drag. The scientific community has known this for a while, but this is the first time anyone has been able to actually quantitatively measure the force and say, for certain, the paradox is solved.”
Wei’s findings will be presented at the 61st Annual Meeting of the American Physical Society (APS) Division of Fluid Dynamics in San Antonio on Monday.
Wei said the research team will likely continue to investigate the flow dynamics and force generation of other marine animals, such as sea otters, which could yield new insight into how different species have evolved as a result of their swimming proficiency.
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Image 2: A single frame from a research video tracking the flow of water around Primo, a retired U.S. Navy bottlenose dolphin. Credit: Rensselaer/Tim Wei
Image 3: The same frame, but with visualized information illustrating the water flow. The arrows indicate in which direction the water is moving, and the colors indicate the speed. The red and dark blue arrows signify the fastest-moving water. Credit: Rensselaer/Tim Wei
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