Archive for the ‘fluid dynamics’ Category

The secret of how the mako shark swims so fast lies in its flexible scales

March 8th, 2019
A shortfin mako shark off the coast of Cancun, Mexico. Tiny flexible scales on its skin control flow separation as it swims, reducing pressure drag.

Enlarge / A shortfin mako shark off the coast of Cancun, Mexico. Tiny flexible scales on its skin control flow separation as it swims, reducing pressure drag. (credit: YouTube/Guy Harvey)

Mako sharks can swim as fast as 70 to 80 MPH, earning them the moniker "cheetahs of the ocean." Now scientists at the University of Alabama have determined one major factor in how mako sharks are able to move so fast: the unique structure of their skin, especially around the flank and fin regions of their bodies. The team described their work at the American Physical Society's 2019 March meeting this week in Boston.

University of Alabama engineer Amy Lang conducted a series water tunnel experiments in her lab to test samples of real mako shark skin from the animal's flanks, using a technique called particle image velocimetry to measure the velocity of the water flowing over and around the skin. Anyone who has touched a shark knows the skin feels smooth if you stroke from nose to nail. Reverse the direction, however, and it feels like sandpaper. That's because of tiny translucent scales, roughly 0.2 millimeters in size, called "denticles" (because they strongly resemble teeth) all over the shark's body, especially concentrated in the animal's flanks and fins. It's like a suit of armor for sharks.

Mako sharks have evolved a distinct passive "bristling" aspect on some of their scales to swim faster. Lang's lab coordinated their project with biologists at the University of South Florida, who imaged shark skin and mapped out the scales, noting particularly how many of the scales were capable of this passive bristling and the angles at which such bristling occurs. They found that near regions like the nose, the scales aren't especially flexible, more like molars embedded in the skin. But near the flanks and fins, the scales are much more flexible.

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Posted in APS March Meeting, biophysics, fluid dynamics, mako shark, Physics, science | Comments (0)

Georgia Tech scientists figured out how maggots can eat so much, so fast

February 17th, 2019
Studying the collective feeding behavior of black soldier fly larvae.

Enlarge / Studying the collective feeding behavior of black soldier fly larvae. (credit: Hu lab/Georgia Tech)

How do the larvae of black soldier flies eat so much, so fast, despite their tiny size? Scientists at Georgia Tech have been studying this "collective feeding" behavior and found that one strategy for maximizing the larvae's feeding rate involves forming maggot "fountains." The scientists described the results in a recent paper in the Journal of the Royal Society Interface, along with an entertaining video showing a swarm of larvae consuming an entire pizza in just two hours.

"This is the first time, as far as I know, that we've really tried to quantify how much they were able to eat, and how they are able to do it," said graduate student and co-author Olga Shishkov, who demonstrated the research on Saturday at the American Association for the Advancement of Science meeting in Washington, DC. It's not the first time she's had fun demonstrating the maggots' hearty appetite in creative ways: last year, she videotaped the critters devouring a heart-shaped donut for Valentine's Day.

Shishkov's advisor is David Hu, who runs a biolocomotion laboratory at the Georgia Institute of Technology studying how various creatures move. He is perhaps best known for his work with fire ants, but his lab also studies cat tongues, water striders, snakes, various climbing insects, mosquitos, and, of course, black soldier fly larvae.

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Posted in Biology, collective behavior, fluid dynamics, Physics, science | Comments (0)

It’s the drag that helps the humble hagfish slime predators so quickly

January 17th, 2019

Courtesy of University of Wisconsin, Madison.

The homely hagfish might look like just your average bottom feeder, but they have a secret weapon: they can unleash a full liter of sticky slime in less than one second. That slime can clog the gills of a predatory shark, for instance, suffocating it. Scientists are unsure just how the hagfish (affectionately known as a "snot snake") accomplishes this feat, but a new paper in the Journal of the Royal Society Interface suggests that turbulent water flow (specifically, the drag such turbulence produces) is an essential factor.

Scientists have been studying hagfish slime for years because it's such an unusual material. It's not like mucus, which dries out and hardens over time; hagfish slime stays slimy, giving it the consistency of half-solidified gelatin. That's due to long, thread-like fibers in the slime, in addition to the proteins and sugars that make up mucin, the other major component. Those fibers coil up into "skeins" that resemble balls of yarn. When the hagfish lets loose with a shot of slime, the skeins uncoil and combine with the salt water, blowing up more than 10,000 times its original size.

Yet the precise mechanism for slime deployment is still poorly understood, according to co-author Gaurav Chaudhary of the University of Illinois, Urbana-Champaign. Recent research showed that sea water is essential to the formation of the slime, and that hagfish skeins can unravel spontaneously if ions in the sea water mixes the adhesives that hold the fibrous threads together in skeins. Chaudhary says that what's missing in this earlier work is taking the fast time scales into account. A 2014 study, for instance, showed that any spontaneous unraveling of the skeins would take several minutes—yet the hagfish deploys its slime in about 0.4 seconds.

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Posted in Biology, fluid dynamics, hagfish, Physics, science, slime and mucus | Comments (0)

The secret to champagne’s universal appeal is the physics of bubbles

December 31st, 2018
Making champagne is fairly simple, but the physics behind its bubbly delights is surprisingly complex.

Enlarge / Making champagne is fairly simple, but the physics behind its bubbly delights is surprisingly complex. (credit: Jon Bucklel/EMPICS/PA/Getty Images)

It's New Year's Eve, and revelers around the globe will be breaking out the bubbly in massive quantities to usher in 2019. Why do humans love champagne and other fizzy beverages so much, when most animals turn up their noses when it's offered? Roberto Zenit, a physicist at Mexico's National Autonomous University of Mexico, and Javier Rodriguez-Rodriguez of the Carlos III University of Madrid in Spain, posit in the November issue of Physics Today that carbonation triggers the same pain receptors in our deep brains that are activated when we eat spicy food.

"This bubbly sensation you have when you drink a carbonated beverage basically triggers similar taste buds," said Zenit. "Champagne is just wine; what makes it special is the carbonation. It's a sad day when you drink flat champagne."

He and Rodriguez-Rodriguez study the behavior of various fluids (including paints), and carbonation is a particularly fascinating topic within that discipline. When the bubbles in champagne burst, they produce droplets that release aromatic compounds believed to enhance the flavor further. (When bubbles in a carbonated beverage like beer don't burst, the result is a nice thick head of foam.) And here's another interesting fact: the bubbles in champagne "ring" at specific resonant frequencies, depending on their size. So it's possible to "hear" the size distribution of bubbles as they rise to the surface in a glass of champagne.

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Posted in 12 days of Christmas, bubbles, champagne, fluid dynamics, foam, Physics, science, Wine | Comments (0)

Study: modern masters like Jackson Pollock were “intuitive physicists”

December 26th, 2018
<em>Collective Suicide</em> (1936), by Mexican muralist David A. Siqueiros, is an example of the "accidental painting" technique developed by the artist.

Enlarge / Collective Suicide (1936), by Mexican muralist David A. Siqueiros, is an example of the "accidental painting" technique developed by the artist. (credit: A. Aviram/MOMA, New York, via R. Zenit)

There's rarely time to write about every cool science story that comes our way. So this year, we're running a special Twelve Days of Christmas series of posts, highlighting one story that fell through the cracks each day, from December 25 through January 5. Today: the fluid dynamics of modern painting techniques.

In the 1930s, a small group of New York City artists began experimenting with novel painting techniques and materials, including Mexican muralist David A. Siqueiros and Jackson Pollock. For the last few years, a team of Mexican physicists has been studying the physics of fluids at work in those techniques, concluding that the artists were "intuitive physicists," using science to create timeless art.

"One of the things I have come to realize is that painters have a deep understanding of fluid mechanics as they manipulate their materials," said Roberto Zenit, a physicist at the National Autonomous University of Mexico who is leading the research. "This is what fluid mechanicians do. The objective is different, but the manipulation of these materials that flow is the same. So it is not a surprise that fluid mechanics has a lot to say about how artists paint."

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Posted in 12 days of Christmas, art, fluid dynamics, Gaming & Culture, Jackson Pollock, painting, painting techniques, Physics, science | Comments (0)

Physics can explain the fastball’s unexpected twist, new study finds

November 23rd, 2018
Los Angeles Dodgers pitcher Clayton Kershaw delivers the pitch during the first inning against the Boston Red Sox in Game Five of the 2018 World Series at Dodger Stadium.

Enlarge / Los Angeles Dodgers pitcher Clayton Kershaw delivers the pitch during the first inning against the Boston Red Sox in Game Five of the 2018 World Series at Dodger Stadium. (credit: Sean M. Haffey/Getty Images)

The fastball is, as its name implies, the fastest pitch in major league baseball, reaching speeds in excess of 100 MPH, and ideally arriving at the strike zone before the batter can react. Sometimes those fastballs make an unexpected twist that can make or break the outcome of a game. What accounts for differences between pitches? It all comes down to spin speed, spin axis, and the orientation of the ball.

So says Barton Smith, a mechanical and aerospace engineer (and staunch baseball fan) at Utah State University. He studies the complicated physics of how a pitcher's biomechanics can influence the air dynamics of a baseball. Smith presented his findings earlier this week at a meeting of the American Physical Society's Division of Fluid Dynamics in Atlanta, Georgia.

There's some colorful history to the study of baseball pitches, most notably the heated debate in the 1940s and 1950s around whether a curve ball really does curve, or whether it's just a trick of perception. St. Louis Cardinals pitcher Dizzy Dean had this to say to skeptics: "Ball can't curve? Shucks, get behind a tree and I'll hit you with an optical illusion." Dean was right. Curve balls really curve—and we know why in part because of research in the 1950s by Lyman Briggs, a former director of the National Bureau of Standards (now the National Institute of Standards and Technology in Gaithersburg, MD).

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Posted in Baseball, fastball, fluid dynamics, Magnus effect, Physics, pitches, science | Comments (0)

What we can learn about crowd behavior by watching the Tour de France

November 19th, 2018
Cyclists hit the 18th stage between Trie-sur-Baise and Pau, southwestern France, in the 2018 Tour de France.

Enlarge / Cyclists hit the 18th stage between Trie-sur-Baise and Pau, southwestern France, in the 2018 Tour de France. (credit: Jeff Pachoud/AFP/Getty Images))

Check out the aerial footage of bicyclists competing in the annual Tour de France and you'll notice that riders tend to spontaneously group themselves into a diamond-shaped pattern. Jesse Belden, a researcher at the Naval Undersea Warfare Center, says such patterns emerge because riders are trying to stay close to their competitors while avoiding collisions.

Belden, an avid cyclist himself, described his work at a meeting of the American Physical Society's Division of Fluid Dynamics in Atlanta, Georgia. While watching coverage of the Tour de France, especially the aerial footage, he became fascinated by the formations of the group of cyclists. They resembled flocks of starlings or schools of fish—both examples of so-called "collective behavior" in nature. And he found himself wondering how one might model the behavior of riders in a peloton.

The study of swarming and other collective behavior in animals is a booming field, with scientists studying the group dynamics of murmurations of starlings, ubiquities of sparrows, swarms of midges, armies of fire ants, and schools of fish, among other examples in nature. The aim is to better understand the underlying mechanisms, with an eye toward identifying possible universal laws governing such behavior—a task made more difficult by the fact that there are slightly different mechanisms behind the collective behavior of each of the aforementioned groups.

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Posted in collective behavior, fluid dynamics, Peloton, Physics, science, sports, swarms, tour de france | Comments (0)

Insect-inspired microfluidics could help Ant Man and the Wasp breathe

November 18th, 2018
Scott Lang, aka Ant-Man (Paul Rudd), and Hope van Dyne, aka the Wasp (Evangeline Lilly), would need 100 times more oxygen than usual at smaller scales.

Enlarge / Scott Lang, aka Ant-Man (Paul Rudd), and Hope van Dyne, aka the Wasp (Evangeline Lilly), would need 100 times more oxygen than usual at smaller scales. (credit: Marvel Studios)

The ability to rapidly shrink down to bug size (and beyond) gives Ant-Man and the Wasp tremendous advantages. But it also comes with some scale-related drawbacks, most notably, more difficult breathing. Trick out their suits with insect-inspired microscale air pumps, compressors, and molecule filters, combined with the fictional "Pym particle" technology, et voila! Problem solved.

Anne Staples, a bioengineer at Virginia Tech, and her graduate student Max Mikel-Stites first outlined the respiratory difficulties Ant-Man and the Wasp would likely face while insect-sized in a paper published this summer in the fledgling journal Superhero Science and Technology. (Can I just say how delighted I am that this journal exists?) The group researches respiration at the microscale, using insects as models. They described their work at a meeting of the American Physical Society's Division of Fluid Dynamics in Atlanta, Georgia.

Mikel-Stites, a fan of the Marvel cinematic universe, was stoked for Ant-Man and the Wasp's release. So one day in the lab last spring, the conversation naturally turned to how difficult it would be for the superheroes to breathe when insect-sized. "Applying that perspective to Ant-Man and the Wasp seemed like a straightforward thing to do," says Mikel-Stites, who admits to being a bit nitpicky when it comes to science in the movies. And he couldn't stop thinking about the breathing problems that our superheroes would inevitably face.

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Posted in Ant-Man, biophysics, fluid dynamics, Gaming & Culture, marvel studios, microfluidics, Physics, science, The Wasp | Comments (0)