FYFD

Tag: biology

  • Stingray Eyes

    Stingray Eyes

    With their flexible, flattened shape, rays are some of the most efficient swimmers in the ocean. But, at first glance, it seems as if their protruding eyes and mouth would interfere with that streamlining. A new study uses computational fluid dynamics to tackle the effects of these protrusions on stingray hydrodynamics.

    With their digital stingrays, the team found that the animal’s eyes and mouth created vortices that accelerated flow over the front of the ray and increased the pressure difference across its top and bottom surfaces. The result was better thrust and the ability to cruise at higher speeds. Overall, the ray’s eyes and mouth increased its hydrodynamic efficiency by more than 20.5% and 10.6%, respectively. The lesson here: looks can be deceiving when it comes to hydrodynamics! (Image credit: D. Clode; research credit: Q. Mao et al.)

  • Animals Lapping

    Animals Lapping

    Without full cheeks, cats, dogs, and many other animals cannot use suction to drink. Instead, these animals press their tongue against a fluid and lift it rapidly to draw up a column of liquid. They then close their mouth on the liquid before it breaks up and falls down. (Cats are a bit neater about it, but as the high-speed images above show, dogs use the same method.)

    A new study takes a look at the mathematics behind this feat, specifically how long it takes for the liquid column to break up. Normally, we describe that problem using the Plateau-Rayleigh instability, but in its usual form, the PR instability doesn’t account for the kind of acceleration drinking animals apply to the fluid. This new study modifies the equations to account for acceleration and finds that the predicted time it takes for breakup is consistent with the timing of animals closing their mouths on the water. In other words, cats and dogs are likely timing their lapping to maximize the amount of water they catch with each bite. (Image credits: top – C. van Oijen, others – S. Jung et al. 1, 2; research credit: S. Jung)

  • Spiral Shark Intestines

    Spiral Shark Intestines

    We’ve seen previously just how fluid dynamically impressive sharks are on the outside, but today’s study demonstrates that they’re just as incredible on the inside. Researchers used CT scans of more than 20 shark species to examine the structure of their intestines. Sharks have spiral intestines that come in four different varieties; two of those types look like a stacked series of funnels (either pointing upstream or downstream). These funnel-filled spirals, the researchers found, are incredibly good at creating uni-directional flow without any moving parts, much like a Tesla valve does. The spiral structure also seems to slow down digestion, which may factor into the shark’s ability to go long periods between meals. Incredibly, the fossil record indicates that spiral intestines — in some form — evolved in sharks about 450 million years ago — before mammals even existed! Clearly we engineers are way behind sharks when it comes to controlling flows!

    Animation of a 3D scan of a shark's intestine, showing the spiral internal structure.

    (Image credit: top – D. Torobekov, scan – S. Leigh; research credit: S. Leigh et al.; via NYTimes; submitted by Kam-Yung Soh)

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    Sandsculpting Bees

    Building sandcastles is more than a pastime for the bumblebee-mimic digger bee. This species of bee collects water into an abdominal pouch, then uses it to wet sand to help her sculpt her nest. She’ll use the material she digs out to create a protective turret over the nest’s entrance, and once her eggs are laid and stocked with food, she’ll deconstruct the turret to rebury the nest and keep her brood safely hidden. (Image and video credit: Deep Look)

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    Keeping Cool in the Cretaceous

    I love that fluid dynamics can bring new insights to other subjects, like this study on how heavily-armored ankylosaurs avoided heat stroke. Scans of ankylosaur skulls show a complicated, twisty nasal cavity that researchers likened to a child’s crazy straw. Using numerical simulations, they showed that the airflow through these passages acts like a heat exchanger. As air gets drawn into its body, it warms up from exposure to blood vessels lining the nasal cavity; that means that, simultaneously, the hot blood is getting cooled. Those blood vessels lead up to the animal’s brain, indicating that these twisted cavities essentially serve as air-conditioning for the sauropod’s brain! (Image and video credit: Scientific American; research credit: J. Bourke et al.; via J. Ouellette)

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    Moths in Flight

    As student engineers, we often use fixed-wing aircraft to build our intuition for flight, but nature has so many other incredible examples to offer. Here we see high-speed video of seven different moth species taking off, and understanding fixed-wing flight won’t help you here at all! These moths have small, rough, and incredibly flexible wings — all characteristics an aircraft designer typically avoids. Yet these insects are agile, fast, and capable fliers at a scale that continues to thwart engineers. Some of the earliest pioneers of flight watched birds for inspiration; for small crafts, there’s no better teacher than insects. (Image and video credit: A. Smith/AntLab)

  • Sea Sponge Hydrodynamics

    Sea Sponge Hydrodynamics

    The Venus’s flower basket is a sea sponge that lives at depths of 100-1000 meters. Its intricate latticework skeleton has long fascinated engineers for its structural mechanics, but a new study shows that the sponge’s shape benefits it hydrodynamically as well.

    The sea sponge’s skeleton is predominantly cylindrical, with tiny gaps that allow water to flow through it and helical ridges alongside its outer surface to strengthen it against the deep-sea currents surrounding it. Through detailed numerical simulations, researchers found that both of these features — the holes and the ridges — serve fluid mechanical purposes for the sponge. The porous holes of the sea sponge drastically reduce flow in the sponge’s wake (third image), which provides major drag reduction for the sea sponge. That drag reduction makes it easier for the sponge to stay rooted to the ocean floor.

    The helical ridges, on the other hand, create low-speed vortices within the sea-sponge’s body cavity (second image). Such vortices increase the time water spends inside the sponge, likely helping it to filter-feed more efficiently. The additional vorticity comes at the cost of slightly increased drag but not enough to outweigh the savings from its porosity. (Image and research credit: G. Falcucci et al.; via Nature; submitted by Kam-Yung Soh)

  • The Froghopper’s Incredible Suction

    The Froghopper’s Incredible Suction

    The tiny froghopper feeds on the sap in xylem, a feat that requires overcoming more than a megapascal of negative pressure. Plants, as you may recall, transport water and nutrients from their roots to their leaves through negative pressure, essentially pulling on the water as if it were a rope. So drinking that sap is not as simple as making a hole and waiting for sap to flow. Instead, froghoppers must generate even more suction than the plant. Some scientists have been so skeptical that such a feat is even possible that they’ve disputed whether plants are truly at such high negative pressures.

    But a new study shows that froghoppers can, indeed, generate immense suction – up to nearly 1.5 megapascals. (By comparison, humans generate less than a tenth of that suction, even on a stubborn milkshake.) The researchers used two complementary methods to prove the insects’ ability. First, they studied the anatomy of the pumplike structure in the froghoppers’ heads, where the suction is generated, and determined the insects’ sucking potential from a simple calculation of force divided by area. Then, they observed feeding froghoppers in a chamber where they could measure their metabolic rates through carbon dioxide output. As the froghoppers fed, their metabolic rates spiked to 50 – 85% higher than when at rest. Only when the xylem tensions exceeded the theoretical biomechanical limits for froghopper suction did the tiny insects seem to stop feeding. (Image and research credit: E. Bergman et al.; via Science News; submitted by Kam-Yung Soh)

  • “The Goblet of Fire”

    “The Goblet of Fire”

    Sometimes the mundane events of life hide extraordinary phenomena. This award-winning photograph by Sarang Naik shows yellow-brown spores streaming off a mushroom during monsoon season. The plume is abstract and beautiful; you could easily mistake it for the flames of an Olympic torch. But common as they are, the lowly mushroom hides interesting depths. To get their spores to travel further, mushrooms actually generate their own breezes! (Image credit: S. Naik; via Big Picture Competition)

    With the Olympics kicking off today, FYFD will follow our usual tradition of Olympic-themed posts for the next couple weeks, so be sure to come back each day for the latest featured sport!

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    Unusual Insects Taking Off

    What do you do when you’re an insect researcher with a high-speed camera? Why, film all sorts of unusual insects from your backyard as they take off and fly! Here Dr. Adrian Smith of Ant Lab shows us a slew of insects that are not unusual for their rarity — you can probably find many of these in your own yard — but they are rarely seen in insect flight research. Like many of the species we’ve seen before, lots of these fliers use a figure-8 wingstroke to stay aloft. But one feature that really struck me as I watched was how amazingly flexible many of their wings were. For many of them, parts of their wings actually curl back on themselves during parts of the stroke. As engineers, our first instinct would be to avoid that kind of complexity, but I expect that it must give the insects some kind of benefit — otherwise nature would have eliminated it. (Image and video credit: Ant Lab/A. Smith; via Colossal)