FYFD

Tag: biology

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    Underwater Snakes, Gusty Flying, and Microswimmers

    If you like your fluid dynamics with a healthy dose of biology, this video’s for you! Learn about the hydrodynamics of snake strikes, how birds fly in gusty crosswinds, and the mathematical underpinnings of a microswimmer’s journey. This is the final video in our FYFD/JFM collaboration featuring research from the 2017 APS DFD meeting. If you missed any of the previous videos, you can see them all here. Which one is your favorite? Would you like to see the series continue? Let me know in the comments or on Twitter! (Image and video credit: N. Sharp and T. Crawford)

  • Rattling Feathers for Attention

    Rattling Feathers for Attention

    Peacocks are known for their colorful mating displays, but it turns out there’s more to them than meets the eye. To help them gain a penhen’s attention, peacocks will sometimes rattle their train-feathers. The sound this makes is mostly below the range of human hearing, but the rustle creates subtle vortices in the air that cause the feathers atop a peahen’s head to vibrate. Playing back the sound at peahens from typical train-rattling distances also gets the females’ attention. Researchers found the playback makes peahens’ crests vibrate at a resonant frequency, suggesting that these feathers are for more than display; they’re used for communication as well! (Image and research credit: S. A. Kane et al.; video credit: Science)

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    The Clever Cat’s Tongue

    Cats spend almost a quarter of their waking hours grooming, and their tongues are wonderfully specialized for this task, allowing them to clean, cool, and untangle themselves with ease. Anyone who’s ever been licked by a cat knows their tongues feel sandpaper-y. This is due to rear-facing hook-like structures called papillae that have a stiffness comparable to human fingernails.

    The papillae are hollow, and their U-shaped tip helps them wick up saliva, which the cat deposits deep into its undercoat when it licks. Although the papillae only hold about 5% of the volume of saliva on the cat’s tongue, this wicking action is key because most of the tongue surface can’t reach the inner coat; only the papillae do. The saliva that reaches these dense inner hairs is important not only for cleaning the fur, but for helping the cat cool off. As the saliva evaporates, it carries heat away with it, just like sweating does for us.

    The papillae are key to untangling fur, but their shape also makes it easy to remove hairs caught on the tongue. Researchers built a 3D-printed cat-inspired hair brush to show how efficient and easy to clean a cat’s tongue can be! (Video credit: Science; research credit: A. Noel and D. Hu)

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    Rivers in the Sky

    The water cycle is quite a bit more complicated than what we learn in elementary school, and the environment around us contributes to that cycle in invisible but vital ways. In this video, Joe Hanson of It’s Okay to Be Smart pulls back the veil on this in the context of the Amazon river basin and how the Amazon rainforest itself creates an atmospheric river that carries more water than its namesake river.

    Trees release water into the air almost constantly as they transpire. And to trigger that water to fall as rain, trees can release other compounds that serve as a nucleus around which raindrops can form. The condensing raindrops form clouds, which lower the air pressure and create winds, thereby creating an atmospheric river flowing from the Atlantic back up the Amazon River. That stream carries rain that feeds the rainforest and the Amazon River, continuing the cycle. (Video and image credit: It’s Okay to Be Smart)

  • Hovering

    Hovering

    Nectar-drinking species of hummingbirds and bats are both excellent at hovering – one of the toughest aerodynamic feats – but they each have their own ways of doing it. Hummingbirds (bottom) use a nearly horizontal stroke pattern that’s quite symmetric on both the up- and downstroke. To keep generating lift in the upstroke, they twist their wings strongly midway through the stroke. So although hummingbirds get most of their lift from the downstroke, they get quite a bit from the upstroke as well.

    Bats, on the other hand, use an asymmetric wingbeat pattern when hovering. Bats flap in a diagonal stroke pattern, using a high angle of attack in the downstroke and an even higher one during the upstroke. They also retract their wings partially during the upstroke. This flapping pattern gives them weak lift during the upstroke, which they compensate for with a stronger downstroke. Compared to non-hovering bat species, nectar-drinking bats do get more lift during the upstroke, but they’re nowhere near as good as the hummingbirds. The bats compensate by having much larger wings compared to their body size. Bigger wings mean more lift.

    In the end, the two types of hovering cost roughly the same amount of power per gram of body weight. That’s great news for engineers designing the next generation of flapping robots because it suggests two very different, but equally power-efficient methods for hovering. (Image credit: Lentink Lab/Science News, source; research credit: R. Ingersoll et al.; via Science News; submitted by Kam Yung-Soh) 

  • Hydraulics Make Spiders So Creepy

    Hydraulics Make Spiders So Creepy

    There’s something about the way spiders move that many of us find inherently creepy. And that something, it turns out, is fluid dynamical. Unlike humans and other vertebrates, spiders don’t move using two sets of opposing muscles. The natural state of their multi-jointed legs causes them to flex inward. This is why dead spiders have their legs all curled up.

    To walk, spiders use hydraulic pressure. They pump a fluid called hemolymph into their legs to force them to straighten. If you look closely, you’ll notice that spiders’ legs always connect to the front section of their body. This is called the cephalothorax, and it acts like a sort of bellows that controls the pressure and flow of hemolymph. It moves the hemolymph around the spider’s body in a fraction of a second, allowing spiders to be quite fast, but something about the movement still feels off for those of us used to vertebrate motion. Happy Halloween, everyone!  (Image credit: R. Miller, source; see also; submitted by jpshoer)

  • Ants Avoid Traffic Jams by Giving Up

    Ants Avoid Traffic Jams by Giving Up

    Both ants and traffic are well-connected to fluid dynamics, even if they are not, strictly speaking, fluids. As it happens, ant traffic has interesting implications not only for human transit but for avoiding clogs in crowds or when pouring granular materials. 

    Ants tend to dig narrow tunnels. This helps individual ants recover from potential slips, but it also makes clogging more likely. Researchers studying the behavior of individual ants during tunnel digging found that ants entering the tunnel often turn around without collecting a grain and carrying it away. When they encounter heavy traffic, they simply reverse direction and give up. So 70% of the work of digging was done by only 30% of the ants. This seemingly unfair division of labor actually optimizes the overall traffic flow and work output for the ants as a whole. Without this instinct to turn around and ease the jam, incoming ants would cascade the traffic and worsen the jamming. (Image and research credit: J. Aguilar et al.; see also Physics Today)

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    Flying on Flexible Wings

    Bats are incredible and rather unique among today’s fliers. Like birds, they flap to produce their lift and thrust, but where birds have relatively stiff wings, a bat’s wings are flexible. The thin webbing of skin stretched between the bat’s finger joints has muscles inside it that fire as the mammal flaps. This means that the bat may actively control just how stiff its wing is as it flies.

    Compared to other natural and manmade fliers, the bat is incredibly agile and stable, able to recover from wind gusts in less than a full wingbeat cycle. They also have some incredible acrobatic capabilities. When preparing to perch, a bat loses almost all of its aerodynamic lift but still manages to maneuver itself so it flips over and grabs hold. Check out the full video above to learn more about these fascinating animals. (Video and image credit: Science Friday; research credit: S. Swartz and K. Breuer)

    Editor’s Note: I’ll be travelling through the end of the month with limited email access. The blog should continue posting uninterrupted, but if you contact me, just know it may be awhile before I can get back to you. Thanks! – Nicole

  • The Livers of Our Rivers

    The Livers of Our Rivers

    To the naked eye, mussels and other bivalves don’t appear to be doing much. But these filter feeders are hard at work. The mussel takes in water through its incurrent siphon (on the right side in this image), and tiny cilia move the water through its gills, which filter out plankton and other edibles. Wastewater flows out the exacurrent siphon, seen here as the plume coming out the top of the mussel.

    Mussel species are important indicators of the health of both fresh and marine water bodies. Because they’re stationary and they are constantly processing the water, the health of these bivalves is indicative of the ecosystem’s overall health. (Image credit: S. Allen, source)

  • How Mantas Filter But Never Clog

    How Mantas Filter But Never Clog

    Manta rays spend much of their time leisurely cruising through the water with their meter-wide mouths open. As they swim, they filter plankton, which makes up most of their diet, from the water. And they do so without ever clogging. 

    The inside of the manta’s mouth is lined with gill rakers (upper right), a series of comb-like teeth. When flow hits the leading edge of these (bottom), it creates a vortex that accelerates any particles caught in the flow. They essentially ricochet along the top of the gill rakers, getting led straight into the manta’s digestive system – while excess water gets deflected between the gill rakers and back out the manta’s gills. To drive this, all the manta has to do is swim; with the right flow speed, the shape of the gill rakers handles all the filtration with no additional effort. (Image credit: manta ray – G. Flood; gill rakers – M. Paig-Tran; flow vis – R. Divi et al., source; research credit: M. Paig-Tran et al.; via The Atlantic; submitted by Kam-Yung Soh)