FYFD

Category: Phenomena

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    Dutch Water Works

    The Netherlands have a long history of extraordinary public works when it comes to water management. With much of the country’s land lying at or below sea level, massive civil engineering infrastructure is a necessity. In this Practical Engineering video, Grady takes us on a tour of Dutch water works, from the centuries-old techniques that allowed farmers to claim arable land from marshes to the unbelievably massive structures that protect the Dutch coastline from flooding and storm surges.

    For the Dutch, these projects, expensive as they are to build and maintain, are cheaper than the cost of inaction, as numerous devastating floods of the past have taught them. Although the goals are often the same — shortening the coastline, protecting land and people — the techniques are constantly evolving, especially as ecological needs of non-human species are taken into account. (Video and image credit: Practical Engineering)

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  • Kolmogorov Turbulence

    Kolmogorov Turbulence

    Turbulent flows are ubiquitous, but they’re also mindbogglingly complex: ever-changing in both time and space across length scales both large and small. To try to unravel this complexity, scientists use simplified model problems. One such simplification is Kolmogorov flow: an imaginary flow where the fluid is forced back and forth sinusoidally. This large-scale forcing puts energy into the flow that cascades down to smaller length scales through the turbulent energy cascade. Here, researchers depict a numerical simulation of a turbulent Kolmogorov flow. The colors represent the flow’s vorticity field. Notice how your eye can pick out both tiny eddies and larger clusters in the flow; those patterns reflect the multi-scale nature of turbulence. (Image credit: C. Amores and M. Graham)

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    How Sunflowers Follow the Sun

    Sunflower blossoms face east, presenting their blooms to the morning sun and the bees that come exploring with it. But before they grow their massive flower, each plant spends the day following the sun, greeting it in the east and tracking it westward all day. Overnight, the plant reorients eastward to start over again. The motion occurs thanks to the plant internally shifting its water supply. During the day, it swells cells on the east-facing side of the plant, gradually lengthening that side and causing the plant to tip westward. At night, it switches to swelling the west-facing side. Why go to all this trouble? By following the sun, the plant is able to photosynthesize and grow more effectively. (Video and image credit: Deep Look)

    Sunflower plants follow the sun during the day and reset overnight.
    Sunflower plants follow the sun during the day and reset overnight.
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    Bubbly Tornadoes Aspin

    Rotating flows are full of delightful surprises. Here, the folks at the UCLA SpinLab demonstrate the power a little buoyancy has to liven up a flow. Their backdrop is a spinning tank of water; it’s been spinning long enough that it’s in what’s known as solid body rotation, meaning that the water in the tank moves as if it’s one big spinning object. To demonstrate this, they drop some plastic tracers into the water. These just drop to the floor of the tank without fluttering, showing that there’s no swirling going on in the tank. Then they add Alka-Seltzer tablets.

    As the tablets dissolve, they release a stream of bubbles, which, thank to buoyancy, rise. As the bubbles rise, they drag the surrounding water with them. That motion, in turn, pulls water in from the surroundings to replace what’s moving upward. That incoming water has trace amounts of vorticity (largely due to the influence of friction near the tank’s bottom). As that vorticity moves inward, it speeds up to conserve angular momentum. This is, as the video notes, the same as a figure skater’s spin speeding up when she pulls in her arms. The result: a beautiful, spiraling bubble-filled vortex. (Video and image credit: UCLA SpinLab)

    Composite image showing far (left) and close (right) views of a bubbly vortex in a rotating water tank.
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    Why Nature Loves Fractals

    Trees, blood vessels, and rivers all follow branching patterns that make their pieces look very similar to their whole. We call this repeating, self-similar shape a fractal, and this Be Smart video explores why these branching patterns are so common, both in living and non-living systems. For trees, packing a large, leafy surface area onto the smallest amount of wood makes sense; the tree needs plenty of solar energy (and water and carbon dioxide) to photosynthesize, and it has to be efficient about how much it grows to get that energy. Similarly, our lungs and blood vessels need to pack a lot of surface area into a small space to support the diffusion that lets us move oxygen and waste through our bodies. Non-living systems, like the branches of viscous fingers or river deltas or the branching of cracks and lightning, rely on different physics but wind up with the same patterns because they, too, have to balance forces that scale with surface area and ones that scale with volume. (Video and image credit: Be Smart)

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  • “Kirigami Sun”

    “Kirigami Sun”

    Kirigami is a variation of origami in which paper can be cut as well as folded. Here, researchers look at flow through a cut kirigami sheet and how that flow changes with the cuts’ length. In the top central image, white lines mark the paper boundaries. As the cut gaps get larger, flow through them transitions from a continuous jet to swirling vortex shedding. Along the bottom, we see similar patterns emerge in the wake of uniformly-cut sheets, too. On the right, the flow comes through in jets; moving leftward, it transitions to an unsteady vortex shedding flow. (Image credit: D. Caraeni and Y. Modarres-Sadeghi)

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    Behind the San Antonio River Walk

    How do you manage necessary updates to an iconic landmark like the San Antonio River Walk without disrupting its function? That’s the concept behind this Practical Engineering video, which shows how the city removed and replaced two control gates for the River Walk without ever changing the water level. It’s a neat view both into the engineering of civil water infrastructure and into the practical considerations of how construction on these systems works. (Video credit: Practical Engineering)

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    Galloping Bubbles

    A buoyant bubble rises until it’s stopped by a wall. What happens, this video asks, if that wall vibrates up and down? If the vibration is large enough, the bubble loses its symmetry and starts to gallop along the wall. Using numerical simulations, the team determined the flow around the bubble. They also demonstrate several possible applications for this behavior: sorting bubbles by size, traversing mazes, and cleaning a surface. (Video and image credit: J. Guan et al.)

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    How CO2 Gets Into the Ocean

    Our oceans absorb large amounts of atmospheric carbon dioxide. Liquid water is quite good at dissolving carbon dioxide gas, which is why we have seltzer, beer, sodas, and other carbonated drinks. The larger the surface area between the atmosphere and the ocean, the more quickly carbon dioxide gets dissolved. So breaking waves — which trap lots of bubbles — are a major factor in this carbon exchange.

    This video shows off numerical simulations exploring how breaking waves and bubbly turbulence affect carbon getting into the ocean. The visualizations are gorgeous, and you can follow the problem from the large-scale (breaking waves) all the way down to the smallest scales (bubbles coalescing). (Video and image credit: S. Pirozzoli et al.)

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    A Pitcher Plant’s Rain-Triggered Trap

    Pitcher plants all use slippery rims and sticky digestive juices to capture and trap their insect prey. But two species of pitcher plant independently evolved an extra trap: a rain-activated springboard lid. Both the Seychelles pitcher plant and the slender pitcher plant — separated geographically by 6000 kilometers — have a springy, near-horizontal “lid” that sticks out over their pitcher. The underside of the surface is slippery, though less so than the pitcher’s lip and walls. Unsuspecting ants crawl under the lid, confident that they can keep their footing, and then — bang — a rain drop hits the springboard. That impact catapults the insect directly into the drink. There’s no escaping now.

    How did two widely separated, independently evolving plants both settle on this technique? Scientists think it was random chance. Pitcher plants are highly variable in their pitcher size, shape, and features. The scientists suggest that by trying lots of random combinations, these two species hit upon a particular arrangement that works really well for them. (Video and image credit: Science)

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