FYFD

Category: Phenomena

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    Testing Structures Against Hurricane Storm Surge

    When hurricanes hit coasts, they bring with them incredible storm surge, which puts buildings right in the middle of ocean waves. To understand how to better protect against those conditions, engineers use facilities like the Directional Wave Basin to create smaller-scale versions of hurricanes. In this Practical Engineering video, Grady visited during a test that compared two identical one-third-scale houses subjected to the same storm conditions–except that one house had an additional foot (3ft at real-scale) of elevation. The results are pretty spectacular.

    This isn’t a short video, but it’s well-worth a watch. I think Grady does a great job of explaining why engineers need (admittedly) expensive facilities like this one to help guide both engineering and regulatory decisions. (Video and image credit: Practical Engineering)

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    Drag Reduction Via Bubbles

    To help reduce greenhouse emissions, businesses are exploring systems that reduce a container ship’s drag by releasing bubbles beneath them. But how do bubbles reduce drag? To find out, researchers simulated a bubbly flow that mimics the underside of a moving ship. By playing with the balance between inertial forces, buoyancy, and surface tension, they were able to sweep through conditions that the bubbles could experience.

    The best performance comes when bubbles stick together and coat the entire underside of the surface. In that case, they measured a nearly 40% reduction in the drag. But other conditions were not so fortuitous; in fact, with poorly chosen conditions, adding bubbles could actually increase the drag. (Video and image credit: S. Di Georgio et al.)

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    When the Meniscus Disappears

    When we first learn about states of matter, we’re taught about three: solid, liquid, and gas. In a solid, atoms are held close to one another–typically, but not always, in an orderly lattice structure. In liquids and gases, atoms are free to slip, slide, bounce, and move. So what really separates a liquid from a gas?

    Animation of liquid and gaseous carbon dioxide reaching the supercritical phase.

    That’s the question at the heart of this video by Steve Mould, in which he explores a weird fourth phase of matter: supercritical fluids. This phase has the diffusive properties of a gas and the solvent properties of a liquid–without really being either one.(Video and image credit: S. Mould)

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    Swirling Without Blades

    A ring of hydrogen bubbles rises, rotating clockwise, in this video of electrolysis. But there are no fan blades to cause this swirl, so why do the bubbles rotate? The answer is a Lorentz force induced by the electromagnetic set-up of the experiment. Watch to see how researchers manipulate the Lorentz force to affect the flow. (Video and image credit: Y. Cho et al.)

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    Understanding Schlieren

    Schlieren techniques are one of my favorite forms of flow visualization. They cleverly make the invisible visible through an optical set-up that’s sensitive to changes in density. They’re great–as seen in the examples here–for seeing local buoyant flows like the plumes that rise from a candle, or for making gases like carbon dioxide visible. They’re also excellent for visualizing shock waves.

    In this video, physicist David Jackson explains how one particular flavor of schlieren–one using a spherical mirror–works. There are lots of other possible schlieren set-ups, too, though each one has its quirks. (Video and image credit: All Things Physics; submitted by David J.)

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    Connecting Canals

    Before the rise of railroads, canals provided critical commercial shipping infrastructure for many locations worldwide. But connecting canals at different elevations required locks–sometimes a whole series of them–as in the case of Scotland’s Union Canal and the Forth and Clyde Canal. In the canals’ heyday, navigating the 11 locks between them took the better part of a day–one of many reasons that canals fell out of use over time.

    When Scotland decided to reconnect the canals in the 1990s, they picked a very different solution for this elevation challenge: the Falkirk Wheel. Grady walks us through the clever engineering of this impressive piece of infrastructure in this Practical Engineering video. (Video and image credit: Practical Engineering)

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  • Inside Cepheid Variable Stars

    Inside Cepheid Variable Stars

    Cepheid variable stars pulsate in brightness over regular periods. That’s one reason astronomers use them as a standard candle to judge distances–even for stars well outside our galaxy. In this image, researchers display a simulation of convection inside a Cepheid eight times more massive than our sun. The colors represent vorticity, with zero vorticity in white.(Image credit: M. Stuck and J. Pratt)

    A research poster showing a simulation of convection inside a Cepheid variable star with 8 solar masses.
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    Recreating Atmospheric Rivers

    During the winter months, those of us living in the mid-latitudes sometimes experience atmospheric rivers. Formed from the interaction of cold winter storms with warm, moist tropical air, atmospheric rivers can deliver intense rainfall across long distances. In this video, the UCLA SpinLab team shows how you can recreate the effect with a relatively simple and affordable DIYnamics apparatus. (Video and image credit: UCLA SpinLab)

  • Sprites and ELVES

    Sprites and ELVES

    Although we are most familiar with the white, branching lightning caused by electrical discharge between clouds and the ground, there are many types of lightning. This fortuitous image captures two: tentacled red sprites and ring-like ELVES. Sprites extend upward from the top of a thunderstorm, in a large but weak flash that lasts only seconds. ELVES appear as a rapidly-expanding disc, thought to be caused by an energetic electromagnetic pulse moving into the ionosphere. They were first discovered in footage from a 1992 Space Shuttle mission. (Image credit: V. Binotto; via APOD)

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  • “Broken Water, Like Broken Glass”

    “Broken Water, Like Broken Glass”

    How can you break water? By accelerating it so quickly that the pressure drop forms cavitation bubbles. Here, a steel piston rests against a transparent plate, all underwater. When a hammer strike accelerates the piston away at around 1000g, the severe pressure drop tears the water into bubbles (bottom, left). As the bubbles expand, the nearby piston squishes them into pancakes (bottom, center). As they continue growing, the bubbles press into one another, squeezing thin ridges of water between them. The result (center) resembles broken glass. (Image credit: J. da Silva et al.)

    A research poster showing cavitation in water between a plate and piston.
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