FYFD

Tag: fluid dynamics

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    Dissolution and Crystallization

    A colorful assortment of salts dissolve and recrystallize in this microscopic timelapse video by retired engineer Jay McClellan. Every step is a gorgeous rainbow of color as the cobalt, copper, and sodium chlorides dissolve, mix, and change. Though we don’t see what’s going on in the water, fluid dynamics are a critical component of both dissolution and crystallization. In the former, concentration gradients change the water’s density, driving buoyant flows. For the latter, crystallization comes out of evaporation, where surface tension often determines where solid particles get left behind. (Video and image credit: J. McClellan; via Colossal)

  • Flettner Rotors Spin Anew

    Flettner Rotors Spin Anew

    In the 1920s, the world saw a new sort of marine propulsion, ships with one or more tall, smokeless cylinders. These Flettner rotors, named for their inventor, would spin in the wind, generating lift to propel the boat, much as a sail would. (The difference is that the rotor uses the Magnus effect.)

    The market crash that kicked off the Great Depression spelled an end to the rotorship, but the idea is getting revived as industries search for greener forms of ship propulsion. Although the Flettner rotor still uses fuel (to spin the rotor), it can complete a voyage on only a small fraction of the fuel needed for conventional propulsion. (Image credit: Getty Images; via PopSci)

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    The Forces on an Arch Dam

    Although they’re iconic, arch dams like the Hoover Dam are relatively unusual. In this Practical Engineering video, Grady looks at the forces a dam needs to withstand and where and why an arch dam is useful. It’s a good reminder that even water that (for the most part) isn’t moving is still a challenge to deal with. (Video and image credit: Practical Engineering)

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  • Predicting Sea States

    Predicting Sea States

    Transferring cargo between ships and landing aircraft on carriers requires predicting how the waves will behave for the next few minutes. That’s a notoriously difficult task for several reasons: rough seas can hide a ship radar’s view and the inherent nonlinearity of ocean waves means that they can occasionally coalesce unexpectedly large (“rogue“) waves, seemingly from nowhere.

    A new study describes a technique for improving sea state predictions. In their model, the team first use multiple radar returns to average out gaps in the current wave state data, then feed that interpolated data into a prediction algorithm that includes nonlinearities up to the third-order. The results, they found, gave far better predictions than current techniques, some of which had errors 3 times as high. (Image credit: R. Ding; research credit: J. Yao et al.; via APS News)

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  • Zoom Into the Sun

    Zoom Into the Sun

    Fall into our nearest star in this gorgeous high-resolution view of the Sun. Taken by Solar Orbiter, a joint NASA-ESA mission, the image stretches from the fiery photosphere — full of filaments and prominences — to the wispy yet unbelievably hot corona. It’s well worth clicking through to zoom in and around the full size image. (Image credit: ESA & NASA/Solar Orbiter/EUI Team, E. Kraaikamp; via Gizmodo)

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  • Icelandia

    Icelandia

    Photographer Rosita Dimitrova describes Iceland as “an absolute heaven” for aerial photography like this featured image. This plethora of images from Dimitrova and fellow IAPOTY finalists backs up that sentiment. The landscape wears its influences openly; it is shaped by water, ice, wind, and lava into stunning abstract shapes like these. (Image credit: Various/IAPOTY; via Colossal)

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  • Watch Hagfish Slime Unfurl

    Watch Hagfish Slime Unfurl

    The eel-like hagfish has one of the best defenses in the ocean. When threatened, it releases a slime that clogs the gills of its predator but allows the hagfish itself to slough off the slime and escape. The hagfish slime’s secret weapon is long protein threads, which are initially rolled into bundles called skeins. Seen above, these skeins resemble the yarn skeins knitters and crocheters buy, but a hagfish’s skeins are only as big as the width of a human hair.

    When water flows by quickly enough, the thread in a skein begins to unwind and stretch out. With enough threads unwound, the slime gets stretchy and viscous. Researchers found that it takes relatively little flow to begin this unwinding because the adhesion between threads and the surrounding fluid is higher than the thread-to-thread sticking power. (Research and image credit: M. Hossain et al., video)

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  • Martian Polar Spiral

    Martian Polar Spiral

    The North Pole of Mars is a raised spiral, and each winter a new layer, roughly a meter thick, of carbon dioxide ice gets deposited over it. Strong cold winds rush down from the center of the pole. Mars’s spin creates a Coriolis effect that makes the winds spiral out as they descend. When they cross a depression in the surface, it creates a vortex that erodes the depression deeper. As the depressions deepen and merge, they form the troughs seen here. For more, see this post. (Image credit: ESA/DLR/FU Berlin; NASA MGS MOLA Science Team; via APOD)

  • Tracing the Origins of Ocean Waters

    Tracing the Origins of Ocean Waters

    The Sub-Antarctic Mode Waters (SAMW) lie in the southern Indian Ocean and the east and central Pacific Ocean, where they serve as an important sink for both heat and carbon dioxide. Scientists have long debated the origins of the SAMW’s waters, and a new study may have an answer.

    Researchers combined data from ocean observations with a model of the Southern Ocean to essentially trace the SAMW’s ingredients back to their respective origins. The results showed that about 70% of the Indian Ocean’s SAMWs came from subtropical waters, but those waters contributed to only about 40% of the Pacific’s SAMWs. Pacific SAMWs had their largest contributions from upwelling circumpolar waters.

    Understanding where a SAMW’s waters came from helps scientists predict how those waters will mix and how much heat and carbon they can absorb. (Image credit: NASA; research credit: B. Fernández Castro et al.; via Eos)

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    What Limits a Siphon

    Siphons are a bit mind-boggling for anyone who has internalized the idea that water always flows downhill. But gravity actually allows a siphon’s water to flow up and over an obstacle, provided certain conditions are met. Steve Mould digs into the details of those conditions in this video, where he searches for the maximum height a siphon can reach.

    A quick note on terminology: Steve explains that the siphon breaks when water near the top starts “boiling.” Other sources may use the term “cavitating” for this sudden phase change. There’s not–to my knowledge–a generally-agreed-upon definition that clearly distinguishes between boiling and cavitation in this situation. Whichever term you use, the water in the siphon doesn’t care; either way, it’s experiencing a local pressure that’s so low that it switches from a liquid state (where it can resist tensile forces) to a gaseous one (where it cannot resist tension). (Video and image credit: S. Mould)

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