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Search results for: “waves”

  • Predicting Meteotsunamis

    Predicting Meteotsunamis

    Meteotsunamis, or meteorological tsunamis, are large waves driven by weather rather than seismic energy. Although they occur along shorelines throughout the world, forecasters have very little infrastructure in place to predict or detect them. But a new study of an April 2018 meteotsunami on Lake Michigan (pictured above) has provided evidence that existing models may be able to forecast these events.

    The Lake Michigan meteotsunami was driven by an atmospheric gravity wave, which carried with it a substantial pressure drop. Most of the time such waves travel faster or slower than water waves, and there is little to no interaction. But on this day, the atmospheric wave and the water waves were traveling at the same speed in the same direction, creating a resonance that strengthened the water wave.

    Using existing National Oceanic and Atmospheric Administration (NOAA) models, researchers were able to reconstruct the event digitally, with results that agreed well with observations. That success means that forecasters may be able to predict the events ahead of time, potentially saving lives. (Image credit: D. Maglothin; research credit: E. Anderson and G. Mann; via Gizmodo)

  • Snail Locomotion

    Snail Locomotion

    Snails and other gastropods move using their single muscular foot and a viscoelastic fluid they secrete. Muscular waves in the foot run from tail to head and are transmitted to the ground through the thin, sticky mucus layer without the snail ever fully detaching from the surface. The characteristics of this mucus layer are critical to the snail’s locomotion. As a movement cycle begins, the mucus behaves like an elastic solid. As the muscular wave approaches, it shears the fluid, increasing its stress and ultimately reaching the yield point, where the gel begins to flow. Once the wave passes, the mucus quickly transitions back to its elastic solid behavior. The net result of each cycle is an asymmetric force that propels the snail forward while keeping it adhered to whatever surface it’s crawling on.

    Many animals rely on similarly complex fluids to move, attack prey, defend against predators, or enable their reproduction. Check out this review article for more examples. (Image credit: A. Perry; see also P. Rühs et al.; submitted by Pascal B.)

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    Underwater Explosions and Submarines

    In the early days of submarines, it did not take physicists and engineers long to discover how destructive underwater explosions can be. In this Slow Mo Guys video, Gav gives us a glimpse of that destruction using a model submarine in a fish tank and several small explosives. You’ll have to be quick to notice the initial shock waves that ripple through the tank, but the footage captures spectacular detail on some of the slower-moving phenomena. You can see the uneven ripples of the explosion bubble’s surface as it expands. There are some great shots from the front and side showing the bubbly vortex ring that forms when the explosion hits the side of the tank wall (something that wouldn’t happen out in the ocean, of course). You can even catch a glimpse of some unexploded powder streaking out of the explosion. (Image and video credit: The Slow Mo Guys)

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    Kelvin Wakes

    Whether you’re watching ducks cruise by on a pond or a boat making its way across the ocean, you’ve probably noticed a distinctive V-shaped wake. This shape is known as a Kelvin wake, and it forms because waves in water don’t all move at the same speed. Instead, the speed a wave travels at depends on its wavelength; smaller wavelengths travel slower than larger ones, a phenomenon known as dispersion. The characteristic shape of a Kelvin wake is the result of many waves of different wavelength (and therefore speed) added together. (Video and image credit: Minute Physics)

  • Acidic Sea Spray

    Acidic Sea Spray

    As waves crash and break, they generate a spray of droplets — known as aerosols — that make their way into the atmosphere. Researchers investigated the chemistry of these aerosol droplets by generating spray in a wave tank filled with ocean water. They found that aerosol droplets are far more acidic than the ocean they come from, and the smaller the droplet, the more acidic it is. This acidification happens in a matter of minutes, as acidic gases interact with the spray. Their findings will be critical for accurately modeling the climate connections between our oceans and atmosphere. (Image credit: Elle; research credit: K. Angle et al.; via OceanBites; submitted by Kam-Yung Soh)

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    Coastal Erosion

    The same dynamic forces that make coastlines fascinating create perennial headaches for engineers trying to maintain coastlines against erosion. This Practical Engineering video discusses some of the challenges of coastal erosion and how engineers counter them.

    In a completely undeveloped coastline, waves and storms erode the shoreline while rivers and currents replenish sand through sedimentation. Manmade structures tend to strengthen erosion processes while disrupting the sedimentation that would normally counter it. Beach nourishment — where sand gets dredged up and deposited on a beach — is an engineered attempt to replace natural sedimentation.

    Dunes, mangrove forests, and wetlands are all nature’s way of protecting and maintaining coastlines. We engineers are still learning how to both utilize and protect shorelines. (Image and video credit: Practical Engineering)

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    Breaking Bubbles

    What do a nineteenth-century war ship, a sardine-hunting shark, and a viral bottle trick have in common? Cavitation! The phenomenon of cavitation occurs when a fluid is accelerated such that its local pressure drops below the vapor pressure. As a result, bubbles form and then violently collapse, creating shock waves that can damage nearby surfaces or stun prey. Dianna explains — and reveals some cool historical context that was new to me! — in the video above. (Image and video credit: Physics Girl)

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    Slow Mo Pulse Jet Engine

    Pulse jet engines rely on their shape to maintain combustion without moving parts. The pressure waves that travel through the engine pump fresh oxygen into the combustion chamber and then ignite it with exhaust remaining from the last cycle. In this Slow Mo Guys video, we get to see that process in action. It’s a pretty neat view of combustion in a working engine, but these guys are definitely not going to win any awards for safety measures. Seriously, don’t try this at home! (Image and video credit: The Slow Mo Guys)

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    Seismic Events Reveal Ocean Temperatures

    Decades ago, researchers proposed sending sound waves through the ocean to measure its temperature. Although the technique worked, it ran into noise pollution issues, but now it’s back, using naturally-occurring seismic events as the sound source.

    When fault lines shift, they generate seismic waves that travel through the ocean as sound. When they reach a land mass, the waves get converted back into seismic energy that’s then picked up by a receiver. Knowing the distance from the source to the receiver and the time necessary for the wave to travel, scientists can then determine the average temperature of the water based on the speed of sound.

    The technique can track temperature changes down to thousandths of a degree. Based on more than a decade of seismic data from the Indian Ocean, researchers found almost double the temperature increase measured by a different sensor network. (Image and video credit: Science; research credit: W. Wu et al.; submitted by Kam-Yung Soh)

  • Jets Beneath Leidenfrost Drops

    Jets Beneath Leidenfrost Drops

    When a droplet impacts, it’s not unusual for converging ripples to form an upward jet, like the one seen here. But under the right circumstances, jets can form downward, too. This study looks at the ultrafast jets that can form beneath an impacting Leidenfrost drop.

    These Leidenfrost drops are striking a surface much hotter than their boiling point, so a large vapor cavity forms quickly beneath them. Using x-ray imaging, the researchers were able to capture the dynamics of this cavity’s formation and collapse (Image 2). The field of view in the animation shows only a portion of the drop’s cavity, so Image 3 may help you orient relative to the drop at large.

    Initially, we see the center of the droplet hitting the surface, followed by the fast growth of a vapor cavity. Rippling capillary waves converge on top of the cavity, creating a pinch-off. From there, a bubble rises up while a fast jet shoots downward. (Image credit: water jet – A. Min, others – S. Lee et al.; research credit: S. Lee et al.)

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