FYFD

Tag: numerical simulation

  • A Fluidic Space Telescope

    A Fluidic Space Telescope

    A telescope’s resolution is set by the size of its reflective surface. Our largest space telescope, JWST, has a 6.5-meter reflector, the largest we could manage given manufacturing constraints and the need to launch it in a rocket. To reach even larger sizes, researchers are considering a new type of reflector: one made of liquid.

    A fluidic telescope has some obvious advantages: surface tension makes it atomically smooth, and liquids can be packed into any convenient shape for launch. But there are challenges, also. Like, what happens to the reflector when you point it in an new direction?

    That’s what this study looks at, mathematically. Using a mathematical model of a 50-meter-wide, millimeter-thick fluid, the researchers analyzed how different maneuvers over the telescope’s lifetime would affect the image quality.

    Shifting the reflector creates perturbations in the surface, initially at the mirror’s edges. Over time, those perturbations move toward the center of the mirror and, at the same time, decay. The team found that, while typical space telescope operations distorted parts of the mirror beyond the limits of good optical quality, the inner 80% of the mirror could remain undisturbed for twenty or more years. That would be like having a 40-meter telescope in orbit with more than 6x the resolution of JWST. (Image credit: NASA; research credit: I. Gabay et al.)

    An artist's conception of a fluidic space telescope, made with a liquid reflecting surface tens of meters wide.
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  • On Dolphin Turbulence

    On Dolphin Turbulence

    Dolphins are such fast and agile swimmers that, naturally, scientists have long wanted to understand how they swim so well. A recent study draws on numerical simulation to analyze the flow a dolphin creates when flapping its tail.

    The resulting flow is highly turbulent–researchers were only able to simulate up to a fraction of a dolphin’s actual Reynolds number–with both large-scale vortices and a cascade of smaller ones. The largest vortices, shown here in white, form on the upper and lower surface of the dolphin’s tail, then slide off the tail in a vortex ring. It’s these vortex rings, the researchers found, that provide the bulk of a dolphin’s thrust.

    The smaller-scale vortices, in contrast, get formed by the large vortices, and they make little to no contribution to the dolphin’s propulsion. Interestingly, these results suggest that we might be able to describe the propulsion of dolphins and other highly turbulent swimmers by focusing only on the largest scales in the flow. (Video, image, and research credit: Y. Motoori et al.; via Ars Technica)

    Animation of the simulated flow from a swimming dolphin.
    Animation of the simulated flow from a swimming dolphin.
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  • Understanding Pollen Dispersal

    Understanding Pollen Dispersal

    When the wind blows, trees shift and sway, reconfiguring their shape and their leaves in response. For parts of the year, that flow can also pluck pollen grains off the tree, carrying them on the winds. A new computational simulation models this pollen dispersal from a tree, with the aim of eventually integrating into a tool for urban planners.

    Trees are an important component to fighting climate change, especially in cities, because they cool their surroundings in addition to providing fresh oxygen. But urban planners recognize the downsides to trees, too–allergies, anyone?–and, with the right tools, they could maximize the trees’ advantages while minimizing pollen spread for allergy-sufferers. (Image credit: M. Köles; research credit: T. Dbouk et al.; via Physics World)

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    Schooling at Scale

    Relatively simple visual and hydrodynamic signals are enough to make digital fish school in ways that resemble living ones. Here, researchers look at what happens when well-behaved schools of fish get too big. The researchers first demonstrate that their schools behave reasonably at one hundred members, either in a schooling configuration or a group milling around a central region.

    At one thousand fish, the schools are still reasonably coherent and sensible. But at fifty thousand fish, the picture is drastically different. Neither schooling nor milling groups are able to remain together. They fracture and scatter into smaller groupings. (Video and image credit: H. Hang et al.)

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  • Richtmyer-Meshkov Instability

    Richtmyer-Meshkov Instability

    If you send a shock wave through a magnetized plasma–something that happens in both supernova explosions and inertial confinement fusion–it can trigger an instability known as the Richtmyer-Meshkov instability. The image above shows a form of this, taken from a simulation. Rather than treating the plasma as a single idealized fluid, the researchers represented it as two fluids: an ion fluid and an electron fluid. This allowed them to better capture what happens when certain components of the plasma react to changes faster than others do.

    The image itself shows the electron number density across the fluid, where darker colors represent higher electron number density. The interface between high and low-densities shows a roll-up instability that resembles the Kelvin-Helmholtz instability, but there are also regions of mushroom-like plumes that more closely resemble Rayleigh-Taylor instabilities.

    The authors note that these structures don’t appear in simulations that represent a plasma as a single fluid; you need the two-fluid representation to see them. (Image and research credit: O. Thompson et al.)

  • Improving Turbulence Models

    Improving Turbulence Models

    Calculating turbulent flows like those found in the ocean and atmosphere is extremely expensive computationally. That’s why forecasting models use techniques like Large Eddy Simulation (LES), where large physical scales are calculated according to the governing physical equations while smaller scales are approximated with mathematical models. Researchers are always looking for ways to improve these models–making them more physically accurate, easier to compute, and more computationally stable.

    In a new study, researchers used an equation-discovery tool to find new improvements to these models for the smaller turbulent scales. They started by doing a full, computationally expensive calculation of the turbulent flow. The equation-discovery tool then analyzed these results, looking to match them to a library of over 900 possible equations. When it found a form that fit the data, the researchers were then able to show analytically how to derive that equation from the underlying physics. The result is a new equation that models these smaller scales in a way that’s physically accurate and computationally stable, offering possibilities for better LES. (Image credit: CasSa Paintings; research credit: K. Jakhar et al.; via APS)

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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.)

  • Icy or Rocky Giants?

    Icy or Rocky Giants?

    On the outskirts of our solar system, two enigmatic giants loom: Uranus and Neptune. In terms of mass and size, both resemble many of the exoplanets discovered in recent years. Within our own solar system, these planets are known as “icy giants,” but a new study suggests that moniker may be wrong.

    Pinning down the interior composition of a planet is tough on limited measurements. In the case of these outer planets, our main data is gravitational, recorded from visiting spacecraft. That information cannot tell us directly what the composition of a planet is, but it gives constraints for what materials could produce such a gravitational field.

    Hubble images of Uranus (left) and Neptune (right).

    In their simulation, researchers began with random interior configurations for Uranus and Neptune, then had the model iterate through configurations to simultaneously match the gravitational measurements while satisfying the thermodynamic and physical constraints of a stable planet. By repeating the process several times, the researchers created a catalog of potential interiors for Uranus and Neptune. And while some were water-rich–consistent with the “icy giant” title–others were remarkably rocky.

    The team suggests that we may need to retire that moniker and consider the possibility that these worlds are more like our own than we thought. To find out which is true, we will need more spacecraft to visit our frigid neighbors, to provide new gravitational measurements and other observations. (Image credit: NASA/ESA/A. Simon/M. Wong/A. Hsu; research credit: R. Morf and L. Helled; via Physics World)

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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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  • Thermal Tides Drive Venusian Winds

    Thermal Tides Drive Venusian Winds

    Venus is a world of extremes. A full rotation of the world takes 243 Earth days, but winds race around the planet at a speed that makes a Category 5 hurricane look sedate. Just what drives these winds has been an ongoing question for planetary scientists. A recent study suggests that tides are a major contributor to this superrotation.

    Unlike Earth’s tides, Venus’s are not gravitational in origin. Instead, Venusian tides are thermal, driven by heating in the sunward side of the atmosphere. This creates a diurnal tide, which cycles once per Venusian day and pumps momentum toward the tops of Venus’s clouds. The new analysis–rooted in both observations and numerical simulation–finds that diurnal tides are the primary driver behind the planet’s incredibly fast winds. (Image credit: NASA/JPL-Caltech; research credit: D. Lai et al.; via Eos)

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