magnetohydrodynamics

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Earth is not the only planet in our solar system with auroras. As the solar wind—a stream of rarefied plasma from our sun—blows through the solar system, it interacts with the magnetic fields of other planets as well as our own. Saturn’s magnetic field second only to Jupiter’s in strength. This strong magnetosphere deflects many of the solar wind’s energetic particles, but, as on Earth, some of the particles get drawn in along Saturn’s magnetic field lines. These lines converge at the poles, where the high-energy particles interact with the gases in the upper reaches of Saturn’s atmosphere. As a result, Saturn, like Earth, has impressive and colorful light displays around its poles. (Image credit: ESA/Hubble, M. Kornmesser & L. Calçada, source video; via spaceplasma)

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Solar magnetohydrodynamics

The sun is a magnetohydrodynamics (MHD) system that is not well understood. It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating:

The first is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone. These waves travel upward and dissipate in the corona, depositing their energy in the ambient gas in the form of heat. The other is magnetic heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in the form of large solar flares and myriad similar but smaller events—nanoflares. Currently, it is unclear whether waves are an efficient heating mechanism.

The field of MHD was initiated by Hannes Alfvén, for which he received the Nobel Prize in Physics in 1970. He described the class of MHD waves now known as Alfvén waves. Observations show that all waves except Alfvén waves have been found to dissipate or refract before reaching the corona. Current research focus has therefore shifted towards flare heating mechanisms.

The magnetic filament above erupted on April 19, 2010. The black “hair-like object” is a speck of dust on the CCD camera.

Credit: SDO/AIA

During a solar flare, magnetic field lines on the sun are often visible due to the flow of plasma—charged particles—along the lines. According to theory, these magnetic lines should remain intact, but they are sometimes observed breaking and reconnecting with other lines. An interdisciplinary team of researchers suggests that turbulence may be the missing link. In their magnetohydrodynamic simulation, they found that the presence of chaotic turbulent motions made the magnetic line motion entirely unpredictable, whereas laminar flows behaved according to conventional flux-freezing theory. (Photo credit: NASA SDO; Research credit: G. Eyink et al.; via SpaceRef; submitted by jshoer)

MHD prospects is the place to find scientific papers about MHD propulsion and MHD power generation: Jean-Pierre Petit’s work on supersonic flight without shock wave by eletromagnetic force field.

Professional work overview in MHD Plasma physics and magnetohydrodynamics (MHD) MHD Power generation Coanda effect and air-breathing MHD accelerators

MHD aerodynes

MHD flow control and supersonic without shock wave
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Accretion Disks

Accretion flows are ubiquitous in astrophysics: they occur around protostars, accreting compact objects in binary systems, and supermassive black holes at the cores of galaxies. Much of professor James M. Stone's work has concerned studies of the local hydrodynamic and magnetohydrodynamics (MHD) processes that can lead to outward angular momentum transport in accretion disks. As computers become more powerful, previous studies of local patches of an accretion flow are being expanded into global studies that encompass the entire disk.

Accretion flows that cannot cool via emission of radiation become vertically thick and nearly spherical. Thus, they are intrinsically multidimensional. To study the structure and evolution of non-radiative accretion flows, 2D (axisymmetric) hydrodynamical simulations were performed using a non-uniform grid that spanned more than two decades in radius.

The most striking property of the flow is the large fluctuations produced by strong convection. Convective eddies transport a lot of mass both inwards and outwards, but the net mass accretion rate is very small and set by the properties of the flow near the inner boundary. A vanishingly small accretion rate may help to explain the deficit of high energy emission observed from accreting compact sources.

While understanding the properties of hydrodynamical accretion flows is important, it is generally agreed that angular momentum transport is in fact mediated by magnetic stresses. Thus, repeating the global simulations of non-radiative accretion flows with MHD calculations is vital.

Credit: James M. Stone

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New photographs showing ultra-fine structure in the sun's chromosphere and photosphere have been released. They offer a fascinating view into the magnetohydrodynamics of the sun, where the fluid behaviors of plasma are constantly modified by the sun’s magnetic field. The left image shows fine-scale magnetic loops rooted in the photosphere, while the right image shows our clearest photo yet of a sunspot. The dark central portion is the umbra, where magnetic field lines are almost vertical; it’s surrounded by the penumbra, where field lines are more inclined. Further out, we see the regular convective cell structure of the sun. (Photo credit: Big Bear Solar Observatory/NJIT; via io9 and cnet)

Jean-Pierre Petit (born 5 April 1937, Choisy-le-Roi) is a French scientist, senior researcher at National Center for Scientific Research (CNRS) as an astrophysicist in Marseille Observatory, now retired. His main working fields are fluid mechanics, kinetic theory of gases, plasma physics applied in magnetohydrodynamics power generation and propulsion as well as topology and astrophysics applied in cosmology. He is a pioneer in magnetohydrodynamics and has worked out the principle and techniques of parietal MHD converter. In cosmology, he worked on the bi-gravity theory.

Read the full paper at: http://www.scirp.org/journal/PaperInformation.aspx?PaperID=49656

DOI: 10.4236/jemaa.2014.610027 

Author(s)
Tzu H. Hsieh, Huan J. Keh

Affiliation(s)
Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan.
Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan.

ABSTRACT
The quasi-steady electromagnetophoretic motion of a spherical colloidal particle positioned at the center of a spherical cavity filled with a conducting fluid is analyzed at low Reynolds number. Under uniformly applied electric and magnetic fields, the electric current and magnetic flux density distributions are solved for the particle and fluid phases of arbitrary electric conductivities and magnetic permeabilities. Applying a generalized reciprocal theorem to the Stokes equations modified with the resulted Lorentz force density and considering the contribution of the magnetic Maxwell stress to the force exerted on the particle, which turns out to be important, we obtain a closed-form formula for the migration velocity of the particle valid for an arbitrary value of the particle-to-cavity radius ratio. The particle velocity in general decreases monotonically with an increase in this radius ratio, with an exception for the case of a particle with high electric conductivity and low magnetic permeability relative to the suspending fluid. The asymptotic behaviors of the boundary effect on the electromagnetophoretic force and mobility of the confined particle at small and large radius ratios are discussed. gjreww140916

KEYWORDS
Electromagnetophoresis, Magnetohydrodynamics, Lorentz Force, Colloid

Okay, so this is a pretty standard fan-SBURB adventure.

Only the game is called SMOON and the players are all werewolves (think Werewolf: The Forsaken, but without the spirit world).

The eight phases of the moon, and the symbol that accompanies them represent each wolf.
All of their lands have some connection to werewolf lore.
The key to winning is inside the moons of Prospit and Derse.

An epic of Ferocity and Philosophy, Rage and Instinct, Friendship and Kinship.

Wow.

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For a little Friday fun, enjoy this timelapse of magnetic putty consuming magnets. Really this is a bit of slow-motion magnetohydrodynamics. The magnet’s field exerts a force on the iron-containing putty, which, because it is a fluid, cannot resist deformation under a force. As a result, the putty will flow around the magnet, eventually coming to a stop once it reaches equilibrium, with its iron equally distributed around the magnet. Assuming the putty is homogeneously ferrous (i.e. the iron is mixed equally in the putty), that means the putty will stop moving when the magnet is at its center of mass.  (Video credit: J. Shanks; submitted by Neil K.)

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Solar Storms: 10 Hottest Facts
Our Sun is located 24-26,000 light years from the center of the Milky Way. It circles the galaxy every 225-250,000 years, at a speed of 220 kilometers per second. The sun is a medium size star, a Yellow Dwarf, G type main sequence. It’s about one million times the size of planet Earth. Core temperature:15,000,000 °C. Surface temperature: 5,500 °C. The sun emits a steady stream of charged particles, the solar wind, at 450 km per second. It increases in strength during active periods, every 11 years or so. Active periods are marked by an increase in sunspots. Sunspots are Earth-sized regions where intense magnetic fields prevent hot gas from reaching the surface, driving temperatures down to around 4,000°C. They often correspond to active regions. Where magnetic activity drives the formation of coronal loops, or prominences. Solar flares. And Solar tsunamis, technically “fast-mode magnetohydrodynamical waves.” In February 2009, the Stereo spacecraft detected one that rose to 100,000 km high, and raced outward at 250 kilometers per second. It was associated with an eruption of gas and magnetic fields called a coronal mass ejection. A CME can blast a billion tons of matter out at 10 to 12 million kilometers per hour. A CME sends a pulse of solar plasma to the limits of the solar system, where it can impact planets or spacecraft. We see its arrival in spectacular aurora. They form when solar particles rain down on Earth’s atmosphere, causing oxygen and nitrogen atoms to glow.

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Ferrofluids are known for their fascinating behaviors when subjected to magnetic fields, especially for the distinctive peaks they can form. In this video, we see a very thin ferrofluid drop on a pre-wetted surface just as a uniform perpendicular magnetic field is applied. Immediately the droplet breaks up into tiny isolated peaks that migrate out to the circumference. The interface breaks down from center, where the drop height is largest, and moves outward. Simultaneously, the diffusion of ferrofluid from the circumferential droplets into the surrounding fluid lowers the magnetization of those droplets, making it more difficult for them to repel their neighbors. As a result, they drift outward more slowly and get caught by the faster-moving droplets from within. (Video credit: C. Chen)

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Last night marked the 2013 Ig Nobel Prize Award Ceremony, in which researchers are honored for work that “makes people LAUGH and then THINK”. Historically, the field of fluid dynamics has been well-represented at the Ig Nobels with some 13 winners across the fields of Physics, Chemistry, Mathematics, and—yes—Fluid Dynamics since the awards were introduced in 1991. This is in stark contrast to the awards’ more famous cousins, the Nobel Prizes.

Since the introduction of the Nobel Prize in 1901, only two of the Physics prizes have been fluids-related: the 1970 prize for discoveries in magnetohydrodynamics and the 1996 prize for the discovery of superfluidity in helium-3. Lord Rayleigh (a physicist whose name shows up here a lot) won a Nobel Prize in 1904, but not for his work in fluid dynamics. Another well-known Nobel laureate, Werner Heisenberg, actually began his career in fluid dynamics but quickly left it behind after his doctoral dissertation: “On the stability and turbulence of fluid flow.”

This is not to suggest that no fluid dynamicist has done work worthy of a Nobel Prize. Ludwig Prandtl, for example, revolutionized fluid dynamics with the concept of the boundary layer (pdf) in 1904 but never received the Nobel Prize for it, perhaps because the committee shied from giving the award for an achievement in classical physics. General consensus among fluid dynamicists is that anyone who can prove a solution for turbulence using the Navier-Stokes equation will likely receive a Nobel Prize in addition to a Millennium Prize. In the meantime, we carry on investigating fluids not for the chance at glory, but for the joy and beauty of the subject. (Image credits: Improbable Research and Wikipedia)

A droplet of glycerol coalescing in silicone oil while subjected to strong electric fields exhibits a whip-like instability reminiscent of fireworks. Check out videos of the phenomenon or see the paper for more information. Happy Independence Day to our American readers!

For more fun, holiday-themed high-speed video, check out PopSci’s fireworks videos.

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The auroras at Earth’s poles are much more than pretty lights. This video explains their formation; fluid mechanics (specifically magnetohydrodynamics) play a major role in the convective transport of heat inside the sun as well as the movement of the plasma that makes up a solar storm that interacts with Earth’s magnetic field and produces the auroras.