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  • 1
    Electronic Resource
    Electronic Resource
    MAGNETOHYDRODYNAMICS IN MATERIALS PROCESSING (1999)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 31 (1999), S. 273-300 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Magnetic fields can be used to melt, pump, stir, and stabilize liquid metals. This provides a nonintrusive means of controlling the flow of metal in commercial casting and refining operations. The quest for greater efficiency and more control in the production of steel, aluminum, and high-performance superalloys has led to a revolution in the application of magnetohydrodynamics (MHD) to process metallurgy. Three typical applications are described here, chosen partially on the basis of their general interest to fluid dynamicists, and partially because of their considerable industrial importance. We look first at magnetic stirring, where a rotating magnetic field is used to agitate and homogenize the liquid zone of a partially-solidified ingot. This is a study in Ekman pumping. Next, we consider magnetic damping, where an intense, static magnetic field is used to suppress fluid motion. In particular, we look at the damping of jets, vortices, and turbulence. We conclude with a discussion of the magnetic destabilization of liquid-liquid interfaces. This is of particular importance in aluminum production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fluid.31.1.273
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Unstable breakup of a linearly accelerated, dense plasma (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1237-1246 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A dense plasma, accelerated by magnetic pressure, is used in an electromagnetic launcher to propel small masses. Such plasmas have been observed to disperse or fragment, and this has been related to a loss of projectile acceleration. We are concerned here with the potential mechanisms of plasma breakup, and with the associated limitations on projectile velocity. An unsteady, one-dimensional model of the plasma is described, which incorporates a simple correction for the effect of wall ablation. Two limiting cases are examined, one where ablation is small, and another where it is large. For the first of these cases, we show that a reduction in magnetic pressure will induce a decelerating body force at the tail of the plasma. It is shown that, if this force is generated on a time scale comparable with the dynamic relaxation time of the plasma, it is accompanied by a substantial reduction in plasma density. To the extent that this results in a loss of plasma conductivity, such a force reversal could lead to the formation of multiple current paths. For the second case, we show that a high level of ablation results in the formation of a parasitic current sheet at the tail of the plasma. Again, this is accompanied by a local deceleration of the tail. It is a matter of debate as to whether or not this leads to fragmentation of the plasma. However, irrespective of whether breakup occurs, the formation of such a current sheet imposes an upper limit on the achievable projectile velocity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347309
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  • 3
    Electronic Resource
    Electronic Resource
    The importance of secondary flow in the rotary electromagnetic stirring of steel during continuous casting (1987)
    Springer
    Flow, turbulence and combustion 44 (1987), S. 241-259 
    Details
    ISSN: 1573-1987
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper considers some aspects of the flow generated in a circular strand by a rotary electromagnetic stirrer. A review is given of one-dimensional models of stirring in which the axial variation in the stirring force is ignored. In these models the magnetic body force is balanced by shear, all the inertial forces being zero (except for the centripetal acceleration). In practice, the magnetic torque occurs only over a relatively short length of the strand. The effect of this axial dependence in driving force is an axial variation in swirl, which in turn drives a secondary poloidal flow. Dimensional analysis shows that the poloidal motion is as strong as the primary swirl flow. The principle force balance in the forced region is now between the magnetic body force and inertial. The secondary flow sweeps the angular momentum out of the forced region, so that the forced vortex penetrates some distance from the magnetic stirrer. The length of the recirculating eddy is controlled by wall shear. This acts, predominantly in the unforced region, to diffuse and dissipate the angular momentum and energy created by the body force.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00412016
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  • 4
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    Proton-neutron multiplet states and isomers in the odd-odd nucleus I122 (2019)
    American Physical Society
    Details
    Publication Date: 2019-08-13
    Print ISSN: 2469-9985
    Electronic ISSN: 2469-9993
    Topics: Physics
    Published by American Physical Society
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  • 5
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    Near-field investigation of turbulence produced by multi-scale grids (2012)
    American Institute of Physics
    Details
    Publication Date: 2012-03-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 6
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    A simple model for the streamwise fluctuations in the log-law region of a boundary layer (2009)
    American Institute of Physics
    Details
    Publication Date: 2009-05-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 7
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    Identifying Turbulent Energy Distributions in Real, Rather than Fourier, Space (2005)
    American Physical Society
    Details
    Publication Date: 2005-11-14
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 8
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    Scaling laws for planetary dynamos (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-10
    Description: We propose new scaling laws for the properties of planetary dynamos. In particular, the Rossby number, the magnetic Reynolds number, the ratio of magnetic to kinetic energy, the Ohmic dissipation timescale and the characteristic aspect ratio of the columnar convection cells are all predicted to be power-law functions of two observable quantities: the magnetic dipole moment and the planetary rotation rate. The resulting scaling laws constitute a somewhat modified version of the scalings proposed by Christensen and Aubert. The main difference is that, in view of the small value of the Rossby number in planetary cores, we insist that the non-linear inertial term, ${\boldsymbol u} \cdot \nabla {\boldsymbol u}$ , is negligible. This changes the exponents in the power-laws which relate the various properties of the fluid dynamo to the planetary dipole moment and rotation rate. Our scaling laws are consistent with the available numerical evidence.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
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    Dynamos driven by helical waves: scaling laws for numerical dynamos and for the planets (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-11
    Description: We derive scaling relationships for planetary dynamos based on a balance between energy production and Joule dissipation, and between the curl of the buoyancy and Coriolis forces. These scaling relationships are deduced for the particular case of dynamos driven by helical waves, but are shown to have a much broader applicability. They are consistent with the evidence of the numerical dynamos, yielding predictions consistent with published empirical scaling laws and also with the observed transition from dipolar to multipolar dynamos. A direct comparison with the observational evidence for the planets is hampered by the fact that we do not know what sets the smallest scale of the motion in the planets. Nevertheless, we use our scaling relationships to show that the traditional assumption that the Elsasser number is of order unity is inconsistent with the observation that the gas-giant dynamos are dipolar dynamos, as is the more recent suggestion that the strength of the dipole is independent of rotation rate and controlled by the buoyancy flux alone. On the other hand, we show that the observational data is consistent with the hypothesis that a dipolar dynamo saturates at the lowest permissible magnetic energy compatible with a given buoyancy flux.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
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    Planetary dynamos driven by helical waves - II (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-12
    Description: In most numerical simulations of the Earth's core the dynamo resides outside the tangent cylinder and may be crudely classified as being of the α 2 type. In this region the flow comprises a sea of thin columnar vortices aligned with the rotation axis, taking the form of alternating cyclones and anticyclones. The dynamo is thought to be driven by these columnar vortices within which the flow is observed to be highly helical, helicity being a crucial ingredient of planetary dynamos. As noted in Davidson, one of the mysteries of this dynamo cartoon is the origin of the helicity, which is observed to be positive in the south and negative in the north. While Ekman pumping at the mantle can induce helicity in some of the overly viscous numerical simulations, it is extremely unlikely to be a significant source within planets. In this paper we return to the suggestion of Davidson that the helicity observed in the less viscous simulations owes its existence to helical wave packets, launched in and around the equatorial plane where the buoyancy flux is observed to be strong. Here we show that such wave packets act as a potent source of planetary helicity, constituting a simple, robust mechanism that yields the correct sign for h north and south of the equator. Since such a mechanism does not rely on the presence of a mantle, it can operate within both the Earth and the gas giants. Moreover, our numerical simulations show that helical wave packets dispersing from the equator produce a random sea of thin, columnar cyclone/anticyclone pairs, very like those observed in the more strongly forced dynamo simulations. We examine the local dynamics of helical wave packets dispersing from the equatorial regions, as well as the overall nature of an α 2 -dynamo driven by such wave packets. Our local analysis predicts the mean emf induced by helical waves, an analysis that rests on a number of simple approximations which are consistent with our numerical experiments, while our global analysis yields exact integral relationships between the mean emf induced by the wave packets and the large-scale dipole and azimuthal field. Combining these local and integral equations yields a kinematic model for an α 2 -dynamo driven by helical waves. Order-of-magnitude estimates based on these equations suggest that such a dynamo is indeed feasible.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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