• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.26.2-26.2
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• 2009

The Solar and Space Weather Research Group (SOS) in Korea Astronomy and Space Science Institute (KASI) is constructing the Space Weather Prediction Center since 2007. As a part of the project, we are developing automatic real-time system of the global 3-D magnetohydrodynamics (MHD) simulation. The MHD simulation model of earth's magnetosphere is designed as modified leap-frog scheme by T. Ogino, and it was parallelized by using message passing interface (MPI). Our work focuses on the automatic processing about simulation of 3-D MHD model and visualization of the simulation results. We used PC cluster to compute, and virtual reality modeling language (VRML) file format to visualize the MHD simulation. The system can show the variation of earth's magnetosphere by the solar wind in quasi real time. For data assimilation we used four parameters from ACE data; density, pressure, velocity of solar wind, and z component of interplanetary magnetic field (IMF). In this paper, we performed some initial tests and made a animation. The automatic real-time system will be valuable tool to understand the configuration of the solar-terrestrial environment for space weather research.

• Nuclear Engineering and Technology
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• v.49 no.1
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• pp.82-91
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• 2017

Liquid alloy systems have a high degree of thermal conductivity, far superior to ordinary nonmetallic liquids and inherent high densities and electrical conductivities. This results in the use of these materials for specific heat conducting and dissipation applications for the nuclear and space sectors. Uniquely, they can be used to conduct heat and electricity between nonmetallic and metallic surfaces. The motion of liquid metals in strong magnetic fields generally induces electric currents, which, while interacting with the magnetic field, produce electromagnetic forces. Electromagnetic pumps exploit the fact that liquid metals are conducting fluids capable of carrying currents, which is a source of electromagnetic fields useful for pumping and diagnostics. The coupling between the electromagnetics and thermo-fluid mechanical phenomena and the determination of its geometry and electrical configuration, gives rise to complex engineering magnetohydrodynamics problems. The development of tools to model, characterize, design, and build liquid metal thermomagnetic systems for space, nuclear, and industrial applications are of primordial importance and represent a cross-cutting technology that can provide unique design and development capabilities as well as a better understanding of the physics behind the magneto-hydrodynamics of liquid metals. First studies for the development of computational tools for the design of liquid metal electromagnetic pumps are discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.589-596
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• 2008

Performance of a pulsed heat source high temperature inert gas plasma MHD electrical power generator, which can be one of the candidates of space-based laser-to-electrical power converter, is examined by a time dependent two dimensional numerical simulation. In the present MHD generator, the inert gas is assumed to be ideally heated to about $10^4K$ pulsed-likely within short time(${\sim}1{\mu}s$) in a stagnant energy input volume, and the energy of high temperature inert gas is converted to the electricity with the medium of pure inert gas plasma without seeding. The numerical simulation results show that an enthalpy extraction ratio(=electrical output energy/pulsed heat energy) of several tens of % can be achieved, which is the same level as the conventional seeded non-equilibrium plasma MHD generator. Although there still exist many phenomena to be clarified and many problems to be overcome in order to realize the system, the pulsed heat source high temperature inert gas MHD generator is surely worth examining in more detail.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.310-313
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• 2008

Magnetohydrodynamics (MHD) devices have received considerable attention in recent years as a means to either improve the propulsive characteristics of hypersonic cruise missiles or as a means to generate power at low cost in drag and weight aboard scramjet powered vehicles. Based on more complete physical models than previously used, it is here argued that the use of MHD is not valuable in improving the performance of hypersonic propulsion systems through prevention of boundary layer separation or power bypass. This is due to the inevitable high amount of Joule heating accompanying MHD flow control having considerable undesired adverse effects on the engine performance. On the other hand, preliminary estimates indicate that MHD is likely to succeed in generating high amounts of power with little additional drag to feed megawatt-class energy weapons on-board scramjet engines.

• Nuclear Engineering and Technology
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• v.51 no.3
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• pp.654-664
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• 2019

The geometrical and electromagnetic variables of a rectangular-type magnetohydrodynamic (MHD) circulation system are optimized to solve MHD equations for the active decay heat removal system of a prototype Gen-IV sodium fast reactor. Decay heat must be actively removed from the reactor coolant to prevent the reactor system from exceeding its temperature limit. A rectangular-type MHD circulation system is adopted to remove this heat via an active system that produces developed pressure through the Lorentz force of the circulating sodium. Thus, the rectangular-type MHD circulation system for a circulating loop is modeled with the following specifications: a developed pressure of 2 kPa and flow rate of $0.02m^3/s$ at a temperature of 499 K. The MHD equations, which consist of momentum and Maxwell's equations, are solved to find the minimum input current satisfying the nominal developed pressure and flow rate according to the change of variables including the magnetic flux density and geometrical variables. The optimization shows that the rectangular-type MHD circulation system requires a current of 3976 A and a magnetic flux density of 0.037 T under the conditions of the active decay heat removal system.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.48.4-48.4
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• 2019

Small-scale shear flows are ubiquitous in the universe, and astrophysical plasmas are often magnetized. We study the thermal condensation instability in magnetized plasmas with shear flows in relation to filamentary structure formation in cool structures in the universe, representatively solar prominences and supernova remnants. A linear stability analysis is extensively performed in the framework of magnetohydrodynamics (MHD) with radiative cooling, plasma heating and anisotropic thermal conduction to find the eigenfrequencies and eigenfunctions for the unstable modes. For a shear velocity less than the Alfven velocity of the background plasma, the eigenvalue with the maximum growth rate is found to correspond to a thermal condensation mode, for which the density and temperature variations are anti-phased (of opposite signs). Only when the shear velocity in the k-direction is near zero, the eigenfunctions for the condensation mode are of smooth sinusoidal forms. Otherwise each eigenfunction for density and temperature is singular and of a discrete form like delta functions. Our results indicate that any non-uniform velocity field with a magnitude larger than a millionth of the Alfven velocity can generate discrete eigenfunctions of the condensation mode. We therefore suggest that condensation at discrete layers or threads should be quite a natural and universal process whenever a thermal instability arises in magnetized plasmas.

• Journal of The Korean Astronomical Society
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• v.55 no.6
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• pp.215-220
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• 2022

To seek an atmospheric heating mechanism operating on the Sun we investigated a heating source generated by a downflow, both of which may arise in a magnetic loop dynamically formed on the Sun via flux emergence. Since an observation shows that the illumination of evolving magnetic loops under the dynamic formation occurs sporadically and intermittently, we performed a magnetohydrodynamic simulation of flux emergence to obtain a high-cadence simulated data, where temperature enhancement was identified at the footpoint of an evolving magnetic loop. Unlike a rigid magnetic loop with a confined flow in it, the evolving loop in a low plasma β atmosphere is subjected to local compression by the magnetic field surrounding the loop, which drives a strong supersonic downflow generating an effective footpoint heating source in it. This may introduce an energy conversion system to the magnetized atmosphere of the Sun, in which the free magnetic energy causing the compression via Lorentz force is converted to the flow energy, and eventually reduced to the thermal energy. Dynamic and thermodynamic states involved in the system are explained.

• Journal of The Korean Astronomical Society
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• v.56 no.2
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• pp.225-229
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• 2023

We investigated an emerging magnetic loop dynamically formed on the Sun, which has the effective footpoint heating source that may play a key role in heating a solar atmosphere with free magnetic energy in it. It is suggested that the heating source could be related to local compression of a plasma in the emerging loop by means of Lorentz force, which converts the magnetic energy to the internal energy of the plasma that is used to reaccelerate a decelerated downflow along the loop, eventually generating the source when the kinetic energy of the downflow is thermalized. By analyzing very high-cadense data obtained from a magnetohydrodynamic simulation, we demonstrate how the local compression is activated to trigger the generation of the heating source. This reveals a characteristic of the emerging loop that experiences a dynamic loop-loop interaction, which causes the local compression and makes the plasma gain the internal energy converted from the magnetic energy in the atmosphere. What determines the characteristic that could distinguish an illuminated emerging loop from a nonilluminated one is discussed.

• Nuclear Engineering and Technology
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• v.37 no.5
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• pp.401-422
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• 2005

We review here research and development progress achieved in US Plasma Chamber technology roughly over the last decade. In particular, we focus on two major programs carried out in the US: the APEX project (1998-2003) and the US ITER TBM activities (2003-present). The APEX project grew out of the US fusion program emphasis in the late 1990s on more fundamental science and innovation. APEX was commissioned to investigate novel technology concepts for achieving high power density and high temperature reactor coolants. In particular, the idea of liquid walls and the related research is described here, with some detailed examples of liquid metal and molten salt magnetohydrodynamic and free surface effects on flow control and heat transfer. The ongoing US ITER Test Blanket Module (TBM) program is also described, where the current first wall/blanket concepts being considered are the dual coolant lead lithium concept and the solid breeder helium cooled concepts, both using ferritic steel structures. The research described for these concepts includes both thermofluid MHD issues for the liquid metal coolant in the DCLL, and thermomechanical issues for ceramic breeder packed pebble beds in the solid breeder concept. Finally, future directions for ongoing research in these areas are described.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.659-665
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• 2017

When an electrically conducting fluid flows through a staggered tube bank, the heat transfer and fluid flow features are changed by the externally introduced magnetic field. This study provides a numerical investigation of this phenomenon. Heat and fluid flows are investigated for unsteady laminar flows at Reynolds numbers of 50 and 100 with the Hartmann number gradually increasing from zero to 100. As the Hartmann number increases, and owing to the effects of the introduced magnetic field, the velocity boundary layer near the tube wall is thinned, the flow separation is delayed downstream, and the shrinkage of a recirculation zone formed near the rear side is observed. Based on these thermo-fluid deformations, the resulting changes in the local and average Nusselt number are investigated.