• 한국자기학회:학술대회 개요집
• /
• 한국자기학회 2008년도 Asian Magnetics Conference
• /
• pp.216.2-216.2
• /
• 2008

• 천문학회보
• /
• 제38권2호
• /
• pp.60.2-60.2
• /
• 2013

Electron magnetohydrodynamic (EMHD) turbulence provides a fluid-like description of small-scale magnetized plasmas. Most EMHD turbulence studies consider "balanced" EMHD turbulence. However, imbalanced EMHD turbulence has never been studied. In this study, we numerically study "imbalanced" EMHD turbulence. Imbalanced turbulence means that wave packets moving in one direction have high amplitudes or strong perturbations than the others. In driven imbalanced EMHD turbulence, non-zero magnetic helicity is injected. When magnetic helicity is injected at a scale, we expect to have inverse cascade of magnetic helicity, as well as magnetic energy, in three-dimensional (3D) EMHD turbulence. For no helicity injection, we do not observe inverse energy cascade. However, when magnetic helicity is injected, inverse cascade of magnetic helicity is clearly observed. Magnetic energy also shows inverse cascade. In EMHD turbulence, it is well known that magnetic energy on scales smaller than the energy injection scale is forward-cascading quantity and the magnetic energy spectrum follows a k^{-7/3} one. On the other hand, the inverse-cascading entity on scales larger than the energy injection scale is uncertain. If the magnetic helicity is inverse-cascading quantity, we will obtain a k^{-5/3} magnetic energy spectrum. In our simulations, we do observe energy spectrum consistant with k^{-5/3} on large scales. Therefore, we confirm that magnetic helicity indeed is the inverse-cascading entity in 3D EMHD turbulence.

• 대한기계학회논문집B
• /
• 제34권1호
• /
• pp.53-59
• /
• 2010

본 논문에서는, 자기유체역학(MHD)을 기반으로 마이크로 채널 내부에 다중 와류 유동을 발생시키는 새로운 형태의 카오스 마이크로 믹서를 제안한다. 제안된 마이크로 믹서의 마이크로 채널 내부에는 양측면과 바닥면에 전극들이 배치되어 있다. 배치된 전극들에 인가되는 전압 조건에 따라 다양한 형태로 로렌츠 힘이 유도되며, 이렇게 유도된 로렌츠 힘은 마이크로 채널 내부 유체의 추진 및 혼합을 야기할 수 있다. 제안된 MHD 마이크로 믹서의 혼합 양상을 평가하기 위해 3 차원 전산유체역학 시뮬레이션을 수행하였다. 이를 통해 다양한 유동 조건에 대해 MHD 마이크로 믹서의 혼합 성능을 평가하였다.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
• /
• pp.39.2-39.2
• /
• 2010

Field line resonances (FLRs) observed in the magnetosphere often have the amplitude of a few nT, which indicates that dB/B roughly satisfies ~0.01. It is well known that the FLRs are excited by compressional waves via mode conversion, but there has been no apparent criterion on the maximum amplitude in the regime of linear approximations. Such limited range of amplitude should be understood by including nonlinear saturation of FLRs, which has not been examined until now. In this study, using a three-dimensional magnetohydrodynamic (MHD) simulation code, we examine the evolution of nonlinear field line resonances (FLRs) in the cold plasmas. The MHD code used in this study allows a full nonlinear description and enables us to study the maximum amplitude of FLRs. When the disturbance is sufficiently small, it is shown that linear properties of MHD wave coupling are well reproduced. In order to examine a nonlinear excitation of FLRs, it is shown how these FLRs become saturated as the initial magnitude of disturbances is assumed to increase. Our results suggest that the maximum amplitude of FLRs become saturated at the level of the same order of dB/B as in observations. In addition, we discuss the role of both linear terms and nonlinear terms in the MHD wave equations.

• Nuclear Engineering and Technology
• /
• 제51권3호
• /
• pp.654-664
• /
• 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.

• Advances in nano research
• /
• 제16권4호
• /
• pp.427-434
• /
• 2024

Latest advancement in field of fluid dynamics has taken nanofluid under consideration which shows large thermal conductance and enlarges property of heat transformation in fluids. Motivated by this, the key aim of the current investigation scrutinizes the influence of thermal radiation and magnetohydrodynamic on the laminar flow of an incompressible two-dimensional Williamson nanofluid over an inclined surface in the presence of motile microorganism. In addition, the impact of heat absorption/generation and Arrhenius activation energy is also examined. A mathematical modeled is developed which stimulate the physical flow problem. By using the compatible similarities, we transfer the governing PDEs into ODEs. The analytic approach based on Homotopy analysis method is introduced to impose the analytic solution by using Mathematica software. The impacts of distinct pertinent variable on velocity profiles are investigated through graphs.

• 천문학회보
• /
• 제40권2호
• /
• pp.38.2-38.2
• /
• 2015

Development of a new code for magnetohydrodynamic (MHD) phenomena in fusion plasma is under progress through a collaboration between plasma physicists, mathematicians, and astrophysicists. The code employs approaches different from those of existing codes. For instance, it is based on a finite difference scheme of high-order and high accuracy, complying conservation laws. The new code will have characteristics distinguished from those of commonly used code such as M3D and NIMROD. Here we will report the progress of the code development.

• 대한수학회보
• /
• 제47권2호
• /
• pp.231-249
• /
• 2010

Asymptotic behavior of three-dimensional mixed, periodic and rotating magnetohydrodynamic system is investigated as the Rossby number goes to zero. The system presents the difficulty to be singular and mixed, that is hyperbolic in the vertical direction and parabolic in the horizontal one. The divergence free condition and the spectral properties of the penalization operator are crucial in the proofs. The main tools are the energy method, the Schochet's method and products laws in anisotropic Sobolev spaces.

• 천문학회보
• /
• 제37권1호
• /
• pp.84.2-84.2
• /
• 2012

We studied the controlling parameters of flux emergence with a focus on the relation between the configuration of coronal magnetic field and the pre-emeged state of subsurface magnetic field. We performed a series of magnetohydrodynamic simulations (dynamic model) and find an interesting result on the twist of coronal magnetic field, that is, the coronal magnetic field formed via flux emergence actually contains less amount of twist (relative magnetic helicity normalized by magnetic flux) than what is expected in kinematic models for global-scale solar eruptions. Based on this result, we propose another possible mechanism for producing these global-scale solar eruptions.

• 천문학회보
• /
• 제42권2호
• /
• pp.59.4-59.4
• /
• 2017

We present a way of quantitatively characterizing solar active regions on the basis of their evolutionary paths. To determine characteristic properties of active regions with different sizes and configurations, we use a physics-based model to derive a relation between emerged magnetic flux and injected magnetic helicity (Flux-Helicity relation), the former of which gives scale information while the latter represents the magnetic field configuration of an active region. We demonstrate how this relation provides evolutionary paths of active regions and determines their characteristic properties, through a comparison with modeled active regions obtained from magnetohydrodynamic simulations.