• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.83-93
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• 1995

A numerical and experimental investigation on the flow characteristics in the rectangular duct of an MHD propulsion system has been carried out. In numerical analysis, three-dimensional, steady-state, viscous, incompressible electrically conducting fluid flow under the influence of uniformly applied magnetic and electric fields was treated using a finite-difference technique. It was found from the numerical study that when the Lorentz force is weak, the typical parabolic velocity profile under a laminar flow condition changes to an M shaped profile near the electrode region and that the pressure increases linearly from the inlet toward the outlet of the MHD duct under constant electro-magnetic field. In experiment, thrust of the MHD propulsion system can be controlled easily by varying electrode current. The measured pressure gradient along the MHD duct is proportional to the Lorentz force, which is in agreement with the numerical results.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.2
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• pp.82-90
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• 2011

The small precision spindle motors in the high value-added products including the visible home appliances such as DLP projector require not only the energy conversion devices but also high efficiency, low vibration and sound operation. However, the spindle motors using the conventional ball bearing and sintered porous metal bearing have following problems, respectively: the vibration by the irregularity of balls and the short motor life cycle by the ball's abrasion and higher sound noises by dry contact between shaft and sleeve. In this paper, it is proposed that the spindle motor with a fluid dynamic bearing is suitable for the motor to drive the color wheel of the DLP(digital lightening processor) in the visible home appliances. The proposed spindle motor is composed of the fluid dynamic bearing with both the radial force and the thrust force. The fluid dynamic bearing is solved by the finite element analysis of the mechanical field with the Reynolds equations. The magnetic part of spindle motor, which is a type of Brushless DC Motor, is designed by the electro-magnetic field analysis coupled with the Maxwell equation. And the load capacity and the friction loss of fluid dynamic bearing are analyzed to bearing clearance variation by the fabrication error in designed motor. The design of the proposed motor is implemented by the load torque caused by the eccentricity and the unbalance of the fluid dynamic bearing when the motors are fabricated in error. The prototype of the motor with the fluid dynamic bearing is manufactured, and experiment results show the vibration, sound, and phase current at no load and color wheel load of the motors in comparison. The high performance characteristics with the low vibration, the low acoustic noise and the optimal mechanical structure are verified by the experimental results.

• Journal of Korea Foundry Society
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• v.25 no.4
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• pp.156-160
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• 2005

There are many factors that influence solidification behavior during continuous casting, e.g. include superheat, casting speed, cooling rate and holding time. However, when melt is stirred by electromagnetic force, there would be some changes in its solidification behavior compared to that of the ordinary casting process. In this study, the billets of A356 alloy with a diameter of 3 inch were fabricated with electromagnetic stirring under various conditions of superheat, casting speed and input voltage of electro magnetic stirring (EMS) device. The microstructure was also investigated under the various casting conditions and electromagnetic input voltages. When increase in input voltage, the microstructure was changed from dendritic to rosette type and finally to spheroidal. With pouring temperature, casting speed and electromagnetic input voltage were $650^{\circ}C$, 100 mm/min and 140 V, respectively, the billet with a diameter of 3 inch, which has a uniform dispersed spheroidal particles in the whole area of billet except for the surface area, was manufactured.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.955-964
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• 2011

In renewable energy system such as flywheel energy storage system, wind power and solar power, the motor/generator is the important key for offering the electric energy to the electric loads. For example, the heavy and large flywheel is rotated by electromagnetic torque of pemanent magnet synchronous motor (PMSM) and, in case of a breakdown of electric current, the PMSM used as generator supplies electric energy for the various electric utilities using mechanical rotation energy of the flywheel. Thus, design of a motor/generator should be performed in effort to reduce cogging torque and electromagnetic loss for high efficiency. In our paper, a slotless permanent magnet synchronous motor/generator (SPMSM/G) with output power 15kW at the rotor speed 18000rpm is designed from electromagnetic analysis and dynamic performance analysis. In analytical approach, design parameters such as back electro-motive force (back EMF), inductance and electromagnetic torque are derived from analytical method which is one of the electromagnetic analysis method. And using the design parameters, this paper deal with system design considering the driving characteristics and electric load in required power. Finally, the analytical results are verified by the experiment and finite element method (FEM).

• Proceedings of the KIEE Conference
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• 1999.11a
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• pp.1-3
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• 1999

EM (ElectroMagnetic) pump is used for the purpose of transporting liquid sodium coolant with electrical conductivity in the LMR(Liquid Metal Reactor). (In the present study, pilot EM pump has been designed by using of equivalent circuit method which is commonly employed to analyze linear induction machines for the test of removal of residual heat. The length and diameter of the pump have fixed values of 840 mm and 101.6 mm each by taking account of geometrical size of circulation loop for the installation of EM pump. Flowrate versus developing pressure is related from Laithwaite's standard design formula and the characteristic analyses of developing force and efficiency are carried out according to change of input frequency. From the characteristic curve, input frequency of 13 Hz is determined as the design frequency. On the other hand, The annular air gap size of 6.05 mm is selected not to bring about too much hydraulic loss. Resultantly design analysis makes pump have the electrical input of 604 VA and the hydrodynamical capacity of 1.3 bars and 40 l/min.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.130-132
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• 2002

Because of the continuous growth of energy consumption and also the tendency to site power lines and pipelines along the same route, the close proximity of power lines and buried metallic pipelines has become more and more frequent. Therefore there has been and still is a slowing concern about possible hazards resulting from the influence of power lines on metallic pipelines. Underground pipelines that run parallel to or in close proximity to power lines are subjected to induced voltages caused by the time-varying magnetic fields produced by the power line currents. The induced electro- motive force cause currents circulation in the pipeline and voltages between the pipeline and surrounding earth. This paper analyzes the induced voltage on the gas pipelines buried in parallel with 22.9kV distribution lines. Their magnitude depends on the length of parallelism and on the distance between distribution lines and pipeline.

• Journal of Korea Foundry Society
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• v.40 no.3
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• pp.61-65
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• 2020

Rheo-diecasting with stirring has been used in many material industries. As the 4th Industrial Revolution approaches the world, eco-friendly high-strength and light-weight materials become more important. Casting methods have been studied and used for aluminum-alloy automobile parts. This study carried out the effect analysis of the micro-structure and mechanical properties, such as yield/ultimate tensile strength, elongation, and hardness, of A356 using the 6-pole EMS (electro-magnetic stirring) casting process with a high electromagnetic force. As a result, the hardness and elongation of the A356 after T6 heat-treatment show a significant improvement, respectively, by 20% and 50%.

• Journal of IKEEE
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• v.22 no.3
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• pp.759-766
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• 2018

This paper presents a high-speed axial-flux machine which utilizes the idea of sinusoidal shaped pole combined with a consequent iron-pole. The target of the proposed machine is the cost reduction of the relatively expensive Samarium-Cobalt (SmCo) permanent magnet (PM) material and the torque per PM volume improvement by using sinusoidal consequent-pole rotor. The effectiveness of the proposed machine is validated by comparing it with conventional consequent-pole and with conventional PM machines using 3-D finite element method (FEM) simulations. The comparison and analysis is done in terms of back electro-motive force (back-EMF) harmonic contents, torque per PM volume and torque ripple characteristics. The simulation results show that the proposed machine is suitable and cost-effective for high-speed and high torque per PM volume applications. Furthermore, due to the consequent pole, the magnetic flux saturation and the overload current torque-capability are also presented and discussed in the paper.

• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.13-15
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• 1998

EM(Electro Magnetic) pump is used for the purpose of transporting liquid sodium coolant with electrical conductivity in the LMR(Liquid Metal Reactor). In the present study. pilot EM pump has been designed by using of equivalent circuit method which is commonly employed to analyze linear induction machines for the test of removal of residual heat. The length and diameter of the pump have fixed values of 840 mm and 101.6 mm each by taking account of geometrical size of circulation loop for the installation of EM pump. Flowrate versus developing pressure is related from Laithwaite's standard design formula and the characteristic analyses of developing force and efficiency are carried out according to change of input frequency. From the characteristic curve, input frequency of 13 Hz is determined as the design frequency. On the other hand, The annular air gap size of 6.05 mm is selected not to bring about too much hydraulic loss. Resultantly design analysis makes pump have the electrical input of 604 VA and the hydrodynamical capacity of 1.3 bars and 40 l/min.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.218.2-218.2
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• 2014

그래핀은 높은 전기 전도도와 열전도도, 기계적 강도를 가지고 있고 동시에 높은 전자이동도($200,000cm^2{\cdot}V{\cdot}^1{\cdot}s{\cdot}^1$) 특성을 갖는 물질로써 차세대 소재로 각광받고 있다. 하지만 그래핀을 소자에 응용하기 위해서는 전사공정과 lithography 공정 과정에서 발생되는 PMMA(Poly methyl methacrylate) residue를 완벽하게 제거해야 하는 문제점이 있다. 특히, lithography 공정 중 완벽하게 PMMA residue 가 제거되지 않고 잔류해 있을 경우에 소자의 life time, performance에 악영향을 준다는 보고가 있다. 이와같은 문제를 해결하기 위해 화학적 cleaning, 열처리를 통한 cleaning, 전류 인가에 의한 cleaning과 같은 방법들을 이용하여 그래핀의 PMMA residue를 제거하는 공정들이 보고되고 있지만, 화학적 cleaning 방법의 경우 chloroform 이라는 독성물질 사용으로 인해 산업적으로 응용이 어렵고, 열처리 방법은 전극 등의 금속이 $200^{\circ}C$ 이상의 높은 온도에서 장시간 노출될 경우 쉽게 손상을 입으며, 전류 인가에 의한 cleaning 방법은 국부적으로만 효과를 볼 수 있기 때문에 lithography 공정 후 PMMA residue를 효과적으로 제거하기에는 한계를 보이고 있다. 본 연구에서는 Ar을 이용하는 Ion beam 시스템을 통해 beam energy를 제어함으로써 PMMA residue를 효과적으로 제거하는 연구를 진행하였다. 최적화된 플라즈마 발생 조건을 찾기 위해 QMS(Quadrupole Mass Spectrometer)를 이용하여 입사하는 ion energy와 flux 양을 컨트롤 하였고, 250 W에서 최적화된 ion energy distribution 영역이 존재한다는 것을 확인할 수 있었다. 또한, 25 Gauss 정도의 electro-magnetic field를 이용하여 Ar의 ion energy를 10 eV 이하로 낮추어 damage를 최소화함으로써 효과적으로 그래핀을 cleaning 할 수 있었다. Cleaning과정에서 ion bombardment에 의해 발생한 damage는 $250^{\circ}C$에서 6시간 동안 annealing 공정을 거치면서 회복되는 것을 Raman spectroscopy의 D peak ($1335cm{\cdot}^1$) / G peak ($1572cm{\cdot}^1$) ratio 로 확인할 수 있었고, PMMA residue의 cleaning 여부는 G peak ($1580cm{\cdot}^1$)의 blue shift와 2D peak ($2670cm{\cdot}^1$)의 red shift를 통해 확인하였다. 그리고 AFM (Atomic Force Microscopy)을 이용하여 cleaning 공정과정에서 RMS roughness가 4.99 nm에서 2.01 nm로 감소하는 것을 관찰하였다. 마지막으로, PMMA residue의 cleaning 정도를 정량적으로 분석하기 위해 XPS (X-ray Photoelectron Spectroscopy)를 이용하여 sp2 C-C bonding이 74.96%에서 87.66%로 증가함을 확인을 할 수 있었다.