• 한국자기학회지
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• 제16권2호
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• pp.149-156
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• 2006

자기 기록 시스템은 시간의 흐름에 따라 기록 밀도는 높아지고 있고 또한 기록 속도 역시 빨라지고 있다. 더욱 빠른 기록 속도의 요구 치로 인하여 자기 기록 헤드에 인가되어지는 기록 주파수 역시 높아져야 하고 또한 기록이 일어나는 기록 미디어의 회전 속도 역시 빨라져야 한다. 이와 같은 두 가지 요건은 헤드와 기록 미디어에서 와전류를 발생시키게 된다. 기록 헤드에서는 기록 주파수에 의해 발생되는 와전류가 존재한다. 그리고 기록 미디어에서는 기록 주파수에 의해 발생되는 와전류와 회전하는 미디어의 선속도에 의해 발생하는 와전류가 존재하게 된다. 본 논문에서는 비선형 3차원 유한 요소법을 이용하여 자기 기록 헤드에서 발생하는 와전류와 기록 미디어에서 발생하는 두 종류의 와전류의 분포를 분석하고 이와 같이 발생한 와전류가 자기 기록시스템에서 자기 기록 필드에 미치는 영향에 대해서 연구하였다.

• 한국해안해양공학회지
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• 제13권1호
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• pp.46-55
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• 2001

비선형 파랑 모형을 이용하여 해안류를 산정하는 모형이 소개되었다. 기존의 잉여응력을 이용한 수치모형 결과와 비교하였으며, 두 수치모형의 타당성 검토를 위하여 PIV 시스템으로 획득한 실험자료와도 비교하였다. 방파제 및 잠제 후면에서 형성되는 해안류에 대하여 서로 비교한 결과, 소용돌이 흐름의 형태는 유사하나 관측 결과와 비교하여 수치 모형 결과가 대체로 과소평가되고 있다.

• 수산해양기술연구
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• 제56권2호
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• pp.114-125
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• 2020

In order to understand the currents around Hampyung Bay and Haeje Peninsula, 2D numerical simulations for tidal currents and tide-induced residual currents were carried out. Dominant semidiurnal tidal currents have reversing form and flow NNE-SSW from northern Haeje Peninsula to Songi Island, E-S at northern Haeje Peninsula and NNW-SSE in Hampyung Bay. In flood, a part of currents from Imja Island~Nakwhol Island flow along the main stream flowing northeast at offshore region and the rest flow into Hampyung Bay flowing east along the northern coast of Haeje Peninsula. In ebb, currents from Hampyung Bay flow west along the northern coast of Haeje Peninsula and run together with the main stream flowing southeast at offshore region. The currents create an anticyclonic circulation in flood and a cyclonic circulation in ebb around Haeje Peninsula including Hampyung Bay. Tidal currents are accumulated on Doripo which located at the entrance of Hampyung Bay and show high current velocities. Tidal currents and tide induced residual currents are weak at the inside of Hampyung Bay which has narrow entrance, shallow water depth and wide intertidal zone. An anticyclonic eddy is formed around Gaksi Island as a result of tide induced residual currents. In northern coast of Haeje Peninsula, slow constant currents flow east. It is expected that a gradual change of sediment and an increase of flushing time for suspended materials are carried by tidal currents occurring in Hampyung Bay.

• Journal of Magnetics
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• 제20권2호
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• pp.138-147
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• 2015

The unique nano-scale inter-lamellar microstructure and unparalleled heat treatment process give our developed metal powder composite its outstanding magnetic property for power inductor & motor applications. Compared to the conventional polycrystalline Fe or amorphous Fe-Cr-Si-B alloys, our unique designed inter-lamellar microstructure strongly decreases the intra-particle eddy current loss at high frequencies by blocking the mutual eddy currents. The combination of optimum permeability, magnetic flux and extremely low core loss makes this powder composite suitable for high frequency applications well above 10 MHz. Moreover, it can be also possible to SMC core for high speed motor applications in order to increase the motor efficiency by decreasing the core loss.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.613-616
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• 1998

In this paper, a model of a Eddy-current probe coil with a ferrite core in the presence of a half-space with a layer is developed. The half-space with a layer is accounted for by computing the appropriate Green's function by using Bessel transforms. Upon introducing equivalent Amperian currents within a core to explain effect to a impedance change in the coil due to a (ferrite) core, we derive a volume integral equation, The integral equation is transformed via the method of moments into a vector-matrix equation, which is then solved using a linear equation solver. Through the above processing, we computed impedance value in a Eddy-current probe coil due to a conductivity change of layer.

• 대한기계학회논문집A
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• 제32권8호
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• pp.654-659
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• 2008

This paper is to suggest a concept design of the permanent magnet type magnetic resonance imaging (MRI) device based on the parameter optimization method. Pulse currents in the gradient coils will introduce the effect of eddy currents in the ferromagnetic material, which will worsen the quality of imaging. In order to equalize the magnetic flux in the MRI device for good imaging, the eddy current effect in the ferromagnetic material must be taken into account. This study attempts to use the design of experiment (DOE) and the response surface method (RSM) for equalizing the magnetic flux of the permanent magnet type MRI device using that the magnetic flux can be calculated directly using a commercial finite element analysis package. As a result, optimal shapes of the pole and the yoke of the PM type MRI device can be obtained. The commercial package, ANSYS, is used for analyzing the magnetic field problem and obtaining the resultant magnetic flux.

• 한국수산과학회지
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• 제27권4호
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• pp.397-403
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• 1994

Circulations in Deukryang Bay are investigated using a numerical shallow water model. In the flow fields observed at four stations, north-south velocity components are dominant. In the model, the circulation forced by $M_2$-tide basically corresponded well to the observations. The model shows the strong currents in the mouth and the eastern part in the bay with about 60 cm/s and 50 cm/s, respectively. The model also shows the eddies in the tidal residual currents. To investigate the mechanism of eddy formation some numerical experiments are carried out. The results show that inertial and topographic effects play an important role in the eddy formation.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권2호
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• pp.93-101
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• 2000

This paper presents a novel method for the transient of eddy currents in the dampers of a super-conducting synchronous generator(SCG). The method proposes a 2-D corrected model which takes into account the influence of leakage fluxes of the field winding ends by increasing the effective air gap in order to consider the high precision of the analysis for the conventional 2-D model. The electromagnetic fields for the corrected model are analyzed by the time-stepping finite element method, thus the eddy currents in the dampers and electro-motive forces(EMF) in the stator windings are calculated. As the results, it is proved the presented method is comparatively accurate by comparing measured phase EMF values and the simulation ones, where about 6.4% error at the maximum value of EMF is occurred between them.

• Journal of Magnetics
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• 제17권1호
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• pp.27-32
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• 2012

Transcranial magnetic stimulation requires an electric field composed of dozens of V/m to achieve stimulation. The stimulation system is composed of a stimulation coil to form the electric field by charging and discharging a capacitor in order to save energy, thus requiring high-pressure kV. In particular, it is charged and discharged in capacitor to discharge through stimulation coil within a short period of time (hundreds of seconds) to generate current of numerous kA. A pulse-type magnetic field is formed, and eddy currents within the human body are triggered to achieve stimulation. Numerous pulse forms must be generated to initiate eddy currents for stimulating nerves. This study achieved high internal pressure, a high number of repetitions, and rapid switching of elements, and it implemented numerous control techniques via introduction of the half-bridge parallel load method. In addition it applied a quick, accurate, high-efficiency charge/discharge method for transcranial magnetic stimulation to substitute an inexpensive, readily available, commercial frequency condenser for a previously used, expensive, high-frequency condenser. Furthermore, the pulse repetition rate was altered to control energy density, and grafts compact, one-chip processor with simulation to stably control circuit motion and conduct research on motion and output characteristics.

• 한국전기전자재료학회논문지
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• 제15권5호
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• pp.460-467
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• 2002

This paper deals with the distribution characteristics of the current density and axial magnetic flux density on the vacuum interrupter with axial magnetic field type using 3 dimension finite element analysis. An axial magnetic field parallel to the current flow in the arc column can improve the current breaking capacity of vacuum interrupter by affecting the arc mode. The axial magnetic flux density on the contact electrode surface is analyzed by inputting external current as a function of the transient time for sine half wave. And it also is analyzed within the gap distance of the contact electrode. The peak value of current but is decreased with the descending current on the contact electrode surface and within the gap distance of the contact electrode. The residual magnetic field is generated on the contact electrode surface and within the gap distance in the instant of zero current, which is due to the influence of eddy currents. The phase shift due to eddy currents, defined as time difference between the maximum value of current and axial magnetic field, is about 1ms in the center point of gap distance.