• 천문학회지
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• 제37권1호
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• pp.55-59
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• 2004

We have developed a two fluid solar wind model from the Sun to 1 AU. Its basic equations are mass, momentum and energy conservations. In these equations, we include a wave mechanism of heating the corona and accelerating the wind. The two fluid model takes into account the power spectrum of Alfvenic wave fluctuation. Model computations have been made to fit observational constraints such as electron($T_e$) and proton($T_p$) temperatures and solar wind speed(V) at 1 AU. As a result, we obtained physical quantities of solar wind as follows: $T_e$ is $7.4{\times}10^5$ K and density(n) is $1.7 {\times}10^7\;cm^{-3}$ in the corona. At 1 AU $T_e$ is $2.1 {\times} 10^5$ K and n is $0.3 cm^{-3}$, and V is $511 km\;s^{-1}$. Our model well explains the heating of protons in the corona and the acceleration of the solar wind.

• 한국수소및신에너지학회논문집
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• 제29권3호
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• pp.292-298
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• 2018

The contamination of photovoltaic (PV) cells reduces the incidence of sunlight and reduces the power generation output of PV cells. The main factor influencing the contamination of PV cells installed outdoors is the fine dust in the air, but the influence of temperature, humidity, rain and wind can be considered. In this paper, experiments on the contamination of PV cells according to the fine dust density, the temperature and humidity of air were investigated. As results of this study, the contamination area of PV cells increases with contamination time and cumulative fine dust density in the air. The contamination of PV cells increases when the temperature is low and the humidity is high. Also, as the contamination of PV cells is affected to the wind, the deviation of contamination area is happened.

• 천문학논총
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• 제12권1호
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• pp.111-143
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• 1997

We have developed a spherical FCT code in order to simulate the interaction of supernova remnants with stellar wind bubbles. We assume that the density profile of the supernova ejecta follows the Chevalier mode1(1982) where the outer portion has a power-law density distribution($\rho{\propto}\gamma^{-n}$) and the SN ejecta has a kinetic energy of $10^{51}$ ergs. The structure of wind bubble has been calculated with the stellar mass loss rate $\dot{M}=5\times10^{-6}M_{\odot}/yr$ and the wind velocity $\upsilon=2\times10^3$ km/s We have simulated seven models with different initial conditions In the first two models we computed the evolution of SNRs with n=7 and n=14 in the uniform medium The numerical results agree with the Chevalier's similarity solution at early times. When all of the power-law portion of the ejecta is swept up by the reverse shock, the evolution slowly converges to the Sedov-Taylor stage. There is not much difference between the two cases with different n's The other five models simulate SNRs produced inside wind bubbles. In model III, we consider the SN ejecta of 1.4 $M_{\odot}$ and the radius of bubble ~2.76 pc so that ratio of the mass $\alpha(=M_{W.S}/M_{ej}$ is 2. We follow the complex hydrodynamic flows produced by the interaction of SN shocks with stellar shocks and with the contact discontinuities, In the model III, the time scale for the SN shock to cross the wind shell $\tau_{cross}$ is similar to the time scale for the reverse shock to sweep the power-law density profile $\tau_{bend}$. Hence the SN shock crosses the wind shell. At late times SN shock produces another shell in the ambient medium so that we have a SNR with double shell structure. From the numerical results of the remaining models, we have found that when $\tau_{cross}/\tau_{bend}\leq2$, or equivalently when $\alpha\leq50$, the SNRs produced inside wind bubbles have double shell structure. Otherwise, either the SN shock does not cross the wind shell or even if it crosses at one time, the reverse shock reflected at the center accelerates the wind shell to merge into the SN shock Our results confirm the conclusion of Tenorio-Tagle et a1(1990).

• 태양에너지
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• 제11권1호
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• pp.27-40
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• 1991

에너지 소비 구조의 개선을 목적으로 한 자연에너지 이용시스템의 도입이 전력 계통의 계획 운용에 미치는 영향을 다목적 최적화 방법을 이용하여 평가하는 방법이 논하여 지고 있다. 본 연구에서는 시험 제작한 태양열과 풍력 에너지를 주체로하는 자연에너지 복합 이용시스템이 특정 지역에 복수 도입되어 지는 경우 전력 통계 운용에 의한 경제성, 안정성, 환경에 대한 영향 평가 방법을 검토하였다. 연구 방법은 대상 지역의 일사 분포와 풍속 분포에 의해서 취득 가능한 에너지를 산정하여 전력 계통 부하의 형상에 미치는 영향을 구하였고, 다음에는 대상 기간에 의한 최적 발전 배분을 결정하여 경제성, 안정성, 환경 지표 등의 평가를 하였다. 지금까지는 자연에너지 이용시스템의 도입에 대하여 경제적 측면만 논의되었지만, 본 연구에서 제한된 방법에 의해 안정성과 환경 보전의 영향을 고려한 평가 방법도 가능하다는 것을 나타내었다.

• 수산해양기술연구
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• 제31권3호
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• pp.256-263
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• 1995

득량만에서 발생되는 수괴의 연직 구조의 변동을 역학적으로 규명하기 위하여 Simpson and Hunter(1974)와 Simpson and Bowers(1981)의 에너지식을 이용하여 수괴의 연직 환합과 관련된 바람, 태양 그리고 조류 에너지를 계산하여 보았다. 그 결과 바람에너지에 비하여 태양 에너지와 조류에너지가 약 10배 종도 큼을 알 수 있었다. 그리고 태양 에너지의 경우 관측 기간 동안 큰 변동이 없는 반면 조류의 경우 대조기와 소조기대의 에너지가 약 10배 정도 차이가 남을 알 수 있었다. 이러한 결과로 미루어 볼 때 하계 득량만의 수괴의 연직 구조변동은 대.소조기 변동에 따른 조류의 세기에 의하여 결정됨을 잘 알 수 있었다. 그리고 태풍에 의한 에너지의 변동을 살펴보기 위하여 Fujita의 경험적인 태풍 모델을 도입하여 태풍이 득량만의 좌측과 우측을 통과할 때의 에너지의 변동을 살펴보았다. 그 결과 태풍 에너지는 조류 에너지의 크기와 매우 비슷하며 특히 대조기때의 조류 에너지의 크기와 매우 유사함을 알 수 있었다. 여기서 주목되는 것은 득량만에서 연직 혼합을 일으키는 10-15m/sec의 바람 에너지의 크기와 30-40cm/sec 세기의 조류가 가지고 있는 조류에너지의 크기가 매우 비슷함을 알 수 있다. 따라서 득량만의 경우 조류에 의한 수괴의 연직 혼합의 세기는 태풍 에너지와 거의 비슷함을 알 수 있다. 이러한 결과를 미루어 볼 때 대조기때의 득량만의 조류 에너지는 거의 태풍 통과시 바람 에너지와 거의 비슷함을 알 수 있었다. 이러한 연구는 Simpson(1981)의 결과와도 매우 유사하게 나타났다.

• Journal of Magnetics
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• 제16권4호
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• pp.374-378
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• 2011

Axial Field Permanent Magnet (AFPM) generators are widely applied for the small wind turbine because of the higher power density per unit weight than that of the conventional radial field generator. It is caused by the disc shaped rotor and the stator structures. The generally used AFPM generator, AFER-NS generator, is composed of the two side's external rotors and non-slotted stator without stator core. However, the output voltage and the output power are limited by the large reluctance by the long air-gap flux paths. In this paper, the design study of AFIR-S generator having double side's slotted stator core is accomplished to improve the output generation characteristics. The electromagnetic design analysis and the design improvement of the suggested AFIR-S generator are studied. Firstly, the electromagnetic design analysis was done to increase the power density. Secondly, the design optimizations of the rotor pole-arc ratio of permanent magnet are accomplished to increase the output power and to reduce the cogging torque. Finally, the output performances of AFER-NS and AFIR-S generator are compared with each other. For this study, 3D FEA is applied for the design analysis because of three dimensional electromagnetic structures.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.6-8
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• 2002

This paper presents the design and finite-element(FE) analysis of an axial-flux permanent-magnet synchronous generator using neodymium-iron-boron(NdFeB) magnets for directly coupled wind turbines. For the high energy density and light weight, an axial-flux permanent-magnet(PM) generator type is used. The simple magnetic equivalent circuit approach is used for initial design iteration, and the finite-element method is applied to analyze the detailed characteristics.

• 천문학논총
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• 제11권1호
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• pp.91-107
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• 1996

We determine analytically the onset of thin-shell formation time of fast wind bubble with power-law energy injection $E_{in}=E_0t^s$, and power-law ambient density structure, ${\rho}_0(r)={\bar{\rho}}(r/{\bar{r}})^{-{\omega}}$. Thin-shell formation time, $t_{sf}$ can be estimated by minimizing the total time elapsed before the complete cooling of shocked gas. For uniform medium (${\omega}=0$) and constant energy injection (s = 1), the onset of shell formation is found to be at $t_{sf}=5.2{\times}10^3yr$, which agrees Quite well with the results of FCT 1D numerical calculation. We solve the line transfer problem with previous result derived by numerical calculation in order to calculate line profile of [OIII] (${\lambda}=5007{\AA}$) forbidden line. In general, radiative outer shell causes the formation of double peaked line profile. Each peak corresponds to approaching and receeding shells with large velocities. Our line profiles show good agreements with observation of expanding shell structure.

• Journal of Astronomy and Space Sciences
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• 제32권1호
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• pp.1-11
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• 2015

Earth's magnetopause separating the fast and often turbulent magnetosheath and the relatively stagnant magnetosphere provides various forms of free energy that generate low-frequency surface waves. The source mechanism of this energy includes current-driven kinetic physical processes such as magnetic reconnection on the dayside magnetopause and flux transfer events drifting along the magnetopause, and velocity shear-driven (Kelvin-Helmholtz instability) or density/pressure gradient-driven (Rayleigh-Taylor instability) magnetohydro-dynamics (MHD) instabilities. The solar wind external perturbations (impulsive transient pressure pulses or quasi-periodic dynamic pressure variations) act as seed fluctuations for the magnetopause waves and trigger ULF pulsations inside the magnetosphere via global modes or mode conversion at the magnetopause. The magnetopause waves thus play an important role in the solar wind-magnetosphere coupling, which is the key to space weather. This paper presents recent findings regarding the generation of surface waves (e.g., Kelvin-Helmholtz waves) at the Earth's magnetopause and analytic and observational studies accountable for the linking of the magnetopause waves and inner magnetospheric ULF pulsations, and the impacts of magnetopause waves on the dynamics of the magnetopause and on the inner magnetosphere.

• KEPCO Journal on Electric Power and Energy
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• 제5권3호
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• pp.229-233
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• 2019

Large-scale High Temperature Superconducting (HTS) wind power generators suffer from high electromagnetic force and high torque due to their high current density and low rotational speed. Therefore, the torque and Lorentz force of HTS wind power generators should be carefully investigated. In this paper, we proposed a Performance Evaluation System (PES) to physically test the structural stability of HTS coils with high torque before fabricating the generator. The PES is composed of the part of a pole-pair of the HTS generator for estimating the characteristic of the HTS coil. The 10 MW HTS generator and PES were analyzed using a 3D finite element method software. The performance of the HTS coil was evaluated by comparing the magnetic field distributions, the output power, and torque values of the 10 MW HTS generator and the PES. The magnetic flux densities, output power, and torque values of the HTS coils in the PES were the same as a pole-pair of the 10 MW HTS generator. Therefore, the PES-based evaluation method proposed in this paper can be used to estimate the critical characteristics of the HTS generator under high magnetic field and high torque before manufacturing the HTS wind turbines. These results will be used effectively to research and manufacture large-scale HTS wind turbine generators.