• Nuclear Engineering and Technology
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• 제49권6호
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• pp.1143-1156
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• 2017

This paper describes recent development activities of the GENESIS code, which is a transport code for heterogeneous three-dimensional geometry, focusing on applications to reactor core analysis. For the treatment of anisotropic scattering, the concept of the simplified Pn method is introduced in order to reduce storage of flux moments. The accuracy of the present method is verified through a benchmark problem. Next, the iteration stability of the GENESIS code for the highly voided condition, which would appear in a severe accident (e.g., design extension) conditions, is discussed. The efficiencies of the coarse mesh finite difference and generalized coarse mesh rebalance acceleration methods are verified with various stabilization techniques. Use of the effective diffusion coefficient and the artificial grid diffusion coefficients are found to be effective to stabilize the acceleration calculation in highly voided conditions.

• 한국농림기상학회지
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• 제5권2호
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• pp.70-80
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• 2003

본 연구에서는 KoFlux네트워크 타워 관측소의 하나인 광릉 낙엽 활엽수림에서 최초로 직접 관측된 이산화탄소 플럭스를 보고한다. 2002년 6월부터 8월까지 에디 공분산 시스템을 다른 기상 관측 기기들과 함께 30 m 타워에 설치하였다. 관측 장소가 계곡과 같은 경사지에 위치해 있음에도 불구하고 관측된 난류 특성이, 제한된 풍향(즉, 90$\pm$45$^{\circ}$)의 경우, 평평하고 균질한 이상적인 장소에서 관측된 것들과 크게 다르지 않았다. 관측 자료 회수율은 비록 낮았으나, 분석된 예비 결과는 고무적이고, 연구해야 할 가치가 있는 것으로 나타났다. 이류 항을 무시하면, 생태계의 순 $CO_2$ 교환(NEE)은 6월에서 8월까지 약 -1.2에서 0.7 mg m$^{-2}$ s$^{-1}$의 범위를 보였다. 약한 난류가 야간 NEE에 미치는 효과를 마찰 속도(u*)및 저류 항의 산출과 관련하여 살펴보았다. 낮은 u*가 NEE에 미치는 영향은 약 0.2 m s$^{-1}$의 문턱 값을 기점으로 뚜렷하게 나타났다. 야간 NEE에 미치는 저류 항의 역할은 거의 나타나지 않았는데, 이는 밤 동안 산림 내에 축적된 $CO_2$가 경사면을 따라 배수류로 빠져나갔기 때문인 것으로 사료된다. 이는 또한 저류 항을 한 높이에서만 관측된 농도 자료를 사용함으로 생긴 오차로 인한 인위적인 결과일 수도 있다. 쌍곡선 광 반응식을 적용한 결과, 관측된 NEE 변화의 80% 이상이 설명되어, 이 산림 지역의 $CO_2$ 교환이 주로 빛에 의해 조절됨을 보여주었다. 이러한 관계식은 계절에 걸쳐 빠진 자료를 채워 넣는 자료 처리 과정에 효과적으로 사용될 수 있다. 마지막으로, 선형류 모형에 근거한 간단한 규모 분석에 의하면, 이류항의 효과가 NEE산출에 큰 영향을 미칠 수 있는 것으로 나타났다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.272-277
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• 1997

The axial bearing using two ring type permanent magnets to support the weight of a flywheel is proposed to reduce the bearing loss in a flywheel energy storage , system. Two permanent magnet makes stable force in axial direction but unstable force in lateral direction. The lateral unstable stiffness is identified quantitatively using flux analysis, and then through the rotor dynamic analysis on a rigid flywheel system the unstable effects on the system by the stiffness is investigated.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.1-7
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• 2001

One of the important applications of a contact melting process is a latent thermal energy storage system owing to its high heat flux and small temperature variation. In some previous works, the split fins have been employed in order to enhance the melting rate. In the present work, the direct contact melting was experimentally investigated using an ice as specimen for both split and non-split fins. It was shown that the contact melting by split fins increases the melting rate compared to that of non-split ones.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 A
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• pp.46-48
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• 1999

This paper treated the design and characteristics of high speed motor/generator with ring wound stator for the flywheel energy storage system. The most important advantages of the ring-wound motor is the slotless stator, i.e. no cogging torque, no space harmonic of air-gap flux density, etc. Because of these advantages, ring wound type motor is suitable to operate at the high speed.

• 한국농림기상학회:학술대회논문집
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• 한국농림기상학회 2015년도 하계 학술발표논문집
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• pp.40-44
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• 2015

• 한국소음진동공학회논문집
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• 제20권8호
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• pp.717-726
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• 2010

For the application into a 1 kWh flywheel energy storage system(FESS), this paper presents the design scheme of radial and axial hybrid magnetic bearings which use bias fluxes generated by permanent magnets. In particular, the axial hybrid magnetic bearing is newly proposed in this paper, in which a permanent magnet is arranged in axial direction so that it can support the rotor weight as well as provide a bias flux for axial magnetic bearing. Such hybrid magnetic bearings consume very low power, compared with conventional electromagnetic bearings. In this paper, to stably support a 140 kg flywheel rotor without contact, design process is explained in detail, and magnetic circuit analysis and three-dimensional finite element analysis are carried out to determine the design parameters and predict the performance of the magnetic bearings.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
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• pp.467-471
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• 2003

The large synchronous motor for the pumped-storage plant(or SFC : Static Frequency Converter) has to be brought up to 100$\%$ rated speed and synchronized with the AC power network. Starting the motor from rest is achieved by switching current into the stator winding so that interaction between this stator current and the rotor flux will cause the correct direction of torque to be developed so that the motor turns in the required direction. Starting ranges of the synchronous motor are divided into three regions. The first region Is at standstill, the second that is called by the forced commutation is from standstill to 5-8$\%$ of rated speed, and the third, which is called by the natural commutation, is from 5-8$\%$ of rated speed to 100$\%$ rated speed. So this paper describes three regions of the control techniques of the pumped-storage synchronous motor drive.

• 정보저장시스템학회논문집
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• 제2권4호
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• pp.240-244
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• 2006

As high-definition television(HDTV) broadcasting becoming more generalized, there have been many researches and developments about a large storage capacity and a fast data transfer rate in optical disk drives (ODD). Pickup actuators must have high flexible mode frequencies and large gain margins. Flexible modes are caused by the flexibility of moving parts in the actuator and a servo bandwidth is limited by them. As a result, the system becomes unstable for high-speed operations in high density reading and recording. In this paper, we suggest improved modeling method in considering of the bonding layer. And, the flexible mode frequency of actuator is improved by Design of Experiments of lens holder. The Magnet circuit is designed considering the relation with the moving part. Through improving the yoke design, the magnetic flux is changed and the DC tilt is reduced. Consequently, we designed an actuator which has a high flexible mode frequency and a large gain margins.

• 설비공학논문집
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• 제24권2호
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• pp.190-195
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• 2012

In this study, as a complementary study of the former study on indoor thermal environment in a tower type apartment house at tropical nights, a field measurement was conducted in winter season. Mainly, characteristics of heat storage and heat emission in apartment structures, in this study, were investigated. As results, indoor air temperature was changed in the range of $22.5^{\circ}C{\pm}1.0^{\circ}C$, and followed not the change of outdoor air temperature but the changed pattern of floor surface temperature. Wall surface temperature was unresponsive to the change of floor surface temperature compared with the change of indoor air temperature because wall structure was composed of concrete which has large heat capacity, and was changed in the range of $22.3^{\circ}C{\pm}0.6^{\circ}C$. Heat was stored continuously into the structures of wall and ceiling through the measurement term. and this means that a large heat capacity of the apartment structure acts as a disadvantage in winter season, too. As a total review of the study with the former study, a large heat capacity of the apartment structure acts against indoor thermal comfort in winter season as well as in summer season.