• Nuclear Engineering and Technology
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• 제29권3호
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• pp.186-195
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• 1997

When asymmetric thermal-hydraulic conditions occur between cold legs, the core inlet temperature will be nonuniform if the coolant is not mixed perfectly in the lower plenum. These uneven core inlet conditions may induce the change in core power distribution. Thus realistic prediction of thermal mixing is important in such abnormal conditions. In this study, reactor internals, which are scaled down as to conserve the flow area ratio, are set up in the model of KORI Unit 1 with the scaling factor of 1/710 by volume and coolant temperatures are measured beneath the lower core plate. Based on experimental results, the ability of COMMIX-1B code to simulate the coolant mixing phenomena in the lower plenum is estimated. The results show that complete mixing never occurs in any conditions and the mixing pattern is characterized according to the plant type.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.218-222
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• 2011

이리듐 촉매의 국산화 개발과정에서 고온/고압으로 인한 촉매파손, 유실, 소결현상 등이 관찰되었고, 이렇게 손상된 촉매대로 인하여 추력기의 성능이 저하된다고 보고되었다. 이에 본 논문의 연구에서는 촉매대를 1차원 다공질성 매질로 가정, 모델링하여 수치해석코드를 개발하였다. 개발된 수치해석코드는 실험데이터와 비교하여 검증하였으며, 촉매유실에 의해 변하게 되는 촉매대의 공극률을 변화시켜 다양한 경우의 촉매유실을 가정하여 해석을 수행하였다. 이를 통하여 촉매유실이 하이드라진과 암모니아의 분해반응에 끼치는 영향을 연구하였다.

• 한국농림기상학회지
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• 제20권4호
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• pp.313-320
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• 2018

2018년 봄, 갑작스러운 이상저온으로 인해, 전북, 경기 남부지역 등을 중심으로 개화된 과수 작목의 꽃이 얼어 죽는 일이 발생하였다. 2000년대 들어서면서 전 세계적으로 빈번하게 발생하고 있는 이상기후 현상으로 인해, 사회 여러 분야에 경제적인 피해와 악영향이 증가 하고 있다. 최근의 기후변화는 지구온난화와 더불어, 지역 기후의 정상 범위로부터 벗어나는 기상이변의 발생빈도 또한 증가할 것으로 예상된다. 기후변화가 농작물 생산에 미치는 영향을 파악하기 위해서는 이러한 이상기상 현상을 정확하게 파악하고 이에 따른 농작물의 영향을 분석할 필요가 있다. 본 연구에서는 배, 복숭아, 사과 작물이 실제 재배되고 있는 국내 주산 지역에 대하여 기후변화 시나리오를 이용하여, 미래 개화일의 변화를 각각 예측하고, 개화 후 온도 분포를 정량화함으로써, 미래의 저온 발생 추세를 전망하였다. 그 결과 온난화로 인해 개화기는 현재 재배중인 지역을 대상으로 모든 과종에 대하여 현재 평년을 기준으로, 미래 평년(2071-2100)에는 약 20일 정도 앞당겨 질 것으로 예상되었으며, 개화 후 저온의 분포는 과종, 지역 별로 일정 부분 차이가 있음을 확인할 수 있었다. 본 연구는 일부 과수 작목 및 품종에 한해 진행된 연구결과를 제시한 것으로, 차후 다양한 품종 및 작목으로 연구를 확대한다면, 미래 농업부문 대책 마련에 기여할 수 있을 것으로 기대된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1562-1563
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• 2011

Partial discharge measurement is one of the effective diagnostic techniques to predict abnormal high voltage dielectric insulation conditions of the electric equipments. Recently partial discharge diagnostic techniques were also utilized to evaluate the cryogenic dielectric insulation of high temperature superconducting electric equipment in liquid nitrogen. Generally, liquid nitrogen at 77 K is used used as the cryogenic and dielectric media for many high temperature superconducting high voltage applications. When a quench in the superconductor occurs, bubbles are generated which can affect the dielectric properties of the liquid nitrogen. So in order to reduce the bubble formation, subcooled nitrogen was also employed for this purpose. In this work, investigation of partial discharge characteristics of subcooled liquid nitrogen were conducted in order to clarify the retardation of partial discharge initiation voltage according to the different subcooling temperature of liquid nitrogen. And also the relation of partial discharge phenomena and the activities of bubbles were analyzed. It was observed that PD inception voltages shows rather different characteristics according to the decrease of subcooling temperature and the activities of bubbles were strongly influenced by temperature of the subcooled liquid nitrogen.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2274-2276
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• 1999

In this work, temperature rise and eddy current distribution on the enclosure and conductor of 3 pole gas insulated switchgear were investigated using analytical and experimental measures. The design of the diameters of the conductors and the enclosures of a meal clad gas insulated switchgear is primarily based on the insulation requirements. It is very difficult problem to predict the temperature rise of enclosed switchgear due to the complexity of the phenomena of heat transfer and existence of eddy current loss. To overcome this situations, we focused on the eddy current distribution on the enclosure of switchgear caused by high current 3 pole conductor as a fundamental basis. The experimental results about temperature distribution of 3 pole gas insulated switchgear were reported and measurements are compared with predictions of three-dimensional thermal model for eddy current analysis. As a result, three dimensional numerical analysis found to be in close relationship with experimental results and thermal model is efficient to predict the abnormal temperature rise in switchgear.

• Environmental Engineering Research
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• 제16권3호
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• pp.175-183
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• 2011

The climate of the $21^{st}$ century is likely to be significantly different from that of the 20th century because of human-induced climate change. An extreme weather event is defined as a climate phenomenon that has not been observed for the past 30 years and that may have occurred by climate change and climate variability. The abnormal climate change can induce natural disasters such as floods, droughts, typhoons, heavy snow, etc. How will the frequency and intensity of extreme weather events be affected by the global warming change in the $21^{st}$ century? This could be a quite interesting matter of concern to the hydrologists who will forecast the extreme weather events for preventing future natural disasters. In this study, we establish the extreme indices and analyze the trend of extreme weather events using extreme indices estimated from the observed data of 66 stations controlled by the Korea Meteorological Administration (KMA) in Korea. These analyses showed that spatially coherent and statistically significant changes in the extreme events of temperature and rainfall have occurred. Under the global climate change, Korea, unlike in the past, is now being affected by extreme weather events such as heavy rain and abnormal temperatures in addition to changes in climate phenomena.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.911-914
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• 1992

We have investigated the micro-discharge in plasma display panel using 2 dimensional 2 fluid MHD equations. Plasma display utilizes the physical phenomena of the normal glow or abnormal glow and is considered to be able to provide the largest display area among various flat panel. 2 fluid, 2 dimensional Magneto-Hydro-Dynamic equations are applied to Computational field of 100${\times}$800${\mu}m^2$. Time varing glows and after-glows were investigated for 11 $\mu$sec. We obtained the distribution of the microscopic variables such as the density, temperature, velocity of Ne+Ar0.1% gas plasma. During the first 6$\mu$ sec, glow discharge dued to DC pulse was investigated. Time varing phenomena of after-glow was also investigated during the last 5 $\mu$set. From results, it was found that the driving efficiency of a DC Plasma Display Panel could be improved when the diffusion of ions and electrons are controlled by the pulses applied to the auxiliary anode.

• 한국수자원학회논문집
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• 제40권4호
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• pp.299-311
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• 2007

최근 들어 세계의 연중 기후 변화에 주된 요인으로써 엘니뇨와 같은 현상이 매우 잦아졌다. 많은 기상수문학자들이 강수와 유량에 대한 엘니뇨 남방진동의 영향에 대해 연구하고 있지만, 수문변량들은 큰 지역적 변동을 갖고 있기 때문에 결정적인 인과관계를 찾아내는데 있어서 많은 어려움이 있다. 본 연구에서는 엘니뇨-남방진동과 한국에서의 수문변량들 간의 계절석 관계를 고찰하였다. 엘니뇨-난방진동을 정량적으로 표현해 주는 지수로써 남방진동지수를 사용하였고, 월강수량 자료, 월평균기온 자료 그리고 댐의 월유입량 자료를 표준정규분포를 가지는 표준정규지수로 변환하여 사용하였다. 계절적 관계를 파악하기 위해 난방진동지수와 수문변량의 월 자료는 봄 (3월-5월), 여름(6윌-8월), 가을(9월-11월) 그리고 겨울 (12윌-2월)로 분류되었다. ENSO episode에 대한 수문변량들의 조건부 초과확률과 분포형태를 바탕으로 분석을 수행한 결과 전반적으로 Warm ENSO episode의 경우 강수량 증가와 기온 상승과 관련이 있고, Cold ENSO episode의 경우 강수량 감소와 기온 하강과 관계가 있다. 그러나 일부 지역에서는 이러한 전반적인 결과와 상이한 결과가 나타나기도 하였다.

• International Journal of Advanced Culture Technology
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• 제11권3호
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• pp.83-88
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• 2023

The increasing global average temperature and the emergence of various abnormal climate phenomena are already being experienced in reality. The problems arising from climate change are expanding and becoming catastrophic, despite the efforts of various organizations to prevent them. In order to avoid climate issues from becoming black elephants, we conducted interviews with emergency planning officer from various institutions to identify potential X-events caused by climate change. The results of analyzing the anticipated X-events by these emergency planning officer revealed a chain of ripple effects associated with their occurrence. This implies that once an X-event happens, its influence is broader and more significant. Through this study, we aim to share the understanding of the ripple effects of climate X-events with many people, raising awareness of the severity of climate issues. We hope that this will serve as a starting point for more institutions, individuals, and nations to make efforts in resolving climate problems, turning X-events into opportunities rather than crises.

• 대기
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• 제26권1호
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• pp.193-201
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• 2016

An anomalous cold-weather period occurred during January 2011 in East Asia, and this study investigates the event by focusing on the blocking phenomena formed at Northeastern Asia. The area of cold weather is determined to represent the characteristic features of abnormal cold temperature. The 2010/11 winter is divided into three periods P1, P2 (cold period), and P3. For the cold area ($30-50^{\circ}N$, $115-135^{\circ}E$) the corresponding cold period P2 is determined to be 39 days from 23 December 2010 through 30 January 2011. During P1 and P3 temperature anomalies from the climatological mean are small with large standard deviation compared to those of P2, which has large negative anomaly and small standard deviation. The period P2 is dominated by blocking, which was determined by distributions of 500-hPa geopotential height and potential temperature on the 2 PVU surface. Correlation-coefficient analyses show that during P2 the temperature in the cold area is related with pressure of Northeastern Asia, while the temperature during P1 and P3 is related with pressure of Northwest of Korea. Also, during P1 and P3 the temperature pattern shows eastward propagation, but during P2, a stationary pattern. All the observations imply that, during the cold period P2, the temperature in the cold area is related with blocking in Northeastern Asia. During P1 and P3 temperature pattern is related with 500-hPa geopotential height in Siberia, and this relationship is also observed in the climatological mean state.