• 해양환경안전학회지
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• 제17권2호
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• pp.179-185
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• 2011

예인선 A호와 B호가 재킷을 실은 부선을 예인하기 위하여 진도 벽파항에서 출항하여 진도대교 부근 조력발전소 예정지로 운항 중 예인능력을 갑자기 상실하고 진도대교로 표류하여 바지선에 실려 있던 대형 철구조물인 일명 '재킷'이 제1진도대교 교각 및 중앙부 상판과 충돌한 사고가 발생하였다. 이 사고로 바지선에 살려 있던 조력 발전소 건설용 철구조물이 진도대교 중앙부 하단지점 바다로 추락했으며 제1진도대교 교각 1개가 일부 파손되고 상판의 바람막이도 세 군데가 구겨지는 등의 피해가 발생했다. 본 연구에서는 상기의 해양사고와 관련하여 부선의 운항경로가 갑자기 바뀌며 예인력을 상실하였던 해역의 시간대별 조류속도를 추정하고, 재킷을 실은 부선을 예인하기 위한 적정한 예인력을 산정함과 동시에 당시 기상 상황 하에서의 부선의 예인 안전성을 검토하고자 한다.

• 한국위성정보통신학회논문지
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• 제8권3호
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• pp.10-14
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• 2013

본 논문에서는 저전력 기술인 DVFS (Dynamic Voltage Frequency Scaling) 응용을 위하여, 동작주파수의 변화에도 소비전력이 일정한 특성을 갖는 전류모드 회로를 적용함에 있어서, 저속 동작에서 소비전력이 과다한 전류모드 회로의 문제점을 전류모드 회로에서 sub-threshold 영역 동작의 MOSFET을 적용함으로써 소비전력을 최소화하는 설계기술을 소개한다. 회로설계는 MOSFET BSIM 3모델을 사용하였으며, 시뮬레이션한 결과, strong-inversion 동작일 때 소비전력은 $900{\mu}W$이었으나, sub-threshold 영역으로 동작하였을 때, 소비전력이 $18.98{\mu}W$가 되어, 98 %의 소비전력의 절감효과가 있음을 확인하였다.

• 신재생에너지
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• 제8권2호
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• pp.6-13
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• 2012

Due to global warming, the need to secure an alternative resource has become more important nationally. Having very strong current on the west coast with up to 10 m tidal range, there are many suitable site for the application of TCP (Tidal Current Power) in Korea. On the south west regions between many islands that create strong current in the narrow channels. The rotor is one of the essential components which can convert tidal current energy into rotational energy to generate electricity. The design optimization of rotor is very important to maximize the power production. The performance of rotor can be determined by various parameters including number of blades, shape, sectional size, diameters and etc. This paper introduces the multi-layer vertical axis tidal current power system which can be applied to offshore jetties and piers effectively. Various cases of VAT turbine were designed. Specifically, the number of blades and turbine shape are changed in several cases. Also, performance analysis was carried out by CFD.

• 천문학회보
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• 제36권2호
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• pp.100.2-100.2
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• 2011

The dynamical evolution of the Earth's magnetosphere loaded with a transiently enhanced ring current is studied by numerical magnetohydrodynamic (MHD) simulation. Two cases with different values of the primitive ring current are considered. In one case, the initial ring current is strong enough to create a magnetic island in the magnetosphere. The magnetic island readily reconnects with the earth-connected ambient field and is destroyed as the system approaches a steady equilibrium. In the other case, the initial ring current is not so strong, and the initial magnetic field configuration bears no magnetic island, but a wake of bent field lines, which is smoothed out through the relaxing evolution of the magnetosphere. The relaxation time of the magnetosphere is found to be about five to six minutes, over which the ring current is reduced to about a quarter of its initial value. Before reaching a steady state, the magnetosphere is found to undergo an overshooting expansion and a subsequent contraction. Fast and slow magnetosonic waves are identified to play an important role in the relaxation toward equilibrium.

• 한국태양에너지학회 논문집
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• 제27권3호
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• pp.29-35
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• 2007

In accordance with Madrid and Kyoto Protocols, a 10kw wind turbine installed about 625m away from the King Sejong Station in the Antarctica has been in operation successfully. The current location of the wind turbine has different geographic surroundings from the previous candidate site considered in 2005 and that makes re-evaluation of wind resource at the current site including geographic effects necessary. Especially, strong wind flow derived by steep and complex terrain is dominant in the Antarctica so that computational flow analysis is required. The wind rose measured at the previous and current installation location are identical with strong meteorological correlation but prevailing directions of wind power density are different because of local wind acceleration due to complex terrain. Numerical analysis explains which effects brings this discordance between the two sites, and a design guideline required for additional wind turbine installation has been secured.

• 기술사
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• 제29권3호
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• pp.87-93
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• 1996

Lightening is a phenomenon in which electric charges accumulated in the air due to a strong ascending air current are instantly discharged. As the air current rises, the steam in the air turns into hail and grows to a certain size. Thunderclouds brought together by the ascending air current when the earth's surface is heated by strong summer sunlight produce what are called heat thunderstorms. Compared to transistors and IC's that operate at several volts, lightening induces voltages of from several 100 to several 10,000 volts and sometimes causes great damage, such as destroying equipment or delaying communication. The following describes the cause of lighting damage and basic idea behind countermeasures against such damage.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.376-377
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• 2007

In accordance with Madrid and Kyoto Protocols, a 10kW wind turbine installed about 625m away from the King Sejong Station in the Antarctica has been in operation successfully. The current location of the wind turbine has different geographic surroundings from the previous candidate site considered in 2005 and that makes re-evaluation of wind resource at the current site including geographic effects necessary. Especially, strong wind flow derived by steep and complex terrain is dominant in the Antarctica so that computational flow analysis is required. The wind rose measured at the previous and current installation location are identical with strong meteorological correlation but prevailing directions of wind power density are different because of local wind acceleration due to complex terrain. Numerical analysis explains which effects brings this discordance between the two sites, and a design guideline required for additional wind turbine installation has been secured.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.150-150
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• 2010

Carbon nanotubes have drawn attention as one of the most promising emitter materials ever known not only due to their nanometer-scale radius of curvature at tip and extremely high aspect ratios but also due to their strong mechanical strength, excellent thermal conductivity, good chemical stability, etc. Some applications of CNTs as emitters, such as X-ray tubes and microwave amplifiers, require high current emission over a small emitter area. The field emission for high current density often damages CNT emitters by Joule heating, field evaporation, or electrostatic interaction. In order to endure the high current density emission, CNT emitters should be optimally fabricated in terms of material properties and morphological aspects: highly crystalline CNT materials, low gas emission during electron emission in vacuum, optimal emitter distribution density, optimal aspect ratio of emitters, uniform emitter height, strong emitter adhesion onto a substrate, etc. We attempted a novel approach to fabricate CNT emitters to meet some of requirements described above, including highly crystalline CNT materials, low gas emission, and strong emitter adhesion. In this study, CNT emitters were fabricated by filtrating an aqueous suspension of highly crystalline thin multiwalled CNTs (Hanwha Nanotech Inc.) through a metal mesh. The metal mesh served as a support and fixture frame of CNT emitters. When 5 ml of the CNT suspension was engaged in filtration through a 400 mesh, the CNT layers were formed to be as thick as the mesh at the mesh openings. The CNT emitter sample of $1{\times}1\;cm^2$ in size was characteristic of the turn-on electrical field of 2.7 V/${\mu}m$ and the current density of 14.5 mA at 5.8 V/${\mu}m$ without noticeable deterioration of emitters. This study seems to provide a novel fabrication route to simply produce small-size CNT emitters for high current emission with reliability.

• Ocean and Polar Research
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• 제36권2호
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• pp.165-177
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• 2014

In an effort to investigate the structure and variability of the coastal current in the East Sea, a moored ADCP observation was conducted off Uljin from late May to mid-October 2006. Owing to the transition of season from summer to autumn, the features of the current and wind can be divided into two parts. Until mid-August (Part-I), a southward flow is dominant at all depths with a mean alongshore velocity of 4.2~8.9 cm/s but northward winds are not strong enough to reverse the near-surface current. During Part-II, a strong northward current occurs frequently in the upper layer but winds are predominantly southward including two typhoons that have deep-reaching influence. Profile of mean velocity has three layers with a northward velocity embedded at 12~28 m depth. The near-surface current of Part-II significantly coheres with winds at 4-8 day periods with a phase lag of about 12 hours. The modal structure of the current obtained by EOF analysis is: (1) Mode-1, having 83.6% of total variance, represents the current in the same direction at all depths corresponding to the southward North Korean Cold Current (NKCC). (2) Mode-2 (11.7%) reveals a two-layer structure that can be explained by the northward East Korean Warm Current (EKWC) in the upper layer and NKCC in the lower. (3) Mode-3 (2.6%) has three layers, in which the EKWC is reversed near the surface by opposing winds. This mode is particularly similar to the mean velocity profile of Part-II.

• Journal of the korean society of oceanography
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• 제38권3호
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• pp.122-134
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• 2003

Low-pass filtered time series of wind, coastal temperature, sea level and current were analyzed to understand the coastal upwelling processes in the southeast coast of Korea. Southerly winds favorable for coastal upwelling were dominant in summer of 1997. Total period of four major wind events amounts to 58 days during one hundred days from June to early September. Coastal temperature is most sensitive to variations of wind. The time lag between the onset of southerly (northerly) winds and decrease (increase) of temperature is 3-18 hours. In the frequency domain the coherent bands have periods of 2.4 and 4.0-5.4 days with respective phase lags of 17 and 27-37 hours. Despite the sensitive response, the magnitude of temperature change is not quantitatively proportional to the intensity or duration of the wind, because it depends on the degree of baroclinic tilting of isotherms built dynamically by the strong Tsushima Warm Current (TWC). Current is particularly strong near the coast and has a large vertical shear during the upwelling periods, which is associated with the baroclinic tilting. Both of current and sea level are poorly coherent with wind or temperature except for the period of 4 days.