• Nuclear Engineering and Technology
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• 제54권2호
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• pp.554-564
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• 2022

The natural circulation phenomena occurring in fully integrated nuclear reactors are associated with a unique formation mechanism. The phenomenon results from a structural feature of these reactors involving upward flow from the core, located in the central-bottom region of a single vessel, and downward flow to the steam generator in the annulus region. In this study, to understand the natural circulation in a single vessel involving a multi-layered flow path, single-phase and two-phase natural circulation tests were performed using the SMART-ITL facility, and validation analysis of the TASS/SMR-S code was performed by comparing the corresponding test results. Three single-phase natural circulation tests were sequentially conducted at 15%, 10%, and 5% of full-scaled core-power without RCP operation, following which a two-phase natural circulation test was successively conducted with an artificial discharge of coolant inventory. The simulation capability of the TASS/SMR-S code with respect to the natural circulation phenomena was validated against the test results, and somewhat conservative but reasonably comparative results in terms of overall thermalhydraulic behavior were shown.

• 한국자동차공학회논문집
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• 제18권5호
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• pp.108-114
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• 2010

The injection nozzle of an electro-hydraulic injector is being opened and closed by movement of a injector's needle which is balanced by pressure at the nozzle seat and at the needle control chamber, at the opposite end of the needle. In this study, the effects of needle movement in a piezo-driven injector on unsteady cavitating flows behavior inside nozzle were investigated by cavitation numerical model based on the Eulerian-Lagrangian approach. Aimed at simulating the 3-D two-phase flow behavior, the three dimensional geometry model along the central cross-section regarding of one injection hole with real design data of a piezo-driven diesel injector has been used to simulate the cavitating flows for injection time by at fully transient simulation with cavitation model. The cavitation model incorporates many of the fundamental physical processes assumed to take place in cavitating flows. The simulations performed were both fully transient and 'pseudo' steady state, even if under steady state boundary conditions. As this research results, we found that it could analyze the effect the pressure drop to the sudden acceleration of fuel, which is due to the fastest response of needle, on the degree of cavitation existed in piezo-driven injector nozzle.

• Earthquakes and Structures
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• 제10권5호
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• pp.1049-1066
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• 2016

An approximate analysis is presented for multi-story setback buildings subjected to ground motions. Setback buildings with mass and stiffness discontinuities are common in modern architecture and quite often they are asymmetric in plan. The proposed analysis provides basic dynamic data (frequencies and peak values of base resultant forces) and furthermore an overview of the building response during a ground excitation. The method is based on the concept of the equivalent single story system, which has been introduced by the author in earlier papers for assessing the response of uniform in height buildings. As basic quantities of the dynamic response of elastic setback buildings can be derived by analyzing simple systems, a structural layout of minimum elastic rotational response can be easily constructed. The behavior of such structural configurations, which is basically translational into the elastic phase, is also examined into the post elastic phase when the strength assignment of the various bents is based on a planar static analysis under a set of lateral forces simulating an equivalent 'seismic loading'. It is demonstrated that the almost concurrent yielding of all resisting elements preserves the translational response, attained at the end of the elastic phase, to the post elastic one.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2000년도 제14회 학술강연논문집
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• pp.6-6
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• 2000

On-orbit thermal behavior of KOMPSAT (Korea Multi-purpose Satellite) propulsion system employing hydrazine (N$_2$H$_4$) liquid monopropellant is addressed. Thermal control performance to prevent propellant freezing in spacecraft-operational orbit was verified by flight telemetry data obtained during LEOP (Launch and Early Operation Phase). Results are depicted in terms of temperature history during several orbits selected and are compared with acceptable temperature ranges of system components. Cyclic behavior of temperature is reduced into duty cycles of the avionics heaters and subsequently converted into the electrical power required to keep away from propellant freezing. Temperature of each component which was achieved under on-ground thermal-balanced condition of spacecraft, is presented for comparison with the flight data, additionally.

• 한국가스학회지
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• 제7권3호
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• pp.32-43
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• 2003

이 연구는 단성분계(메탄)과 다성분계(천연가스) 하이드레이트의 상평형 조건을 관찰하고, 반응시간에 따른 하이드레이트 생성 거동을 관찰하여 비교 분석하였다. 단성분과 다성분계 하이드레이트의 차이점은 크게 유도지체시간과 안정 영역이다. 반응시 다성분계 하이드레이트는 가스의 성분들이 서로 다른 농도변화를 나타내었으며, 제조된 하이드레이트를 해리시켰을 때도 서로 다른 해리 속도에 의해 각 가스 성분들의 농도가 변화되었다. 압력이 6 MPa이고, 온도가 276.65 K이며, 교반속도가 600 rpm일때 다성분계 하이드레이트 제조시 메탄이외의 여러 가스 성분들에 의해 하이드레이트 핵 생성이 빠르게 진행되어 유도지체시간은 짧다. 그리고 단성분계 하이드레이트는 단일 성분으로 이루어져 있으므로 안정 영역이0.055 mole of $CH_4$/mole of water에서 보다 뚜렷하게 관찰되고, 다성분계 하이드레이트는 안정 영역이 0.04 mole of $CH_4/$mole of water에서 관찰된다.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.27-34
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• 2001

This experimental study is to investigate the intermittent spray characteristics of the multi-hole diesel nozzle with a 2-spring nozzle holder. Without changing the total orifice exit area, its hole number varied from 3($d_n=0.42mm$) to 8($d_n$=0.25mm). Through the use of the 2-D PDPA(phase Doppler particle analyzer), the droplet diameter and the velocity of the diesel spray injected intermittently from the multi-hole nozzle into the still ambient were measured. And the calculations of time-resolved diameters, SMD and AMD were made. The results can be summarized as follows. The spray of the multi-hole nozzle consisted of three parts. These are the leading edge, the central part and the trailing edge. And most of droplets produced at the trailing edge of spray. In the spray flow field, the measuring position which represented the intermittent spray characteristics well was near the nozzle tip. But at the downstream of the spray, its characteristics disappeared, and spray behavior showed a quasi steady state regardless of the time evolution of the spray. The overall mean SMD of the spray increased with the spray development, and showed their maximum value near 1.5ms regardless of hole number.

• 공업화학
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• 제19권4호
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• pp.421-426
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• 2008

본 연구에서는 다양한 조성의 다중벽 탄소 나노튜브/폴리스티렌 복합체들을 유화제를 이용한 용액공정을 이용하여 제조하였다. 이때, 분자량이 다른 3종의 폴리스티렌(PS-1 : ${\bar{M}}_n$ = 101500 g/mole, PS-2 : ${\bar{M}}_n$ = 89900 g/mole, PS-3 : ${\bar{M}}_n$ = 85000 g/mole)을 사용하였다. 복합체에서 매트릭스로 사용된 폴리스티렌의 임계흐름온도($T_{cf}{\sim}195^{\circ}C$) 이상과 이하인 $210^{\circ}C$ 및 $180^{\circ}C$에서의 열적 거동을 동적 유변측정기를 이용하여 측정하였다. 복합체의 저장 탄성율, 손실탄성율 및 용융점도는 복합체내에서 다중벽 탄소 나노튜브 함량이 증가함에 따라 증가하였으며, 용융점도의 경우에는 다중벽 탄소 나노튜브 함량이 2 wt%에서 5 wt% 사이에서 가장 큰 증가가 관찰되었다. $210^{\circ}C$의 유변특성 거동에 의하면, 특정 다중벽 탄소 나노튜브 함량에서 복합체의 점성 특성이 탄성특성으로 전이되는 현상이 관찰되었으며, 이때 다중벽 탄소 나노튜브 함량은 MWCNT/PS-1, MWCNT/PS-2 및 MWCNT/PS-3 조성에 대해 각각 3.5 wt%, 3.2 wt 및 3.0 wt%를 나타내었다.

• 한국표면공학회지
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• 제44권6호
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• pp.269-276
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• 2011

Phase evolution and tribological behavior of Cr-Mo-N multi compositional films with different interlayer were investigated. The films were deposited by hybrid PVD (Physical Vapor Deposition) system consisted of dc unbalanced magnetron (UBM) sputtering and arc ion plating (AIP) sources. A pure molybdenum (Mo) was used as sputtering target and also a pure Cr was used as AIP target to form the Cr-Mo-N films. Various growth planes were found, no textured surface, in all of the multi composition films. Maximum value of microhardness was measured in Cr-Mo-N film with Mo interlayer as 29 GPa. Composition film was mainly showed the aspect of the adhesive wear than CrN film. The friction coefficient was decreased from 0.6 for pure CrN coating to 0.35 for Cr-Mo-N film with Mo interlayer. This result may come from the formation of metal oxide tribo-layer which is known as solid lubricant during the wear test.

• 한국지진공학회논문집
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• 제7권6호
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• pp.101-108
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• 2003

실험장비의 용량 제약, 경제적인 이유 등으로 지진하중에 대한 구조물의 동적 거동을 연구할 경우, 보편적으로 축소모형이 많이 적용되고 있다. 그러나 구조물의 지진응답은 비탄성 거동을 나타내기 때문에 거동예측이 복잡함에도 불구하고, 축소모형의 지진실험 결과로부터 원형구조물의 지진응답을 유추하기 위한 상사법칙의 연구는 미비한 실정이다. RC구조물의 축소모형 제작 시 상사율이 커지면 상대적으로 부가질량이 증가하며, 또한 굵은 골재 크기의 영향으로 원형구조물과 축소모형의 제작에 동일한 재료를 사용하지 않는 것이 바람직하다. 따라서 동일한 재료를 사용하지 않을 경우, 상사법칙은 기하학적인 상사율과 재료적인 등가탄성계수비에 의존하게 된다. 본 연구에서는 원형구조물과 축소모형에 각각 적용되는 normal-concrete와 micro-concrete의 재료 비선형성을 파악하기 위해 압축강도시험을 수행하여, 재료의 거동구간을 등가의 다단계로 나누어 등가탄성계수비를 적용시킴으로써 지진손상의 정도를 고려할 수 있는 Equivalent multi-phase similitude law를 유도하였다. 이러한 상사법칙을 적용한 유사동적실험 알고리즘을 구축하여 수치해석적인 검증을 수행하여 유사동적실험의 적용성을 확인하였다.

• 한국재료학회지
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• 제25권11호
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• pp.612-615
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• 2015

In this work, on-site corrosion behavior of heat resistant tubes of T91, used as components of a superheater in a power plant for up to 25,762 h, has been investigated using scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDS), and electron backscattered diffraction(EBSD), with the objectives of studying the composition, phase distribution, and evolution during service. A multi-layer structure of oxide scale was found on both the steamside and the fireside of the tube surface; the phase distribution was in the order of hematite/magnetite/spinel from the outer to the inner matrix on the steamside, and in the order of slag/magnetite/spinel from the outer to the inner matrix on the fireside. The magnetite layer was found to be rich in pores and cracks. The absence of a hematite layer on the fireside was considered to be due to the low oxygen partial pressure in the corrosion environment. The thicknesses of the hematite and of the slag-deposit layer were found to exhibit no significant change with the increase of the service time.