• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1514-1524
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• 2019

Hydrogen-steam gas mixture may be injected into containment with flow regime varying both spatially and transiently due to wall effect and pressure difference between primary loop and containment in severe accidents induced by loss of coolant accident. Preliminary CFD analysis is conducted to gain information about the helium flow regime transition process from jet to buoyancy plume for forthcoming experimental study. Physical models of impinging jet and wall condensation are validated using separated effect experimental data, firstly. Then helium transportation is analyzed with the effect of jet momentum, buoyancy and wall cooling discussed. Result shows that helium distribution is totally dominated by impinging jet in the beginning, high concentration appears near gas source and wall where jet momentum is strong. With the jet weakening, stable light gas layer without recirculating eddy is established by buoyancy. Transient reversed helium distribution appears due to natural convection resulted from wall cooling, which delays the stratification. It is necessary to concern about hydrogen accumulation in lower space under the containment external cooling strategy. From the perspective of experiment design, measurement point should be set at the height of connecting pipe and near the wall for stratification stability criterion and impinging jet modelling validation.

• 디지털융복합연구
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• 제9권6호
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• pp.153-163
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• 2011

본 연구는 참여정부의 '전시작전통제권(이후 전작권) 전환 결정에 영향을 미친 군사 및 정치적 요인을 분석하는데 있다. 전작권 전환의 결정요소들에 관한 조사는 문헌연구를 우선 실시하고 추가적으로 AHP를 이용하여 타당성을 제고하였다. 분석결과로, '한미동맹의 비대칭성' 측면에서는 한국 방위에 부정적인 효과가, '한미동맹의 상호의존성' 측면에서는 한국군의 전구작전 주도능력 구비에 긍정적인 효과가, '참여정부의 진보정권 이익' 측면에서는 한국군의 자위권 제고에 긍정적인 효과가 나타났다. AHP 분석결과로 '참여정부의 진보정권 이익'측면의 "한국의 자위권 행사"가 가장 높게, '한미동맹의 비대칭성’측면의 "북한의 위협 감소" 가 가장 낮은 것으로 조사되었다. 본 연구는 참여정부의 전작권 전환의 결정요인을 AHP를 이용하여 군사 및 정치적 측면에서 분석하였다는데 의의가 있다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.208-208
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• 1999

It is found that with increasing power, the measured electron energy distribution by Langmuir probe evolves into a Druyvesteyn-like electron energy distribution in the low-pressure regime of 1mTorr in a small inductively coupled plasma. Electron bounce resonance is introduced to explain the transition of the electron energy distribution against the rf power, The energy diffusion coefficients which determine the shape of the electron energy distribution in elastic range are calculated with and without electron bounce resonance. This electron energy distribution transition is well explained by the electron bounce resonance.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2067-2072
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• 2007

Understanding of the impinging behavior of an electrically charged spray is essential in determining appropriate operating conditions for electro-spraying of paints, surface coating materials and insecticides. In the present work, as an initial step, the wall impact of an electrically charged droplet has been experimentally investigated. The charged drops were directed on the surface of a paraffin wax, and the impinging behavior was visualized and recorded using a CCD camera to identify the impingement regime. The spread-rebound boundary for the charged drop turned out to be smaller compared to that for an electrically neutral droplet under the same surface condition. The shift of the transition criterion is considered to be due to the discrepancy between the maximum spread ratio of the electrically charged droplet and that of the neutral droplet.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.153-154
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• 2002

Wear map of silver coatings on AISI 52100 has been constructed to delineate the wear transition behavior with the change in operating conditions in various environments. Three main regimes were clearly identified: (i) elastic/plastic deformation of silver coating without failure. (ii) mild wear regime after initial failure of silver coating and (iii) severe wear regime. In the mild wear regime, the contact surfaces were covered with transfer layers of agglomerated wear particles. The transfer layer acted as a protective layer and resulted in low friction even after the initial failure of the coated films, whose characteristics were strongly dependent on both the operating and environmental conditions. Also, the existence of the critical sliding speed, above which no transfer layer was able to form, was discussed in the work.

• 한국대기환경학회지
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• 제29권2호
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• pp.211-216
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• 2013

For diffusion limited cluster agglomerates the ratio of the mobility radius to the radius of gyration $R_m/R_g$ vs. N and the ratio of the mobility radius to the radius of primary particle $R_m$/a are determined using experimental data obtained with DMA-APM and tandem DMA over a range of Knudsen numbers extending into the transition region where there is a lack of data. It was found that in slip regime with the number of primary particles between 100 and 400, datapoints are found to be between the two asymptotic lines for the continuum and free molecular regimes as those datapoints are plotted in both $R_m/R_g$ vs. N and $R_m$/a vs. N.

• 설비공학논문집
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• 제14권10호
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• pp.833-843
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• 2002

The present experimental and numerical investigations are performed for the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin- friction coefficients have been measured for the fully developed flow of water and glycerine-water solution (44%) with the inner cylinder rotating at speed of 0∼600 nm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime.

• Journal of Mechanical Science and Technology
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• 제17권4호
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• pp.562-570
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• 2003

This experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and of 0.4% aqueous solution of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0～600 rpm. Also, the visualization of vortex flows has been performed to observe the unstable waves. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and. then, it gradually approach to zero for the turbulent flow regime. Consequently, the critical (bulk flow) Reynolds number Re$\_$c/ decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.

• 한국경제지리학회지
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• 제17권3호
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• pp.567-584
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• 2014

이 글은 김영삼 정권하의 노동정치의 성격과 그 변화과정을 체계적으로 분석한다. 분석의 결과는 'IMF 경제위기'를 계기로 노동정치는 '갈등적 다원주의'에서 '사회적 합의주의'로 전환되었으며, 그 전환은 경제위기에 의해 촉발되었고, 변동의 방향은 정권적 차원의 제도적 맥락과 사회연합의 역학에 의해 규정되었음을 보여준다. 이 분석 결과가 함의하는 바는 경제위기나 국제적 압력이 노동정치의 변화 양상 및 방향을 규정짓는 변수가 아니고, 사회연합의 역학적 구도와 내용이 행위자들에게 새로운 인식과 전략적 선택을 강요하며, 이는 행위자들의 상호작용을 통해 최종적으로 노동정치의 변동을 낳는다는 점이다.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.73-83
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• 2019

It is important to clarify the mechanisms of molten-fuel-pool sloshing behavior that might be encountered during a core disruptive accident of sodium-cooled fast reactors. In this study, motivated by acquiring some evidence for understanding the characteristics of this behavior at more realistic conditions, a number of experiments are newly performed by injecting nitrogen gas into a water pool with the accumulation of solid particles. To achieve comprehensive understanding, various parameters including particle bed height, particle size, density, shape, gas pressure along with the gas-injection duration, were employed. It is found that due to the different interaction mechanisms between solid particles and the gas bubble injected, three kinds of regimes, termed respectively as the bubble-impulsion dominant regime, the transitional regime and the bed-inertia dominant regime, could be identified. The performed analyses also suggest that under present conditions, all our experimental parameters employed can have noticeable impact on the regime transition and resultant sloshing intensity (e.g. maximum elevation of water level at pool peripheries). Knowledge and fundamental data from this work will be used for the future verifications of fast reactor severe accident codes in China.