• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.241-246
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• 1996

An analytical model to calculate rate of vapor generation due to heterogeneous wall nucleation in flashing flow is developed. In the present model, an important parameter of the vapor generation term, i.e. nucleation site density is calculated by integrating its probability distribution function with respect to active cavity radius. The limits of integration are minimum and maximum active cavity radii, and these are formulated using an active cavity model for nucleate boiling. This formulation, therefore. can statistically account for the effect of surface specific thermo-physical and geometric conditions on the vapor generation rate and flashing inception. For verifying the adequacy of the present model, steady state two-fluid and the bubble transport equations are solved with applicable constitutive equations. The applicable region of the bubble transport equation is also extended to churn-turbulent flow regime to predict interfacial area concentration at high void fraction. Predicted results in terms of axial pressure and void fraction profiles along the channels are compared with experimental data of Super Moby Dick and BNL Reasonable agreements have been achieved and this shows the applicability of the present model to flashing flow analysis.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.105-109
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• 1996

The calculation of the total power required at the Continuous Extrusion Forming(CONFORM) has been performed by the theoretical analysis of three transformation regions(primary grip length and extrusion grip length, flashing). In this study, that was performed by five transformation regions(biting, upsetting, filling, extruding, flashing)and four transformation regions(biting, upsetting and filling, extruding, flashing) and then results of theoretical analyses were compared with experimental results. Results of analysis by four and five transformation regions than that of three transformation regions in the CONFORM showed in a good agreement with experimental results.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.384-389
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• 2002

This study was aimed to evaluate the weldability and optimize the welding conditions for flash butt welding of 780MPa grade steel applied to the automotive bumper reinforcement. And then the relationship between the welding conditions and the joint performance relating specifically to coil-joining steel would be established. The effect of welding conditions between flashing and upsetting process was elucidated. Microstructure observation of the joint indicated that the decarburized band was mainly changed with upsetting process. Width of HAZ was also related to the upsetting conditions rather than the flashing conditions. Generally maximum hardness at HAZ was correlated with $C_{eq}$ of steel and the empirical relationship was obtained to estimate the HAZ properties. Tensile elongation at the joint was usually decreased with increasing the initial clamping distance. Investigation of fracture surface after tensile and bending tests reveal that the origin of cracking at the joint was oxide inclusions composed of $SiO_2$, MnO, $Al_2$ $O_3$, and/or FeO. The amount of inclusions was dependent on the composition ratio of Mn/Si in steel. If this ratio was above 4, the amount of inclusions was low and then the resistance to cracking at the joint was enough to maintain the joint performance. It was obtained that the flashing process influenced the conditions for the energy input to establish uniform or non-uniform molten layer, while the upsetting conditions influenced the joint strength. Heat input variable during flashing process was also discussed with the joint properties.

• Nuclear Engineering and Technology
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• 제52권1호
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• pp.37-50
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• 2020

A passive containment cooling system (PCCS) has been developed as advanced safety feature for innovative power reactor (iPOWER). Passive systems are inherently less stable than active systems and the PCCS encountered the flashing-induced instability previously identified. The objective of this study is to develop stability maps for flashing-induced instability using MARS (Multi-dimensional Analysis of Reactor Safety) code. Firstly, we conducted a series of sensitivity analysis to see the effects of time step size, nodalization, and alternative MARS user options on the onset of flashing-induced instability. The riser nodalization strongly affects the prediction of flashing in a long riser of the PCCS, while time step size and alternative user options do not. Based on the sensitivity analysis, a standard input and an analysis methodology were set up to develop the stability maps of PCCS. We found out that the calculated equilibrium quality at the exit of the riser as a stability boundary above 5 kW/㎡ was approximately 1.2%, which was in good agreement with Furuya's results. However, in case of a very low heat flux condition, the onset of instability occurred at the lower equilibrium quality. In addition, it was confirmed that inlet throttling reduces the unstable region.

• 한국가스학회지
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• 제4권1호
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• pp.69-76
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• 2000

BLEVE로 인한 위험을 평가하기 위한 프로그램, BLEVE ESTIMATOR를 이용하여 온도에 따른 폭발량과 Flashing mass를 계산하였고, 부천 가스충전소의 사고를 모델로 피해를 예측하였으며, 상용프로그램인 Dupont의 SAFER 프로그램과 비교하였다. 폭발량과 Flashing mass는 폭발온도의 증가에 따라 지수함수로 증가하였으며, Propane이 n-Butane보다 상대적으로 높게 나타났다. 용기의 온도, 압력, 충전비가 높을수록 Overpressure가 높게 나타났다.

• 대한공간정보학회지
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• 제20권3호
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• pp.109-115
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• 2012

보행자의 안전은 교통 및 도로행정의 가장 중요한 부분이 되어지고 있다. 국가에서도 보행자의 안전을 확보하기 위한 다양한 정책들이 시도되고 있으며 특히 횡단보도에서의 보행자 안전은 매우 절실한 상황이다. 본 연구에서는 횡단보도상에서의 보행자 사고를 감소시키기 위하여 무선제어가 가능한 도로표지병 시스템을 설계하여 제안하고자 한다. 무선제어 도로표지병 시스템은 보행자와 운전자의 가시성을 향상시키는 기능을 수행할 수 있어, 보행자를 보호하고 보행자의 안전을 확보할 수 있게 해준다. 또한 비용측면에서도 기존에 이용되는 유사한 도로표지병 시스템을 사용하는 것보다 효과적으로 구축할 수 있다는 장점이 있다.

• 한국수소및신에너지학회논문집
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• 제30권6호
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• pp.585-592
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• 2019

In this study, a flashing boiling phenomenon of pressurized water jet was numerically studied and validated against an experimental data in the literatures. The volume of fluid (VOF) technique was used to consider two-phase behavior of water, while the homogeneous relaxation model (HRM) model was used to provide the velocity of phase change. During the flashing boiling through a nozzle, a mach disk was observed near nozzle exit because of pressure drop resulting from two-phase under-expansion. The flashing jet structure, local distributions of temperature/vapor volume fraction/velocity, and position of the mach disk were examined as nozzle inlet temperature changed.

• 대한교통학회지
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• 제31권5호
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• pp.16-25
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• 2013

이 연구는 신호 교차로에서의 점멸 신호 운영과 교통사고와의 관계를 다루고 있다. 연구의 목적은 야간 황색 점멸 신호 운영의 안전효과를 분석하는데 있다. 이를 위해 이 연구는 청주시 190개 신호교차로를 비교그룹방법을 사용하여 도로기능별 신호운영의 안전성 평가에 중점을 두고 있다. 주요 결과는 다음과 같다. 첫째, 두 도로유형(간선기능과 집산기능) 모두 야간점멸신호 도입시 사고가 증가하는 것으로 분석되었다. 둘째, 그룹 A(간선기능)에서는 사고건수 19%, 사상자수 36%, 심각사고건수 15% 및 중상이상 사상자수 14%가 증가한 것으로 평가되었다. 셋째, 그룹 B(집산기능)에서는 사고건수는 50%, 사상자수는 64%, 심각사고건수 41%, 그리고 중상이상 사상자수는 77% 증가한 것으로 분석되었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2483-2488
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• 2008

To mitigate the effects of cavitation and flashing, several types of orifices have been installed in the pipeline of new nuclear power plants. To review the effects of wall thinning caused by flow-accelerated corrosion by the types of orifices, which are cone and plate, and the relation between flow behavior and local wall thinning, experiments and numerical analyses for the downstream pipe of two types of orifices were performed. The experimental results in terms of static pressure obtained for the experimental facilities were compared with those of three-dimensional (3D) numerical analyses using the FLUENT code. As the results of review of flow-accelerated corrosion effects based on the experiment and numerical analysis, it was identified that the orifice of cone-type can be comparatively mitigated the effects of cavitation and flashing, but can not be mitigated the effect of flow-accelerated corrosion.

• 자동차안전학회지
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• 제15권3호
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• pp.43-52
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• 2023

When a children's school bus stops on the road, the operator enables an amber flashing light (indicating stopping or slowing) or a red flashing light (indicating that children are getting on and off). Drivers of vehicles passing by the stopped school bus, as well as vehicles in adjacent lanes to the school bus must stop temporarily. However, many drivers are not aware of the laws and do not comply with them, so children are exposed to an increased risk of being hit, especially at night as the color recognition of the vehicle is significantly lower than during the day. In our experiments, messages and shapes using light were projected to the front and rear of a parked school bus, in addition to its red lights flashing.