• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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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.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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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.

• Proceedings of the KWS Conference
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• 2002.10a
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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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• v.52 no.1
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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.

• Journal of the Korean Institute of Gas
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• v.4 no.1 s.9
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• pp.69-76
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• 2000

Explosion Quantities and flashing mass resulting from the variation of temperature are calculated by a computer program, BLEVE ESTIMATOR, to carry out the risk assessment of BLEVE. The damages caused by the BLEVE are estimated under the explosion of the simulation condition similar to the Puchun LP gas station accident, and the results are compared with the commercial program SAFER of Dupont CO. Explosion quantities and flashing mass increase exponentially with the increase of explosion temperature. These values for propane are relatively higher than those for n-butane. In conditions of higher vessel temperature, vessel pressure, and liquid ratio of containment, higher overpressures are calculated.

• Journal of Korean Society for Geospatial Information Science
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• v.20 no.3
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• pp.109-115
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• 2012

Pedestrian safety is becoming a major priority on the nation's roadway policy. Numerous strategies have been experimented with nationwide in an attempt to reduce the accidents of pedestrian-vehicle crashes, especially in pedestrian crosswalk. We suggest the wireless controlled in-pavement flashing light system to reduce the accident at pedestrian crosswalk. We have recommended the use of wireless controlled systems as a tool to manage the In-pavement flashing light system that have retain high visibility goals for pedestrian preserving or enhancing pedestrian safety. Then we have compared this system with any other legacy systems in respect of cost and effects.

• Journal of Hydrogen and New Energy
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• v.30 no.6
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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.

• Journal of Korean Society of Transportation
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• v.31 no.5
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• pp.16-25
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• 2013

This study deals with the relationships between flashing operation and traffic accident at signalized intersections. The objective of this study is to analyze safety effects of the yellow flashing operation at night. In pursuing the above, this study gives particular attention to evaluating the safety results from signal operation of Cheongju's 190 signalized intersections using before-after evaluation with comparison group that are categorized by highway function. The main results are as follow. First, the numbers of traffic accidents and of fatalities/injuries in two highway types (arterial and collector road) have increased after operating the yellow flashing signal at night. Second, the numbers of accidents, fatalities/injuries, severe accidents and of fatalities/severe injuries in group A(arterial) have increased by 19%, 36%, 15% and 14%, respectively. Finally, the numbers of accidents, fatalities/injuries, severe accidents and fatalities/severe injuries in group B (collector) have increased by 50%, 64%, 41% and 77%, respectively.

• Proceedings of the KSME Conference
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• 2008.11b
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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.

• Journal of Auto-vehicle Safety Association
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• v.15 no.3
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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.