• Journal of Advanced Marine Engineering and Technology
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• v.24 no.4
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• pp.486-493
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• 2000

Flow mechanism around air flow sensor of electronic control engine, especially Karman vortex type, was investigated experimentally. The two-dimensional flow characteristics in the intermediate wake region behind a triangular vortex-generator respectively apex forward facing, apex backward facing and vertical flat plates following after apex forward facing(i.e vortex-flowmeter) were investigated at Reynolods number of $ReH=1.4\times10^4$; H is the width of a triangular vortex-generator. The vortex shedding frequency for wide Reynolds number from $7\times10^3$ to $2.1\times10^4$ was also surveyed. The velocity component was measured by X-type hot wire anemometer at 8H downstream from the bluff body. The coherent structure of the intermediate wake behind a bluff body was obtained by conditional phase average technique. As a result, it was verified that the vertical flat plates following after apex forward triangular vortex-generator make not only more linear relation between free stream velocity and vortex shedding frequency but also more periodic vortex in the vicinity of the center of wake.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.85-92
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• 2004

As a research to develop a SCRAM jet engine is actively conducted, a necessity to produce a high-enthalpy flow in a laboratory is increasing. In order to develop the SCRAM-jet engine, stabilized combustion in a supersonic flow-field should be attained, in which a duration time of flow is extremely short. Therefore, a mixing process of breathed air and fuel, which is injected into supersonic flow-fields is one of the most important problem. Since, the flow inside SCRAM jet engine has high-enthalpy, an experimental facility is required to produce such high-enthalpy flow-field. In this study, a detonation-driven shock tunnel was built and was used to produce high-enthalpy flow. Further-more, SCRAM jet engine model equipped backward-facing step was installed at test section and flow-fields were visualized using color-schlieren technique and high speed video camera. The fuel was injected perpendicular to the flow of Mach number three behind backward-facing step. The height of the step, distance of injection and injection pressure were changed to investigate the effects of step on a mixing characteristic between air and fuel. The schlieren photograph and pressure histories show that the fuel was ignited behind the step.

• Nuclear Engineering and Technology
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• v.49 no.1
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• pp.124-133
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• 2017

In-vessel retention by passive external reactor vessel cooling under severe accident conditions is a viable approach for retention of radioactive core melt within the reactor vessel. In this study, a new and versatile coating technique known as "cold spray" that can readily be applied to operating and advanced reactors was developed to form a microporous coating on the outer surface of a simulated reactor lower head. Quenching experiments were performed under simulated in-vessel retention by passive external reactor vessel cooling conditions using test vessels with and without cold spray coatings. Quantitative measurements show that for all angular locations on the vessel outer surface, the local critical heat flux (CHF) values for the coated vessel were consistently higher than the corresponding CHF values for the bare vessel. However, it was also observed for both coated and uncoated surfaces that the local rate of boiling and local CHF limit vary appreciably along the outer surface of the test vessel. Nonetheless, results of this intriguing study clearly show that the use of cold spray coatings could enhance the local CHF limit for downward-facing boiling by > 88%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.5
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• pp.418-422
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• 1998

The Co-Cr films are one of the most suitable candidates for perpendicular magnetic recording media. The facing targets sputtering(FTS) system has a advantage of preparing films over a wide range of working gas pressure on plasma-free substrate. In this study, we investigated the possibility of employing FTS system for depositing Co-Cr films. The Co-Cr thin films were deposited with various sputter gas pressure($P_Ar$, 0.1~10mTorr) by using FTS apparatus at temperature of $40^{\circ}C and 220^{\circ}C$, respectively. Crystallographic and magnetic characteristics were evaluated by x-ray diffractometry (XRD) and vibrating sample magnetometer(VSM), respectively. Under argon gas pressure at 0.1mTorr, films with morphologically dense microstructure, good c-axis orientation and higher coercivity were obtained. It has been confirmed that the FTS system is very useful for preparing Co-Cr thin film recording media.

• Nuclear Engineering and Technology
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• v.35 no.4
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• pp.274-285
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• 2003

Film boiling heat transfer coefficients for a downward-facing hemispherical surface are measured from the quenching tests in DELTA (Downward-boiling Experimental Loop for Transient Analysis). Two test sections are made of copper to maintain Bi below 0.1. The outer diameters of the hemispheres are 120 mm and 294 mm, respectively. The thickness of both the test sections is 30 mm. The effect of diameter on film boiling heat transfer is quantified utilizing results obtained from the two test sections. The measured heat transfer coefficients for the test section with diameter 120 mm lie within the bounding values from the laminar film boiling analysis, while those for diameter 294 mm are found to be greater than the numerical results on account of the Helmholtz instability. There is little difference observed between the film boiling heat transfer coefficients measured from the two test sections. In addition, the higher thermal conductivity of copper results in the higher minimum heat flux in the tests. For the test section of diameter 120 mm, the Leidenfrost point is lower than that for the test section of diameter 294 mm. Destabilization of film boiling propagates radially inward for the 294 mm test section versus radially outward for the 120 mm Test Section.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.3
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• pp.507-514
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• 2009

Large eddy simulation code was developed to predict the turbulent flows over backward-facing steps including a recirculating flow phenomena. Localized dynamic ksgs-equation model was employed as a LES subgrid model and the LES solver was implemented on parallel computer consisting of 16 processors to reduce computational costs. The results of laminar flow showed qualitative and quantitative agreements between current simulations and experimental results availablein literatures. The simulation of the turbulent flows also yielded reasonable results. From these results, it can be expected that developed LES code will be very useful to analyze the combustion in stabilities and noise of a practical combustor in the future.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.3
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• pp.289-294
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• 2021

Tungsten (W) is used as a facing material for nuclear fusion reactors, and it is used in conjunction with structural materials such as copper alloy (CuCrZr), graphite, or stainless steel. On the other hand, since tungsten is a material with a high melting point, a method that can be manufactured at a lower temperature is important. Therefore, in this study, tungsten, which is a facing material, was attempted to be manufactured using a pressure sintering method. Material properties of sintered tungsten materials were analyzed for each solvent using two types of solvents, acetone and polyethylene glycol. The sintered tungsten material using acetone as a solvent exhibited a hardness value of about 255 Hv, and when polyethylene glycol was used, a hardness value of about 200 Hv was shown. The flexural strength of the sintered tungsten material was 870 MPa and 307 MPa, respectively, when acetone and polyethylene glycol were used as solvents. The sintered tungsten material using acetone as a solvent caused densification between particles, which served as a factor of increasing the strength.

• International Journal of Computer Science & Network Security
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• v.22 no.4
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• pp.254-260
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• 2022

The purpose of this study was to identify the obstacles facing gifted students with learning disabilities (GSLDs) from the point of view of their teachers in the Makkah region and to find suggested solutions to overcome these obstacles. The study covered Makkah, Jeddah and Taif and used semi-structured interviews which included open-ended questions. The study findings indicated that there were several educational obstacles including the absence of adapted courses or specialized teachers for GSLDs category and the insufficient time for the students to express their talents. According to the findings, there were also societal obstacles including the society's failure to expect the presence of talents along with disabilities, or its denial or rejection of their talents in addition to ridiculing them. The findings also confirmed the existence of administrative obstacles including the lack of community partnership. There were also family obstacles such as the family's lack of encouragement for the students, and ignorance of the nature of GSLDs. The study came up with a number of solutions and proposals related to awareness, educational institutions, education and competitions for talented people with learning disabilities.

• Land and Housing Review
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• v.12 no.2
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• pp.79-89
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• 2021

This simulation based study analyzed the horizontal daylight distribution on the floor and ceiling of a small office space based on window orientations and interior window blind positions. South and north facing windows were each tested without window blinds and with window blinds at 45° and 180° (horizontal). The study showed that the illuminance value was highest 1m from the window. On the floor and ceiling, the difference in illuminance value was the greatest and least in December and June, respectively. The indoor illuminance value was highest when there was no window blind and under south-facing conditions. The greatest illuminance difference occurred between window blinds positioned at 45° and 180°. Under north-facing conditions, windows without blinds or with blinds at 45° had the least impact on indoor illuminance with illuminance being more evenly distributed.

• Korean Journal of Environment and Ecology
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• v.30 no.3
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• pp.376-385
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• 2016

Through the vegetation survey of Geumcheon Valley on the south-facing slope and the other side of the valley, Jedanggol on the north-facing slope in Taebaeksan Provincial Park, the characteristics of vegetation structure and change by slope and altitude were examined. From Geumcheon Valley(850m) via the ridge(1,380m) to Jedanggol(950m), thirty plots at intervals of 50m altitude were selected for investigation. According to the results of the analysis, Acer pictum subsp. mono, Fraxinus rhynchophylla, Betula davurica and Lindera obtusiloba were observed only in the south-facing slope, while Sorbus commixta, Prunus padus, Prunus maackii and Acer komarovii were observed only in the north-facing slope. However, Quercus mongolica, Betula costata, Cornus controversa, Tilia amurensis, Acer pseudosieboldianum and Magnolia sieboldii were found to be distributed over both the slopes. The analysis of ordination found that the vegetation was distributed discontinuously by slope. Especially, the vegetation of the north-facing slope appeared to be affected by the direction that the slope faces. Quercus mongolica community, which is the dominant species at an altitude of over 1,200m, was determined to be affected by elevation factor. The maximum age of the major trees was as follows: Betula costata and Quercus mongolica were estimated to be 53-year-old and 113-year-old respectively.