• Korean Journal of Hydrosciences
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• v.3
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• pp.97-104
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• 1992

To design the minor structures in the small watersheds, it is required to calculate the peak discharge. For these calculations the simple peak flow prediction equations, the unit hydrograph method. the syntheic unit hydrograph methods or the runoff simulation models are adopted. To use these methods it is generally requried to know the amount and the distributions of the design rainfall; which are the uniform distribution, the trangular distribution, the trapezoidal distribution, or the Huff type distribution. In this study, the peak discharges are calculated by the different rainfall distributions and the results are compared.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.201-210
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• 2002

Experiments were done for performance and flow characteristics of a counter-rotating axial flow fan. Performance curves of a counter-rotating axial flow fan were obtained and compared by varying the blade pitch angles. The fan characteristic curves were obtained following the Korean Standard Testing Methods for Turbo Fans and Blowers (KS B 6311). The fan flow characteristics were measured using a five-hole probe and a slanted hot-wire. The velocity profiles between the hub and tip of the fans were measured and analyzed at the peak efficiency point. The peak efficiency of the counter-rotating axial flow fan was improved about 15% respectively, compared with the single rotating axial fan. The single rotating axial flow fan showed relatively law efficiency due to the swirl velocities behind rotor exit which produced pressure losses. The counter-rotating axial flow fan showed that the swirl velocity generated by the front rotor was eliminated by the rear rotor and the associated dynamic pressure is recovered in the from of the static pressure rise.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1532-1539
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• 2019

This paper analyzes a new method for reducing boiling water reactor fuel temperature during a Loss of Coolant Accident (LOCA). The method uses a device called Reverse Flow Restriction Device (RFRD) at the inlet of fuel bundles in the core to prevent coolant loss from the bundle inlet due to the reverse flow after a large break in the recirculation loop. The device allows for flow in the forward direction which occurs during normal operation, while after the break, the RFRD device changes its status to prevent reverse flow. In this paper, a detailed simulation of LOCA has been carried out using the U.S. NRC's TRACE code to investigate the effect of RFRD on the flow rate as well as peak clad temperature of BWR fuel bundles during three different LOCA scenarios: small break LOCA (25% LOCA), large break LOCA (100% LOCA), and double-ended guillotine break (200% LOCA). The results demonstrated that the device could substantially block flow reversal in fuel bundles during LOCA, allowing for coolant to remain in the core during the coolant blowdown phase. The device can retain additional cooling water after activating the emergency systems, which maintains the peak clad temperature at lower levels. Moreover, the RFRD achieved the reflood phase (when the saturation temperature of the clad is restored) earlier than without the RFRD.

• Journal of Korea Water Resources Association
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• v.36 no.5
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• pp.725-740
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• 2003

Urbanization concerned with concentration of population, activity and expanding the urban changes a natural environmental, and human activity in urban area causes the appearance of a new hydrologic cycle system. This study is carried out the analysis for the characteristics of runoff variation in urban areas with progress of urbanization. To simulate the mechanics of runoffs on small urban watershed, the ILLUDAS model is used in this study. From the analysis of the urban-runoff processes in small urban area with the progress of urbanization, the following conclusions is obtained. It is found in the results of calculated geographical parameter that peak time is quickened by 15∼35 minutes rather than the urbanization before. Also, in the analysis of the peak rate of runoff, the peak flow rise by 60 % than the urbanization before.

• Journal of KSNVE
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• v.11 no.2
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• pp.285-291
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• 2001

The impingement of a weak shock wane discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Experiments were carried out to validate the present computations. The effects of the flat plate and baffle plate sizes on the impinging flow field over the flat plate were investigated. Shock Mach number was varied in the range from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• Journal of Environmental Health Sciences
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• v.31 no.1
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• pp.1-6
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• 2005

This study was conducted to identify the runoff characteristics of non-point source according to rainfall in Nam watershed. Land-uses of the Nam watershed were surveyed paddy field 4.5%, crop field 6.8%, mountainous 78.7%, urban 2.4%, and etc. 7.7%. Mean runoff coefficients in each area were observed Ⅰ area 0.08, Ⅱ area 0.08, and Ⅲ area 0.05. In the relationship between the rainfall and peak-flow, correlation coefficients(r) were investigated Ⅰ area -0.8609, Ⅱ area 0.6035, and Ⅲ area -0.4913. In the relationship between the antecedent dry period and first flow runoff, correlation coefficients(r) were investigated Ⅰ area -0.9093, Ⅱ area -0.1039, and Ⅲ area -0.7317. The discharge of pollutant concentrations relates to the flow rate of storm-water. In the relationship between the rainfall and watershed loading, exponent values of BOD, COD, SS, and T-N were estimated to 1.2751, 1.2003, 1.3744, and 1.1262, respectively.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.562-567
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• 2000

The Impingement of a weak shock wave discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Experiments were carried out to validate the present computations. The effects of the flat plate and baffle plate sizes on the impinging flow field over the flat plate were investigated. Shock Mach number was vaned in the range from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.202-202
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• 2011

Thermal energy storage(TES) cooling system using cheaper electricity of off-peak time has been applied to relief a significant portion of the peak demand of electricity during the daytime in summer. Slurry ice type thermal energy storage cooling system is one kind of more efficient ice-thermal energy storage cooling system than Ice-on-Coil type or Encapsulated type TES cooling system, even though, which are more popular TES system. This study is experimented to observe flow pattern and formation of slurry ice in reversing flow to improve efficiency of heat transfer between fluid and freezing tube.

• Journal of Korean Society of Water and Wastewater
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• v.7 no.1
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• pp.29-36
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• 1993

The complex nature of low flow mixing in natural channels has been investigated using both laboratory experiments and the numerical solution of a proposed mathematical model that is based on a set of mass balance equations describing the mixing and mass exchange mechanisms. Laboratory experiments, which involved collection of channel geometry, hydraulic, and dye dispersion test data, were conducted in a model of four pool and riffle sequences in a 49-m long tilting flume. The experimental results show that flow over the model pool-riffle sequences is highly non-uniform. Concentration-time curves are significantly skewed with long tails. Comparison between measured and predicted concentration-time curves shows good agreement in the general shape, peak concentration and time to peak. The proposed model shows significant improvement over the conventional one-dimensional dispersion model in predicting natural mixing processes in open channels under low flow conditions through pools and riffles.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.67-68
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• 2006

We prepared the AZO thin film with different $O_2$ gas flow rate. the AZO thin films were deposited on glass substrate at room temperature, working gas pressure of 1mTorr. the electrical, structural and optical properties of AZO thin films were investigated by using Hall Effect measurement system, X-ray Diffractometer (XRD) and UV-VIS spectrometer. From the results, we could obtain that AZO thin film with low resistivity of $8.5{\times}10^{-4}{\Omega}cm$ was exhibited in specific $O_2$ gas flow rate. Also, the transmittance of over 80% in visible range was observed in specific $O_2$ gas flow rate. In all of the AZO thin film with the transmittance of over 80%, diffraction peak of (002) direction was observed, while amorphous peak was observed in the AZO thin film with the low transmittance.