• Korean Journal of Environmental Agriculture
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• v.14 no.1
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• pp.7-14
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• 1995

This research was conducted to apply the QUAL2E model to be adopted to the Nam river under current water quality conditions. The survey area of total 60 Km was divided into five reaches. Each reach was then subdivided into the uniform computational elements of 1.5 Km. Based on the stream characteristics, nine sampling stations consisting of six at main streams and three at tributaries were selected. The field data were obtained from the selected stations twice during October of 1991 and May of 1992, which represented the cold weather and low flow, also the warm weather and low flow conditions, respectively. As the results of sensitivity analysis of the model, the important parameters were the rates of BOD decay, Org-N oxidation, $NH_3-N$ oxidation, Org-P decay. The calibrated and verified results by QUAL2E model were correlation coefficient of $0.45{\sim}0.94$. The results displayed a good agreement between the variables of the field measurements and the model simulations, indicating a potential use of the QUAL2E model for the water quality assessment in the Nam River.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.2
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• pp.983-989
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• 2013

The current research reviewed the design conditions that would maximize the efficiency of the hybrid collector that combines in one unit "cyclone-inertial impaction-bag filter". The computational analysis for the shape of cyclone entry predicts that a design that installs the guide vane at the entry of the tangential type cyclone brings a high-rpm and powerful vortex, very effective in promoting the deflection of coarse particles from the streamline at the cyclone. As the lower part of the cyclone is venturi-shaped, however, a strong flow downward of 4 to 5 m/sec persists through the lower part of the hopper, revealing the likely reentrainment of collected dust. And the removal of the venturi at the lower part of the cyclone would solve the problem of the reentrainment of collected dust. The acceleration of the flow velocity through the adjustment of the gap of the collision baffle would increase the effect of collision, but as the interference with the dust separation is expected, the original design should be kept for the baffle.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.248-254
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• 2015

There has been no previous study on technology development of large capacity drainage pump for rescue sinking ship in the country. The agricultural drainage pump was widely used for rescue sinking ship but this pump has several problems such as efficiency, low displacement and malfunction in winter. Therefore, this paper proposes to solve the problems for swiftly rescue sinking ship and develops the drainage pump system that has $20m^3/min$ mass flow rate specification at suction head 8 m. The centrifugal pump type the most commonly used in the field of naval architecture and ocean engineering was selected and designed based on the requirement specification. The blade design of impeller was derived from the Stepanoff coefficient and requirement specification and used computational fluid dynamics to review the target mass flow rate according to the impeller RPM at design operating conditions. We also performed structure analysis of the impeller to find structurally vulnerable points for the pump in service and completed the theoretical design of drainage pump system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.527-539
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• 2018

The subway used by many passengers is required to maintain a safe and comfortable environment and PSD (Platform Screen Door) must be installed in the platform after reinforcing the standard in 2003. In the previous research, in case of subway fire to control it, it is necessary to design the optimal ventilation and smoke exhaust system according to equipment capacity of the smoke exhaust system. Therefore, in this study, based on the results of previous research, three-dimensional numerical analysis was performed for the CO gas and smoke flow by the subway ventilation system in case of platform fire. As a result of this study, it was found that in case of emergency, if only the upper-level smoke exhaust system is activated, the risk of evacuation is high due to CO gas (653.8 ppm) and smoke concentration ($768.4mg/m^3$). And when all the smoke exhaust systems are activated and only the fire side PSD is opened, CO gas (36.0 ppm) and smoke concentration ($26.2mg/m^3$) are detected and the propagation range of smoke flow was reduced. When all the smoke exhaust systems are activated and only the fire side PSD is closed, it was analyzed as the most effective ventilation mode in the evacuation environment due to the absence of smoke-recirculation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.4
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• pp.326-335
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• 2014

Aerodynamic characteristics of the small two-stage turbo blower were investigated using commercial CFD tool(ANSYS CFX Ver. 14.5) in this paper. Turbo blower, which is a centrifugal type of turbomachinery, is used in various industries. It is used for application that required high static pressure rising at relatively small volumetric flow rate. In order to understand the mechanism of static pressure rising, the aerodynamic characteristics of the small two-stage turbo blower are analyzed at high rotating speed in this study. The k-${\omega}$ SST turbulence model, which is good at prediction of adverse pressure gradient flows, was applied. The CFD results of the turbo blower are validated by performance test. The static pressure rising of the turbo blower is nonlinearly increased over the first stage and the second stage. The secondary flow occurred at guide vanes, between the casing and the first impeller shroud, and the bottom of the impeller disk. As a result, It is required that whole fluid area is analyzed to predict aerodynamic characteristics of small two-stage turbo blower. and the result should be selected with considering for error from experiment and CFD.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.26-35
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• 2016

As a potential clean energy resource, the production and consumption of hydrogen gas are expected to gradually increase, so that hydrogen related studies are also increasing. The thermal and chemical properties of hydrogen result in its high flammability; in particular, there is a high risk if leaks occur within an enclosed space. In this study, we applied the computational fluid dynamics method to conduct a numerical study on the leakage behavior of hydrogen gas and compared these numerical study results with an experimental study. The leakage hole diameter was selected as an important parameter and the hydrogen gas dispersion behavior in an enclosed space was investigated through various analytical methods. Moreover, the flammable regions were investigated as a function of the leakage time and leakage hole size. We found that the growth rate of the flammable region increases rapidly with increasing leakage hole size. We also investigated the relation between the mass flow rate and the critical time when the hydrogen gas reaches the ceiling. The analysis of the monitoring points showed that the hydrogen gas dispersion behavior is isotropic and independent of the geometry. We found that the concentration of gas in an enclosed space is affected by both the leakage flow rate and amount of gas accumulated in the enclosure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.618-627
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• 2016

This study numerically analyzes the characteristics of the velocity distribution for each location of a square-sectional $180^{\circ}$ bent duct using a Reynolds Stress Turbulent model. The flow parameters were varied, including the working fluids, inlet velocity, surface roughness, radius of curvature, and hydraulic diameter. The boundary conditions for computational fluid dynamics analysis were inlet temperatures of air and water of 288 K and 293 K, inlet air velocity of 3-15 m/s, inner surface roughness of 0-0.001 mm, radius of curvature of 2.5-4.5 D, and hydraulic diameter of 70-100 mm. The working fluid characteristics were highly affected by changes in the viscous force. The maximum velocity profiles in the bent duct were indicated when the $90^{\circ}$ section was in the region of X/D=0.8 and the $180^{\circ}$ section was in the region of Y/D=0.8. Lower surface roughness and higher radius of curvature resulted in a higher rate of velocity change. Also, an efficient measuring location downstream of the bent duct is suggested since the flow deviations were the most stable when the straight duct length was in the region of L/D=30. The minimum deviations at the same velocity conditions according to the hydraulic diameter were mostly indicated in the range of L/D=15-30 based on the standard deviation characteristics.

• Journal of the Korean Institute of Gas
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• v.23 no.3
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• pp.20-26
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• 2019

Selective catalytic reduction(SCR) method is widely used among various methods for reducing nitrogen oxides in combustion devices of coal power plant. In the present study, the computational fluid dynamic analysis was accomplished to derive the optimal shape of ammonia-dilution air mixing device in a ammonia injection grid. The distribution characteristics of flow and $NH_3$ concentration had been elucidated for the reference shape of ammonia mixing device(Case 1). In the mixing device of Case 1, it could be seen that $NH_3$ distribution was shifted to the wall opposite to the inlet of the ammonia injection pipe. For the improvement of $NH_3$ distribution, the case(Case 2) with closing one upper injection hole and 4 side injection holes, the case(Case 3) with installing horizontal plate at the upper of ammonia injection pipe, the case(Case 4) with installing horizontal plate and horizontal arc plate at he upper of ammonia injection pipe were investigated by analyzing flow and $NH_3$ concentration distributions. From the present study, it was found that the % RMS of $NH_3$ for Case 4 was 4.92%, which was the smallest value among four cases, and the range of $R_{NH3}$ also has the optimally uniform distribution, -10.82~8.34%.

• Journal of Internet Computing and Services
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• v.17 no.2
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• pp.19-28
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• 2016

Internet traffic has been significantly increasing due to the development of information and communication networks and the growing numbers of cell phone users that access networks. This paper connects to this issue by presenting a way to detect and analyze a typical DDoS attack that results in Internet breaches and network attacks, which are on the increase. To achieve this goal, we improve features and GUI of the existing ATMSim analysis package and use it. This package operates on a network flow-based analysis method, which means that normal traffic collected through an internal LAN at the Korean Bible University campus as well as anomaly traffic with DDoS attacks are generated. Self-similarity processes are used to analyze normal and anomaly traffic that are collected and generated from the improved ATMSim. Our numerical results obtained from three Hurst parameter estimate techniques show that there is quantitatively a significant difference between normal traffic and anomaly traffic from a self-similarity perspective.

• Journal of the Korean Institute of Gas
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• v.24 no.2
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• pp.1-8
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• 2020

Centrifugal pump is a facility that transfers energy to fluid through centrifugal force, which is usually generated by rotating the impeller at high speed, and is a major process facility used in many LNG production bases such as vaporization seawater pump, industrial water and fire extinguishing pump using seawater. to be. Currently, pumps in LNG plant sites are subject to operating conditions that vary depending on the amount of supply desired by the customer for a long period of time. Pumps in particular occupy a large part of the consumption strategy at the plant site, and if the optimum operation condition is not available, it can incur enormous energy loss in long term plant operation. In order to solve this problem, it is necessary to identify the performance deterioration factor through the flow analysis and the result analysis according to the fluctuations of the pump's operating conditions and to determine the optimal operation efficiency. In order to evaluate operation efficiency through experimental techniques, considerable time and cost are incurred, such as on-site operating conditions and manufacturing of experimental equipment. If the performance of the pump is not suitable for the site, and the performance of the pump needs to be reduced, a method of changing the rotation speed or using a special liquid containing high viscosity or solids is used. Especially, in order to prevent disruptions in the operation of LNG production bases, a technology is required to satisfy the required performance conditions by processing the existing impeller of the pump within a short time. Therefore, in this study, the rotation difference of the pump was applied to the ANSYS CFX program by applying the modified 3D modeling shape. In addition, the results obtained from the flow analysis and the curve fitting toolbox of the MATLAB program were analyzed numerically to verify the outer diameter correction theory.