• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.5
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• pp.931-940
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• 2001

In this paper, I propose Fuzzy Policing Mechanism(FPM) over ATM networks for the control of traffic which is unpredictable and bursty source. The FPM is consist of counter, subtracter and Fuzzy Logic Controller(FLC). The FLC is divided to fuzzifier, inference engine and defuzzifer The output of FLC inputs to the subtractor and it controls the counter. The counter works as a switch in transmission of cells. In simulation, I compared the FPM with the Leaky Bucket algorithm(LBM) in cell loss probability and performance characteristics. As a result, FPM gives lower cell loss probability than that of LBM and has good response behavior The FPM efficiently controls the transmission of packets which are variable traffic source and, it also has good selectivity.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.1
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• pp.24-34
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• 2009

DPF(Diesel Particulate Filter)s have been used to reduce the most of PM(particulate matters) from the exhaust emissions of diesel engine vehicles. Metal foam is one of promising materials for the DPFs due to its cost effectiveness, good thermal conductivity and high mechanical strength. It can be fabricated with various pore sizes and struct thickness and coated with catalytic wash-coats with low cost. In order to design metal foam filter and analyze the flow phenomena, pressure drop and filtration experiment are carried out. Partial DPF which has PM reduction efficiency of more than 50 % is designed in this paper. Also, CFD analysis are performed for different configurations of clean filters in terms of pressure drop, uniformity index, and velocity magnitude at face of filter. Filter thickness and the gap between front and rear filters are optimized and recommended for manufacturing purpose.

• Journal of Korean Society on Water Environment
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• v.22 no.1
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• pp.30-36
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• 2006

This study was carried out to evaluate the performance of Modified Ludzsck Etinger (MLE) process with waste oyster shell media in aerobic tank. Influent flow was 36 L/d and the order of reactor was anoxic, aerobic and sedimentation tank and unit hydraulic retention time was 2 hr, 6 hr and 4 hr, respectively. Sludge recycling rate in sedimentation tank and internal recycling rate were 100%. Media fill rate in aerobic tank was 5%, 10% and 17% and fluid MLSS concentration in aerobic tank was 3000~4000 mg/L. Average TCOD removal rate was 91~93%, TBOD 92~96%, SS 95~96% and when media fill rate was 10% or more, in organic compound removal it could satisfy with wastewater discharge standard. Average total nitrogen removal rate was 70~76% and average total phosphorous removal rate was 58~65%. With media fill rate increasing, total phosphorous average removal rate also increased. For it was that released calcium ion from waste oyster shell reacted with soluble phosphorous. From these experiment results, the MLE process using waste oyster shell as media is a practical method for advanced sewage treatment in rural area.

• Journal of the Semiconductor & Display Technology
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• v.14 no.3
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• pp.61-66
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• 2015

Recently, the major trends of NIL are high throughput and large area patterning. For UV NIL, if it can be proceeded in the non-vacuum environment, which greatly simplifies tool construction and greatly shorten process times. However, one key issue in non-vacuum environment is air bubble formation problem. In this paper, numerical analysis of bubble defect of UV NIL is performed. Fluent, flow analysis focused program was utilized and VOF (Volume of Fluid) skill was applied. For various resist-substrate and resist-mold angles, effects of velocity inlet and residual layer thickness of resist on bubble defect formation were investigated. The numerical analyses show that the increases of velocity inlet and residual layer thickness can cause the bubble defect formation, however the decreases of velocity inlet and residual layer thickness take no difference in the bubble defect formation.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.6
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• pp.763-769
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• 2010

Thanks to the rapid advancement of computational power and development of numerical methods, Computational fluid dynamics techniques are being used widely for the prediction of ship resistance performance. In the present study, an automatic tool was developed to facilitate hull form modification, consequent mesh generation, and flow analysis for parametric study. It is a tedious job to go back and forth between geometry modification and mesh generation for every hull form variation. With the developed tool, users can make multiple hull form variation and their hull form performance prediction easily in a few simple steps. The verification of the developed tool was done by applying it to resistance performance parametric study of a generic POD propulsion cruise ship with different lengths of bow and stern. It is believed that the tool can be extended to more sophisticated hull form variation and help optimize the ship performance more efficiently.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.27 no.4
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• pp.9-20
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• 2019

A military aircraft generally includes external stores such as fuel tanks or external arming, depending on the purpose of the operation. When a store is dropped from a military aircraft at high subsonic, transonic, or supersonic speeds, the aerodynamic forces and moments acting on the store can be sufficient to send the store back into contact with the aircraft. This can cause damage to the aircraft and endanger the life of the crew. In this study, time accurate computational fluid dynamics (CFD) with dynamic moving grid (moving and deformable mesh, MDM) technique has been used to accurately calculate store trajectories. For the verification of the present numerical approach, a wind tunnel test model for the wing-pylon-finned store configuration has been considered and analyzed. The comparison results for the ejected store trajectories between the present numerical analysis and the wind tunnel test data at the Mach number of 0.95 and 1.2 are presented. It is also importantly shown that the numerical parameter of MDM technique gives significant effect for the calculated store trajectory in the low-supersonic flow such as Mach 1.2.

• Journal of the Semiconductor & Display Technology
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• v.8 no.3
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• pp.31-37
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• 2009

This paper presents one and two dimensional simulation results with discontinuous features (shocks) of capacitively coupled rf plasmas. The model consists of the first two and three moments of the Boltzmann equation for the ion and electron fluids respectively, coupled to Poisson's equation for the self-consistent electric field. The local field and drift-diffusion approximations are not employed, and as a result the charged species conservation equations are hyperbolic in nature. Hyperbolic equations may develop discontinuous solutions even if their initial conditions are smooth. Indeed, in this work, secondary electron emission is shown to produce transient electron shock waves. These shocks form at the boundary between the cathodic sheath (CS) and the quasi-neutral (QN) bulk region. In the CS, the electrons emitted from the electrode are accelerated to supersonic velocities due to the large electric field. On the other hand, in the QN the electric field is not significant and electrons have small directed velocities. Therefore, at the transition between these regions, the electron fluid decelerates from a supersonic to a subsonic velocity in the direction of flow and a jump in the electron velocity develops. The presented numerical results are consistent with both experimental observations and kinetic simulations.

• Archives of Plastic Surgery
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• v.48 no.3
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• pp.254-260
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• 2021

Background Myelomeningocele is a frequently seen condition at tertiary care hospitals. Its treatment involves a variety of plastic reconstructive techniques. Herein, we present a series of myelomeningocele patients treated using keystone flaps. Methods We gathered information regarding soft tissue reconstruction and the use of bilateral keystone flaps to treat myelomeningocele patients. We obtained data from clinical records and recorded the demographic characteristics of mothers and children with the condition. The size, level of defect, and complications detected during the follow-up were analyzed. Results A series of seven patients who underwent bilateral keystone flaps for myelomeningocele closure was analyzed. There were no cases of midline or major dehiscence, flap loss, necrosis, surgical site infections, or cerebrospinal fluid leakage. No revision procedures were performed. Minor complications included one case with minimal seroma and three cases with areas of peripheral dehiscence that healed easily using conventional measures. Conclusions The use of keystone flaps is an adequate option for closure of dorsal midline soft tissue defects related to myelomeningocele. This technique offers predictable results with an acceptable spectrum of complications. Robust blood flow can be predicted based upon anatomical knowledge.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.35-35
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• 2023

The main reason for its instability is sediment scouring downstream of hydraulic structures. Both physical and numerical models have been used to investigate the influence of soil properties on scour hole geometry. Nevertheless, no research has been conducted on resistance parameters that affect sedimentation and erosion. In addition, auxiliary structures like wing walls, which are prevalent in many real-world applications, have rarely been studied for their impact on morphology. The hydraulic characteristics of steady flow through a boxed culvert are calibrated using a 3D Computational Fluid Dynamics model compared with experimental data in this study, which shows a good agreement between water depth, velocity, and pressure profiles. Test cases showed that 0.015 m grid cells had the lowest NRMSE and MAE values. It is also possible to quantify sediment scour numerically by testing roughness/d₅₀ ratios (c_s) and diversion walls at a meander flume outlet. According to the findings, c_s = 2.5 indicates a close agreement between numerical and analytical results of maximum scour depth after the culvert; four types of wing walls influence geometrical deformation of the meander flume outlet, resulting in erosion at the concave bank and deposition at the convex bank; two short headwalls are the most appropriate solution for accounting for small changes in morphology. A numerical model can be used to estimate sediment scour at the meander exit channel of hydraulic structures based on the roughness parameter of soil material and headwall type.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.1
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• pp.16-24
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• 2022

A computational study of combined thermal and solutal convection (double diffusive convection) in a sealed crystal growth reactor is presented, based on a two-dimensional numerical analysis of the nonlinear and strongly coupled partial differential equations and their associated boundary conditions. The average Nusselt numbers for the source regions are greater than those at the crystal regions for 9.73 × 10³ ≤ Gr_t ≤ 6.22 × 10⁵. The average Nusselt numbers for the source regions varies linearly and increases directly with the thermal Grashof number form 9.73 × 10³ ≤ Gr_t ≤ 6.22 × 10⁵ for aspect ratio, Ar (transport length-to-width) = 1 and 2. Additionally, the average Nusselt numbers for the crystal regions at Ar = 1 are much greater than those at Ar = 2. Also, the occurrence of one unicellular flow structure is caused by both the thermal and solutal convection, which is inherent during the physical vapor transport of Hg₂Br₂. When the aspect ratio of the enclosure increases, the fluid movement is hindered and results in the decrease of thermal buoyancy force.