• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1294-1303
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• 1993

The fully developed turbulent momentum and heat transfer induced by the square-ribed roughness elements on the inner wall surface in concentric annuli is studied analytically based on a modified turbulence model. The analytical results of the fluid flow is verified by experiment. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, fluid Reynolds number and for heat transfer, fluid Prandtl number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantages from the overall efficiency point of view.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.44-53
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• 2004

This paper is to investigate the combustion characteristics with a three dimensional chemical reacting flow on the aspect ratio of an exit configuration of the slit type nozzle for the fuel injection and to device the methods of combustion／mixing enhancement. The results show that both inside inflow and slit side vertices should be considered from a viewpoint of the mixing. The combustion efficiency becomes the smallest at aspect ratio, where the aspect ratio is less and more than unity, respectively. The total pressure loss becomes the largest at aspect ratio of unity due to the high penetration. All results imply that a streamwise very long slit is desirable with respect to the combustion and the pressure loss.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.3
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• pp.9-15
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• 2008

Nozzle flow analyses of $30\;ton_f$-class KARI liquid rocket engine for high altitude propulsion are carried out using a chemically frozen and equilibrium flow analysis code developed previously. It is considered that the combined frozen- and shifting- equilibrium analysis is cost-effective regarding the convergence characteristics and modeling uncertainties, though the non-equilibrium analysis is most reliable approach. A dependable performance prediction could be attainable through the present analyses that account for the recombination process and thermal and kinetic energy recovery during the expansion process with viscous effects.

• Journal of the Korean Institute of Gas
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• v.6 no.1 s.17
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• pp.74-80
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• 2002

This study was carried out for the purpose of safety evaluation about the ventilation system (according to the structure of confined room, the position and size of vent window, the amount of blowing air, e.t.c.), which is equipped in one of KOGAS underground valve stations. Particularly, the effect of the fans placed in the upper region was focused in detail. Numerical simulation was conducted in order to predict the features of flow pattern and the diffusion of natural gas concentration. This work examined the ventilation system and resulted in proposing an optimal design of ventilation system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.11
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• pp.905-911
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• 2015

In this study, to examine the effect of a hole size change(smaller hole diameter) in the outer region of the lower-support-structure-bottom plate(LSSBP) on the reactor core-inlet flow-distribution, simulations were conducted with the commercial CFD software, ANSYS CFX R.15. The predicted results were compared with those of the original LSSBP. Through these comparisons, it was concluded that a more uniform distribution of the mass flow rate at the core-inlet plane could be obtained by reducing the hole size in the outer region of the LSSBP. Therefore, from the nuclear regulatory perspective, design change of the hole pattern in the outer region of the LSSBP may be desirable in terms of improving both the mechanical integrity of the fuel assembly and the core thermal margin.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3B
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• pp.335-343
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• 2008

A hydrodynamic numerical model, ESCORT, which enables wetting-and-drying simulation, is developed. The model is verified by applying it at the Mokpo coastal zone together with the MIKE21 model. This paper deals in only 2-dimensional aspects remaining 3-dimensional function for further research. To begin with, MIKE21 model is applied at the whole area where MIKE21 had been applied several times to produce boundary conditions for the main area. Unlike the whole area of uniform grid, main area adopts telescoping grid for ESCORT model and nested grid for MIKE21 model. The results of both model show not only good agreement for the values of water depth and tidal velocity between computed and observed ones, but also plausible wetting-and-drying simulation. However, ESCORT model needs some improvement of efficiency.

• Journal of Broadcast Engineering
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• v.21 no.4
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• pp.493-505
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• 2016

Among modern computer vision and video surveillance systems, the pedestrian counting system is a one of important systems in terms of security, scheduling and advertising. In the field of, pedestrian counting remains a variety of challenges such as changes in illumination, partial occlusion, overlap and people detection. During pedestrian counting process, the biggest problem is occlusion effect in crowded environment. Occlusion and overlap must be resolved for accurate people counting. In this paper, we propose a novel pedestrian counting system which improves existing pedestrian tracking method. Unlike existing pedestrian tracking method, proposed method shows that average filter tracking method can improve tracking performance. Also proposed method improves tracking performance through frame compensation and outlier removal. At the same time, we keep various information of tracking objects. The proposed method improves counting accuracy and reduces error rate about S6 dataset and S7 dataset. Also our system provides real time detection at the rate of 80 fps.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.103-111
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• 2024

Axial-flow fans are used to transport fluids in relatively low-pressure flow regimes, and a variety of design variables are employed. The tip geometry of an axial fan plays a dominant role in its flow and noise performance, and two of the most prominent flow phenomena are the tip vortex and the tip leakage vortex that occur at the tip of the blade. Various studies have been conducted to control these three-dimensional flow structures, and winglet geometries have been developed in the aircraft field to suppress wingtip vortices and increase efficiency. In this study, a numerical and experimental study was conducted to analyze the effect of winglet geometry applied to an axial fan blade for an air conditioner outdoor unit. The unsteady Reynolds-Averaged Navier-Stokes (RANS) equation and the FfocwsWilliams and Hawkings (FW-H) equation were numerically solved based on computational fluid dynamics techniques to analyze the three-dimensional flow structure and flow noise numerically, and the validity of the numerical method was verified by comparison with experimental results. The differences in the formation of tip vortex and tip leakage vortex depending on the winglet geometry were compared through a three-dimensional flow field, and the resulting aerodynamic performance was quantitatively compared. In addition, the effect of winglet geometry on flow noise was evaluated by numerically simulating noise based on the predicted flow field. A prototype of the target fan model was built, and flow and noise experiments were conducted to evaluate the actual performance quantitatively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.415-420
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• 2020

Crowd flows occur in metropolitan railway transit stations, terminals, multiple buildings, and stadiums and are important in ensuring the safety as well as smooth flow of pedestrians in these facilities. In this study, the author developed a new computational analysis method for crowd flow dynamics and applied it to models of transit connecting paths. Using the analysis method, the potential value of the exit was assigned the smallest value, and the potential value of the surrounding grids gradually increased to form the overall potential map. A pathline map was then constructed by determining the direction vector from the grid with large potential value to the grid and small potential. These pathlines indicate basic routes of passenger flow. In all models of the analysis object, the pedestrians did not move to the first predicted shortest path but instead moved using alternative paths that changed depending on the situation. Even in bottlenecks in which pedestrians in both directions encountered each other, walking became much smoother if the entry time difference was dispersed. The results of the analysis show that a method for reducing congestion could be developed through software analysis such as passenger flow analysis without requiring hardware improvement work at the railway station.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.8
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• pp.749-754
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• 2010

Knowledge of the characteristics of airflow in nasal cavities is essential to understand the physiological and pathological aspects of nasal breathing. In our laboratory, a series of experimental investigations on the nasal airflow was conducted; airflow in models of normal and deformed nasal cavities under both constant and periodic flow conditions was studied by PIV. Some of the patients with asymmetric nasal cavities experience pain or discomfort, while other patients with asymmetric nasal cavities do not experience pain. Airflows inside asymmetric nasal cavities with and without obstructions due to a bent nasal septum are investigated both experimentally by PIV and numerically by using the general-purpose FVM code in order to determine the reason for the above-mentioned discrepancy. The comparisons between two cases are tried. Heat and humidity distribution are investigated numerically.