• Journal of computational fluids engineering
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• v.1 no.1
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• pp.81-87
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• 1996

The aerodynamic charateristics of high speed train can be improved by well-designing of its fore-body shape. In this paper, as a way of the design a fore-body shape which has optimal aerodynamic charasteristics, 9 models of fore-body shapes are proposed and the change of aerodynamic charateristics is studied through calculations of flow field around high speed train for each fore-body shape. The flow field around high speed trains are calculated using Thin-Layer Navier-Stokes equation and Chimera grid technique. The application of Chimera grid technique to these flow calculations over high speed train which has ground plane under the train makes grid generation easily. As a computaional algorithm, Pulliam and Chaussee's Diagonal algorithm, the modified form of the Beam and Warming's AF scheme which operates on block-tridiagonal matrices, is selected to reduce computaional time. Introducing hole points flag concept to this Diagonal algorithm. a algorithm for Chimera grid is generated. The variational trends of aerodynamic characteristics are studied from the results of flow calculations around high speed trains for 9 fore-body shapes.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.503-508
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• 2004

Preform design techniques have been investigated to reduce die wear and forming load and to improve material flow, filling ratio, etc. In hot forging processes, a thin deformed part of a workpiece, known as a flash, is formed in the narrow gap between the upper and lower tools. Although designers make tools that generate a flash intentionally in order to improve flow properties, excessive flash increases die wear and forming load. Therefore, it is necessary to make a preform shape that can reduce the excessive flash without changing flow properties. In this paper, a new preform design technique is proposed to reduce the excessive flash in a metal forging process. After a finite element simulation of the process is carried out with an initial billet, the flow of material in the flash region is traced from the final shape to the initial billet. The region belonging to the flash is then easily found in the initial billet. The finite element simulation is then carried out again with the modified billet from which the selected region has been removed. In several iterations of this technique, the optimal preform shape that minimizes the amount of flash without changing the forgeability can be obtained.

• Journal of Korean Society on Water Environment
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• v.36 no.6
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• pp.489-499
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• 2020

Effective science-based management of the basin water resources requires an understanding of the characteristics of the streams, such as the baseflow discharge. In this study, the base flow was estimated in the two watersheds with the least artificial factors among the Nakdong River watersheds, as determined using the chemical hydrograph separation technique. The 16-year (2004-2019) discontinuous observed stream flow and electrical conductivity data in the Total Maximum Daily Load (TMDL) monitoring network were extended to continuous daily data using the TANK model and the 7-parameter log-linear model combined with the minimum variance unbiased estimator. The annual base flows at the upper Namgang Dam basin and the upper Nakdong River basin were both analyzed to be about 56% of the total annual flow. The monthly base flow ratio showed a high monthly deviation, as it was found to be higher than 0.9 in the dry season and about 0.46 in the rainy season. This is in line with the prevailing common sense notion that in winter, most of the stream flow is base flow, due to the characteristics of the dry season winter in Korea. It is expected that the chemical-based hydrological separation technique involving TANK and the 7-parameter log-linear models used in this study can help quantify the base flow required for systematic watershed water environment management.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.351-359
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• 2004

Velocity-type repisratory air flow transducer measures dynamic pressure converted from air velocity based on the we1l-known Bernoulli's principle. It requires multiple velocity sampling holes on the flow plane. Measurement error theoretica1ly estimated by computer simulation was demonstrated to significantly reduce by unequally locating the velocity sampling holes. The flow plane was divided into multiple equi-area rings and the sampling holes were located on the circles also equally dividing each ring's area, which decreased measurement error down to 1/5 of the simple equi-radius ring division method. Also, less than 1 ％ relative error was estimated with 4 or more sampling holes. The present technique was less sensitive by <1/2 to the velocity profile change compared to the euqi-radius sampling. Therefore, the present unequal distance velocity sampling technique should be of great use to design the structure of the velocity-type respiratory air flow transducer.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.4
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• pp.93-103
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• 2012

A suction-saturation control technique based on flow pump system was developed to investigate hydraulic properties in unsaturated soils. The flow pump system is designed based on the principle of the axis-translation technique and triaxial equipment, and gives the suction-time and suction-saturation curves, the primary relationship needed for interpreting the response of unsaturated soils and link between theory and the material properties in unsaturated soil mechanics. Using the suction-saturation control technique, suction-time relationship and soil-water retention curve (SWRC) during hydraulic hysteresis were investigated with different net confining pressures and porosities. Three types of soils-two sands and a silt were used in this paper. This paper showed the effect of the hysteresis on the SWRC due to different net confining pressures and porosities. This means that a careful decision must be made as to which condition is to be modeled, since the delicate difference of the conditions in physical modeling can cause the different experimental output.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.647-652
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• 2015

A fully coupled finite element analysis (FEA) technique was developed for analyzing the discharge phenomena and dielectric liquid flow while considering surface charge density effects in dielectric flow guidance. In addition, the simulated speed of surface charge propagation was compared and verified with the experimental results shown in the literature. Recently, electrohydrodynamics (EHD) techniques have been widely applied to enhance the cooling performance of electromagnetic systems by utilizing gaseous or liquid media. The main advantage of EHD techniques is the non-contact and low-noise nature of smart control using an electric field. In some cases, flow can be achieved using only a main electric field source. The driving sources in EHD flow are ionization in the breakdown region and ionic dissociation in the sub-breakdown region. Dielectric guidance can be used to enhance the speed of discharge propagation and fluidic flow along the direction of the electric field. To analyze this EHD phenomenon, in this study, the fully coupled FEA was composed of Poisson's equation for an electric field, charge continuity equations in the form of the Nernst-Planck equation for ions, and the Navier-Stokes equation for an incompressible fluidic flow. To develop a generalized numerical technique for various EHD phenomena that considers fluidic flow effects including dielectric flow guidance, we examined the surface charge accumulation on a dielectric surface and ionization, dissociation, and recombination effects.

• Journal of the Korean Society of Visualization
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• v.14 no.2
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• pp.18-24
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• 2016

This paper presents an experimental investigation to visualize cross-sectional two-phase flow structure and identify liquid-gas interface for condensation of steam at a low mass flux in a slightly inclined tube using the axial-viewing technique, which permits to look directly into flow during condensation of steam. In this technique, two-phase flow is viewed along the axis of a pipe by locating a high-speed video camera in front of a viewer that is fitted at the outlet of the pipe. A short section of the pipe is illuminated and is recorded through the viewer, which is kept free of liquid by mildly introducing air. Experiments were conducted in a pipe of 19.05 mm in inner diameter at atmospheric pressure. Cross-sectional two-phase flow structure is obtained at a steam mass flux of $2.62kg/m^2s$ as a function of steam quality in the range from 0.5 to 0.9. The results show that stratified-wavy flow is a unique flow pattern observed in the scope of the present study. Condensate film thickness, stratification angle and void fraction were measured from the obtained flow structure images. Finally, heat transfer coefficient was calculated using the measurement data and discussed in comparison with existing correlations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.9
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• pp.722-727
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• 2009

The effect of the intake flow on the spray structure of a high pressure 11-hole fuel injector were examined in a single cylinder optical direct injection spark ignition (DISI) engine. The effects of injection timing and in-cylinder charge motion were investigated using the 2-dimensional Mie scattering technique. It was confirmed that in the homogeneous charge mode, the in-cylinder swirl charge motion played a major role in the fuel spray distribution during the induction stroke rather than the tumble flow. But, in the stratified charge mode, the effect of the in-cylinder charge was not so large that the injected spray pattern was nearly maintained and the increase of in-cylinder pressure by the upward moving piston reduced the fuel spray penetration.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.6
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• pp.86-95
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• 2002

This paper suggests the new technology to control metal flow in order to reduce the number of preforming and the machining for the cold forged product with complex geometry. This technology is the combined forming that consists of bulk and sheet forming with double action dies. To analyze the process, finite element simulation has been performed. The proposed technology is applied to hub model that is part of air conditioner clutch. The purpose of this study is to investigate the material now of hub through the relative-velocity control of punch and mandrel using the flow control forming technique.

• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.17-26
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• 2001

Self flue gas recirculation flow is an effective method for low NOx emission in the regenerative low NOx burner. The object of this study is to analyze the self flue gas recirculating flow by varying jet velocity of the combustion air. Fuel and air flow rates are fixed and combustion air jet nozzle diameters are 13, 6.5 and 5mm. The stoichiometric line is obtained from the concentration of the fuel using an acetone PLIF technique. It is found that the self flue gas recirculating flow is entrained into that line using a two color PIV technique. As the jet velocity of combustion air is increased, the flue gas entrainment rate into the stoichiometric line is increased. This result suggests that NOx emission can be reduced due to the effects of flue gas which is lowering the flame temperatures.