• Journal of The Korea Institute of Healthcare Architecture
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• v.10 no.2
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• pp.71-82
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• 2004

The purpose of this study is to analyze the wind velocity ratio in respect of layout types of housing in multi-family housing. The wind velocity ratio is a difference of wind velocity between on the leeward and on the windward side of multi-family housing. The layout types of housing are grid layout pattern of linear type, mixture pattern of Linear type + tower type and layout pattern of tower type. The planning of wind flow is an induced technique to increase in wind velocity in the city and multi-family housing. This study investigates wind velocity ratio into layout types of housing. consequently, analysis were basic design data for the planning techique of wind flow suggested.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.3
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• pp.214-224
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• 2004

A large cage system for the purpose of fishes farming in the open sea was influenced by various forces from the ocean environment. The deformation of the cage by these forces affects the safety of the cage itself, as well as that of the cultivated creatures. In this research, theoretical model was established to analyzing dynamic movement influenced by current for cage. Also, to increase the accuracy of calculations, the reduction ratio of flow speed acquired using the flume tank experiment. Applying the reduction ratio of flow speed to the numerical calculation, the calculation values were compared with the measured values in the flume tank experiment using cage model. The results were as follows ; 1. When the flow speed of the flume tank is fixed, the decrease of the velocity of flow which is passed the upper panel side is proportion to the increase of porosity ratio of netting. 2. When the porosity ratio is fixed, the increase of the velocity of flow which is passed the upper panel side is proportion to the increase of velocity of flow. 3. When the porosity ratio and the flow speed of the flume tank are fixed, the decrease of the velocity of flow which is passed the upper panel side is proportion to the increase of attack angle. 4. As a result of comparison between the underwater shape by simulation which is applying the reduction ratio of flow speed from the experiment using plane netting and that by model experiment, it was found out that the result of the simulation was very close to that of model gear within ${\pm}$ 5 % error range.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.242-250
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• 2006

The impacts of equivalence ratio on the flow structure and flame dynamics in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.311-314
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• 2006

The supersonic flow around tandem cavities was investigated by three- dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes(RANS) equation with the $\kappa-\omega$ thrbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split using van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge-Kutta method. The aspect ratio of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two-dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the fire cavity flow cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.433-436
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• 2009

This study is concerned with an effect of frictional condition in a forward/backward combined extrusion process. Generally, the material flow of the billet is influenced by the corners of the die cavity, the ratio in reduction in area, and thickness ratio of backward can thickness to forward can thickness. In addition, the frictional condition in contact area between the billet and the punch/die also affect the material flow. This paper investigated the effect of frictional condition for variable friction factors. The FEM simulation has been carried out in order to examine the effect of frictional condition. Deformation patterns and flow characteristics were examined in terms of design parameters such as extruded length ratio etc. Die pressure exerted on the die-workpiece interface is calculated by the simulation results and analyzed for safe tooling. Therefore the numerical simulation works provide a combined extrusion process of stable cold forging process planning to avoid the severe damage on the tool.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.632-635
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• 2007

Detention pond has an important role in peak flow reduction to mitigate flood damage. Design of detention pond is accomplished through the preliminary stage, planning stage, and design stage in general. New development projects produce increased peak flow and flow amounts. In this case it is necessary to design the detention pond easily and simply. The simple procedure of detention pond design is proposed in this study. The relevant variables are peak flow ratio ($\alpha$) for the before and after development, and storage ratio which is ratio of storage volume to flow amounts. Simplified method for the detention pond design with runoff reduction is easily used for practical purposes.

• Nuclear Engineering and Technology
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• v.38 no.1
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• pp.69-80
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• 2006

Fluid-elastic instability in an air-water two-phase cross-flow has been experimentally investigated using two different arrays of straight tube bundles: normal square (NS) array and rotated square (RS) array tube bundles with the same pitch-to-diameter ratio of 1.633. Experiments have been performed over wide ranges of mass flux and void fraction. The quantitative tube vibration displacement was measured using a pair of strain gages and the detailed orbit of the tube motion was analyzed from high-speed video recordings. The present study provides the flow pattern, detailed tube vibration response, damping ratio, hydrodynamic mass, and the fluid-elastic instability for each tube bundle. Tube vibration characteristics of the RS array tube bundle in the two-phase flow condition were quite different from those of the NS array tube bundle with respect to the vortex shedding induced vibration and the shape of the oval orbit of the tube motion at the fluid-elastic instability as well as the fluid-elastic instability constant.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.5
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• pp.54-66
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• 2002

A grid-based hydrological model, CELTHYM, capable of estimating base flow and surface runoff using only readily available data, was used to assess hydrologic impacts caused by land use change on Little Eagle Creek (LEC) in Central Indiana. Using time periods when land use data are available, the model was calibrated with two years of observed stream flow data, 1983-1984, and verified by comparison of model predictions with observed stream flow data for 1972-1974 and 1990-1992. Stream flow data were separated into direct runoff and base flow using HYSEP (USGS) to estimate the impacts of urbanization on each hydrologic component. Analysis of the ratio between direct runoff and total runoff from simulation results, and the change in these ratios with land use change, shows that the ratio of direct runoff increases proportionally with increasing urban area. The ratio of direct runoff also varies with annual rainfall, with dry year ratios larger than those for wet years shows that urbanization might be more harmful during dry years than abundant rainfall years in terms of water yield and water quality management.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.592-597
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• 2003

Thrust vector control using a coflow-counterflow concept is achieved by suction and blowing through a slot adjacent to a primary jet which is shrouded by a suction collar. In the present study, the flow characteristics of thrust vectoring is investigated using a numerical method. The nozzle has a design Mach number of 2.0, and the operation pressure ratio is varied to obtain various flow features of the nozzle flow. Test conditions are in the range of the nozzle pressure ratio from 6.0 to 10.0, and a suction pressure from 90kPa to 35kPa. Two-dimensional, compressible Navier-Stokes computations are conducted with RNG ${\kappa}-{\varepsilon}$ turbulence model. The computational results provide an understanding of the detailed physics of the thrust vectoring process. It is found that an increase in the nozzle pressure ratio leads to increased thrust efficiency but reduces the thrust vector angle.

• Journal of Korea Foundry Society
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• v.20 no.3
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• pp.197-207
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• 2000

Al-Si alloys were solidified in a rotating cylindrical mold by a vertical centrifugal casting process. Under a certain casting condition, there are four distinct zones such as the chill zone, the primary fine columnar zone, the equiaxed zone, and the secondary coarse columnar zone from the mold wall. The columnar-equiaxed transition (CET) and the equiaxed-columnar transition (ECT) were measured as functions of solute content, flow rate (mold velocity), pouring temperature and mold temperature. Within the critical value of solute content, as the flow rate increases, the columnar-equiaxed transition were found, but not the equiaxed-columnar transition. The aspect ratio of the primary columnar zone was more affected by the solute content than the flow rate. However the aspect ratio of the equiaxed zone was more affected by the flow rate than the solute content. The aspect ratio of the secondary columnar zone was affected by both the flow rate and the solute content.