• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.82-84
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• 2003

Watershed boundaries and flow paths within the watershed are the most important factors required in watershed analysis. Most often the derivation of watershed boundaries and stream network and flow paths is based on topographical maps but spatial variation of flow direction is not clearly understandable using this method. Water resources projects currently use 1: 50, 000-scale ground survey or aerial photography-based topographical maps to derive watershed boundary and stream network. In basins, where these maps are not available or not accessible it creates a real barrier to watershed geo-spatial analysis. Such situations require the use of global datasets, like GTOPO30. Global data sets like ETOPO5, GTOPO30 are the only data sets, which can be used to derive basin boundaries and stream network and other terrain variations like slope aspects and flow direction and flow accumulation of the watershed in the absence of topographic maps. Approximately 1-km grid-based GTOPO 30 data sets can derive better outputs for larger basins, but they fail in flat areas like the Karkheh basin in Iran and the Amudarya in Uzbekistan. A new window in geo-spatial hydrology has opened after the launching of the space-borne satellite stereo pair of the Terra ASTER sensor. ASTER data sets are available at very low cost for most areas of the world and global coverage is expected within the next four years. The DEM generated from ASTER data has a reasonably good accuracy, which can be used effectively for hydrology application, even in small basins. This paper demonstrates the use of stereo pairs in the generation of ASTER DEMs, the application of ASTER DEM for watershed boundary delineation, sub-watershed delineation and explores the possibility of understanding the drainage flow paths in irrigation command areas. All the ASTER derived products were compared with GTOPO and 1:50,000-based topographic map products and this comparison showed that ASTER stereo pairs can derive very good data sets for all the basins with good spatial variation, which are equal in quality to 1:50,000 scale maps-based products.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.27-30
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• 2008

Wall correction method for wind tunnel test is reviewed and applied to the numerical experimental results obtained at the wind tunnel condition. The corrected lift coefficient agrees well with the reference data generated from the grid having very far boundary However the corrected drag coefficient presents some deviation from the reference data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2062-2072
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• 1991

The effect of free stream turbulence on the flow characteristics behind a circular cylinder is investigated in the present experimental study. The various free stream turbulent intensities are generated by different combinations of cylinder locations and grid shapes. Split film sensor with constant temperature anemometer is used to measure the local instantaneous velocity components. Experimental results demonstrate the large scale coherent structures are rapidly distorted and the Strouhal number is decreased with increasing free stream turbulent intensity.

• Journal of Ocean Engineering and Technology
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• v.10 no.3
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• pp.62-73
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• 1996

Numerical simulation is made of the three-dimensional wave breaking motion about a part of a floating offshore structure containing a circular cylinder mounted vertically onto a lower hull in regular periodic gravity wave generated by a numerical wave maker. TUMMAC-VIII finite-difference method is newly developed for such a problem. By use of density-function technique the three-dimensional wave breaking motion is approximately implenented in the framework of rectangular grid system. A porosity technique is devised for the implementation of the no-slip bydy boundary conditions. The generation of breaking waves by the interaction of incident waves with the structure is well simulated and interesting features of breaking waves are revealed with containing degree of quantitative and qualitative accuracy.

• Journal of the Korean Society of Visualization
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• v.5 no.2
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• pp.20-25
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• 2007

The geometry of a commercial passenger airplane is realized based on a Boeing 747-400 model through the photographic scanning and reverse engineering. The each element consisting of the plane such as fuselage, wing, vertical fin, stabilizer and engines, is individually generated and then the whole body is assembled by the photomodeler. The maximum error in the realized airplane is about 1.4% comparing with the real one. The three-dimensional inviscid steady compressible governing equations are solved in the unstructured tetrahedron grid system, and in a finite volume method using STAR-CD when the airplane flies at the cruise condition. The pressure distribution on the surface and the wing-tip vortices are visualized, and in addition to the aerodynamics coefficients, lift and drag are estimated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.106-109
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• 2006

The purpose of this study is to analyze the installed performance of the PW206C turbo shaft engine used in the development of the smart UAV(Unmanned Ariel Vehicle) by KARI(Korean Aerospace Research Institute). It mainly aims to investigate performance behavior at installed conditions using both inlet and exhaust losses generated by CFD analysis of the ducts. The ways employed to be able to analyze the performance extensively were mainly rallied out by performing design point analysis of the engine where the performance simulation results from the commercial program 'GASTURB 9' used for simulation were used as inlet boundary condition for the ducts in CFD program The use of CFD tool involve modeling of the ducts to conform with the stipulated shape and sizes as defined by KARI with a grid density that allows reasonable flow characteristics applicable to aircraft components. Respective values of Shaft horse power obtained by varying flight Mach number, Gas generator RPM and Altitude considering several losses inclusive of those estimated by use of CFD tool were then plotted at three conditions with the ECS-OFF, ECS-MAX and at un-installed condition. Reasonable results were obtained as a result of using computational fluid dynamics that can hence be justified as an alternative tool for use in future flow analysis of engine and components.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.6
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• pp.860-873
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• 1998

In a low speed open-type wind tunnel, a group of parallel wakes downstream of two dimensional grid model consisting of several circular cylinders were experimentally investigated to study the response of the wake flows to the acoustic excitation, in hoping to promote the understanding of the underlying mechanism behind the gross flow change due to artificial excitation. In the unexcited wake flows, the development of the individual wakes behind cylinders was almost uniform for the ratio of the spacing to the cylinder diameter of s/d.geq.1.5. For smaller s/d, however, the jet streams issued through the gaps between the cylinders became biased in one side and the cylinders had wakes of different sizes. At s/d=1.25, the gap flow directions change in time, leading to unstable wake patterns. Further reduction in s/d made this unstable flip-flopping of the jets stable. The most effective excitation frequency was found to be in the Strouhal number range of St=0.5-0.6. This frequency was related to the vortex shedding. At s/d=1.75, the excitation frequency was 2 or 4 times the vortex shedding frequency. When the flow was excited at this frequency, the vortex sheddings were energized, and pairings between neighboring vortices were generated. Also, the merging process between individual wakes was accelerated. The unstable and unbalanced wake patterns at s/d=2.15 were made stable and balanced. The unstable and unbalanced wake patterns at s/d=2.15 were made stable and balanced. For smaller spacing of s/d .leq,1.0, the acoustic excitation became less effective in controlling the flow.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.1
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• pp.35-41
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• 2006

The steel foundries with electric arc furnaces handling metal scraps have recently gained an attention as a potential source of dusts. The present study focuses on the analysis of dust emissions and removals during furnace charging and melting processes by commercial CFD software named FLUENT. A body fitted grid system consisting of 880,000 meshes was first generated by Gambit for the electric arc furnace with the capacity of 60 ton/cycle and then FLUENT was invoked to solve the corresponding NavierStokers equation for the momentum, temperature and dust concentration. The entire processes from metal charging to metal melting were simulated to investigate the unsteady behaviors of fluid flows and dust concentrations. The model simulation results showed that as the top of the electric arc furnace opened for metal charging, hot plumes bursted out from the furnace rose strongly by buoyance and escaped mostly through the main hood. Therefore, the capacity of main hoods determined the vent efficiency in the metal charging process. As the furnace was closed after the metal charging and the metal melting processes was followed, the hot flow stream stretching from the furnace to the main hood was dissipated fast and the flow from the inlet of the bottom of the left hand side to the main and monitoring hoods constituted the main stream. And there was only a slow flow in the right hand side of the furnace. Therefore, the dust concentrations were calculated higher in the left hand side of the furnace, which was consistent with observations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.6305-6314
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• 2015

This study presents numerical simulations of mean flow and turbulence structure of an open channel with submerged vegetation. Filtered Navier-Stokes equations are solved using large-eddy simulation (LES). The immersed boundary method (IBM) is employed based on a Cartesian grid. The numerical result is compared with experimental data of Liu et al. (2008) and shows that simulated results coincided reasonably with experimental data within the average error of 10%. Strong vortices are generated at the interface between vegetated and non-vegetated regions with spanwise extent. The generation of turbulence induced by shear at the interface is interfered with wake turbulence, resulting turbulence intensity maximum. Turbulence produced by shear affects the flow in vegetated region and the penetration depth increases with an increase in the submergence ratio. This result can be used to understand sediment transport mechanisms in the vegetated region.

• Water for future
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• v.28 no.2
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• pp.115-124
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• 1995

A GIS is capable of extracting various hydrological factors from DEM(digital elevation model). One of important tasks for hydrological analysis is the division of watershed. It can be an essential factor among various geometric characteristics of watershed. In this study, watershed itself and other geometric factors of watershed are extracted from DEM by using GIS technique. The manual process of tasks to obtain geometric characteristics of watershed is automated by using the functions of ARC/INFO software as GIS package. Scanned data was used for this study and it is converted to DEM data. Various forms of representation of spatial data are handled in main module and GRID module of ARC/INFO. GRID module is used on a stream in order to define watershed boundary, so it would be possible to obtain the watersheds. Also, a flow direction, stream networks and orders are generated. The results show that GIS can aid watershed management and research and surveillance. Also the geometric characteristics parameters of watershed can be quantified with ease using GIS technique and the hardsome process can be automated.