• Proceedings of the Korea Water Resources Association Conference
• /
• 2018.05a
• /
• pp.325-325
• /
• 2018

The main purpose of this study is to suggest the more reliable flow direction methods within the framework of DEM by investigating the existing methodologies. To this end SFD(single flow direction method), MFD(multiple flow direction method) and IFD(Infinite flow direction method) are applied to determination of flow direction for water particles in Jeonjeokbigyo basin, and then assessed with respect to the variation of flow accumulation. As the main results the different patterns of flow accumulation are found out from each application of flow direction methods. As the flow dispersion increases on DEM contributing areas to outlet grow in sequence of SFD, IFD, MFD but contribution of individual pixels into outlet decreases. Especially MFD and IFD tend to make additional hydrologic abstraction from rainfall excess due to the flow dispersion within flow paths on DEM. Based on parameter estimation for power law distribution by maximum likelihood flow accumulation can be thought of as scale invariance factor. Combination of several flow direction methods could give rise to the more realistic water flow on DEM through separate treatment of flow direction methods for dispersion and aggregation effects of water flow within different topographies.

• Journal of Korea Water Resources Association
• /
• v.54 no.11
• /
• pp.933-942
• /
• 2021

The surface image velocimetry was developed to measure river flow velocity safely and effectively in flood season. There are a couple of methods in the surface image velocimetry. Among them the spatio-temporal image velocimetry is in the spotlight, since it can estimate mean velocity for a period of time. For the spatio-temporal image velocimetry analyzes a series of images all at once, it can reduce analyzing time so much. It, however, has a little drawback to find out the main flow direction. If the direction of spatio-temporal image does not coincide to the main flow direction, it may cause singnificant error in velocity. The present study aims to propose a new method to find out the main flow direction by using a fast Fourier transform(FFT) to a spatio-temporal (image) volume, which were constructed by accumulating the river surface images along the time direction. The method consists of two steps; the first step for finding main flow direction in space image and the second step for calculating the velocity magnitude in main flow direction in spatio-temporal image. In the first step a time-accumulated image was made from the spatio-temporal volume along the time direction. We analyzed this time-accumulated image by using FFT and figured out the main flow direction from the transformed image. Then a spatio-temporal image in main flow direction was extracted from the spatio-temporal volume. Once again, the spatio-temporal image was analyzed by FFT and velocity magnitudes were calculated from the transformed image. The proposed method was applied to a series of artificial images for error analysis. It was shown that the proposed method could analyze two-dimensional flow field with fairly good accuracy.

• Journal of Korean Society on Water Environment
• /
• v.34 no.4
• /
• pp.391-398
• /
• 2018

The main purpose of this study is to suggest and recommend the more reliable flow direction methods within the framework of DEM and power law distribution, by investigating the existing methodologies. To this end SFD (single flow direction method), MFD (multiple flow direction method) and IFD (Infinite flow direction method) are applied to analyze the determination of a flow direction for the water particles as seen in the Jeonjeokbigyo basin, and then assessed with respect to the variation of flow accumulation in that region. As the main results revealed, the study showed the different patterns of flow accumulation are found out from each applications of flow direction methods utilized in this study. This brings us to understand that as the flow dispersion on DEM increases, in this case the contributing areas to the outlet grow in sequence of SFD, IFD, MFD, but it is noted that the contribution of individual pixels into outlet decreases at that time. In what follows, especially with the MFD and IFD, the result tends to make additional hydrologic abstraction from rainfall excess, as noted due to the flow dispersion within flow paths on DEM. Based on the parameter estimation for a power law distribution, which is frequently used for identify the aggregation structure of complex system, by maximum likelihood flow accumulation can be thought of as a scale invariance factor. In this regard, the combination of flow direction methods could give rise to the more realistic water flow on DEM, as revealed through the separate flow direction methods as utilized for dispersion and aggregation effects of water flow within the available different topographies.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.7
• /
• pp.2289-2297
• /
• 1996

Flows in the combustion chamber near the spark plug are measured using LDv.A single cylinder DOHC S.I. engine of compression ratio 9.5:1 with a transparent quartz window piston is used. Combustion chamber shape is semi-wedge type. Measured data are analyzed using the ensemble averaged analysis and the cycle resolved analysis which uses FFT Filtering. Turbulent intensity and mean velocity are studied in the main flow direction and the normal to main flow direction as a function of engine speeds. The results shows that the turbulent intensity obtained by the ensemble averaged analysis is greater than that calculated by the cycle resolved analysis. Especially, the ensemble averaged analysis shows increase in turbulence at the end of compression stroke although the cycle resolved analysis shows increase only in the cycle-by-cycle variation with no noticeable increase in turbulence. The mean velocity in the main flow direction increase as engine speed increase. But the mean velocity normal to the main flow does not show such increase. Turbulent intensity in both direction increase in proportion to engine speeds. The magnitude of turbulent intensity is about 0.3 ~ 0.4 times the mean piston speeds at the end of the compression stroke.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2002.04a
• /
• pp.301-302
• /
• 2002

Virtual cyclones have been the subject of aerosol separation studies since they were first developed by Torczynski and Rader (1996). In the virtual cyclone (originally referred to as the anticyclone), the main particle-laden flow follows a wall that curves away from the original flow direction rather than curving into the original direction, as in a cyclone. Although a wall forms the inner boundary of the main flow, its outer boundary is formed by an adjacent flow, often a confined recirculating flow, into which particles are transferred by centrifugal action. (omitted)

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2845-2850
• /
• 2007

Flow-induced forces on two identical nearby circular cylinders immersed in the cross flow at Re =100 were numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of flow-induced forces are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of force coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for drag coefficient and lift coefficient for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow-induced forces on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2851-2856
• /
• 2007

Flow patterns in the presence of two identical nearby circular cylinders at =100 were numerically studied. We considered all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. Eight distinct flow patterns were identified based on vorticity contours and streamlines, which are Base-Bleed, Biased-Base-Bleed, Shear- Layer-Reattachment, Induced-Separation, Vortex-Impingement, Flip-Flopping, Modulated Periodic, and Synchronized-Vortex-Shedding. Collecting all the numerical results, we propose a general flow pattern diagram for flows past the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use this diagram to distinguish flow patterns in the presence of two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• Journal of computational fluids engineering
• /
• v.13 no.3
• /
• pp.14-20
• /
• 2008

In this investigation, flow patterns past two identical nearby spheres at Re=300 were numerically studied. We considered all possible arrangements of the two spheres in terms of the distance between the spheres and, the angle inclined with respect to the main flow direction. It turns out that significant changes in shedding characteristics are noticed depending on how the two spheres are positioned. Collecting all the numerical results obtained, we propose a diagram for flow pattern on the distance vs. angle plane. The perfect geometrical symmetry implied in the flow configuration allows one to use that diagram to identify flow patterns past two identical spheres arbitrarily positioned in physical space with respect to the main flow direction.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.8
• /
• pp.724-732
• /
• 2007

Flow patterns in the presence of two identical nearby circular cylinders at Re=100 were numerically studied. We considered all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. Eight distinct flow patterns were identified based on vorticity contours and streamlines, which are Base-Bleed, Biased-Base-Bleed, Shear-Layer-Reattachment, Induced-Separation, Vortex-Impingement, Flip-Flopping, Modulated Periodic, and Synchronized-Vortex-Shedding. Collecting all the numerical results, we propose a general flow pattern diagram for flows past two nearby cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use this diagram to distinguish flow patterns in the presence of two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.9
• /
• pp.754-763
• /
• 2007

Flow-induced forces on two identical nearby circular cylinders immersed in the cross flow at Re=100 were numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of flow-induced forces are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of force coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for drag coefficient and lift coefficient for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow-induced forces on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.