• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.325-325
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• 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 Korean Society on Water Environment
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• v.34 no.4
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• pp.391-398
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• 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.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.31-38
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• 2005

Three-dimensional flow over the sand dunes have been studied numerically by using Large-Eddy Simulation (LES) method. In the direction of initial flow and span direction cyclic boundary conditions are imposed for velocity and pressure. The movement of the sand dune which is formed by converging wind direction has been investigated. The numerical method employed in this study can be divided into three parts: (i) calculation of the air flow over the sand dune using standard MAC method with a generalized coordinate system; (ii) estimation of the sand transfer caused by the flow through the friction; (iii) determination of the shape of the sand surface. Since the computational area has been changed due to step (iii), (i)-(iii) are repeated. The simulated dune, which has initially elliptic cross section, extends at the converging direction, which is known as linear dunes.

• The Korean Journal of Rheology
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• v.11 no.2
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• pp.153-158
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• 1999

An improved method to predict preferred direction of gas in gas assisted injection molding processes is introduced. Resistance of resin flow is defined and this resistance of resin flow is not directly related to the resistance of gas flow. Pressure drop requirement was believed to be proportional to the resistance to gas flow in our previous work. Instead of using the pressure drop requirement, velocity of resin should be compared to predict the gas flow direction. This method predicts the gas flow direction from the knowledge of process variables such as resin flow length, cross section area of cavity, melt temperature, and short shot. A simulation package was used to confirm the method.

• KIEE International Transactions on Power Engineering
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• v.5A no.4
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• pp.412-415
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• 2005

The recent requirement for faster and more frequent solutions has encouraged the consideration of parallel implementations using decentralized processors. Distributed multi-processor environments can potentially greatly increase the available computational capacity and decrease the communication burden, allowing for faster Optimal Power Flow (OPF) solutions. This paper presents a mathematical approach to implementing distributed OPF using the alternating direction method (ADM) to parallelize the OPF. Several IEEE Reliability Test Systems were adopted to demonstrate the proposed algorithm.

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

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.11
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• pp.1424-1428
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• 1999

This paper presents a mathematical decomposition coordination method to implementing the distributed optimal power flow (OPF), wherein a regional decomposition technique is adopted to parallelize the OPT. The proposed approach is based on the Alternating Direction Method (ADM), a variant of the conventional Augmented Lagrangian approach, and makes it possible the independent regional AC-OPF for each control area while the global optimum for the entire system is assured. This paper is an extension of our previous work based on the auxiliary problem principle (APP). The proposed approach in this paper is a completely new one, however, in that ADM is based on the Proximal Point Algorithm which has long been recognized as one of the attractive methods for convex programming and min-max-convex-concave programming. The proposed method was demonstrated with IEEE 50-Bus system.

• Journal of Biomedical Engineering Research
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• v.8 no.1
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• pp.75-80
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• 1987

With the conventional CW Doppler velocity meter, bl-directional velocities cannot be separated. The new CW Doppler system uses quadrature detection and phase rotation to produce simultaneous independent audio and velocity signals for forward and reverse blood flow direction, is fabricated. Specially, this system shows that phase rotation method for flow direction separation provides easy and satisfactory feature. From in vivo blood flow measurement, we can easily differentiate typical artery flow from vein flow, and measure both velocity characteristics qualitatively.

• The KSFM Journal of Fluid Machinery
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• v.20 no.1
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• pp.59-64
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• 2017

Diverter is an essential element in gravimetric calibration method of flowmeter. Error of diverter are influenced by flow velocity profile of nozzle outlet, motion velocity of diverter and detecting location. That's why, time detection position of diverter is tuned through repetitive test for minimizing error of diverter. Further the diverter must be compared with the other institutions test since the influence on the accuracy of the flow meter used in the test. In this paper, errors (flow velocity profile of nozzle outlet, motion velocity of diverter and detecting location) of diverter are decreased by produced uni-direction diverter and error of gravimetric calibration system is decreased. Uni-direction diverter is calibrated by gravimetric calibration system with precision flowmeter, the flowmeter is calibrated by pipe prover and other institutions and uni-direction diverter is evaluated. Uni-direction diverter is not influenced by flow velocity profile of nozzle outlet, motion velocity of diverter and detecting location. As a result, Uni-direction diverter can calibrate in wider scope since increasing ratio of maximum and minimum flow rate of uni-direction diverter.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.147-152
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• 1998

2-D flow fields are studied by using a shared memory parallel computer with a parallel flow analysis program which uses domain decomposition method and MPI library for data exchange at overlapped interface. Especially, effects of directional domain decomposition on parallel efficiency are studied for 2-D Lid-Driven cavity flow and flow through square cavity. It is known from the present study that domain decomposition along the main flow direction gives better parallel efficiency in 1-D partitioning than along the other direction. 2-D partitioning, however, is less sensitive to flow directions and gives good parallel efficiency for most of the cases considered.