• Geomechanics and Engineering
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• v.27 no.5
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• pp.433-445
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• 2021

Artificial ground freezing (AGF) is a commonly used geotechnical support technique that can be applied in any soil type and has low environmental impact. Experimental and numerical investigations have been conducted to optimize AGF for application in diverse scenarios. Precise simulation of groundwater flow is crucial to improving the reliability these investigations' results. Previous experimental research has mostly considered horizontal seepage flow, which does not allow accurate calculation of the groundwater flow velocity due to spatial variation of the piezometric head. This study adopted vertical seepage flow-which can maintain a constant cross-sectional area-to eliminate the limitations of using horizontal seepage flow. The closure time is a measure of the time taken for an impermeable layer to begin to form, this being the time for a frozen soil-ice wall to start forming adjacent to the freeze pipes; this is of great importance to applied AGF. This study reports verification of the reliability of our experimental apparatus and measurement system using only water, because temperature data could be measured while freezing was observed visually. Subsequent experimental AFG tests with saturated sandy soil were also performed. From the experimental results, a method of estimating closure time is proposed using the inflection point in the thermal conductivity difference between pore water and pore ice. It is expected that this estimation method will be highly applicable in the field. A further parametric study assessed factors influencing the closure time using a two-dimensional coupled thermo-hydraulic numerical analysis model that can simulate the AGF of saturated sandy soil considering groundwater flow. It shows that the closure time is affected by factors such as hydraulic gradient, unfrozen permeability, particle thermal conductivity, and freezing temperature. Among these factors, changes in the unfrozen permeability and particle thermal conductivity have less effect on the formation of frozen soil-ice walls when the freezing temperature is sufficiently low.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.06a
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• pp.188-194
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• 1995

In this paper, several application examples of a forging simulator POSFORM were introduced with some forged parts for verification purpose, found in cold or hot forging companies. the forging simulator was also introduced in brief. The simulated results and the actually forged ones were compared in shape or metal flow. It has been shown that the design approach based on the forging simulator is most efficient in reducing design tryouts and development cost and accumulating design experience and technology effectively.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.671-680
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• 2007

The objective of this work is to reduce drag on a bluff body within a viscous flow by applying suction or injection of fluid along the surface of the body. In addition to minimizing drag, the optimal solution tends to reduce boundary layer separation and flow recirculation. When discretized by finite elements, the optimal control problem can be posed as a large-scale nonlinearly-constrained optimization problem. The constraints correspond to the discretized form of the Navier-Stokes equations. Unfortunately, solving such large-scale problems directly is essentially intractable. We developed several Sequential Quadratic Programming methods that are tailored to the structure of the control problem. Example problems of laminar flow around an infinite cylinder in two dimensions are solved to demonstrate the methodology. We use these optimal control techniques to study the influence of number of suction/injection holes and location of holes on the resulting optimized flow. We compare the proposed SQP methods against one another, as well as against available methods from the literature, from the point of view of efficiency and robustness. The most efficient of the proposed methods is two orders of magnitude faster than existing methods.

• Journal of Korea Water Resources Association
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• v.51 no.10
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• pp.895-903
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• 2018

There are a large number of weirs installed in rivers of Korea, and these characteristics are not common in other countries. When the flow passes through a structure such as a weir, discontinuous flow occurs. In terms of numerical simulation, it affects the numerical instability due to the balance between the flow term and the source term. In order to solve these problems, many researchers used empirical formulas or numerical scheme simplification. Recently, researches have been conducted to use more accurate numerical scheme. K-River was developed to reflect the characteristics of domestic rivers and calculate the discontinuous flow more accurately. For the verification of K-River, 1) numerical experiment simulations with a bump in the bed, 2) laboratory experiment of hydraulic jump simulation, 3) real river were performed. K-River verified its applicability by simulating results similar to the exact solution and observed value in all simulations.

• Journal of Digital Convergence
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• v.17 no.4
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• pp.137-147
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• 2019

This paper studies the effect of content information quality of u-tourism information system on flow theory and satisfaction. The purpose of the research is to generate and propose flow-related information to satisfy tourists with content information quality. The meaning of this paper is to derive success factors for verifying satisfaction of content information quality to tourists, establish hypotheses as research models, and evaluate verification. The differentiation of this study is the design implementation of u-fusion tourism information system by combining flow relation information with flow theory. The contribution of this paper is the generation of flow related information and the elicitation of success factors of contents quality of u-tourism information system. The advantage is that tourists can be patterned by symbolization and the pattern can be illustrated. The limitations of this paper are limited to small areas, and the lack of objectivity is required and future tasks are needed to compensate for them.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.11
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• pp.1411-1416
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• 2020

In this paper, we propose a method of extraction analysis of blood flow area on color doppler ultrasonography by using 4-directional contour tracking and K-Means algorithm. In the proposed method, ROI is extracted and a binarization method with maximum contrast as a threshold is applied to the extracted ROI. 4-directional contour algorithm is applied to extract the trapezoid shaped region which has blood flow area of brachial artery from the binarized ROI. K-Means based quantization is then applied to accurately extract the blood flow area of brachial artery from the trapezoid shaped region. In experiment, the proposed method successfully extracts the target area in 28 out of 30 cases (93.3%) with field expert's verification. And comparison analysis of proposed K-Means based blood flow area extraction on 30 color doppler ultrasonography and brachial artery blood flow ultrasonography provided by a specialist yielded a result of 94.27% accuracy on average.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.68-72
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• 2008

NUFLEX is a general purpose thermo/fluid flow analysis program which has various physical models including spray. In NUFLEX, spray models are composed of breakup and collision models of droplet. However, in case of diesel engine, interaction between wall-film and impingement model considering heat transfer is not coded in NUFLEX. In this study, Lee & Ryou impingement & wall-film model considering heat transfer is applied to NUFLEX. For the verification of this NUFLEX program, numerical results are compared with experimental data. Differences of film thickness and radius between numerical results and experimental data are within 10% error range. The results show that NUFLEX can be used for comprehensive analysis of spray phenomena.

• 한국IT서비스학회:학술대회논문집
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• 2008.11a
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• pp.337-340
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• 2008

To take the re-use of software, we need to study the efficient integration method of source programs. When the source programs are merged, it is required the steps of verification for any non-interference on non-identical parts of them. The traditional techniques of the program integration verify non-interference of source programs through the simple comparison of statements of source programs. We propose the efficient integration method using data flow analysis in the programs. A study comparing test results from the traditional method and the proposed method has found that the proposed method is more efficient than the traditional method.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.46-53
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• 1998

An inverse method for the subsonic and transonic airfoil design was developed using the Euler equations. Two testcases were performed. One was a verification of the method using the supercritical airfoil of the Korean mid-sized (100 passengers class) transport aircraft. The other was the design of an airfoil showing a good cruising performance (L/D ratio) in the high subsonic flow regime. These testcases demonstrated the efficiency and the robustness of the design method in the present study.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.10
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• pp.102-108
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• 2011

The existing power flow has a single direction to the line end but the bidirectional power flow will possibly occur depending on the output capacity in the 22.9[kV] distribution power system connected with the dispersed generation(DG). So these characteristics would influence the power system management. The DG have many advantages such as assistance source, Load share etc. So the utility must apply the bidirectional protection system so as to maximize an advantage of DG. This paper describes the field test case of bidirectional protective device in order to investigate the device performance when applied to bidirectional power system. We have tested in the power system test site of KEPCO and these tests provide the basis for performance verification test of bidirectional protective device in the power system.