• ETRI Journal
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• v.31 no.1
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• pp.42-50
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• 2009

A new method for simulating voltage and current distributions in transmission lines is described. It gives the time domain solution of the terminal voltage and current as well as their line distributions. This is achieved by treating voltage and current distributions as distributed state variables (DSVs) and turning the transmission line equation into an ordinary differential equation. Thus the transmission line is treated like other lumped dynamic components, such as capacitors. Using backward differentiation formulae for time discretization, the DSV transmission line component is converted to a simple time domain companion model, from which its local truncation error can be derived. As the voltage and current distributions get more complicated with time, a new piecewise exponential with controllable accuracy is invented. A segmentation algorithm is also devised so that the line is dynamically bisected to guarantee that the total piecewise exponential error is a small fraction of the local truncation error. Using this approach, the user can see the line voltage and current at any point and time freely without explicitly segmenting the line before starting the simulation.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.671-674
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• 2002

Pressure compensating temperature control valve(TCV) is one of the important control devices, which is used to maintain the constant temperature of working fluid in power and chemical plants. The ratio of cylinder hole diameters of inlet and outlet is the main design parameters of TCV. So this needs to be investigated to improve the function of control of temperature and void fraction. In this study, numerical analysis is carried out with various ratios of cylinder hole diameters of the inlet and outlet in the TCV. Especial1y, the distribution of the static pressure Is investigated to calculate the new coefficient($C_{\upsilon}$) and resistance coefficient(K). The governing equations are derived from making using of three-dimensional Naver-Stokes equations with standard $k-{\varepsilon}$ turbulence model and SIMPLE algorithm. Using a commercial code, PHOENICS, pressure and flow fields in TCV are calculated with different inlet and outlet diameters of the cylinder hole for cold and hot water passages.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.98-105
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• 1997

The behaviour of alloys in the semi-solid state strongly depends on the imposed stress state and on the morphology of the phase which can very from dendritic to globular. The estimation of behaviour characteristic in the compression simulation with seim-solid materials are calculated by finite element method with proposed algorithm. The proposed theoretical model and a various boundary conditions for compression process is investigated with the coupling calculation between the liquid phase flow and the solid phase deformation. The simulation process considering soldification phenomena is performed to the isothermal conditions of two dimensional problems. To analysis of compression process by using semi-solid materials, a new stress-strain relationship is described, and compression analysis is performed by viscoelastic model for the solid phase and the Darcy's law for the liquid flow. The calculated results for compression force and ram displacement will be compared to experimental data.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.7
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• pp.45-55
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• 1997

Electircal characteristics of HgCdTe photodiodes with a heterostructure to achieve high performance are analyzed numerically. A two-dimensional device simulator which can handle a HgCdTe heterostructure, was developed for this work. The effects of band nonparabolicity, carrier degeneracy, and band-offset of heterointerace are included in a carrier transport model. A unified generation-recombination model includes simultaneously phonon-assisted tunneling and pure tunneling of carriers via traps is newly employed for describing the electric field and temperature dependency of dark current effectively. Furthermore, to accurately predict the effect mole fraction variations on genration rates, ray-trace algorithm is incorporated in the our simulator. Under the various circumstances such as dark, illumination, and surface states, electrical properties of planar heterostructure photodiode are presented and those of homojunction are compared. These results serve as a explanation of cap layer's role on performance.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.183-190
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• 2001

Topology optimization. has been evolved into a very efficient conceptual design tool and has been utilized into design engineering processes in many industrial parts. In recent years, topology optimization has become the focus of structural optimization design and has been researched and widely applied both in academy and industry. Traditional topology optimization has been using homogenization method and optimality criteria method. Homogenization method provides relationship equation between structure which includes many holes and stiffness matrix in FEM. Optimality criteria method is used to update design variables while maintaining that volume fraction is uniform. Traditional topology optimization has advantage of good convergence but has disadvantage of too much convergency time and additive checkerboard prevention algorithm is needed. In one way to solve this problem, element remove method is presented. Then, it is applied to many examples. From the results, it is verified that the time of convergence is very improved and optimal designed results is obtained very similar to the results of traditional topology using 8 nodes per element.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.326-329
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• 2009

In order to analyze the effect of leveling conditions on residual stress evolution of hot rolled high strength steels, a numerical algorithm was developed. It was able to implement the effect of plastic fraction (intermesh) in leveling, line tension, work roll bending, and initial residual stress and curl distribution. The effect of work roll bending on residual stress and curl were studied by using the developed program. The validity of simulated results was verified from comparison with the experimentally measured residual stress and curl in a sheet.

• Education of Primary School Mathematics
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• v.3 no.1
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• pp.63-77
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• 1999

We introduce what is the meaning of problem and problem solving and also different type of problems and problem-solving strategies were discussed in this paper, with suggestions for teaching both Polya's four-step strategy and specific problem solving strategies. Many real and concrete examples of routine and nonroutine problems in elementary school mathematics are introduced. Especially, we have researched on the actual condition how children in elementary school think about multiplication of fraction for the routine problem. As a result, we have noticed that children have diverse thinking in their own way and also concrete expressions are much better effective than algorithm showing in textbook.

• IE interfaces
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• v.25 no.2
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• pp.178-186
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• 2012

The DRAM module is an important part of servers, workstations and personal computer. Its malfunction causes a lot of damage on customer system. Therefore, customers demand the highest quality products. The company applies DRAM module Outgoing Quality Assurance Inspection(OQA) to secures the highest quality. It is the key process to decides shipment of products through sample inspection method with customer oriented tests. High fraction of defectives entering to OQA causes inevitable high quality cost. This article proposes the application of ensemble learning to classify the lot status to minimize the ratio of wrong decision in OQA, observing a potential in reducing the wrong decision.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.9
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• pp.403-408
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• 1986

In this paper, the method to improve the efficiency of an induction motor at light load is discussed. Efficiency of induction motor can be very substantially improved by keeping the slip frequency as constant. Therefore, to simplify the control loop, algorithm which maintain constant slip frequency and control the input voltage is adopted. Simplified high efficiency drive of induction motor using PLL technique is suggested. In order to verify the validity of this system, the test results are compared with those obtained by optimal slip drive system and then we found closer to the optimal efficiency. For example its efficiency is improved from 18[%] to 42[%] at a few fraction of the full load (20[%]).

• Journal of Communications and Networks
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• v.13 no.4
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• pp.339-344
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• 2011

Base station coordination has received much attention as a means to reduce the inter-cell interference in cellular networks. However, this interference reducing ability comes at the expense of increased feedback, backhaul load and computational complexity. The degree of coordination is therefore limited in practice. In this paper, we explore the trade-off between capacity and feedback load in a cellular network with coordination clusters. Our main interest lies in a scenario with multiple fading users in each cell. The results indicate that a large fraction of the total gain can be achieved by a significant reduction in feedback. We also find an approximate expression for the distribution of the instantaneous signal to interference-plus-noise ratio (SINR) and propose a new effective scheduling algorithm.