• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.652-659
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• 2000

The purpose of this study is to present the most effective numerical scheme to calculate the unsteady flows. In order to calculate the flow quantities of flow past a circular cylinder, Three-time level and five convective schemes are applied to unsteady and convective terms, respectively. The values obtained are compared with those from the existing experimental and numerical studies. At Reynolds numbers up to 160, time intervals can be expanded 10 times of Implicit Euler scheme using Three-time level method, and it is found that QUICK and CUI schemes work much stable than others even if less grid density conditions. The combination of Three-time level and QUICK scheme gives high resolutions for laminar unsteady problems with PC level.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.88-89
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• 2017

This paper investigates the design of multi-winding coupled inductor for minimum inductor current ripple in rapid traction battery charger systems. Based on the general circuit model of multi-winding coupled inductor together with the operating principles of dc-dc converter, the relationship between the ripple size of inductor current and the coupling factor is derived under the different duty ratio. The optimal coupling factor which corresponds to a minimum inductor ripple current becomes -(1/n-1), i.e. a complete inverse coupling without leakage inductance, as the steady-state duty ratio operating point approaches 1/n, 2/n, … or (n1)/n. In an opposite manner, the optimal coupling factor value of zero, i.e. zero mutual inductance, is required when the steady-state duty ratio operating point approaches either zero or one.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.195-196
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• 2015

This paper investigates the design of coupled inductor for minimum inductor current ripple in rapid traction battery charger systems. Based on the general circuit model of coupled inductor together with the operating principles of dc-dc converter, the relationship between the ripple size of inductor current and the coupling factor is derived under the different duty ratio. The optimal coupling factor which corresponds to a minimum inductor ripple current becomes -0.5, i.e. a complete inverse coupling without leakage inductance, as the steady-state duty ratio operating point approaches 1/3 or 2/3. In an opposite manner, the optimal coupling factor value of zero, i.e. zero mutual inductance, is required when the steady-state duty ratio operating point approaches either zero or one. Coupled inductors having optimal coupling factor can minimize the ripple current of inductor and battery current resulting in a reliable and efficient operation of battery chargers.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.486-487
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• 2012

In this paper, novel three-port active power decoupling (APD) method for applying 250[W] micro-inverter. This type using third port for active power decoupling stores the surplus energy and supplies sufficient energy to grid. Conventional decoupling circuit is applied in single phase grid connected micro-inverter especially single-stage configuration like flyback-type DC-AC inverter. In this passive power decoupling method, electrolytic capacitor with large capacitance is needed for decoupling from constant DC power and instantaneous AC power. However the decoupling capacitor is replaced with film capacitor by using APD, thus the overall system can achieve smaller size and long lifespan. Proposed three-port flyback inverter is verified by design and simulation.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1781-1783
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• 2005

To evaluate the grid-connected Photovoltaic(PV) system performance, as a medium size, a 120 kW PV system which was consisted of solar cells, PCS, 150kVA transformer station and utility grid was designed and constructed.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.4 no.1
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• pp.58-71
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• 1986

A Digital Terrain Model (DTM) consists of two components;one is sampling of the terrain imformation, and the other is interpolation. The present study aims at the investigation of the accuracy and efficiency of Moving Average and Linear Prediction interpolation methods by numerical experiment. Basic input data are the elerations in square grid which procured by photogrammetry, and the accuracy of each interpolation is investigated on different grid size, terrain type and pattern of reference points.

• ETRI Journal
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• v.42 no.6
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• pp.815-826
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• 2020

We propose a two-dimensional (2D) scattering-center-extraction (SCE) method using sparse recovery based on the compressive-sensing theory, even with data missing from the received radar cross-section (RCS) dataset. First, using the proposed method, we generate a 2D grid via adaptive discretization that has a considerably smaller size than a fully sampled fine grid. Subsequently, the coarse estimation of 2D scattering centers is performed using both the method of iteratively reweighted least square and a general peak-finding algorithm. Finally, the fine estimation of 2D scattering centers is performed using the orthogonal matching pursuit (OMP) procedure from an adaptively sampled Fourier dictionary. The measured RCS data, as well as simulation data using the point-scatterer model, are used to evaluate the 2D SCE accuracy of the proposed method. The results indicate that the proposed method can achieve higher SCE accuracy for an incomplete RCS dataset with missing data than that achieved by the conventional OMP, basis pursuit, smoothed L0, and existing discrete spectral estimation techniques.

• Progress in Superconductivity and Cryogenics
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• v.11 no.4
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• pp.25-28
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• 2009

In order to apply superconducting electric machineries such as a Superconducting Fault Current Limiter (SFCL) to the power grid, the single module should be connected in series to have reasonable size. Superconducting tapes in the module also should be stacked to satisfy requirements such as large operation current of the power grid. This is because a single superconducting tape has restricted applicable current capacity. Moreover especially in SFCL at the fault, there should be equal voltage distribution in series-connected SFCL modules. In this paper, we investigated the voltage distribution in fault current of series-connected YBCO coated conductors (CC). Depending on characteristics of the CC samples such as critical current, even voltage distribution could be achieved or not. In addition, the effect of stacked CC on the change of voltage distribution comparing to non-stack cases in series connection was confirmed by experiments. As the CC stacked, voltage difference could be reduced.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.6
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• pp.412-421
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• 2023

As the demand for mechatronic systems and high performance increases in the machinery industry, the importance of improving friction characteristics is emphasized. During relative movement of objects, friction and wear occur on two surfaces in contact, and various methods are being designed to increase the lifespan and energy efficiency of machines. The energy increase effect using lubricants is a well-known method. In this study, a micro-sized rectangular grid pattern was produced by applying a precise micro-pattern photo lithography process. Rectangular grid patterns of the same shape and friction behavior according to the size of the pattern were produced in convex and concave shapes, and the tribological characteristics of each were analyzed.

• Wind and Structures
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• v.15 no.4
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• pp.313-329
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• 2012

There have existed for a number of years good practice guidelines for the use of Computational Fluid Dynamics (CFD) in the field of wind engineering. As part of those guidelines, details are given for the size of flow domain that should be used around a building of height, H. For low-rise buildings, the domain sizes produced by following the guidelines are reasonable and produce results that are largely free from blockage effects. However, when high-rise or tall buildings are considered, the domain size based solely on the building height produces very large domains. A large domain, in most cases, leads to a large cell count, with many of the cells in the grid being used up in regions far from the building/wake region. This paper challenges this domain size guidance by looking at the effects of changing the domain size around a tall building. The RNG ${\kappa}-{\varepsilon}$ turbulence model is used in a series of steady-state solutions where the only parameter varied is the domain size, with the mesh resolution in the building/wake region left unchanged. Comparisons between the velocity fields in the near-field of the building and pressure coefficients on the building are used to inform the assessment. The findings of the work for this case suggest that a domain of approximately 10% the volume of that suggested by the existing guidelines could be used with a loss in accuracy of less than 10%.