• Journal of Korea Water Resources Association
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• v.47 no.11
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• pp.1095-1105
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• 2014

A spatial downscaling method using the Support Vector Machine (SVM) Regression for 25 km Tropical Rainfall Measuring Mission (TRMM) Monthly precipitation is proposed. The nonlinear relationship among hydrometeorological variables and precipitation was effectively depicted by the SVM for predicting downscaled grid precipitation. The accuracy of spatially downscaled precipitation was estimated by comparing with rain gauge data from sixty-four stations and found to be improved than the original TRMM data in overall. Especially the positive bias of the original TRMM data was effectively removed after the downscaling procedure. The spatial distributions of 25 km and 1 km grid precipitation were generally similar, while the local spatial trend was better detected by 1 km grid precipitation. The downscaled grid data derived from the proposed method can be applied in hydrological modelling for higher accuracy and further be studied for developing optimized downscaling method incorporation other regression methods.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.386-389
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• 2008

Forming limit diagram is created by graphical illustration indicating major and minor strain. In order to provide the criterion for forming safety, FLC(forming limit curve) need to be fitted to the diagram. However, the standard method for the strain measurement and FLC plotting are not fixed yet, which results in inconvenience in digitalized analysis. In this study, new construction method for FLC was suggested in order to minimize operator dependency. For this purpose, major and minor strain were measured automatically and analyzed. Then, a second order equation is adopted to fit the FLC. Optimized by response surface method was performed to ensure particular characteristics of the FLC.

• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.252-253
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• 2013

현재 계통 연계형 인버터에서 필터 크기를 줄이고 동적특성을 개선하며 필터의 성능향상을 하기 위해 LCL필터의 사용이 증가하고 있다. LCL필터를 설계함에 있어 계통측으로 흘러들어가는 전류의 THD를 줄이는 것이 설계의 주된 목적이지만, 인버터측의 인덕터에 흐르는 전류의 최대치를 고려함으로써 필터에서의 전력손실을 줄이고 시스템전체의 효율을 높게 가져갈 수 있다. 본 논문에서는 계통 연계형 인버터의 LCL 필터설계에 있어서 인버터측 인덕터의 전류 리플의 최대치를 분석하고 이를 고려하여 필터설계를 하고 있다. 이 설계를 통해 컴퓨터 시뮬레이션과 실험을 통하여 타당성을 검증한다.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.65-66
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• 2011

독립부하가 존재하는 계통연계 인버터에서 LCL필터 설계시 계통으로 주입하는 전류뿐만 아니라 독립부하 전압품질도 고려되어야 한다. 또한, LCL필터의 가격과 부피측면을 고려하여 고조파 감쇠율은 기준을 만족하면서 인덕턴스와 캐패시턴스는 가능한 작게 설계하는 것이 중요하다. 본 논문에서는 계통전류의 고조파 기준은 만족하고, LCL필터 모델로부터 구해지는 전달함수를 이용하여 계통연계시와 독립운전시 모두 독립부하의 전압품질이 만족하도록 필터설계를 한다. 또한, 독립부하 전압리플, 인덕터 부피, 무효전류량, 시스템 대역폭에 가중치를 적용한 LCL필터 최적설계 방법을 제안한다.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.884-889
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• 2001

Combustion chamber crevices in SI engines are identified as the largest contributor to the engine-out hydrocarbon emissions. The largest of crevice region is the piston ring pack crevice. To predict and understand the oxidation process of piston crevice hydrocarbons, a 3-dimensional numerical simulation method was developed. A engine shaped computational mesh with moving grid for piston and valve motions was constructed. And a 4-step oxidation model involving 7 species was used and the 16 coefficients in the rate expressions were optimized based on the results from a detailed chemical kinetic mechanism for the oxidation condition of engine combustion chamber. Propane was used as a fuel in order to eliminate oil layer absorption and liquid fuel effect.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.929-936
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• 2004

In the present work, shape of the mixing vane in Plus7 fuel assembly has been optimized numerically using three-dimensional Reynolds-averaged Navier-Stokes analysis of flow and heat transfer. Standard $k-{\epsilon}$ model is used as a turbulence closure. The Response surface method is employed as an optimization technique. The objective function is defined as a combination of heat transfer rate and inverse of friction loss. Bend angle and base length of mixing vane are selected as design variables. Thermal-hydraulic performances for different shapes of mixing vane have been discussed, and optimum shape has been obtained as a function of weighting factor in the objective function.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.1-8
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• 2001

A CFD-based design method for transonic axial compressor blades was developed based on three-dimensional Navier-Stokes flow physics. The method employs a sectional three-dimensional (S3D) analysis concept where the three-dimensional flow analysis is performed on the grid plane of a span station with spanwise flux components held fixed. The S3D analysis produced flow solutions nearly identical to those of three-dimensional analysis, regardless of the initialization of the flow field. The sectional design based on the S3D analysis can include three-dimensional effects of compressor flows and thus overcome the deficiencies associated with the use of quasi-three-dimensional flow physics in conventional sectional design. The S3D design was first used in the inverse triode to find the geometry that produces a specified target pressure distribution. The method was also applied to optimize the adiabatic efficiency of the blade sections of Rotor 37. A new blade was constructed with the optimized sectional geometries at several span stations and its aerodynamic performance was evaluated with three-dimensional analyses.

• Advances in Energy Research
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• v.4 no.2
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• pp.163-176
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• 2016

Rapid depletion of fossil based oil, coal and gas reserves and its greater demand day by day necessitates the search for other alternatives. Severe environmental impacts caused by the fossil fire based power plants and the escalating fuel costs are the major challenges faced by the electricity supply industry. Integration of Distributed Generators (DG) especially, wind and solar systems to the grid has been steadily increasing due to the concern of clean environment. This paper focuses on a new simple and fast load flow algorithm named Backward Forward Sweep Algorithm (BFSA) for finding the voltage profile and power losses with the integration of various sizes of DG at different locations. Genetic Algorithm (GA) based BFSA is adopted in finding the optimal location and sizing of DG to attain an improved voltage profile and considerable reduced power loss. Simulation results show that the proposed algorithm is more efficient in finding the optimal location and sizing of DG in 15-bus radial distribution system (RDS).The authenticity of the placement of optimized DG is assured with other DG placement techniques.

• Progress in Superconductivity
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• v.12 no.2
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• pp.124-128
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• 2011

We have developed a high-$T_C$ SQUID magnetometer system to measure magnetocardiograms of laboratory rats. White noise of the measurement system was about 50 fT/$Hz^{1/2}$ when measured in a magnetically shielded box. We optimized the measurement position to obtain clear MCG wave from rat's small heart by using grid measurements. With the optimization, the MCG signal was successfully detected with the peak amplitude of about 50 pT. We could observe well defined P-, QRS-, and T-wave from the rat MCG. The results suggest that the developed system has a strong potential to monitor the progress of heart disease model using laboratory rat.

• Transactions of Materials Processing
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• v.15 no.9 s.90
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• pp.648-653
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• 2006

In this study, the characteristics of Wire Electrical Discharge Machining(WEDM) of the high-hardened mold steel were investigated. WEDM experiments have been carried out based on parameter of wire diameter, pulse on time, pulse off time, feed rate and cycle etc. From the results, the optimized WEDM cycle of RIGOR steel has been revealed as $5{\sim}7$ times. Also, geometrical accuracy of the Core Pin is dependent on WEDM wire radius machining condition and wire chattering.