• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.193_194
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• 2009

본 논문은 장기 전압 안정도 분석을 위한 프로그램 개발을 목적으로 한다. 장기 전압 불안정 현상은 전력 계통에 투입되어 있는 무효전력과 관련된 제어기 중에서 그 동작특성이 수 분에서 수십 분에 이르는 제어기에 의해 발생한다. 기존에 장기 전압 안정도 분석에는 상용툴의 Full-time Domain 알고리즘을 이용하였다. 하지만 기존의 Full-time Domain 알고리즘에 의해 장기 전압 안정도 분석을 하게 되면 그 연산 시간이 매우 오래 걸릴 뿐만 아니라, 시적분에 의한 수치 에러로 인하여 정확성을 보장할 수 없다. 본 논문에서는 장기 전압안정도 분석을 하기 위해 준동적 시모의 알고리즘(Quasi-Steady-State Algorithm)을 도입하였다. 준동적 시모의 알고리즘을 적용한 프로그램을 보이고, 이에 따fms 모의를 한구전력계통에 적용하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.128.1-128.1
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• 2011

In amorphous silicon and crystalline silicon(a-Si:H/c-Si) heterojuction solar cells, intrinsic hydrogenated amorphous silicon(a-Si:H) films play an important role to passivate the crystalline silicon wafer surfaces. We have studied the correlation between the surface passivation quality and nature of the Si-H bonding at the a-Si:H/c-Si interface. The samples were obtained by VHF-CVD under different deposition conditions. The passivation quality and analysis of all structures studied was performed by means of quasi steady state photoconductance(QSSPC) methods and fourier transform infrared spectrometer(FTIR) measurements respectively.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1998.10b
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• pp.10-10
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• 1998

The growth process of solid grains in a liquid matrix is usually explained in tem1S of Ostwald ripening. The variation of growth (dissolution) rate as a function of grain size during Ostwald ripening predicted that the dissolution rate becomes very large as grain size decreases but the growth rate of a large grain is rather limited. Therefore. a rather uniform size distribution of grain size is maintained once after the quasi-equilibrium state is reached. Quite frequently, however, the exaggerated grain growth (EGG) is observed to occur: only a limited number of grains grow exceptionally. From the observation that the EGG occurs only for the faceted grains with apparently straight solid-liquid interfaces, the EGG is suggested to be the consequence of growth process controlled by 2-dimensional nucleation. In this study, the result by computer calculation on the grain growth process controlled by various mechanisms will be given.

• Steel and Composite Structures
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• v.19 no.4
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• pp.789-809
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• 2015

This paper presents experimental and numerical studies into the structural behavior of a high performance corbel type composite connection adopted in Raffles City of Hangzhou, China. Physical tests under both monotonic and quasi-static cyclic loads were conducted to investigate the load carrying capacities and deformation characteristics of this new type of composite connection. A variety of structural responses are examined in detail, including load-deformation characteristics, the development of sectional direct and shear strains, and the history of cumulative plastic deformation and energy. A three-dimensional finite element model built up with solid elements was also proposed for the verification against test results. The studies demonstrate the high rigidity, strength and rotation capacities of the corbel type composite connections, and give detailed structural understanding for engineering design and practice. Structural engineers are encouraged to adopt the proposed corbel type composite connections in mega high-rise buildings to achieve an economical and buildable and architectural friendly engineering solution.

• Proceedings of the KAIS Fall Conference
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• 2012.05a
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• pp.177-181
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• 2012

Association is an important contribution to the overall hydrogen bonding in surfactant systems, especially in systems of colloidal and biological interest. Amphiphile systems, especially micelle and microemulsion systems, showed highly non-ideal behavior due to the intermolecular association and intramolecular association. The objective of this research is to present a lattice fluid equation of state that combines the quasi-chemical nonrandom lattice fluid model with modified Veytsman statistics for intra + inter molecular association to calculate phase behavior for mixture containing surfactant systems. The present EOS could correlate the literature data well for mixtures containing nonionic surfactant systems.

• Journal of Korea Foundry Society
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• v.9 no.1
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• pp.39-48
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• 1989

A basic three dimensional thermal model has been developed to simulate the solidification sequence for gravity die casting process. The finite difference method was used to analyze the solidification process during all the casting cycles. The prediction of die temperature in the quasi-steady state was analyzed by the boundary element method. The influence of die cooling on the heat flow in the cast/mold system was also investigated. Predictions of the computer simulation on temperature profiles and location of shrinkage defects were in good agreement with those observed in experimental die castings. Models of computer simulation which is developed by this work can be useful for the design and process control of die casting.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.24-26
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• 2005

This paper presents a framework for determining control strategies against unwanted tripping actions of relay operation that plays a very important role in cascading events leading to voltage collapse. The framework includes an algorithm for quick identification of possible zone 3 relay operation during voltage instability. The proposed approach comes up with control strategy of load shedding at the selected location with active power and relay margin criteria. In addition, Quasi Steady-State (QSS) simulation is employed to obtain time-related information which is valuable for both the timing and amount of control. The methodology is demonstrated through the modified New England 39-bus system.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.12-14
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• 2005

Security problem has been a fundamental issue in the operation and planning of power system. Voltage instability is widely recognized as an important issue of power system blackout. As far as real-time operation is concerned, there is a need for appropriate tools to identify dangerous contingencies, assess security margins and suggest corrective actions. In this paper, we propose the framework design of Voltage Security Assessment(VSA) using QSS(Quasi Steady-State) analysis method in order to implement fast time domain simulation engine as a major part of VSA.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.411-413
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• 2005

Static approaches usually employed in voltage stability analysis are based on the pre-determined scenarios of varying load and generation patterns. Thus, even though the approaches are applied to the same system condition, one may obtain different voltage instability phenomena using different scenarios. In the stage of concrete control strategy determination against voltage instability, dynamic approaches with full-time and/or quasi steady-state simulations need to be applied in order to confirm the effectiveness of the established control strategies. This paper describes the ULTC and dynamic load models, and discusses characteristics of the models.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.865-871
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• 2004

The safety evaluations of railway wheel sets make use of the static fracture toughness obtained in ingot materials. The static fracture toughness of wheelset materials has been extensively studied by experiments, but the dynamic fracture toughness with respect to wheel set materials has not been studied enough yet. It is necessary to evaluate the characteristics of the fracture mechanics depending on each location for a full-scale wheel set for high-speed trains, because the load state for each location of the wheel set while running is different the contact load between the wheel and rail, cyclic stress in the wheel plate, etc. This paper deals with the fracture toughness depend on load rates. The fracture toughness depending on load rate data shows that once the downward curve from quasi-static values was reached, subsequent values showed a slow increase with respect to the impact velocity. This means that dynamic fracture toughness should be considered in the design code of the wheelset material.