• JSTS:Journal of Semiconductor Technology and Science
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• 제5권3호
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• pp.159-167
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• 2005

Quantization effects (QEs), which manifests when the device dimensions are comparable to the de Brogile wavelength, are becoming common physical phenomena in the present micro-/nanometer technology era. While most novel devices take advantage of QEs to achieve fast switching speed, miniature size and extremely small power consumption, the mainstream CMOS devices (with the exception of EEPROMs) are generally suffering in performance from these effects. In this paper, an analytical model accounting for the QEs and poly-depletion effects (PDEs) at the silicon (Si)/dielectric interface describing the capacitance-voltage (C-V) and current-voltage (I-V) characteristics of MOS devices with thin oxides is developed. It is also applicable to multi-layer gate-stack structures, since a general procedure is used for calculating the quantum inversion charge density. Using this inversion charge density, device characteristics are obtained. Also solutions for C-V can be quickly obtained without computational burden of solving over a physical grid. We conclude with comparison of the results obtained with our model and those obtained by self-consistent solution of the $Schr{\ddot{o}}dinger$ and Poisson equations and simulations reported previously in the literature. A good agreement was observed between them.

• Journal of Ship and Ocean Technology
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• 제12권1호
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• pp.16-27
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• 2008

The interaction between advancing ships and the waves generated by them plays important roles in wave resistances and ship motions. Wave breaking phenomena near the ship bow at different speeds are investigated both numerically and experimentally. Numerical simulations of free surface profiles near the fore bodies of ships are performed and visualized to grasp the general trend or the mechanism of wave breaking phenomena from moderate waves rather than concentrating on local chaotic irregularities as ship speeds increase. Navier-Stokes equations are differentiated based on the finite difference method. The Marker and Cell (MAC) Method and Marker-Density Method are employed, and they are compared for the description of free surface conditions associated with the governing equations. Extra effort has been directed toward the realization of extremely complex free surface conditions at wave breaking. For this purpose, the air-water interface is treated with marker density, which is used for two layer flows of fluids with different properties. Adaptation schemes and refinement of the numerical grid system are also used at local complex flows to improve the accuracy of the solutions. In addition to numerical simulations, various model tests are performed in a ship model towing tank. The results are compared with numerical calculations for verification and for realizing better, more efficient research performance. It is expected that the present research results regarding wave breaking and the geometry of the fore body of ship will facilitate better hull form design productivity at the preliminary ship design stage, especially in the case of small and fast ship design. Also, the obtained knowledge on the impact due to the interaction of breaking waves and an advancing hull surface is expected to be applicable to investigation of the ship bow slamming problem as a specific application.

• 한국조경학회지
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• 제26권3호
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• pp.78-78
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• 1998

The purpose of this research is to develop a CAD-based program for data analysis of digital elevation model(DEM) on the aspect of landscape assessment. When handling DEM data as a visual simulation of topographic landscape, it is basic interest to analyze visible area and visualize visual sensitivity distributions. In reference with landscape assessment, more intuitive and interactive visualizing tools are needed, specially in area of visual approach. For adaptability to landscape assessment, algorithmic approaches to visibility analysis and concepts for visual sensitivity calculation in this study were based on processing techniques of entity data control functions used in AutoCAD drawing database. Also, for the purpose of quantitative analysis, grid-type 3DFACE entities were adopted as mesh unit of DEM structure. Developed programs are composed of main part named VSI written in AutoLISP and two of interface modules written in dialog control language(DCL0 for user-oriented interactive usage. Definitions of camera points(view points) and target points(or observed area) are available alternatively in combined methods of representing scenic landscape, scenery, and sequential landscape. In the case of scene landscape(single camera to fixed target point), only visibility analysis in available. And total visibility, frequency of cumulative visibility, and visual sensitivity analysis are available in other cases. Visual sensitivity was thought as view angle(3 dimensional observed visual area) and the strengths were classified in user defined level referring to statistical characteristics of distribution. Visibility analysis routine of the VSI was proved to be more effective in the accuracy and time comparing with similar modules of existing AutoCAD third utility.

• 전기학회논문지P
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• 제64권2호
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• pp.57-61
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• 2015

Current research and development efforts and other projects for energy storage systems (ESS) have recently been gaining attention. This is due to the many applications where ESS, particularly batteries, can be used. Among these are peak shaving, frequency regulation, and stabilization of renewable energy output. KEPCO has completed the construction and demonstration of a 4-MW battery energy storage system (BESS) located in Jeju City to verify its practicability in the power grid. KEPCO Research Institute has also been developing technology for the commercialization of BESS, and has been conducting a trial run of a 52-MW ESS (28MW + 24MW of Seo-Anseong and Shin-Yongin substations) constructed in 2014 for frequency regulation. This paper discusses the development of operation methods, as well as an operation user interface, for the safe operation and monitoring of BESS used for frequency regulation in a power system. Included are operation and simulation methods for various normal and transient frequency situations that can be experienced by a power system. Also discussed are the results obtained after applying these methods to the 4-MW BESS and the 52-MW ESS, both used for frequency regulation. The technology in this paper will be applied to 500MW ESS for frequency regulation of KEPCO by 2017. It is expected that this technology helps a safe and reliable operation and control of ESS for frequency regulation through its continuous upgrade.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2009년도 추계학술대회
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• pp.613-616
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• 2009

평택항의 원양어선 회사에서 정보현황은 선박 배치도와 철판과 자석 등으로 구성된 수작업에 의한 현황판 보드를 이용하고 있다. 유비쿼터스 네트워크를 기반으로 하는 인터넷 웹 애플리케이션 환경에서 매 시간마다 접수된 항해중인 37척의 원양선박정보를 인터넷에 연결된 PC에서 표시하는 연구를 한다. Flash 기술 기반의 RIA의 활용을 통해 3단 가로 그리드 구성으로 Digital Dash-Board을 구성하여 6대양에 운항중인 선박항해위치 및 위도, 경도 표시는 물론 각종 정보를 visual하게 display한다. 운영자 및 사용자에게 편의성을 높일 수 있고, 실시간 데이터를 활용해서 역동적인 Web Application 구축에 중점을 두었다.

• 정보처리학회논문지:소프트웨어 및 데이터공학
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• 제10권7호
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• pp.263-270
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• 2021

강화학습은 학습을 통해 최적의 행동정책을 탐색하는 기법으로써, 재난 상황에서 효과적인 인명 구조 및 재난 대응 문제 해결을 위해 많이 활용되고 있다. 그러나, 기존 재난 대응을 위한 강화학습 기법은 상대적으로 단순한 그리드, 그래프와 같은 환경 혹은 자체 개발한 강화학습 환경을 통해 평가를 수행함에 따라 그 실용성이 충분히 검증되지 않았다. 본 논문에서는 강화학습 기법을 실세계 환경에서 사용하기 위해 기존 개발된 재난 시뮬레이션 환경의 복잡한 프로퍼티를 활용하는 강화학습 환경 구성과 활용 결과를 제시하고자 한다. 본 제안 강화학습 환경의 구성을 위하여 재난 시뮬레이션과 강화학습 에이전트 간 강화학습 커뮤니케이션 채널 및 인터페이스를 구축하였으며, 시뮬레이션 환경이 제공하는 고차원의 프로퍼티 정보의 활용을 위해 비-이미지 피쳐 벡터(non-image feature vector)에 이미지 변환방식을 적용하였다. 실험을 통해 본 제안 방식이 건물 화재 피해도를 기준으로 한 평가에서 기존 방식 대비 가장 낮은 건물 화재 피해를 기록한 것을 확인하였다.

• 한국해양공학회지
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• 제33권4호
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• pp.313-321
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• 2019

The prediction of the hydrodynamic performance of a planing hull vessel is an important and challenging topic for computational fluid dynamic (CFD) applications to naval hydrodynamics. In this paper, the resistance and planing attitude analysis for a Fridsma hull, which is a prismatic planing hull, in still water are numerically studied using OpenFOAM. OpenFOAM is an open source code package based on C++ libraries and the finite volume method (FVM) for the discretization of the RANS equation. The volume of fluid method (VOF) is used to capture the water-air interface and the SST ${\kappa}-{\omega}$ model is used for the turbulence simulation. The overset mesh method is used to capture the large motion of the hull at higher speeds. Before the extensive analysis, uncertainty analyses using various time steps and grid sizes were performed for one ship speed case of Fn = 1.19. The results of the present study are compared with those of a model test, other CFD research, and Savitsky's empirical formula. The results of the present study, following the trend of other CFD results, slightly over predict the resistance and under predict the sinkage and, more significantly, the trim.

• Steel and Composite Structures
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• 제42권3호
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• pp.407-426
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• 2022

Superior to traditional welded studs, high strength friction-grip bolted shear connectors facilitate the assembling and demounting of the composite members, which maximizes the potential for efficiency in the construction and retrofitting of new and old structures respectively. Hence, it is necessary to investigate the structural properties of high strength friction-grip bolts used in steel concrete composite beams. By means of push-out tests, an experimental study was conducted on post-installed high strength friction-grip bolts, considering the effects of different bolt size, concrete strength, bolt tensile strength and bolt pretension. The test results showed that bolt shear fracture was the dominant failure mode of all specimens. Based on the load-slip curves, uplifting curves and bolt tensile force curves between the precast concrete slab and steel beam obtained by push-out tests, the anti-slip performance of steel-concrete interface and shear behavior of bolt shank were studied, including the quantitative analysis of anti-slip load, and anti-slip stiffness, frictional coefficient, shear stiffness of bolt shank and ultimate shear capacity. Meanwhile, the interfacial anti-slip stiffness and shear stiffness of bolt shank were defined reasonably. In addition, a total of 56 push-out finite element models verified by the experimental results were also developed, and used to conduct parametric analyses for investigating the shear behavior of high-strength bolted shear connectors in steel-concrete composite beams. Finally, on ground of the test results and finite element simulation analysis, a new design formula for predicting shear capacity was proposed by nonlinear fitting, considering the bolt diameter, concrete strength and bolt tensile strength. Comparison of the calculated value from proposed formula and test results given in the relevant references indicated that the proposed formulas can give a reasonable prediction.

• 한국지하수토양환경학회지:지하수토양환경
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• 제28권5호
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• pp.1-11
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• 2023

The phenomenon of sediment resuspension in rivers and lakes causes contaminants (heavy metals and nutrients) accumulated in the sediment to leach into the overlying water. As a result, it can lead to changes in toxic effects and eutrophication in the aquatic ecosystem. In this regard, it is important to quantitatively determine the amount of contaminants leached during sediment resuspension. In this study, methods for assessing the amount of released contaminants and the types of contaminants potentially released due to sediment resuspension were studied and summarized. Methods for assessing leaching can be divided into three groups based on the principle of causing resuspension: (i) the oscillating grid chamber method, (ii) the mechanical stirrer method, and (iii) the shaker method. It was confirmed that the types of contaminants that can potentially be released include heavy metals bound to sulfides, as well as exchangeable and labile forms of heavy metals and nutrients. To effectively manage stable aquatic ecosystems in the future, a simplified leaching test method is needed to assess in advance the risks (i.e., changes in toxic effects and eutrophication) that sediment resuspension may pose to aquatic ecosystems.

• 지질공학
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• 제33권1호
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• pp.105-119
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• 2023

기후 변화에 따라 용수 공급량은 줄어들고 있으며, 해안 및 도서지역은 지하수의 의존도가 높아 활용 가능한 용수의 양이 줄어들고 있다. 지속 가능한 해안 도서 지역의 물 공급을 위해 현재의 상태를 정확히 진단하고 효율적인 용수의 배분 및 관리가 필요하다. 해안 도서 지역의 지하수 흐름의 정밀한 분석을 위해 제주 동부의 성산유역을 대상으로 해안 담지하수 유출량을 산정하였다. 중요 매개변수인 담수층의 두께의 산정은 다심도 관측공에서 측정되는 전기전도도를 이용하여 수직적인 보간을 통해 추정하는 방법과 Ghyben-Herzberg의 이론적인 비율을 이용하여 추정하는 방법을 사용하였다. Ghyben-Herzberg의 비율을 사용한 값은 변화하는 담-염수 경계면의 정밀한 추정이 불가능하며, 전기전도도로 분석한 값은 담-염수 경계면의 현재 상태를 나타낼 수 있다. 매개변수는 가상의 격자에 분포시키고, 각각의 격자에 대한 해안 담지하수 유출 유량의 평균을 유역 대표 유량으로 결정하였다. 유역 규모의 연도별 해안 담지하수 유출량 산정과 유량 분포를 나타냈으며, 2018년에서 2020년까지의 해안 담지하수 유출량은 전기전도도로 추정한 담수층의 두께를 적용한 방법은 6.27 × 10⁶ m³/year, Ghyben-Herzberg의 비율을 적용한 방법은 10.87 × 10⁶ m³/year로 나타났다. 본 연구에서 나타낸 결과는 해안 도서지역의 정밀한 물수지 분석 등을 이용하여 지속가능한 용수의 공급을 결정하는 정책의 근거 자료로 활용할 수 있다.