• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전기설비전문위원
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• pp.233-234
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• 2008

We observed internal space charge behavior for two types of epoxy composites under dc electric fields to investigate the influence of water at high temperature. In the case of glass/epoxy specimen, homocharge is observed at water-treated specimen, and spatial oscillations become clearer in the water-treated specimens. Electric field in the vicinity of the electrodes shows the injection of homocharge. In aramid/epoxy specimens, heterocharge is observed at water-treated specimens, i.e. negative charge accumulates near the anode, while positive charge accumulates near the cathode. Electric field is enhanced just before each electrode. In order to further examine the mechanism of space charge formation, we have developed a new system that allows in situ space charge observation during ion migration tests at high temperature and high humidity. Using this in situ system.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.99-107
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• 2017

In this work, the nutation control of rigid spacecraft with only two momentum wheels is addressed by applying the feedback linearization technique. In this strategy, the primary performance index is to regulate the nutational angle by the momentum control of wheels. The spacecraft attitude equations of motion are transformed to a general linearized form by feedback linearization technique, including a guaranteed control law promising the internal dynamics stability to accomplish the nutation angle small. It is proven that the configuration of inertia properties plays a key role in analyzing spacecraft energy level. The behavior of the momentum wheels is also studied analytically and numerically. Finally, the effectiveness of the proposed nonlinear control law for the momentum transfer is verified by conducting numerical simulations.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.86-92
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• 2010

A metal diaphragm compressor has been widely used for supplying a high pressures gas. This compressor mainly consists of gas oil space and metal diaphragm. Gas sucked in the gas space is compressed by an oscillating metal diaphragm existed between the gas and oil space. A non-return discharge and suction check-valve are components of the compressor that draw off the compressed oil and gas. Those components are self-actuated by differential pressures. Therefore, the rapid response and stable operating conditions are required. In the present study, to find out the dynamic behavior of the suction, discharge valve and diaphragm compressor, the unsteady flow field has been investigated numerically by using the unsteady two-way FSI (Fluid Structure Interaction) simulation method, $k-{\omega}$ turbulent model and mesh deformation.

• Bulletin of the Korean Chemical Society
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• 제28권3호
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• pp.447-450
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• 2007

Trap effects on the formation of space-charge field (SCF) associated with the photorefractivity of nonlinear optical polymers were studied by the Monte Carlo simulation using modified Gaussian disorder model. The charge transport dynamics influenced by the presence of trap molecules controls the formation of SCF via the charge distribution. Temporal behavior of SCF formation and SCF dependence on the trap depth are discussed in terms of the concentration and distribution of charges (holes and ionized acceptors) developed following illumination of light. The correlation of the trap depth and the energetic disorder is presented for an optimal efficiency for the SCF formation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.2307-2308
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• 2008

We observed internal space charge behavior for two types of epoxy composites under dc electric fields to investigate the influence of water at high temperature. In the case of glass/epoxy specimen, homocharge is observed at water-treated specimen, and spatial oscillations become clearer in the water-treated specimens. Electric field in the vicinity of the electrodes shows the injection of homocharge. In aramid/epoxy specimens, heterocharge is observed at water-treated specimens, i.e. negative charge accumulates near the anode, while positive charge accumulates near the cathode. Electric field is enhanced just before each electrode. In order to further examine the mechanism of space charge formation, we have developed a new system that allows in situ space charge observation during ion migration tests at high temperature and high humidity. Using this in situ system.

• Architectural research
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• 제17권2호
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• pp.57-64
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• 2015

In architectural planning, previous cases of similar spatial program provide important data for architectural design. Case-based reasoning (CBR) paradigm in the field of architectural design is closely related to the designing behavior of a planner who makes use of similar architectural designs and spatial programs in the past. In CBR, spatial graph can be constituted with most fundamental data, which can provide a method of searching spatial program by using visual graphs. This study developed a system for CBR that can analyze the similarity through graph comparison and search for buildings. This is an integrated system that is able to compare space similarity of different buildings and analyze their types, in addition to the analysis on a space within a single structure.

• Journal of Communications and Networks
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• 제8권3호
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• pp.275-285
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• 2006

Suitable for multi-input multi-output (MIMO) communications, the joint beamforming space-time block coding (JBSTBC) scheme is proposed for high-speed downlink transmission. The major functionality of the scheme entails space-time block encoder and joint transmit and receive eigen-beamformer (EBF) incorporating with block-ordered layered decoder (BOLD), and its operating principle is described in this paper. Within these functionalities, the joint EBFs will be utilized for decorrelating fading channels to cause an enhancement in the spatial diversity gain. Furthermore, to fortify the capability of layered successive interference cancellation (LSIC) in block-ordered layered decoding process, this paper will develop a simple ad-hoc transmit power discrimination scheme (TPDS) based on a particular power discrimination function (PDF). To confirm the superior behavior of the proposed JBSTBC scheme employing ad-hoc TPDS, computer simulations will be conducted under various channel conditions with the provision of detailed mathematical derivations for clarifying its functionality.

• Structural Engineering and Mechanics
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• 제41권6호
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• pp.735-750
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• 2012

This paper presents a comparison between two different procedures to deal with the geometric nonlinear analysis of space trusses, considering its structural stability aspects. The first nonlinear formulation, called positional, uses nodal positions rather than nodal displacements to describe the finite elements kinematics. The strains are computed directly from the proposed position concept, using a Cartesian coordinate system fixed in space. The second formulation, called corotational, is based on the explicit separation between rigid body motion and deformed motion. The numerical examples demonstrate the performances and the convergence of the responses for both analyzed formulations. Two numerical examples were compared, including a lattice beam with postcritical behavior. Despite the two completely different approaches to deal with the geometrical nonlinear problem, the results present good agreement.

• Steel and Composite Structures
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• 제38권4호
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• pp.447-462
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• 2021

In this work, we consider a problem in the context of thermoelectric materials with memory-dependent derivative for a half space which is assumed to have variable thermal conductivity depending on the temperature. The Lamé's modulii of the half space material is taken as a function of the vertical distance from the surface of the medium. The surface is traction free and subjected to a time dependent thermal shock. The problem was solved by using the Laplace transform method together with the perturbation technique. The obtained results are discussed and compared with the solution when Lamé's modulii are constants. Numerical results are computed and represented graphically for the temperature, displacement and stress distributions. Affectability investigation is performed to explore the thermal impacts of a kernel function and a time-delay parameter that are characteristic of memory dependent derivative heat transfer in the behavior of tissue temperature. The correlations are made with the results obtained in the case of the absence of memory-dependent derivative parameters.

• 한국조경학회지
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• 제48권1호
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• pp.35-45
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• 2020

본 연구는 현대사회에서 도시민의 행태를 지원하는 공간으로 공원에 주목하였다. 현대의 도시공원은 특정한 역할을 하는 공간으로 국한되지 않으며, 공공의 성격을 가지고 있어 이용자의 이용행태에 따라 그 기능·의미가 변화할 수 있다. 또한, 현재 온라인상의 데이터는 방문할 공원의 선택 혹은 공원 이용행태의 결정을 지원하는 단계로 접어들었다. 이에 본 연구는 빅데이터의 자료 기반의 특징인 시계열 분석이 가능하도록 데이터를 수집할 수 있는 최초 년도인 2000년부터 2018년까지 여의도공원·여의도 한강공원과 양재 시민의 숲의 행태 변화를 빅데이터 기법인 텍스트마이닝(Text Mining)과 소셜 네트워크(Social Network;사회연결망)분석을 활용하여 분석하였다. 연구결과의 요약은 다음과 같다. 먼저 시간의 흐름에 따라 주요 이용행태와 행태에 영향을 미치는 요소에 변화가 있었다. 여의도공원·여의도 한강공원의 이용행태는 제 I시기는 '타다'(동적행태), 제 II시기는 '찍다'(정보통신서비스 행태), 제 III시기는 '걷다'(동적행태), 제 IV시기는 '먹다'(에너지원 행태)로 시간의 흐름에 따라 주요 행태가 다양하게 변화하는 모습이고, 양재 시민의 숲은 제 I시기는 '걷다'(동적행태), 제 II시기는 '걷다'(동적행태), 제 III시기는 '걷다'(동적행태), 제 IV시기는 '놀다'(동적행태)로 주로 동적행태 위주의 행태가 나타나는 것으로 나타났다. 주요 행태에 영향을 미치는 요소로 여의도공원·여의도 한강공원은 스포츠 및 레저, 문화·예술, 여가와 관련된 요소가 도출되었고, 양재 시민의 숲은 자연자원 요소가 도출되어 주요 이용행태에 영향을 미치는 요소에 차이가 있었다. 다음으로 대상지의 행태는 시기별로 특정 행태에 집중화되어 있으며, 차후 발생하는 행태를 선택하거나 제약하는 역할을 하는 것으로 나타났다. 이러한 결과는 대상지에 다양한 행태가 일어나지 않을 뿐만 아니라, 공간, 시설 등이 골고루 활용되지 않고 있다는 것을 알 수 있다. 연구결과의 흥미로운 점은 두 공원에서 공통적으로 눈에 띄게 급증한 행태는 에너지원 행태(먹다, 마시다)와 소비행태(사다, 대여하다)이다. 에너지원 행태는 두 공원에서 모두 제 III시기에서 제 IV시기 사이에 10배 이상으로 치솟았으며, 다른 행태와 빈도에서 큰 차이를 보이며 월등히 높았다. 또한, 공원에 방문하는 시민들은 식음료비, 자전거 등의 대여비, 이밖에 행사 참여 등과 관련된 소비의사가 있으며, 공원이 도심 내 휴식공간에서 지역경제 활성화라는 측면에서 본다면 긍정적으로 평가할 수 있을 것이다. 본 연구는 데이터 기법을 활용하여 도시공원 이용행태를 분석하였다는 점과 오늘날 도시공원은 휴식, 산책 등의 역할을 넘어서 시대적인 트렌드를 반영하며, 소비 성향이 나타나는 놀이공간으로 성향이 변화하였다는 결과를 도출하였다는 점에서 큰 의의가 있다. 현대 도시공원에서 일어나는 행태는 양과 내용이 과거와 다르게 변화하고 있다. 그러므로 빅데이터를 통해 수집되는 대규모 집단의 행태를 유형화하고, 이러한 결과를 바탕으로 이루어지는 다학제적인 논의를 통해 오늘날 도시공원을 시민들이 어떻게 이용하고 있는지를 보다 명확하게 이해할 수 있을 것이다.