• 대한기계학회논문집A
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• 제22권4호
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• pp.715-722
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• 1998

A large electric system of a vacuum circuit breaker(VCB) has been studied for the electro-thermal analysis by finite element methods. Since the heat generation in VCB causes not only energy loss but deterioration of the VCB system with oxidization of parts, the overheating of the system must be prevented. For the analysis, a finite element formulation is derived for both electric analysis and thermal analysis that are coupled together. Two sets of formulations are uncoupled after finite dimensional approximation. First, the electric potential is obtained for the entire field and scaled to the given electric current. The electric field obtained is then used to calculate the heat generation in the VCB system including contacts and connections for the calculation of the temperature distribution in the entire domain. The finite element analysis is carried out to study the effect of shapes and locations of contacts and connections. From the results, the existing VCB has been modified to enhance its capacity with reduction of heat generation and temperature elevation.

• 설비공학논문집
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• 제14권12호
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• pp.1031-1038
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• 2002

The effects of casing shape on the performance and interaction between the impeller and casing in a small-size turbo-compressor are investigated. Numerical analysis is conducted for the compressor with circular and single volute casings from inlet to discharge nozzle. In order to predict the flow pattern inside the entire impeller, vaneless diffuer and casing, calculations with multiple frames of reference method between the rotating and stationery parts of the domain are carried out. For compressible turbulent flow fields, the continuity and three-dimensional time-averaged Wavier-Stokes equations are employed. To evaluate the performance of two types of casings, the static pressure and loss coefficients are obtained with various flow rates. Also, static pressure distributions around casings are studied for different casing shapes, which are very important to predict the distribution of radial load. To prove the accuracy of numerical results, measurements of static pressure around casing and pressure difference between the inlet and outlet of the compressor are peformed for the circular casing. Comparisons of these results between the experimental and numerical analyses are conducted, and reasonable agreement is obtained.

• 한국해양공학회지
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• 제21권4호
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• pp.8-14
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• 2007

A particle method recognized as one of gridless methods has been developed to investigate incompressible viscous flaw. The method is more feasible and effective than conventional grid methods for solving the flaw field with complicated boundary shapes or multiple bodies. The method is consists of particle interaction models representing pressure gradient, diffusion, incompressibility and the boundary conditions. In the present study, the models in case of various simulation condition were checked with the analytic solution, and applied to the two-dimensional Poiseuille flow in order to validate the developed method.

• 전기학회논문지P
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• 제66권3호
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• pp.129-134
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• 2017

We investigated theoretically the quantum optical transition properties of Si, in quasi 2-Dimensinal Landau splitting system, based on quantum transport theory. We apply the quantum transport theory (QTR) to the system in the confinement of electrons by square well confinement potential under linearly polarized oscillating field. We use the projected Liouville equation method with Equilibrium Average Projection Scheme (EAPS). In order to analyze the quantum transition, we compare the temperature and the magnetic field dependencies of the QTLW and the QTLS on four transition processes, namely, the intra-leval transition process, the inter-leval transition process, the phonon emission transition process and the phonon absorption transition process.

• 한국멀티미디어학회논문지
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• 제3권3호
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• pp.241-252
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• 2000

이 논문에서는 2차원 영상의 외곽선 정보를 이용하여 추출한 바이스펙트럼과 가중치 퍼지 분류기를 이용하여 영상의 이동, 회전, 크기 변화에 무관한 패턴 인식 기법을 제안하고, 그 인식 결과를 LVQ(Learning Vector Quantization)를 이용한 신경망 분류기와 비교하였다. 3차 큐물런트를 근간으로하는 바이 스펙트럼은 각 영상의 외각선 정보에 적용되어 15개의 특징값들을 추출한다. 이 특징 벡터들은 영상의 이동, 회전, 크기 변화에 무관한 특징을 가지며 2차원 평면 영상의 대표값으로 사용되어 패턴 분류를 위해 가중치 퍼지 분류기의 입력으로 들어간다. 서로 다른 8가지 비행기들의 평면 영상을 이용하여 실험한 결과들은 제안된 인식 시스템의 성능이 상대적으로 우수함을 보였다.

• 한국정밀공학회지
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• 제21권4호
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• pp.57-63
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• 2004

This paper describes a method for digitizing the compound surfaces which are comprised of several unknown feature shapes such as base surface, and draft wall. From the reverse engineering's point of view, the main step is to digitize or gather three-dimensional points on an object rapidly and precisely. As well known, the non-contact digitizing apparatus using a laser or structured light can rapidly obtain a great bulk of digitized points, while the touch or scanning probe gives higher accuracy by directly contacting its stylus onto the part surface. By combining those two methods, unknown features can be digitized efficiently. The paper proposes a digitizing methodology using the approximated surface model obtained from laser-scanned data, followed by the use of a scanning probe. Each surface boundary curve and the confining area is investigated to select the most suitable digitizing path topology, which is similar to generating NC tool-paths. The methodology was tested with a simple physical model whose shape is comprised of a base surface, draft walls and cavity volumes.

• Computers and Concrete
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• 제15권5호
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• pp.735-758
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• 2015

This work deals with unilateral effect of quasi-brittle materials, such as concrete. For this propose, a two-dimensional meso-scale model is presented. The material is considered as a three-phase material consisting of interface zone, matrix and inclusions - each constituent modeled by an appropriate constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes randomly placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements developed here in order to capture the effects of phase debonding and interface crack closure/opening. As an initial approximation, the inclusion is modeled as linear elastic as well as the matrix. Our main goal here is to show a computational homogenization-based approach as an alternative to complex macroscopic constitutive models for the mechanical behavior of the quasi-brittle materials using a finite element procedure within a purely kinematical multi-scale framework. A set of numerical examples, involving the microcracking processes, is provided. It illustrates the performance of the proposed model. In summary, the proposed homogenization-based model is found to be a suitable tool for the identification of macroscopic mechanical behavior of quasi-brittle materials dealing with unilateral effect.

• Geomechanics and Engineering
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• 제7권3호
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• pp.317-333
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• 2014

The study of the mechanical behavior of rockfill materials under three-dimensional loading conditions is a current research focus area. This paper presents a microscale numerical study of rockfill deformation and strength characteristics using the Combined Finite-Discrete Element Method (FDEM). Two features unique to this study are the consideration of irregular particle shapes and particle crushability. A polydisperse assembly of irregular polyhedra was prepared to reproduce the mechanical behavior of rockfill materials subjected to axial compression at a constant mean stress for a range of intermediate principal stress ratios in the interval [0, 1]. The simulation results, including the stress-strain characteristics, relationship between principal strains, and principal deviator strains are discussed. The stress-dilatancy behavior is described using a linear dilatancy equation with its material constants varying with the intermediate principal stress ratio. The failure surface in the principal stress space and its traces in the deviatoric and meridian plane are also presented. The modified Lade-Duncan criterion most closely describes the stress points at failure.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.39.2-39.2
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• 2011

With the steady increase in the demand for flexible devices, mainly in display panels, researchers have focused on finding a novel material that have excellent electrical properties even when it is bended or stretched, along with superior mechanical and thermal properties. Graphene, a single-layered two-dimensional carbon lattice, has recently attracted tremendous research interest in this respect. However, the limitations in the growing method of graphene, mainly chemical vapor deposition on transition metal catalysts, has posed severe problems in terms of device integration, due to the laborious transfer process that may damage and contaminate the graphene layer. In addition, to lower the overall cost, a fabrication technique that supports low temperature and low vacuum is required, which is the main reason why solution-based process for graphene layer deposition has become the hot issue. Nonetheless, a direct deposition method of large area, few-layered, and uniform graphene layers has not been reported yet, along with a convenient method of patterning them. Here, we report an evaporation-induced technique for directly depositing few layers of graphene nanosheets with excellent uniformity and thickness controllability on any substrate. The printed graphene nanosheets can be patterned into desired shapes and structures, which can be directly applicable as flexible and transparent electrode. To illustrate such potential, the transport properties and resistivity of the deposited graphene layers have been investigated according to their thickness. The induced internal flow of the graphene solution during tis evaporation allows uniform deposition with which its thickness, and thus resistivity can be tuned by controlling the composition ratio of the solute and solvent.

• 방송공학회논문지
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• 제14권1호
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• pp.81-84
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• 2009

본 논문은 시점에 따른 형상의 변화를 이용하여 물체의 특성을 나타내는 기법을 제안한다. 구체적으로, 3차원 물체의 여러 시점별 형상을 추출한 후, 이를 지역적 선형 사상을 통해 차원 축소하여 저차원 분포를 생성하고, 이를 이용하여 물체의 특성을 나타낸다. 또한, 생성된 점집합들에 반복적 최근접점 기법 및 푸리에 변환을 적용하여 유사한 모델을 검색하는 기법과 그 결과를 제시한다. 제안하는 기법은 다양한 시점에서의 형상 자체만이 아니라 시점에 따른 형상의 변화도 물체의 특성을 표현한다는 것을 보여주며, 검색 등 물체 특성을 표현하는데 적용될 것으로 기대된다.