• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.830-837
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• 2010

Since it started the researches on a maglev train on 1960, Germany and Japan arrived to putting to practical use level and accomplished most tests from their test-line. Korea is in progress the preparation for a practical use of low-speed maglev train in 110 [km/h] class and Korea Railroad Research Institute(KRRI) is in progress of a research about core technology of maglev system for high-speed tube train of 700 [km/h] class. In this paper, authors suggest an effective design method of Linear Synchronous Motor(LSM) for high-speed tube train of 700 [km/h] class which has a wound type electro-magnet. Then, authors calculate a variety of properties by changing speed of the LSM model which is designed by a method based on some theoretical equations. Then, authors verify the validity of the method based on some theoretical equations through a verification of property values by Finite Element Method(FEM) analysis method. Finally, in order to design a shape of pole-shoe part of LSM electro-magnet which is hard to design with a basic design method, authors analyze a transition of property values by changing a pole-shoe width and current of the electro-magnet through an analytical method by FEM.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.479-482
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• 2008

In order to more closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, the thermal-fluid characteristics of high current vacuum arcs were calculated by a commercial multiphysics package, ANSYS, in order to obtain Joule heat, Lorentz force and the interactions with flow variables. We assumed the diffused-mode arc within an AMF vacuum interrupter. It was found with four different currents that the temperature distributions on the anode surface are diffused uniformly without concentration in 7kA for both types (cup and coil-type). But the arc plasma transition and an increase of thermal flux density for increasing the applied current have caused the change of temperature distributions on the anode surface. We should need further studies on the two-way coupling method and radiation model for arc plasmas in order to accomplish the advanced analysis method for multiphysics.

• 한국실내디자인학회논문집
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• 제19권3호
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• pp.22-29
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• 2010

Recent days, transition to ecological thought is being accelerating by environmental impact with a sustainable development. This symptom is no exception in architecture area. So is vernacular design affecting on modern architecture in many ways in terms of economical aspect and eco-friendly environment as well. Natural energy like solar power, environment, and terrestrial heat that applied in vernacular architecture is also widely accepted in name of 'sustainable energy' of which a design applied with ventilation and airing of natural wind is very useful & pragmatic in terms of economical reason. Accordingly, this study examined a relation between vernacular architecture and natural wind and compared it with traditional type and its feature of ventilation & airing. Ventilation & airing applied in the past can be divided into three categories: methods by convection, natural element, and architectural type. All these methods gave some pleasant felling indoors when there were no artificial energies. Even in modern age, such a ventilation & airing is being used with traditional type in different variety of materials, and it will be developed with modern technology without any extra cost in terms of sustainable expansion, and opened for further researches.

• 터널과지하공간
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• 제14권3호
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• pp.229-240
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• 2004

연안대수층은 주요한 지하수 공급원으로서 이용될 수 있다. 그러나 연안대수층의 개발은 해수침투에 의한 대수층 오염을 야기할 수도 있다. 이에 따라 개발과정에서는 적절한 양수량과 양수정의 배치가 매우 중요하고, 이 들의 영향은 용질이동과 유동해석이 가능한 수치해석적 기법들을 적용하여 평가할 수 있다. 이 연구에서는 연안 자유면 대수층 모델에 대해 양수량 및 수리지질학적 변수들이 해수침투 특성에 미치는 영향을 SWICHA 코드를 이용하여 수치해석적으로 검토하였다. 수치해석과정에서는 유동 및 용질의 상호작용이 고려되었다. 경계 조건, 수리지질변수 등의 변화에 따른 해수담수 경계부에서의 염수 확산대 분포, 양수정 부근에서의 수두변화 등이 분석되었다.

• Journal of Welding and Joining
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• 제17권6호
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• pp.84-89
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• 1999

Most of ferrous b.c.c weld materials may experience martensitic transformation during rapid cooling after welding. It is well known that volume expansion due to the phase transformation could influence on the relaxation of welding residual stress. To apply this effect practically, it is a prerequisite to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. For this purpose, the analysis is carried out in two regions. i.e., heating and cooling, because the variation of material properties following a phase transformation in cooling is different in comparison with the case in heating, even at the same temperature. The variation of material properties following phase transformation is considered by the adjustment of specific heat and thermal expansion coefficient, and the distribution of residual stress in analysis is compared with that of experiment by previous study. consequently, in this study, simplified numerical procedures considering phase transformation, which based on a commercial finite element package was established through comparing with the experimental data of residual stress distribution by other researcher. To consider the phase transformation effect on residual stress relaxation, the transition of mechanical and thermal property such as thermal expansion coefficient and specific heat capacity was found by try and error method in this analysis.

• 오토저널
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• 제12권1호
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• pp.26-32
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• 1990

This study investigated a method for the determination of the J-integral for a tough glassy polymer such as polycarbonate plates by using the method of caustics. Comparing the values of J-integral determined by a numerical analysis and by the method of caustics, the method of caustics was found to be an effective experimental technique for the determination of the J-integral. The ratio between two J-integrals determined by the method of caustics and by finite element method converged into 1 within the limit of low load. However, it was noticed that the greater the plastic zone at the crack tip was, the lower the J-integral obtained by the reflect method of caustics. This difference may be deduced from the damage at the crack tip such as craze appeared in the polycarbonate plate. It was confirmed that the ratio of longitudinal diameter( $D_{l}$ ) to transverse diameter ( $D_{t}$) of caustics generally converged into 1 at the low load. The transition of the state of stress at the vicinity of a crack tip from plane strain to plane stress was deduced by noticing that the longitudinal diameter( $D_{l}$ ) grew faster than the transverse diameter( $D_{t}$) of caustics within the higher load range.

• 한국주조공학회지
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• 제36권5호
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• pp.147-152
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• 2016

Aluminum has been used as an alternative material for copper, due to its good electrical and thermal conductivities. However, small quantities of transition elements such as Ti and V affect the conductivities of aluminum. Therefore, in this study, the influence of B addition to reduce the effects of Ti and V on the conductivities of aluminum was investigated. Both the electrical and thermal conductivities of aluminum were improved with addition of B up to 0.05 wt%, while the conductivities were gradually reduced with an excess amount of B. SEM-EDS and XRD results exhibited that B reacted with Ti and V element to form diborides, such as $TiB_2$ and $VB_2$ phase, and those diborides tended to settle down to the bottom of the crucible because their densities were higher than that of aluminum melt. As a result, B reduced the deleterious effects of Ti and V, and the electrical and thermal conductivities of aluminum were improved.

• 세라미스트
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• 제22권1호
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• pp.36-55
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• 2019

Atomically thin two-dimensional (2D) nanomaterials, including transition metal dichalcogenides (TMDs), graphene, boron nitride, and black phosphorus, have opened up new opportunities for the next generation optoelectronics owing to their unique properties such as high absorbance coefficient, high carrier mobility, tunable band gap, strong light-matter interaction, and flexibility. In this review, photodetectors based on 2D nanomaterials are classified with respect to critical element technology (e.g., active channel, contact, interface, and passivation). We discuss key ideas for improving the performance of the 2D photodetectors. In addition, figure-of-merits (responsivity, detectivity, response speed, and wavelength spectrum range) are compared to evaluate the performance of diverse 2D photodetectors. In order to achieve highly reliable 2D photodetectors, in-depth studies on material synthesis, device structure, and integration process are still essential. We hope that this review article is able to render the inspiration for the breakthrough of the 2D photodetector research field.

• Structural Engineering and Mechanics
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• 제37권2호
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• pp.197-213
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• 2011

Concrete is a heterogeneous material exhibiting quasi-brittle behaviour. While homogenization of concrete is commonly accepted in general engineering applications, a detailed description of the material heterogeneity using a mesoscale model becomes desirable and even necessary for problems where drastic spatial and time variation of the stress and strain is involved, for example in the analysis of local damages under impact, shock or blast load. A mesoscale model can also assist in an investigation into the underlying mechanisms affecting the bulk material behaviour under various stress conditions. Extending from existing mesoscale model studies, where use is often made of specialized codes with limited capability in the material description and numerical solutions, this paper presents a mesoscale computational model developed under a general-purpose finite element environment. The aim is to facilitate the utilization of sophisticated material descriptions (e.g., pressure and rate dependency) and advanced numerical solvers to suit a broad range of applications, including high impulsive dynamic analysis. The whole procedure encompasses a module for the generation of concrete mesoscale structure; a process for the generation of the FE mesh, considering two alternative schemes for the interface transition zone (ITZ); and the nonlinear analysis of the mesoscale FE model with an explicit time integration approach. The development of the model and various associated computational considerations are discussed in this paper (Part 1). Further numerical studies using the mesoscale model for both quasi-static and dynamic loadings will be presented in the companion paper (Part 2).

• 한국방재학회지
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• 제2권4호
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• pp.40-47
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• 2002

Since it is important to understand the bio-climatic change in Seoul for ecological city planning in the future, this paper gives an overview on bio-climate analysis of urban environments at Seoul. We analyzed its characteristics in recent years using the observations of 24 of Automatic Weather Station (AWS) by Korea Meteorological Administration (KMA). In urbanization, Seoul metropolitan area is densely populated and is concentrated with high buildings. This urban activity changes land covering, which modifies the local circulation of radiation, heat and moisture, precipitation and creating a specific climate. Urban climate is evidently manifested in the phenomena of the increase of the air temperature, called urban heat Island and in addition urban sqall line of heavy rain. Since a city has its different land cover and street structure, these form their own climate character such as climate comfort zone. The thermal fold in urban area such as the heat island is produced by the change of land use and the air pollution that provide the bio-climate change of urban eco-system. The urban wind flow is the most important climate element on dispersion of air pollution, thermal effects and heavy shower. Numerical modeling indicates that the bio-climatic transition of wind wake in urban area and the dispersion of the air pollution by the simulations of the wind variation depend on the urban land cover change. The winds are separately simulated on small and micro-scale at Seoul with two kinds of kinetic model, Witrak and MUKLIMO.