• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.136-140
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• 2000

It is desirable to predict springback quantitatively and accurately for the tool and process design in sheet stamping operations, however, it is blown very difficult. The result of springback analysis by the finite element method is sensitively influenced by numerical factors such as blank element size, number of integration point, punch velocity, contact algorithm etc. In the present work, a parametric study by Taguchi method is performed in order to evaluate the influence of numerical factors on springback Quantitatively and to obtain the combination of numerical factors which yields the best approximation to experimental data. Since springback is determined by the residual stress after forming process, it is important to evaluate stress distribution accurately. The oscillation in the time history curve of stress obtained by explicit FEM says that the stress solution at termination time is in very unstable state. Therefore, a variability study is also carried out in this study in order to assess the stability of implicit springback analysis starting from the stress solution by explicit forming simulation. The 2D draw bending process, one of the NUMISHEET '93 benchmark problems, is adopted as an application model.

• 전산구조공학
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• 제8권4호
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• pp.189-198
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• 1995

비압축성 물체를 위한 일반적인 유한요소 공식화는 흔히 사용되는 사각형요소에서조차 압력해의 진동화(oscillations) 또는 pressure modes 현상을 나타낸다. 압력해의 안정화를 위한 규준은 소위 Babuska-Brezzi 안정조건이며, 위의 요소들은 이 조건을 만족시키지 못한다. 본 연구에서는 선형변위해와 상수값의 압력해를 갖는 사각형요소 사용시 압력해를 안정화시키기 위해 요소의 변에서 발생하는 불연속압에 근거한 압력연속여분치를 사용한다. 이 압력여분치를 비압축성 탄성론으로부터 유도되는 Q1P0요소에 적용하며 매개변수의 변화에 따른 수치해의 안정화의 정도를 연구한다. 압력해는 압력 여분치 사용시 안정화될 수 있으며, 해의 안정화는 매개변수에 민감성을 나타내었다.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 1999년도 제1회 학술대회논문집(KIASC 1st conference 99)
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• pp.177-181
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• 1999

Cold Neutron Source(CNS) facility comprises moderator circulation system, helium cooling system, neutron guide and auxiliary sistems. To increase the amount of cold neutron, the thermal neutron should pass cold moderator at cryogenic temperature. As cold moderator in Hanaro, the liquid hydrogen or liquid deuterium will be used and the temperature in operation will be used and the temperature in operation will be maintained to be $250^{\circ}C$ below zero. To maintain the moderator at this cryogenic temperature. He refrigerator is used to cool it down in thermosiphon having natural circulation. As a part of the conceptual design of Hanaro CNS, study on the characteristics of moderators, design of moderator chanmber and cooling method were done through the collaboration of Korea Atomic Energy Research Institute and Petersburg Nuclear Physics Institute. During the collaboration, a program for the design of moderator cooling system design concept through the parametric study using this program. In the parametric study, the effect of the moderator type on the design parameters was investigated. Also, the requirements on the performance test for the cooling system, which will be made before the basic design, were investigated.

• International Journal of Aeronautical and Space Sciences
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• 제16권1호
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• pp.50-63
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• 2015

Explosive bolts are one of pyrotechnic release devices, which are highly reliable and efficient for a built-in release. Among them, ridge-cut explosive bolts which utilize shock wave generated by detonation to separate bolt body produce minimal fragments, little swelling and clean breaks. In this study, separation phenomena of ridge-cut explosive bolts or ridge-cut mechanism are computationally analyzed using Hydrocodes. To analyze separation mechanism of ridge-cut explosive bolts, fluid-structure interactions with complex material modeling are essential. For modeling of high explosives (RDX and PETN), Euler elements with Jones-Wilkins-Lee E.O.S. are utilized. For Lagrange elements of bolt body structures, shock E.O.S., Johnson-Cook strength model, and principal stress failure criteria are used. From the computational analysis of the author's explosive bolt model, computational analysis framework is verified and perfected with tuned failure criteria. Practical design improvements are also suggested based on a parametric study. Some design parameters, such as explosive weights, ridge angle, and ridge position, are chosen that might affect the separation reliability; and analysis is carried out for several designs. The results of this study provide useful information to avoid unnecessary separation experiments related with design parameters.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.525-530
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• 2007

Although just developed in recent years, curved box girder has widely used in modern highway system due to their load resistance capacity as well as aesthetic considerations. According to recent literature reviews on curved box girder designs, distortional load was not considered as much as it deserves to be. In practice, the effect of distributional force is very small in straight bridge systems but yet unknown how it is in curved bridge systems. For the reason, this paper will show up an extensive parametric study on distortional behavior of curved box girder with trapezoidal section. Based on Dabrowski formulas, using finite element method, various bridges were investigated. In this study, following parameters will be included: span length, curvature radius, section height, section width, and internal section angle (web slope). From the obtained results, some initial geometric parameters are proposed for curved box girder bridges.

• 한국수소및신에너지학회논문집
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• 제22권6호
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• pp.819-826
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• 2011

The proton exchange membrane fuel cell (PEMFC) is regarded as the most promising alternative power sources for unmanned aerial vehicle (UAV) due to its high energy density and silent operation. Since there are many load changes during UAV flight, thermal management is one of the important factor for the performance of PEMFC. In order to reduce the UAV weight for the stable operation of UAV, thermal management system (TMS) studied in this work does not use the fan but use the air flowing into UAV by UAV flight. In order to develop the passive type heat exchanger (HEX) for 1kW PEMFC, four types of HEXs are fabricated and their cooling performances are compared. The parametric study on the cooling performance of HEXs has performed with the variation of operating parameters such as mass flow rates and inlet temperature of air and coolant. Type 4 has the best performance in every case. This study can be helpful to achieve the optimal design of HEX for PEMFC powered UAV.

• Steel and Composite Structures
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• 제6권4호
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• pp.285-302
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• 2006

This paper describes the design and behaviour of cold-formed stainless steel slender circular hollow section columns. The columns were compressed between fixed ends at different column lengths. The investigation focused on large diameter-to-plate thickness (D/t) ratio ranged from 100 to 200. An accurate finite element model has been developed. The initial local and overall geometric imperfections have been included in the finite element model. The material nonlinearity of the cold-formed stainless steel sections was incorporated in the model. The column strengths, load-shortening curves as well as failure modes were predicted using the finite element model. The nonlinear finite element model was verified against test results. An extensive parametric study was carried out to study the effects of cross-section geometries on the strength and behaviour of stainless steel slender circular hollow section columns with large D/t ratio. The column strengths predicted from the parametric study were compared with the design strengths calculated using the American Specification, Australian/New Zealand Standard and European Code for cold-formed stainless steel structures. It is shown that the design strengths obtained using the Australian/New Zealand and European specifications are generally unconservative for the cold-formed stainless steel slender circular hollow section columns, while the American Specification is generally quite conservative. Therefore, design equation was proposed in this study.

• Computers and Concrete
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• 제23권4호
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• pp.281-294
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• 2019

The post-fire behavior of structural elements and the cooling process has always been one of the main concerns of the structural engineers. The structures can be cooled at different rates, where they affect the structure's behavior. In the present study, a numerical model has been developed using the Abaqus program to investigate the effect of cooling rate on the post-fire behavior of the CFST column. To verify the model, results of an experimental study performed on CFST columns within a full heating and cooling cycle have been used. In this model, coMParison of the residual strength has been employed in order to examine the behavior of CFST column under different cooling rates. Furthermore, a parametric study was carried out on the strength of steel and concrete, the height of the specimens, the axial load ratio and the cross-sectional shape of the specimen through the proposed model. It was observed that the cooling rate affects the behavior of the column after the fire, and thus the higher the specimen's temperature is, the more effect it has on the behavior. It was also noticed that water cooling had slightly more residual strength than natural cooling. Furthermore, it was recognized from the parametric study, that by increasing the strength of steel and concrete and the load ratio, as well as modifying the cross-sectional shape from circular to square, residual strength of column at the cooling phase was less than that of the heating phase. In addition, with reducing column height, no change was witnessed in the column behavior after the cooling phase.

• 대한건축학회연합논문집
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• 제21권6호
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• pp.31-40
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• 2019

This study aims to establish Nammun-ro 2ga in Cheongju city in the 1960s as three-dimensional digital information data for the restoration of urban archetypes. For this purpose, referring to the existing restoration map and model of Cheongju urban area in the 1960s, and the results of this study are as follows. Firstly, the buildings that can be generally classified are prepared through the modeling of parametric families. Secondly, the untypical models(combined and broken roofs, atypical and large scale buildings) of them are simply performed through solid modeling. And then, these simplified models are simulated through a sky view, a walking sight, and information analysis. Through this study, it will be possible to visualize and regenerate the low and dense area of Cheongju city in the 1960s.

• 한국건축시공학회지
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• 제21권6호
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• pp.617-627
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• 2021

본 연구에서는 공동주택의 리모델링 시 기초보강공법의 하나인 하중전이 장치를 이용한 기초보강공법에 대해 3차원 유한요소 수치해석 연구를 수행하였다. 실대형 현장실험을 통해 수치모형을 검증하였고, 매개변수 해석을 통해 하중전이장치의 마찰계수, 말뚝의 축강성이 기초보강공법의 성능에 미치는 영향을 확인하였다. 그 결과 하중전이 장치를 이용한 기초보강공법은 보강 중, 보강 후에도 기존 말뚝에 작용하는 하중을 자유롭게 조절가능함을 확인하였다.