• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.185-188
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• 2007

액체 및 고체추진기관의 내열부품으로 사용하기 위하여 Liquid Silicon Infiltration(액체 실리콘 함침) 공정이 적용된 C/SiC 복합재료를 개발하였다. 탄소섬유 및 탄소직물을 사용하여 필리멘트 와인딩, 테이프 롤링 및 인벌루트 적층 공법이 사용된 다양한 탄소 프리폼이 제작되었다. 내열 부품으로써의 열구조 성능을 극대화시키기 위하여 SiC 함유량, 열처리 조건, 수지 및 기상 함침 조건을 변화시키면서 시편을 제작하고 평가하였다. C/SiC 복합재료를 액체 및 고체추진기관의 내열부품으로 사용하기 위하여 연소시험을 수행하였으며 내열 성능 해석을 위한 수학적 삭마 모델이 개발되었다.

• 대한조선학회논문집
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• 제43권6호
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• pp.667-674
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• 2006

Accurate prediction of ship dynamics, particularly roll motion, is very important in ship safety. In the past, empirical or vortex based methods were commonly used for the hydrodynamic roll damping predictions but they could not be applied to practical ship roll motion cause of limitations about geometries ad design conditions. Recently RANS-based techniques are developed for the practical ship motion analysis. In this study, RANS based roil analysis about a rectangular cylinder with WAVIS developed by MOERI/KORDI are performed and compared with the experimental data and other RANS results.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.659-666
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• 2009

As the density and height of the buildings nearby subway lines get higher, the unprecedented residents' appeals for noise are on the rise. Furthermore, in accordance with the revision of enforcement regulations on the Noise and Vibration Control Act, the night time noise standards have been reinforced by 5dB effective on January 1st 2010 and the appropriate measures shall be taken accordingly. For the settlement of the public grievances against noise and vibration generated on tracks in at-grade and elevated section, the installation of continuously-welded-rail, rail lubrication system, improved fastening system and higher noise barrier is currently executed. Nevertheless, the noise and vibration levels in some areas are still exceeding the limits required in the regulation. Among the measures, an installation of higher noise barrier or noise tunnel seems to be the most effective way; however, it has limitations owing to the structural stability of existing elevated structures. The paper in consideration of the local conditions and foreign practices discusses the installation of fairing system under the train body as an noise insulation panel in order to reduce the rolling noise and under-carriage noise. Based on the result of this study, a performance verification test during actual train operation is in progress for further study.

• 소성∙가공
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• 제9권1호
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• pp.72-79
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• 2000

Dynamic recrystallization (DRX), which may occur during hot deformation, is important for the microsturctural evolution of 304 stainless steel. Especially, the current interest in modelling hot rolling demands quantitative relationships among the thermomechanical process variables, such as strain, temperature, strain rate, and etc. Thus, this paper individually presents the relationships for flow stress and volume fraction of DRX as a function of processing variables using torsion tests. The hot torsion tests of 304 stainless steel were performed at the temperature range of 900~110$0^{\circ}C$ and the strain rate range of 5x10-2~5s-1 to study the high temperature softening behavior. For the exact prediction of flow stress, the equation was divided into two regions, the work hardening (WH) and dynamic recovery (DRV) region and the DRX region. Especially, The flow stress of DRX region could be expressed by using the volume fraction of DRX (XDRX). Since XDRX was consisted of the critical strain($\varepsilon$c) for initiation of dynamic recrystallization (DRX) and the strain for maximum softening rate ($\varepsilon$*), that were related with the evolution of microstructure. The calculated results predicted the flow stress and the microstructure of the alloy at any deformation conditions well.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.185-191
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• 2002

In this study a 3-dimensional analytical model is developed, which can analyses dynamic responses of curved bridges subject to moving vehicles. A 5-axle semi-trailer is modeled to simulate the actual tire forces that are redistributed by vehicle rolling effect due to the centrifugal force. The 1-span curved bridge with two steel box girders is modeled using the frame elements. The dynamic response characteristics of curved box girder bridges are examined and compared for two different support conditions. One is the case that two shoes are arranged at the outer sides of box girders with larger space between the two shoes and the other is that two shoes at the center of each box girder. In the curved bridges, the dynamic effect of moving vehicles influences the reaction force much more than other responses, such as displacement or stress, especially the upward reaction of inner-radius shoes. It is more advantageous for the reaction considering dynamic effect when shoes are arranged further at the outer sides of box girders than when shoes at the center of each box. The shoes for curved bridges with two-box girder system should be arranged to have larger distance.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권12호
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• pp.627-632
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• 2001

There are claims that ESE(Early streamer emission) Air terminals offer a vastly increased zone of protection over that of traditional lightning rods by causing the emission of an upward streamer/leader that will propagate towards the tip of downward leader at an early stage in the attachment process than would occur for a simple rod in the same geometrical configurations. This paper shows the results of comparing test a particular type of ESE air terminals with a simple rod conducted in the KEH HV laboratory, which are lightning impulse voltage test, flashover direction test and corona emission current measurement. The results from this test show a completely random scattering of flashovers to the conventional and ESE air terminals under identical electrics] and geometrical conditions, and thus shows no advantage of one terminal over the other.

• 전기학회논문지P
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• 제65권3호
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• pp.158-164
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• 2016

In this paper, a high frequency flyback type zero voltage soft switching PWM DC-DC converter using IGBTs is proposed. Effective applications for this power converter can be found in auxiliary power supplies of rolling stock transportation and electric vehicles. This power converter is basically composed of active power switches and a flyback high frequency transformer. In addition to these, passive lossless snubbers with power regeneration loops for energy recovery, consisting of a three winding auxiliary high frequency transformer, auxiliary capacitors and diodes are introduced to achieve zero voltage soft switching from light to full load conditions. Furthermore, this power converter has some advantages such as low cost circuit configuration, simple control scheme and high efficiency. Its operating principle is described and to determine circuit parameters, some practical design considerations are discussed. The effectiveness of the proposed power converter is evaluated and compared with the hard switching PWM DC-DC converter from an experimental point of view and the comparative electromagnetic conduction and radiation noise characteristics of both DC-DC power converter circuits are also depicted.

• 소성∙가공
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• 제24권3호
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• pp.212-217
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• 2015

SmartCrown is a system to control the plate crown by shifting the sine-shaped work rolls in the axial direction. The control range of the plate crown depends on a depth of sine-shaped roll profile because the roll radius varies continuously along the axial direction. When the roll profile is changed to improve the control range, the contact stress between the work roll and the back-up roll also changes. In the current study, the contact stress for various profiles and rolling conditions were analyzed using the finite element method and compared with results from Hertzian contact theory. A submodel method is used to increase the accuracy of the finite element analysis. The analysis results showed that the maximum increase in the contact stress was only 53MPa, so it is anticipated that no back-up roll spalling will occur.

• 소성∙가공
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• 제21권4호
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• pp.234-239
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• 2012

This study examines the forming properties and forming loads needed to increase the edge thickness on the external face of a plate using finite element analysis(FEA). Recently, forming optimization techniques within FEA are being extensively used in designing the optimal forming conditions for processes like forging, extrusion, rolling, and spinning. Most of these existing forming operations involve reducing the volume per unit length, but research for increasing volume per unit length is not very extensive. For this study we chose an automotive engine flywheel which is a welded assembly of a plate and a gear with each component having a different thickness. We considered a forming technique to increase the thickness in order to allow the machining of the gear directly on the external face of plate alleviating the need for a weld. To study various forming techniques, we used the finite element method with the flow stress of material and incremental forming steps. We conclude from this study that the analysis of forming properties and forming loads by using the finite element analysis and testing is useful as a method to increase the thickness per unit length.

• 한국재료학회지
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• 제21권11호
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• pp.581-586
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• 2011

This study describes a hydrogen embrittlement evaluation of the subsurface zone in 590DP steel by micro-Vickers hardness measurement. The 590DP steel was designed to use in high-strength thin steel sheets as automotive materials. The test specimens were fabricated to 5 series varying the chemical composition through the process of casting and rolling. Electrochemical hydrogen charging was conducted on each specimen with varying current densities and charging times. The relationship between the embrittlement and hydrogen charging conditions was established by investigating the metallography. The micro-Vickers hardness was measured to evaluate the hydrogen embrittlement of the subsurface zone in addition to the microscopic investigation. The micro-Vickers hardness increased with the charging time at the surface. However, the changing ratio and maximum variation of hardness with depth were nearly the same value for each test specimen under the current density of 150 mA/$cm^2$ and charging time of 50 hours. Consequently, it appears that hydrogen embrittlement in 590DP steel can be evaluated by micro-Vickers hardness measurement.