• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3155-3160
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• 2010

Nowadays, most car manufactures have tried to improve fuel efficiency and corrosion resistance of car body. Therefore, use of high strength steels and coated steel becomes more and more increased. In this study, spot weld characteristics according to lap sequence of sheets were analyzed using simulation method for three different steel sheet of car body which were EDDQ class coated steel with 0.7t, high strength steel 440R with 1.2t and advanced high strength steel DP 590 with 1.0t. Using simulation, weldability was evaluated by nugget size of welded zone according to nugget growth curve and welding current with respect to lap sequence of sheets. Contact resistance of each sheets contact point was used to analyze formation of nugget and optimal lap sequence was suggested.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.9-9
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• 2008

일반적으로 섬광법으로 열전도율을 구하기 위해서는 섬광법으로 열확산계수를 측정하고, 시차주사열량계(Differential Scanning Calorimetry, DSC)로 비열측정을 하며 아르키메데스의 원리를 이용한 용적밀도를 구하여 이들 각각의 값을 사용하여 열전도율을 얻는다. 따라서 열전도율을 정밀하게 측정하기 위해서는 이 세 가지 물성치를 측정할 때 수반되는 오차요인을 종합적으로 검토하여 개선하는 것이 매우 중요하다. 섬광법으로 열확산계수를 측정할 때 시료의 전면에 조사되는 빛의 흡수율을 향상시키고 배면에서의 온도상승의 감지를 증대할 목적으로 시료 양면에 흑연코팅을 하게 된다. 이때 코팅된 흑연이 시료에 부가적으로 열저항을 증가시켜서 열확산계수를 측정하는데 가장 큰 오차요인이 되고 있다. 한편 비열은 대부분 DSC로 측정하는데, 시료와 용기의 열접촉 정도에 따라 큰 오차요인이 되기도 한다. 본 연구에서는 열확산계수를 정밀하게 측정하기 위해서 시료에 부가적인 열저항으로 작용하는 흑연코팅의 두께와 시료배면에서의 온도상승곡선 간의 상관관계를 실험식으로 도출하였으며 이방법은 열확산계수를 정밀하게 측정하는데 매우 유효한 방법임이 입증되었다. 또한 DSC의 접촉에서의 문제점을 해결하기 위해서 시료배면에서의 무차원 시간축(t/$t_{max}$)을 도입하였으며. 무차원 시간축에 따른 온도상승 곡선에서 표준시료와 측정시료의 half time($t_{1/2}$)의 0.5 배와 1.5배 사이 구간을 적분한 뒤 비교하여 열량계산으로부터 비열을 구하는 방법을 새롭게 개발하였으며 기존의 DSC에 비하여 정밀도를 향상시킬 수 있었다. 결론적으로 새롭게 제안된 측정기법들은 열확산계수 및 비열 혹정 시의 근본적인 오차요인을 혁신적으로 해결함으로써 정밀하고 신뢰성 있는 열전도율을 측정할 수 있음을 입증할 수 있었다.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.177-181
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• 2005

Although there are many ways to measure the diameter of a cylindrical object, in this study, the diameter of a cylindrical objects were measured by the geometric optical method and interference-diffraction method which are two kinds of tipical non-contact methods. In geometric optical method, the curved laser beam is formed on the cylindrical surface by spreading the inclined laser beam using the cylindrical lens. The curve is captured by CCD camera and the diameter is calculated by geometry. And the interference and diffraction patterns of investigated cylindrical objects are analyzed in interference-diffraction method. In this study, the cylindrical objects, whose diameters are $0.05\;mm\;\~\;100.50\;mm$ were measured by the geometric optical method and interference-diffraction method. The results show that in each method, the relative errors of the measurement are within $2\%$ and $1\%$, respectively and these non-contact methods can be applied in the quick measurement of many objects.

• Journal of Astronomy and Space Sciences
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• v.16 no.2
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• pp.217-266
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• 1999

The light curves of the representative 6 contact binary stars observed by OGLE Project of searching for dark matter in our Galaxy have been analyzed by the method of the Wilson and Devinney Differential Correction to find photometric solutions. The orbital inclinations of these Devinney Differential Correction to find photometric solutions. The orbital inclinations of these binaries are in the range of $52^{circ}-69^{\circ}$ which is lower than that of the solar neighborhood binaries. The Roche lobe filling factor of these binaries are distributed in large range of 0.12 - 0.90. Since absence of spectroscopic observations for these binaries we have found masses of the 6 binary systems based on the intersection between Kepler locus and locus derived from Vandenberg isochrones in the mass - luminosity plane. Then absolute dimensions and distances have been found by combining the masses and the photometric solutions. The distances of the 6 binary systems are distributed in the range of 1 kpc- 6 kpc. This distance range is the limiting range where the contact binaries which have period shorter than a day are visible. Most contact binaries discovered in the Baade window do not belong to the Galactic bulge.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.241-250
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• 2011

The new gerotor developed in this paper has an inner rotor in which a circular arc is inserted between the hypocycloid and epicycloid curves, whereas the outer rotor is designed using the simulation results for the rotor and a modification method. The new gerotor has no cusps and loops and no limit on the eccentricity. We increase the average flow rate by adding a new design parameter, $\gamma$, which is the inclined angle of the inner rotor at the intersection of the hypocycloid and the circular arc. A calculation method to calculate the chamber area is also developed. This method can also be used to calculate the flow rate and flow rate irregularity when the contact points are unknown. The control of eccentricity and $\gamma$ is expected to lead to an efficient rotor.

• Composites Research
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• v.27 no.6
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• pp.213-218
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• 2014

This paper predicted the strength of mechanical joint of composites under bending load by means of the characteristic curve method. The method has been employed only for tensile and compression load conditions, but in this study, this method was extended to the bending load condition. For the finite element analysis (FEA), the nonlinear analysis was conducted considering the contact and friction effects between composite material and pin. The failure strength and mode on characteristic curve were evaluate with Tsai-Wu failure theory. To validate the results of FEA, the experiments were conducted to find out the failure load by applying bending moment on the composite specimens. The results showed reasonable agreements with theoretical results. These results lead to a conclusion that the characteristic curve method can be applied to predict the bending strength of mechanical joint of composites.

• Journal of the Korean Society for Railway
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• v.20 no.2
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• pp.165-172
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• 2017

High frequency squeal noise can be generated when a railroad vehicle runs a sharp curved section; this noise causes environmental complaints and excessive wear on the wheel and the railroad track. In this paper, curved squeal noise experiments on a commercial railway were carried out to investigate this phenomenon. The relationship of the squeal noise pressure level, the frequency characteristics, the railway running speed, and the modal behavior of the wheel were investigated. At the same time, the lateral motion of the wheel relative to the rail was captured using a video camera; wheel movement was calculated when the noise was generated. queal noise occurred at the highest level at the inner front wheel; this phenomena is considered to be related to the lateral vibration response characteristics of the wheel. It can be seen that the magnitude of this squeal noise is not directly related to the increase in vehicle speed.

• Proceedings of the KIEE Conference
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• 2008.04b
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• pp.211-213
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• 2008

배전선로는 항상 각종 공작물과 아주 가까운 상태에서 존재하고 있어 배전선로 근접 작업 시 전력선에 근접으로 인한 섬락 또는 접촉으로 작업원이 감전 재해를 입을 수 있으며 또는 비, 바람, 조류 등에 의한 이물 접촉으로 설비 고장을 유발 시킬 수 있다. 이러한 감전재해 및 설비고장을 예방하기 위하여 22.9kV-y 전력선의 직선부분에 사용할 수 있는 직선형 방호관을 개발하여 건설현장 주변의 전력선에 방호조치 함으로서 전력선 근접 작업 시 작업종사자의 안전 확보에 이바지함은 물론 정전사고방지에도 크게 기여하여 왔다. 그러나 22.9kV-y 배전선로의 점퍼선부분과 변압기의 인상선 등 곡선으로 되었거나 구불구불한 형상으로 된 부위는 직선형 방호관으로는 방호조치가 불가능하여 산업안전보건법이 정한 산업안전기준에 관한 규칙 제327조 제2호에 의한 방호조치를 취하지 않고 근접작업이 진행되어 감전재해와 정전사고가 발생되어 왔었다. 한전에서 협력업체와 공동으로 연구개발한 소용돌이형 점퍼선방호관을 그동안 방호조치를 취하지 못한 점퍼선이나 구불구불한 전력선부위에 방호조치를 함으로서 감전재해의 예방과 정전사고 발생을 획기적으로 감소시킬 것으로 기대된다.

• Journal of Astronomy and Space Sciences
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• v.12 no.1
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• pp.44-53
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• 1995

BVRI observatins of AW UMa were made from March to April during 13 nights in 1994 using the 35cm Schmidt-Cassegrain telescope of Department of Astronomy and Space Science, Chungbuk National University. A total of 1092 observations (273 in B, 273 in V, 273 in R, 273 in I) were obtained. We constructed the light curves of BVRI with these observations. The one time of primary minimum light of JD Hel 2449456.1502 and the two times of secondary minimum light of JD Hel 2449456.1502 and JD Hel 2449447.1567 were determined from our observations. Orbital period change of -0.d00000394 was determined from O-C diagram which was constructed with collected times of minimum lights. Mass transfer rate of $-6.4\times10^{-7}M_\odot/year$ was derived using the period changing ratio. It is suggested that the inhomogeneous distribution of transferred matter around the secondary component would produce the irregular light variation of the AW UMa system.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.2
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• pp.6-11
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• 2000

In this paper, suggesting a new linearly -graded depletion edge approximation, the current-voltage characteristics of an n-type short-channel GaAs MESFET device has been analyzed by solving the two dimensional Poisson's equation in the depletion region. In this model, the expressions for the threshold voltage, the source and the drain ohmic resistance, and the drain current were derived. As a result, typical Early effect of a short channel device was shown and the ohmic voltage drop by source and drain contact resistances could be explained. Furthermore our model could analyze both the short-channel device and the long-channel device in a unified manner.