• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.95-103
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• 2015

This paper presents the effects of the tool shape on the geometrical characteristics of flat end-milled side walls. A tool shape is characterized by such parameters as helix angle, number of cutting edges, and diameter. The geometrical characteristics of the side walls are represented by the surface profiles in the feed and axial directions, which are orthogonal to each other. The geometrical defects in each direction are estimated based on the instantaneous apparent cutting areas, which are represented by the interference area between the tool and workpiece and that between the cutting edge and workpiece. It is confirmed that a geometrical defect in the feed direction is formed when the tool leaves the workpiece and the curvature of the tool path changes. Defects in the axial direction are also found in the side walls, except for the defect zone in the feed direction. An up-cut using an end-mill with a steeper helix angle, a greater number of cutting edges, and a smaller diameter are thus found to improve the geometrical accuracy of end-milled side walls.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.386-388
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• 2009

차세대 에너지로 연료전지가 각광을 받고 있는 현재, 세계 각국에서는 연료전지의 상용화를 위해 노력하고 있다. 그러나 촉매분야에서 백금계 촉매의 사용량의 문제에 따른 매장량 한계점과 귀금속이라는 문제점이 존재하기 때문에 이에 대하여 대책강구가 필요한 시점이다. 이에 백금 촉매의 활성을 증대하고자 나노 크기의 제어 연구가 진행되고 있다. 또한, 촉매의 구조적인 면에 따라 촉매의 활성이 달라지는 점을 착안하여 백금계의 나노 형상 조절 연구와 백금계 촉매를 대체할 비백금계의 촉매 개발 연구가 활발히 진행되어지고 있다. 이에 본 연구는 백금계 촉매 중 Pd을 polyol process에 의한 나노 형상 조절을 통하여 단위 질량당(or 단위 부피당) 촉매의 활성을 높이고자 하였다. Polyol process에서는 환원제, 계면활성제, 온도, 시간, 기타 첨가제에 따라 나노 형상이 다르게 조절되는데, 이에 계면활성제로 PVP를 사용하고, 반응속도 및 형상조절을 위해 다양한 첨가제를 이용하여 polygonal Pd NPs을 형성하였다. 본 나노 형상 조절에서는 첨가제와 온도가 가장 큰 영향을 미치는 요인으로 착안하여 그에 따른 polygoanl Pd NPs의 사이즈 조절을 통해 전기화학 특성이 차이의 연구에 중점을 두었다. 이에 따라 나노 형상 조절이 된 Pd촉매를 이용하여 상용화된 촉매(Pd/C(XC-72R))에 비하여 전기화학적인 특성의 차이와 Pd 촉매의 촉매적 특성의 효과를 보고자 한다.

• Journal of Energy Engineering
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• v.6 no.1
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• pp.52-57
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• 1997

Dynamic characteristics of compressible flow fields in super-circled constricted tube have been studied numerically. By applying MacCormack's explicit scheme, time marching method with predictor/corrector step, Euler equation is solved to find characteristics of fluid flow in a constricted tube where a two-dimensional inviscid compressible flow is assumed. The effects of tube diameter and aspect ratios on the pressure variations are discussed extensively. The results of the developed numerical schemes are compared with those of commercial FLUENT code, and show a good agreement.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.279-284
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• 2015

본 논문은 하중에 따른 변화정도에 초점을 맞추어 PSC girder길이의 증가를 위해 Co-rotational Plane Beam with Arbitrary Section Solver를 통하여 비선형 구조해석을 진행하여 Jeon, S., Choi, M., and Kim, Y. 등에 의해 제시된 Decked girder의 구조적 우수성을 검증하고, 이를 보완한 새로운 단면형상의 PSG girder를 제시하였다. 도출된 결과 값은 탄성방정식을 통하여 얻은 값과 비교하여 신뢰성을 검증하였다. 해석을 통하여 단순히 girder 상단부 플랜지의 길이를 증가시키는 것은 girder의 변형정도를 줄이는데 큰 영향을 주지 않는 다는 사실을 알 수 있었고 girder 상단부 플랜지와 중심부를 연결하는 부분의 단면형상을 좀 더 두껍게 함으로 하중에 따른 girder의 변형량을 크게 감소시킬 수 있었다.

• Journal of ILASS-Korea
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• v.8 no.4
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• pp.39-45
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• 2003

The Objective of this study is to investigate the effect of internal swiller angle and swirl chamber aspect ratio of nozzle on spray characteristics for application of spray system in micro fabrication process. The macro-spray characterictics such as the spray angle and breakup process were obtained by photographs illustrating atomization. The micro-spray characteristics such as droplet size and axial velocity were measured by using PDA with swirler angle and swirl chamber aspect ratio. The swiller angles were $13.5^{\circ},\;27^{\circ},\;and\;40.5^{\circ}$. The swirl chamber aspect ratios were 1.2, 1.6, and 2.0. It was found that the smaller swirl chamber aspect ratio was, the larger axial velocity and drop size were.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.29-36
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• 2001

Same as-built drawings in national roadway bridges in Korea were examined. As a result, many bridge piers were found whose aspect ratios are in the vicinity of 2.5. These columns are expected to do shear-flexure behaviour, but the previous research works considered flexure behaviour columns only. In the study, therefore, a shear-flexure behaviour column was selected as the model pier, and quasi static test on the full and 1/2 scale models was carried out. From the test results, the scale effect on the seismic performance evaluation was analyzed, and the seismic performance of the model bridge pier without seismic details was evaluated by the capacity spectrum method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.181-181
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• 2004

3 차원 형상측정기술(3-D Profile Measurement Method)은 가공품의 치수검사 및 형상측정 등의 공학분야뿐만 아니라 최근에는 의류산업 및 의학산업은 물론 오락산업의 가상현실 구현 등 여러 분야로 점차 사용이 확대되고 있다. 이러한 요구를 만족시킬 수 있는 광학을 바탕으로 한 비접촉 3 차원 형상측정방법(Non-contacting 3-D Profile Measuring Method)은 고속, 고정밀도 측정이 가능하기 때문에 활발히 연구되고 있다. 광학을 이용한 대표적인 3 차원 비접촉 측정방법의 하나인 영사식 무아레는 그림자식 무아레의 단점인 격자의 크기가 측정물체보다 커야 한다는 점과 측정물체와 격자사이의 거리 제한 문제를 해결하였으며, 위상이동법을 사용함으로서, 무아레 무늬 형태의 영향을 받지 않고 측정이 가능해졌다.(중략)

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.50-55
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• 2015

This study examined the relationship between the shape of the inside of the PRV and the cavitation of the water supply system of an apartment house. In this paper, nine types of PRV with different gaps and shapes were analyzed numerically using a 3D model embedded in the commercial code, ANSYS-CFX. The lowest pressure and the maximum velocity occurred at the narrow gap, which is located at the between the stem and the disk. When the gap size was increased, the vapor volume fraction was always greater than 0, but the vapor volume fraction of the type of expansion pipe approached 0. These results indicate that the cavitation of PRV can be reduced by a shape change to the type of expansion pipe.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.2
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• pp.82-91
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• 1999

Projectile shapes of the superdetonative ram accelerator have great effects on shock structures, detonation wave formation, and ram acceleration characteristics. In this study, cone-cylinder-cone, a baseline projectile configuration of the superdetonative combustion mode, double-cone configurations and power-law shape, have been numerically investigated to analyze the effect of the front/rear configuration changes, on the flow field around the projectile, detonation wave formation process, and projectile acceleration characteristics. Hence, a ram projectile configuration with conspicuously improved acceleration characteristics has been proposed by adjusting the double cone angle and height. The results provide useful information for the ram accelerator design optimization study.

• Clean Technology
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• v.7 no.2
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• pp.141-149
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• 2001

The effects of various factors such as adsorption temperature, interstitial velocity, species and concentration of adsorbates(benzene and toluene) and aspect ratio(L/D) on adsorption characteristics were investigated in a fixed bed with activated carbon. The breakthrough time in a fixed bed was decreased with the increasing of adsorption temperature, interstitial velocity and concentration of adsorbates. The interstitial velocity, concentration of adsorbates and adsorption temperature had influenced considerably upon the MTZ(mass transfer zone) and LUB(length of unused bed) obtained through the breakthrough curves, while aspect ratio(L/D) had smaller effect than former factors. Especially, the concentration of adsorbates among factors have the largest effect on MTZ and LUB. From comparison with the model isotherms, such as the Langmuir, Freundlich and Langmuir-Freundlich, the experimental isotherm data of benzene and toluene agreed farily well to three adsorption isotherm models.