• Tribology and Lubricants
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• 제27권6호
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• pp.338-343
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• 2011

Laser surface texturing (LST) methods are widely applied now to reduce friction and improve reliability of machine components such as thrust bearings, mechanical face seals and piston rings, etc. In this paper, the effect of dimple shapes on the lubrication characteristics of parallel thrust bearing are studied using a commercial computational fluid dynamics (CFD) code, FLUENT. Pressure and streamline distributions, variations of supporting load, leakage flow rate and friction force, are compared for three different dimple sectional shapes such as circle, pyramid and rectangle type. The lubrication characteristics are highly affected by dimple shapes and number of dimples. The pyramid type dimple shape can support the highest load while the rectangle type is the best in friction reduction.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.117-118
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• 2006

The objective of this paper is to investigate into bending and failure characteristics of ISB panel with dimple shapes as inner structures. Through three-points bending test, the force-displacement curve and the failure shape are obtained to examine the deformation pattern, characteristic data including maximum load and displacement at the maximum load and failure pattern for the ISB panel. In addition, the influence of design parameters for ISB panel on the bending stiffness and failure mode has been found. From the results of the experiments, it has been shown that bending and failure characteristics of the ISB panel can be controlled by the ratio of radius and the direction of the material.

• Tribology and Lubricants
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• 제28권3호
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• pp.136-141
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• 2012

In this paper, we investigated the friction characteristics of $W100^{\circ}{\o}L25m$ ellipse type surface pattern, on bearing steel. These characteristics are researched by utilizing a pin-on-disk wear test machine, under various velocities and other conditions. The reduction of friction is a necessary requirement for the improved efficiency of industrial parts. As the speed increases, there is a decrease in the effect of the dimple of friction characteristic in low velocity, with substantially little change to density. Conversely, as the load increases, the test direction of ellipse type dimple pattern, resulting in a difference in the texture of these two components. At a dimple density of 7.5% the friction characteristic is easily demonstrated, with a consistent change in both speed and load.

• Tribology and Lubricants
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• 제24권6호
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• pp.368-373
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• 2008

This paper will investigate the friction characteristics of a 100m Hexagonal Array, Micro-scale Dimple Pattern, on bearing steel. These characteristics are researched by utilizing a pin-on-disk wear test machine, under various test conditions. The reduction of friction is a necessary requirement for the improved efficiency of this machine. As the speed increases, there is a decrease in the effect of the dimple of friction characteristic, with substantially little change to density. Conversely, as the load increases, the dimple pattern grows larger, resulting in a difference in the texture of these two components. At a dimple density of 10% the friction characteristic is easily demonstrated, with a consistent change in both speed and load.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2352-2356
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• 2008

Heat transfer and performance characteristics have been investigated for a rectangular wavy duct with dimple or protrusion arrays. The test duct was 15mm in height and 105mm wide. The print diameter of the dimple/protrusion wall was 12.99mm and the depth/height of the dimple/protrusion was 3.75mm. Local heat transfer coefficients on the dimple/protrusion wall were measured using a transient TLC technique. The Reynolds number was varied from 3,000 to 10,000. For the wavy duct tested in this study, adverse static pressure characteristics occurred at turning region of the wavy duct due to secondary flows. For the wavy duct with protrusion array, higher heat transfer enhancement level of 7.4 times than smooth straight case in maximum was obtained at low Reynolds number due to the high heat transfer enhancement by vortex flows. Also, the protrusion array increased the performance level of 3.0 at low Reynolds number of 3,000.

• 한국가스학회지
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• 제19권6호
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• pp.62-66
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• 2015

LNG선이나 해양플랜트 같은 설비나 구조물은 작동 조건을 고려할 때, 특히 부재마다 가지는 고유한 연성 취성천이온도(Ductile to Brittle Transition Temperature, DBTT)를 고려하여 설계되어야 한다. 본 연구에서는 해양플랜트 및 LNG선에 hull plate로 쓰이는 A-grade 연강(mild steel)에 대해 DBTT를 샤르피 V-노치(CVN) 실험을 통해 알아보았고 파괴형상을 통한 파괴거동을 살펴보았다. 그 결과 온도가 감소함에 따라 충격 흡수에너지는 감소함을 보였다. Upper shelf energy region과 lower shelf energy region이 나타나고 그 사이 구간의 천이점을 통해 DBTT가 결정되었다. 파괴형상에서는 upper shelf energy region에서 수많은 딤플이 연성파괴 형상으로 관찰되고 lower shelf energy region에서는 전형적인 취성파단형상이 관찰되었다. 이를 통해 BCC 구조를 가지는 A-grade 연강은 upper shelf energy 구역과 lower shelf energy구역을 보이고 그 사이 구간의 천이점에서 급격하게 온도가 떨어지는 DBTT구간을 뚜렷하게 보이는 특성을 알 수 있었다.

• 소성∙가공
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• 제14권8호통권80호
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• pp.718-724
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• 2005

An efficient finite element method has been introduced for analysis of metallic sandwich plates subject to bending moment. A full model 3-point bending FE-analysis shows that the plastic behavior of inner structures appears only at the load point. The unit structures of sandwich plates are defined to numerically calculate the bending stiffness and strength utilizing the recurrent boundary condition for pure bending analysis. The equivalent models with the same bending stiffness and strength of full models are then designed analytically. It is demonstrated that the results of both models are almost the same and the FE-analysis method incorporating the equivalent models can reduce the computation time effectively. The dominant collapse modes are face buckling and face yielding. Since the inner dimpled structures prevent face buckling, sandwich plates with inner dimpled shell structure can absorb more energy than other types of sandwich plates during the bending behavior.

• Journal of Welding and Joining
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• 제15권6호
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• pp.57-65
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• 1997

A study was undertaken to determine the influence of welding variables such as shielding and plasma gases, torch standoff, travel speed and heat input, etc. on the quality of plasma arc welds in Zircaloy-4 sheet, 2mm thick. Effect of shielding gases and their flow rates on the mechanical properties of Zircaloy-4 welds by plasma arc welding were determined in terms of tensile, bardness and bend tests. The microstructure and fracture surface of Zircaloy-4 welds were investigated by optical and scanning electron microscopies. In addition, the causes of porosity and undercut in plasma arc welds of Zircaloy-4 were also investigated. Zircaloy-4 weld bead width and depth by helium shielding gas showed a wider and deeper than those by argon. It was found that Zircaloy-4 welds with shielding gas of helium did dxhibit a little smoother and uniform weld beads than those with shielding gas of argon. It was also found that the optimum gas flow rates for Zircaloy-4 welding were 0.45l/min for plasma gas with Ar and 4.5 - 6 l/min for shielding gas with He. In addition, there was no big difference in the microstructure and fracture surface of the weld metals made by either Ar shielding gas or He shielding gas.

• 한국강구조학회 논문집
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• 제29권2호
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• pp.123-134
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• 2017

풍력발전 타워용 종방향 보강 원형단면 강재 쉘에 대하여 재료 및 기하학적 비선형 유한요소법(GMNIA)으로 극한압축강도 해석을 수행하였다. 보강 쉘의 반경 대 두께비, 초기변형 형상 및 진폭, 종방향보강재의 면적 및 간격 등의 주요 설계 파라미터가 압축력을 받는 보강 쉘의 극한강도에 미치는 영향을 분석하였으며, DNV 설계기준에 의한 설계좌굴강도와 유한요소해석으로 구한 극한압축강도를 비교하였다. 기하학적 초기결함의 형상은 선형 좌굴해석으로부터 구한 좌굴모드 및 제작 과정에서 용접으로 발생하는 딤플 변형을 고려하였다. 해석 대상 보강 쉘의 반경 대 두께비는 50~200이며, 종방향보강재는 횡비틀림좌굴과 국부좌굴이 발생하지 않도록 DNV 설계기준에 따라 두께와 돌출폭을 결정하였다.

• 한국산학기술학회논문지
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• 제17권7호
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• pp.31-41
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• 2016

본 연구에서는 발전소 응축기를 모사할 수 있는 프로그램을 개발하고 발전소 응축기에 전열 촉진관 적용시 얻을 수 있는 여러 효과에 대하여 검토하였다. 평활관을 촉진관으로 교체한다면, 전열량의 증가에 따른 수증기 응축 온도가 내려가게 되므로 발전소의 효율이 증가하게 된다. 따라서 촉진관을 사용하면 기존 설비를 그대로 두고서도 상당량의 전력 여유도를 확보할 수 있다. 고려된 전열 촉진관은 외경 22.2 mm 티타늄 재질의 코류게이트 관, 리브 조도 낮은 핀관, 삼차원 조도 낮은 핀관이다. 내측 조도의 경우 최적 조도 높이가 존재하였다. 또한 삼차원 조도 낮은 핀관이 다른 두 형상보다 우수하게 나타났다. 삼차원 조도의 경우 원주 방향으로 인접한 딤플 사이에서 흐름 방향으로 선회류가 유발되고 이 선회류에 의하여 열전달이 촉진되기 때문이다. 600 MW 발전소 응축기에 전열 촉진관을 적용하면 0.5 MW~1.3 MW 가량의 추가 전력을 생산할 수 있다. 또한 냉각수 온도가 올라가면 추가 전력도 증가한다. 실제로 발전소 응축기에 적용하기 위해서는 열 성능 외에도 화울링, 부식, 기계적 특성 등이 고려되어야 한다.