• 천문학회보
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• 제40권1호
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• pp.80.2-80.2
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• 2015

We present spatial and chemical distributions of Carbon-Enhanced Metal-Poor (CEMP) stars in the Milky Way's halo, as observed by the Baryon Oscillation Spectroscopic Survey (BOSS). Although the BOSS was designed to obtain spectra of galaxies and quasars, it also observed numerous metal-poor main-sequence turnoff stars for the purpose of flux calibration. The stars observed in the BOSS are two magnitudes fainter (15.5 < g < 19.2) than those in the legacy SDSS, thus it is an extremely useful sample to probe the distant halo. Using effective temperatures, surface gravities, [Fe/H], and [C/Fe] derived for these stars by the SEGUE Stellar Parameter Pipeline (SSPP), we investigate the spatial distribution of [Fe/H] and [C/Fe], the distribution of [C/Fe], and frequency of CEMP stars among these stars. These tools enable characterization of the origin of the halo and its initial mass function.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.332-337
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• 2009

Recently, boss and rib test based on backward extrusion process was proposed to quantitative evaluate the interfacial friction condition in bulk forming process. In this test, the tube-shaped punch with hole pressurizes the workpiece so that the boss and rib are formed along the hole and outer surface of the punch. It was experimentally and numerically revealed that the height of boss is higher than that of the rib under the severe friction condition. This work is focused on the effect of the punch design and friction condition on deformation pattern in boss and rib test. From the boss and rib test simulations, it was found that there is slight variation in both the heights of boss and rib according to the length of punch land, nose radius, and face angle. However the hole diameter of the punch and the clearance between the punch and die have a significant influence on the heights of the boss and rib. In addition, the effect of flow stress was also investigated on the deformation patterns through FE simulations.

• 한국추진공학회지
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• 제20권6호
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• pp.29-37
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• 2016

본 논문에서는 유한요소해석을 이용하여 복합재 연소관의 금속 보스에 대한 형상 최적설계기법을 제안하였다. 복합재 연소관의 구조 안전성을 위해 연소관 내압에 의한 돔 부위의 섬유응력과 보스 체결 볼트의 응력을 제한하였고, 경량화를 위해 보스의 무게를 목적함수로 설정하였다. 또한 반응표면법을 이용하여 특성치에 대한 반응표면모델을 구축하였다. 그리고 분산분석을 이용해 각 특성치에 대한 설계변수의 유의성을 평가하고 회귀분석을 통해 구축된 모델의 적합성을 검증하였다. 최적화를 위해 순차이차계획법 알고리즘을 이용하였고, 도출된 최적형상에 대한 구조해석을 수행함으로써 제안한 기법의 효용성을 검증하였다.

• 한국추진공학회지
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• 제23권4호
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• pp.21-27
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• 2019

연소가스에 의한 내압 조건에서 필라멘트 와인딩 공법으로 제작되는 복합재 연소관은 돔에서 구조적으로 취약해진다. 본 논문에서는 압력분포비(PDR) 변화에 따른 복합재 돔의 파열압력을 비교하기 위해 유한 요소 해석을 수행하였다. 돔 내/외면 응력, 금속 보스 체적을 산출함으로써, 정량적으로 복합재 연소관의 성능을 비교하였다. 그 결과, PDR 2.5-3.0에서 파손 모드의 임계점이 존재함을 확인하였다. PDR 2.5-3.5 설계는 연소관 파열압력의 변동 없이 금속 보스 무게 감량이 가능하며, 돔 형상 및 오프닝 크기에 대해 설계 기준값이 변경되므로 해석 및 시험을 통한 규명이 필요하다.

• Tribology and Lubricants
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• 제36권3호
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• pp.168-192
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• 2020

In recently designed diesel engines, the running conditions for piston-pin bearings have become severe because of the higher combustion pressure and increased temperature. Moreover, the metal removal from the bushing material has strongly reduced the ability of the antifriction material to accept asperity contacts. Therefore, it is necessary to find ways of reducing wear scar on the connecting-rod small-end bushing and piston-pin boss bearing related to the higher combustion pressure on the power cell of an engine. In this work, the position and level of material removal from the surfaces of the bushing and bearing under such severe operating conditions - for example, maximum power and torque conditions of a passenger car diesel engine - are estimated for several combinations of surface roughness. First, piston-pin rotating motion is investigated by calculating the friction coefficient at piston-pin bearings, the oil film thickness, and the frictional torques induced by hydrodynamic shear stress. Subsequently, the wear scarring on the surfaces of a connecting-rod small-end bushing and two piston-pin boss bearings related to piston-pin rotational motion is numerically calculated under the maximum power and torque operating conditions. This work is helpful to determine the reasonable surface roughness of the bushing and bearing for reducing wear volume occurring at the interface between a bearing and a shaft.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1996년도 추계학술대회 논문
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• pp.180-186
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• 1996

Using carbon steel or ceramic as a shaft material of monolithic and slited insert ring clamped on it. The fitting strengths of the sgrink fitted assemblies measured from room temperature to 30$0^{\circ}C$ and following conclusions were obtained as results of this investigation. 1) The fitting condition under which the shrink fitted assemble was stronger than that using simple fit in high temperature. 2) When both material of the 30mm-diameter shaft and 55mm-diameter boss are SM45C the clamping torque is increased 2.7times as the interference increases 3 times from 20${\mu}{\textrm}{m}$ at the contact length of 6mm monolithic fit. 3) When only the material of boss is changed to STS 304 the clamping torque is increased at the rate of 37.3N.m per 1mm increase of the contact length at the interference of 50${\mu}{\textrm}{m}$ monolithic fit.

• Composites Research
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• 제17권5호
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• pp.1-6
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• 2004

HDPE (high density polyethlyne) 라이너와 금속 boss를 가진 복합재료 압력용기가 필라멘트 와인딩 공정에 의해 개발되었다. 이 용기의 끝 부위는 dome-shape 부위 그리고 용기의 중앙부는 cylinder-shape로 형성되었다. 용기를 구성하는 재료인 HDPE, 수지 그리고 강화섬유와 같은 용기재료에 대해 환경실험이 1년 이상 실행되었다 Boss 설계는 FEM 해석으로 가스 누출을 최대한 방지해 주는 것으로 확인되었다. 실험적인 방법에 의해 가장 이상적인 fiber tension이 얻어졌고, image analyzer에 의해 측정된 섬유의 체적율, $\textrm{V}_{f}$,는 실린더에서 55.4 %, dome part에서 55.6 % 이었다. Winding pattern은 용기의 파괴가 실린더 부위에서 일어나도록 dome 부위의 복합재료 두께조절을 하도록 프로그램 되었다 경화 중 용기는 돌려졌었고 고정 내부압력 0.62 bar를 가함으로서 최종용기의 파괴압력이 28 % 향상되었다. Under-wound, fully wound된 용기의 파괴 및 피로시험결과를 충족하였다.