• Journal of Astronomy and Space Sciences
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• 제32권3호
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• pp.269-279
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• 2015

Future space missions will have larger telescopes in order to look deeper into space while improvising on spatial resolution. The primary mirrors for these telescopes will be so large that using a monolithic mirror will be nearly impossible because of the difficulties associated with its fabrication, transportation, and installation on a launch vehicle. The feasibility of launching these huge mirrors is limited because of their small launch fairing diameter. The aerodynamic shape of the fairing requires a small diameter, but the height of the launch vehicle, which is available for designers to utilize, is larger than the fairing diameter. This paper presents the development of an axial deployment mechanism based on the screw jack principle. The mechanism was designed and developed, and a prototype was constructed in order to demonstrate a lab model.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.285-288
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• 2004

This study presents a numerical procedure to optimize the shape of dimple surface to enhance turbulent heat transfer in rectangular channel. The response surface based optimization method is used as an optimization technique with Reynolds-averaged Wavier-Stokes analysis of fluid flow and heat transfer with shear stress transport (SST) turbulence model. The dimple depth-to -dimple print diameter ratio, channel height- to- dimple print diameter ratio. and dimple print diameter-to-pitch ratio are chosen as design variables. The objective function is defined as a linear combination of heat transfer coefficient and friction drag coefficient with a weighting factor. Full factorial method is used to determine the training points as a mean of design of experiment.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1996년도 제6회 학술강연회논문집
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• pp.209-216
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• 1996

The shape variation of billet was investigated by numerical method and spray forming work with variation of average substrate withdrawal velocity$\bar{V}$, withdrawal velocity change interval $\Delta$t and velocity deviation from average velocity $V_{dev}$. The shape and diameter with large$\bar{V}$, $\Delta$t, $V_{dev}$ vary seriously. When $\bar{V}$, $\Delta$t, $V_{dev}$ are smaller, the shape of billet is more simillar to that of the billet with constant withdrawal velocity. The average diameter of billet is determined by only $\bar{V}$, independent of $\Delta$t, $V_{dev}$. With $\bar{V}$, : 0.2 mm/sec $\Delta$t: 200 sec and $V_{dev}$. : 0.2mm/sec billet of constant diameter 230mm$\times$ height 1000mm were manufactured.

• 한국환경과학회지
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• 제13권10호
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• pp.929-938
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• 2004

Sludge discharger applied the principle of the air lift pump was investigated experimentally for the different design( diameter of discharge pipe, diameter and height of the inside and outside wall) and operating parameters(air flow rate, water level). And it was conducted that performance comparison about sludge discharger and conventional air lift pump. The result indicated that discharged liquid were increased with the increase of air flow rate and water level and decrease distance between inside and outside wall. The discharge pressure was increased with an increase of air flow rate and a decrease of the diameter of the discharge pipe, for both the sludge discharger and the airlift pump. The discharge pressures of the sludge discharger were 3-6 times higher than those of the air lift pump.

• 소성∙가공
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• 제33권4호
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• pp.291-300
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• 2024

To compare the lubrication performance improvement of different laser texturing surface treatment patterns, ring-shaped specimens were prepared by processing line and dot patterns using a fiber laser device. Ring compression tests were conducted to compare the reduction rates of the inner diameter corresponding to the same height reduction of the specimens. Laser processing conditions were set to create patterns with a depth of 9㎛ and a width of 45㎛. Ring specimens were processed with varying spacings between dots and lines. The forging lubricant TECTYL FORM CF 351S was uniformly applied to the upper and lower compression tools, and the rings were compressed by 40% using a hydraulic press, after which the inner diameter was measured. The comparison of inner diameter reduction rates indicated that pattern processing improves lubrication performance, with line patterns being more effective than dot patterns in enhancing lubrication performance.

• 한국분무공학회지
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• 제10권1호
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• pp.10-16
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• 2005

To investigate the effect of shockwave on diesel spray characteristics under ultra high pressure injection, the velocity of spray tip and shock wave were investigated using the visualization of spray by schlieren method. Spray characteristics such as the spray radius, height, and droplets size were analyzed. It is found in this study that shock wave, produced by ultra high injection pressure, propagates faster than spray tip. Spray radius of right side of nozzle tip was shorter than that of left side and spray height of right side of nozzle tip was thicker than that of left side. Droplets sue was increased at 414MPa in injection pressure because of pressure gradient between inner and outer of tile spray caused by shockwave.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.241-247
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• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with ones roughened by five different shapes. The effects of rib shape geometries and Reynolds number are examined. The rib height-to-duct hydraulic diameter, pitch-to-height ratio, and aspect ratio of channel width to height are fixed at e/De=0.0476, P/e=8, and W/H=2.33, respectively. To understand the mechanisms of the heat transfer enhancements, the measurements of the friction factors are also conducted in the smooth and rough channels. The data indicates that the triangular type rib has a substantially higher heat transfer performance than any other ones in the range we studied.

• 동력기계공학회지
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• 제5권2호
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• pp.30-35
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• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with one wall roughened by five different shapes. The effects of rib shape geometries and Reynolds number are examined. The rib height-to-duct hydraulic diameter, pitch-to-height ratio, and aspect ratio of channel width to height are fixed at $e/D_e=0.0476$, P/e=8, and W/H=2.33, respectively. To understand the mechanisms of the heat transfer enhancements, the measurements of the friction factors are also conducted in the smooth and rough channels. The data indicate that the triangular type rib has a substantially higher efficiency index than any other ones in the range we studied.

• 설비공학논문집
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• 제2권3호
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• pp.177-187
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• 1990

This paper presents that in the Korean Ondol Heating System using hard coal as an usual fuel, what effects an insulation of chimney with the low temperature gas flow has on the optimum chimney height which gives a maximum gas weight flow rate under the general weather data and actual design condition of chimney is compared with the bared chimney and studied. And also, the effects of chimney materials and diameter, dimensionless temperature difference, insulating materials and thickness which have on the optimum chimney height were researched and a good results increasing a maximum gas weight flowrate is obtained by insulating the chimney.

• Structural Engineering and Mechanics
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• 제51권3호
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• pp.361-375
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• 2014

The main aim of this paper is to investigate the relationship between thickness and height of the axially symmetric cylindrical reinforced concrete (RC) walls by the help of a meta-heuristic optimization procedure. The material cost of the wall which includes concrete, reinforcement and formwork, was chosen as objective function of the optimization problem. The wall thickness, compressive strength of concrete and diameter of reinforcement bars were defined as design variables and tank volume, radius and height of the wall, loading condition and unit cost of material were defined as design constants. Numerical analyses of the wall were conducted by using superposition method (SPM) considering ACI 318-Building code requirements for structural concrete. The optimum wall thickness-height relationship was investigated under three main cases related with compressive strength of concrete and density of the stored liquid. According to the results, the proposed method is effective on finding the optimum design with minimum cost.