• International Journal of Fluid Machinery and Systems
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• 제9권3호
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• pp.229-236
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• 2016

Exergetic analysis was introduced in optimization of a rotating equilateral triangular internal cooling channel with staggered square ribs to maximize the net exergy gain. The objective function was defined as the net exergy gain considering the exergy gain by heat transfer and exergy losses by friction and heat transfer process. The flow field and heat transfer in the channel were analysed using three-dimensional Reynolds-averaged Navier-Stokes equations under the uniform temperature condition. Shear stress transport turbulence model has been selected as a turbulence closure through the turbulence model test. Computational results for the area-averaged Nusselt number were validated compared to the experimental data. Three design variables, i.e., the angle of rib, the rib pitch-to-hydraulic diameter ratio and the rib width-to-hydraulic diameter ratio, were selected for the optimization. The optimization was performed at Reynolds number, 20,000. Twenty-two design points were selected by Latin hypercube sampling, and the values of the objective function were evaluated by the RANS analysis at these points. Through optimization, the objective function value was improved by 22.6% compared to that of the reference geometry. Effects of the Reynolds number, rotation number, and buoyancy parameter on the heat transfer performance of the optimum design were also discussed.

• 한국해양공학회지
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• 제24권4호
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• pp.13-22
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• 2010

While a caisson used for breakwater is carried by a floating dock, accompanying stability problem by its existing motions in the dock is quite important and should be pre-checked against sea environmental condition. In the stability analysis, the acceleration, velocity, angle of roll and pitch motions are important to calculate frictional force and separation force. If separation force becomes bigger than frictional force, serious collision may be occurred between caisson and floating dock. In this study, stability evaluation during the transportation of a caisson on floating dock for breakwater was performed by using a commercial program, HydroD and CHARM3D/HARP.

• 천문학회보
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• 제37권1호
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• pp.91.1-91.1
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• 2012

지구 자기권의 입자분포는 지구 자기권의 상태와 태양풍의 물리적 상황에 따라 다르다. 가령, 정지궤도에서 고에너지 입자의 flux가 낮아지는 것이 관측된다. 이러한 flux dropout 기간은 대부분 storm main phase에 해당된다. 반면 태양풍의 속력이 상대적으로 높은 HSS(high speed stream)기간 동안에는 대부분 정지궤도에서의 고에너지 입자 flux가 높아지며 radiation belt의 고에너지 입자들의 seed electron 역할을 할 것으로 예상하고 있다. 본 연구에서는 GOSE 11 위성의 electron flux data와 태양풍의 속도를 이용하여 HSS, quiet time, flux dropout 기간을 정의 하였다. 또한, 지구로부터 7~8Re 떨어진 night side지역을 radiation belt의 trapping boundary 바로 바깥 경계지역과 같다고 가정하였다. 그리고 각 기간 동안 이 경계지역에서 입자들의 분포와 관련된 물리적 조건을 결정하는 것을 목표로 하였다. 이는 방사선 벨트 내부에서의 역학적 진화에 영향을 미칠 수 있다. 2007년 6월부터 2010년 8월까지 이러한 경계지역에 THEMIS 위성이 위치했을 때 ESA와 SST의 omni-directional flux를 이용하여 에너지에 대한 입자플럭스 분포 함수를 산출하였다. 또한 각 기간에 평균한 분포 함수를 가장 잘 나타낼 수 있는 해석적 함수를 도출하였다. 추가로, 경계지역에서의 입자들의 pitch angle 분포 패턴도 결정 하였다. 이 결과는 방사선 벨트의 전산모사에서 실질적인 경계 조건으로 사용될 수 있다.

• 대한기계학회논문집B
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• 제25권1호
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• pp.96-107
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• 2001

An unsteady numerical simulation was performed to analyze flow structures behind a local suction/blowing in a flat-plate turbulent boundary layer. The local forcing was given to the boundary layer flow by means of sinusoidally oscillating jet. A version of the unsteady $\kappa$-$\xi$-f(sub)u model (Rhee and Sung 2000) was employed. The Reynolds number based on the momentum thickness was about Re(sub)$\theta$=1700. The forcing frequency was varied in the range 0.011$\leq$f(sup)+$\leq$0.044 with a fixed forcing amplitude A(sub)o=0.4. The predicted results were compared and validated with the experimental data. It was shown that the unsteady locally-forced boundary layer flow is predicted well by the $\kappa$-$\xi$-f(sub)u model. The effect of the pitch angle of local forcing on the reduction of skin friction was also examined.

• 대한기계학회논문집B
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• 제28권9호
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• pp.1051-1057
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• 2004

A numerical optimization procedure for the shape of three-dimensional channel with angled ribs mounted on one of the walls to enhance turbulent heat transfer is presented. The response surface method is used as an optimization technique with Reynolds-averaged Wavier-Stokes analyses of flow and heat transfer. SST turbulence model is used as a turbulence closure. Computational results for local heat transfer rate show reasonable agreements with experimental data. The pitch-to-height ratio of the rib and rib height-to-channel height ratio are set to be 9.0 and 0.1, respectively, and width-to-rib height ratio and attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with weighting factor. Full-factorial experimental design method is used to determine the data points. Optimum shapes of the channel have been obtained in the range from 0.0 to 0.1 of weighting factor.

• 한국기계가공학회지
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• 제6권3호
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• pp.65-70
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• 2007

Generally, the core component of small precise optical device demands high accuracy of manufacturing processes. Although, the geometry of it is simple, the manufacturing technique to materialize is categorized as the ultra-precision machining and it must be done with the specialized machines and by the trained operator. Typical examples of small precise optical device are laser printer and phone camera. As a core part of laser printer, polygon mirror is used in laser scanning unit(LSU). It couldn't be fabricated with conventional machine but specified machine for polygon mirror machining. In this study, Polygon mirror with 16 surfaces was manufactured in the process of ultra-precision fly-cutting with Al material and investigated optimum machining conditions in terms of feedrate, pitch per cycle and depth of cut. Owing to process of polishing has bad influence on reflection angle, surface roughness, $R_{max}$=10nm, and form error, $Ra={\lambda}/10({\lambda}=632nm)$, are prerequisites for polygon mirror.

• 복식
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• 제53권1호
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• pp.67-75
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• 2003

From ancient times. lotus pattern had esthetic factor and symbolic factor. Lotus pattern was introduced to China, and it was grafted together with Chinese peculiar culture symbol system, thereafter it has changed and developed. The Chinese taking a serious view meaning that things include, and they frequently use several lucky omen patterns in their everyday life. In this study, I investigated laying stress on symbolism about Lotus patterns of China lucky omen patterns, and I wanted to present possibility that can approach to Chinese culture in new angle. Through result of this study, symbol of Lotus patterns can divide two directions. First, symbol by natural properties of lotus are same as following. 1. Lotus grows in the mud, but it is uncontaminated - clearness and uprightness, 2. Root, branches, loaves and flowers are vegetative together, and all of basis and branches are exuberant. - plenty, 3. Bear fruit simultaneously with blooming, and it is procreant. - fecundity and many descendants. Symbol that use same pronunciation and intention are same as following. 1. 'Lian(연)'-'Lian(연)' : repeatability, continuance, plenty and intercommunicate, 2. 'Lian(연)'-'Lian(염)': integrity, 3. 'He (하)'-'He(화)' : peace, harmony and combination, 4. 'He(하)'-'He(하)' : clear river, 5.'He(하)'-'He(하)' ; all work goes well. When the Chinese use lotus patterns in lucky omen patterns, same pronunciation and pitch of Chinese language more prominent than natural properties or the image of Buddhism. I guess that it cause praying individual's peace and happiness more serious than philosophical meaning or symbol that base in Buddhism for ordinary people.

• 대한기계학회논문집
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• 제16권4호
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• pp.649-657
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• 1992

본 연구에서는 스테핑 모터의 토크특성과 전동시스템의 미스얼라인 먼트에 의 한 플리편심을 고려하여 스페핑 모터 구동 타이밍벨트 전동시스템의 전동오차에 관한 이론 및 실험적 연구를 수행하고, 전동오차 감소를 위한 설계 개선 기초자료를 얻고자 한다.

• Journal of Advanced Marine Engineering and Technology
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• 제30권2호
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• pp.275-283
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• 2006

Experiment and three dimensional numerical investigations of incompressible turbulent flow through square channels with one- and two-sided ribbed walls are performed to determine pressure drop and heat transfer. The CFX(version 5.7) software package is used for the computation. The ribbed walls have a $45^{\circ}$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The numerical results coincide with experimental data that obtained for $7,600{\le}Re{\le}24.900$, the pitch-to-rib height ratio (p/e) of 8.0. and the rib height-to-channel hydraulic diameter ratio ($e/D_h$) of 0.0667. The results show that values of local heat transfer coefficient and friction factor in the channel with two-sided ribbed wall are higher than those in the channel with one-sided ribbed walls.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.260-267
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• 2001

The objective of this study was to investigate the characteristics of jet flow and heat transfer caused by trapezoid rods array in impinging jet system. In this study, trapezoid rods have been set up in front of flat plate to serve as a turbulence promoter. The bottom width of trapezoid rod was W=4, 8mm and oblique angle were $80^{\circ}$. The space from rods to the heating surface was C=1, 2, 4mm, the pitch between each rods was P=30, 40, 50mm, and the distance from nozzle exit to flat plate was H=100, 500mm. This results were compared with the case without trapezoid rods. As a result, when rods are installed in front of the impinging plate, the acceleration of the jet flow and the eddies due to the rods seem to contribute to the heat transfer enhancement. Among test conditions, the heat transfer performance was best for the condition of W=8mm, C=1mm, P=30mm and H/B=10. The maximum heat transfer rate is about 1.9 times larger than that without trapezoid rods.