• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.252-263
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• 1997

Steady-state two-dimensional natural convective heat transfer in horizontal cylindrical annuli was studied by solving the governing equations based on the primitive variables. Emphasis was put on the occurrence of the multiple solutions at a given set of parameter values, and on the determination of the bifurcation points at which those multiple solutions begin to branch out. The multicellular flow pattern from the results of melting process in an isothermally heated horizontal cylinder for high Rayleigh numbers, was used as initial guesses for the field variables. This was succeeded in new bifurcation point to tetracellular solutions for an identical set of parameter variables of previous works. The close examination of flow pattern transition around bifurcation point was also conducted. It was found that the mechanisms of flow transition are different depending on the critical Rayleigh number of bifurcation point.

• Journal of Energy Engineering
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• v.11 no.4
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• pp.299-305
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• 2002

The present experimental and numerical investigations are performed on the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully devel-oped flow of water and that of 0.2％ CMC-water solution at a inner cylinder rotational speed of 0∼600 rpm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually decreased for turbulent flow regime.

• Journal of KSNVE
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• v.11 no.3
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• pp.428-436
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• 2001

The rotating inner cylinder executes a periodic translational motion in concentric annulus while the outer one is stationary. In the study of flow-induced vibrations and relaxed instabilities, it is of interest to evaluate the fluid-dynamic forces acting on the rotating inner cylinder. In the present work, the governing equations for the confined flow are expressed as Navier-Stokes equations, including the steady and unsteady terms. The fluid parameters for steady flow generated by the rotating cylinder are determined analytically while the unsteady ones by the oscillatory motion are evaluates by a numerical method based on the spectral collocation method. In order to validate the numerical approach, the numerical results are compared wish the analytical ones given by existing theories, for simple cases where the both approaches are applicable. Good agreement was found between the results. It is found the effects of the Reynolds number, defined by rotating velocity, on the fluid-dynamic forces are important for the case of relatively low oscillatory Reynolds number, defined by oscillatory frequency : j.e., in case of $Re_\omega\gg Re_S$.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.19-22
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• 2005

As the optical communication industry is developed, the demand of optical communication part is increasing. $ZrO_2$ ceramic ferrule is very important part which can determines the transmission efficiency and information quality to connect the optical fibers. In general $ZrO_2$ ceramic ferrule is manufactured by grinding process because the demands precision is very high. And the co-axle grinding process of $ZrO_2$ ceramic ferrule is to make its concentricity all of uniform before centerless grinding. When co-axle grinding of ferrule supported by two pin, pin chucking alignment accuracy is very important. This paper deals with the analysis of the chucking alignment experiment with parallel error on the micro feeding equipment. Thus, if possible be finding highly good the chucking alignment of two pin.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.516-519
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• 2004

As the optical communication industry is developed, the demand of optical communication part is increasing. ZrO$_2$ ceramic ferrule is very important part which can determines the transmission efficiency and information quality to connect the optical fibers. In general ZrO$_2$ ceramic ferrule is manufactured by grinding process because the demands precision is very high. And the co-axle grinding process of ZrO$_2$ ceramic ferrule is to make its concentricity all of uniform before centerless grinding. This paper deals with the analysis of the process parameters such as grinding wheel speed, grinding feedrate and regulating wheel speed as influential factors, on the concentricity and surface finish developed based on Taguchi's experimental design methods. Taguchi s tools such as orthogonal array, signal-to-noise ratio, factor effect analysis, etc. have been used for this purpose optimal condition has been found out. Thus, if possible be finding highly efficient and quality grinding conditions.

• Computational Structural Engineering
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• v.3 no.3
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• pp.141-146
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• 1990

This study is on a seismic analysis of absorber rod in KMRR Reactivity Control Mechanism. The model being studied is two coaxial tubes(control absorber rod and flow tube) immersed in the water and partially coupled(overlap) by water gap. The hydrodynamic mass effects by the water in each surrounding conditions are considered in the model. The natural frequencies, stresses and displacements of the system due to Safe Shutdown Earthquake are computed in the cases of in-phase modes and out-of-phase modes of two coaxial tubes. The results show that maximum stresses are well below the allowable limit but the maximum displacements at the ends of both tubes are so much that the absorber rod contacts with the flow tube(or surrounding wall).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1108-1118
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• 2009

A Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source of the order of $950^{\circ}C$ for nuclear hydrogen generation, which can produce hydrogen from water or natural gas. A primary hot gas duct (HGD) as a coaxial double-tube type cross vessel is a key component connecting a reactor pressure vessel and an intermediate heat exchanger in the VHTR. In this study, a structural sizing methodology for the primary HGD of the VHTR is suggested in order to modulate a flow-induced vibration (FIV). And as an example, a structural sizing of the horizontal HGD with a coaxial double-tube structure was carried out using the suggested method. These activities include a decision of the geometric dimensions, a selection of the material, and an evaluation of the strength of the coaxial double-tube type cross vessel components. Also in order to compare the FIV characteristics of the proposed design cases, a fluid-structure interaction (FSI) analysis was carried out using the ADINA code.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.1
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• pp.8-15
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• 2005

This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and $0.2\%$ aqueous of sodium carboxymethyl cellulose(CMC), respectively, when the inner cylinder rotates at the speed of $0\~500$ rpm. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. This study shows the change of skin friction coefficient and wall shear stress corresponding to the variation of rotating speed of the inner cylinder, radius ratio, eccentricity, and working fluids.

• Korean Journal of Applied Biomechanics
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• v.16 no.3
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• pp.75-83
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• 2006

The purpose of this study was to investigate steady-state force depression following active muscle shortening in human tibialis anterior muscle during voluntary contractions. Subjects (n = 7; age $24{\sim}39$ years; 7 males) performed isometric reference contractions and isometric-shortening-isometric contractions, using maximal voluntary effort. Force depression was assessed by comparing the steady-state isometric torque produced following active muscle shortening with the purely isometric reference torque obtained at the corresponding joint angle. In order to test for effects of the shortening conditions on the steady-state force depression, the speed of shortening were changed systematically in a random order but balanced design. Ankle dorsiflexion torque and joint angle were continuously measured using a dynamometer. During voluntary contractions, muscle activation of the tibialis anterior and the medical gastrocnemius was recorded using surface electromyography. Force depression during voluntary contractions, with a constant level of muscle activation, was 12 %, on average over all subjects. Force depression was independent of the speeds of shortening ($13.8{\pm}2.9%$, $10.3{\pm}2.6%$ for 15 and 45 deg/sec over 15 deg of shortening, respectively). The results of this study suggest that steady-state force depression is a basic property of voluntarily-contracting human skeletal muscle and has functional implication to human movements.

• Vending industry
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• v.8 no.3
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• pp.66-69
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• 2008

"자판기는 왜 네모나기만 하지?" "자판기는 왜 단순 물품판매 기능만 있는 거지? 다른 기능들이 있어도 좋을 텐데..." 단지 호기심어린 동심의 시각만이 아니더라도 이런 궁금증 한번 가져 봤을 법하다. "왜? 왜"하며 고개를 갸우뚱하게 만든다는 것은 그만큼 '블루오션'의 영역도 넓다는 얘기이다. 자판기의 경우 누구도 한계영역을 규정지어 놓은 것도 아닌데 '단순 물품판매 기능'에다 '획일적인 디자인'에 묶여 있는 게 보통이다. 새로운 시각으로 자판기를 다기능화하려는 선각자적인 시도들은 무모한 도전으로 규정지어지기 일 수이고, 이런 환경에서 자판기는 자기 복제만 되풀이 할 뿐 별다른 발전이 없게되는 상황에 이른다. 무궁무진한 아이디어 지향적이라는 특성을 장점으로 하는 자판기가 '단순 획일화'의 벽을 뛰어 넘지 못하는 게 안타깝다. 해법은 자판기 상상력이 충분히 발현될 수 있는 시장환경이 조성되어야 한다는 점이다. 지금 당장만 중시하는 단기적 시장논리로 자판기 가능성의 싹을 죽여 버리는 토양에서 혁신이 일어나기란 정말 힘들다. 이런 점에서 볼 때 금호에 소개하는 지문인식 광고 커피자판기가 시사하는 바가 크다. 핵심은 이제 이런 제품에 대한 관심이 높아졌으면 하는 점이다. 허무맹랑하다고? 사업리스크가 크다고? 이런 선입견을 가지고 새로운 가치를 원천적으로 차단해 버린다면 자판기는 항상 '그 모양 그 꼴' 일수밖에 없다. 새로운 시장을 만들고 발전시키는 것은 항상 무모할 것 같은 도전에서 나온다. 이번에 소개되는 지문인식 광고 커피자판기는 현재 한 개인의 사업모델이기는 하지만 새로운 미래형 자판기 트랜드가 될 수 있다는 점을 주목했다. 단지 개인의 발명차원의 사업모델을 소개하는 이유가 여기에 있다. 자판기의 새로운 가치를 찾고 영역을 확대한다는 측면에서 한번 머리를 '릴렉스'하게 해보자. 자판기 분야에 전혀 경험도 없지만 뜨거운 열정으로 지문인식 광고자판기를 특허 출원한 벤처 청년 황고연이 제시하는 "자판기 상상력"의 세계를 따라가 봤다.