• 설비공학논문집
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• 제12권2호
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• pp.150-160
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• 2000

Turbulent natural convective flow and heat transfer in a square enclosure with horizontal partition are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. Partitions carried with the upward, downward, and both control plates are attached perpendicularly to the one of the vertical insulated walls, respectively. The low Reynolds number $k-\varepsilon$ model is adopted to calculate the turbulent thermal convection. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of partition, the position of control plates, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for water(Pr=4.95). When the control plates are attached at the edge of partition, the stability of oscillating flow grows wrose with the increase of Rayleigh number and the partition length. The heat transfer rate has been reducer than that of no control plate due to the restraint of control plates with the increase of Rayleigh number.

• Steel and Composite Structures
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• 제10권4호
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• pp.297-315
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• 2010

This paper is concerned with free vibration characteristics and natural frequency of horizontally curved composite plate girder bridges. Three-dimensional finite element models are developed for the girders using the software package LUSAS and analyses carried out on the models. The validity of the finite element models is first established through comparison with the corresponding results published by other researchers. Studies are then carried out to investigate the effects of total number of girders, number of cross-frames and curvature on the free vibration response of horizontally curved composite plate girder bridges. The results confirm the fact that bending modes are always coupled with torsional modes for horizontally curved bridge girder systems. The results show that the first bending mode is influenced by composite action between the concrete deck and steel beam at low subtended angle but, on the girders with larger subtended angle at the centre of curvature such influence is non-existence. The increase in the number of girders results in higher natural frequency but at a decreasing rate. The in-plane modes viz. longitudinal and arching modes are significantly influenced by composite action and number of girders. If no composite action is taken into account the number of girders has no significant effect for the in-plane modes.

• 설비공학논문집
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• 제3권4호
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• pp.222-230
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• 1991

Conjugate heat transfer by steady laminar natural convection from a conducting tube with two vertical axial fins has been studied by a finite difference numerical procedure under basic conditions; $Ra=10_6$, Pr = 5 and $L_F=0.15$. The maximum local tube Nusselt number appears at ${\theta}=140^{\circ}$ for $L_F=0.06$, at ${\theta}=130^{\circ}$ for $L_F=0.30$ and at ${\theta}=120^{\circ}$ for $L_F=0.30$, $L_F=0.06$, respectively. The maximum mean Nusselt number shows at $L_F=0.18$ for the downward fin and at $L_F=0.12$ for the upward fin. Therefore the optimized fin length is $L_F{\approx}0.15$ under these conditions. At $L_F=0.15$, the mean Nusselt number by increasing Rayleigh number is remarkably increased for downward fin and then is slowly increased except for downward fin, it by increasing Prandtl number is apparently increased at $Pr{\leq}2$, and slightly increased at Pr>2.

• 한국초등수학교육학회지
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• 제21권1호
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• pp.195-214
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• 2017

표준화된 자연수 곱셈 알고리즘3)은 곱셈의 계산 과정을 간략화한 것으로, 올림이 있는 자연수 곱셈의 경우 올림하는 수를 피승수의 위에 작게 표기하고 있다. 하지만 이러한 올림하는 수 표기 방식은 승수가 한 자리 수인 경우에만 교과서에 제시되고 있어, 승수가 두 자리 수인 경우에는 교사와 학생들이 자기 나름의 표기 방식을 선택하도록 요구하고 있다. 이에 본 연구는 현행 교과서에서의 올림이 있는 자연수 곱셈의 알고리즘 접근 방법을 살펴보고, 3, 4, 5, 6학년 학생들의 올림이 있는 자연수 곱셈 알고리즘에서 나타나는 올림하는 수 표기 방식을 분석하였다. 또한, 핀란드 수학 교과서와 선행 연구에 나타난 올림이 있는 자연수 곱셈 알고리즘 지도 내용을 분석함으로써 자연수 곱셈 알고리즘의 제시 방법에 대한 시사점을 추출하였다. 그 결과로 다음과 같이 제안한다. 첫째, 교사용 지도서나 교과서에 올림하는 수를 표기하는 방법에 대한 예시가 필요하다. 둘째, 올림하는 수를 체계적으로 표기하는 것의 좋음을 학생이 인식하도록 지도되어야 한다. 셋째, 대안적인 자연수 곱셈 알고리즘과 올림하는 수 표기 방법에 대한 교사의 이해가 요구된다.

• 대한기계학회논문집B
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• 제20권9호
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• pp.2981-2990
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• 1996

Dual solutions for steady natural convection of air between two horizontal concentric cylinders are numerically investigated in the range of $D_i$/TEX>/L(=diameter of inner cylinder/gap width)$\leq$10. It is found that, when the Rayleigh number based on the gap width exceeds a certain critical value, a new flow pattern forming two counter-rotating eddies in the half of the annulus can be realized, which is different from the crescent-shaped flow commonly observed. In the new flow pattern, the fluid near the top of the hot inner cylinder moves downward. This solution is found for D$_{i}$/L.geq.0.3, but not for$D_i$/TEX>/L$\leq$0.2. As $D_i$/TEX>/L increase, the critical Rayleigh number is decreased, and tends to a finite limit.t.

• 설비공학논문집
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• 제6권3호
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• pp.259-266
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• 1994

Natural convection within a wedge-shaped enclosure has been studied numerically by finite difference method. Radial surfaces of the wedge are isothermally hot and cold while circumferential surfaces are insulated. Results show isotherms, streamlines and velocity profiles as well as Nusselt number distributions for a Rayleigh number range of $10^3$ to $10^5$. In addition, it is found that there is a wedge angle as shown the minimum mean Nusselt number for using an insulated enclosure.

• Journal of Advanced Marine Engineering and Technology
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• 제22권6호
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• pp.844-853
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• 1998

Natural and forced convection experiments were carried out in order to investigate the effects of channel spacing gap between protrusions and number of rows of protrusion, In natural convection the optimum channel spacing was found to be approximately 20mm regardless of the protrusion gaps. For optimum channel spacing the heat transfer coefficients were converged to an asymptotic value after the fourth row. The heat transfer coefficient for each row approaches to constant values for protrusion gaps larger than 10 mm. An experimental correlation has been suggested by using a modified Rayleigh number based on the dimensionless characteristic length(G/L). In forced convec-tion the heat transfer coefficients were not merged to an asymptote until the fifty row and increases as the channel spacing at the constant Reynolds number decreases.

• 대한기계학회논문집
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• 제19권11호
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• pp.3072-3083
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• 1995

The numerical simulation on the three-dimensional natural convection heat transfer in the enclosure with heat generating chip is performed, and the effects of convective heat loss and vents are also examined. The effects of the Rayleigh number and outer Nusselt number (Nu$_{0}$) on the maximum chip temperature and the fractions of heat loss from the hot surfaces are investigated. The results show that conduction through the substrate is dominant in heat dissipation. With the increase of Rayleigh number, heat dissipation through the chip surfaces increases and heat loss through the substrate decreases. Maximum dimensionless temperature with vents is found to decrease about 40% compared to the one without vents at Nu$_{0}$=0.l. It is also shown that effects of size and location of the vents are negligible.ble.

• 설비공학논문집
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• 제12권8호
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• pp.755-762
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• 2000

Natural convection of air in a horizontal annulus with the inner cylinder cooled by the application of a constant heat flux and the isothermally heated outer cylinder is considered. The bifurcation phenomenon of flow patterns and the heat transfer characteristics are numerically investigated. The zero initial condition induces a unicellular flow in a half annulus. A bicellular flow consisting of two counter-rotating eddies in a half annulus can be obtained above a certain critical Rayleigh number. A transition from the bicellular to the unicellular flow occurs with a decrease in Rayleigh number. Hysteresis phenomena have not been observed. In the regime of dual flows, the overall Nusselt number of the bicellular flow is greater than that of the unicellular flow.

• Clinical and Experimental Reproductive Medicine
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• 제27권3호
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• pp.253-259
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• 2000

Objective: To verify the effect of Matrigel, a ECM complex from Engelbreth-Holm-Swarm (EHS) mouse sarcoma on the preimplantation development and apoptosis of mouse fertilized eggs. Method: Late pronucleus stage eggs were cultured through the blastocyst stage in the presence of Matrigel (0.5%, v/v). Characteristics of apoptosis and cell number assesed by Hoecst staining and TUNEL labeling at the blastocyst stage, respectively. Results: Morphological development, number of cells per embryo was significantly increased but rate and number of TUNEL positive nuclei of the embryo were decreased in the presence of Matrigel. Conclusion: This result suggested that at low concentration of Matrigel improves both viability and morphological development in the preimplantation mouse embryos.