• Proceeding of EDISON Challenge
• /
• 2012.04a
• /
• pp.29-32
• /
• 2012

변장비의 변화가 사각실린더에 작용하는 유체력에 미치는 영향을 알기 위해 EDISON_열유체를 사용하여 수치해석을 하였다. 낮은 레이놀즈수 영역($100{\leq}Re{\leq}200$)에서 사각실린더의 변장비(W/H)를 0.5, 0.75, 1, 2로 변화시키며 해석을 수행하였고, 레이놀즈수와 변장비에 따른 스트로할수(St), 항력계수($C_D$), 양력계수($C_L$)를 비교하였다. 본 논문에서는 레이놀즈수와 실린더의 변장비가 스트로할수, 항력계수, 양력계수에 미치는 영향을 알아보는 데 중점을 두었다. 해석결과 레이놀즈수가 증가하고 변장비가 감소할수록 스트로할수, 항력계수, 양력계수가 증가하는 것을 확인하였다. 본 논문을 통해서 레이놀즈수와 사각실린더의 변장비가 사각실린더에 작용하는 유체력에 영향을 미친다는 것을 알 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.1
• /
• pp.95-103
• /
• 1992

Laminar natural convection heat transfer from an isothermal rectangular beam attached to horizontal and vertical adiabatic plates has been studied for various aspect ratios of the beam and Grashof numbers. The local Nusselt number was increased with decreasing H/B for the constant beam width, B, and with increasing H/B for the constant beam height, H. The total mean Nusselt number of the vertical type was higher than that of horizontal type in the range of H/B.leq.0.52, but reversed in the H/B>0.52 at constant beam width. The total mean Nusselt number of the horizontal type was generally higher than that of vertical type at constant beam height. The total mean Nusselt number of the vertical type was higher than that of horizontal type in the range of H/B.leq.0.43 at constant wetted perimeter, but reversed in the H/B$\leq$0.43.

• Solar Energy
• /
• v.10 no.1
• /
• pp.22-30
• /
• 1990

Steady laminar natural convection heat transfer from a square beam with a horizontal adiabatic plate has been studied numerically for various Grashof numbers and beam shapes. The heat transfer from a square beam increases as the dimensionless beam width W / L decreases. The mean Nusselt number of the upper surface is minimum at W / L = 1.0, maximum at W / L = 0.25 and that of the side surface is minimum at W / L = 0.25, maximum at W / L = 1.0. The increases of the total mean Nusselt number with increasing Grashof number is dominated by the beam width.

• Composites Research
• /
• v.27 no.2
• /
• pp.37-41
• /
• 2014

Fiber reinforced composite materials have outstanding specific strength and specific stiffness. So the use of composite materials increases in various kinds of industrial fields including sports goods such as bicycles. Composite materials are used to make structural parts with various kinds of shapes. Specially, rectangular composite tubes are used to make a few of composite bicycle frames, but there has been a few of research on this issue. Rectangular composite tubes are designed to have appropriate radius of curvature and endure bending and torsional loads. In this research, nine kinds of rectangular composite tubes having aspect ratios 1:1, 1:1.5, 1:2 and radius of curvatures R5, R10, R15 were fabricated. The carbon fiber reinforced composite material was used to make tubes having same cross sectional areas. The stacking sequence of tubes is $[0/90/{\pm}45]s$. Experimental evaluation was accomplished to apply bending and torsional load to the tubes. Experimental results show that bending and torsional characteristics depend on radius of curvature and aspect ratio of rectangular composite tubes.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.6
• /
• pp.16-22
• /
• 2004

Unsteady vortex shedding behind a rectangular cylinder near a wall influences both increasing of drag and dynamic stability of heavy vehicle, bridge or building. Incompressible Averaged Navier-Stokes equation with modified ${\varepsilon}-SST$ turbulence model is adapted for investigating the flow field between the rectangular cylinder and the wall. In case the vortex shedding happens, not only the averaged maximum velocity is higher than other cases, but the position of the maximum velocity is closer to the lower surface of rectangular cylinder. On this study, it is confirmed that the vortex shedding behind a rectangular cylinder can be suppressed by the passive control method added by horizontal and vertical fences to the lower surface of rectangular cylinder.

• Solar Energy
• /
• v.11 no.2
• /
• pp.63-69
• /
• 1991

A Steady laminar natural convection heat transfer from two isothermal square beams attached to a vertical adiabatic plate has been studied numerically. The results have been obtained for dimensionless beam spacings, $0.5{\le}D/L{\le}3.0$, and for Gr=5000-10000 at ${\phi}_2/{\phi}_1=1.0$. 1. The local Nusselt number from the beam surface is increased with the dimension-less beam spacing D/L. but that of the downward surface of the lower beam is almost same as the D/L increases. And, the local Nusselt number from the upward surface of a lower beam is greatly increased with D/L. 2. The beam spacings of the maximum mean Nusselt number for the downward surface of an upper beam and the upward surface of a lower beam occur at. D/L =2.6 and 2.0 respectively. 3. The beam spacing for the maximum total mean Nusselt number occurs at D/L = 2.6.

• Korean Journal of Social Welfare Studies
• /
• no.39
• /
• pp.287-314
• /
• 2008

This paper tests the stigma hypothesis and administration hypothesis on the illegal take-up group and non take-up group in the National Livelihood Security Program. A set of survey data, using multinomial logistic model, was analyzed for this purpose. Compared with the legal take-up group, the feature of illegal take-up group which has more workable household supports the administration hypothesis - the low skill of means-test office would increase the possibility of benefit fraud. The features of non take-up group support both the stigma hypothesis - the stigma prevents eligible person from participating in the social assistance program, and the administration hypothesis - the administration office is apt to make error to deny the eligibility of person who has supposed family supporters.

• Journal of Power System Engineering
• /
• v.10 no.1
• /
• pp.25-33
• /
• 2006

거칠기가 한 벽면과 두 벽면에 설치된 사각채널에서 비압축성 유체유동과 열전달을 조사하기위해 3차원 수치모사를 행하였다. CFX (version 5) software package 를 사용하여 계산하였다. 거친 벽은 $45^{\circ}$경사진 거칠기가 설치되어 있다. 채널의 4 벽면은 일정한 열 유속으로 가열하였다. 수치계산 결과는 실험값과 잘 일치 하였다. 연구의 조건은 거칠기 피치와 높이의 비가 8이고, 거칠기 높이와 채널 수력직경의 비가 0.067이며, 레이놀즈수의 범위는 7,600에서 24,900이었다. 연구의 결과는 열전달계수와 마찰계수는 사각채널에서 거친 벽면의 수가 클수록 증가 함을 보였다.

• Composites Research
• /
• v.20 no.3
• /
• pp.8-16
• /
• 2007

Bending collapse of light-weight square tubes used for vehicle structure components is a dominant failure mode in oblique collision and rollover of vehicles. In this paper bending performances of aluminum-GFRP hybrid tube beams were evaluated in relation with bending deformation behavior and energy absorption characteristics. Aluminum/GFRP hybrid tube beams fabricated by inserting adhesive film between prepreg and metal layer were used in the bending test. Failure mechanisms of hybrid tubes under a bending load were experimentally investigated to analyze the bending performance as a function of ply orientation and composite layer thickness. Ultimate bending moments and energy absorption capacity of hybrid tube beams were obtained from the measured load-displacement corves. It was found that aluminum/GFRP hybrid tubes could be converted to rather stable collapse mode showing excellent energy absorption capacity in comparison to the pure aluminum tube beams. In particular, the hybrid tube beam with $[0^{\circ}/90^{\circ}]s$ composite layer showed a large improvement by about 78% in energy absorption capacity and by 29% in specific energy absorption.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.8
• /
• pp.91-100
• /
• 2004

A Green's function approach is adopted for analyzing the thermoelastic deformations and stresses of a plate made of functionally graded materials(FGMs). The solution to the 3-dimensional unsteady temperature is obtained by using the laminate theory. The fundamental equations for thermoelastic problems are derived in terms of out-plane deformation and in-plane force, separately. The thermoelastic deformation and the stress distributions due to the bending and in-plane forces are analyzed by using a Green's function based on the Galerkin method. The eigenfunctions of the Galerkin Green's function for the thermoelastic deformation and the stress distributions are approximated in terms of a series of admissible functions that satisfy the homogeneous boundary conditions of the rectangular plate. Numerical analysis for a simply supported plate is carried out and effects of material properties on unsteady thermoclastic behaviors are discussed.