• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.700-712
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• 1997

The flowfield generated by a 2-D rotating cylinder on a plane moving at freestream velocity was experimentally investigated in a wind tunnel to simulate aerodynamic characteristics of rotating wheels of an automobile. In the flowfield around a rotating cylinder at 3*10$^{3}$ < Re$_{d}$<8*10$^{3}$, unique mean flow and turbulence characteristics were confirmed by hot-wire measurements as well as frequency analysis, which was supported by flow visualization. In the vicinity of a rotating cylinder, a unique turbulence structure on .root.over bar u'$^{2}$ profiles was formed in hump-like shape at 1 < y/d < 3. A peak frequency which characterized the effect of a rotating cylinder had the same value of the rotation rate of a cylinder. In case of cylinder rotation, the depths of mean velocity -defect and turbulent-shear regions were thickened by 20-40% at 0 < x/d < 10 compared with the case of cylinder stationary. Far downstream beyond x/d > 10, the flowfield generated by a rotating cylinder showed self-similarity in the profiles of mean velocity and turbulence quantities. The effect of a rotating cylinder was independent of its rotation rate and Reynolds number in the measurement range.

• Journal of Power System Engineering
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• v.13 no.4
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• pp.24-30
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• 2009

본 연구에서는 기존에 널리 사용되어져 온 Wavier-Stokes 방정식을 풀이하는 전통적인 CFD 해석에서 벗어나 최근에 그 응용 분야를 넓혀가고 있는 LBM의 해석코드를 개발하고, 이를 이용하여 이차원 채널속에 놓여진 쇄기형 물체 주위의 유동특성을 조사하였다. D2Q9 격자계 및 Bhatnagar-Gross-Krook (LBGK) 모델을 채택하였으며, 수치해석 결과는 기존의 실험결과의 잘 일치하였다. 쇄기형 물체에서 와의 형성 및 방출 Reynolds 수 범위는 $32{\leq}Re{\leq}620$ 이며, 원형실린더에서 알려진 Karman 와열을 형성하는 주기적인 와방출은 대칭적인 와가 형성된 후 $Re{\geq}85$부터 시작되며 Reynolds 수의 증가에 따라 와 방출 주파수는 증가되었다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.337-344
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• 2000

The wavelet analysis technique is applied in the spectral domain to efficiently represent the multi-scale features of the impedance matrices. In this scheme, the 2-D quadtree decomposition (applying the wavelet transform to only the part of the matrix) method often used in image processing area is applied for a sparse moment matrix. CG(Conjugate-Gradient) method is also applied for saving memory and computation time of wavelet transformed moment matrix. Numerical examples show that for rectangular cylinder case the non-zero elements of the transformed moment matrix grows only as O($N^{1.6}$).

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.6
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• pp.541-548
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• 2000

An area light source in the three dimensional space shines past a scene polygon, to generate two types of shadow volumes for each scene polygon, i.e., one with partial occlusion and the other with the complete occlusion. These are called, penumbra and umbra, respectively. In this paper, consider the problem for computing the umbra of a convex polygon from convex quadric light sources such as circles, ellipses, spheres, ellipsoids and cylinders. First, we give characteristics of the boundary surfaces of the umbra and then propose an algorithm for generating the umbra using them.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.1-8
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• 2001

With uniform heat generation within the wall of the cylinder placed in a cross flow, heat flows by conduction in the circumferential direction due to the asymmetric nature of the fluid flow around the perimeter of the cylinder. The circumferential heat flow affects the wall temperature distribution to such an extent that in some cases significantly different results may be obtained for geometrically similar surfaces. In the present investigation, the effects of circumferential wall heat conduction on local convective heat transfer is investigated for the case of forced convection around horizontal cylinder in cross flow of air. Two-dimensional temperature distribution $T_w$/(${\gamma}$,${\theta}$) is presented through the numerical analysis. The one-dimensional and two-dimensional solutions are in good agreement with experimental results of local heat transfer coefficients.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.56-63
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• 1985

Methods for evaluating the added masses of square and hexagonal structures with fluid gap are presented. For a sufficiently small fluid gap, an analytical expression for the added mass is found using the method of matched asymptotic expansion. Experimental data and numerical results using finite element method are also obtained for various sizes of fluid gap. It is shown that added masses increase in inverse proportion to the fluid gap as it becomes smaller. Experimental data, theoretical and numerical results are in good agreement.