• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 추계학술대회 논문집 학회본부
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• pp.385-387
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• 1994

Optical interconnections are more attractive than electronic interconnections because of their higher speed, freedom from planar constraints, immunity to electromagnetic interference effects and higher interconnection capacity. Volume hologram is one of the best way to implement optical interconnections. Diffraction efficiency and crosstalk effect are very important things for ensuring independent interconnections. Recently, a general systematic method that can handle a large number of superposed volume gratings in anisotropic host material is presented. In this study for numerical analysis of diffraction, above method is programmed in general form near Bragg angle. Diffraction orders for variation of grating strength are determined by comparing with the coupled-mode method. The effects of parameter variation are considered. Parameters include vertical and azimuthal incident angle, wavelength and interaction length. Diffraction analyses are also performed for intra-mode and inter-mode diffractions.

• 한국콘텐츠학회논문지
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• 제10권6호
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• pp.1-9
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• 2010

최근 들어, 3D 입체 영화와 TV 등 3차원 입체 영상 디스플레이에 대한 관심이 매우 높다. 안경을 끼는 불편함을 해결하기 만들어진 무안경식 3차원 입체 영상 디스플레이를 위해서는 렌즈 어레이 카메라로부터 만들어지는 기초영상(elemental images)을 생성해야 한다. 렌즈 어레이에 여러 카메라가 배치되므로 주어진 3차원 가상공간에 대해 기초영상을 생성하는데 많은 시간이 소요되며, 특히 고용량의 바이오메디컬 자료에 대해서는 더 많은 시간이 소요된다. 본 논문에서는 이러한 문제를 좀더 효율적으로 개선하기 위해 주어진 자료의 효율적 렌더링을 위해 옥트리(Octree)를 구성한 후, GPU(graphics processor units)를 이용하여 렌더링하는 기법을 제시한다. 실험 결과, 제시된 기법이 기존 방법과 비교하여 많은 개선이 있었지만 아직도 더 효율적인 기법의 개발이 요구된다.

• 한국콘텐츠학회논문지
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• 제11권3호
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• pp.9-17
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• 2011

최근 들어, 안경식 3D TV 등장으로 3D 입체 콘텐츠의 활성화가 기대된다. 안경식의 불편함을 해소하기 위해 무안경식 3차원 입체 영상 디스플레이에 대한 연구가 활발히 진행되고 있다. 이 연구에서 렌즈 어레이(lens array)로부터 만들어지는 기초영상(elemental images)을 생성하는 것이 필수적이다. 그러나 렌즈 어레이를 구성하는 렌즈의 개수가 증가함에 따라 기초영상을 생성하는데 많은 시간이 소요되고 있으며, 고용량의 볼륨데이터에 대해서는 더 많은 시간이 소요되고 있다. 본 논문에서는 이러한 문제를 좀 더 효율적으로 개선하기 위해 CUDA 기반의 OpenCL를 사용하여 집적영상을 생성하는 기법을 제시한다. 제안된 방법을 세 종류인 Tesla C1060, Geforce 9800GT와 Quadro FX 3800 그래픽 카드를 갖는 PC 환경에서 실험하였으며, 실험 결과 최근 연구 결과[11] 보다 약 20배 정도 성능 개선이 있었다.

• 한국콘텐츠학회논문지
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• 제12권6호
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• pp.1-8
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• 2012

대부분 집적영상 기법에서는 사각형 렌즈 어레이가 사용되고 있으며, 이로 인해 집적된 빛의 분포는 사각격자 형태로 기록된다. 그러나 육각형 렌즈 어레이를 사용하면, 사각형 렌즈 어레이보다 더 높은 밀도의 빛의 분포와 이상적인 원형 렌즈에 가깝게 이미지를 기록 또는 재생 할 수 있다[4]. 육각형 렌즈 어레이 요소영상을 병렬 처리 기법을 사용하여 생성하기 위해서는 요소영상을 구성하는 각 화소에 대하여 그 화소가 속할 육각형 렌즈를 결정해야하고, 이 과정은 화면에 출력되는 모든 화소에 대하여 진행 되며 많은 계산량이 요구된다. 본 논문에서는 3D 볼륨 데이터를 사용하여 육각형 렌즈 어레이에 대한 요소영상을 생성하기 위해 OpenCL를 사용한 병렬 처리 기법을 제안한다. 제안 된 방법을 위한 실험에는 Male [$128{\times}256{\times}256$화소] 볼륨데이터를 사용하였으며, 실험 결과 $20{\times}20$개의 육각형 렌즈 어레이에 대해 요소영상을 초당 20~60장 생성할 수 있었다.

• Journal of electromagnetic engineering and science
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• 제8권3호
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• pp.100-109
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• 2008

The finite volume time domain(FVTD) technique faces serious limitations in simulating electromagnetic scattering at high frequencies due to requirements related to discretization. A modified FVTD method is proposed for electrically large, perfectly conducting scatterers by partially incorporating a time-domain physical optics(PO) approximation for the surface current. Dominant specular returns in the modified FVTD method are modeled using a PO approximation of the surface current allowing for a much coarser discretization at high electrical sizes compared to the original FVTD scheme. This coarse discretization can be based on the minimum surface resolution required for a satisfactory numerical evaluation of the PO integral for the scattered far-field. Non-uniform discretization and spatial accuracy can also be used in the context of the modified FVTD method. The modified FVTD method is aimed at simulating electromagnetic scattering from geometries containing long smooth illuminated sections with respect to the incident wave. The computational efficiency of the modified FVTD method for higher electrical sizes are shown by solving two-dimensional test cases involving electromagnetic scattering from a circular cylinder and a symmetric airfoil.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 추계 학술대회논문집
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• pp.47-52
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• 2002

We present an improved Lagrangian vortex method in 2-D incompressible unsteady viscous flows, which is based on a mesh-free integral approach of the velocity-vorticity formulation. Vorticity fields are represented by discrete vortex blobs that are updated by the Lagrangian vorticity transport with the particle strength exchange scheme. Velocity fields are expressed in a form of the Helmholtz decomposition, which are calculated by a fast algorithm of the Biot-Savart integration with a smoothed kernel and by a well-established panel method. No-slip condition is enforced through viscous diffusion of vorticity from a solid body into field. The vorticity flux is determined in such a way that spurious slip velocity vanishes. Through the comparison with the existing finite volume scheme for the transient vortical flows around an impulsively started cylinder at Reynolds number Re=550, we would obtain a more accurate scheme for vortex methods in complicated flows.

• 한국해양공학회지
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• 제1권1호
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• pp.33-38
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• 1987

The first order mation responses of a floating structure and the hydrodynamic forces in regular waves are obtained by means of the linear potential theory. The first order potential is obtained directly from the numerical solution of the improved Green integral equation which is characterized by the combined surface distribution of sources and normal doublets. The mean second order wave drift force is also calculated by means of the near field method. It seems that the present method gives more accurate numerical results than other methods and the agreement between numerical and experimental results appears to be satisfactory.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.15-28
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• 1998

As an alternative for solving the incompressible Navier-Stokes equations, we present a vorticity-based integro-differential formulation for vorticity, velocity and pressure variables. One of the most difficult problems encountered in the vorticity-based methods is the introduction of the proper value-value of vorticity or vorticity flux at the solid surface. A practical computational technique toward solving this problem is presented in connection with the coupling between the vorticity and the pressure boundary conditions. Numerical schemes based on an iterative procedure are employed to solve the governing equations with the boundary conditions for the three variables. A finite volume method is implemented to integrate the vorticity transport equation with the dynamic vorticity boundary condition . The velocity field is obtained by using the Biot-Savart integral derived from the mathematical vector identity. Green's scalar identity is used to solve the total pressure in an integral approach similar to the surface panel methods which have been well-established for potential flow analysis. The calculated results with the present mettled for two test problems are compared with data from the literature in order for its validation. The first test problem is one for the two-dimensional square cavity flow driven by shear on the top lid. Two cases are considered here: (i) one driven both by the specified non-uniform shear on the top lid and by the specified body forces acting through the cavity region, for which we find the exact solution, and (ii) one of the classical type (i.e., driven only by uniform shear). Secondly, the present mettled is applied to deal with the early development of the flow around an impulsively started circular cylinder.

• 천문학논총
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• 제26권1호
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• pp.25-35
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• 2011

A diagnostic tool has been proposed to convert the observed surface distribution of hydrogen recombination line intensities into the radial distributions of the electron temperature and the density in HII regions. The observed line intensity is given by an integral of the volume emission coefficient along the line of sight, which comprises the Abel type integral equation for the volume emission coefficient. As the emission coefficient at a position is determined by the temperature and density of electrons at the position, the local emission coefficient resulted from the solution of the Abel equation gives the radial distribution of the temperature and the density. A test has been done on the feasibility of our diagnostic approach to probing of HII regions. From model calculations of an HII region of pure hydrogen, we have theoretically generated the observed surface brightness of hydrogen recombination line intensities and analyzed them by our diagnostic tool. The resulting temperatures and densities are then compared with the model values. For this case of uniform density, errors in the derived density are not large at all the positions. For the electron temperature, however, the largest errors appear at the central part of the HII region. The errors in the derived temperature decrease with the radial distance, and become negligible in the outer part of the model HII region.

• 한국해양공학회지
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• 제25권2호
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• pp.62-66
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• 2011

In this paper, a liquid-filled long membrane container resting on a horizontal foundation is considered. All of the quantities are normalized to obtain similarity solutions. A system of nonlinear ordinary differential equations with undetermined boundary conditions is solved analytically. The integration of the curvature gives the solutions, which are expressed in terms of the elliptic integrals. A method for finding the shape and characteristic values is proposed for a given cross-sectional volume. The validity of these solutions is confirmed, and some results are shown for characteristic values and shapes.