• Proceedings of the Korea Water Resources Association Conference
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• 1995.05a
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• pp.67-72
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• 1995

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4B
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• pp.725-733
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• 2000

In this paper, we propose a modified boundary block merging technique for the texture coding of MPEG-4. We propose an ORP(Optimized Region Partitioning) method that partition the VOP-based reference position to minimize the number of coding blocks. The merging possibility is improved by adding +90。and -90。 Rotation merging. We propose a MRM(Multiple Rotation Merging) method which applies the rotation merging in the order of 180。, +90。and -90。. If a pair of boundary blocks has low correlation, existing BBM's padding technique is not efficient. Our padding after merging method gives better result even if it has low correlation. The proposed method showed 5 ~8(%) coding bit reduction at the same PSNR values compared to BBM method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1829-1834
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• 2006

In this raper in order to recover sharp object boundaries we propose a new efficient stereo matching algorithm in which window size is varied to the distance from the boundaries of object. To this end, the processing region is divided into small subregions with a same area and the disparities of the center pixels in the subregions are calculated using a area-based algorithm with multiple windows. From the this disparity map we can find the edges of the contracted objects. The disparities of original image are obtained using the gradient constraint that means the disparity of the center pixel is similar to the ones of the remaining pixels in the subregion. from the experimental results it is found that the proposed algorithm is very good for recovering sharp object boundaries compared to the similar different algorithm.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.429-435
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• 2007

The present study proposed a method fer simulating reflective boundary conditions in Boussinesq wave propagation model by lining lateral boundaries like breakwaters and seawalls with artificial sponge layers. In order to find out the reflective characteristics of sponge layers, 1D numerical experiments were performed varying the relative sponge width (sponge width/wave length). The results showed that the reflection coefficient can be effectively realized from no reflection to full reflection simply by adjusting the relative sponge width. Based on the results, a multiple regression formula was proposed to delineate the relationship among the reflection coefficient and other dimensionless variables. Finally, the reflective sponge layer was applied to a semi-infinite breakwater, demonstrating that it can also be successfully employed in 2D applications.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.89-99
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• 1998

한국형 차세대원자로에서는 비상노심 안전주입수가 저온관을 통하지 않고 원자로용기에 직접 주입된다. 원자로용기의 가압열충격과 열수력적 관점에서 최적의 노즐위치를 결정하기 위해서 전산유체역학을 활용하였다. 상용 전산유체코드인 CFX를 이용하여 원자로 하향유로를 모사하는 해석대상 격자를 다중불록으로 형성한 다음 유동장을 비압축성 Navier-Stokes 운동량 방정식, 에너지 방정식과 표준 k-ε 난류모형 등으로 모형화하여 3차원 비정상상태 계산을 수행하였다. CFX에서는 경계 밀착좌표계, 비엇물림격자와 SIMPLE 알고리즘을 사용한다. 본 연구결과 원자로용기의 가압열충격 관점에서 가장 보수적인 사고인 증기관 파단사고시에도 열적혼합이 잘 일어나 가압열충격이 발생할 가능성이 없는 것으로 판단되며 안전주입수 노즐이 저온관 바로 위에 위치할 때 원자로 하향유로 내의 온도 분포가 가장 균일하여 열적 혼합 관점에서는 최적의 위치로 판단된다.

• The Journal of the Acoustical Society of Korea
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• v.31 no.1
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• pp.11-18
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• 2012

In this paper, the occurrence of a stopband phenomenon when an acoustic wave propagates through periodically corrugated ducts is discussed using theoretical and BEM analyses. A 2-D duct with sinusoidally corrugated upper and lower walls is considered. When the magnitude of the sinusoidal corrugation is sufficiently small compared to the duct's height, the wave equation is solved with the multiple scaling perturbation method. Then stopbands for Bragg and non-Bragg resonances are computed from the condition where frequency becomes a complex number. A 2-D BEM analysis is performed to compute insertion loss of the duct, and stopbands are confirmed as predicted by analytical analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1878-1885
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• 1999

Ultrasonic technique which is one of the most common nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristic of scattering sign al from internal defects. Therefore, a numerical analysis of ultrasonic scattering field due to defect profiles is absolutely needed for the accurate, quantitative estimation of internal defects. In this paper, the SH-wave scattering by multi-cavity defects and inclusion using Elastodynamic Boundary Element Method is studied. The effects of shape and distance of defects on transmitted and reflected fields are considered. The interaction of multi-cavity defects in SH-wave scattering is also investigated. Numerical calculations by the BEM have been carried out to predict near field solution of scattered fields of ultrasonic SH-wave. The presented results can be used to improve the detection sensitivity and pursue quantitative nondestructive evaluation for inverse problem.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.45-52
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• 2005

Recent observations based on geological evidence and laboratory tests confirm that complex segmentation of hydraulic fractures is common phenomena. It is expected that the segmentation causes mechanical interaction between the fractures and affects fracture opening and measured net pressure. In this study, therefore, the opening of the fractures is computed using boundary collocation method to evaluate the mechanical interaction quantitatively. Also, improved boundary collocation method is suggested to evaluate the displacement of the fracture wall accurately and the reliability of this method is confirmed by comparing with that of the finite element method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.9
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• pp.805-815
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• 2010

This paper studies the influence of internal moving fluid and flow-induced structural instability of multi-wall carbon nanotubes conveying fluid. Detailed results are demonstrated for the variation of natural frequencies with flow velocity, and the flow-induced divergence and flutter instability characteristics of multi-wall carbon nanotubes conveying fluid and modelled as a thin-walled beam are investigated. Effects of various boundary conditions, Van der Waals forces, and non-classical transverse shear and rotary inertia are incorporated in this study. The governing equations and three different boundary conditions are derived through Hamilton's principle. Numerical analysis is performed by using extended Galerkin's method which enables us to obtain more exact solutions compared with conventional Galerkin's method. This paper also presents the comparison between the characteristics of single-wall and multi-wall carbon nanotubes considering the effect of van der Waals forces. Variations of critical flow velocity for different boundary conditions of two-wall carbon nanotubes are investigated and pertinent conclusion is outlined.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.5
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• pp.440-446
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• 1996

The multiple-ridged circular waveguides is analyzed using Fourier series and the mode matching technique. The enforcement of the boundary conditions yields the simultaneous equations for the field coefficient inside the waveguides. The simultaneous equations are solved to represent a dispersion relation in an analytic series form. The numerical computation is performed to illustrate the behavior of the cutoff wavenumbers in terms of number, length and angle of ridges. The presented series solution is exact and rapidly-convergent so that it is efficient for numerical computation. A simple dispersion relation based on the dominant mode analysis is obtained and is shown to be very accurate for most practical applications.