• Journal of Korea Water Resources Association
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• v.38 no.8 s.157
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• pp.691-698
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• 2005

A series of experiments has been performed to investigate the flapping motion, which has been generally considered as an intrinsic characteristic of plane flow, of the horizontal merging buoyant jet discharged into stationary ambient water. For Horizontal merging buoyant jets, the flapping motions has been observed and the average onsets of flapping motion coincided with the start of merging transition. The Strouhal number, which describes the measure of frequency of vortices on the flow boundary with respect to the local properties of the flow, varies and converges to a constant value over merging transition. Considering the merging transition and the variation of local flow properties, the characteristics of flapping motion of plane flow can be applied to merging buoyant jets.

• Journal of KIISE:Software and Applications
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• v.33 no.10
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• pp.862-867
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• 2006

To restore image degraded by blur and additive noise in the optical and electrical system, a regularized iterative restoration is used. A regularization operator is usually applied to all over the image without considering the local characteristics of image in conventional method. As a result, ringing artifacts appear in edge regions and the noise is amplified in flat regions. To solve these problems we propose an adaptive regularization iterative restoration considering the characteristic of edge and flat regions using directional regularization operator. Experimental results show that the proposed method suppresses the noise amplification in flat regions, and restores the edge more sharply in edge regions.

• Journal of Korea Multimedia Society
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• v.5 no.4
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• pp.399-404
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• 2002

To restore image degraded by motion blur and additive noise, it is very difficult. In conventional restoration method, regularization is usually applied to all over the image without considering the local characteristics of image. As a result, ringing artifacts appear in edge regions and the noise amplification is introduced in flat regions. To solve this problem we propose an adaptive restoration method using directional regularization operator considering edges and the regularization operator with no direction for flat regions. We verified that the proposed method showed better results in the resolution. As a result it showed visually better image and improved better ISNR further than the conventional methods.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.2
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• pp.5-9
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• 2015

Thermal management becomes serious in 3D stacked IC because of higher heat flux, increased power generation, extreme hot spot, etc. In this paper, we reviewed the recent developments of thermal management for 3D stacked IC which is a promising candidate to keep Moore's law continue. According to experimental and numerical simulation results, Cu TSV affected heat dissipation in a thin chip due to its high thermal conductivity and could be used as an efficient heat dissipation path. Other parameters like bumps, gap filling material also had effects on heat transfer between stacked ICs. Thermal aware circuit design was briefly discussed as well.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.9
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• pp.95-103
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• 1998

This paper proposes an image segmentation algorithm based on fusion of range and intensity images. Based on Bayesian theory, a priori knowledge is encoded by the Markov random field (MRF). A maximum a posteriori (MAP) estimator is constructed using the features extracted from range and intensity images. Objects are approximated by local planar surfaces in range images, and the parametric space is constructed with the surface parameters estimated pixelwise. In intensity images the ${\alpha}$-trimmed variance constructs the intensity feature. An image is segmented by optimizing the MAP estimator that is constructed using a likelihood function based on edge information. Computer simulation results shw that the proposed fusion algorithm effectively segments the images independentl of shadow, noise, and light-blurring.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1209-1215
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• 2012

Experiments with premixed flames in a tube have been conducted to investigate the transition phenomenon from a laminar flat flame to turbulent motions. To induce this phenomenon, a flat flame is formed in a tube. Then, the local velocity at the center of the flat flame surface is increased using $CO_2$ laser irradiation. The deformed flame front propagates with an increase in the total flame surface and oscillating instability. Eventually, the flame front accelerates explosively, and it shows turbulent flame motions with a strong noise. The dynamic behaviors of the flame front prior to the turbulent motions are analyzed in this study to elucidate this process. The physical model of the process is presented according to observations.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.335-335
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• 2021

하천의 홍수터는 평상시 수면위로 노출되어 국민의 여가생활을 위한 공원, 주차장 등으로 활용되다 홍수기 수위가 상승하면 침수되는 하천공간이다. 홍수범람 면적 또는 홍수위 산정을 위한 수치모의 시, 홍수의 평면적인 변화를 분석하기 위해서는 1차원 모의결과와 지형정보를 연계하여 범람면적을 산정하거나 2차원 수치모형의 격자를 대상공간에 대하여 구축한 후 모의를 수행한다. 1차원 수치모형은 계산효율이 우수하고 지류의 합류에 의한 영향을 다수 반영하거나, 긴 구간의 하천단면 구축을 통하여 경계조건이 수치해석 결과에 미치는 영향을 최소화할 수 있는 장점이 있다. 그러나 지형의 영향으로 발생하는 국부적인 유속변화와 유향의 평면적인 분포에 의해 발생하는 범람면적의 변화를 반영하기 어렵다. 홍수범람을 고려하여 제작하는 홍수위험지도는 2차원 수치모형의 결과를 기반으로 한다. 2차원 수치모형은 하도의 만곡, 제방의 형상 등과 같은 지형에 의한 유속장의 변화, 흐름영역의 수축 및 확대에 의한 유속의 변화 등을 자세히 반영할 수 있는 장점이 있다. 반면에 수치격자 생성 및 계산결과 도출에 소요되는 시간이 길고 계산영역 설정의 한계로 인하여 경계조건이 흐름해석결과에 영향을 미칠 수 있는 문제점이 있다. 이와 같은 문제점을 해결하기 위하여 국내외적으로 1차원과 2차원 수치해석기법을 연계하여 하나의 모형으로 구축한 1-2차원 수치해석 모형이 개발 또는 적용되고 있다. 1-2차원 연계해석기법은 1차원 해석영역과 2차원 해석영역을 연계함에 있어서 흐름방향 연계와 횡방향 연계로 구분할 수 있다. 본 연구에서는 1차원과 2차원 수치해석을 연계하는 기법에 따라서 발생하는 수치모의결과를 비교하고 적용성을 검토하였다. 수리실험 관측결과가 있는 사례에 모형을 적용한 후, 한강지형에 수치모형을 적용하고 그 결과를 비교한다. 또한, 계산에 소요되는 시간을 비교하기 위하여 2차원 수치격자의 해상도를 다양하게 적용하여 수치실험을 수행한다. 분석결과를 기반으로 홍수위험지도 제작, 홍수위산정 및 홍수예보 등에 새로운 기술의 적용성을 검토한다.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.255-266
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• 1999

The objective of this experiment is to observe the elastic and inelastic behaviors of high-rise reinforced concrete frames having non-seismic details. To do this, a building frame designed according to Korean seismic code and detailed in the Korean conventional practice was selected. A 1:12 scale plane frame model was manufactured according to similitude law. A reversed lateral load test and a monotonic pushover test were performed under the displacement control. To simulate the earthquake effects, the lateral force distribution was maintained to be an inverse triangle by using a whiffle tree. From the tests, base shears, crack pattern, local rotations in the ends of critical members and the relations between interstory drift versus story shear are obtained. Based on test results, conclusions are drawn on the implications of the elastic and inelastic behaviors of a high-rise reinforced concrete frame having non-seismic details.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.197-207
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• 2005

Design analysis for underground spaces requires evaluating stability related to heading collapses. A failure mode is one of the critical factors in the conventional methods of stability evaluation. Identification of failure modes is, therefore, essential in securing safe construction. In this study failure modes at the tunnel heading in cohesionless soils are investigated using physical model tests for various tunnel depths and ground surface inclinations. Test results showed that the effect of depth and the inclination of ground surface on a failure mode are of significance. It is identified that, with an increase in depth, failure modes become localized in a region close to tunnel face. It is also known that an increase in the inclination of ground surface results in inclined an d wide failure modes. Numerical simulation of laboratory tests was performed, and shown that the numerical analysis is useful in identifying the heading failure modes, particularly for large underground spaces.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.3
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• pp.309-316
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• 2015

A state-based peridynamic model is able to describe a general constitutive model from the standard continuum theory. The response of a material at a point is dependent on the deformation of all bonds connected to the point within the nonlocal horizon region. Therefore, the state-based peridynamic model permits both the volume and shear changes of the material which is promising to reproduce the complicated dynamic brittle fracture phenomena, such as crack branching, secondary cracks, cascade cracks, crack coalescence, etc. In this paper, the two-dimensional state-based peridynamic model for a linear elastic plane stress solid is employed. The damage model incorporates the energy release rate and the peridynamic energy potential. For brittle glass materials, the impact of the crack-parallel compressive stress waves on the crack branching pattern is investigated. The peridynamic solution for this problem captures the main features, observed experimentally, of dynamic crack propagation and branching. Cascade cracks under strong tensile loading and secondary cracks are also well reproduced with the state-based peridynamic simulations.