• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.3
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• pp.183-190
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• 2019

This paper introduces a near-tip grid refinement and explores its usefulness in the crack analysis by the natural element method(NEM). As a sort of local h-refinement in finite element method(FEM), a NEM grid is locally refined around the crack tip showing high stress singularity. This local grid refinement is completed in two steps in which grid points are added and Delaunay triangles sharing the crack tip node are divided. A plane strain rectangular plate with symmetric edge cracks is simulated to validate the proposed local grid refinement and to examine its usefulness in the crack analysis. The crack analysis is also simulated using a uniform NEM grid for comparison. Unlike the uniform grid, the refined grid provides near-tip stress distributions similar to the analytic solutions and the fine grid. In addition, the refined grid shows higher convergence than the uniform grid, the global relative error to the total number of grid points.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.11-22
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• 1987

A plane buoyant jet discharged vertically upward into a crossflow is analyzed by numerical solution of the governing equations of continuity, momentum and constituent transport. The turbulent transport is modelled by the Prandtl's mixing length theory. In the numerical solution procedure, the governing equations are transformed by stream function and vorticity transport, non-dimensionalyzed by discharge velocity, slot width, and parameters representing flow characteristics, and solved by Gauss-Seidel iteration method with successive underrelaxation. The numerical experiments were performed for the region of established flow of buoyant jet in the range of discharge densimetric Froude number of 4 to 32 and in the range of velocity ratio of 8 to 15, which is the ratio of discharge velocity to crossflow velocity. Variations of velocities and temperatures, flow patterns and vorticity patterns of receiving water due to buoyant jet were investigated. Also investigated are the effects of velocity ratio and discharge densimetric Froude number on the trajectories of buoyant jet. Computed are velocities, temperatures and local densimetric Froude numbers along the trajectory of the buoyant jet. Spreading rate and dispersion ratio were analyzed in terms of discharge densimetric Froude number, local densimetric Froude number and distance from the source along the jet trajectory. It was noted that the similarity law holds in both the profiles of velocity and temperatures across the jet trajectory and the integral type analysis of Gaussian distribution is applicable.

• Journal of KIISE
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• v.41 no.9
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• pp.666-673
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• 2014

This paper proposes a scalable face recognition method for unconstrained face databases, and shows a simple experimental result. Existing face recognition research usually has focused on improving the recognition rate in a constrained environment where illumination, face alignment, facial expression, and background is controlled. Therefore, it cannot be applied in unconstrained face databases. The proposed system is face feature extraction algorithm for unconstrained face recognition. First of all, we extract the area that represent the important features(landmarks) in the face, like the eyes, nose, and mouth. Each landmark is represented by a high-dimensional LBP(Local Binary Pattern) histogram feature vector. The multi-scale LBP histogram vector corresponding to a single landmark, becomes a low-dimensional face feature vector through the feature reduction process, PCA(Principal Component Analysis) and LDA(Linear Discriminant Analysis). We use the Rank acquisition method and Precision at k(p@k) performance verification method for verifying the face recognition performance of the low-dimensional face feature by the proposed algorithm. To generate the experimental results of face recognition we used the FERET, LFW and PubFig83 database. The face recognition system using the proposed algorithm showed a better classification performance over the existing methods.

• Korean Journal of Optics and Photonics
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• v.18 no.6
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• pp.375-382
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• 2007

The Shack-Hartmann wavefront sensor is composed of a lenslet array generating the spot images from which local slope is calculated and overall wavefront is measured. Generally the principle of wavefront reconstruction is that the spot centroid of each lenslet array is calculated from pixel intensity values in its subaperture, and then overall wavefront is reconstructed by the local slope of the wavefront obtained by deviations from reference positions. Hence the spot image of each lenslet array has to remain in its subaperture for exact measurement of the wavefront. However the spot of each lenslet array deviates from its subaperture area when a wavefront with large local slopes enters the Shack-Hartmann sensor. In this research, we propose a spot image searching method that finds the area of each measured spot image flexibly and determines the centroid of each spot in its area Also the algorithms that match these centroids to their reference points unequivocally, even if some of them are situated off the allocated subaperture, are proposed. Finally we verify the proposed algorithm with the test of a defocus measurement through experimental setup for the Shack-Hartmann wavefront sensor. It has been shown that the proposed algorithm can expand the dynamic range without additional devices.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.2
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• pp.82-90
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• 2002

BDD have become widely used for various CAD applications because Boolean functions can be represented uniquely and compactly by using BDD. The size of the BDD representation for a function is very sensitive to the choice of orderings on the input variable. Therefore, it is very important to find a good variable ordering which minimize the size of the BDD. Since finding an optimal ordering is NP-complete, several heuristic algorithms have been proposed to find good variable orderings. In this paper, we propose a variable ordering algorithm, Faster-${\mu}$0, based on the ${\mu}$0(microcanonical optimization). In the Faster-${\mu}$0 algorithm, the initialization phase is replaced with a shifting phase to produce better solutions in a fast local search. We find values for algorithm parameters experimentally and the proposed algorithm has been experimented on well known benchmark circuits and shows superior performance compared to various existing algorithms.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.621-629
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• 1992

This study is concerned with an application of the Boundary Element Method to 2-dimensional elastoplastic stress analysis on the material nonlinearities. The boundary integral formulation adopted an initial stress equation in the inelastic term. In order to determine the initial stress increment, the increment of initial elastic strain energy due to elastic increment in stressstrain curve was used as the convergence criterion during iterative process. For the validity of this procedure, the results of B.E.M. with constant elements and NISA with linear elements where compared on the thin plate with 2 edge v-notches under static tension and the thick cylinder under internal pressure. And this paper compared the results of using unmedical integral with the results of using semi-analytical integral on the plastic domain integral.

• Journal of Korean Society of Steel Construction
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• v.13 no.1
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• pp.9-18
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• 2001

many steel tubular truss as roof structures are used of the large span structures Steel tubular sectioned truss has the structural merits in compared with other sections such as H, L-shape sections However it occurs local buckling at the joint of branch in truss and it makes the deterioration of loading capacity Loading capacity and deformation characteristics of truss joints are very complicate so it is very hard to predict exact solution of them Therefore this thesis dealt with T-type joints of steel circular hollow sectioned truss. A series of experimental scheme were planned and mainly experimental parameters were : ratio of diameter of branch-diameter of main chord(d/D). diameter-thickness(T/D) of main chord. In this paper predicted yield load capacity using by closed ring analysis method additionally compared with that of suggested by closed ring analysis method additionally compared with that of suggested by other countries.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.939-946
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• 2005

The stiffness properties of heterogeneous concrete materials and their degradation were investigated at different-levels of observations with aids of the opportunities and limitations of multi-resolution wavelet analysis. The successive Haw transformations lead to a recursive separation of the stiffness properties and the response into coarse-and fine-scale features. In the limit, this recursive process results in a homogenization parameter which is an average measure of stiffness and strain energy capacity at the coarse scale. The basic concept of multi-resolution analysis is illustrated with one and two-dimensional model problems of a two-phase particulate composite representative of the morphology of concrete materials. The computational studies include the meso-structural features of concrete in the form of a hi-material system of aggregate particles which are immersed in a hardened cement paste taking due to account of the mismatch of the two elastic constituents.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.518-518
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• 2023

자연하천에서 오염물질의 혼합 거동은 비균일한 지형학적 요인으로 인해 매우 복잡한 특성을 나타낸다. 일반적으로 오염물질 거동 모델링에서는 수체에서의 혼합을 Fick의 법칙에 따라 유속에 의한 이송과 난류에 의한 확산으로 계산하고, 국부적인 정체현상 등에 의한 non-Fickian 혼합을 야기하는 하천의 특성을 기하학적 지형 형상으로 구현하여 실제 현상에 근접한 혼합 거동을 재현한다. 하지만 계산의 효율성을 위하여 모델링의 차원을 낮추는 경우, 하천의 지형을 경계조건으로 고려할 수 없게 된다. 특히, 1차원 모델링의 경우 하천의 비균일성을 무시하고 1개의 유선으로 간주하며, 이 경우 non-Fickian 물질이동 해석을 위한 추가적인 현상학적 해석이 필요하다. 지난 50년간, non-Fickian 물질이동 해석을 위한 다양한 현상학적 모형이 제시되어 왔다. 하천을 흐름영역과 정체영역으로 구분하고 두 개의 영역 사이의 물질교환 속도를 모델링하거나, Random walk 개념으로 물질이 이동하는 경우와 이동하지 않는 경우를 확률론적으로 모델링하거나, 물질이 정체되었을 때 다시 빠져나오는 시간을 모델링하는 경우가 그 예이다. 본 연구에서는 선행연구에서 제시한 음함수 형태의 현상학적 모형을 기반으로, 수치적 반복계산 없이 상류 경계에서 임의의 형태의 농도곡선(shape-free breakthrough curve)을 갖는 오염물질운(cloud)이 일정 거리를 유하하며 발생하는 변화를 예측할 수 있는 해를 제시한다. 본 연구의 방법론은 추적법(routing procedure)을 활용한 Fickian 혼합 해석, 전달함수(transfer function) 형태의 정체시간분포 해석, 그리고 라플라스 도메인에서의 해석해 유도를 포함한다. 본 연구에서 제시된 해는 2020년 경상북도 김천시에 위치한 감천의 4.5 km 구간에서 수행한 추적자 실험의 현장 자료를 통해 정확도를 검증하여 타당성을 입증하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.2048-2052
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• 2009

최근 우리나라는 선진 외국과 같이 하천자연환경 보전에 대한 관심이 증가하고 있다. 이에 따라 하천은 단순한 치수 및 이수 뿐만 아니라 다양한 자연 그대로의 환경적 잠재기능을 복원하는 방향으로 전환되고 있다. 하천복원은 하도내 식생, 여울과 소, 기타 국부적인 자연 서식처를 제공하기 때문에 하천단면 축소, 하천식생에 의한 흐름과 조도 변화 및 하상의 변동으로 인하여 홍수해가 발생할 것이라는 역기능도 발생시킨다. 본 연구에서는 수위-유량자료가 부족한 하천 유역을 대상으로 생태공학적 접근을 고려한 식생 설치를 상정하여 하천의 식생복원에 따른 홍수위 안정성 검토를 실시하였다. 이를 위해, HEC-RAS를 이용하여 수리학적 요소들을 산출하고, 도출된 값들을 연직 2차원 수리해석에 입력하는 방법을 사용하여 대상구간의 식생 전 후 홍수위를 산정하였다. 그 결과, 식생전 후의 수위차는 $0.00^{\sim}1.25m$로 계산되어 식생으로 인해 최고 1.25m의 수위 상승 효과가 발생하였다. 가용할 자료가 부족한 하천의 식생복원에 따른 수리안정성 검토시 위 두 방법을 연계 이용한다면 하천복원 전후의 수리특성 변화를 정확히 파악할 수 있을 것으로 판단된다.