• Computers and Concrete
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• 제16권5호
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• pp.669-682
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• 2015

Degradation of reinforced concrete (RC) structures due to chloride penetration followed by reinforcement corrosion has been a serious problem in civil engineering for many years. The numerical simulation methods at present are mainly finite element method (FEM) and finite difference method (FDM), which are based on mesh. Mesh generation in engineering takes a long time. In the present article, the numerical solution of chloride transport in concrete is analyzed using radial point interpolation method (RPIM) and element-free Galerkin (EFG). They are all meshless methods. RPIM utilizes radial polynomial basis, whereas EFG uses the moving least-square approximation. A Galerkin weak form on global is used to attain the discrete equation, and four different numerical examples are presented. MQ function and appropriate parameters have been proposed in RPIM. Numerical simulation results are compared with those obtained from the finite element method (FEM) and analytical solutions. Two case of chloride transport in full saturated and unsaturated concrete are analyzed to test the practical applicability and performance of the RPIM and EFG. A good agreement is obtained among RPIM, EFG, and the experimental data. It indicates that RPIM and EFG are reliable meshless methods for prediction of chloride concentration in concrete structures.

• Ocean Systems Engineering
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• 제2권2호
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• pp.137-145
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• 2012

Recent developments in underwater image recognition methods have received large attention by the ocean engineering researchers. In this paper, an improved bi-dimensional empirical mode decomposition (BEMD) approach is employed to decompose the given underwater image into intrinsic mode functions (IMFs) and residual. We developed a joint algorithm based on BEMD and Canny operator to extract multi-pixel edge features at multiple scales in IMFs sub-images. So the multiple pixel edge extraction is an advantage of our approach; the other contribution of this method is the realization of the bi-dimensional sifting process, which is realized utilizing regional-based operators to detect local extreme points and constructing radial basis function for curve surface interpolation. The performance of the multi-pixel edge extraction algorithm for processing underwater image is demonstrated in the contrast experiment with both the proposed method and the phase congruency edge detection.

• 한국정밀공학회지
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• 제23권9호
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• pp.200-207
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• 2006

In this paper a new approach which combines implicit surface scheme and NURBS surface interpolation method is proposed in order to generate a complete surface model from unorganized point cloud data. In the method a base surface was generated by creating smooth implicit surface from the input point cloud data through which the actual surface would pass. The implicit surface was defined by a combination of shape functions including quadratic polynomial function, cubic polynomial functions and radial basis function using adaptive domain decomposition method. In this paper voxel data which can be extracted easily from the base implicit surface were used in order to generate rectangular net with good quality using the normal projection and smoothing scheme. After generating the interior points and tangential vectors in each rectangular region considering the required accuracy, the NURBS surface were constructed by interpolating the rectangular array of points using boundary tangential vectors which assure C$^1$ continuity between rectangular patches. The validity and effectiveness of this new approach was demonstrated by performing numerical experiments for the various types of point cloud data.

• 한국음향학회지
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• 제33권2호
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• pp.118-125
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• 2014

역문제에 기반한 음향 온도 측정법에서는 단면의 음속 분포 계산이 필수적이며, 이를 위하여 단면 외곽에 위치한 센서들 간의 지연시간을 계측하고, 이를 입력으로 하는 전달행렬과 계수 벡터를 이용한 역문제를 이용하여 음속 분포를 예측한다. 그러나, 센서 개수의 부족으로 인하여 충분한 수의 음향 경로가 확보되지 못하면, 지연시간 벡터의 개수가 한정될 수 있다. 지연시간 벡터의 개수는 공간 해상도와 관련 있으며, 부족한 지연시간 벡터의 개수는 공간 해상도의 저하를 초래하여 정확한 온도 재구성 결과를 얻지 못할 수 있다. 본 연구에서는 이 문제를 해결하기 위하여, 실제 측정된 지연시간으로부터 온도장을 재구성 한 뒤, 임의의 경로에 해당하는 지연시간을 재구성 된 온도장으로부터 재형성하여 지연시간 벡터의 개수를 증가시켰다. 측정된 지연시간 벡터와 재형성 된 지연시간 벡터를 함께 사용할 경우, 음향 경로의 개수가 증가하므로 공간 분해능의 향상을 기대할 수 있다. 임의의 온도 분포를 가지는 2차원 단면을 수치 예제로서 채택하였고, 측정된 지연시간만을 이용한 결과와 재형성 된 지연시간을 함께 사용한 재구성 결과를 비교하였다. 그 결과, 재형성 된 지연시간과 측정된 지연시간을 함께 사용한 경우의 온도 재구성 오차가 측정된 지연시간만을 사용한 온도 재구성 오차보다 최대 15 % 감소하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.184-187
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• 2003

Complete prediction of second order permeability tensor for three dimensional circular braided preform is critical to understand the resin transfer molding process of composites. The permeability can be predicted by considering resin flow through the multi-axial fiber structure. In this study, permeability tensor for a 3-D circular braided preform is calculated by solving a boundary problem of a periodic unit cell. Flow field through the unit cell is obtained by using a 3-D finite volume method (FVM) and Darcy's law is utilized to obtain permeability tensor. Flow analysis for two cases that a fiber tow is regarded as impermeable solid and permeable porous medium is carried out respectively. It is found that the flow within the intra-tow region of the braided preform is negligible if inter-tow porosity is relatively high but the flow through the tow must be considered when the porosity is low. To avoid checkerboard pressure field and improve the efficiency of numerical computation, a new interpolation function for velocity variation is proposed on the basis of analytic solutions. Permeability of the braided preform is measured through a radial flow experiment and compared with the permeability predicted numerically.

• 디지털산업정보학회논문지
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• 제12권4호
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• pp.107-114
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• 2016

Recently, 3D related technology has become a hot topic for IT. 3D technologies such as 3DTV, Kinect and 3D printers are becoming more and more popular. According to the flow of the times, the goal of this study is that the general public is exposed to 3D technology easily. we have developed a web-based application program that enables 3D modeling of facial front and side photographs using a mobile phone. In order to realize 3D modeling, two photographs (front and side) are photographed with a mobile camera, and ASM (Active Shape Model) and skin binarization technique are used to extract facial height such as nose from facial and side photographs. Three-dimensional coordinates are generated using the face extracted from the front photograph and the face height obtained from the side photograph. Using the 3-D coordinates generated for the standard face model modeled with the standard face as a control point, the face becomes the face of the subject when the RBF (Radial Basis Function) interpolation method is used. Also, in order to cover the face with the modified face model, the control point found in the front photograph is mapped to the texture map coordinate to generate the texture image. Finally, the deformed face model is covered with a texture image, and the 3D modeled image is displayed to the user.

• 한국항공우주학회지
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• 제38권6호
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• pp.547-556
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• 2010

항공기의 안전성 확보 및 투하되는 탄의 정확도 증대를 위한 새로운 개념의 활공비행체 개발이 많은 기업에서 진행 중에 있다. 항공기의 장착 공간 및 활공거리 증대를 고려하여 세장비가 큰 전개되는 날개를 채택하는 것이 일반적이다. 큰 세장비의 날개 구조물은 상대적으로 낮은 강성에 의하여 과도한 탄성변형 뿐 아니라 플러터 발생의 가능성이 높아지게 된다. 본 연구는 큰 세장비 날개에 대하여 유체-공력 연계기법을 이용, 구조변형에 의한 공력특성의 변화 및 플러터 발생가능성에 대하여 검토하였다. 공기력 계산을 위하여 FLUENT 코드가 구조 동특성 해석을 위하여 ABAQUS 상용코드가 사용되었으며, 국부지지 방사기저함수로 구성된 Code-bridge를 이용한 입력 자료의 보간 및 사상을 수행하였다. 해석 결과 고려된 활공 조건에서 구조 변형에 의한 공력 특성의 변화가 발생하는 것이 관측되었으며, 이에 의한 진동도 계속적으로 발생되는 것으로 표현되었다.

• Wind and Structures
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• 제28권1호
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• pp.31-47
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• 2019

The accurate prediction of snow distributions under the wind action on roofs plays an important role in designing structures in civil engineering in regions with heavy snowfall. Affected by some factors such as building shapes, sizes and layouts, the snow drifting on roofs shows more three-dimensional characteristics. Thus, the research on three-dimensional snow distribution is needed. Firstly, four groups of stepped flat roofs are designed, of which the width-height ratio is 3, 4, 5 and 6. Silica sand with average radius of 0.1 mm is used to model the snow particles and then the wind tunnel test of snow drifting on stepped flat roofs is carried out. 3D scanning is used to obtain the snow distribution after the test is finished and the mean mass transport rate is calculated. Next, the wind velocity and duration is determined for numerical simulations based on similarity criteria. The adaptive-mesh method based on radial basis function (RBF) interpolation is used to simulate the dynamic change of snow phase boundary on lower roofs and then a time-marching analysis of steady snow drifting is conducted. The overall trend of numerical results are generally consistent with the wind tunnel tests and field measurements, which validate the accuracy of the numerical simulation. The combination between the wind tunnel test and CFD simulation for three-dimensional typical roofs can provide certain reference to the prediction of the distribution of snow loads on typical roofs.

• 한국수자원학회논문집
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• 제55권3호
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• pp.245-255
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• 2022

수질 보호를 위한 정기 계획을 세우는 과정에서 다양한 지표를 이용해 수자원의 수질 추이를 평가하는 일이 필요하며 이는 수역 관리에서 널리 사용하는 방법이다. 본 연구에서는 1995년부터 2020년까지 이란 대수층의 수질 매개변수 자료를 수집, 검토하고, 통계적으로 검증하여 연도별 구획도를 만들었다. 이를 위해 지리정보체계(GIS), 거리 반비례 가중법(IDW), 방사 기저함수(RBF), 포괄 선형 보간법(GPI), 단순, 일반, 범용의 세 유형을 포함하는 Kriging과 Co-Kriging기법을 이용하였다. 이어 최소 불확실성과 최소 구획 오차에 ASE와 RMSE를 포함하는 두 값의 근접도를 더한 것을 최적 모델로 선택하였다. 마지막으로 각 매개변수에 대해 선택한 복합 모델을 Schuler와 Wilcox 지수와 조합하여 구획화했다. 이란의 지하 수자원에 대한 종합평가 결과는 수자원의 59%는 농업용수로, 39.86%는 음용수에 부적합한 등급으로 분류되어 이란 지하수 수질이 위기에 처해 있음을 보여주었다. 마지막으로 추출 결과를 검증하기 위해 지하 수질 지수(GWQI)로 수질의 공간 변화를 평가한 결과 이란의 대수층이 적은 수위변화에도 매우 민감하며 지하수 양도 매우 부족하다는 것을 확인할 수 있었다.