• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제26권1호
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• pp.1-14
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• 1998

Various numerical methods for the two dimensional shallow water equations have been applied to the problems of flood routing, tidal circulation, storm surges, and atmospheric circulation. These methods are often based on the Alternating Direction Implicity(ADI) method. However, the ADI method results in inaccuracies for large time steps when dealing with a complex geometry or bathymetry. Since this method reduces the performance considerably, a fully implicit method developed by Wilders et al. (1998) is used to improve the accuracy for a large time step. Finite Difference Methods are defined on a rectangular grid. Two drawbacks of this type of grid are that grid refinement is not possibile locally and that the physical boundary is sometimes poorly represented by the numerical model boundary. Because of the second deficiency several purely numerical boundary effects can be involved. A boundary fitted curvilinear coordinate transformation is used to reduce these difficulties. It the curvilinear coordinate transformation is used to reduce these difficulties. If the coordinate transformation is orthogonal then the transformed shallow water equations are similar to the original equations. Therefore, an orthogonal coorinate transformation is used for defining coordinate system. A multigrid (MG) method is widely used to accelerate the convergence in the numerical methods. In this study, a technique using a MG method is proposed to reduce the computing time and to improve the accuracy for the orthogonal to reduce the computing time and to improve the accuracy for the orthogonal grid generation and the solutions of the shallow water equations.

• 한국기계가공학회지
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• 제15권2호
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• pp.38-45
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• 2016

Since a 5-axis machine tool has two rotary axes, it offers numerous advantages, such as flexible accessibility, longer tool life, better surface finish, and more accuracy. Moreover, it can conduct whole machining by rotating the rotary feed axes while setting the fixture at once without re-fixing in contrast to conventional 3-axis machining. However, it is difficult to produce complicated products that have a hollow shape. In contrast, 3D printing can produce an object with a complicated hollow shape easily and rapidly. However, because of layer thickness and shrinkage, its surface finish and dimensional accuracy are not adequate. Therefore, this study proposes hybrid technology by integrating the advantages of these two manufacturing processes. 3D printing was used as the additive manufacturing rapidly in the whole body, and 5-axis machining was used as the subtractive manufacturing accurately in the joining and driving places. The reliability of the proposed technology was verified through a comparison with conventional technology in the aspects of processing time, surface roughness. and dimensional accuracy.

• Nuclear Engineering and Technology
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• 제13권2호
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• pp.73-84
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• 1981

B$\Phi$rrensen은 3차원적 노심분석에 긴 시간이 요구되는 유한차분법의 대안으로서 경수형 원자로의 전체출력분포를 계산하는데 한가지의 coarse mesh 방법을 제안하였다. 이 방법은 계산시간이 매우 짧은 것으로 알려져 있지만. 그 계산의 정확도에 대한 것은 아직까지 알려져 있지 않다. 본 논문에서는 B$\Phi$rrensen의 방법을 IAEA benchmark 문제와 RIS$\Phi$ benchmark 문제에 적용시켜서 계산시간과 정확도에 대해서 고찰하였다. 두 문제에서 노심-반사체와의 경계조건과 B$\Phi$rrensen의 모델상수들의 개선으로 출력분포 계산의 정확도를 상당히 높힐 수 있었다.

• 한국도로학회논문집
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• 제18권1호
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• pp.73-83
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• 2016

PURPOSES : The purpose of this study is to develop a method for improving the accuracy of analysis results obtained from a two-dimensional (2-D) numerical analysis model of continuously reinforced concrete pavement (CRCP). METHODS : The analysis results from the 2-D numerical model of CRCP are compared with those from more rigorous three-dimensional (3-D) models of CRCP, and the relationships between the results are recognized. In addition, the numerical analysis results are compared with the results obtained from field experiments. By performing these comparisons, the calibration factors used for the 2-D CRCP model are determined. RESULTS : The results from the comparisons between 2-D and 3-D CRCP analyses show that with the 2-D CRCP model, concrete stresses can be overestimated significantly, and crack widths can either be underestimated or overestimated by a slight margin depending on the assumption of plane stress or plane strain. The behaviors of crack width in field measurements are comparable to those obtained from the numerical model of CRCP. CONCLUSIONS : The accuracy of analysis results from the 2-D CRCP model can be improved significantly by applying calibration factors obtained from comparisons with 3-D analyses and field experiments.

• 대한기계학회논문집A
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• 제21권6호
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• pp.918-924
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• 1997

A method for measuring the accuracy of rotating objects was studied. Rotating axis errors are significant; such as the spindle error of a manufacturing machine which results in the surface roughness of machined work pieces. Three capacitance type displacement sensors were used to measure the rotating master ball position. The sensors were mounted to the three orthogonal points on the spindle axis. The measurement data were analyzed and shown for rotating spindle accuracy, not only for average roundness error but also for spindle volumetric positional error during the revolutions. This method is simple and economical for industrial field use with regular inspection of rotating machines using portable equipment. Measuring and analyzing time using this method takes only a couple of hours. This method can also measure microscopic amplitude and 3-dimensional direction of vibrating objects.

• 한국측량학회지
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• 제17권3호
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• pp.311-320
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• 1999

본 연구에서는 두만강 하류지역 다분광 TM영상의 변환기법과 그에 대한 감독분류방법을 비교 분석하였다. 총체적 분류 정확도는 최대우도법이 높으며 식생은 MNF와 TC 변환 영상에서 비교적 좋은 분류 결과를 얻을 수 있다. MNF, TC, NDVI 등 영상들로 구성된 7차원 영상은 3차원 영상보다 좋은 결과를 나타내며 그 중에서도 최대우도법의 분류 결과가 제일 좋았다. 다분광 영상은 두만강 지역 경제 개발 계획과 산업 입지 선정에 중요한 기초자료로 활용될 수 있다.

• 한국멀티미디어학회논문지
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• 제11권12호
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• pp.1635-1648
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• 2008

The extraction of important features in cancer cell image analysis is a key process in grading renal cell carcinoma. In this study, we applied three-dimensional (3D) texture feature extraction methods to cell nuclei images and evaluated the validity of them for computerized cell nuclei grading. Individual images of 2,423 cell nuclei were extracted from 80 renal cell carcinomas (RCCs) using confocal laser scanning microscopy (CLSM). First, we applied the 3D texture mapping method to render the volume of entire tissue sections. Then, we determined the chromatin texture quantitatively by calculating 3D gray-level co-occurrence matrices (3D GLCM) and 3D run length matrices (3D GLRLM). Finally, to demonstrate the suitability of 3D texture features for grading, we performed a discriminant analysis. In addition, we conducted a principal component analysis to obtain optimized texture features. Automatic grading of cell nuclei using 3D texture features had an accuracy of 78.30%. Combining 3D textural and 3D morphological features improved the accuracy to 82.19%. As a comparative study, we also performed a stepwise feature selection. Using the 4 optimized features, we could obtain more improved accuracy of 84.32%. Three dimensional texture features have potential for use as fundamental elements in developing a new nuclear grading system with accurate diagnosis and predicting prognosis.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1181-1194
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• 2019

A new moving-mesh Finite Volume Method (FVM) for the efficient solution of the two-dimensional neutron diffusion equation is introduced. Many other moving-mesh methods developed to solve the neutron diffusion problems use a relatively large number of sophisticated mathematical equations, and so suffer from a significant complexity of mathematical calculations. In this study, the proposed method is formulated based on simple mathematical algebraic equations that enable an efficient mesh movement and CV deformation for using in practical nuclear reactor applications. Accordingly, a computational framework relying on a new moving-mesh FVM is introduced to efficiently distribute the meshes and deform the CVs in regions with high gradient variations of reactor power. These regions of interest are very important in the neutronic assessment of the nuclear reactors and accordingly, a higher accuracy of the power densities is required to be obtained. The accuracy, execution time and finally visual comparison of the proposed method comprehensively investigated and discussed for three different benchmark problems. The results all indicated a higher accuracy of the proposed method in comparison with the conventional fixed-mesh FVM.

• 대한토목학회논문집
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• 제32권2B호
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• pp.123-130
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• 2012

천수방정식의 수치모형에 MLP(Multi dimensional Limiting Process)기법을 적용한 후 수치모의를 통해 MLP의 수치 진동 제어 성능을 검증하였다. MLP기법은 2, 3차원에서 기존의 TVD 제어자(limiter)들보다 안정적이며 정확한 수치모의를 가능하게 한다. 다차원에서 정확하고 안정적인 수치모의가 가능하도록 개발된 MLP기법은 압축성 유체를 표현하는 2, 3차원 오일러 방정식에 적용되어 기존의 제어자들에 비해 그 뛰어난 성능이 검증된 바 있다. 하지만 천수방정식에 적용된 예는 없으며, 이에 본 연구는 천수방정식에 MLP를 적용하고 천수방정식 수치모형 검증에 주로 사용되는 수치모의를 통해 MLP의 진동 제어 성능을 검증하였다. 모의 결과, MLP는 2차원 천수방정식에 있어서도 기존의 제어자들과 비교하여 수치진동을 보다 잘 제어하는 것으로 판단된다. MLP 사용으로 인해 불연속면 근처에서 정확도가 향상되었고 수치진동이 발생하지 않아 보다 안정적인 모의가 하게 되었다.

• 디지털융복합연구
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• 제17권2호
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• pp.347-353
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• 2019

최근 추천 시스템들은 고차원 데이터를 사용할 수 있는 시스템으로 발전하고 있다. 그러나 고차원 데이터는 차원을 확장시켜 알고리즘 복잡도가 증가하여 추천 항목의 정확도를 저하시킬 수 있다. 또한 데이터의 희소성(Sparsity) 문제가 발생할 수 있어 사용자들에게 적합한 추천 항목을 제공하는 것이 어렵다. 본 연구에서는 Fuzzy-AHP를 이용하여 사용자들의 주관적 기준의 데이터를 객관적 기준으로 분류한 후, 퍼지 연관규칙 분석을 이용하여 반복적 패턴을 띄는 규칙들을 활용하는 알고리즘을 제안하였다. 본 연구에서 적용된 알고리즘이 고차원 데이터의 문제점들을 어떻게 완화하는지 확인하기 위해 사용자 수의 변화에 따른 5-fold Cross Validation을 진행하였다. 그 결과 본 알고리즘이 적용된 시스템의 정확도는 Fuzzy-AHP만을 적용한 시스템보다 12.5% 정도 정확도가 우수하였고, 데이터의 희소성 문제도 완화할 수 있다는 것을 확인하였다.