• 한국컴퓨터정보학회논문지
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• 제19권10호
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• pp.13-21
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• 2014

집합 커버링 문제는 대표적인 조합 최적화 문제들 중 하나로서 n개의 열로부터 일부를 선택하여 m개의 행을 커버하되 비용을 최소화하는 문제로 정의된다. 본 논문에서는 집합 커버링 문제를 해결하기 위한 정수 계획법 기반 지역 탐색의 적용 방안을 제시하고 있다. 정수계획법 기반 지역 탐색은 이웃해를 탐색하여 현재해를 반복적으로 개선하는 지역 탐색 기법의 일종으로서 이웃해를 생성하기 위한 알고리즘으로 정수계획법을 사용한다. 본 논문에서 제시한 기법의 효과를 검증하기 위해 OR-Library의 테스트 데이터를 대상으로 실험을 수행하였다. 실험 결과, 모든 테스트 데이터에 있어서 정수계획법 기반 지역 탐색을 통해 지금까지 알려진 가장 좋은 해를 탐색할 수 있었다. 특히 4개의 테스트 데이터에 대해서는 지금까지 알려진 가장 좋은 해보다 더 좋은 해를 도출할 수 있음을 확인할 수 있었다.

• 디지털융복합연구
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• 제11권11호
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• pp.443-448
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• 2013

개미군락시스템(Ant Colony System, ACS)은 조합 최적화 문제를 해결하기 위한 기법으로 생물학적 기반의 메타휴리스틱 접근법이다. 지나간 경로에 대하여 페로몬을 분비하고 통신 매개물로 사용하는 실제 개미들의 추적 행위를 기반으로 한다. 최적 경로를 찾기 위해서는 보다 다양한 에지들에 대한 탐색이 필요하다. 기존 개미군락시스템의 지역 갱신 규칙에서는 지나간 에지에 대하여 고정된 페로몬 갱신 값을 부여하고 있다. 그러나 본 논문에서는 현재 선택한 노드에 대한 이전 iteration 에서 방문한 총 빈도수를 고려한 페로몬 부여 방법을 지역갱신규칙에 사용하고자 한다. 탐색을 위해서는 부경로를 이용한 ACS알고리즘을 사용하였다. 보다 많은 정보를 탐색에 활용함으로써 기존의 방법에 비해 지역 최적화에 빠지지 않고 더 나은 해를 찾을 수 있다.

• 한국컴퓨터정보학회논문지
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• 제29권4호
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• pp.1-8
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• 2024

순회 외판원 문제(TSP)는 잘 알려진 조합 최적화 문제 중 하나이다. 지역 탐색은 TSP를 해결하기 위한 한 가지 방법으로 사용되어 왔다. Greedy Random Insertion(GRI)은 지역 탐색을 위한 효과적인 이웃해 생성 방법으로 알려져 있다. GRI는 현재해로부터 일부 도시들을 무작위로 선택하고 그 도시들을 한 번에 하나의 도시만 고려하여 현재 부분해의 최적 위치로 삽입한다. 본 논문에서는 먼저 Full Greedy Insertion(FGI)이라는 또 다른 그리디 이웃해 생성 방법을 제안한다. FGI는 GRI와 마찬가지로 삽입 위치를 하나씩 결정하되 남은 모든 도시들을 한꺼번에 고려하여 결정한다. 그리고 본 논문에서는 GRI와 FGI를 결합하는 방법을 제시한다. 결합 방법에서는 시뮬레이티드 어닐링 내에서 매 반복 시 GRI 또는 FGI를 무작위로 선택하여 실행한다. 실험 결과에 의하면, FGI 단독으로는 성능이 매우 우수한 것은 아니다. 그러나 결합 방법은 GRI를 포함한 기존의 지역 탐색 방법들보다 우수한 성능을 발휘함을 확인하였다.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2230-2241
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• 2006

This paper presents a sole application of boundary element method to the conjugate heat transfer problem of thermally developing laminar flow in a thick walled pipe when the fluid velocities are fully developed. Due to the coupled mechanism of heat conduction in the solid region and heat convection in the fluid region, two separate solutions in the solid and fluid regions are sought to match the solid-fluid interface continuity condition. In this method, the dual reciprocity boundary element method (DRBEM) with the axial direction marching scheme is used to solve the heat convection problem and the conventional boundary element method (BEM) of axisymmetric model is applied to solve the heat conduction problem. An iterative and numerically stable BEM solution algorithm is presented, which uses the coupled interface conditions explicitly instead of uncoupled conditions. Both the local convective heat transfer coefficient at solid-fluid interface and the local mean fluid temperature are initially guessed and updated as the unknown interface thermal conditions in the iterative solution procedure. Two examples imposing uniform temperature and heat flux boundary conditions are tested in thermally developing region and compared with analytic solutions where available. The benchmark test results are shown to be in good agreement with the analytic solutions for both examples with different boundary conditions.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.47-51
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• 2005

Using satellite images, an optimal solution to water motion has been presented in this study. Since temperature patterns are suitable tracers in water motion, Sea Surface Temperature (SST) images of Caspian Sea taken by MODIS sensor on board Terra satellite have been used in this study. Two daily SST images with 24 hours time interval are used as input data. Computation of templates correspondence between pairs of images is crucial within motion algorithms using non-rigid body objects. Image matching methods have been applied to estimate water body motion within the two SST images. The least squares matching technique, as a flexible technique for most data matching problems, offers an optimal spatial solution for the motion estimation. The algorithm allows for simultaneous local radiometric correction and local geometrical image orientation estimation. Actually, the correspondence between the two image templates is modeled both geometrically and radiometrically. Geometric component of the model includes six geometric transformation parameters and radiometric component of the model includes two radiometric transformation parameters. Using the algorithm, the parameters are automatically corrected, optimized and assessed iteratively by the least squares algorithm. The method used in this study, has presented more efficient and robust solution compared to the traditional motion estimation schemes.

• 한국통신학회논문지
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• 제32권5B호
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• pp.295-303
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• 2007

An algorithm is proposed to seek a local optimal solution of the network utility maximization problem in a wireless mesh network, where the architecture being considered is an infrastructure/backbone wireless mesh network. The objective is to achieve proportional fairness amongst the end-to-end flows in wireless mesh networks. In order to establish the communication constraints of the flow rates in the network utility maximization problem, we have presented necessary and sufficient conditions for the achievability of the flow rates. Since wireless mesh networks are generally considered as a type of ad hoc networks, similarly as in wireless multi-hop network, the network utility maximization problem in wireless mesh network is a nonlinear nonconvex programming problem. Besides, the gateway/bridge functionalities in mesh routers enable the integration of wireless mesh networks with various existing wireless networks. Thus, the rate optimization problem in wireless mesh networks is more complex than in wireless multi-hop networks.

• 대한전기학회논문지:전력기술부문A
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• 제52권3호
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• pp.183-192
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• 2003

This paper presents the real-time implemented distance relay algorithm which the fault distance is estimated with only local terminal information. When a single-phase-to-earth fault on a two-parallel transmission line occurs, the reach accuracy of distance relay is considerably affected by the unknown variables which are fault resistance, fault current at the fault point and zero- sequence current of sound line The zero-sequence current of sound line is estimated by using the zero sequence voltage which is measured by relaying location Also. the fault resistance is removed at the Process of numerical formula expansion. Lastly, the fault current through a fault point is expressed as a function of the zero-sequence current of fault line, zero-sequence current of sound line, and line, and fault distance. Therefore, the fault phase voltage can be expressed as the quadratic equation of the fault distance. The solution of this Quadratic equation is obtained by using a coefficient of the modified quadratic equation instead of using the square root solution method. After tile accurate fault distance is estimated. the mote accurate impedance is measured by using such an information.

• Structural Engineering and Mechanics
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• 제76권4호
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• pp.505-512
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• 2020

This paper presents an error estimation technique for 2-D crack analysis by an enriched natural element (more exactly, enriched Petrov-Galerkin NEM). A bare solution was approximated by PG-NEM using Laplace interpolation functions. Meanwhile, an accurate quasi-exact solution was obtained by a combined use of enriched PG-NEM and the global patch recovery. The Laplace interpolation functions are enriched with the near-tip singular fields, and the approximate solution obtained by enriched PG-NEM was enhanced by the global patch recovery. The quantitative error amount is measured in terms of the energy norm, and the accuracy (i.e., the effective index) of the proposed method was evaluated using the errors which obtained by FEM using a very fine mesh. The error distribution was investigated by calculating the local element-wise errors, from which it has been found that the relative high errors occurs in the vicinity of crack tip. The differences between the enriched and non-enriched PG-NEMs have been investigated from the effective index, the error distribution, and the convergence rate. From the comparison, it has been justified that the enriched PG-NEM provides much more accurate error information than the non-enriched PG-NEM.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.229-244
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• 2019

Weak form integral equations are developed to investigate the flapwise bending vibration of the rotating beams. Rayleigh and Eringen nonlocal elasticity theories are used to investigate the rotatory inertia and Size-dependency effects on the flapwise bending vibration of the rotating cantilever beams, respectively. Through repetitive integrations, the governing partial differential equations are converted into weak form integral equations. The novelty of the presented approach is the approximation of the mode shape function by a power series which converts the equations into solvable one. Substitution of the power series into weak form integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of the non-trivial solution for resulting system of equations. Accuracy of the proposed method is verified through several numerical examples, in which the influence of the geometry properties, rotatory inertia, rotational speed, taper ratio and size-dependency are investigated on the natural frequencies of the rotating beam. Application of the weak form integral equations has made the solution simpler and shorter in the mathematical process. Presented relations can be used to obtain a close-form solution for quick calculation of the first five natural frequencies of the beams with flapwise vibration and non-local effects. The analysis results are compared with those obtained from other available published references.

• Smart Structures and Systems
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• 제18권3호
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• pp.425-448
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• 2016

In this paper, a new Pigeon Colony Algorithm (PCA) based on the features of a pigeon colony flying is proposed for solving global numerical optimization problems. The algorithm mainly consists of the take-off process, flying process and homing process, in which the take-off process is employed to homogenize the initial values and look for the direction of the optimal solution; the flying process is designed to search for the local and global optimum and improve the global worst solution; and the homing process aims to avoid having the algorithm fall into a local optimum. The impact of parameters on the PCA solution quality is investigated in detail. There are low-dimensional functions, high-dimensional functions and systems of nonlinear equations that are used to test the global optimization ability of the PCA. Finally, comparative experiments between the PCA, standard genetic algorithm and particle swarm optimization were performed. The results showed that PCA has the best global convergence, smallest cycle indexes, and strongest stability when solving high-dimensional, multi-peak and complicated problems.