• Structural Engineering and Mechanics
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• 제17권1호
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• pp.51-68
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• 2004

Since the linear elastic fracture analysis has been proved to be insufficient in predicting the failure of strain hardening materials, a number of fracture concepts have been studied which remain applicable in the presence of plasticity near a crack tip. This work thereby presents a new finite element model to predict the elastic-plastic crack-tip field and fatigue life of center-cracked panels(CCP) with ductile fracture under large-scale yielding conditions. Also, this study has been carried out to investigate the path-dependence of J-integral within the plastic zone for elastic-perfectly plastic, bilinear elastic-plastic, and nonlinear elastic-plastic materials. Based on the incremental theory of plasticity, the p-version finite element is employed to account for the accurate values of J-integral, the most dominant fracture parameter, and the shape of plastic zone near a crack tip by using the J-integral method. To predict the fatigue life, the conventional Paris law has been modified by substituting the range of J-value denoted by ${\Delta}J$ for ${\Delta}K$. The experimental fatigue test is conducted with five CCP specimens to validate the accuracy of the proposed model. It is noted that the relationship between the crack length a and ${\Delta}K$ in LEFM analysis shows a strong linearity, on the other hand, the nonlinear relationship between a and ${\Delta}J$ is detected in EPFM analysis. Therefore, this trend will be depended especially in the case of large scale yielding. The numerical results by the proposed model are compared with the theoretical solutions in literatures, experimental results, and the numerical solutions by the conventional h-version of the finite element method.

• 전산구조공학
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• 제8권4호
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• pp.137-148
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• 1995

이차원 선형탄성파괴역학 문제에서 인장모우드 상태의 응력확대계수를 명료하게 산정할 수 있는 독립적 적분경로에 근거를 둔 새로운 J-적분 균열모델이 제안되었다. 이 방법은 p-수렴 개념에 기초를 두며 기존의 유한요소 컴퓨터코드에 쉽게 적용할 수 있다. 본 연구에서는 균열선단에서의 응력상태가 조사되었으며, 균열선단으로부터 떨어진 정규거리로 표현되는 서로 다른 적분경로에 따라 J-적분치가 유한요소해석시 Rice의 이론처럼 경로에 독립적인 해를 얻을 수 있는지 분석되었다. 세가지 수치예제인 중앙균열판, 일변균열판과 양변균열판과 양변균열판의 p-수렴 해석결과가 종래의 h-수렴법에 의한 해석결과와 비교되었으며, 또한 이 결과는 제안된 방법의 정확성과 수치적 안정성을 보여주고 있다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제18권4호
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• pp.305-316
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• 2014

The Hodge-Helmholtz decomposition splits a vector field into the unique sum of a divergence-free vector field (solenoidal part) and a gradient field (irrotational part). In a bounded domain, a boundary condition needs to be supplied to the decomposition. The decomposition with the non-penetration boundary condition is equivalent to solving the Poisson equation with the Neumann boundary condition. The Gibou-Min method is an application of the Poisson solver by Purvis and Burkhalter to the decomposition. Using the $L^2$-orthogonality between the error vector and the consistency, the convergence for approximating the divergence-free vector field was recently proved to be $O(h^{1.5})$ with step size h. In this work, we analyze the convergence of the irrotattional in the decomposition. To the end, we introduce a discrete version of the Poincare inequality, which leads to a proof of the O(h) convergence for the scalar variable of the gradient field in a domain with general intersection property.

• Journal of Electrical Engineering and Technology
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• 제5권4호
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• pp.597-605
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• 2010

This paper presents a contribution to parameter identification of a non-linear system using a new strategy to improve the genetic algorithm (GA) method. Since cost function plays an important role in GA-based parameter identification, we propose to improve the simple version of GA, where weights of the cost function are not taken as constant values, but varying along the procedure of parameter identification. This modified version of GA is applied to the induction motor (IM) as an example of nonlinear system. The GA cost function is the weighted sum of stator current and rotor speed errors between the plant and the model of induction motor. Simulation results show that the identification method based on improved GA is feasible and gives high precision.

• Transactions on Control, Automation and Systems Engineering
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• 제3권4호
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• pp.268-271
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• 2001

In this paper, we propose a simplified pollution adaptive mesh generation algorithm using singular elements. The algorithm based on the element pollution error indicator concentrate on boundary nodes. The automatic mesh generation method is followed by either a node-relocation or a node-insertion method. The boundary node relocation phase is introduced to reduce pollution error estimates without increasing the boundary nodes. The node insertion phase greatly improves the error and the factor with the cost of increasing the node numbers. It is shown that the suggested r-h version algorithm combined with singular elements converges more quickly than the conventional one.

• 방송공학회논문지
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• 제12권6호
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• pp.611-623
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• 2007

H.264|AVC 영상 압축부호화 국제 표준은 영상의 효율적인 압축을 위하여 화면 내 프레임뿐만 아니라 화면 간 프레임에서도 다양한 블록 크기로 화면 내 예측을 수행할 수 있도록 설계되어 있다. 그러나 이는 영상 부호화 처리 시간의 급격한 증가를 초래하여 부호화기의 실시간 응용에 걸림돌이 될 수 있다. 본 논문에서는 먼저 화면 내 예측 부호화 수행 여부에 대한 조기 결정 방법과 화면 내 예측 부호화 수행 시 부호화하고자 하는 블록의 영상 내용 특성과 QP값의 변화에 따른 부호화 대상 주변 블록 모드 정보를 이용하여 만들어진 조건부 확률을 이용하여 화면 내 예측 부호화를 고속화하는 방법을 제안한다 제안된 방법은 기본적으로 화면 간 프레임 부호화에 있어서 화면 내 예측 수행 여부에 대한 조건을 결정하고, 화면 내 예측이 사용될 경우 부호화하고자 하는 블록의 내용 특성과 부호화된 주변 블록의 결정 모드를 고려하여 화면 내 예측을 고속화하는 것이다. 본 논문의 실험은 H.264|AVC의 참조 소프트웨어인 JM 11.0을 사용하여 검증하였으며, 제안된 방법을 사용하였을 경우 무시할 수 있을 정도의 PSNR 감소와 비트율 증가를 가져 왔으며, 전체 부호화 시간은 최대 41.63%가 단축되는 효과를 얻을 수 있었다.

• 전기의세계
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• 제49권9호
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• pp.9-16
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• 2000

A receding horizon $H_{\infty}$ predictive control method is derived by solving a min-max problem in non-recursive forms. The min-max cost index is converted to a quadratic form which for systems with input saturation can be minimized using QP. Through the use of closed-loop prediction the prediction of states the use of closed-loop prediction the prediction of states in the presence of disturbances are made non-conservative and it become possible to get a tighter $H_{\infty}$ norm bound. Stability conditions and $H_{\infty}$ norm bounds on disturbance rejection are obtained in infinite horizon sence. Polyhedral types of feasible sets for sets and disturbances are adopted to deal with the input constraints. The weight selection procedures are given in terms of LMIs and the algorithm is formulated so that it can be solved via QP. This work is a modified version of an earlier work which was based on ellipsoidal type feasible sets[15].

• Wind and Structures
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• 제5권2_3_4호
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• pp.301-316
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• 2002

An important goal of computational wind engineering is to impact the design process with simulations of flow around buildings and bridges. One challenging aspect of this goal is to solve the Navier-Stokes (NS) equations accurately. For the unsteady computations, an adaptive finite element technique may reduce the computer time and storage. The preliminary application of a p-version as well as an h-version adaptive technique to computational wind engineering has been reported in previous paper. The details on the implementation of p-adaptive technique will be discussed in this paper. In this technique, two posteriori error estimations, which are based on the velocity and vorticity, are first presented. Then, the polynomial order of the interpolation function is increased continuously element by element until the estimated error is less than the accepted. The second through sixth orders of hierarchical functions are used as the interpolation polynomials. Unequal order interpolations are used for velocity and pressure. Using the flow around a circular cylinder with Reynolds number of 1000 the two error estimators are compared. The result show that the estimated error based on the velocity is lower than that based on the vorticity.

• International Journal of Control, Automation, and Systems
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• 제1권2호
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• pp.178-183
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• 2003

This work is a modified version of an earlier work that was based on ellipsoidal type feasible sets. Unlike the earlier work, polyhedral types of invariant and feasible sets are adopted to deal with input constraints. The use of polyhedral sets enables the formulation of on-line algorithm in terms of QP (Quadratic Programming), which can be solved more efficiently than semi-def algorithms. A simple numerical example shows that the proposed method yields larger stabilizable sets with greater bounds on disturbances than is the case in the earlier approach.

• 한국전산유체공학회지
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• 제19권3호
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• pp.85-90
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• 2014

The purpose of this study is to develop a new Meshless Method to solve 2-D compressible flow problems numerically. This paper includes a revised Least Square method that improves robustness compared with its original version by removing excessive numerical oscillation which occurs when points are randomly distributed. Numerical analyses of hypersonic flow over a blunt body were carried out using the method, then robustness, accuracy and convergence of their results were compared with those obtained from the original method.