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배경셀의 수와 관련한 무요소법을 이용한 캔틸레버 보의 정적해석
이창계,이상진 대한건축학회지회연합회 2008 대한건축학회지회연합회 학술발표대회논문집 Vol.2008 No.1
A meshless method based on the radial point interpolation method(RPIM) is used to analyze cantilever beam. Meshless methods have been considered is a very attractive as new computational method since it does not need mesh generation in analysis procedure. Especially, RPIM, using radial basis function(RBF), has an advantage that do not consider the essential boundary condition. In order to demonstrate the accuracy of the adopted meshless method, numerical examples are tackled with multiple elastic moduli and the different number of background cell. Numerical results are compared with the reference solution produced by finite element analysis program FEAP.
이창계,Sundararajan Natarajan,이정재 한국전산구조공학회 2023 한국전산구조공학회논문집 Vol.36 No.5
This study introduces a smoothed finite-element implementation into the phase-field framework. In recent years, the phase-field method has recieved considerable attention in crack initiation and propagation since the method needs no further treatment to express the crack growth path. In the phase-field method, high strain-energy accuracy is needed to capture the complex crack growth path; thus, it is obtained in the framework of the smoothed finite-element method. The salient feature of the smoothed finite-element method is that the finite element cells are divided into sub-cells and each sub-cell is rebuilt as a smoothing domain where smoothed strain energy is calculated. An adaptive quadtree refinement is also employed in the present framework to avoid the computational burden. Numerical experiments are performed to investigate the performance of the proposed approach, compared with that of the finite-element method and the reference solutions.
이창계,Sundararajan Natarajan 한국전산구조공학회 2024 한국전산구조공학회논문집 Vol.37 No.3
본 논문에서는 평활화 유한요소법(Smoothed finite element method)을 도입한 응력 기반 구배 탄성론(Gradient elasticity)의 2차원 경계치 문제에 대한 연구를 수행하였다. 구배 탄성론은 기존 탄성론에서는 표현할 수 없는 미소규모의 크기 의존적인 기계적 거동을 설명하기 위해 제안되었다. 구배 탄성체론에서 고차 미분 방정식을 두 개의 2차 미분 방정식으로 분할하는 Ru-Aifantis 이론을 사용하기 때문에 평활화 유한요소법에 적용이 가능하게 된다. 본 연구에서 경계치 문제를 해결하기 위해 평활화 유한 요소 프레임워크에 스태거드 방식(Staggered scheme)을 사용하여 국부 변위장과 비국부 응력장을 평활화 영역 및 요소에서 각각 계산하였다. 구배 탄성에서 중요한 변수인 내부 길이 척도의 영향을 측정하기 위해 일련의 수치 예제를 수행하였다. 수치 해석 결과는 제안한 기법이 내부 길이 척도에 따라 균열 선단과 전위 선에 나타나는 응력 집중을 완화할 수 있음을 보여준다. This paper presents two-dimensional boundary value problems of the stress-based gradient elasticity within the smoothed finite element method (S-FEM) framework. Gradient elasticity is introduced to address the limitations of classical elasticity, particularly its struggle to capture size-dependent mechanical behavior at the micro/nano scale. The Ru-Aifantis theorem is employed to overcome the challenges of high-order differential equations in gradient elasticity. This theorem effectively splits the original equation into two solvable second-order differential equations, enabling its incorporation into the S-FEM framework. The present method utilizes a staggered scheme to solve the boundary value problems. This approach efficiently separates the calculation of the local displacement field (obtained over each smoothing domain) from the non-local stress field (computed element-wise). A series of numerical tests are conducted to investigate the influence of the internal length scale, a key parameter in gradient elasticity. The results demonstrate the effectiveness of the proposed approach in smoothing stress concentrations typically observed at crack tips and dislocation lines.
비선형 비압축성 물질의 해석을 위한 3차원 Smoothed FEM
이창계,이정재 대한건축학회 2019 大韓建築學會論文集 : 構造系 Vol.35 No.9
This work presents the three-dimensional extended strain smoothing approach in the framework of finite element method, so-called smoothedfinite element method (S-FEM) for quasi-incompressible hyperelastic materials undergoing the large deformations. The proposed method isknown that the incompressible limits, such as over-estimation of stiffness and distorted mesh sensitivity, can be overcome in two dimensions. Therefore, in this paper, the idea of Cell-based, Edge-based and Node-based strain smoothing approaches is extended to three-dimensions. Theconstruction of subcells and smoothing domains for each methods are explained. The smoothed strain-displacement matrix and the stiffnessmatrix are obtained on each smoothing domain in the same manner with two-dimensional S-FEM. Various numerical tests are studied todemonstrate the validity and accuracy of 3D-S-FEM. The obtained results are compared with analytical solutions to express the efficacy ofthe methods. 본 연구에서는 2차원 변형률 평탄화기법을 유한요소기법에 도입한 Smoothed Finite Element Method를 비선형 비압축성 물질의 해석을 위하여 3차원으로 확대하였다. 각 기법의 하위요소 생성 및 평탄화 영역의 생성 기법을 설명하고, 변형률-변위 행렬 및 강성행렬 계산법을 설명하였다. 이를 바탕으로 비선형 해석을 위한 정식화를 수행하고 그에 따른 여러 수치예제를 수행하였다. 제안된 기법의 해는 정해 및 참조해와 비교하여 그 우수성을 입증하고자 한다.
Strain smoothing 기법을 이용한 비압축성 초탄성물질의 동적해석
이창계(Lee, Changkye),김동건(Kim, Dong-Keon),Zeike A. Taylor 대한건축학회 2017 대한건축학회 학술발표대회 논문집 Vol.37 No.1
This work aims to propose the nonlinear dynamic analysis using the strain the smoothing approach. Lower-order triangular and tetrahedral elements are widely used since complex geometries can be easily generated. However, such elements often face the over-estimation of stiffness (often called locking) when problems are involved non-linear large deformations, and they also suffer from severely distorted meshes. In this paper, we introduce the strain-smoothed approach (or smoothed finite element method) to handle such weaknesses of linear triangular and tetrahedral elements, and propose the strain-smoothed explicit dynamic analysis algorithm. Numerical tests show following results: the proposed algorithm efficiently avoids deleterious locking, and at the same lever of accuracy strain-smoothing requires less number of elements than FEM.
부식 수준 및 균열폭에 따른 부식된 철근과 콘크리트 계면의 부착-미끄러짐 거동
조상현,기성훈,이정재,이창계 한국구조물진단유지관리공학회 2023 한국구조물진단유지관리공학회 논문집 Vol.27 No.1
In this paper, the effect of corrosion level and crack width on the cohesive strength-slip behavior of corroded steel rebar and concrete interfaceis conducted. The existing studies mainly focus on the decrease in bond strength with respect to the level of corrosion; there are, however, few studieson the decrease in cohesive strength according to the crack width of the concrete surface due to corrosion. Therefore, in this study, a series of testsfor the cohesive strength, slip behavior and mass loss of the reinforcing bar is evaluated at the surface of corroded rebar and concrete. It is found thatthe tendency to decrease the bond strength is closely related to the crack width rather than the corrosion level. Hence, to determine the degradationperformance for the bond strength-slip behavior relation, the occurrence of cracks on the concrete surface can be a suitable index. 본 논문에서는 부식된 철근과 콘크리트 계면의 부착강도-슬립거동에 있어 부식수준 및 균열폭의 영향에 대한 연구를 수행하였다. 기존의 연구는 주로 부식수준에 따른 부착강도 저하에 초점을 맞추고 있으나 부식에 의한 콘크리트 표면 균열폭에 따른 부착강도 저하에 관한연구는 매우 적다. 따라서 본 연구에서는 부식된 철근과 콘크리트 접합부의 부착강도, 슬립 거동 및 철근의 질량손실 등을 평가하고 균열폭 대비 접합성능을 확인하기 인발시험을 실시하였다. 그 결과로 표면 균열폭에 따른 접착강도 저하의 경향성이 부식수준에 따른 경향성보다 균등하게 나타났다. 따라서 부식수준에 비해 콘크리트 표면 균열 발생 여부가 부착강도-슬립거동 관계의 성능저하를 판단하기에 적합한 것으로 판단된다.
Mark Joseph Calubad,이정재,이창계 대한건축학회지회연합회 2023 대한건축학회연합논문집 Vol.25 No.3
This review study discusses the utilization of Terrestrial Laser Scanner (TLS) 3D point cloud data in representing geometry for structural health monitoring (SHM) applications, particularly the so-called Scan-to-FEM method. The existing studies related to the topic are intensively presented and discussed along with the advantages and disadvantages of the modelling methods: meshing by whole and cross-section. Two case studies are conducted to show both modelling methods used for geometry representation for Scan-to-FEM method. Meshing by whole and cross-section methods result in the relative errors of respective 2.79% and 1.4% in the maximum displacement vector sum, compared to their reference models constructed by ABAQUS. It is also seen that the density and clarity of 3D point cloud data can bring well-shaped geometry for FE analysis and consequently produce good accuracy.