• 대한조선학회지
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• 제22권1호
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• pp.21-30
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• 1985

This paper deals whth the buckling as well as postbuckling analysis of axisymmertric shells taking the initial deflection effects into account. Incremental equilibrium equations, based on the principle of virtual work, were derived by the finite element method, the successive step-by-step Newton-Raphson iterative technique was adopted. To define the transition pattern of postbuckling behavior from the prebuckling state more accurately, a simple solution method was developed, i.e. the critical load was calculated by the load extrapolation method with the determinant of tangent stiffness matrix and the equilibrium configuration in the immediate postbuckling stage was obtained by perturbation scheme and eigenvalue analysis. Degenerated isoparametric shell elements were used to analyse the axisymmetric shell of revolution. And by the method developed in this paper, the computer program applicable to the nonlinear analysis of both thin and moderately thick shells was constructed. To verify the capabilities and accuracies of the present solution method, the computed results were compared with the results of analytical solutions. These results coincided fairly well in both the small deflection and large deflection ranges. Various numerical analyses were done to show the effect of initial deflection and shape of shells on buckling load and postbuckling behavior. Futhermore, corrected directions of applied loads at every increment steps were used to determine the actual effects of large deflection in non-conservative load systems such as hydrostatic pressure load. The following conclusions can be obtained. (1) The method described in this paper was found to be both economic and effective in calculating buckling load and postbuckling behavior of shell structure. (2) Buckling and postbuckling behavior of spherical caps is critically dependent upon their geometric configuration, i.e. the shape of spherical cap and quantities of the initial deflection. (3) In the analysis of large deflection problems of shells by the incremental method, corrections of the applied load directions are needed at every incremental step to compensate the follower force effects.

• 해양환경안전학회지
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• 제10권1호
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• pp.29-33
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• 2004

지금까지의 강구조설계에서는 일반적인 탄성좌굴개념을 적용하고 있다. 왜냐하면 현재까지의 실적선의 데이터와 경험적인 방법에 의해 도출된 여러 가지 룰에 의한 데이터가 상당히 신뢰할만한 정도를 갖고 있기 때문이라고 판단하기 때문이다. 그러나, 최근들어 판두께가 박판인 고장력강재가 선체에 폭넓게 사용되어지면서 탄성좌굴발생 시점이 빨라졌으며 이에따른 탄소성거동을 정확히 예측할 필요성이 대두되고 있다. 이에 본 연구에서는 선체의 이중저 판넬구조에서 압축하중을 받을때의 실제판부재의 주변지지조건을 네가지로 이성화하여 해석하였으며, 이때 실제 필연적으로 존재하게 되는 열가공에 의한 비대칭형 초기처짐을 적용하였고, 비선형해석기법으로서는 Arc-length method를 적용하였고 해석코드는 범용유한요소법 소프트웨어로 잘 알려진 ANSYS를 사용하였다.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2004년도 춘계학술발표회
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• pp.121-125
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• 2004

본 연구에서는 비선형 유한요소법을 적용하여 면내압축방향의 하중이 작용하는 경우, 유공판에 대하여 유공의 크기를 변화시켜가며, 최종강도 시리즌 해석을 수행하고 설계식을 도출하였다. 연속판 조건을 고려하여 모델링 범위를 결정하였으며, 주변 경계조건의 영향을 충분히 고려하기 위하여 주변 보강재를 포함하여 실제의 선박구조를 선정하였다. 또한, 보강재의 크기 및 형상의 영향을 조사하기 위하여 보강재 치수 및 종류를 변수로 한 시리즈 해석을 수행하고, 개발된 설계식의 적용성을 검토하였다.

• 전자공학회논문지S
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• 제36S권8호
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• pp.81-87
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• 1999

일반거인 피쳐검출 및 추적 알고리즘에는 Garbor-jet를 이용한 elastic bunch graph matching (EBGM), rotation normalized cross-correlation (NCC-R) 및 화소의 고유치를 이용한 Shi-Tomasi-Kanade(STK) 알고리즘 등이 있다. 이들 중에서 EBGM, NCC-R은 피쳐모델에 의해 피쳐를 검출하지만 STK 알고리즘은 피쳐를 자동적으로 검출하는 특징을 가진다. 본 논문에서는 STK알고리즘인 Newton-Raphson (NR) 추적의 초기화 문제를 해결하기 위해서 모델링된 피쳐영역에서 STK 알고리즘으로 피쳐를 검출한 후, NR 방법으로 피쳐를 추적할 때, NR 방법에 의한 피쳐추적의 정확성을 개선시키기 위해 block matching agorithm (BMA)-NR 방법을 제안하였다. NR 방법에 의한 피쳐변위수렴시 BMA-NR 방법이 NBMA-NR (no BMA-NR)방법보다 피쳐추적의 정확성이 향상되었는데, 이는 NR의 서치영역크기로 인한 국소 최소치(local minimum) 문제를 해결하였기 때문이다.

• Structural Engineering and Mechanics
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• 제45권5호
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• pp.677-691
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• 2013

A semi-analytical finite strip method is developed for analyzing the post-buckling behavior of rectangular composite laminated plates of arbitrary lay-up subjected to progressive end-shortening in their plane and to normal pressure loading. In this method, all the displacements are postulated by the appropriate harmonic shape functions in the longitudinal direction and polynomial interpolation functions in the transverse direction. Thin or thick plates are assumed and correspondingly the Classical Plate Theory (CPT) or Higher Order Plate Theory (HOPT) is applied. The in-plane transverse deflection is allowed at the loaded ends of the plate, whilst the same deflection at the unloaded edges is either allowed to occur or completely restrained. Geometric non-linearity is introduced in the strain-displacement equations in the manner of the von-Karman assumptions. The formulations of the finite strip methods are based on the concept of the principle of the minimum potential energy. The Newton-Raphson method is used to solve the non-linear equilibrium equations. A number of applications involving isotropic plates, symmetric and unsymmetric cross-ply laminates are described to investigate the through-thickness shearing effects as well as the effect of pressure loading, end-shortening and boundary conditions. The study of the results has revealed that the response of the composite laminated plates is particularly influenced by the application of the Higher Order Plate Theory (HOPT) and normal pressure loading. In the relatively thick plates, the HOPT results have more accuracy than CPT.

• Steel and Composite Structures
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• 제29권6호
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• pp.785-802
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• 2018

In this paper, two different computational methods, called Rayleigh-Ritz and collocation are developed to estimate the ultimate strength of composite plates. Progressive damage behavior of moderately thick composite laminated plates is studied under in-plane compressive load and uniform lateral pressure. The formulations of both methods are based on the concept of the principle of minimum potential energy. First order shear deformation theory and the assumption of large deflections are used to develop the equilibrium equations of laminated plates. Therefore, Newton-Raphson technique will be used to solve the obtained system of nonlinear algebraic equations. In Rayleigh-Ritz method, two degradation models called complete and region degradation models are used to estimate the degradation zone around the failure location. In the second method, a new energy based collocation technique is introduced in which the domain of the plate is discretized into the Legendre-Gauss-Lobatto points. In this new method, in addition to the two previous models, the new model named node degradation model will also be used in which the material properties of the area just around the failed node are reduced. To predict the failure location, Hashin failure criteria have been used and the corresponding material properties of the failed zone are reduced instantaneously. Approximation of the displacement fields is performed by suitable harmonic functions in the Rayleigh-Ritz method and by Legendre basis functions (LBFs) in the second method. Finally, the results will be calculated and discussions will be conducted on the methods.

• 한국환경농학회지
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• 제8권1호
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• pp.37-46
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• 1989

본 연구는 호소의 2차원 수질해석을 위해 흐름의 기본 방정식과 확산이송 방정식에 유한요소법을 도입하여 모의한 것으로, 얻은 결론은 다음과 같다. 1.단순화된 1차원 수로에서의 모형검정 결과 수치해와 정확해가 거의 일치하므로 모형의 알고리즘이 잘 구성 되었음이 입증되며, 적용결과 실측치와의 비교에서도 만족할만한 결과가 도출되어 모형의 적용 가능성이 시사되었다. 2. 삽교호의 BOD, COD, T-N, T-P, 및 SS의 농도분포가 2차원적으로 해석되었다. 3. 비점오염원의 비중이 높아 오염부하량 산정이 어려운 T-N, T-P를 사용하지 않고 COD를 모의 하므로서 부영양상태를 예측할 수 있도록 하였다. 본 연구결과는 하구언 및 방조제 등으로 인한 호수와 같이 수심에 비해 폭이 넓은 자연수역의 수질 해석에 적용될 수 있으며 이를 활용하므로서 용수취수지점의 선택, 하천 방류수의 처리기준 선정등, 수자원의 효율적인 이용 관리와 수질 대책 수립에 이용될 수 있을 것으로 판단된다.

• 한국농공학회지
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• 제29권4호
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• pp.73-92
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• 1987

Formulation of the geometric optimization for truss structures based on the elasticity theory turn out to be the nonlinear programming problem which has to deal with the cross-sectional area of the member and the coordinates of its nodes simultaneously. A few techniques have been proposed and adopted for the analysis of this nonlinear programming problem for the time being. These techniques, however, bear some limitations on truss shapes, loading conditions and design criteria for the practical application to real structures. A generalized algorithm for the geometric optimization of the truss structures, which can eliminate the above mentioned limitations, is developed in this study. The algorithm proposed utilizes the two-levels technique. In the first level which consists of two phases, the cross-sectional area of the truss member is optimized by transforming the nonlinear problem into SUMT, and solving SUMT utilizing the modified Newton Raphson method. In the second level, which also consists of two phases the geometric shape is optimized utillzing the unindirectional search technique of the Powell method which make it possible to minimize only the objective functlon. The algorithm proposed in this study is numerically tested for several truss structures with various shapes, loading conditions and design criteria, and compared with the results of the other algorithms to examine its applicability and stability. The numerical comparisons show that the two- levels algorithm proposed in this study is safely applicable to any design criteria, and the convergency rate is relatively fast and stable compared with other iteration methods for the geometric optimization of truss structures. It was found for the result of the shape optimization in this study to be decreased greatly in the weight of truss structures in comparison with the shape optimization of the truss utilizing the algorithm proposed with the other area optimum method.

• 대한조선학회논문집
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• 제55권4호
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• pp.297-305
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• 2018

In a shipyard, block lifting is an important process in the production of ships and offshore structures. Block lifting is a sensitive process because lifting blocks have to be erected with exact positions and orientations. If we use a numerical method for the process, it is important to find tensions of wires and positions of equalizers to maintain the initial equilibrium position of the block. At this time, equations of motion of the block should be solved to calculate the initial equilibrium position of the block. Because the solving technique changes according to the number of equalizers, a suitable equation for the corresponding problem is required. In this study, three types of equations are proposed to find the initial equilibrium position of the block according to the number of equalizers. The Newton-Raphson's method is used to solve nonlinear simultaneous equations and the optimization method is used to determine the appropriate solution to the undetermined problem. To evaluate the applicability of the proposed methods, the dynamic simulations are performed using the tensions calculated from the proposed methods, and the results are discussed. The results show that the proposed methods can be effectively used to determine initial equilibrium position of the block for the block lifting.

• Coupled systems mechanics
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• 제1권4호
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• pp.361-379
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• 2012

This paper presents a fully coupled three-dimensional solver for the analysis of interaction between pulsatile flow and large deformation structure. A partitioned time marching algorithm is employed for the solution of the time dependent coupled discretised problem, enabling the use of highly developed, robust and well-tested solvers for each field. Conservative transfer of information at the fluid-structure interface is combined with an effective multi-predict-correct iterative scheme to enable implicit coupling of the interacting fields at each time increment. The three-dimensional unsteady incompressible fluid is solved using a powerful implicit time stepping technique and an ALE formulation for moving boundaries with second-order time accurate is used. A full spectrum of total variational diminishing (TVD) schemes in unstructured grids is allowed implementation for the advection terms and finite element shape functions are used to evaluate the solution and its variation within mesh elements. A finite element dynamic analysis of the highly deformable structure is carried out with a numerical strategy combining the implicit Newmark time integration algorithm with a Newton-Raphson second-order optimisation method. The proposed model is used to predict the wave flow fields of a particular flow-induced vibrational phenomenon, and comparison of the numerical results with available experimental data validates the methodology and assesses its accuracy. Another test case about three-dimensional biomedical model with pulsatile inflow is presented to benchmark the algorithm and to demonstrate the potential applications of this method.