• 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.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.376-386
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• 2020

The aim of this study was to develop a new efficient strategy that uses the Vector form Intrinsic Finite-element (VFIFE) method to conduct the static and dynamic analyses of marine pipes. Nonlinear problems, such as large displacement, small strain, and contact and collision, can be analyzed using a unified calculation process in the VFIFE method according to the fundamental theories of point value description, path element, and reverse motion. This method enables analysis without the need to integrate the stiffness matrix of the structure, because only motion equations of particles established according to Newton's second law are required. These characteristics of the VFIFE facilitate the modeling and computation efficiencies in analyzing the nonlinear dynamic problem of flexible pipe with large deflections. In this study, a three-dimensional (3-D) dynamical model based on 3-D beam element was established according to the VFIFE method. The deep-sea flexible pipe was described by a set of spatial mass particles linked by 3-D beam element. The motion and configuration of the pipe are determined by these spatial particles. Based on this model, a simulation procedure to predict the 3-D dynamical behavior of flexible pipe was developed and verified. It was found that the spatial configuration and static internal force of the mining pipe can be obtained by calculating the stationary state of pipe motion. Using this simulation procedure, an analysis was conducted on the static and dynamic behaviors of the flexible mining pipe based on a 1000-m sea trial system. The results of the analysis proved that the VFIFE method can be efficiently applied to the static and dynamic analyses of marine pipes.

• 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.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.390-397
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• 2003

A three-dimensional (3D) inversion technique has been developed for interpretation of magnetotelluric (MT) data. The inversion method is based on the linearized least-squares (Gauss-Newton) method with smoothness regularization. In addition to the underground 3D resistivity distribution, static shifts are also treated as unknown parameters in the inversion. The forward modeling is by the staggered-grid finite difference method. A Bayesian criterion ABle is applied to search the optimum trade-off among the minimization of the data misfit, model roughness and static shifts. The method has been applied to several MT datasets obtained at geothermal fields in Japan and other Asian countries. In this paper, two examples will be discussed: one is the data at the Ogiri geothermal area, southwestern Japan, and the other is at the Pohang low-enthalpy geothermal field, southeastern Korea. The inversion of the Ogiri data has been performed stably, resulting in a good fitting between the observed and computed apparent resistivities and phases. The recovered 3D resistivity structure is generally similar to the two-dimensional (2D) inversion models, although the deeper portion of the 3D model seems to be more realistic than that of the 2D model. The 3D model is also in a good agreement with the geological model of the geothermal reservoirs. 3D interpretation of the Pohang MT data is still preliminary. Although the fitting to the observed data is very good, the preliminary 3D model is not reliable enough because the station coverage is not sufficient for a 3D inversion.

• 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.

• 한국강구조학회 논문집
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• 제10권3호통권36호
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• pp.487-495
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• 1998

스페이스 프레임 구조물은 내부 기둥이 없는 대공간을 덮을 수 있다는 장점 때문에 현재의 많은 구조가와 설계자들에게 큰 관심을 받고 있다. 본 연구에서 다루는 강성구조 이산화시스템인 스페이스 트러스는 기하학적 비선형항이 포함된 대변형 이론을 이용한 유한요소법을 응력해석 방법으로 사용하며, 비선형최적화에 적합한 GINO(General Interactive Nonlinear Optimizer) 프로그램을 이용하여 구조물에 대한 전체체적을 목적함수로 하고 부재의 축력강도, 세장비, 처짐 및 국부좌굴 등으로 제약조건식을 유도하여 최적 설계를 하고자 한다.

• 한국태양에너지학회 논문집
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• 제25권1호
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• pp.87-96
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• 2005

본 논문은 압력차로 인한 유체의 유동장에서 서스펜션의 입자 밀도를 분포 규명하기 위해 적용할 수 있는 Electric Impedance Tomography (EIT)의 새로운 기법에 대한 효율성을 다루고 있다. Regularized Newton-Raphson iterative method를 근간으로 inverse problem의 해를 구하는데, 이는 곧 목적 함수(object function)를 몇 가지의 제한조건(constraints) 하에서 최소화시키는 과정이라 할 수 있다. 한편, 관련 forward problem은 유한요소법(FEM)을 이용하여 해결하며, 기존의 연구와는 달리 선형 형상 함수(linear shape function)를 이용하여 전도도가 연속적인 물성치로 유동장에 분포되어 있는 것으로 가정하였다. 여러 경우의 test run에 대한 결과는 본 논문에서 적용한 방법론의 타당성을 보여 주고 있다. 태양에너지의 추출을 위해 직접촉식 열교환기가 종종 이용되고 있는데, 본 연구는 열교환기 내부의 분산 유체에 대한 해석에 일조를 할 수 있을 것으로 기대된다.

• 한국지반공학회지:지반
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• 제12권6호
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• pp.87-100
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• 1996

본 연구에서는 동반논문(오세붕 & 이승래, 1996)에서 정식화한 비등방경화 구성모델에 대한 내재적인 응력적분 알고리즘의 정확성과 효율성을 검증하였다. 비배수 삼축압축시험경로에 대한 오차평가를 통하여 정확도해석을 수행하였고 수치적인 굴착해석예제를 수행함으로써 정확도 및 수렴도를 분석하였다. 그 결과 제안된 알고리즘이 비등방경화 구성관계에 대하여 음력을 정화하게 적분하고 Newton 법을 이용한 비선형 해석시에 점근적인 2차 수렴도를 확보함을 알 수 있었다. 그리고 이러한 검증을 토대로 지반의 초기조건 및 시공단계를 고려한 유한요소법을 이용하여 실제 굴착문제를 해석하였다. 비등방경화 구성관계를 이용함으로써, 추정된 벽체의 변위는 Cainflay모델에 비하여 실제와 더 유사한 해석결과를 얻을 수 있었다.

• 한국HCI학회:학술대회논문집
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• 한국HCI학회 2006년도 학술대회 1부
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• pp.1222-1227
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• 2006

본 연구의 목적은 객체의 형상정보(3D mesh)와 색/질감정보(image)를 이용하여 텍스쳐 맵핑된 고품질의 가상모델을 생성하는데 있다. 3 차원 형상정보에 대응하는 이미지 상의 텍스쳐 좌표 관계를 구하기 위해 오브젝트 좌표계와 카메라 좌표계 사이의 변환행렬, 카메라의 초점거리, 카메라 CCD 와 프레임상의 이미지 사이의 aspect ratio 를 파라미터로 하는 3D-2D 정합을 수행한다. 이러한 3D-2D 정합을 효율적으로 수행하기 위하여, 카메라 내부파라미터 검정단계, 신뢰도가 높은 초기해 설정단계, 비선형 최적화(Newton method) 단계로 접근한다. 또한, 색/질감정보로 이용되는 객체의 이미지는 촬영조건에 의해 스펙큘러(specular)나 이미지 픽셀값의 포화상태(saturation) 등의 결점을 포함한다. 영상내의 스펙큘러 좌표와 3D-2D 정합의 결과를 이용하여 촬영 당시의 광원을 추정하고, 근사화된 빛반사도 함수(BRDF)를 이용하여, 텍스쳐의 픽셀값 변조를 통해 이미지 촬영 당시의 광원효과가 제거된 디퓨즈 텍스쳐를 획득한다. 본 연구에서는 퐁(Phong)의 모델을 근사화한 빛 반사도 함수 모델로 사용하였다.

• Steel and Composite Structures
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• 제29권3호
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• pp.319-332
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• 2018

This paper investigates the free vibration of geometrically imperfect functionally graded car-bon nanotube-reinforced composite (FG-CNTRC) beams that are integrated with two sur-face-bonded piezoelectric layers and subjected to a combined action of a uniform temperature rise, a constant actuator voltage and an in-plane force. The material properties of FG-CNTRCs are assumed to be temperature-dependent and vary continuously across the thick-ness. A generic imperfection function is employed to simulate various possible imperfections with different shapes and locations in the beam. The governing equations that account for the influence of initial geometric imperfection are derived based on the first-order shear deformation theory. The postbuckling configurations of FG-CNTRC hybrid beams are determined by the differential quadrature method combined with the modified Newton-Raphson technique, after which the fundamental frequencies of hybrid beams in the postbuckled state are obtained by a standard eigenvalue algorithm. The effects of CNT distribution pattern and volume fraction, geometric imperfection, thermo-electro-mechanical load, as well as boundary condition are examined in detail through parametric studies. The results show that the fundamental frequency of an imperfect beam is higher than that of its perfect counterpart. The influence of geometric imperfection tends to be much more pronounced around the critical buckling temperature.