• 충청수학회지
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• 제20권4호
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• pp.419-432
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• 2007

Double-diffusive convection inside a triangular porous cavity is studied numerically. Galerkin finite element method is adopted to derive the discrete form of the governing differential equations. The first-order backward Euler scheme is used for temporal discretization with the second-order Adams-Bashforth scheme for the convection terms in the energy and species conservation equations. The Boussinesq-Oberbeck approximation is used to calculate the density dependence on the temperature and concentration fields. A parametric study is performed with the Lewis number, the Rayleigh number, the buoyancy ratio, and the shape of the triangle. The effect of gravity orientation is considered also. Results obtained include the flow, temperature, and concentration fields. The differences induced by varying physical parameters are analyzed and discussed. It is found that the heat transfer rate is sensitive to the shape of the triangles. For the given geometries, buoyancy ratio and Rayleigh numbers are the dominating parameters controlling the heat transfer.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.409-412
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• 2000

Much research efforts have been made on the structure and properties of metals deformed to severe plastic deformation (SPD). Being deformed to SPD, ultra-fine grains (UFG) are usually formed, and UFG structure exhibits fundamental differences in original physical properties. One method often used to obtain SPD is equal channel angular pressing (ECAP). In order for this technique to be exploited, it is important to understand the deformation behavior during the ECAP processing with respect to friction. The finite element method (FEM) has been used to investigate this issue.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.220-223
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• 2000

A method of calculating the natural frequency corresponding to the modes of vibration of beams and tower structures, with irregular cross sections and with arbitrary boundary conditions was developed and reported by Kim, D. H. in 1974. In this paper, the result of application of this method to the three span continuous reinforced concrete bridge with elastic intermediate supports is presented. Such bridge represents either concrete or sandwich type three span bridge on polymeric supports for passive control or on actuators for active control The concrete slab is considered as a special orthotropic plate. The influence of the modulus of the foundation and $D_{22}$, $D_{12}$, $D_{66}$ stiffnesses on the natural frequency is thoroughly studied.

• Journal of Advanced Marine Engineering and Technology
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• 제36권6호
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• pp.794-801
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• 2012

유한요소법은 구조물의 정적해석과 동적해석의 강력한 도구로 이용되고 있다. 정적인 해석에 있어서는 상당히 정확도가 높지만 진동해석에서는 여전히 정확성이 떨어진다. 주파수응답함수(FRF)는 저주파 영역에서는 비교적 쉽게 맞출 수 있으나 고주파 영역으로 가면 실제 구조물이 나타내는 현상과는 차이가 커지고, 감쇠의 해석적 발견의 어려움으로 인하여 진동 진폭을 예측하기 어렵다. 따라서 구조물의 형상에 따라 유한요소법을 적절히 수정하여서 적용할 필요가 있다. 여기에서는 평판에 대하여 유한요소 해석을 하고, 실험을 통하여 결과를 비교하고, 차이를 보정하는 방법을 제시하고자 한다. 전혀 가공하지 않은 평판의 데이터를 그대로 이용할 경우 같은 구조물의 해석 결과인지 의심스러울 정도이지만, 영계수만의 조정으로도 상당히 근접한 해석 결과를 보인다. 그러나 이 역시 한계가 있어서 유전알고리즘을 이용한 모델의 치수의 조정과 감쇠계수의 추정을 통하여 거의 완벽한 모델을 제안할 수 있었다.

• Geomechanics and Engineering
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• 제14권3호
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• pp.211-224
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• 2018

In this paper, a predictive method accounting for the scaling effects of rockfill materials in the numerical deformation analysis of rockfill dams is developed. It aims to take into consideration the differences of engineering properties of rockfill materials between in situ and laboratory conditions in the deformation analysis. The developed method is based on the modification of model parameters used in the chosen material model, which is, in this study, an elasto-plastic model with double yield surfaces, i.e., the modified Hardening Soil model. Datasets of experimental tests are collected from previous studies, and a new dataset of the Nam Ngum 2 dam project for investigating the scaling effects of rockfill materials, including particle size, particle gradation and density, is obtained. To quantitatively consider the influence of particle gradation, the coarse-to-fine content (C/F) concept is proposed in this study. The simple relations between the model parameters and particle size, C/F and density are formulated, which enable us to predict the mechanical properties of prototype materials from laboratory tests. Subsequently, a 3D finite element analysis of the Nam Ngum 2 concrete face slab rockfill dam at the end of the construction stage is carried out using two sets of model parameters (1) based on the laboratory tests and (2) in accordance with the proposed method. Comparisons of the computed results with dam monitoring data indicate that the proposed method can provide a simple but effective framework to take account of the scaling effect in dam deformation analysis.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.211-221
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• 1998

Thermal behavior on the cylinder block of a 4-cylinder, 4-stroke 2.0L SOHC gasoline engine was numerically and experimentally analyzed. The numerical calculation was performed using the finite element method. The cylinder block was modelled as a three dimensional finite element by considering its geometry. The physical domain was devided into hexahedron elements. 16 thermocouples were installed at points of 2mm inside from cylinder wall near top ring of piston in cylinder block, which points have suffered major thermal loads and suggested as proper measurement points for engine design by industrial engineers. Under full load and 9$0^{\circ}C$ coolant temperature condition, temperature behavior of cylinder block according to engine speed were analyzed. The results showed that temperature rose gradually to conform to a function of 2nd~4th order of engine speed at intake side, exhaust and siamese side, respectively. As engine load was changed from 100 to 50% by 25% step, temperature curve also conformed to 2nd~7th order function of engine speed. Temperature differences by load condition were similar among 100, 75% and 50%. Under full load and coolant temperature of 11$0^{\circ}C$, temperature behavior were also analyzed and the result also showed conformance to 2n d~7th order function of engine speed. Temperature curve was transferred in parallel upwards corresponding coolant temperature rise.

• Structural Engineering and Mechanics
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• 제5권3호
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• pp.269-281
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• 1997

The overall buckling mode in a composite steel-concrete beam over an internal support is necessarily lateral-distortional, in which the bottom compressive range displaces laterally and twists, since the top flange is restrained by the nearly rigid concrete slab. An efficient finite element method is used to study elastic lateral-distortional buckling in composite beams whose steel portion is tapered. The simplified model for a continuous beam that is presented herein is a fixed ended cantilever whose steel portion is tapered, and is subjected to moment gradient. This is intended to give an insight into distortion in a continuous beam that occurs in the negative bending region, and the differences between the cantilever representation and the continuous beam are highlighted. An eigenproblem is established, and the buckling modes and loads are determined in the elastic range of structural response. It is found from the finite element study that the buckling moment may be enhanced significantly by using a vertical stiffener in the region where the lateral movement of the bottom range is greatest. This enhancement is quantified in the paper.

• 한국도로학회논문집
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• 제19권1호
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• pp.73-80
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• 2017

PURPOSES : This paper presents a comparison study between dynamic and static analyses of falling weight deflectometer (FWD) testing, which is a test used for evaluating layered material stiffness. METHODS: In this study, a forward model, based on nonlinear subgrade models, was developed via finite element analysis using ABAQUS. The subgrade material coefficients from granular and fine-grained soils were used to represent strong and weak subgrade stiffnesses, respectively. Furthermore, the nonlinearity in the analysis of multi-load FWD deflection measured from intact PCC slab was investigated using the deflection data obtained in this study. This pavement has a 14-inch-thick PCC slab over fine-grained soil. RESULTS: From case studies related to the nonlinearity of FWD analysis measured from intact PCC slab, a nonlinear subgrade model-based comparison study between the static and dynamic analyses of nondestructive FWD tests was shown to be effectively performed; this was achieved by investigating the primary difference in pavement responses between the static and dynamic analyses as based on the nonlinearity of soil model as well as the multi-load FWD deflection. CONCLUSIONS : In conclusion, a comparison between dynamic and static FEM analyses was conducted, as based on the FEM analysis performed on various pavement structures, in order to investigate the significance of the differences in pavement responses between the static and dynamic analyses.

• Steel and Composite Structures
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• 제28권3호
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• pp.319-329
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• 2018

The field around additional cutout of the floor beam web in orthotropic bridge deck was subjected to high stress concentration, especially the weld toe between floor beam and U shaped rib and the free edge of the additional cutout. Based on different considerations, different geometrical parameters of additional cutout were proposed in European, American and Japanese specifications, and there remained remarkable differences among them. In this study, considering influence of out-of-plane deformation of floor beam web and U shaped rib, parameter analysis for additional cutout under typical load cases was performed by fine finite element method. The influence of additional cutout shape and height to the stress distribution around the additional cutout were investigated and analyzed. Meanwhile, the static and fatigue test on this structure details was carried out. The stress distribution was consistent with the finite element analysis results. The fatigue property for additional cutout height of 95mm was slightly better than that of 61.5 mm.

• 대한의용생체공학회:의공학회지
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• 제8권1호
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• pp.57-62
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• 1987

본 연구에서는 8-node cubic element로서 3차원 흉부모델을 구성하였고 또한 3차원 정상상태 유한요소법 코드를 FORTRAN을 이용하여 개발하였다. 프로그램의 출력은 각 node의 전위. 각 요소의 전ㄹ. 그리고 Z축방향으로의 각 층에서 총 전류이다. 이 흉부모델을 이용한 임피던스혈량측정법에서의 기초임피던스 ($Z_0$)를 계산하였다. 일반화된 라플라스 방정식을 정전위와 무전속 경계조건을 적용하여 풀었다. 또한, 전극간의 전위차와 $Z_0$의 계산값이 실측치와 근접하였으므로 이 모델이 인체의 흉뷰화 유사함을 확인하였다.