• Computational Structural Engineering
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• v.11 no.1
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• pp.179-190
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• 1998

A geometrically nonlinear finite element formulation of spatial cable networks is presented using two cable elements. Firstly, derivation procedures of tangent stiffness and mass matrices for the space truss element and the elastic catenary cable element are summarized. The load incremental method based on Newton-Raphson iteration method and the dynamic relaxation method are presented in order to determine the initial static state of cable nets subjected to self-weights and support motions. Furthermore, static non-linear analysis of cable structures under additional live loads are performed based on the initial configuration. Challenging example problems are presented and discussed in order to demonstrate the feasibility of the present finite element method and investigate static nonlinear behaviors of cable nets.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.666-672
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• 2017

Our research team is developing a 6-DOF manipulator for narrow workspaces in press forming processes, such as placing PEM nuts on the bottom of a chassis. In this paper, kinematic analysis was performed for the position control of the manipulator, along with structural analyses for position accuracy with different payloads. First, the Denavit-Hatenberg (DH) parameters are defined, and then the forward and backward kinematic equations are presented using the DH parameters. The kinematic model was verified by visual simulation using Coppelia Robotics' virtual robot experimentation platform (V-REP). Position accuracy analysis was performed through structural analyses of deflection due to self-weight and deflection under full payload (5 kgf) in fully opened and fully folded states. The maximum generated stress was 22.05 MPa in the link connecting axes 2 and 3, which was confirmed to be structurally safe when considering the materials of the parts.

• Journal of Korean Society of Steel Construction
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• v.21 no.6
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• pp.563-574
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• 2009

This paper briefly describes the fundamental strategies--path-tracing, pin-pointing, and path-switching--in the computational elastic bifurcation theory of geometrically non-linear single-load-parameter conservative elastic spatial structures. The stability points in the non-linear elasticity may be classified into limit points and bifurcation points. For the limit points, the path tracing scheme that successively computes the regular equilibrium points on the equilibrium path, and the pinpointing scheme that precisely locates the singular equilibrium points were sufficient for the computational stability analysis. For the bifurcation points, however, a specific procedure for path-switching was also necessary to detect the branching paths to be traced in the post-buckling region. After the introduction, a general theory of elastic stability based on the energy concept was given. Then path tracing, an indirect method of detecting multiple bifurcation points, and path switching strategies were described. Next, some numerical examples of bifurcation analysis were carried out for a trussed stardome, and a pin-supported plane circular arch was described. Finally, concluding remarks were given.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.2
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• pp.119-128
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• 2016

In a performance-based design, the structural safety is estimated from pre-defined damage states and corresponding damage indices. Both damage states and damage indices are well defined for above-ground structures, but very limited studies have been performed on underground structures. In this study, we define the damage states and damage indices of a cut-and-cover box tunnel which is one of typical structures used in metro systems, under a seismic excitation from a series of inelastic frame analyses. Three damage states are defined in terms of the number of plastic hinges that develop within the structure. The damage index is defined as the ratio of the elastic moment to the yield moment. Through use of the proposed index, the inelastic behavior and failure mechanism of box tunnels can be simulated and predicted through elastic analysis. In addition, the damage indices are linked to free-field shear strains. Because the free-field shear strain can be easily calculated from a 1D site response analysis, the proposed method can be readily used in practice. Further studies are needed to determine the range of shear strains and associated uncertainties for various types of tunnels and site profiles. However, the inter-linked platform of damage state - damage index - shear wave velocity - shear strain provides a novel approach for estimating the inelastic response of tunnels, and can be widely used in practice for seismic designs.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10a
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• pp.343-345
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• 2001

요약해석(abstract interpretation)이란 래티스(lattice)로 표현되는 요약된 공간에서 프로그램을 수행함으로써 프로그램의 성질을 분석하는 방법이다. 요약해석에서 프로그램의 분석 결과는, 정보가 없는 상태에서 시작하여 더 이상 정보의 증가가 없을 때까지 프로그램을 반복해서 수행함으로써 얻어지는 고정점(fixpoint)에 의하여 표현된다. 본 연구에서는 이러한 고정정 계산의 속도를 높이기 위하여 이전 반복의 계산 결과를 최대한 이용하는 방법을 제시한다. 그리고 제시된 방법을 상수 및 이명 분석의 구현에 적응하여 실제로 분석 속도가 증가함을 보였다.

• Membrane Journal
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• v.8 no.1
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• pp.1-10
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• 1998

액체 상태에서 물질이 확산되는 현상을 자유 부피의 개념으로 해석하고자 하는 노력은 1959년에 Cohen과 Turnbull에 의해서 시작되었다. 그들은 액체의 부피를 두 부분으로 나누었는데, 하나는 분자가 차지하고 있는 점유 부피(Occupied volume)이고, 다른 하나는 자유 부피(Free-volume)로서 무작정한 열적 유동에 의해서 재분배된다. 온도의 변화에 의해 부피가 변하는 것은 이 자유 부피의 변화때문이며, 점유 부피는 온도에는 무관함 것으로 갖주하였다. 분자가 액체 상태에서 이동하려면 이웃에 충분한 크기의 자유 부피 공간이 존재해야한다. 따라서, 분자의 확산은 분자가 이들 자유 부피 공간들로 도약하는 것이다. Cohen-Turnbull의 이론에서는 순수한 액체의 자기 확산 계수(Self-diffusion conefficient)는 자유 부피의 무작정한 유동에 의하여 임계 크기의 공간이 생성되는 확률과 관련이 있다. Cohen-Turnbull 자유 부피 이론은 그 후 많은 사람들에 의해서 수정되었고, 그중에서 현재 가장 널리 사용되는 것은 Fujita의 이론과 Vrentas-Duda의 이론이다. 두 이론 모두 확산 데이터를 correlation하는데는 문제가 없으나, Vrentas-Duda의 이론만이 확산계수를 예측할 수 있는 능력이 있다. 또한, 고분자와 용매의 도약 단위의 몰 질량이 같을때에 Vrentas-Duda의 이론은 Fujita의 이론과 같아지므로, Fujita의 이론은 Vrentas-Duda의 이론의 특수한 경우라고 할 수 있다. 따라서, 본 논문에서는 Vrentas-Duda 자유 부피 이론만을 다루기로 하겠다.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.345-349
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• 2004

하천의 수량 정보는 내용이 다양하고 공간적${\cdot}$시간적 특성을 갖고 있어 정보의 종류와 양이 광범위해지고 있다. 따라서 하천에서 홍수기에 유출량을 정확히 해석하고 예측한다는 것은 매우 어려울 일이다. 본 연구에서는 이들 수문자료들을 수집하고 홍수유출량을 예측하기 위해 신경망 모형과 상태공간 모형을 이용하여 홍수 유출 예측 모형을 구성하고 금강수계 주요지점에 적용하여 그 적용성을 확인한 후 예측력이 우수한 신경망 모형을 이용하여 Web상에서 홍수 유출량을 예측할 수 있는 시스템을 개발하였다. 개발된 시스템은 자료수집모듈, 유출예측모듈 등으로 구성하여 누구나 Web 상에서 유출량을 예측할 수 있도록 개발되었다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.4
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• pp.365-376
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• 2016

Population of urban areas is rapidly increased due to urbanization. This situation leads to lack of surface space. So, underground space has been developed for resolving the problem of congested urban areas. Many studies have researched for this situation. However, previous studies mainly focused on behaviour of structures. Researches about behaviour of soil are lacked. For this reason, this study has investigated interactive behaviour between embedded pile and its surrounding ground due to tunnelling. Soil deformation is observed by the close range photogrammetric method and image processing in the model test. These data are compared with numerical analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.1001-1011
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• 2006

It is a general agreement that exact statistical solutions can be found by a Monte Carlo technique. Due to difficulties, however, in the numerical generation of random fields, which satisfy not only the probabilistic distribution but the spectral characteristics as well, it is recognized as relatively difficult to find an exact response variability of a structural response. In this study, recognizing that the random field assumes a constant over the domain under consideration when the correlation distance tends to infinity, a semi-theoretical solution of response variability is proposed for general structures. In this procedure, the probability density function is directly used. It is particularly noteworthy that the proposed methodology provides response variability for virtually any type of probability density function, and has capability of considering correlations between multiple random variables.

• Tunnel and Underground Space
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• v.8 no.3
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• pp.200-208
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• 1998

This research is intended to investigate the behavior of the jointed rock under various loading conditions: static or dynamic load. The distributed state concept (DSC) is based on the idea that the response of the joint can be related to and expressed as the response of the reference states : relative intact (RI) and fully adjusted (FA) states. In the DSC, an initially RI joint modifies continuously through a process of natural self-adjustment, and a part of it approaches the FA state at randomly disturbed locations in the joint areas. In this study, based on the DSC concept, RI state, FA state, and disturbance function (D) are defined for characterizing the behavior of rock joint. From the results of this research, it can be stated that DSC model is capable of capturing the physical behavior of jointed rock such as softening and hardening and considering the size of joint and roughness of joint surface.