• 한국광학회지
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• 제19권1호
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• pp.80-83
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• 2008

광집게는 매질보다 큰 굴절률을 가지는 마이크로 크기의 구형 유전체를 강하게 집속되는 레이저를 이용해서 포획하고 움직이는 도구이다. 본 논문에서는 FDTD 방법을 이용해서 포획 힘을 계산하고, 그 방법을 설명하였다. 강하게 집속되는 레이저는 nonparaxial Gaussian beam을 이용해서 표현하였으며, 레이저가 대상물체와 매질에서 진행하는 것은 FDTD 방법을 이용해서 시뮬레이션 하였다. 레이저를 계산공간 전체에서 해석적으로 표현하기 위해서 scattered field formulation을 이용하였다. FDTD 방법을 이용해서 대상물체의 안팎의 전자기장을 시뮬레이션하고, 그 결과를 이용해서 Maxwell's stress tensor에 기반하여 포획 힘을 계산하였다.

• Steel and Composite Structures
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• 제24권5호
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• pp.523-536
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• 2017

A layerwise (LW) formulation based on the Galerkin method is presented to investigate the three-dimensional stress state in long sandwich plate which is subjected to tension force and pure bending moment. Based on the Galerkin method and the LW discretization approach, the equilibrium equations of elasticity for the long plate are written in the weak form and discretized through the thickness of the plate. The discretized equations are written in terms of displacement components of the numerical layers. The governing equations of the plate are solved analytically for the free edge boundary conditions. The distribution of stress state especially the 3D stress state in the vicinity of the edges of the sandwich plate which is subjected to tension and pure bending is studied. In order to increase the accuracy, the out of plane stresses are obtained by integrating the equilibrium equations of elasticity. The convergence and accuracy of the predictions are studied and various numerical results are presented for distribution of the in-plane and out of plane stresses in symmetric and un-symmetric sandwich plates.

• Structural Engineering and Mechanics
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• 제15권2호
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• pp.199-223
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• 2003

The formulation of a non-linear shear deformable shell element is presented for the solution of stability problems of stiffened plates and shells. The formulation of the geometrical stiffness presented here is exactly defined on the midsurface and is efficient for analyzing stability problems of thick plates and shells by incorporating bending moment and transverse shear resultant force. As a result of the explicit integration of the tangent stiffness matrix, this formulation is computationally very efficient in incremental nonlinear analysis. The element is free of both membrane and shear locking behaviour by using the assumed strain method such that the element performs very well in the thin shells. By using six degrees of freedom per node, the present element can model stiffened plate and shell structures. The formulation includes large displacement effects and elasto-plastic material behaviour. The material is assumed to be isotropic and elasto-plastic obeying Von Mises's yield condition and its associated flow rules. The results showed good agreement with references and computational efficiency.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.174-178
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• 1991

In this paper, we present a unified approach for the control of manipulator motions and active forces based on the operational space formulation. The end-effector dynamic model is used in the development of a control system in which the generalized operational space end-effector forces are selected as the command vector. A "generalized position and force specification matrix" is used for the specification of space of motions and forces in which manipulator is to be controlled. Flexibility in the force sensor, end-effector, and environment are discussed.discussed.

• 한국전산구조공학회논문집
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• 제18권4호통권70호
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• pp.385-393
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• 2005

본 논문에서는 기하학적으로 비선형인 유연한 Timoshenko 보의 대변위 운동방정식에 유한요소를 사용하여 정식화하였다. 비선형 구속방정식은 라그랑지 상수를 이용하여 운동방정식에 통합되었다. 정식화하는 과정과 수치해석에서 선형과 비선형 영향을 파악하였고, 코리올리스(Coriolis)힘과 회전자(Gyroscopic)힘의 효과는 관성력과 감쇠력과는 달리 일반적인 외력으로 간주하여 해석할 수 있었다. Newmark의 시간적분과 Newton-Raphson 반복법을 사용한 수치예제를 통해 정식화의 효용성을 보여주었다.

• 전산구조공학
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• 제7권4호
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• pp.69-83
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• 1994

평면 뼈대구조물의 매우 큰 변형에 대하여 정확한 비선형 유한요소의 정식화 과정을 나타내었다. 유한요소의 구성은 변화되는 재료의 기준 물성치에 근거를 두고 형성하였으며 매우 큰 변형을 받는 재료의 성질을 명확하게 특정지어 진응력-변형율 관계식을 직접 적용할 수 있도록 하였다. 큰회전과 작은 변형율을 받는 문제들을 형성하기 위하여 Co-rotation 접근 방법을 사용하였다. 큰 변형을 일으키는 요소의 문제를 해결하기 위하여 직선보 형태의 유한요소를 사용하였으며 개개의 유한요소의 정식화는 축방향력의 영향을 고려하여 미소 처짐보이론을 바탕으로 형성하였다. 본 연구에서 형성된 큰 변형에 대한 비선형 유한요소의 타당성을 확인하기 위해 몇몇 수치해들을 해석하고 검토하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.175-181
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• 1999

The present work is an attempt to calculate the steady state pressure and perturbed pressure of journal bearings that has a helical groove. A coordinate is fitted to the helical groove and governing equation is derived by applying generalized coodinate system to the divergence formulation method. This method makes it possible to deal with an arbitrary configuration of a lubricated surface. The dynamical response of shaft-bearing system is calculated using the bearing reaction force and external force.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.538-547
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• 2005

This paper presents the shaking table testing method, only using building specimen as an experimental part taking into account the dynamic soil-structure interaction based on the substructure method. The Parmelee's soil stiffness is used as an assumed soil model in here. The proposed methodologies are summarized as: (1) Acceleration feedback method is the one that the shaking table is driven by the motion, corresponding to the acceleration at foundation of the total SSI system. This is found by observing the fed-back accelerations of superstructure and using the interaction force based on the acceleration formulation. (2) Velocity feedback method is the one that the shaking table is driven by the motion, corresponding to the velocity at foundation of the total SSI system. This is found by observing the fed-back accelerations of superstructure and using the interaction force based on the velocity formulation. The applicability of the proposed methodologies to the shaking table test is investigated and experimentally verified in this paper.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.212-217
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• 1993

A 2-dimensional FEM/GEM program was developed for analyzing forming processes of an arbitrarily shaped draw-die, in which plane strain condition is assumed and linear line elements are employed. FEM formulation adopted a new algorithm for solving force equilibrium as well as non-penetration condition simultaneously. For the case of numerical divergence at nearly final forming stages and the initial guess in Newton-Raphson iterations, geometric force equilibrium method(GEM) is also introduced. The developed program was tested with the simulation of stamping processes of automotive bonnet inner pannel in order to verify the usefulness and validity of FEM/GEM formulation.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.141-148
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• 2007

We present an immersed boundary (IB) method for 3D simulation of flappingflags in a uniform flow. The proposed formulation is manipulated on the basis of an efficient Navier-Stokes solver adopting the fractional step method and a staggered Cartesian grid system. A direct numerical method is developed to calculate the flag motion, with the elastic force treated implicitly. The fluid motion defined on an Eulerian grid and the flag motion defined on a Lagrangian grid are independently solved and the mass of flag is handled in a natural way. An additional momentum forcing is formulated from the flag motion equation in a way similar with the direct-forcing IB formulation and acts as the interaction force between the flag and ambient fluid. A series of numerical tests are performed and the present results are compared qualitatively and quantitatively with previous studies. The instantaneous flag motion is analyzed under different conditions and surrounding vortical structures are identified. The effects of physical parameters on the flapping frequency are studied.