• 한국항공우주학회지
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• 제30권1호
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• pp.36-43
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• 2002

압전적층판의 비선형 열압전탄성 거동에서의 스냅-스루 현상을 뉴튼-랩슨기법에 호길이법을 적용하여 수치적으로 규명하였다. 층별변위장이론과 von Karman 변형률-변위 관계식을 적용하여 열압전탄성 복합적층 평판에 대한 비선형 유한요소정식화를 수행하였다. 다양한 압전 작동모드에 따라 대칭 및 편심된 구조모델에 대하여 정적 및 동적 관점에서 비선형 열압전탄성 거동과 진동특성을 연구하였다. 본 연구에서는 압전 작동기를 사용하여 유연한 열적 구조물들의 성능을 향상시킬 수 있는 가능성과 새로운 현상학적인 발견인 열압전탄성 스냅핑 거동이 좌굴된 압전탄성 복합적층 평판에서 과도한 압전작동력이 작용하는 경우에 발생할 수 있음을 제시하였다.

• 한국군사과학기술학회지
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• 제2권2호
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• pp.148-156
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• 1999

유한요소기법을 적용하여 열하중을 받는 원통형 복합적층 패널의 좌굴후 거동해석 및 진동 특성을 연구하였다. 열적 대변형을 고려하기 위해 층별변위장이론을 바탕으로 한 von-Karman 비선형 변위-변형률 관계식을 적용하였다. 원통형 패널의 스냅핑 현상을 해석하기 위해서 원통형 호길이법이 사용되었다. 원통형 패널의 두께비, shallowness angle 그리고 경계조건 등 여러 가지 구조 파라미터에 따라 열적 스냅핑과 진동 특성을 고찰하였다. 열적 스냅핑 특성이 정적인 변형뿐만 아니라 진동 모드 형상 및 순서를 변화시키고 있음을 보여준다.

• Structural Engineering and Mechanics
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• 제40권2호
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• pp.257-277
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• 2011

In this paper the geometrically nonlinear continuum plate finite element model, hitherto not reported in the literature, is developed using the total Lagrange formulation. With the layerwise displacement field of Reddy, nonlinear Green-Lagrange small strain large displacements relations (in the von Karman sense) and linear elastic orthotropic material properties for each lamina, the 3D elasticity equations are reduced to 2D problem and the nonlinear equilibrium integral form is obtained. By performing the linearization on nonlinear integral form and then the discretization on linearized integral form, tangent stiffness matrix is obtained with less manipulation and in more consistent form, compared to the one obtained using laminated element approach. Symmetric tangent stiffness matrixes, together with internal force vector are then utilized in Newton Raphson's method for the numerical solution of nonlinear incremental finite element equilibrium equations. Despite of its complex layer dependent numerical nature, the present model has no shear locking problems, compared to ESL (Equivalent Single Layer) models, or aspect ratio problems, as the 3D finite element may have when analyzing thin plate behavior. The originally coded MATLAB computer program for the finite element solution is used to verify the accuracy of the numerical model, by calculating nonlinear response of plates with different mechanical properties, which are isotropic, orthotropic and anisotropic (cross ply and angle ply), different plate thickness, different boundary conditions and different load direction (unloading/loading). The obtained results are compared with available results from the literature and the linear solutions from the author's previous papers.

• 한국전산구조공학회논문집
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• 제22권5호
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• pp.463-474
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• 2009

기존에 설치되어 있는 구조물의 양면대칭 패치보강은 항상 면내거동만을 유발하나 시공상 어려움이 있다. 반면에 일면 패치보강의 경우 인장력의 증가에 따라 중립축의 위치가 대칭이 아니므로 휨에 대한 강성도가 증가하게 되며, 결과적으로 적층판의 휨을 심화시키게 된다. 이 연구에서는 일면 패치보강된 적층판의 두께방향은 물론이고 원공주위의 응력집중계수를 산정하기 위해 p-수렴 완전층별모델을 제안하였다. 가정된 변위장의 정의를 위해, 임의의 층에서 변위-변형률 관계와 3차원 구성방정식은 2차원 및 3차원 계층적 형상함수의 조합이 사용된다. 원형경계의 기하형상을 나타내기 위해 초유한사상기법이 사용되며, 다른 외삽법을 사용하지 않고 각 층마다 절점에서의 응력값을 직접적으로 얻기위해 가우스-로바토 수치 적분이 수행되었다. 제안된 모델의 정확도와 단순성은 기존의 3차원 유한요소해석과 실험에 의해 구해진 결과들과의 비교를 통해 검증되었다. 또한 정사각형, 원형, 고리형 형상의 다양한 패치보강에 따른 휨효과를 조사하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.5-8
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• 2001

A three node flat triangular element incorporating Layerwise Zig-Zag Theory(HZZT) is developed suitable for analyzing damped laminated composite structures. Using an interdependent kinematic relation, the higher order shear rotations are replaced by in-plane displacements, a transverse displacement and section rotations, which result in three translations and two rotations. Natural frequencies and modal loss factors of cantilevered laminated plates with embedded damping layers are calculated with the zig-zag triangular element and compared to the experimental results and MSC/NASTRAN results using a layered combination of plate and solid elements.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.943-946
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• 2000

Selective laser sintering(SLS) is a solid freeform fabrication process whereby a part is built layerwise by scanning a powder bed. The properties of metal powder are dependent on the heat, it is not easy to do the exact error compensation with analysis and estimation by modeling. This paper suggests that the error is compensated by experimental method and then the accuracy of shape is enhanced by revising of STL file. Also bonding force is measured by an experiment with change of process path.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.423-427
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• 1997

Recently, distributed piezoelectric actuators have drawn attention due to their potential applicability within smart structures. Because they serve not only as active components but also passive components, it is difficult to estimate their characteristics accurately. In this study a finite element method based on layerwise theory has been formulated to analyze the characteristics of the distributed piezoelectric actuators. The present method has the capability to describe more refined strain distribution and more realistic boundary conditions.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.39-44
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• 2002

A three node triangular element with drilling rotations incorporating Improved Layerwise Zig-zag Theory(HZZT) is developed to analyze the vibration of spinning pretwisted composite blades with embedded damping layer. Matching conditions at the interfaces between the damping material and the border material are enforced by setting the shear forces matched and different shear strains along the interfaces. The natural frequencies and modal loss factors of cantilevered pretwisted composite blade with damping core are calculated with the present triangular element enforcing the matching conditions and compared to experimental results and MSC/NASTRAN results using a layered combination of plate and solid elements.

• Steel and Composite Structures
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• 제18권6호
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• pp.1353-1368
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• 2015

A finite element model is presented for the analysis of composite steel-concrete beams based on a refined high-order theory. The employed theory satisfies all the kinematic and stress continuity conditions at the layer interfaces and considers effects of the transverse normal stress and transverse flexibility. The global displacement components, described by polynomial or combinations of polynomial and exponential expressions, are superposed on local ones chosen based on the layerwise or discrete-layer concepts. The present finite model does not need the incorporating any shear correction factor. Moreover, in the present $C^1$-continuous finite element model, the number of unknowns is independent of the number of layers. The proposed finite element model is validated by comparing the present results with those obtained from the three-dimensional (3D) finite element analysis. In addition to correctly predicting the distribution of all stress components of the composite steel-concrete beams, the proposed finite element model is computationally economic.

• 한국소음진동공학회논문집
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• 제23권12호
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• pp.1066-1072
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• 2013

In this work, active control algorithm is adopted to reduce delamination effects of the damaged composite structure and control performance with MFC actuator is numerically evaluated. Finite element model for the damaged composite structure with piezoelectric actuator is established based on improved layerwise theory. In order to achieve high control performance, MFC actuator, which has increased actuating force, is considered as a piezoelectric actuator. Mode shapes and corresponding natural frequencies for the damaged smart composite structure are studied. After design and implementation of active controller, dynamic characteristics of the damaged smart composite structure are investigated.