• Structural Engineering and Mechanics
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• 제13권5호
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• pp.533-542
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• 2002

This paper considers the buckling and post-buckling behavior of empty metal storage tanks under wind load. The structures of such tanks may be idealized as cantilever cylindrical shells, and the structural response is investigated using a computational model. The modeling employs a doubly curved finite element based on a theory by Simo and coworkers, which is capable of handling large displacements and plasticity. Buckling results for tanks with four different geometric relations are presented to consider the influence of the ratios between the radius and the height of the shell (R/L), and between the radius and the thickness (R/t). The studies aim to clarify the differences in the shells regarding their imperfection-sensitivity. The results show that thin-walled short tanks, with R/L = 3, display high imperfection sensitivity, while tanks with R/L = 0.5 are almost insensitive to imperfections. Changes in the total potential energy of tanks that would buckle under the same high wind pressures are also considered.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 박판성형기술의 진보
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• pp.1-9
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• 1994

Three recent developments made at Rensselaer in sheet material forming processes are briefly reviewed in this paper. These advances represent three broad disciplines of Process Simulation, Forming Processes, and Computer-Aided Measurement Methods. The first development deals with simple and quick computer simulation of 2D sheet forming process without depending on popular finite element analysis methods. An analytical method based on a thin shell theory accounts for bending and unbending effects, and is capable of simulating practical sheet metal forming processes under the plane strain condition. The second area is concerned with innovative methods to improve formability of sheet materials by temperature gradient forming. The drawing limit is increased by such an improved temperature gradient forming process. The third and final area deals with a totally new experimental technique to capture 3D geometry data and measure strain distributions of sheet metal parts using a digital 35mm SLR camera.

• Steel and Composite Structures
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• 제26권2호
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• pp.125-137
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• 2018

In this work, the bending and free vibration analysis of multilayered plates and shells is presented by utilizing a new higher order shear deformation theory (HSDT). The proposed involves only four unknowns, which is even less than the first shear deformation theory (FSDT) and without requiring the shear correction coefficient. Unlike the conventional HSDTs, the present one presents a novel displacement field which incorporates undetermined integral variables. The equations of motion are derived by using the Hamilton's principle. These equations are then solved via Navier-type, closed form solutions. Bending and vibration results are found for cylindrical and spherical shells and plates for simply supported boundary conditions. Bending and vibration problems are treated as individual cases. Panels are subjected to sinusoidal, distributed and point loads. Results are presented for thick to thin as well as shallow and deep shells. The computed results are compared with the exact 3D elasticity theory and with several other conventional HSDTs. The proposed HSDT is found to be precise compared to other several existing ones for investigating the static and dynamic response of isotropic and multilayered composite shell and plate structures.

• Composites Research
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• 제14권6호
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• pp.9-15
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• 2001

본 연구에서는 복합재료로 만들어진 박판의 상자형 보에 대만 선형 정적해석을 수행하였다. 복합재료 보의 해석을 위해서 혼합 보 이론을 적용하였으며, 상자형 단면의 벽에 대해 설정이 가능한 여러 가지 구성방정식을 고려할 수 있도록 하였다. 굽힘-비틀림 혹은 인장-비틀림 연성을 갖는 단순한 적층 형상의 복합재료 강자형 보를 예로 들어 보의 정적 거동에 미치는 복합재료의 연성효과를 고찰하였다. 본 해석결과의 타당성을 검증하기 위만 방편으로 상용 구조해석 프로그램을 이용한 정밀 유한요소 구조해석을 수행하였다. 혼합 보 이론을 이용하여 복합재료 상자형 보에 대한 단면상수 등을 해석적으로 결정하였으며, 적절한 구성방정식의 설정 여부가 최종적인 해의 정확도를 결정하는 중요한 요소임을 보였다.

• Structural Engineering and Mechanics
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• 제34권4호
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• pp.491-505
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• 2010

A computational analysis of the nonlinear free vibration of corrugated annular plates with shallow sinusoidal corrugations under uniformly static ambient temperature is examined. The governing equations based on Hamilton's principle and nonlinear bending theory of thin shallow shell are established for a corrugated plate with a concentric rigid mass at the center and rotational springs at the outer edges. A simple harmonic function in time is assumed and the time variable is eliminated from partial differential governing equations using the Kantorovich averaging procedure. The resulting ordinary equations, which form a nonlinear two-point boundary value problem in spatial variable, are then solved numerically by shooting method, and the temperature-dependent characteristic relations of frequency vs. amplitude for nonlinear vibration of heated corrugated annular plates are obtained. Several numerical results are presented in both tabular and graphical forms, which demonstrate the accuracy of present method and illustrate the amplitude frequency dependence for the plate under such parameters as ambient temperature, plate geometry, rigid mass and elastic constrain.

• 대한조선학회논문집
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• 제42권6호
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• pp.631-636
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• 2005

One and three dimensional whipping response analyses of a naval surface combatant subjected to an underwater explosion bubble pulse were carried out to compare the efficiency and accuracy according to the modeling methods. In 1-D analysis, program UNDEXWHIP developed by KIMM was used, which is based on the thin-walled Timoshenko's beam theory and on the modal analysis method using wetted vibratory modes of the hull girder. In 3-D analysis, three finite element models were suggested using LS-DYNA/USA code, such as 3-D beam model considering geometric shape of wetted side shell, coarse and fine 3-D F.E. models. Through the comparison of results from the 1-D and 3-D analyses, it could be confirmed that 1-D analysis result is in good agreement with 3-D analysis ones, and that fine 3-D F.E. model, shock analysis one, is also used both in the shock response and whipping response analyses for the analyst effort and time savings.

• Korea-Australia Rheology Journal
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• 제19권4호
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• pp.191-199
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• 2007

Precision injection molding process is of great importance since precision optical products such as CD, DVD and various lens are manufactured by those process. In such products, birefringence affects the optical performance while residual stress that determines the geometric precision level. Therefore, it is needed to study residual stress and birefringence that affect deformation and optical quality, respectively in precision optical product. In the present study, we tried to predict residual stress, final shrinkage and birefringence in injection molded parts in a systematic way, and compared numerical results with the corresponding experimental data. Residual stress and birefringence can be divided into two parts, namely flow induced and thermally induced portions. Flow induced birefringence is dominant during the flow, whereas thermally induced stress is much higher than flow induced one when amorphous polymer undergoes rapid cooling across the glass transition region. A numerical system that is able to predict birefringence, residual stress and final shrinkage in injection molding process has been developed using hybrid finite element-difference method for a general three dimensional thin part geometry. The present modeling attempts to integrate the analysis of the entire process consistently by assuming polymeric materials as nonlinear viscoelastic fluids above a no-flow temperature and as linear viscoelastic solids below the no-flow temperature, while calculating residual stress, shrinkage and birefringence accordingly. Thus, for flow induced ones, the Leonov model and stress-optical law are adopted, while the linear viscoelastic model, photoviscoelastic model and free volume theory taking into account the density relaxation phenomena are employed to predict thermally induced ones. Special cares are taken of the modeling of the lateral boundary condition which can consider product geometry, histories of pressure and residual stress. Deformations at and after ejection have been considered using thin shell viscoelastic finite element method. There were good correspondences between numerical results and experimental data if final shrinkage, residual stress and birefringence were compared.

• 한국구조물진단유지관리공학회 논문집
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• 제8권2호
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• pp.147-158
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• 2004

많은 장점을 가진 복합재료를 사용한 보강판에 대하여 지금까지 많은 연구자들이 변위법에 근거한 등매개변수 평판 요소와 보요소를 결합한 유한요소법을 사용하여왔다. 이러한 유한요소법은 보요소를 평판 요소의 절점에 대한 강성으로 치환하기 때문에 보강재에 대한 국부적인 거동을 파악할 수 없으며 복합적층 구조인 경우 그 적용성이 제한적이다. 따라서, 본 연구에서는 복합재료 보강판의 해석에 있어 보강재 및 판에 대하여 3차원 쉘요소를 사용하여 거동을 분석하고자 한다. 본 연구에서는 Reissner-Mindlin의 1차 전단변형이론을 사용하였다. 그러나 Reissner-Mindlin이론에 의한 등매개변수 평판 휨 요소는 판의 두께가 얇아지는 경우 일반적으로 전단잠김현상과 가상의 제로에너지 모드가 발생하는데 이를 제거하기 위해 대체전단변형률장을 사용하였다. 폭-두께비, 형상비 뿐만아니라 경사판의 경사각 변화에 따른 임의방향 보강재를 갖는 단순지지된 복합적층 구형 및 경사판에 대한 처짐분포를 비교 분석하였다.

• 한국강구조학회 논문집
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• 제10권1호통권34호
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• pp.47-61
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• 1998

수평곡선 I형교에서는 곡선주형의 초기곡률로 인하여 휨과 비틀림이 서로 연성 되어 복잡한 거동을 하며. 교량전체 거동에 가로보가 미치는 영향이 상당히 크다. 수평곡선 I형교의 거동특성을 파악하기 위해서는 곡선주형과 함께 가로보를 고려하여야 한다. 본 연구에서는 수평곡선 I형교에 대한 자유진동해석을 위하여 곡선주형을 유한요소 모델링하기 위한 곡선보요소와 가로보를 모델링하기위한 직선보요소를 구성하고, 이들 보요소를 사용한 유한요소 해석 프로그램을 개발한다. 곡선보 요소는 초기곡률과 됨을 고려하기 위하여 박판곡선보 이론에 근거하여 2축 대칭단면을 갖는 I형 곡선보에 대한 유한요소 정식화를 통하여 구성되며, 이때 형상함수는 박판곡선보의 선형 정적 평형방정식의 제차해를 사용한다. 직선보 요소는 됨자유도를 포함하여 절점당 7자유도를 갖는다. 개발한 프로그램에서는 직교좌표계를 사용하여 전체 강성행렬과 전체 질량행렬을 구성하며, 고유치를 구하기 위하여 Gupta의 방법을 사용한다. 기존의 연구결과를 이용하여 구성된 곡선보 요소를 비교검증하고, 수치해석 예제를 통하여 개발한 프로그램의 결과와 쉘요소를 사용하여 범용유한요소해석프로그램으로 수행한 결과를 비교한다.

• 한국공간구조학회논문집
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• 제11권1호
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• pp.121-130
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• 2011

스페이스 프레임 구조물은 연속체 쉘 구조물의 원리를 이용하여 매우 넓은 공간을 효과적 으로 덮을 수 있는 구조물이지만 뜀좌굴 및 분기좌굴 등과 같은 불안정거동은 돔형 구조물에서는 더욱 복잡하게 나타난다. 또한 붕괴메커니즘의 이론적 연구와 실험적 연구결과들 사이에서도 많은 차이를 보인다. 본 논문에서는 미적 효과가 크며 단층의 대공간을 확보하기에 적합한 돔형 공간 구조물의 구조 불안정 특성을 접선강성방정식을 이용하여 비선형 증분해석을 수행하고, Rise-span(${\mu}$)비 및 하중모드($R_L$)에 따른 임계점과 분기점의 특성을 돔형 공간구조물의 예제를 통해 고찰하였다. 여기서 불안정점은 증분해석과정을 통해서 예측할 수 있었으며, 예제에서 낮은 ${\mu}$에서는 전체좌굴이, 높은 ${\mu}$의 경우는 절점좌굴이 지배적이며, 낮은 $R_L$에서 정점좌굴이, 높은 $R_L$에서는 전체좌굴이 지배적이고, 전체좌굴이 나타나는 경우, 분기좌굴하중은 완전형상의 극한점좌굴하중의 약 50%에서 70%의 분포를 보였다.