• 소음진동
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• 제8권2호
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• pp.267-273
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• 1998

This study aims at performing sensitivity analysis of piezoelectric smart structure for minimizing radiated noise from the structure, The structure consists of a flat plate on which disk shaped piezoelectric actuator is mounted, and finite element modeling is used for the structure. The finite element modeling uses a combination of three dimensional piezoelectric, flat shell and transition elements so thus it can take into account the coupling effects of the piezoelectric device precisely and it can also reduce the degrees of freedom of the finite element model. Electric potential on the piezoelectric actuator is taken as a design variable and total radiated power of the structure is chosen as an objective function. The objective function can be represented as Rayleigh's integral equation and is a function of normal displacements of the structure. For the convenience of computation, all degrees of freedom of the finite element equation is condensed out except the normal displacements of the structure. To perform the design sensitivity analysis, the derivative of the objective function with respect to the normal displacements is found, and the derivative of the norma displacements with respect to the design variable is calculated from the finite element equation by using so called the adjoint variable method. The analysis results are compared with those of the finite difference method, and shows a good agreement. This sensitivity analysis is faster and more accurate than the finite difference method. Once the sensitivity analysis program is used for gradient-based optimizations, one could achieve a better convergence rate than non-derivative methods for optimal design of piezoelectric smart structures.

• 대한기계학회논문집A
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• 제24권5호
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• pp.1331-1342
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• 2000

In power generation systems a variety of structural components typically operate at high temperature and pressure. Therefore a life assessment methodology accounting for gradual creep fracture is increasingly needed for these components. The most critical defects in such structure are generally found in the form of semi-elliptical surface cracks in the welded tubular joints. Therefore the analysis of a semi-elliptical surface crack in a plate or a shell is an important problem in engineering fracture mechanics. On this background, via shell/line-spring finite element analyses of such surface cracks in the welded T and L joints under various loadings, we investigate J-integral along the crack front We first develop T and L joints auto mesh generation program providing ABAQUS input file composed of shell/line-spring finite elements. We then further develop a T and L joints life assessment program based on the experimental creep crack growth law and auto mesh generation program in a graphical user interface format Finally the remaining life of T and L joints for various analytical parameters are assessed using the developed life assessment program.

• Structural Engineering and Mechanics
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• 제2권2호
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• pp.125-139
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• 1994

A vector algorithm for calculating the stiffness matrices of reinforced concrete shell elements is presented. The algorithm is based on establishing vector lengths equal to the number of elements. The computational efficiency of the proposed algorithm is assessed on a Cray Y-MP supercomputer. It is shown that the vector algorithm achieves scalar-to-vector speedup of 1.7 to 7.6 on three moderate sized inelastic problems.

• 한국항공우주학회지
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• 제32권3호
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• pp.37-44
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• 2004

본 논문에서는 압전재의 재료 비선형성을 고려한 경량 압전 복합재 작동기(LIPCA)의 성능 해석을 수행하였다. 성능 해석을 위해 9절점 쉘 요소 정식화에 바탕을 둔 압전 쉘 요소를 이용하였다. LIPCA의 작동 변위를 보다 정확히 예측하기 위하여, 실험을 통해 얻은 압전 변형률 함수와 증분 정식화를 추가하여 기존 선형 유한요소 프로그램을 수정하였다. 이렇게 개발된 재료 비선형 압전 옐 프로그램을 이용하여 LIPCA의 작동변위를 재 계산하였고, 재료 비선형 해석으로 얻은 작동 변위가 선형 해석으로 계산된 작동 변위 보다 측정 변위에 훨씬 근접함을 확인하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제23권5호
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• pp.702-710
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• 1999

U-shaped bellows are usually used to piping system pressure sensor and controller for refriger-ator. Bellows subjected to internal pressure are designed for the purpose of absorbing deformation. Internal pressure on the convolution sidewall and end collar will be applied to an axial load tend-ing to push the collar away from the convolutions. To find out deformation behavior of bellow sub-jected to internal pressure the axisymmetric shell theory using the finite element method is adopted in this paper. U-shaped bellows can be idealized by series of conical frustum-shaped ele-ments because it is axisymmetric shell structure. The displacements of nodal points due to small increment of force are calculated by the finite element method and the calculated nodal displace-ments are added to r-z cylindrical coordinates of nodal points. The new stiffness matrix of the sys-tem using the new coordinates of nodal points is adopted to calculate the another increments of nodal displacement that is the step by step method is used in this paper. The force required to deflect bellows axially is a function of the dimensions of the bellows and the materials from which they are made. Spring constant is analyzed according to the changing geometric factors of U-shaped bellows. The FEM results were agreed with experiment. Using developed FORTRAN PROGRAM the internal pressure vs. deflection characteristics of a particu-lar bellows can be predicted by input of a few factors.

• 한국항공우주학회지
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• 제31권8호
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• pp.27-35
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• 2003

쉘의 기하 모델링과 해석은 각각 다른 배경과 목적을 가지고 발전되어 왔다. 따라서 기하 모델링과 해석을 통합한 설계 도구를 만들기에 기존의 방법은 적절하지 않다. 본 연구에서는 기하 모델링과 해석, 최적 설계를 통합한 개념을 제시한다. 이것은 B-스플라인 곡면의 표현방법에 기초를 두고 있다. 기하학적으로 정확한 쉘 유한요소를 도입하였으며, 최적 설계 부분에서는 곡면의 조정점을 설계변수로 택하였다. 또한 설계 민감도를 계산하기 위해서 준해석적 방법을 사용했고, 이를 바탕으로 순차적 선형계획법을 이용해 곡면의 형상 최적화를 수행하였다. 이렇게 개발된 통합설계 개념은 곡면의 모델링과 해석에 적합한 도구로 이용될 수 있다.

• 대한토목학회논문집
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• 제29권6A호
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• pp.577-585
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• 2009

이 논문은 원전 격납건물의 극한내압능력 평가와 비선형해석을 수행하기 위하여 개발된 해석프로그램인 9절점 퇴화 쉘 유한요소에 대하여 기술하였다. 개발된 쉘 유한요소는 퇴화 고체기법과 구조물에서 발생하는 횡전단변형도를 고려하기 위하여 Reissner-Mindlin(RM)가정을 도입하였다. 콘크리트의 재료모델은 등가응력-등가변형률의 관계를 이용하여 콘크리트의 응력과 변형률의 수준을 결정하고, 콘크리트에 균열이 발생하면 부착응력을 고려하는 인장강성모델과 균열면에서의 전단전달 메카니즘 그리고 균열면에서 압축강도 감소모델 등으로 재료적 거동을 나타내었다. 또한 균열발생기준으로 압축-인장영역에는 Niwa가 제안한 응력포락선을 도입하였고, 인장-인장영역에는 Aoyagi-Yamada가 제안한 응력포락선을 사용하였다. 개발된 프로그램의 성능은 다양한 수치예제를 통하여 검증하였다. 검증예제 결과로부터 개발된 쉘 유한요소를 이용한 해석결과는 실험결과 또는 다른 해석결과와 유사한 결과를 도출하였다.

• 대한기계학회논문집
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• 제10권3호
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• pp.383-391
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• 1986

본 논문에서는 이들 기본모우드형태가 검토되었고 또한 두께효과와 비대칭성 효과에 따른 고유진동주파수, 모우드형태, 울림주파수의 변화를 수치적 해석과 실험 적 해석방법에 의해 비교검토되었다. 수치해석방법은 유한요소법으로 이용된 프로그 램은 NASTRAN 프로그램이고 모우드의 형태는 Tectronics컴퓨터그래픽을 이용하여 나타 내었다. 실험적방법은 충격햄머법과 F.F.T. 분석장치(Fast Fourier Transformation Analyzer)를 이용하였다.

• Steel and Composite Structures
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• 제10권4호
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• pp.361-371
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• 2010

Enhancement in the seismic buckling capacity of steel tanks caused by the addition of fiber reinforced polymers (FRP) retrofit layers attached to the outer walls of the steel tank is investigated. Three-dimensional non-linear finite element modeling is utilized to perform such analysis considering non linear material properties and non-linear large deformation large strain analysis. FRP composites which possess high stiffness and high failure strength are used to reduce the steel hoop stress and consequently improve the tank capacity. A number of tanks with varying dimensions and shell thicknesses are examined using FRP composites added in symmetric layers attached to the outer surface of the steel shell. The FRP shows its effectiveness in carrying part of the hoop stresses along with the steel before steel yielding. Following steel yielding, the FRP restrains the outward bulging of the tank and continues to resist higher hoop stresses. The percentage improvement in the ultimate base moment capacity of the tank due to the addition of more FRP layers is shown to be as high as 60% for some tanks. The percentage of increase in the tank moment capacity is shown to be dependent on the ratio of the shell thickness to the tank radius (t/R). Finally a new methodology has been explained to calculate the location of Elephant foot buckling and consequently the best location of FRP application.

• 소성∙가공
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• 제26권5호
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• pp.293-299
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• 2017

In this paper, finite element stamping analysis was carried out for the front lower arm to examine the applicability of solid element with damage theory to predict shear fracture phenomena induced by sheared edge as well as deformation mechanisms. Mechanical properties related to deformation and damage theory were determined from tensile test. Shear fracture was predicted by normalized Cockcroft-Latham model with initial imposition of the damage value along the sheared edge. Simulation results illustrated that the analysis with solid element and damage theory predicted edge profile, strain distribution, and forming load more accurately than the analysis with shell element. Simulation with solid element can also predict the shear fracture more exactly comparing to analysis with shell element and forming limit curve.