• 한국지진공학회논문집
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• 제2권4호
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• pp.11-22
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• 1998

본 논문에서는 축대칭 쉘 구조물에서 자오방향과 주변방향의 프리스트레스하중이 작용될 경우에 대한 수학적 모델링을 구하였고 이에 대한 프로그램화를 통하여 지진하중을 주하중으로 한 동적해석을 실시하였다 이때 기하학적으로 축대칭인 구조믈의 특성을 최대한으로 이용할 수 있도록 쉘을 링요소로 모델링하였으며 기하학적 비선형관계식에 의하여 동적 모형식을 유도하였다 프로그램을 통하여 해석한 결과를 프리스트레스하중 하에서 고유진동수에 대한 정해와 비교한 결과 20개정도의 링요소로 모델링하였으며 기하학적 비선형관계식에 의하여 동적 모혀식을 유도하였다 프로그램을 통하여 해석한 결과를 프리스트레스하중 하에서 고유진동수에 대한 정해와 비교한 결과 20개정도의 링요소로 모델링한 경우 에서도 정해와 근접한 해를 얻을 수 있어더 또한 지진하중에 대한 반경방향의 처짐을 해석한 결과 동일 한 크기의 프리스트레스하중이 작용될 때 자오방향의 프리스트레스하중이 작용될경우가 다소 큰 처짐값을 나타내었다 본 연구를 통하여 개발된 모델은 지진하중 하에서의 축대칭 구조물에 대하여 3차원 구조해석을 실시하지 않아도 정해에 근접한 해석결과를 얻을 수있어 설계실무에 크게 활용될수 있을 것이다.

• 한국지진공학회논문집
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• 제3권4호
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• pp.71-82
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• 1999

자오방향 및 주변방향으로 프리스트레스트 하중이 작용된 축대칭 쉘 구조물을 축대칭요소로 모델화하였다 유체-구조물의 상호관계는 접촉면에서 구조물의 가속도에 비례한 부가질량으로 표현하였으며 부가질량은 유체를 비점성 비압축 및 비회전으로 가정하여 유한요소법에 의해 구하였다. 이에 대한 수치해석을 통하여 고유진동해석 및 지진하중을 주하중으로 한 동적해석을 실시하였다 이때 기하학적으로 축대칭인 구조물의 특성을 최대한으로 이용할 수 있도록 쉘을 링요소로 모델링하였으며 기하학적 비선형관계식에 의하여 동적 모형식을 유도하였다 프로그램을 통하여 해석한 결과를 프리스트레스하중 하에서 고유진동수에 대한 정해와 비교한 결과 20개 이내의 링요소로 모델링한 경우에서도 정해와 근접한 해를 얻을수 있었으며 내부유체가 있는 경우에 대한 고유진동수를 문헌과 비교한 결과 근접한 해를 얻을 수 있었다 내부유체의 높이의 증가에 따라 고유진동수는 현저히 감소하였으며 Wave Number가 적을수록 감소폭이 크게 나타났다. 지진하중에 대한 반경방향의 처짐을 해석한 결과 동일한 크기의 프리스트레스하중이 작용될 때 자오방향의 프리스트레스하중이 작용될 경우가 다소 큰 처짐값을 나타내었다.

• 전산구조공학
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• 제10권2호
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• pp.139-148
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• 1997

A finite element method is programmed to analyse the nonlinear behavior of axisymmetric structures. The lst order Mindlin shell theory which takes into account the transversal shear deformation is used to formulate a conical two node element with six degrees of freedom. To evade the shear locking phenomenon which arises in Mindlin type element when the effect of shear deformation tends to zero, the reduced integration of one point Gauss Quadrature at the center of element is employed. This method is the Updated Lagrangian formulation which refers the variables to the state of the most recent iteration. The solution is searched by Newton-Raphson iteration method. The tangent matrix of this method is obtained by a finite difference method by perturbating the degrees of freedom with small values. For the moment this program is limited to the analyses of non-linear elastic problems. For structures which could have elastic stability problem, the calculation is controled by displacement.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.485-497
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• 2017

The pogo phenomenon refers to a type of multidiscipline-related instability found in space launch vehicles. It is caused by coupling between the fuselage structure and other structural propulsion components. To predict the pogo phenomenon, it is essential to undertake adequate structural modeling and to understand the characteristics of the feedlines and the propulsion system. To do this, a modal analysis is conducted using axisymmetric two-dimensional shell elements. The analysis is validated using examples of existing launch vehicles. Other applications and further plans for pogo analyses are suggested. In addition, research on the pogo phenomenon of Saturn V and the space shuttle is conducted in order to constitute a pogo stability analysis using the results of the present modal analysis.

• Journal of Advanced Marine Engineering and Technology
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• 제23권4호
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• pp.504-513
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• 1999

Usually bellows are designed for the purpose of absorbing axial movement. To find out axial stiffness of bellows the axisymmetric shell theory using the finite element method is adopted in this paper. Bellows can be idealised by series of conical frustum-shaped elements because it is axisymmetric shell structure. The force required to deflect bellows axilly is a function of the dimensions of the bellows and the materials from which they are made. The displancements of nodal points due to small increment of force are calculated by the finite element method and the calculated nodal displacements are added to r-z cylinderical coordinates of nodal points. The new stiffness matrix of the system using the new coordinates of nodal points is adopted to calculate the another increments of nodal dis-placements that is the step by method is used in this paper. 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 spring constant can be predicted by input of a few factors.

• Advances in nano research
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• 제15권4호
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• pp.367-384
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• 2023

Natural frequency behavior of graphene platelets reinforced composite (GPL-RC) joined truncated conical-cylindrical- conical shells resting on Winkler-type elastic foundation is presented in this paper for the first time. The rule of mixture and the modified Halpin-Tsai approach are applied to achieve the mechanical properties of the structure. Four different graphene platelets patterns are considered along the thickness of the structure such as GPLA, GPLO, GPLX, GPLUD. Finite element procedure according to Rayleigh-Ritz formulation has been used to solve 2D-axisymmetric elasticity equations. Application of 2D axisymmetric elasticity theory allows thickness stretching unlike simple shell theories, and this gives more accurate results, especially for thick shells. An efficient parametric investigation is also presented to show the effects of various geometric variables, three different boundary conditions, stiffness of elastic foundation, dispersion pattern and weight fraction of GPLs nanofillers on the natural frequencies of the joined shell. Results show that GPLO and BC3 provide the most rigidity that cause the most natural frequencies among different BCs and GPL patterns. Also, by increasing the weigh fraction of nanofillers, the natural frequencies will increase up to 200%.

• 대한기계학회논문집
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• 제9권5호
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• pp.647-654
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• 1985

본 논문에서는 미소한 비대칭 요소를 갖는 축대칭 셸구조물(종형구조물 또는 용접된 압력용기등)의 전산기 이용 도면입력/수정/출력, 체적특성치의 자동결정, 근사 고속 유한요소해석 및 출력을 시각화하는 일관 작업을 수행할 수 있는 전산기이용설계 알고리즘을 개발하고 생산가공에 대한 공리적 접근방법을 전산화하는 전산기이용 공정 계획 알고리즘에 대한 기초적인 연구를 행하였다.

• 대한기계학회논문집
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• 제13권6호
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• pp.1203-1214
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• 1989

본 연구에서는 화이버각도, 경계조건 및 하중형태의 변화에 따라 적층 복합재료원통 셸 구조물의 수치예를 제시하고, NASTRAN수치결과 및 기존 문헌들과 비교하여 구하여진 결과의 타당성을 입증하였다.

• 한국정밀공학회지
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• 제26권10호
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• pp.81-88
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• 2009

Bellows is used to control temperature of a Joule-Thomson micro cryocooler. It is made of Nickelcobalt alloy that retains mechanical properties from cryogenic temperature to temperature of 570K. The geometry of bellows is an axisymmetric shell and Nitrogen with high pressure was charged at temperature of 293K. During cool-down process, the pressure and volume of Nitrogen are changed and must be satisfied with state equation. At cryogenic temperature, Nitrogen can exist as a part liquid and part vapor. Pressure-density-temperature behavior under this vaporliquid phase equilibrium is closely given by the Modified-Benedict-Webb-Rubin(MBWR) state equation. To evaluate deformation of bellows for temperature change, the numerical calculation of the volume within bellows and finite element analysis of bellows under internal pressure were iteratively performed until MBWR state equation is satisfied. The numerical results show that deformation of the bellows can be analyzed by the present method in a wide range of temperature including cryogenic temperature.

• 대한조선학회지
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• 제22권1호
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• pp.21-30
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• 1985

This paper deals whth the buckling as well as postbuckling analysis of axisymmertric shells taking the initial deflection effects into account. Incremental equilibrium equations, based on the principle of virtual work, were derived by the finite element method, the successive step-by-step Newton-Raphson iterative technique was adopted. To define the transition pattern of postbuckling behavior from the prebuckling state more accurately, a simple solution method was developed, i.e. the critical load was calculated by the load extrapolation method with the determinant of tangent stiffness matrix and the equilibrium configuration in the immediate postbuckling stage was obtained by perturbation scheme and eigenvalue analysis. Degenerated isoparametric shell elements were used to analyse the axisymmetric shell of revolution. And by the method developed in this paper, the computer program applicable to the nonlinear analysis of both thin and moderately thick shells was constructed. To verify the capabilities and accuracies of the present solution method, the computed results were compared with the results of analytical solutions. These results coincided fairly well in both the small deflection and large deflection ranges. Various numerical analyses were done to show the effect of initial deflection and shape of shells on buckling load and postbuckling behavior. Futhermore, corrected directions of applied loads at every increment steps were used to determine the actual effects of large deflection in non-conservative load systems such as hydrostatic pressure load. The following conclusions can be obtained. (1) The method described in this paper was found to be both economic and effective in calculating buckling load and postbuckling behavior of shell structure. (2) Buckling and postbuckling behavior of spherical caps is critically dependent upon their geometric configuration, i.e. the shape of spherical cap and quantities of the initial deflection. (3) In the analysis of large deflection problems of shells by the incremental method, corrections of the applied load directions are needed at every incremental step to compensate the follower force effects.