• 한국공간구조학회논문집
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• 제11권1호
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• pp.87-95
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• 2011

본 논문에서는 유한요소해석법을 사용하여 역우산형 쌍곡포물선쉘구조물을 해석하고 그 결과를 기존의 막이론에 의한 설계식의 결과치와 비교하였다. 또한 지붕면의 경사도를 달리하며 경사도에 따른 처짐 및 테두리보와 내부경사리브에 작용하는 부재력, 쉘면에 작용하는 막응력의 변화를 살펴보았다. 해석결과 기존의 막응력에 의한 이론해는 테두리보 및 내부경사리브에 대한 부재력을 과대평가하는 반면 막응력에 대해서는 반대로 과소평가를 하고 있는 것으로 나타났다. 유한요소법에 의해 해석한 지붕의 처짐은 경사도가 낮아짐에 따라 급격하게 증가되는 것으로 나타났다.

• Steel and Composite Structures
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• 제35권2호
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• pp.249-260
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• 2020

The main purpose of this research work is to investigate the free vibration of conical shell structures reinforced by graphene platelets (GPLs) and the elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. To this end, a shell model is developed based on Donnell's theory. To solve the problem, the analytical Galerkin method is employed together with beam mode shapes as weighting functions. Due to importance of boundary conditions upon mechanical behavior of nanostructures, the analysis is carried out for different boundary conditions. The effects of boundary conditions, semi vertex angle, porosity distribution and graphene platelets on the response of conical shell structures are explored. The correctness of the obtained results is checked via comparing with existing data in the literature and good agreement is eventuated. The effectiveness and the accuracy of the present approach have been demonstrated and it is shown that the Donnell's shell theory is efficient, robust and accurate in terms of nanocomposite problems.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.69-72
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• 2004

A new three-node triangular shell element based on higher order zig-zag theory is developed for laminated composite shells with multiple delaminations. The present higher order zig-zag shell theory is described in a general curvilinear coordinate system and in general tensor notation. All the complicated curvatures of surface including twisting curvatures can be described in an exact manner in the present shell element because this element is based on geometrically exact surface representation. The displacement field of the proposed finite element includes slope of deflection, which requires continuity between element interfaces. Thus the nonconforming shape function of Specht's three-node triangular plate bending element is employed to interpolate out-of-plane displacement. The present element passes the bending and twisting patch tests in flat surface configurations. The developed element is evaluated through the eigenvalue problems of composite cylindrical shells with multiple delaminations. Through the numerical examples it is demonstrated that the proposed shell element is efficient because it has minimal degrees of freedom per node. The present shell element should serve as a powerful tool in the prediction of natural frequency and modes of multi-layered thick laminated shell structures with arbitrary-shaped multiple delaminations.

• Structural Engineering and Mechanics
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• 제40권2호
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• pp.191-213
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• 2011

This paper presents an improved 8-node shell element for the analysis of plates and shells. The finite element, based on a refined first-order shear deformation theory, is further improved by the combined use of assumed natural strain method. We analyze the influence of the shell element with the different patterns of sampling points for interpolating different components of strains. Using the assumed natural strain method with proper interpolation functions, the present shell element generates neither membrane nor shear locking behavior even when full integration is used in the formulation. Further, a refined first-order shear deformation theory, which results in parabolic through-thickness distribution of the transverse shear strains from the formulation based on the third-order shear deformation theory, is proposed. This formulation eliminates the need for shear correction factors in the first-order theory. Numerical examples demonstrate that the present element perform better in comparison with other shell elements.

• 한국강구조학회 논문집
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• 제9권1호통권30호
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• pp.3-11
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• 1997

Laminated composite shells exhibit properties comsiderably different from those of the single-layer shell. Thus, to obtain the more accurate solutions to laminated composite shells ptoblems, effects of shear strain should be condidered in analysis of them. A higher-order shear deformation theory requires no shear correction coefficients. This theory is used to determine the buckling loads of elastic shells. The theory accounts for parabolic distribution of the transverse shear through the thickness of the shell and rotary inertia. Exact solutions of simply-supported shells are obtained and the results are compared with the exact solutions of the first-order shear deformation theory, and the classical theory. The present theory predicts the buckling loads more accurately when compared to the first -order and classical theory.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.1-4
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• 2005

A higher order zig-zag shell theory is developed to refine accurately predict deformation and stress of smart shell structures under the mechanical, thermal, and electric loading. The displacement fields through the thickness are constructed by superimposing linear zig-zag field to the smooth globally cubic varying field. Smooth parabolic distribution through the thickness is assumed in the transverse deflection in order to consider transverse normal deformation. The mechanical, thermal, and electric loading is applied in the sinusoidal distribution function in the in-surface direction. Thermal and electric loading is given in the linear variation through the thickness. Especially, in electric loading case, voltage is only applied in piezo-layer. The layer-dependent degrees of freedom of displacement fields are expressed in terms of reference primary degrees of freedom by applying interface continuity conditions as well as bounding surface conditions of transverse shear stresses. In order to obtain accurate transverse shear and normal stresses, integration of equilibrium equation approach is used. The numerical examples of present theory demonstrate the accuracy and efficiency of the proposed theory. The present theory is suitable for the predictions of behaviors of thick smart composite shell under mechanical, thermal, and electric loadings combined.

• Computers and Concrete
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• 제32권2호
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• pp.165-172
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• 2023

The vibration analysis of armchair, zigzag and chiral double-walled carbon nanotubes has been developed by inserting the nonlocal theory of elasticity into thin shell theory. First Donnell shell theory is employed while exercising wave propagation approach. Scale effects are realized by using different values of nonlocal parameters under certain boundary conditions. The natural frequencies have been investigated and displayed for various non-local parameters. It is noticed that on increasing nonlocal parameter, the frequency curve tends to decrease. The frequency estimates of clamped-free boundary condition are less than those of clamped-clamped and simply supported computations. The frequency comparisons are presented for armchair, zigzag and chiral nanotubes. The software MATLAB is used to extract the frequencies of double walled carbon nanotubes.

• 대한기계학회논문집A
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• 제23권11호
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• pp.2040-2049
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• 1999

The Rayleigh-Ritz method is used to investigate the natural frequencies and mode shapes of the ring stiffened cylindrical shells with a rectangular cutout. The cutout is located on the center of the shell. The Love's thin shell theory combined with the discrete stiffener theory is adopted to formulate the analytical model of the shell. The effect of stiffener eccentricity, number, and position on vibration characteristics of the shell is examined. Also the effect of cutout size is examined. By comparison with previously published analytical and new FEM results, it is shown that natural frequencies and mode shapes can be determined with adequate accuracy.

• Steel and Composite Structures
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• 제35권4호
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• pp.567-578
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• 2020

Based on third-order shear deformation shell theory, the present paper investigates post-buckling properties of eccentrically stiffened metal foam curved shells/panels having initial geometric imperfectness. Metal foam is considered as porous material with uniform and non-uniform models. The single-curve porous shell is subjected to in-plane compressive loads leading to post-critical stability in nonlinear regime. Via an analytical trend and employing Airy stress function, the nonlinear governing equations have been solved for calculating the post-buckling loads of stiffened geometrically imperfect metal foam curved shell. New findings display the emphasis of porosity distributions, geometrical imperfectness, foundation factors, stiffeners and geometrical parameters on post-buckling properties of porous curved shells/panels.

• Computers and Concrete
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• 제26권1호
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• pp.53-62
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• 2020

Concrete is the most widely used substance in construction industry, so it's been required to improve its quality using new technologies. Nowadays, nanotechnology offers new frontiers for improving construction materials. In this paper, we study the stability analysis of the Single Walled Carbon Nanotubes (SWCNT) reinforced concrete cylindrical shell embedded in elastic foundation using the Donnell cylindrical shell theory. In this regard, we propose a new explicit analytical formula of the critical buckling load which takes into account the distribution of SWCNT reinforcement through the thickness of the concrete shell using the U, X, O and V forms and the elastic foundation using Winkler and Pasternak models. The rule of mixture is used to calculate the effective properties of the reinforced concrete cylindrical shell. The influence of diverse parameters on the stability behavior of the reinforced concrete shell is also discussed.