• Journal of KSNVE
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• v.6 no.4
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• pp.457-467
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• 1996

The analytical solutions for the free vibration and buckling of cross -ply laminated composite cylindrical shell with the orthogonal stiffeners, i. e., axial stiffeners(stringers) and circumferential stiffeners(rings), are presented using the energy method. The stiffeners are assumed to be an integral part of the shell and have been directly included in analysis(it's called discrete stiffener theory). The effect of the parameters such as the stacking sequences, the shell thickness, the shell length-to-radius ratio are studied. By comparison with the previously published analytical results for the stiffened cylindrical shells, it is shown that natural frequencies can be determined with adequate accuracy.

• Steel and Composite Structures
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• v.19 no.1
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• pp.75-92
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• 2015

In this paper, optimization of cylindrical shells under external pressure to minimize its weight has been studied. Buckling equations are based on standard of ABS underwater vehicles. Dimension and type of circumferential stiffeners, and its distance from each other are assumed as variables of optimization problem. Considering the extent of these variables, genetic algorithms have been used for optimization. To study the effect of hydrostatic pressure on the shell and its fabrication according to the existing standards, geometrical and construction as well as stress and buckling constraints have been used in optimization algorithm and also penalty functions are applied to eliminate weak model. Finally, the best model which has the minimum weight considering the applied pressure has been presented.

• Computational Structural Engineering
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• v.6 no.3
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• pp.81-88
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• 1993

An efficient approach to the buckling analysis of stiffened cylindrical shells with rings and stringers under the axial and the lateral pressure loadings is presented. By this approach, the local buckling as well as overall buckling behavior has been investigated considering the discreteness of stiffeners and appropriate adoption of displacement functions. Some design criteria based on structural stability to determine optimum scantlings of stiffeners are also suggested. It is shown that the optimum scantlings of stiffeners can be designed from the condition of equal local and overall buckling strength.

• Structural Engineering and Mechanics
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• v.73 no.5
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• pp.487-500
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• 2020

Stiffeners can be utilised to enhance the strength of thin-walled wind turbine towers in engineering practise, thus, structural performance of wind turbine towers by means of different stiffening schemes should be compared to explore the optimal structural enhancement method. In this paper two alternative stiffening methods, employing horizontal or vertical stiffeners, for steel tubular wind turbine towers have been studied. In particular, two groups of three wind turbine towers of 50m, 150m and 250m in height, stiffened by horizontal rings and vertical strips respectively, were analysed by using FEM software of ABAQUS. For each height level tower, the mass of the stiffening rings is equal to that of vertical stiffeners each other. The maximum von Mises stresses and horizontal sways of these towers with vertical stiffeners is compared with the corresponding ring-stiffened towers. A linear buckling analysis is conducted to study the buckling modes and critical buckling loads of the three height levels of tower. The buckling modes and eigenvalues of the 50m, 150m and 250m vertically stiffened towers were also compared with those of the horizontally stiffened towers. The numbers and central angles of the vertical stiffeners are considered as design variables to study the effect of vertical stiffeners on the structural performance of wind turbine towers. Following an extensive parametric study, these strengthening techniques were compared with each other and it is obtained that the use of vertical stiffeners is a more efficient approach to enhance the stability and strength of intermediate and high towers than the use of horizontal rings.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.2
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• pp.83-98
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• 2000

자오방향 및 주변방향으로 피르스트레스트 하중이 작용된 축대칭 쉘 구조물을 기하학적으로 축대칭인 구조물의 특성을 최대한으로 이용할 수 있도록 회전 링요소로 모델화하였다 보강링 요소의 모델은 축대칭 쉘요소를 이용하였으며 본체 구조물과 절점에서 부착되있는 것으로 가정하여 이의 편심을 고려하였다 유체-구조물의 상호관계는 접촉면에서 구조물의 가속도에 비례한 부가질량으로 표현하였으며 부가질량은 유체를 비점성 비압축 및 비회전을 가정하여 유한요소법에 의해 구하였다 이에 대한 수치해석을 통하여 고유진동해석 및 지진하중을 주하중으로 한 동적해석을 실시하였다 프로그램을 통하여 해석한 결과를 프리스트레스 하중 하에서 고유진동수에 대한 정해와 비교한 결과 20개의 요소로 모델링한 경우에서도 정해와 근접한 해를 얻을 수 있었다 또한 내부유체가 있는 경우와 링보강을 한 경우에 대한 고유진동수를 문헌과 비교한 결과 근접한 해를 얻을 수 있었다.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.2
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• pp.116-123
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• 2012

This study aims to analyze the strength of pressure hull of a small submarine. The pressure hull of a submarine has to withstand very large differential pressure between hydrostatic pressure in submarine operating depth and atmospheric pressure in inner space of a submarine. To do that, the pressure hull is generally ring-stiffened cylindrical shell under external pressure. In this situation, there are some foreseeable failure modes of the pressure hull such as shell yielding, axisymmetric shell buckling, asymmetric shell buckling, overall buckling and buckling of end closure. We calculated collapse pressures of these failure modes with approximation and empirical formulas. And, to analyze critical buckling pressure, we performed eigenvalue analysis with finite element method tools.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.865-873
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• 2013

This paper proposes a theoretical solution of elastic critical buckling load of infinitely long pipelines with non-uniform thickness under external pressure. The non-uniform cross section of pipelines can be considered as corroded or stiffened pipelines so that this paper can be a fundamental research of pipelines that are essential technology for offshore industries. The theoretical solution of pipelines with non-uniform thickness is derived with an assumption that a cylindrical shell under external pressure can be considered as a simple ring. The eigenfunctions are derived to obtain the critical buckling load. The reduced thickness and the reduced range are considered as variables in parametric analysis. The finite element analysis is performed to verify the theoretical solutions and the results of the analytic method and the finite element method are in good agreement.

• Steel and Composite Structures
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• v.19 no.5
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• pp.1115-1144
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• 2015

Current climate conditions along with advances in technology make further design and verification methods for structural strength and reliability of wind turbine towers imperative. Along with the growing interest for "green" energy, the wind energy sector has been developed tremendously the past decades. To this end, the improvement of wind turbine towers in terms of structural detailing and performance result in more efficient, durable and robust structures that facilitate their wider application, thus leading to energy harvesting increase. The wind tower industry is set to expand to greater heights than before and tapered steel towers with a circular cross-section are widely used as more capable of carrying heavier loads. The present study focuses on the improvement of the structural response of steel wind turbine towers, by means of internal stiffening. A thorough investigation of the contribution of stiffening rings to the overall structural behavior of the tower is being carried out. These stiffening rings are placed along the tower height to reduce local buckling phenomena, thus increasing the buckling strength of steel wind energy towers and leading the structure to a behavior closer to the one provided by the beam theory. Additionally to ring stiffeners, vertical stiffening schemes are studied to eliminate the presence of short wavelength buckles due to bending. For the purposes of this research, finite element analysis is applied in order to describe and predict in an accurate way the structural response of a model tower stiffened by internal stiffeners. Moreover, a parametric study is being performed in order to investigate the effect of the stiffeners' number to the functionality of the aforementioned stiffening systems and the improved structural behavior of the overall wind converter.