• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.04a
• /
• pp.288-291
• /
• 2004

The characteristics of the buckling analysis module for stiffened composite structures were studied in this paper. Composite stiffened structures have geometrical asymmetry and material properties asymmetry. Due to these reason, postbuckling analysis was essential and the characteristics of postbuckling analysis modules for ABAQUS were researched. Static analysis module was considered. By considering the material nonlinearity, progressive failure mechanism was applied and buckling strength was estimated

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.04a
• /
• pp.273-278
• /
• 2011

This work presents an active vibration control of a stiffened hull structure using a flexible macro fiber composite (MFC) actuator. As first step, the governing equation of the hull structure is derived in a matrix form and its dynamic characteristics such as natural frequency are obtained via a finite element analysis (FEA). The natural frequencies obtained from the FEA are compared with those determined from experimental measurement. After formulating the control model in a state space representation, an optimal controller is designed in order to attenuate the vibration of the stiffened hull structure. The controller is then empirically realized through dSPACE and control responses are evaluated in time domain.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.21 no.7
• /
• pp.643-649
• /
• 2011

This work presents an active vibration control of a stiffened hull structure using a flexible macro fiber composite(MFC) actuator. As first step, the governing equation of the hull structure is derived in a matrix form and its dynamic characteristics such as natural frequency are obtained via a finite element analysis(FEA). The natural frequencies obtained from the FEA are compared with those determined from experimental measurement. After formulating the control model in a state space representation, an optimal controller is designed in order to attenuate the vibration of the stiffened hull structure. The controller is then empirically realized through dSPACE and control responses are evaluated in time domain.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.9 no.4
• /
• pp.373-381
• /
• 2017

A Collaborative Optimization (CO) methodology for ring-stiffened composite material pressure hull of underwater vehicle is proposed. Structural stability and material strength are both examined. Lamination parameters of laminated plates are introduced to improve the optimization efficiency. Approximation models are established based on the Ellipsoidal Basis Function (EBF) neural network to replace the finite element analysis in layout optimizers. On the basis of a two-level optimization, the simultaneous structure material collaborative optimization for the pressure vessel is implemented. The optimal configuration of metal liner and frames and composite material is obtained with the comprehensive consideration of structure and material performances. The weight of the composite pressure hull decreases by 30.3% after optimization and the validation is carried out. Collaborative optimization based on the lamination parameters can optimize the composite pressure hull effectively, as well as provide a solution for low efficiency and non-convergence of direct optimization with design variables.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.26 no.3
• /
• pp.21-28
• /
• 1989

The optimun laminated composition of the stiffened composite plates is studied from the view point of buckling strength. The finite element method is applied to the buckling analysis of the composite plates taking into account the effect of shear deformation through the plate thickness. The stiffened plate model is discretized using plate thickness and symmetrically stacked. Parametric study is carried out for the selection of the optimum laminate structure; optimum fiber angle sequence through the thickness. Laminate structure of $[-45^{\circ}/45^{\circ}/90^{\circ}/0^{\circ}]$, is found to give the best buckling strength. For the case of that layer number is more than eight, best result is obtained when layers of the same fiber angle are put together, leaving the laminate has the same fiber angle sequence as a whole.

• Advances in Computational Design
• /
• v.6 no.1
• /
• pp.15-30
• /
• 2021

With improvement in innovative manufacturing technologies, it became possible to fabricate any complex shaped structural design for practical applications. This allows for the fabrication of curvilinearly stiffened pressure vessels and pipes. Compared to straight stiffeners, curvilinear stiffeners have shown to have better structural performance and weight savings under certain loading conditions. In this paper, an optimization framework for designing curvilinearly stiffened composite pressure vessels and pipes is presented. NURBS are utilized to define curvilinear stiffeners over the surface of the pipe. An integrated tool using Python, Rhinoceros 3D, MSC.PATRAN and MSC.NASTRAN is implemented for performing the optimization. Rhinoceros 3D is used for creating the geometry, which later is exported to MSC.PATRAN for finite element model generation. Finally, MSC.NASTRAN is used for structural analysis. A Bi-Level Programming (BLP) optimization technique, consisting of Particle Swarm Optimization (PSO) and Gradient-Based Optimization (GBO), is used to find optimal locations of stiffeners, geometric dimensions for stiffener cross-sections and layer thickness for the composite skin. A cylindrical pipe stiffened by orthogonal and curvilinear stiffeners under torsional and bending load cases is studied. It is seen that curvilinear stiffeners can lead to a potential 10.8% weight saving in the structure as compared to the case of using straight stiffeners.

• Steel and Composite Structures
• /
• v.24 no.5
• /
• pp.591-602
• /
• 2017

A cable-stiffened cylindrical single-layer latticed shell that is reinforced by cable-stiffened system has superior stability behaviour compared with the ordinary cylindrical latticed shell. The layouts of cable-stiffened system are flexible in this structural system, and different layouts contribute different stiffness to the structure. However, the existed few research primarily focused on the simplest type of cable layouts, in which the grids of the latticed shell are diagonally stiffened by prestressed cables in-plane. This current work examines the stability behaviour of the cable-stiffened cylindrical latticed shells with two different types of cable layouts using nonlinear finite element analysis. A parametric study on the effect of cross-sectional of the cables, pretension in cables, joint stiffness, initial imperfections, load distributions and boundary conditions is presented. The findings are useful for the reference of the designer in using this type of structural system.

• Steel and Composite Structures
• /
• v.42 no.4
• /
• pp.427-446
• /
• 2022

Cutouts in the beams or plates are often unavoidable due to inspection, maintenance, ventilation, structural aesthetics purpose, and sometimes to lighten the structures. Therefore, there will be a substantial reduction in the strength of the structure due to the introduction of the cutouts. However, these cutouts can be reinforced with the different patterns of ribs (stiffener) to enhance the strength of the structure. The present study highlights the influence of the elliptical cutout reinforced with a different pattern of ribs on the stability performance of such stiffened composite panels subjected to non-uniform edge loads by employing the Finite element (FE) technique. In the present formulation, a 9-noded heterosis element is used to model the skin, and a 3-noded isoparametric beam element is used to simulate the rib that is attached around a cutout in different patterns. The displacement compatibility condition is employed between the plate and stiffener, and arbitrary orientations are taken care by introducing respective transformation matrices. The effect of shear deformation and rotary inertia are incorporated in the formulation. A new mesh configuration is developed to house the attached ribs around an elliptical cutout with different patterns. Initially, a study is performed on the panels with different stiffener schemes for various ply orientations and for different stiffener depth to width ratios (d_s/b_s) to determine an optimal stiffener configuration. Further, various parametric studies are conducted on an obtained optimal stiffened panel to understand the effect of cutout size, cutout orientation, panel aspect ratio, and boundary conditions. Finally, from the analysis, it can be observed that the arrangement of the stiffener attached to a panel has a major impact on the buckling capacity of the stiffened panel. The stiffener's depth to width ratio also significantly influences the buckling characteristic.

• Steel and Composite Structures
• /
• v.4 no.2
• /
• pp.149-167
• /
• 2004

Offshore platforms have to serve in harsh environments and hence are likely to be damaged due to wave induced fatigue and environmental corrosion. Welded tubular joints in offshore platforms are most vulnerable to fatigue damage. Such damages endanger the integrity of the structure. Therefore it is all the more essential to assess the capacity of damaged structure from the point of view of its safety. Eight internally ring stiffened fatigue damaged tubular joints with nominal chord and brace diameter of 324 mm and 219 mm respectively and thickness 12 mm and 8 mm respectively were tested under axial brace compression loading to evaluate the reserve capacity of the joints. These joints had earlier been tested under fatigue loading under corrosive environments of synthetic sea water and hence they have been cracked. The extent of the damage varied from 35 to 50 per cent. One stiffened joint was also tested under axial brace tension loading. The residual strength of fatigue damaged stiffened joint tested under tension loading was observed to be less than one fourth of that tested under compression loading. It was observed in this experimental investigation that in the damaged condition, the joints possessed an in-built load-transfer mechanism. A bi-linear stress-strain model was developed in this investigation to predict the reserve capacity of the joint. This model considered the strain hardening effect. Close agreement was observed between the experimental and predicted results. The paper presents in detail the experimental investigation and the development of the analytical model to predict the reserve capacity of internally ring stiffened joints.

• Journal of Korean Society of Steel Construction
• /
• v.29 no.1
• /
• pp.61-71
• /
• 2017

The flexural behavior of composite ring stiffened by GFRP and steel pipe is presented in this paper. The effective width is required to construct FEM beam element model to verify the composite flexural behavior of stiffened ring of cylindrical shell structure. The experimental results are compared with the theoretical and FEM results by commercial program ABAQUS to verify the effective width coefficient. The yield, crack and ultimate loads is calculated using theoretical strains that varies depending on yield state and compared with experiment result and FEM results by ABAQUS solid model.