M. Fakoor; P. Mohammadzade; E. Jafari
Volume 11, Issue 2 , October 2017, , Pages 43-51
Abstract
Composite stiffened cylindrical shells are widely used as primary elements in aerospace structures. In the recent years, there has been a growing research interest in optimum design of composite stiffened cylindrical shell structures for stability under buckling load. This paper focuses upon the ...
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Composite stiffened cylindrical shells are widely used as primary elements in aerospace structures. In the recent years, there has been a growing research interest in optimum design of composite stiffened cylindrical shell structures for stability under buckling load. This paper focuses upon the development of an efficient optimization of ring-stringer stiffened cylindrical shell. The optimization problem used in this study involves weight minimization of ring-stringer stiffened composite cylindrical shell with buckling load and stress, which are considered as design constraints. The proposed methodology is based on Particle Swarm Optimization (PSO) algorithm. The material of shell is composite, but the material of stiffeners is considered to be isotropic. The approach adopted in modeling utilizes the Rayleigh-Ritz energy method and the stiffeners are treated as discrete members. In addition, a 3-D Finite Element (FEM) model of the ring-stringer stiffened cylindrical shell is developed that takes into consideration the exact geometric configuration. The results obtained using the Rayleigh-Ritz energy method are compared with those using 3-D FE model. The proposed methodology is implemented on the ring-stringer stiffened cylindrical shell using the PSO algorithm. The obtained results show a 13% reduction in the weight of the ring-stringer stiffened cylindrical shell whilst all the design constraints are satisfied. In addition, the results show that the proposed methodology provides an effective way of solving composite stiffened cylindrical shell design problems.
mostafa ghayour; Ahmad Sedaghat; Mohsen Mohammadi
Volume 8, Issue 1 , March 2011, , Pages 57-67
Abstract
Multi-layer orthotropic finite cylindrical shells with a viscoelastic core in contact with fluids are gaining increasing importance in engineering. Vibrational control of these structures is essential at higher modes. In this study, an extended version of the wave propagation approach using first-order ...
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Multi-layer orthotropic finite cylindrical shells with a viscoelastic core in contact with fluids are gaining increasing importance in engineering. Vibrational control of these structures is essential at higher modes. In this study, an extended version of the wave propagation approach using first-order shear deformation theory of shell motion is employed to examine the free vibration of damped finite cylindrical shells in vacuum or in contact with interior or exterior dense acoustic media. For this purpose, a one-layered viscoelastic finite cylindrical shell and a three-layered orthotropic finite cylindrical shell with a viscoelastic core layer were used. Complex natural frequencies have been extracted and the effects of fluid coupling on real and imaginary parts of natural frequencies have been examined. The results reveal that the fluid reduces the imaginary part as much as the real part of the damped natural frequency but that the proportion of the imaginary to the real part (loss factor) remains rather unchanged. Another aspect of the study involves the investigation of the effect of shell parameter, m, when the circumferential mode number, n, increases on both entities of damped natural frequencies. It is found that by increasing n, the real part of the natural frequency follows a u-shape trend; however, the imaginary part reduces and levels off for higher circumferential numbers. The loss factors remain almost constant for these higher modes. The results of the current approach are finally compared with ABAQUS solutions showing superiority of current approach.
