Isfahan University of Technology
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.