Cylindrical shells, due to their high structural efficiency, play a vital role in a wide range of engineering applications, including the aerospace, marine, an‎d energy industries. In this context, the ever-increasing deman‎d for structures with optimized performance, lower weight, an‎d high resistance to complex operating conditions has led to the development of advanced materials an‎d novel designs. Among these, functionally graded porous materials (FGPM) have shown high potential due to their ability to tailor mechanical properties an‎d reduce weight, as have variable-thickness geometries for optimizing stress distribution. However, the accurate dynamic analysis of these complex structures, especially when they are in contact with a fluid an‎d the phenomenon of fluid-structure interaction (FSI) arises, remains a significant scientific an‎d engineering challenge. A review of the literature confirms a distinct research gap in the free vibration analysis of shells with these simultaneous features. In this research, a comprehensive framework for the analysis of the free vibrations of cylindrical shells made of FGPM with variable thickness in contact with a fluid is presented. The mathematical model of the system is based on the First-order Shear Deformation Theory (FSDT) to describe the shellʹs displacement field, an‎d the potential flow theory to model the ideal fluid (inviscid, incompressible, an‎d irrotational). The effect of fluid interaction is incorporated as a hydrodynamic added mass in the total kinetic energy of the coupled system, an‎d the equations of motion of the coupled system are transformed into a stan‎dard algebraic eigenvalue problem using a solution method based on the Rayleigh-Ritz method. The natural frequencies an‎d vibrational mode shapes are extracted from the solution of this problem. For model validation, its convergence was first eva‎luated, an‎d then its results were compared with data available in the literature, data obtained from the Finite Element Method (FEM), as well as the results of Experimental Modal Analysis (EMA) performed on isotropic samples with constant an‎d stepped thickness, both with an‎d without fluid. The results show that the presence of the internal fluid, due to the added mass effect, noticeably reduces the systemʹs natural frequencies—an effect that is intensified with increasing fluid depth. It was determined that the characteristics of the FGPM, boundary conditions, geometric parameters, an‎d thickness variation patterns (continuous an‎d stepped) have a significant influence on the vibrational behavior. Specifically, it is observed that thickness variations an‎d the presence of the fluid cause an asymmetric distribution of the vibration amplitude in the structure. The results from the proposed solution method, by showing excellent agreement with data available in the literature, numerical results, an‎d experimental data, confirm the validity an‎d reliability of the presented framework. Accordingly, the model developed in this research can be used as an efficient tool for the analysis an‎d optimal design of advanced cylindrical structures in various industrial applications.

سعيد ضيائي راد

علي لقماني

محمد دانش , رضا تيكني