Hossein Zafari

Sandwich cylindrical shells with porous polymeric foam cores and periodically distributed stiffeners are attractive candidates for lightweight control of surrounding acoustic pressure, yet their acoustic scattering in realistic multilayered configurations remains poorly characterized. This study develops an analytical framework for predicting the total scattering cross section of a sandwich cylindrical shell under oblique plane wave incidence for a specific configuration combining a functionally graded (FG) outer facesheet, an FG open-cell porous polymeric foam core, an isotropic inner layer separated by air gaps, orthogrid (ring-string) stiffeners, and coupled interior and exterior acoustic fluids. Structural dynamics are modeled using first-order shear deformation theory and Hamilton's principle, while the foam core is treated as an FG viscoelastic medium with a frequency-dependent complex modulus. Continuity of acoustic pressure and normal velocity at the fluid-structure interfaces couples the interior and exterior acoustic fields and yields the scattered pressure and total scattering cross section. Numerical results show that periodic ring-string stiffening strongly attenuates low-frequency resonances and shifts the first major scattering peak to higher frequencies, thereby reducing low-frequency scattering levels. The stiffened configuration also reduces the peak magnitude of the surrounding acoustic pressure (from approximately ±1.5 Pa to ±1.0 Pa at 10 kHz), indicating a weaker scattered field.

This article presents a novel acoustic analysis of two coaxial cylindrical shells filled with fluid, explicitly considering the effect of fluid viscosity. This factor is crucial for sound-fluid–structure interactions, particularly in systems that experience detrimental vibrations. The cross-sectional architecture consists of a porous functionally graded piezoelectric (PFGP) coating and two coaxial isotropic cylinders separated by a compressible viscous fluid. The entire structure is completely submerged in a uniform inviscid fluid flow, such as water, and the internal acoustic environment is considered a resonant cavity. A power-law relation is employed to characterize the material properties of the PFGP coating in the thickness direction. The motion of viscous fluid substances is modeled with the three-dimensional (3D) Navier–Stokes equations. The governing equations of motion for each layer of the PFGP coating are derived using an orthotropic laminated model based on the exact linear theory of 3D piezoelasticity. In this regard, the classical state-space technique and the transfer matrix mathematical model are used to solve the problem. Guided wave propagation in elastic isotropic cylinders is adapted to Navier's wave equation, allowing for the inclusion of both longitudinal and torsional waves. Helmholtz decomposition is applied to solve these wave equations. To validate the proposed model, the results are compared with findings from other researchers. Overall, the results indicate that fluids with higher viscosity are more effective in reducing noise levels, and the structure oscillates at a lower speed due to enhanced energy dissipation within the rotational flow layer at the solid–fluid interface.

In high-speed trains and automotive and aeronautic structures, the addition of agglomerated graphene nanoplatelets (GNPs) as nanofillers, combined with engineered pores distributed throughout the structure, can significantly reduce the overall weight of the structure while maintaining excellent sound insulation properties. This study presents the acoustic-structural analysis of a functionally graded porous composite cylindrical shell reinforced with agglomerated GNPs, supported by a distributed viscoelastic Winkler–Pasternak foundation for the first time, to the best of our knowledge. The structure is immersed in fluid flow and excited by a plane acoustic wave. The ceramic–metal matrix properties are functionally graded (FG), with porosity and GNPs distributed either uniformly or nonuniformly across the thickness in five distinct patterns. To determine the material properties of the GNP-reinforced composite (GNPRC) shell, the Gaussian random field theory and the Halpin–Tsai micromechanical framework are employed. The third-order shear deformation theory (TSDT) is used to describe the kinematics and constitutive relations of the FG-GNPRC porous cylindrical shell, and Hamilton’s principle is applied to derive the differential equations of motion from the TSDT formulation. The boundary conditions at the fluid–structure interface are then used to characterize the interaction between the acoustic wave and the shell, ensuring that the particle velocities of the acoustic medium on the inner and outer surfaces match the shell’s radial displacement. The proposed model is validated by comparing results with previous research. Finally, the study analyzes strain energy, stresses, energy dissipation due to the viscoelastic foundation’s damping effect and the influence of porosity and GNP distributions, porosity coefficients, GNP weight fractions, external flow, and foundation parameters on acoustic characteristics.