Discrepancy on the free vibration of laminated composite plates coupled to a compressible and incompressible fluid domain

This paper examines the free vibration of laminated composite plates in contact with a water-filled cavity. The fluid compressibility is considered in the analysis. The main objective is to evaluate the natural frequencies of the plate-fluid coupled system, compare the results with those obtained assuming an incompressible fluid domain, and examine the influence of the laminate stacking sequence. Classical and refined plate theories are considered in a compact manner. The Ritz method is used to obtain approximations of the kinetic and potential energy of both the fluid and the plate. The accuracy of the formulation is demonstrated by comparing the results to 3D finite element solutions obtained via commercial software. Parametric studies are carried out to examine the influence of the geometry, lamination angles and boundary conditions on the natural frequencies and the error incurred due to neglecting fluid compressibility. The error is higher when thick, stiff plates with rigid supports are considered. The effect of the fluid domain depth on the natural frequencies depends on the symmetric or antisymmetric nature of the mode shape. The orientation of the laminas becomes highly relevant when rectangular plates with mixed supports are considered.