Natural Vibrations of Composite Cylindrical Shells Partially Filled with Fluid

The paper presents the results of studies of natural vibrations of circular vertical layered cylindrical shells completely or partially filled with a quiescent compressible fluid and subjected to hydrostatic load. The behavior of the elastic structure and the fluid medium is described using the classical shell theory and the Euler equations. The effects of sloshing on the free surface of the fluid are not considered. The linearized equations of motion for shells, together with the corresponding geometric and physical relations, are reduced to a system of ordinary differential equations with respect to new unknowns. The acoustic wave equation is transformed to a system of differential equations using the generalized differential quadrature method. The formulated boundary-value problem is solved by Godunov's method of orthogonal sweep. The natural frequencies of the vibrations are calculated based on the combination of a stepwise procedure and subsequent refinement by the method of dividing in half. The reliability of the obtained results is verified by comparison with the known numerical solutions. The dependence of the lowest vibration frequencies on the ply angle and the fluid level for simply supported, rigidly clamped, and cantilevered two-layer and three-layer cylindrical shells with a fluid are analyzed in detail. It is demonstrated that the possibility of changing the frequencies and vibration modes through a suitable choice of lay-up scheme and the ply angle of the composite material is notably determined by a prescribed combination of boundary conditions for an elastic body.