Eigenfrequencies of prestressed variable stiffness composite shells

The introduction of the variable stiffness concept has broadened the design space for high-performance lightweight composite structures. In particular, when considering prestressed dynamically excited aerospace components, a wider design space allows designers to find more effective solutions with higher overall stiffness and fundamental frequency. In this context, an efficient and versatile Ritz method for the eigenfrequency analysis of prestressed variable stiffness laminated doubly-curved shells is presented. First-order shear deformation theory is considered without further assumptions on the shallowness or on the thinness of the structure. A rational Bézier surface representation is adopted for the description of the shell, allowing general orthogonal surfaces to be represented. The proposed approach is validated by comparison with published benchmark results and finite element solutions, showing great accuracy with 65% to an order of magnitude fewer variables. Due to the reliability and efficiency of the Ritz method for eigenfrequency analysis, original parametric studies are carried out, showing the flexibility given by the variable stiffness concept for finding trade-off solutions for prestressed shell components.