Optimisation of Curvilinear Fibre Paths for Enhanced Aeroelastic Stability of Sandwich Shells with Variable Stiffness Composite Face Sheets

This work addresses the suppression of aeroelastic instabilities—flutter and divergence—in sandwich shell structures operating under supersonic flow conditions. The study focuses on: (1) formulating and validating an efficient computational framework capable of predicting the aeroelastic behaviour of shells with Variable Stiffness Composite Laminates (VSCL) as face sheets; (2) finding optimal fibre paths, which maximize flutter speeds. A layerwise model, where a first-order shear deformation approach is adopted for each layer of the model, is developed to represent the through-thickness response of the composite structure. The inclusion of elastic springs enables the accurate implementation of diverse boundary constraints. Supersonic aerodynamic effects are incorporated via Linear Piston Theory. To find the optimal curvilinear fibre trajectories, allowing the material stiffness to be spatially tailored to each problem, a genetic algorithm is used. Validation and convergence analyses confirm the robustness of the model. The findings indicate that variable-stiffness designs can extend flutter boundaries under certain conditions, though – with the simple curvilinear fibre path functions considered - configurations with straight fibres still yield superior performance for certain geometric and support characteristics. Furthermore, complementary results provide an assessment of how curvilinear fibres influence the non-linear, post-flutter regime, offering insight into the evolution of Limit Cycle Oscillations in VSCL shells.