A novel positive-curvature composite vessel concept for underwater hydrogen storage: Burst and buckling performance

Hydrogen storage vessels for autonomous underwater vehicles must simultaneously resist burst from internal pressure and collapse from external hydrostatic loading. This study investigates composite shells of revolution with positive Gaussian curvature, defined by a semicircular base transitioning via a smooth spline to a tapered apex, at five aspect ratios (L/B = 1.24–4.18) in Carbon T-700, Basalt, and Kevlar epoxy composites. Burst was evaluated via the Tsai–Wu criterion; buckling through linear eigenvalue and nonlinear Riks analyses with first-eigenmode imperfections at three amplitudes (63 cases). Basalt and Kevlar outperformed Carbon in burst across all geometries. Knockdown factors reduced by ∼20% on average across amplitudes, with compact configurations most sensitive (29–34%) and elongated least (∼10%); material dependence within 3.1 percentage points. Burst–buckling comparison revealed material-specific crossovers — Carbon remains burst-limited across all five proposed aspect ratios, Basalt balances both modes at the most compact geometry, Kevlar near Model 2 — identifying three sweet-spot designs. A structural performance index showed the most compact Carbon shell achieves burst efficiency 42% above the sphere while providing 3.8 times the cylinder's buckling efficiency. Twelve of 21 configurations exceed 1000 m collapse depth, the deepest proposed shell reaching 3409 m. The proposed geometry bridges the gap between spheres and cylinders.