A novel FEM approach for the analysis of Type-IV hydrogen storage tank based on the enhanced Refined Zigzag Theory

While high-pressure gas storage is the most practical method for hydrogen transport, it requires extreme internal pressures to compensate for the fuel's low volumetric energy density. Such operational demands lead to severe structural stresses, necessitating high-strength composite materials to achieve an optimal balance between safety and weight efficiency. Consequently, accurate displacement and stress analyses of these multilayered structures are vital for structural optimization. This paper presents a Finite Element (FE) formulation based on the enhanced-Refined Zigzag Theory (en-RZT), specifically tailored for composite pressure vessels. In particular, a quadrilateral flat shell finite element based on the en-RZT is formulated for the first time (ZZen-Q), enabling the analysis of complex, curved multilayered structures. Numerical benchmarks, including static and modal analyses of multilayered plates, cylinders, and tanks, are conducted to evaluate the accuracy and efficiency of the proposed ZZen-Q element against standard shell FE models and high-fidelity 3D FE models. The results demonstrate that ZZen-Q significantly outperform standard shell elements in accuracy with only a marginal increase in nodal degrees of freedom. Furthermore, while providing static and dynamic predictions comparable to high-fidelity 3D models, the en-RZT-based FE approach requires a substantially lower computational effort. These findings position the ZZen-Q shell elements as powerful tools for the preliminary design and optimization of hydrogen storage systems, facilitating rapid, high-performance design iterations prior to final validation.