Bio-inspired adaptive flexible tube wave energy converters: resonant fluid-structure interaction and power extraction

Flexible tube wave energy converters (WECs) are a novel class of devices utilizing deformable materials, offering structural simplicity, broad-band energy conversion, and adaptability to diverse wave conditions. While prior studies have examined their hydro-elastic behaviour, the nonlinear coupling between internal and external fluid fields and its impact on fluid-structure interaction (FSI) responses remain insufficiently understood. This study employs a high-fidelity FSI framework, integrating computational fluid dynamics (CFD) and finite element analysis (FEA), to investigate the dynamic performance of two flexible WEC designs: S3 and Anaconda. Numerical simulations across varying wave conditions reveal distinct dynamic features. The S3 WEC supports multiple internal standing wave modes, enabling broadband resonant energy harvesting, whereas the Anaconda exhibits resonance at a single dominant frequency. Internal fluid flows in both devices show complex three-dimensional motions, challenging conventional one-dimensional flow assumptions. Structural stress distributions also differ, with peak stresses in the S3 aligning with the anti-nodes of internal standing waves, while in the Anaconda, they concentrate near the stern. These findings enhance the understanding of coupled fluid-structure dynamics in flexible WECs and offer theoretical guidance for their design optimization and deployment in real-sea environments.