Wave energy conversion and attenuation of a floating composite-stiffness carpet as a flexible WEC-breakwater hybrid system

Harnessing wave energy through elastic-body-based systems offers a promising pathway toward improving structural survivability and reducing capital expenditure. To achieve maximum wave energy absorption, the hydroelastic motion of generalized (non-rigid-body) modes is crucial but has not been fully exploited, particularly with respect to combination of various materials. This paper proposes a floating flexible wave energy converter (WEC)-breakwater hybrid system consisting of a composite-stiffness carpet. The carpet is fabricated by assembling horizontally connected sub-elastic plates with different stiffnesses. The rigid constraint between adjacent sub-elastic plates is imposed. Multiple power take-off (PTO) units are uniformly deployed in accordance with the stiffness variation pattern that follows wave propagation direction. A mutual coupling study by combining Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) is conducted to focus on the composite-stiffness configuration, stiffness gradient resolution, stiffness discontinuity location and comparison with the homogeneous carpet. Configurations with lower stiffness at facing-wave end outperform those with higher stiffness at incident end. Specifically, for the symmetric configuration with smaller stiffness at both ends, the peak conversion efficiency achieves 61.3 %, while consistently yielding conversion efficiency above 20 % over all simulated wave periods. Furthermore, the configuration featuring progressively increasing stiffness along wave propagation maintains the wave transmission coefficient below 60 % under various wave conditions. Compared with the configuration with uniform stiffness, the composite-stiffness flexible materials improve the peak efficiency and wave attenuation by up to 43.7 % and 66.7 %, respectively. Additionally, significant enhancement is demonstrated as the number of PTO units increase. Overall, the composite-stiffness flexible carpet system exhibits excellent potential for offshore power generation by triggering flexural wave resonance.