A research team has analysed S-shaped buoy configurations with multiple degrees of freedom (multi-DOF) for wave energy converters (WECs) in the shallow-water region of the East China Sea. The study explores how these articulated geometries can simultaneously capture the vertical and pitching motion of waves, widening the frequency band over which the device extracts useful energy compared with single-degree-of-freedom buoys.

The approach addresses a well-known limitation of conventional wave energy converters: their performance drops rapidly when the real, often broad and scattered, wave spectrum does not match the resonant frequency of the device. S-shaped buoys, made up of rigid segments linked by joints, introduce several coupled oscillation modes that allow the response to be tuned with multiple absorption peaks, something particularly relevant in continental shelf coastal zones such as those of the East China Sea, where waves are short-period and highly variable.

The methodology combines hydrodynamic modelling of the multi-DOF buoys with simulations of their behaviour under wave conditions characteristic of the shallow-water region studied. The analysis compares different geometric and joint configurations of the S-shaped structure to identify those that maximise captured power and robustness to changes in wave direction and period, as well as assessing the structural feasibility of the devices in nearshore sites.

The results show that multi-DOF S-shaped configurations outperform conventional single-degree-of-freedom buoys in energy capture within the dominant frequency range of the coastal waves off East China. The study thus provides a design basis for future WEC prototypes intended for shallow waters, an environment where wave energy is abundant but where devices must also withstand complex hydrodynamic loads and prolonged exposure to variable marine conditions.