Experimental study of Overtopping Breakwater for Energy Conversion (OBREC) device under various sea states and structural geometries

Abstract

The Overtopping Breakwater for Energy Conversion (OBREC) harnesses wave energy by capturing overtopping waves into a reservoir on a rubble mound breakwater, generating electricity via low-head turbines using the water level difference. This study enhances understanding of overtopping behavior under varying OBREC geometries and sea states through 140 two-dimensional experimental tests. A novel dimensionless parameter (H*√T*) was introduced to jointly assess wave height and period effects, alongside a new overtopping parameter (N_OT) accounting for wave breaker type. Results reveal distinct overtopping trends linked to the surf similarity parameter (ξ), with plunging breakers below ξ_m-1,0 = 4.2 and surging breakers above this threshold. The N_OT parameter showed strong predictive capability for both breaker types, achieving coefficients of determination of R² = 88 % and R² = 97 % for plunging and surging breakers, respectively. Ramp geometry significantly influences performance: higher ramps reduce overtopping but increase turbine head, gentler breakwater slopes lower overtopping, while gentler reservoir slopes increase it. A predictive equation was developed for both plunging and surging breakers, achieving R² = 82 % and R² = 84 % with low mean relative errors (E = 0.003 and E = 0.016, respectively; E = 0.008 overall). Compared to the best existing model by Iuppa et al., the proposed formula reduced the mean relative error by approximately 98 % and achieved an average R² of 83 %.