Experimental study on wave attenuation and low-velocity wake generation by orifice-type flow-focusing artificial reef arrays

Abstract

This study utilizes a combined experimental and numerical modeling method to examine how the opening ratio of individual orifice-type flow-focusing reefs and the relative spacing (d/D) within reef arrays affect the mechanisms of wave dissipation and current weakening. The results indicate that reefs with moderately small opening ratios exhibit improved comprehensive performance, achieving higher wave dissipation rates while facilitating the formation of extensive and stable low-velocity zones behind the structures. An optimal relative spacing for wave dissipation exists within reef arrays. When d/D < 1, excessive flow resistance generates strong vortices that diminish the dissipation effectiveness. Conversely, when d/D ≥ 3, the synergistic interactions within the reef array are weakened, reducing their combined wave-dissipating effect. Reef arrays satisfying the Bragg resonant reflection condition demonstrate a substantial increase in wave reflection capacity. However, wave attenuation is not primarily governed by reflection, which contributes only a minor portion. Furthermore, an empirical formula for the transmission coefficient, incorporating the effect of spacing, is proposed, demonstrating robustness in predictive capability. These findings support optimized artificial reef design.