Numerical investigation on hydrodynamic and wave attenuation performance of a stepped-type floating breakwater

Floating breakwaters (FBs) are increasingly used for coastal protection in deep-water and environmentally sensitive environments due to their flexibility and lower environmental impact. However, conventional FBs often show limited wave attenuation performance under long-period waves. This study investigates the hydrodynamic performance of a stepped trapezoidal floating breakwater using two-dimensional Reynolds-averaged Navier–Stokes simulations with a Volume-of-Fluid free-surface capturing approach. A systematic parametric study examines the effects of slope angle and step configuration on wave reflection, transmission, and energy dissipation. Results show that smaller slope angles and fewer steps significantly improve wave attenuation compared with conventional FB designs. The optimized configuration reduced the wave transmission coefficient by about 33% and increased the wave energy dissipation coefficient by up to 800% relative to the conventional reference model. The improved performance is attributed to enhanced wave–structure interaction and the formation of complex vortex structures along the stepped surfaces, which intensify turbulence and energy dissipation. Flow field analyses further indicate that repeated flow separation and recirculation around the stepped geometry play an important role in reducing wave reflection and transmission. Overall, the study provides useful insights and practical guidance for the design optimization of floating breakwaters for coastal protection applications.