Wave focusing and sheltering effects of a multi-layered cylindrical structure in regular wave conditions

Inspired by the metamaterial superscatterer in electromagnetics, a multi-layered cylindrical structure has been proposed as an effective design for integrated breakwater–wave energy converter (WEC) systems, enabling both wave energy concentration and wave sheltering. In this study, a computational fluid dynamics (CFD) model is developed to investigate the wave dynamics around this structure, with the numerical predictions showing good agreement with the experimental measurements. A comparative analysis between the multi-layered and single-layered configurations is conducted, and the structure's performance is systematically evaluated with different water depths, wave frequencies, flume widths and wave heights. The results reveal the wave amplification factor of up to 3.6 due to refraction and superposition, while a downstream shadow zone emerges with an 80 % reduction of the wave height. Shallower or deeper water depths reduce the amplification and promote the early recovery of the incident wave profile, while wider flumes significantly extend the shadow zone due to the delayed reflection at the sidewalls. As the nonlinearity of the incident wave increases, both the amplification and sheltering effects are slightly weakened, and the shadow zone ends at a shorter distance from the structure, i.e., 3.2 times the cylinder diameter.