Effects of rectified sinusoidal bar-type Bragg breakwater on harbor resonance mitigation under regular wave excitation

This study investigates the effectiveness of Bragg breakwaters in the form of periodic rectified sinusoidal bars (RSB)—retaining only the crest portion of complete sinusoidal topography—in mitigating harbor resonance induced by regular waves. A series of numerical experiments are conducted using the fully nonlinear Boussinesq model FUNWAVE 2.0, in which the breakwater is deployed at varying distances from the harbor entrance and the effects of bar amplitude, bar number, bar width, and spacing are systematically examined. The results reveal that continuous connection to the harbor entrance amplifies resonant oscillations, whereas finite separation produces periodic variation in mitigation effectiveness with one or more optimal positions. For Modes 3, 4, and 5, when the ratio of bar width to spacing remains below a critical value of approximately 0.7, the resonance intensity can be reduced by up to 78%. The optimal mitigation factor decreases approximately linearly with increasing bar number and amplitude, while the corresponding optimal bar width decreases with increasing amplitude. Notably, these optimal positions remain essentially unchanged under different bar amplitude conditions. These findings demonstrate that RSB-type breakwaters achieve comparable mitigation efficacy using only half the geometric material of complete sinusoidal bars, offering a more efficient and economical engineering alternative for harbor resonance control.