Mechanism analysis on the mitigation of harbor resonance by periodic undulating topography

Gao et al. (2021. Investigation on the effects of Bragg reflection on harbor oscillations. Coastal Engineering, 170: 103977) attempted to utilize Bragg reflection to alleviate harbor resonance, and discovered its significant effectiveness for the first time. The Bragg reflection occurred over periodic topographies deployed outside and parallel to the harbor entrance. However, the inherent mitigating mechanisms were not revealed. In this paper, the Bragg reflection over a patch of sinusoidal bars and its coupling effects with the harbor are studied using a Boussinesq-type model. Different from the previous study, the sinusoidal bars with various numbers and amplitudes are arranged in the manner of an arc layout around rather than parallel to the entrance. A physical process decomposition method is proposed to reveal the inherent mitigation mechanism. Moreover, the condition under which harbor resonance is not excited by incident waves (hereinafter referred to as “harbor non-resonance condition”) is also investigated, and the similarities/differences of mitigation mechanisms between the harbor resonance and non-resonance conditions are discussed. Finally, for the harbor resonance condition, the effects of the number and the amplitude of sinusoidal bars on the best mitigation effect and optimal bar wavelength, which can attain the best mitigation effect, are systematically analyzed.