Topographic effects on wave resonance in the narrow gap between fixed box and vertical wall

Abstract Multiple coastal and offshore structures deployed side by side with narrow gap may be subject to large-amplitude free surface resonance, which can lead to green water on the deck and cause rapid increase of hydrodynamic loading on structures. Here, the resonant motions of the free surface inside a narrow gap between a fixed box and a vertical wall excited by incident regular waves with various wave heights are simulated using a two-dimensional numerical wave tank. The topographies of plane slopes with different inclinations are deployed in front of the vertical wall. The main focus of this paper is on the influences of the topographical variation on the fluid resonance inside the narrow gap. For the first time, it is found that the fluid resonant frequency decreases monotonously with the topographical slope, and both the amplification of the resonant wave height and the reflection coefficient present a pattern of fluctuation with the slope. For all the topographies considered in this paper, both the fluid resonant frequency and the amplification of the resonant wave height are shown to decrease with the incident wave height; while the variation trend of the reflection coefficient with the incident wave height depends on the topographical slope.