Numerical investigations of wave loads on fixed box in front of vertical wall with a narrow gap under wave actions

Violent fluid oscillations may appear inside the narrow gap between multiple structures in close proximity and cause severe damage to such structures and safe operations. Here, based on the OpenFOAM® package, this paper presents a numerical investigation of wave loads during gap resonance between a fixed box and a vertical wall by utilizing a two-dimensional (2D) numerical wave flume. The box-wall system is subjected to incident regular wavesco with various wave heights and frequencies. The topographies of plane slopes with various inclinations are arranged in front of the vertical wall. This paper focuses on the influences of the topographical variation on the wave loads, including the horizontal wave force, the vertical wave force and the moment on the box. It is found that all the frequencies, at which the maximum horizontal wave force, the maximum vertical wave force and the maximum moment appear, decrease with the increase of topographical slope, S, overall. Moreover, these frequencies are also shown to deviate from the fluid resonant frequency to different degrees. For all the incident wave heights considered, both the maximum horizontal wave force and the maximum moment present a pattern of fluctuation with the topographical slope.</p

Investigation on the effects of Bragg reflection on harbor oscillations

Periodic undulating topographies (such as sandwaves and sandbars) are very common in coastal and estuarine areas. Normally incident water surface waves propagating from open sea to coastal areas may interact strongly with such topographies. The wave reflection by the periodic undulating topography can be significantly amplified when the surface wavelength is approximately twice the wavelength of the bottom undulations, which is often called as Bragg resonant reflection. Although the investigations on the hydrodynamic characteristics related to Bragg reflection of a region of undulating topography have been widely implemented, the effects of Bragg reflection on harbors have not yet been studied. Bragg resonant reflection can effectively reduce the incident waves. Meanwhile, however, it can also significantly hinder the wave radiation from the harbor entrance to the open sea. Whether Bragg reflection can be utilized as a potential measure to alleviate harbor oscillations is unknown. In the present study, Bragg reflection and their interactions with the harbor are simulated using a fully nonlinear Boussinesq model, FUNWAVE 2.0. For the purpose, an elongated harbor with constant depth is considered, and a series of sinusoidal bars with various amplitudes and numbers are deployed outside the harbor. The incident waves considered in this paper include regular long waves and bichromatic short wave groups. It is revealed for the first time that for both kinds of incident waves, Bragg resonant reflection can significantly alleviate harbor resonance. The influences of the number and the amplitude of sinusoidal bars on the mitigation effect of harbor resonance and on the optimal wavelength of sinusoidal bars that can achieve the best mitigation effect are comprehensively investigated, and it is found that the former two factors have remarkable influences on the latter two parameters. The present research provides a new option for the mitigation of harbor oscillations via changing the bottom profile, which is feasible as long as the navigating depth is guaranteed.</p