Wave and Hydrodynamic Processes in the Vicinity of a Rubble-Mound, Permeable, Zero-Freeboard Breakwater

Theofano I Koutrouveli,Athanassios A Dimas

doi:10.3390/jmse8030206

Theofano I Koutrouveli, Athanassios A Dimas

Open Access

https://doi.org/10.3390/jmse8030206

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Abstract

A numerical study for the effect of crest width, breaking parameter, and trunk permeability on hydrodynamics and flow behavior in the vicinity of rubble-mound, permeable, zero-freeboard breakwaters (ZFBs) is presented. The modified two-dimensional Navier-Stokes equations for two-phase flows in porous media with a Smagorinsky model for the subgrid scale stresses were solved numerically. An immersed-boundary/level-set method was used. The numerical model was validated for the cases of wave propagation over a submerged impermeable trapezoidal bar and a low-crested permeable breakwater. Five cases of breakwaters were examined, and the main results are: (a) The size of the crest width, B, does not notably affect the wave reflection, vorticity, and currents in the seaward region of ZFBs, while wave transmission, currents in the leeward side, and mean overtopping discharge all decrease with increasing B. A non-monotonic behavior of the wave setup is also observed. (b) As the breaking parameter decreases, wave reflection, transmission, currents, mean overtopping discharge, and wave setup decrease. This observation is also verified by relevant empirical formulas. (c) As the ZFB trunk permeability decreases, an increase of the wave reflection, currents, wave setup, and a decrease of wave transmission and mean overtopping discharge is observed.

Highlights

The role of rubble-mound low-crested breakwaters (LCBs) in coastal protection, whose main advantage is their mild aesthetic impact on the natural environment, is to partially dissipate incident waves
Three three different setups were considered to examine the effect of crest width on different setups were considered toreflection, examine the effect of crest widthasonthe hydrodynamic of wave reflection, overtopping, and setup, well as the flow flow behavior in processes the seaward and leeward regions of thesetransmission, structures
The results indicate the size of the crest width, B, did not notably affect wave

Summary

Introduction

The role of rubble-mound low-crested breakwaters (LCBs) in coastal protection, whose main advantage is their mild aesthetic impact on the natural environment, is to partially dissipate incident waves. In the seaward region of LCBs, the most important wave processes are breaking and reflection, while in their leeward region, the most important ones are overtopping, transmission, and setup. These wave processes induce significant flow processes in the vicinity of LCBs. The influence of the geometrical characteristics of LCBs on wave and flow processes has been studied extensively for emerged or submerged LCBs. The case of zero-freeboard breakwaters (ZFBs), where the crest level of the structure is at the still water level (SWL), is the subject of the present study. In the following literature review, the focus is on experimental and numerical (only depth-resolving flow models) studies of rubble-mound, two-dimensional vertical (2-DV) LCBs

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