Abstract
Coastal plants can significantly dissipate water wave energy and services as a part of shoreline protection. Using plants as a natural buffer from wave impacts remains an attractive possibility. In this paper, we present a numerical investigation on the effects of the emerged vegetation on non-breaking, breaking and broken wave propagation through vegetation over flat and sloping beds using the Reynolds-average Navier-Stokes (RANS) equations coupled with a volume of fluid (VOF) surface capturing method. The multiphase two-equation k-ω SST turbulence model is adopted to simulate wave breaking and takes into account the effects enhanced by vegetation. The numerical model is validated with existing data from several laboratory experiments. The sensitivities of wave height evolution due to wave conditions and vegetation characteristics with variable bathymetry have been investigated. The results show good agreement with measured data. For non-breaking waves, the wave reflection due to the vegetation can increase wave height in front of the vegetation. For breaking waves, it is shown that the wave breaking behavior can be different when the vegetation is in the surf zone. The wave breaking point is slightly earlier and the wave height at the breaking point is smaller with the vegetation. For broken waves, the vegetation has little effect on the wave height before the breaking point. Meanwhile, the inertia force is important within denser vegetation and is intended to decrease the wave damping of the vegetation. Overall, the present model has good performance in simulating non-breaking, breaking and broken wave interaction with the emerged vegetation and can achieve a better understanding of wave propagation over the emerged vegetation.
Highlights
The vegetation patches are proven to be effective in surface wave attenuation, which plays an important role in coastal defense by reducing incoming wave energy, stabilizing shore sediments and improving water quality
The pressure and velocity are calculated by the PIMPLE algorithm, which is a mixture between the splitting of operator (PISO) method and semi-implicit method for pressure-linked equations (SIMPLE) algorithms
The time term is discretized by backward Euler time scheme, the convection term is discretized by the Gauss linear corrected scheme which has higher order than Gauss upwind to minimize numerical diffusion
Summary
The vegetation patches are proven to be effective in surface wave attenuation, which plays an important role in coastal defense by reducing incoming wave energy, stabilizing shore sediments and improving water quality. Wave transmission and attenuation characteristics are important in determining the location and amount of plants required for shore protection applications [1]. The vegetation can significantly alter mean flows, velocity profiles and generate additional turbulence production [2,3,4]. Harada et al [2] demonstrate that the vegetation is as effective as concrete breakwater structures for holding back the sea waves and minimizing wave forces. Due to the increase of coastal flooding and the rising sea-level, the efficiency of vegetation to reduce the wave energy has been generally recognized. Numerous studies have focused on this topic [5,6,7,8,9,10]
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