Numerical modelling of wave and wave-current attenuation by submerged flexible vegetation

Abstract

Recently, coastal protection has developed to one of the most crucial and urgent issues, resulting in a significant number of research studies on the role of vegetation in shore protection. Therefore, numerous studies have been conducted to understand the wave-vegetation interactions and the damping effects of vegetative fields. There is a general agreement that many complex physical processes are involved in the interaction of waves and currents with vegetation. Hence, there is still a need for further research of wave and/or current-vegetation interactions to improve the understanding of eco-hydraulic processes. There are only very few studies that address the effect of currents on wave attenuation by vegetation. From these studies, it is concluded that an underlying current should be taken into account for evaluating wave attenuation by vegetation; ignoring that the effect of underlying currents may result in incorrect predictions of the wave-attenuating capacity of vegetation in tidal environments. Therefore, further research is necessary to enhance the knowledge of wave-current-vegetation interaction and to quantify the effect of underlying currents on wave attenuation by vegetation. This study therefore aims to improve the understanding of the highly complex hydrodynamic processes involved in the attenuation of waves and currents by flexible vegetation. For this purpose, a new porous-media based approach for the modelling of wave attenuation by vegetation is applied using the CFD solver “PorousWaveFoam” in the frame of OpenFOAM®. For flexible vegetation, the most suitable empirical formulation for the deflected plant height within a meadow is introduced in the model, and the extended model is systematically validated against laboratory tests under pure wave and wave-current conditions. A systematic parameter study is performed to better understand the relative contribution of the physical processes to the attenuation of waves by vegetation and thus, to provide a substantially larger dataset for the development of new formulae for the prediction of wave attenuation by flexible vegetation under pure wave and wave-current conditions. The results show that the proposed porous media approach and the developed formulae perform relatively well for predicting wave attenuation by flexible vegetation.