Optimization of the drag coefficient in wave attenuation by submerged rigid and flexible vegetation based on experimental and numerical studies

Abstract

This study investigates wave attenuation due to submerged rigid and flexible vegetation through a combination of experimental and numerical approaches. Accurate reproduction of physical measurements was achieved by adjusting the drag coefficients within the numerical model to account for the influence of wave conditions and vegetation characteristics on wave attenuation. The decay of wave height in both rigid and flexible vegetation fields is closely linked to wave nonlinearity, which can be quantified using the Ursell number. Wave nonlinearity has a more pronounced impact on wave attenuation when rigid vegetation is present compared to flexible vegetation. According to the relationship between the drag coefficient and the Keulegan–Carpenter number, a new drag coefficient formula was proposed based on a revised Keulegan–Carpenter number that considers wave nonlinearity. The deformation of flexible vegetation in response to waves was characterized by introducing the effective vegetation height, which can be correlated with the wave Cauchy number and the stem height ratio. By identifying the transition between rigid and flexible vegetation, an empirical expression encompassing multiple vegetation types was developed by incorporating vegetation flexibility. The derived empirical equation can be implemented in wave simulations with applicability to wave attenuation by vegetation and optimal flood response strategies.