A coupled numerical model for interactions between waves and flexible vegetation blades

Abstract

In this study, we developed a 2-D fully coupled numerical model to investigate interactions between waves and flexible vegetation. The model integrates a flexible vegetation dynamics model—capable of simulating large deflections of vegetation blades under external forcing—into the Reynolds-Averaged Navier-Stokes (RANS) fluid solver NEWFLUME. A two-way coupling methodology transfers hydrodynamic fluid forces to drive blade motion, while the reactive forces from the blade are incorporated as source terms in the fluid momentum equations. The model was validated against experimental data for flexible vegetation under regular wave conditions, demonstrating its capability to predict blade deformation and wave attenuation characteristics. Numerical experiments across a wide range of Cauchy numbers (0.01–10,000) revealed distinct behavioral regimes in how vegetation flexibility affects wave attenuation. When Ca < 1, flexible vegetation behaves similarly to rigid vegetation, whereas Ca > 1 exhibits power-law decay in both wave attenuation rate and hydrodynamic forces. Highly flexible vegetation exhibits up to an 81 % reduction in wave height attenuation rate compared to rigid conditions, with blade motion patterns transitioning from cantilever beam-like oscillations to complex whip-like motions as flexibility increases. Further validation with large-scale experiments confirmed the model's ability to simulate irregular wave attenuation through a flexible vegetation domain. The model captured complex hydrodynamic features, including three-layer mean flow structures under irregular wave conditions and velocity amplification at blade tips that exceed local flow velocities in highly flexible vegetation.