Vegetation stem dynamics under wave loading: Insights from a coupled fluid–structure model

Accurate replication of the stem motion of submerged aquatic vegetation is crucial to gain insights into its capacity for coastal protection and adaptability, such as the wave attenuation capacity and local sediment mobilization. The fluid–structure interaction solver within the numerical model REEF3D::CFD is validated, and then further employed to analyze vegetation stem motion and resulting drag forces, under wave loads using reference experiments, and covering a wide range of material properties and hydrodynamic conditions found in natural aquatic vegetation. Good agreement between simulated and experimental results is achieved for most test cases. This is expressed by less than 10 % deviation of the simulated to the experimental forces and the stem positions relative to the stem length. To investigate possible sources of discrepancies between the numerical and experimental results, the flow field in front of the stem is compared with that measured during the reference experiments. Bending modes of stem movements provide further insights into the complex dynamic behavior of stems. Additionally, the study demonstrates the influence of the model’s built-in damping coefficients on the time-dependent stem movement under wave load for different material types. For all tested material types, the findings suggest that the use of damping coefficients ranging between 1 $\times$ 10^-8 and 1 $\times$ 10^-6 led to the successful replication of the stem dynamics and the resulting drag forces. Accurate predictions of vegetation response to wave loading require careful selection of the governing parameters in the structural model replicating the stem. Considering this, the proposed fluid–structure interaction solver proves highly effective for simulating a wide range of flexible, submerged vegetation stems.