A comprehensive numerical study on the current-induced fluid-structure interaction of flexible submerged vegetation

Submerged vegetation is becoming more and more relevant as a nature-based solution for coastal protection schemes, counteracting the effects of climate change and sea level rise. The numerical model REEF3D has been used to simulate the motion of and forces exerted on flexible vegetation under unidirectional currents. This study emphasizes the critical need for accurate solutions obtained by numerical models to investigate the complex ecosystem services, adopting a direct forcing approach using the immersed boundary method. The fluid- structure interaction capability within the finite difference model is comprehensively evaluated for the simulation of stem motions and forces exerted on flexible vegetation under varying unidirectional flows. Thresholds for numerical parameters, including a minimum number of 25 rigid elements composing the stem, are identified for accurate solutions. The necessity of using large eddy simulations and a Smagorinsky constant of 0.1 to simulate the turbulent flow is demonstrated. The study confirms the accuracy of the implemented fluid-structure interaction model to replicate stem bending (less than 10 % deviation relative to the stem length) and forces across varying hydrodynamic conditions.