Numerical Framework for Interacting Flexible Submerged Aquatic Vegetation Blades

Submerged aquatic vegetation (SAV) plays important roles in riverine and estuarine processes. By attenuating flow and modulating flow turbulence, SAV promotes sediment stability, provides food and shelters for ecologically and economically important species and improves water quality in these environments. Understanding the physical-biological-ecological coupling between SAV structure/function and flow regime is critically important for natural resources management. For flexible SAV, vegetation blades reconfigure their postures, interact with each other and form various patterns under different flow conditions. In this study, we developed a novel structure model that integrate the soft-body dynamics used in computer graphics community to study the collective behavior of SAV blades under different flow conditions. The Absolute Nodal Coordinate Formulation (ANCF) finite element method is employed to model the large deflection of vegetation blades. The soft-body dynamic model is introduced to simulate the blade-to-blade interaction of SAV and to prevent unrealistic physical contact among vegetation blades in dense canopy. The validated structure solver was then applied to study interactions of simple idealized flows with SAV canopy. Arrays of identical thin blades were fixed at the bottom as SAV canopy. Simple vortex flow with different length scale, frequency and flow velocity was applied on top of the vegetation canopy. We also varied the flexibility, density and spatial configuration of SAVs to investigate the effect of stiffness and blade-to-blade interactions on the deflection height of SAV, which influences the drag force and damping effect of vegetation. In addition, the simulation results were used to analyze the characteristic scales of the progressive waving motion in SAV canopy (i.e., monami) and their dependence on vegetation properties.