Hydraulic characteristics and force mechanisms of the perforated floating photovoltaics

Floating photovoltaic (FPV) systems have been widely deployed in renewable-energy development. Their hydraulic characteristics determine hydrodynamic loading and drag force, governing structural safety and cost-effective design. The complex flow field around perforated FPV configurations remains insufficiently characterized. Focusing on this gap, the present work combines physical model experiments and three-dimensional numerical simulations to systematically investigate the hydraulic features and loading mechanisms of perforated FPV. Vortex evolution and through-flow physics originating from the perforated layout are analyzed quantitatively. The effects of porosity, draft ratio, and inflow velocity on skin friction drag, form drag, and overall drag are clarified, and a drag prediction relation is established from the drag-component analysis. The results demonstrate that openings reshape the wake: the original concentrated trailing vortex system of solid FPV breaks into discrete scattered vortices through opening-edge flow separation and shear-layer development. At porosity 0.32, draft ratio 0.25, and incoming flow velocity 0.6 m/s, the perforated model yields 10% larger total drag (+26% form drag and −22% skin drag) relative to its solid counterpart. The skin-drag coefficient follows a negative quadratic dependence on porosity, whereas the form-drag coefficient increases quadratically with porosity and decreases quadratically with draft ratio. A simplified drag-coefficient correlation is proposed, yielding mean absolute relative error of 0.10 and coefficient of determination (R2) of 0.95 for total drag. These results provide quantitative support for hydrodynamic load estimation and structural design of large-scale perforated floating photovoltaic facilities.