Hydrodynamic characteristics of flexible net panels: Drag, wake attenuation, and structural deformation

Flexible net panels used in marine aquaculture undergo hydrodynamic loading, structural deformation, and downstream wake attenuation under current action. In this study, six nylon net panels with different twine diameters, aperture sizes, and solidities were investigated at current velocities of 0.4–0.7 m/s. Flume experiments were combined with computational fluid dynamics and one-way fluid–structure interaction (FSI) to analyze drag characteristics, deformation responses, and downstream velocity attenuation. Numerical–experimental data-fusion methods, including global, linear, and Gaussian process regression corrections, were further applied to reduce the systematic bias in drag-coefficient prediction. The results show that drag force increases nonlinearly with current velocity and is generally higher for panels with smaller apertures and greater solidity. The numerical and empirical drag coefficients are consistently higher than the experimental values because deformation reduces the effective projected area, whereas this feedback is neglected in the one-way FSI model. The proposed correction methods reduce the overall mean absolute percentage error from approximately 20% to about 7%. Higher-solidity panels generate deeper velocity deficits and slower wake recovery, while increasing current velocity extends the wake farther downstream. Meanwhile, the longitudinal offset of the net center decreases by 18.6%–27.0%, whereas the transverse offset increases by 58.1%–72.5%. The reduced displacement increment at higher velocities reflects the combined effects of projected-area reduction and increased geometric resistance. These findings demonstrate that deformation-aware modelling or experimental correction is required for accurate prediction of flexible net hydrodynamics.