Effect of non-uniform biofouling distribution on the drag coefficient of aquaculture nets

Biofouling on aquaculture nettings poses several issues, especially increased drag on net panels or aquaculture structures to which the net is attached, potentially affecting the structural integrity of the infrastructure. Despite biofouling growth on nets not being uniformly distributed, only a few studies have explicitly investigated the influence of naturally fouled nets on drag. In this study, the effects of uniform and non-uniform (half- and quarter-concentrated) hard fouling distributions on the drag coefficient of knotless square net were numerically investigated using a Computational Fluid Dynamics (CFD) approach. Based on the experimental data obtained from the literature, a CFD model was developed, validated, and analyses were undertaken on the effects of fouling distribution on associated drag coefficients of netting panels. At low net solidities less than 0.6, nettings with half- and quarter-concentrated fouling had significantly lower drag coefficients, up to 40% and 35% respectively, than a netting with uniform fouling that had the same solidity. However, the difference in drag coefficient on nettings due to fouling distribution attenuated with a further increase in fouling (net solidity). The correlations of drag coefficient with net solidity for netting panels with half- and quarter-concentrated fouling were proposed, which can provide a conservative drag coefficient estimate for the evaluation of cage safety based on the fouling distribution. This study also highlights the need to take uniformity of fouling distribution on aquaculture nets into consideration when estimating drag force, especially at solidities less than 0.6, as it significantly differs from that of uniform fouling distribution. • At net solidities lower than 0.6, netting with nonuniform fouling show up to 40% lower drag coefficients than a uniformly fouled net with the same solidity. • Differences in drag coefficients between uniform and nonuniform fouling were associated with the alteration of flow patterns behind the net panel. • Correlations were proposed to predict drag coefficients of non-uniformly fouled nets with different net solidities.