Impact of the biological fouling on the hydrodynamic characteristics of nets under different current and attack angle conditions

Abstract

The impact of biological fouling on the hydrodynamic performance of nets is examined in this paper. Since the safety and reliability of the net are threatened by biological fouling, particularly in the context of drag forces and flow characteristics. The drag forces exerted on clean nets and those affected by biological fouling under different attack angles (90° and 45°) are compared. The results highlight that biological fouling increases drag significantly, with 26.2 % to 65.8 % higher drag compared to clean nets within specific solidity ranges. As such, traditional drag coefficient formulas may not accurately predict the drag for biofouling nets. Aside from this, it is found that biological fouling enhances the shielding effect behind net twines, particularly at the 45° attack angle. Notably, significant velocity attenuation and fluctuation behind the aperture center of biofouling nets are observed, especially at the 45° attack angle. Furthermore, how the attack angle affects the vorticity field of biofouling nets on different characteristic planes are also assessed in this paper, aiming to provide insights into understanding how biological fouling alters the flow dynamics around the net structure, potentially affecting its performance and susceptibility to excitations such as currents/waves.