Hydrodynamic interactions between the cylinder and nets of a typical offshore aquaculture structure in steady current: Numerical investigation and coupling mechanism

Abstract

The expansion of aquaculture fish farms into deep sea has become a trend today. Several new types of offshore fish farming structures have been designed and tested in real sea, a typical of which is the semi-submersible structure. To ensure structural safety in harsh sea environment, detailed investigations on the hydrodynamic characteristics of offshore aquaculture structures are necessary and meaningful. The study focuses on the basic components of a semi-submersible net cage, namely the combined cylinder-net structure, and conducts CFD-based numerical research on its hydrodynamic coupling characteristics under uniform flow. The net structure is numerically simulated based on the porous media model. The drag and lift force and corresponding flow field of only the cylinder, only the nets, and the combined cylinder-net structure are measured under different inflow angles and solidity ratios of nets. The results indicate that the presence of the cylinder increases the drag of nets, and its impact on lift force of nets is closely related to the inflow angle. On the other hand, the presence of the net structure also amplifies the resistance of the cylinder. Meanwhile, the disturbance law of the flow field caused by the cylinder and the net structure is analyzed. By combining numerical and existing experimental results, the hydrodynamic coupling mechanism between the cylinder and the net structure is preliminarily revealed. This study indicates that when conducting hydrodynamic analysis of offshore structures such as the new semi-submersible net cage, the hydrodynamic interaction between the columns and the net structure should be considered.