Loads on a vessel-shaped fish cage steel structures, nets and connectors considering the effects of diffraction and radiation waves

Abstract

Vessel-shaped fish cages are a new type of large aquaculture structure consisting of a floating body, steel frames and nets. Unlike in a conventional aquaculture cage, the diffraction and radiation waves induced by the floating body of a vessel-shaped fish cage can induce additional changes to the flow field surrounding the nets. In this paper, the global hydrodynamic responses of the floating body are first calculated in the time domain by the state-space method based on potential theory. The velocity transfer functions around the nets and steel frames induced by the diffraction and radiation waves are attracted, and then their effects on the forces of the nets and steel frames are calculated by Morison equations; thus, the forces/moments of the cross-sections of the main steel structures are calculated by quasi-static method. The forces on the nets and steel frames are then balanced with the motions of the floating body through numerical iterations. Finally, the tensions within the net twines, the loads on the connectors and the cross-sectional forces/moments on the main steel structures are investigated under different waves. It is found that the diffraction and radiation waves introduce a large change in the velocity of the water particle and thus considerably amplify the load effects on the steel structures, nets and connectors.