Deformation and drag force of model square fish cages in a uniform flow

Model experiments were carried out to investigate the performance of different types of 1:8.3-scale model square fish cages in a uniform flow. The model cages were designed using different netting materials, mesh types, and cage depths. Shape deformation, volume reduction, and drag force were used as key parameters to characterize the cage performance. The results indicate that cages using polyethylene netting for the four sides and wire-netting for the bottom generally show better performance than those composed entirely of polyethylene netting; specifically, the former undergoes less shape deformation and volume reduction than the latter. The mesh type (square or diamond mesh) had a noticeable effect on shape deformation and drag force but a limited effect on cage volume reduction. Moreover, for the cages with wire-netting bottom and polyethylene sides, the bottom net tended to drift parallel to its undisturbed orientation when the sides were composed of square mesh netting. In contrast, the bottom net drifted obliquely upward on the downstream side when diamond mesh netting was used for the side nets. It was also confirmed that drag force per unit volume of the cages with wire-netting bottom was larger than that for the cages composed entirely of polyethylene netting.