The net cage is usually equipped with flexible and deformable net under the action of the ocean environment, which makes its hydrodynamic response different from that of the rigid body. Moreover, the netting accounts for a high proportion in the aquaculture platform, and the viscous force on the whole platform cannot be ignored. Based on flexible multibody dynamics and viscous fluid load calculation method, this paper developed a fluid-structure interaction program for evaluating net, and simulated the hydrodynamic force of flexible netting in current in time domain. The basic examples are compared with the hydrodynamic analysis software Orcaflex with 2D model, and the effectiveness of the program in current condition is verified by flume experiment in 3D model. The present method is demonstrated a potential approach for performance evaluation of large aquaculture equipment. These work have laid a foundation for the follow-up evaluation of the wave-induced motion response of large-scale aquaculture platforms.
In the past few decades, cage culture has developed rapidly. With the increasing pressure of globalization and the global demand for aquatic products (Golden et al. 2021), cage culture is experiencing rapid changes, and there is a trend of integrating existing cages and developing more intensive cage culture systems (Ji and Wang, 2020). Especially because of the need for suitable breeding places, marine fishery is gradually developing from the coast to the deep sea. The concept of large-scale aquaculture platforms is put forward to overcome the space limitation of traditional fish farm, and semi-submersible offshore fishing ground is one of the most promising aquaculture equipment, which has excellent wind and wave resistance, good stability, small deformation, strong adaptability, high technical level, high degree of automation, low operating cost and little impact on the environment.
Related enterprises have made several attempts. For example, Norway's Ocean Farm (Buck et al. 2018) is a large-scale frame-type offshore fishing ground equipment, 110 meters in diameter, 67 meters high and 245,000 cubic meters in volume. The first large-scale single-column semi-submersible deep-sea fishing ground "Strait No.1" in China, designed by De Maas SMC, is 140m in diameter, 40m in overall height, 12m in cage height and with 150,000 cubic meters of aquaculture water.