Marine fishery is gradually developing from the coastal area to the deep sea. The semi-submersible offshore fish farm is one of the most foreseeable aquaculture equipment. However, the vast and abundant deep sea also means that the fish farm will be in a harsh marine environment. A model test of a semi-submersible fish farm was carried out in this paper. In order to obtain the hydrodynamic response characteristics of the fish farm, the accelerations on five different positions and mooring forces of the model under different wave conditions and current were measured, the steady-state amplitudes of the first five harmonics experimental acceleration and mooring tension were obtained. The steady-state amplitudes of non-dimensional first-harmonic acceleration at different positions with different wave periods were compared, and the amplitude trends were analyzed. The influence of higher harmonics acceleration on the first ones was investigated. Besides, the amplitude trend of different harmonics acceleration was analyzed under different conditions. Furthermore, the trend and fluctuation range of mooring tension at front and aft positions under different conditions were compared, and the causes of occurrence of the peak value of the instantaneous amplitude were figured out.


New types of aquaculture equipment are gradually put into the ocean to relieve the environmental pressure in coastal area. As a typical new type of aquaculture equipment, semi-submersible fish farm is in a harsher marine environment than the traditional offshore cage. In order to ensure the normal operation of semi-submersible fish farm and the normal survival of aquaculture products, the hydrodynamic performance of which will be the focus of attention. The hydrodynamic analysis of semisubmersible fish farm is similar to that of traditional cage, but there are also differences.

For traditional net cage, Lader et al. (2005, 2007) carried out a series of experiments on different solid ratio of net, and the hydrodynamic forces induced by different current velocity were compared. Fredriksson et al. (2007) compared the experimental data and numerical results of static deformation of a floating collar. By numerical simulation, Huang et al. (2008) studied the hydrodynamic performance of gravity cages induced by wave and current. Taking rigid and flexible floating collars as the object of study, Li and Faltinsen (2016, 2018) carried out model tests of single floating collar under different wave steepness. By comparing the results with that of numerical simulation by WAMIT, the importance of 3D flow, hydroelasticity and strong hydrodynamic frequency dependency was demonstrated; the changes of additional mass and damping coefficients were emphatically analyzed. Xu et al. (2020) studied the drag and wake of an individual long-line mussel dropper using computational fluid dynamics approaches. They found that surface roughness and sharp crowns on the rough cylinder resulted in larger drag coefficients and Strouhal numbers. By numerical simulation, Qin et al. (2020) addressed the probability distribution of the heave motion under irregular waves and extended the conditions of the most probable maximum normalized bending stress distribution of the floating collar. Qin et al. (2020) devised an experimental study of an offshore aquaculture cage induced by wave-structure interactions. The relationship between the first-, second-harmonics acceleration and wave amplitude were analyzed, and the effects of mooring loads were assessed. Concerning the safety and economic efficiency, Liu et al. (2019) conducted a series experiments to obtain the optimum submergence depth of a fish cage. By model test and numerical simulation, Yang et al. (2020) studied the hydrodynamic responses and optimize mooring design factors of a floating rope enclosure. Li et al. (2012) studied the deformation of the floating collar, and they found the flexible effects on the dynamic responses. Kristiansen and Faltinsen (2015) conducted an experiment of a net cage. Results with only waves as well as combined waves and current were obtained.

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