Experimental and numerical study of a semi-submersible offshore fish farm under waves

Abstract

The interaction between the semi-submersible offshore fish farm (SOFF) and waves was investigated by numerical simulations and dedicated model tests. The SOFF generally consists of three main components, such as large pontoon, frame system, and net system. And the hydrodynamic forces cannot be calculated by the same method due to the big difference in the main dimensions of them. Therefore, a hybrid numerical method of direct time domain and indirect time domain for the SOFF was proposed in this paper, and the calculation program was originally developed. In the present numerical method, the three dimensional potential theory was used to calculate the hydrodynamic loads on the large pontoon through indirect time domain, and the Morison equation and screen model were used to calculate the hydrodynamic loads on the frame system and net system, respectively. Then the total hydrodynamic loads on the SOFF at each time step can be obtained, and the motion responses of the SOFF were calculated in the time domain. The model tests were carried out in the wave basin, and the heave and pitch motions with wave periods were obtained. The numerical results were verified by the experimental results. A good agreement exists between the numerical results and experimental results. Then the effects of some key parameters on the motion responses were investigated by the present numerical model, such as draft, wave height and net solidity ratio. The results show that the draught of SOFF has an obvious influence on the heave and pitch motion. In addition, heave and pitch response amplitudes are positively correlated with wave amplitude. And the change of net solidity ratio has a notable effect on the heave motion and pitch motion.