Experimental Study on the Effects of Aquaculture Net Cages on the Motion Responses of a Spar-Type Floating Structure

Abstract An innovative concept for a spar-type floating wind turbine that incorporates aquaculture cages not only meets the Sustainable Development Goals (SDGs) but also optimizes the use of offshore ocean space. The integration of floating offshore wind turbines with aquaculture has the potential to bring economic benefits to both industries. In this feasibility study, a 1/56 scale model of a 2MW Spar floating wind turbine is used and the target cage is silver salmon farming cage with dimensions of around 25 m in diameter and 9 m in depth. An experimental investigation was carried out in an experimental tank to examine the surge, heave and pitch dynamic responses of a spar-type floating offshore wind turbine with aquaculture cages. Under regular wave conditions, aquaculture cages of varying quantities and distances were positioned in front of the spar-type floating structure facing the wave direction, with accelerometers recording the spar-type floating structure’s surge, heave, and pitch motion. The study revealed that cages have a predominantly shadowing influence on the spar’s motion responses, compared to scenarios without cages. This effect is more pronounced when cages are situated nearer to the spar. When wave period was less than 1.0 second, the presence of the cages exerted a more pronounced influence on the movement of the spar. However, when the ratio of incident wavelength to cage diameter is close to 4, the motion responses of the Spar were significantly amplified under the influence of the aquaculture cages. Also, the impact of cages on the spar’s motion is relatively minor, varying from less than 10% for wave periods in excess of 1.2 seconds. Furthermore, the insignificant impact of the number of cages on spar motion attenuation was found but different setting methods will affect the wave field near the cages. The findings of this study possess significant practical and theoretical implications, as they furnish experimental evidence of the feasibility of integrating renewable energy enterprises with marine aquaculture ventures. In summary, the study determined that the deployment of net cages has an almost negligible impact on the oscillatory movements of spar-type floating platforms in most scenarios but reduces the motion amplitudes under specific wave periods. These discoveries provide crucial guidance for future offshore industry operations, indicating the necessity for further investigations to explore the interplays between floating structures and net cages under diverse conditions.