Optimization study of a catenary mooring system for a spar floating wind turbine based on its hydrodynamic responses

In this article, selecting an appropriate mooring system for the spar platform of a wind turbine consisting of chain-cable-chain is investigated based on a meta-heuristic method. A boundary element software is applied to hydrodynamics analysis, and the numerical results are verified by experimental results. According to the characteristics of the experimental mooring system, an appropriate chain is selected for the prototype model, and then a mooring system consisting of chain-cable-chain replaces the chain-based mooring system. Environmental forces have been applied by the conditions of the Caspian Sea. Analysis is done in time domain for irregular wave spectrum of Joint North Sea Wave Project. For the cable in the middle, seven lengths in the range of 30-210 m were considered. The simulations showed that in the cable length of 180 m, the structure exhibits a proper behavior. Also, in order to increase the reliability of the anchor, a portion of the initial chain was reduced and was added to the anchor chain; for this purpose, five different chain lengths from 25 to 65 m have been considered. The results show that for the heave, roll, pitch, and yaw degrees of freedom, the minimum structure oscillation happens in the length of 25 m, finally considering the proper behavior of the structure in the length of 25 m; this length of chain was added to the anchor chain.