Experimental investigation on dynamic responses of a spar-type offshore floating wind turbine and its mooring system behaviour

Abstract

This study investigated the dynamic behaviour of a spar-type offshore floating wind turbine (OFWT) analysed under various wave loads by conducting an experiment campaign. Both the characteristic of the spar platform itself and the spar with realistic moorings have been investigated. A particular focus of the study was the motions of the mooring lines, which were measured at a series of discrete points along one line using an underwater motion capture system, in parallel with tension measurement at the anchor points. The main objective of this study is to provide experimental measured data to validate numerical software on the research of mooring line motions.A free decay test has been carried out to confirm the spar platform motions natural frequencies and damping characteristics. The platform was then subjected to a range of regular and irregular waves to obtain the motion characteristics of the platform and the mooring lines. For the mooring line motions, which has rarely been discussed in published research, a non-linear snatching phenomenon has been observed at the tank for some wave frequencies. This non-linear behaviour shows that snatching leads to the high instantaneous mooring line tensions and platform accelerations could cause the failure of the mooring lines in the real structure.