Response analysis of spar platform with wind turbine

Floating wind turbine platforms are the most economical means for deploying offshore wind turbines in deep waters. The merit of spar platform is the large range of topside payloads, favourable motions compared with other floating structures and minimum hull/deck interface. The main objective of this paper is to present the response analysis of the spar platform supporting a 5MW wind turbine, with taut mooring and with bottom keel plate in regular and random waves, studied experimentally and numerically. This paper presents the details of the studies carried out on a 16-m diameter and 100-m long spar buoy supporting a 90-m tall 5MW wind turbine with 3600-kN weight of nacelle and rotor and 3500-kN weight of tower. The weight of the ballast and the draft of the spar are adjusted in such a way so as to keep the centre of gravity below the centre of buoyancy. The mooring lines are divided into four groups, each of which has four lines. The studies on a 1:100 scale model of the spar with taut mooring configuration are carried out in regular and random waves. The operational significant wave height of 2.5 m and 10-s wave period and the survival significant wave height of 6 m and 18-s wave period at 300-m water depth are considered. The wind speed corresponding to the operational wave height is about 22 knots and this wind speed is considered to be the optimum wind speed for turbines. The heave and surge accelerations at the top of the spar platform were measured and are used for calculating the response, in both regular and random waves. The geometric modelling of the spar was carried out using MULTISURF and was directly exported to WAMIT for subsequent hydrodynamic and mooring system analysis. The numerical results were compared with experimental results and the comparison was found to be good.