An experimental study on global motions and structural internal loads of a 5 MW floating wind turbine supported on a multi-segment semi-submersible hull in shallow water

A good understanding of cross-sectional loads of the support structures of floating wind turbines (FWTs) serves as a basis for achieving a reasonable floater design to ensure its safety and reliability over the lifetime at a low cost. While many studies have investigated global motion responses of FWTs, minimal attention has been directed toward the structural load effect analysis of the support structures. This paper deals with an experimental study of a 5-MW semi-submersible FWT in shallow water, in which a multi-segment hull is manufactured to measure the internal cross-sectional loads of the floater based on strain measurements. Model tests of the FWT are carried out at a 1:50 scale in a wave basin under multiple environmental conditions to investigate the characteristics of global dynamic responses of the FWT and internal cross-sectional loads of the hull. The results unveil that the vertical bending moment of the hull's cross-section is notably influenced by resonant responses in heave and pitch motions, as well as the platform motions within the wave-frequency region. Conversely, the horizontal bending moment remains impervious to resonant responses of the hull in the low-frequency range and is mainly governed by platform motions in the wave-frequency region. In addition, the wind loads also exert a certain influence on the vertical bending moment of the hull, but have limited impact on the horizontal bending moment. This paper contributes to establishing enhanced model test methods and provides a basis for improving the design and analysis of semi-submersible hulls of FWTs.