Floating platforms are used for wind turbines, tidal turbines, solar panels, substations and, potentially, docking stations for UAVs, drones and surface vessels. Platform stability is desirable for mechanical and electrical components, on/off loading of personnel and supplies by ship and helicopter, ease of docking, mitigation of mooring forces and possible platform stress hotspots. For platforms with vertical columns, such as semi-submersibles, this paper demonstrates how pitch motion may be minimised by pumping between columns, coupling the internal water dynamics and the external wave action through linear hydrodynamic modelling. The problem is analysed in the frequency domain giving natural frequencies and then run in the time domain which will allow nonlinear effects such as drag, wind thrust, mooring forces, pipe friction and nonlinear aspects of wave excitation to be added. The example of the well-documented Volturn 15 MW semi-submersible wind platform of the University of Maine is used. Preliminary time-domain results showing minimal pitch are presented for an impulsively-started turbine in irregular waves with significant wave height 2 m and peak periods 6, 10 and 14 s.
Apsley et al. (Mon,) studied this question.