Experimental study on vortex-induced motions of a semi-submersible platform with four square columns, part III: Effects of the collinear irregular and regular wave incidence and current

Aiming to complete the results presented before in Goncalves et al. (2012. Ocean Eng. 54, 150-169) and Goncalves et al. (2013. Ocean Eng. 62, 10-24), this third part of the research work studied the behavior of large-volume SS - semi-submersible platforms due to the VIM - vortex-induced motions under the combined action of current and waves. Small-scale towing tests were carried out to understand the effects of the collinear irregular and regular waves on the VIM of a SS. The results showed that waves influenced the VIM phenomenon and decreased its response amplitudes in specific cases, although the source of this mitigation process does not depend on the wave nature (regular or irregular). Moreover, by using plots of velocity ratio a as function of the KC - Keulegan-Carpenter number, regions of predominance were identified for inertia and viscous forces. The VIM in waves was mitigated for cases with inertia-force predominance, yet it had appeared even in low amplitudes for cases of large KC number at the viscous-force region.