Experimental Investigations Into the Influences of SCRs and Appurtenances on Deepdraft Semisubmersible Vortex Induced Motion Response

Vortex Induced Motion (VIM) response of a deep draft semisubmersible with square columns has been observed various model test conditions and in the field. A good understanding of the VIM phenomenon is desired because VIM can lead to significant SCR fatigue, especially for the larger diameters SCRs. A VIM design guidance was developed from several previous experimental investigations. Those experimental investigations are characterized by hulls with limited detail, and a simplified mooring / SCR system where typically only the stiffness is taken into consideration. A comparative experimental study is performed to identify the differences in VIM response under the absence and presence of hull appurtenances. Further, the VIM responses of a semisubmersible restrained by a mooring system without and with an SCR system are compared. An evaluation of the experimental results leads to an improved understanding of the VIM response at model test scale.