Some Aspects of Vortex Induced Motions of a Multi-Column Floater

An extensive model test program was conducted to explore the effect of various parameters on the Vortex Induced Motion (VIM) response of a four column semi-submersible (Semi) floating platform. The paper describes the model test set-up, important parameters that were modeled (including hull geometry, mass, stiffness and damping properties) and considerations of instrumentation and test methodology. The damping contributions from the moorings and risers have traditionally not been included in a VIM model test setup. This is the first time that the damping characteristics of the moorings and risers are systematically evaluated and included in the model test setup. This paper describes the calculation of the full-scale mooring and riser damping characteristics and, the design and construction of an innovative model test damping mechanism. Besides damping, the effect of varying the Semi draft and external hull appurtenances were also evaluated.