Abstract: The characteristics of vortex-induced motion(VIM) about a semi-submersible platform in deep water are investigated systematically on the basis of the method combining numerical calculation with model test. The model test is carried out in towing tank with four horizontal mooring lines. Computational fluid dynamics (CFD) method based on viscous flow method is applied. The analytical method which is suitable for platform VIM prediction is established. Good mesh mode combined with the technology of mesh deformation and reconstruction is applied to solve non-linear fluid-structure interaction problem. Sway motion and longitudinal offset traits at different flow angles are investigated. Vortex lock-in phenomena are also studied in detail, including lock-in interval at different angles and its relative trait. The evolutionary process of VIM response versus reduced velocity is analyzed. Meanwhile, the development process of VIM response versus time series, as well as the vortex shedding traits in each step is investigated.

Key words: vortex-induced motion (VIM), fluid-structure interaction, sway motion, lock-in phenomena, reduced velocity