Vortex-Induced-Motions (VIM) is a cyclic rigid body motion that is induced by vortex shedding of a large sized floating structure (Spar, Semi-Submersible and Tension-Leg Platform) in deep water. Since the potential impact of VIM on fatigue life of mooring and riser systems can be critical, the study of the VIM phenomenon has drawn considerable attention among offshore engineering community. Despite the effort, there is still lack of understanding the complex fluid-structure interaction phenomenon. To date, it is very much relying on the simplified empirical approach in practical design.
Most of the Semi-Submersibles consist of four rounded-cornered rectangular columns. To investigate the flow interaction between each columns can reveal some physics behind the VIM. In this study, flow past four stationary rounded-corner rectangular columns are tested in the circulating channel and numerically simulated by the Star-CCM+ CFD package. Forces on the columns and the flow characteristics behind the structures are present in this study. A 2-D particle imaging velocimetry (PIV) technic has been adopted in present study to obtain the flow characteristics. The aim of this study is to investigate the interactions between four square columns.