Numerical Investigation of the Vortex Induced Motion of SPAR in Uniform Current

As the development of model ocean engineering techniques, Spar offshore platforms have been widely used in the area of deepwater drilling. Vortex Induced Motions (VIM), as a common phenomena of Spar platforms exposed to flow, is one of the main factors that affect the lifecycle of offshore platforms and should be avoid as much as possible in the design stage. Two common effective ways to mitigate VIM are the configuration of helical strakes and the adjustment of mooring line stiffness. The former could change the flow pattern in the vicinity of Spar hull and the latter can change the eigenfrequency of platforms in still water to avoid resonance frequency. There have been many investigations on Spar VIM both numerically and experimentally. In this paper, VIM of bared cylinder and straked Spar are compared numerically in uniform current at model scale and at different Reynolds numbers. Fundamental study of VIM is done by comparing motion amplitude at different reduced velocity. To predict the motion of Spar, a spring model is employed. To capture the detailed eddy information of the flow, Large Eddy Simulation (LES) is applied. All the simulation are done at a model scale (1:60).