Active and Passive Control of Spar Vortex-Induced Motions

Spars have become an “industry solution” for deepwater developments. Vortex-induced motion (VIM) of spar platforms in currents remains an important design concern. Although strakes are effective at suppressing riser VIM, all three straked classical spars in the Gulf of Mexico have experienced significant VIM events. These are not examples of poor design but indicate a lack of adequate tools for predicting spar VIM. This paper presents the development and validation of unsteady Reynolds-averaged Navier-Stokes (URANS) methods to predict real-world spar VIM behavior. It includes the ability to address rough surfaces and high supercritical Reynolds numbers. The resulting algorithms are used to assess the effectiveness of active and passive control strategies for suppressing spar VIM. Active control consists of injecting high-pressure water tangentially into the boundary layer and is shown to be extremely effective at reducing drag and VIM amplitudes. Passive control utilizes a sleeve to channel high-pressure stagnation flow into the boundary layer and is found less effective.