Numerical Simulation of VIM Response of a Submersible Buoy Using a Semi-Empirical Approach

Abstract

Nowadays, discoveries of petroleum reservoirs are located in ultra deep-water depths. In this scenario, risers systems generally demand submersible buoys to support the riser, in order to reduce weight in floating platform and riser tensioners. Usually, these buoys are installed below 200 meters depth to avoid the wave forces. However, in this condition the sea current cause the Vortex-Induced Motion (VIM) of the buoys, which can increase significantly the riser fatigue damage. Although the VIM phenomenon is similar to Vortex-Induced Vibration (VIV), it generally occurs in rigid bodies with low aspect ratio, where end effects causes tridimensional flow behavior. Therefore, the vortex wake characteristics and the hydrodynamics coefficients found for VIV is no longer valid for VIM. It makes complex the prediction of VIM in buoys. In this paper, a semi-empirical model using hydrodynamic coefficients found for low aspect ratio cylinders are presented. In order to verify accuracy of numerical simulations, results are compared with experimental data presented in the literature and a good agreement is found.