Effect of initial roll or pitch angles on the vortex-induced motions (VIM) of floating circular cylinders with a low aspect ratio

Abstract

The vortex-induced motions (VIM) is a phenomenon that can promote large oscillatory amplitudes on circular platforms in the horizontal plane, such as spar or monocolumn production, storage, and offloading system (MPSO). Floating offshore wind turbines (FOWT) can use a spar-type platform to support the turbine, and due to the wind incidence, roll or pitch angles can occur. The main goal of this work was to experimentally investigate the effect of the initial roll or pitch angles on the VIM amplitudes of a floating circular cylinder with a low aspect ratio. Four different initial angle conditions were carried out, namely vertical, roll angle, positive pitch angle, and negative pitch angle. The Reynolds number range performed was 12,000<R<100,000. The results of VIM amplitudes showed that the yaw motion was affected by the initial pitch angle. The initial pitch angles proved to be responsible for creating a geometric asymmetry of the body and promoted more significant yaw motions than the case without initial angle conditions. The yaw motions started to be substantial after the mean pitch angle of the cylinder reached 3°. The yaw motion increased as the reduced velocity was increased and showed to be essential to be correctly modeled and analyzed in the case of VIM on FOWT.