Abstract
Flow-Induced Motions (FIM) is an issue for multi-column platforms, such as Floating Offshore Wind Turbines (FOWT). The phenomenon can increase the fatigue failure of the mooring and/or cable systems and can also stop the turbine operation. One of the solutions to reduce the wave-induced motions (WIM) of FOWT designs is the inclusion of Heave Plates (HP). HP is used for increasing the added mass and viscous damping for the motions in waves; however, the behavior was not deeply investigated in the presence of currents. FIM model tests were performed for the Jappaku FOWT (JPK), a FOWT developed to operate in Brazilian waters. This paper aims to investigate the presence of FIM on the JPK to show the importance of HP design and to show how HP mitigates FIM. Three different HP dimensions were tested and compared with the condition without HP. In addition, two different incidence angles of the current were tested, namely 0 and 180 degrees. The results showed amplitudes in the transverse direction of around 100% of the diameter of the external platform column for the case without HP, which is larger than the ones observed for the deep-draft (DD) semi-submersible (SS). Conversely, FIM amplitudes decreased when increasing HP dimensions. The presence of the central column played an essential role in FIM. Due to the different diameters of the external and central columns, the FIM presented two different branches of response related to the vortex-shedding frequency around the columns. The results showed that significant FIM could occur for this specific JPK investigation even with HP. The HP design has a positive effect for reducing dynamic behaviors due to the wave and current incidences. Therefore, its design must be included in the preliminary stages of FOWT developments.
