VORTEX- INDUCED VIBRATIONS OF DYNAMIC POWER CABLE FOR FLOATING WIND TURBINES

Dynamic power cables are important structural components of floating renewable energy converters, such as floating wind turbines and other marine energy converters. Similar to marine risers, waves and currents are expected to produce Vortex Induced Vibrations (VIV) of these dynamic power cables. VIV of power cables can lead to a significantly shorter fatigue life if they are of large amplitude and frequency. In the past, numerous studies have been conducted investigating the vortex-induced vibrations of deep-sea risers and umbilicals but as of yet, only a very few studies have focused on dynamic power cables. This research work investigates the VIV of a dynamic power cable for a semi-submersible floating wind turbine based on the NREL offshore 5-MW baseline wind turbine. This study is conducted using the industry standard software tools, Orca-Flex and Shear7. The dynamic power cable has been modelled into a lazy wave configuration and the Milan Wake Oscillator and Iwan and Blevins oscillator models (both from OrcaFlex), and Shear7 are applied to predict the VIV behaviour under differing current conditions. Both uniform and shear currents are considered. In the numerical model simulations, the power cable is subjected to three different current propagation directions (i.e. 0 degrees, 90 degrees and 180 degrees) and current speeds from 0-2.0 m/s. The results indicate that the behaviour of the cable vibrations is strongly dependent on the (i) submerged position of the cable along its length, ( ii) structural and mechanical properties of the cable, (iii) current propagation direction and its magnitude, (iv) Strouhal number, and (v) choice of numerical model.