Vortex-Induced Vibrations of Lazy-Wave Cables by Using Multiple Wake Oscillators

Abstract Dynamic cables with lazy-wave configurations are commonly employed to transmit the electrical power generated from offshore floating wind turbines. Due to the interaction of the cable with the ocean environmental flows such as currents, waves and turbulence, the cable may undergo the vortex-induced vibration (VIV). Such nonlinear fluid-structure interaction dynamics may cause amplified responses, which can potentially reduce the fatigue life of the cable. To avoid cable fatigue damage/failure, numerical prediction of cable responses subjected to VIV is important. The present study numerically models the three-dimensional VIV of a lazy-wave cable with pinned-pinned supports by using multiple wake oscillators capable of simulating the fluctuating hydrodynamic lift and drag force components along the span. These oscillators may be modified to account for the dynamic flow angle of attack at different relative flow-structure velocities. The equations of motions of the lazy-wave cable undergoing VIV are numerically solved by using a finite difference method in both the space and time domains through a predictor-corrector iterative scheme. The model has previously been validated with experimental results for a flexible catenary-shaped cylinder subjected to multidirectional flow (Ma and Srinil [1]). Herein, response amplitudes and frequencies are presented for the lazy-wave cable subjected to uniform perpendicular flow at different incoming velocities. Results show the mean drag effect, motion trajectories and time-space varying responses in in-plane and out-of-plane directions. This preliminary study highlights the effect of perpendicular flow velocity on VIV of the lazy-wave cable that can be further extended to account for omnidirectional flows in convex/concave and oblique directions.