Norwegian Deepwater Program: Damping of Vortex-Induced Vibrations

Vortex-induced vibration (VIV) of a long riser in sheared current is often considered as an energy balance problem: Excitation forces in the power-in region add an equal amount of energy to the system as is dissipated by damping forces outside this region and structural damping. A riser may have different excitation and damping regions depending on the actual oscillation frequency, cross-section properties and local flow velocity. A damping model must hence be able to handle higher and lower flow velocities than the excitation velocity range. In this paper the fluid damping models proposed by Venugopal [1] are compared with the experiments conducted by Gopalkrishnan [2] and Vikestad [3]. The results show that the models are conservative at high and low reduced velocities.