A time domain procedure to predict vortex-induced vibration response of marine risers

This paper introduces a numerical procedure in the time domain to predict vortex-induced vibration (VIV) response of flexible risers exposed to ocean currents. The procedure aims at estimating the forces due to vortex shedding through a semi-empirical approach based on experimental data reported in the technical literature. The force is determined considering an energy balance context: at riser locations under power-in, the VIV will supply energy for the riser motion through an excitation force in-phase with the structure's velocity, and at power-out locations, the vibration will be damped due to a damping lift force opposed to the structure's velocity. A reduced velocity excitation bandwidth is continually verified for each riser position to determine power-in or power-out condition. The added mass variation due to fluid-structure interaction is considered in the calculation of the inertial component of the force. In the case of a multimodal response, the force parameters are estimated relative to the dominant vibration mode. In order to validate the procedure, numerical simulation results were compared to experimental observations reported in the literature. Test cases with risers exposed to uniform and non-uniform flow were used for comparisons. In general, numerical and experimental results showed good correlation.