Characterization of Self Exciting and Self Limiting VIV of Freely Oscillating Riser Pipes in Time Domain

The ability to predict Vortex Induced Vibration (VIV), at least within engineering accuracy, is very important for deep water risers, flowlines, and wellheads. Uncertainty driven designs and operations cost the industry tremendously. Best practice synchronized perfect lock-in response calculations of VIV and VIM (Vortex Induced Motions) has brought new challenges to all subsea, umbilicals, risers, and flowlines (SURF) designs. A new simplified "Wake-Oscillator" model has been developed to characterize self-exciting and self-limiting nature of vortex induced vibration of transversely oscillating cylinders, in time domain.The model is then extended to capture fluid structure interaction due to inline motions and predict associated vortex shedding induced combined in-line and transverse vibration of a freely oscillating cylinder. This is a novel simple engineering type fluid structure coupling model which will provide time dependent force coefficients along the length of risers and flowlines, based on the characterization of self-exciting and self-limiting nature of VIV. A full direct time integration, using the time and space dependent lift forces, results in a more realistic vibration response amplitudes and frequencies including effects from all participating modes