Numerical Simulation On Vortex-Induced Vibration Suppression Of Offshore Riser With Effects Of Wake Interference

In consideration of economy and flexibility,crowded risers have been widely applied on the deep ocean petroleum exploitation.The current will cause the vertical vortex-induced vibration of offshore Riser and endurance failure.Wake interference has a great influence on movement of riser.At present the researches on vortex induced vibration suppression are aimed at the Isolation riser.Actually,Wake interference makes the vortex induced vibration becomes more complicated.The vortex-induced vibration of tandem and parallel risers with effects of wake interference is investigated based on the software FLUENT,dynamic mesh technology and user-defined function,according to actual parameter of the riser.The fluid structure interaction model was presented by solving the Navier-Stokes equations,the turbulence model of RNG and structural dynamic response equation.This paper also analyses that control-Rods,helical strake and fairing suppress Vortex-Induced vibration Suppression of offshore Riser.Lift forces of tandem risers possess asymmetry and increased first and then decreased with spacing.Lift forces is a maximum in the distance of 4 times of the diameter.Lift force of the downstream riser has been greater than the upstream.Tandem arrangement exacerbates the in-line vibration of the downstream riser.Drag force and the fluctuation range increase.Vibrations of the upstream and downstream risers exists phase difference and change with spacing.The vortex shedding is opposite phase on the parallel risers when the distance is more than 4 times of the diameter.Gap flow can suppress the vibration of the parallel risers.Suppression devices reduce frequency of the vortex shedding.Fairing can Suppress Vortex-Induced vibration of the tandem risers when the caudal horn is 45°.However the in-line vibration of downstream riser increases.Vortex-Induced vibration Suppression of fairing doesn't changes with spacing.The angle of ? has a great effect on suppression for control-Rods.Three control-Rods can suppress Vortex-Induced vibration of the upstream riser when ? is 0°.Four control-Rods can suppress Vortex-Induced vibration of the upstream and downstream risers when ? is 45°.Helical strakes suppress Vortex-Induced vibration of the tandem risers but make the drag coefficient increase.