A Numerical and Experimental Study on the Vortex Induced Vibration of a Flexible Riser

摘要

A numerical simulation scheme has been developed for the vortexrninduced vibration (VIV) response of flexible risers and has beenrnvalidated by experimental results.rnWe carried out model experiments in an experimental tank in whichrna flexible riser model was forced to surge by fixing the top end of thernmodel to a forced oscillation apparatus in still water, we then measuredrnthe transverse motion of the riser model caused by the sheddingrnvortices. In these experiments we measured the inline motion (X-Zrnplane) and transverse motion (Y-Z plane) using five CCD cameras forrneach direction.rnWe developed a numerical simulation scheme for the dynamics ofrnflexible risers considering the VIV effects. In this simulation scheme,rnwe first calculated the inline motion of the total model induced by therntop end motion caused by a forced oscillation apparatus, and then byrnintroducing the numerical model of the lift force into the equation ofrntransverse motion, the VIV was calculated.rnAs is well known, the transverse motion affects the drag coefficientrnin the equation of the inline motion, and we recalculated the inlinernmotion again taking into account this effect. Thus iteration scheme wasrnused until the inline and transverse motion converged at the same timernstep. We also improved the numerical lift force model developed inrnprevious studies through analysis and further consideration of thernexperimental results.rnFinally, we validated the accuracy of this numerical scheme byrncomparing the simulation results with the experimental results.