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 vortex induced vibration (VIV) response of flexible risers and has been validated by experimental results. We carried out model experiments in an experimental tank in which a flexible riser model was forced to surge by fixing the top end of the model to a forced oscillation apparatus in still water, we then measured the transverse motion of the riser model caused by the shedding vortices. In these experiments we measured the inline motion (X-Z plane) and transverse motion (Y-Z plane) using five CCD cameras for each direction. We developed a numerical simulation scheme for the dynamics of flexible risers considering the VIV effects. In this simulation scheme, we first calculated the inline motion of the total model induced by the top end motion caused by a forced oscillation apparatus, and then by introducing the numerical model of the lift force into the equation of transverse motion, the VIV was calculated. As is well known, the transverse motion affects the drag coefficient in the equation of the inline motion, and we recalculated the inline motion again taking into account this effect. Thus iteration scheme was used until the inline and transverse motion converged at the same time step. We also improved the numerical lift force model developed in previous studies through analysis and further consideration of the experimental results. Finally, we validated the accuracy of this numerical scheme by comparing the simulation results with the experimental results.