Hydrodynamic performance of flexible risers subject to vortex-induced vibrations

The Vortex-Induced Vibration (VIV) displacements are determined from both the measured accelerations and strains in a series of VIV experiments. Based on the results, the forces in the longitudinal, transversal and tangential directions are estimated by using the finite element method with and without considering the interactions between adjacent elements. The numerical simulation indicates that the method considering the interactions performs better in the estimation of the forces. The component of the transversal force in phase with the acceleration is associated with the added mass coefficient. The estimated added mass coefficients take abnormally high values at the locations where the displacements are small. An improved formula based on the L'Hospital's rule is proposed to deal with this problem. The results show the advantage of this formula in estimating the added mass coefficients at the locations with small VIV displacements.