Numerical simulations of vortex-induced vibrations of slender flexible offshore structures

Vortex-induced vibrations (VIV) of a slender offshore riser are studied. The coupled fluid- structure problem is solved numerically within the framework of strip theory. In each cross-section, the two-dimensional turbulent flow around the cylindrical riser is computed using a specifically designed numerical method which has been thoroughly validated through systematic comparisons between numerical and experimental results. An algorithm has been developed to couple this computational fluid dynamics (CFD) code with DeepLines, a structural software based on a Finite Element Method. The local displacements of the cross-sections are handled within the two-dimensional flow field computations, while the three-dimensional motion of the overall riser is obtained by resolution of the structural problem. Cross-sections are therefore mutually influenced through the global motion of the riser. This coupled approach is then validated on simple tests cases for which quasi-analytical results are available (CFD and modal approach). Finally, comparisons between numerical results and in-situ measurements are presented.