Numerical Investigation for Vortex-Induced Vibrations of Steel-Lazy-Wave-Risers: Part II — CFD Study on Long Flexible Riser

Vortex-Induced Vibration (VIV) is one of the main sources of fatigue damage for long slender risers. Typical VIV assessment of risers is conducted using semi-empirical software tools in which the sectional hydrodynamic coefficients are derived from forced oscillation model tests on short rigid risers. The Steel Lazy Wave Riser (SLWR) with buoyancy sections is an attractive concept for improving fatigue performance in deep water developments, but there is limited model test data available for the hydrodynamic coefficients on SLWR’s. In Part I of the present study (Jang & Kim, 2019), CFD simulations are successfully validated against forced-oscillation model tests. In this paper, the feasibility of using CFD simulations for VIV response of a long flexible SLWR has been studied based on the CFD modeling practice developed in Part I. The CFD simulation is coupled with a simple structural model of the riser, and the structural equations of motions are solved via modal analysis. The simulation results capture all excitation frequencies measured from the model tests.