Prediction model for multidirectional vortex-induced vibrations of catenary riser in convex/concave and perpendicular flows

This study presents an advanced numerical prediction model based on nonlinear wake oscillators for the investigation of multidirectional vortex-induced vibration (VIV) responses a long catenary riser depending structural curved configuration versus incoming flow direction. By considering uniform free-stream aligned with initial curvature plane in convex or concave shape, normal velocity component is nonlinearly sheared owing to spanwise variation inclination angles. different from perpendicular case which spatially constant. To capture influence direction three-dimensionally coupled cross-flow and in-line VIV, distributed are introduced applied simulate fluctuating hydrodynamic lift drag forces that account important effects cylinder inclination, variable vortex excitation frequencies, global–local​ displacement relationships, relative flow-cylinder velocities. The amplified mean force axial tangential also considered. These empirical equations three-dimensional motion, overall governing numerically solved assess multimode, multi-frequency multi-degree-of-freedom responses. Validation carried out VIV flexible straight cylinders experimental results literature. Parametric investigations performed by varying velocities perpendicular, configurations low mass-damping ratio. In-plane (horizontal vertical) out-of-plane features presented discussed terms space–time amplitudes, drag-amplified shape reconfigurations, oscillation lock-in occurrences, dual resonances, orbital motion trajectories, fluid–structure energy transfer, multimodal contributions. Overall highlight geometric orientation characteristics should be recognised incorporated into practical analysis tools.