Vortex-induced vibrations of catenary risers in varied flow angles

Abstract

Vortex-induced vibrations (VIVs) of steel catenary risers (SCR) considering various flow incident angles are modeled and investigated. The dynamics of the flexible cylinder are first described using the Euler-Bernoulli beam theory with the absolute nodal coordinate formulation (ANCF). To capture the nonlinear shear characteristics of the flow, a discrete point vortex theory-based van der Pol wake oscillator is improved by introducing a local reference coordinate system and relative flow velocity. The comparative analysis between the numerical and experimental results demonstrates the numerical model effectively reproduces the multimodal VIVs of curved cylinders with a satisfactory agreement. The VIV response of a real-scale riser is then explored parametrically by varying the flow velocity for incident angles of 0°, 30°, 60°, and 90°. The effects of incident angle on the structural multidirectional response, spatially varying dominant frequency, lock-in position, trajectory, phase evolution, and fluid-structure energy transfer are highlighted. The results of the present study suggest that the three-dimensional excitation coefficients are synchronized and share the same power-in region under oblique flow conditions, which predisposes VIVs of the riser to travelling wave pattern.