Vortex-induced vibrations of a full-scale deepwater riser under typhoon-induced exponential shear flows

Vortex-induced vibration (VIV) poses a primary threat to the fatigue life and structural integrity of deepwater risers. Current offshore design practices and VIV prediction models predominantly rely on idealized uniform or linear shear flows. However, extreme typhoon environments often induce exponential shear flows featuring abrupt spanwise variations in the velocity gradient. Consequently, the VIV response and underlying fluid–structure interaction (FSI) mechanisms under these realistic and extreme flow conditions remain largely unresolved. This paper investigates the VIV behavior of a 3000 m full-scale deepwater drilling riser under typhoon-induced exponential shear flows, using a validated coupled numerical framework that combines the strip-theory-based Discrete Vortex Method (SDVM) for hydrodynamics and the Finite Element Method (FEM) for structural dynamics. Results demonstrate that traditional uniform and linear shear flow assumptions fail to capture the distinct broadband, low-wavenumber-dominated VIV response induced by realistic typhoon shear profiles. A critical “short-input/long-dissipation” FSI energy transfer mechanism is revealed: positive energy input is spatially confined to a high-velocity segment spanning less than 10% of the riser span, while the majority low-velocity section acts as the dominant hydrodynamic damping zone. Furthermore, contrary to conventional engineering understanding, extending the typhoon return period paradoxically suppresses global riser VIV amplitudes, a phenomenon attributed to intensified shear rates that significantly enhance damping effects in non-excitation regions. This work enriches the theoretical framework for VIV analysis of deepwater flexible structures under extreme ocean environments, and the identified localized energy input mechanism provides direct guidance for the anti-typhoon design of deepwater riser systems.