Vortex-Induced Vibration Response of Buoyancy-Assisted Deep-Water Drilling Risers under Exponential Shear Currents

Abstract Deep-water drilling risers operating in offshore environments are subjected to non-linear shear currents, while buoyancy modules (BMs) positioned near the upper region modify the mass distribution and hydrodynamic loading, thereby influencing vortex-induced vibration (VIV) behaviour. This study extends VIV analysis to a BM-fitted riser using a modified wake oscillator model coupled with structural dynamics, implemented through an in-house developed MATLAB framework. The framework captures both cross-flow (CF) and in-line (IL) responses under exponential shear flow, with the governing equations solved using a second-order finite difference scheme and depth-varying axial tension replacing the conventional constant-tension assumption. Model predictions are validated against experimental benchmarks to ensure the fidelity of displacement amplitude. Parametric simulations systematically quantify and compare the isolated effects of sea surface velocity, top tension ratio (TTR), riser wall thickness, and internal fluid density on displacement envelopes, RMS profiles, trajectory characteristics, and frequency spectra. The results indicate that the magnitude of sea-surface current is the dominant excitation factor, while increased TTR strengthens IL–CF coupling and promotes multi-mode excitation. Buoyancy-module layout is shown to critically influence susceptibility to resonance, whereas increased wall thickness and internal fluid density suppress VIV response amplitudes through increased stiffness and inertia. The findings highlight the combined importance of hydrodynamic forcing, buoyancy distribution, and structural configuration in ensuring fatigue integrity and safe operation of deep-water riser systems.