Nonlinear behavior of deep-sea riser based on flow-disturbing robots deployment under wake effect of changes

Severe vortex-induced vibration (VIV) poses a major threat to deep-water riser integrity under complex ocean conditions. To address the active control of riser VIV, this paper introduces a bio-inspired flow-disturbing robot (FDR) design. A nonlinear dynamic model for deep-water risers is established via the variational principle and Kirchhoff's hypothesis, incorporating top tension, internal flow, added mass, and FDR coverage effects. The robot distribution function and experimentally fitted wake oscillator parameters enable efficient numerical solutions using the Newmark-β and Newton–Raphson methods. Model validation against experimental data shows good agreement at FDR coverage below 20%, with root mean square acceleration predictions tending toward conservative engineering estimates. Bayesian optimization derives optimal FDR deployment schemes. Results demonstrate that vibration suppression effectiveness varies significantly with flow velocity—higher velocities yield more pronounced suppression in both cross-flow (CF) and in-line directions. Optimal suppression occurs at the riser mid-section. FDR installation transforms riser nonlinear behavior from chaotic (bare pipe) to quasi-periodic motion with distinct limit cycles and attractors. At 10% coverage, the Lyapunov exponent of CF vibration reduces by up to 48.99% compared to the bare riser. These findings provide a theoretical foundation for engineering applications of riser vibration control using FDRs.