Investigation of vortex-induced vibrations in realistic boundary conditions

Vortex-induced vibrations (VIV) occur when fluid flow around cylindrical structures, such as subsea pipelines and cables, induces vortex shedding, leading to oscillations both perpendicular and inline with the flow. These oscillations can cause fatigue damage and structural failure. Despite extensive research, existing experimental studies often struggle to replicate realworld conditions, particularly seabed proximity and varying flow regimes. To bridge these knowledge gaps, this paper presents results from a new, versatile experimental rig designed to systematically investigate VIV across different flow conditions and structural configurations, including both one-degree-of-freedom (1-DOF) and two-degree-of-freedom (2-DOF) setups. Our findings reveal a significant reduction in VIV amplitudes near the seabed for both cross-flow and inline directions, though the effect is less pronounced in the inline response. Notably, VIV amplitudes were consistently higher in 2-DOF cases compared to 1-DOF at the same gap ratios, highlighting the critical role of multi-directional motion in capturing real-world dynamics. Although the underlying mechanisms require further study, a small increase in turbulence (from 5% to 9 %) further suppressed VIV amplitudes, demonstrating the intricate interplay between environmental conditions and structural response. Furthermore, comparisons with DNV predictive models show both alignment and discrepancies, underscoring the need for refinements in current design frameworks. These insights not only deepen our understanding of VIV mechanisms but also contribute to the advancement of more accurate predictive models for offshore engineering applications.