Fatigue assessment of a free-spanning submarine cable during span development

Submarine cables are essential components of offshore wind power transmission, but local scour and seabed mobility can create and enlarge free spans, increasing susceptibility to vortex-induced vibration (VIV) and fatigue. This study investigates the effect of span development on the fatigue behavior of free-spanning submarine cables, with emphasis on cable-seabed interaction. A time-domain model in OrcaFlex couples a wake oscillator with cable-seabed interaction to account for time-varying span length. Parametric analyses examine normal seabed stiffness, configuration redundancy, and span development direction. Results show that fatigue damage varies strongly with span length and is sensitive to these parameters. Time-varying span histories can produce substantially higher cumulative damage than time-invariant assessments, whereas span duration alone does not determine fatigue accumulation. The proposed framework identifies high-risk stages during span development and supports fatigue assessment of evolving free spans.