Fatigue-life prediction methods of a dynamic power cable for a floating testing platform - a numerical approach

Power cables are often used to connect marine systems to subsea electric grids. These cables are commonly exposed to the cyclic loads resulting from the waves, current and the floater’s motions. Hence, the fatigue life plays a crucial role in the design stage of the behaviour and integrity of power cables. This paper addresses the fatigue-based design of a dynamic power cable deployed to connect a floating testing platform, HarshLab 2.0. Different fatigue-life prediction methods are examined, considering the damage in the steel armour and the conductor cores of the cable. The study is undertaken by estimating each cable component’s long-term cyclic loading and comparing it with its resistance to fatigue damage. In this case, the damage for each variable was derived from σ−N and ϵ−N curves, depending on the selected approach. The design iterative process led to the definition of a Lazy Wave design with a high-level optimisation of some components, e.g., the ballast and buoyancy modules and the bend stiffener. Generally, the behaviour across the cable length is similar between the different fatigue-life approaches, with the most significant expected fatigue damage found in localised hot spots near the bend stiffener and the belly (sag-bend region) of the cable. It is found that, despite a significant difference across the magnitude of fatigue life estimated in sensitive areas, the proposed layout complies with the fatigue life design criteria.