Coupled global-local modelling for dynamic submarine power cables

Abstract

Conventional power transmission cables have been designed to operate in conditions that differ considerably from those experienced by cables servicing floating offshore renewable energy (ORE) device. Cables attached to floating platforms are subject to greater levels of mechanical and electrical stress due to the motion of the platform in a highly energetic offshore environment and are termed dynamic cables. The combination of the different loads from waves, wind and currents, in shallower waters are complex and need to be assessed through a combination of coupled numerical models and experimental tests. Global analyses, assessing the overall motions of the floating platform, moorings and cables, are carried out to provide data to inform the cable design process. Such analyses are highly dependent on the input of local structural response coefficients which are available only through detailed local structural analysis numerically and/or experimentally. There is a strong need to gain a better understanding of the local structural assessment of cable cross-sections and the coupling of the data attained through the local assessments with the global modal. This work incorporates a coupled global-local numerical model of a dynamic subsea cable attached to a floating point-absorber buoy. The results indicate the sensitivity of the global analysis to the locally determined structural results, primarily bending stiffness and tensile stiffness. In the case of the South West Moorings Test Facility (SWMTF) buoy and the lightweight composite armoured cable, bending stiffness is a key governing parameter and axial stiffness is not a governing parameter. The paper will be of use to researchers and practitioners in the areas of cable designers, technology development and design certification.