Session: 06-13-01 Towed and Undersea Cables and Pipes, Mooring, and Buoy Technology

Submission Number: 157521

Insights on the Fatigue-Limit-State Assessments of HVDC Cable Bundles 

High-Voltage Direct Current (HVDC) cables offer energy savings over alternating current (AC) cables. They are often bundled together in a configuration comprising two main conductors and a smaller fiber optic / earth cable to facilitate the efficiency of installation in the offshore renewable energy sector. Should any sections of the cable be exposed in span on (near) the seabed then fatigue life is an intrinsic limit state of HVDC cable bundles, which often feature lead sheaths to achieve dry insulation conductors.

The fatigue limit state (FLS) of a single cable spanning on the seabed is recommended to be assessed following DNV-RP-F105 (2017) adopting either the response or the force model. However, the dual-cylindrical geometry of HVDC bundles leads to uncertain but potentially significant differences in the response amplitudes, added mass coefficient and hydrodynamic drag coefficient compared with those suggested by DNV for a single cable. Griffiths et al. (2024) specifically investigates the hydrodynamic force of cable bundles under wave and current conditions where the dual cylinders are arranged with a range of orientations, whilst the numerical study of Zhu et al. (2023) investigates the in-line and cross-flow VIV responses where the cable bundle is modeled as a round-ended rectangular elongate-cylinder. The results by Griffiths et. al. (2024) and Zhu et. al. (2023) suggest that the hydrodynamic force coefficients could be considered as functions of flow parameters and cable orientations in FLS assessment to give a pragmatic means of evaluating HVDC bundle fatigue limit states consistent with the principles of DNV-RP-F105.

In this work, we capture the cross-flow/in-line VIV response amplitudes, added mass coefficient and hydrodynamic force coefficients more relevant to cable bundles, and then integrate them into DNV’s FLS assessment model. After this, sensitivity analysis is conducted by varying these parameters together with some cable mechanical properties in reasonable ranges. Finally, the difference in fatigue life comparing between a single cable and a cable bundle is demonstrated. Some initial analyses show that the fatigue life of a cable bundle can be 1000 times longer than that of a single cable, indicating that further exploration on the FLS assessment method of cable bundles will lead to significant benefits.

Presenting Author: Yunfei Teng Aurora Offshore Engieering Ltd.

Presenting Author Biography: Dr. Teng Yunfei is employed at South China University of Technology, and also serves as a part-time consultant for offshore engineering at Aurora Offshore Engineering in Australia. His main research areas include the study of seabed boundary layer flow, the interaction among seabed, flow, and structures.