Abstract

Abstract Floating offshore wind turbines (FOWTs) are an opportunity for large energy consumers in the oil and gas industry to reduce emissions. As the oil and gas structures are often installed in deep waters, the connecting power cables conventionally laying on the seabed have very long transmission distances leading to power losses and large cable sizes. In the present study, the novel concept of a suspended power cable between a FOWT and a Floating Production Storage and Offloading Unit (FPSO) in a large water depth of 1000 m is investigated. In this study, the power cable is kept floating between the sea surface and the seabed without touching neither of them. The power cable configuration is varied. A catenary configuration is investigated, as well as two configurations with subsea buoys attached at different locations along the cable. The OC3-Hywind 5 MW reference FOWT is set up with a deepwater mooring system and a spread moored FPSO is modeled having characteristics similar to existing FPSOs. Simulations are carried out in the analysis program OrcaFlex. Environmental conditions for the Campos Basin, Brazil, are assumed. The different configurations are evaluated in a steady-state analysis. The largest tensions occur for the catenary configuration, whereas it shows the lowest cable excursions and hang-off declination. A suspended configuration with buoys attached results in lower tensions that are below common limits but has larger excursions. This setup is studied further with a dynamic analysis. The tension at floater hang-off increases compared to steady-state results. The floater motions and the current seem to be the main factors influencing the suspended cable. The design of a suspended cable configuration is a balance between cable tensions and excursions, versus the amount and distribution of buoyancy attached.

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