Design Optimisation of Power Cable, Shared Electrical Line and Mooring configurations for Floating Offshore Wind Turbines

I løpet av de foregående tiårene har den globale etterspørselen etter elektrisitet vært økende på grunn av sosial og økonomisk fremgang. Sammen med klimaendringsutfordringen åpner et ønske om alternative løsninger muligheter for fornybar energi. En gren av fornybar energi er havvindsteknologi. Det er en økende kraft på energimarkedet og dets distribusjon har økt kraftig de siste årene. Prosjekter kan være store, og vindturbinene kan jobbe nærmere til deres optimale effektivitet på grunn av mer jevne vindforhold sammenlignet med på land. Bunnfast offshore vindmøller har et høyt standardiseringsnivå i dag, men er begrenset til et visst vanndyp. Dermed er trenden er å gå lenger offshore med flytende konsepter for enda bedre vindressurser og større sosial aksept. Foreløpig oppnår ikke flytende havvindsteknologi lave energikostnader (LCOE), noe som betyr konkurransekraft, sammenlignet med andre energikilder ennå, men dette forventes å endre seg ved videre utvikling. Områder for kostnadsreduksjon er forbedringer av teknologi og design. Kostnaden for flytende havvindturbiner er dominert av kapitalutgiftene. Kraftkabler er utsatt for store belastninger på grunn av væske-kabel-jord interaksjoner under kombinerte bølger og strømforhold og representerer en stor kostnad. Det er også verdt å merke seg at 80 % av alle offshore vindforsikringskrav er relatert til elektriske kabler. Derfor, for å redusere kostnadene, bør utstyret utformes langvarig, holdbart, optimalt utformet og med minst mulig innvirkning på miljøet. Derfor har hovedmålet med den foreslåtte PhD studien vært å optimalisere kraftkabel konfigurasjoner av flytende havvindturbiner. Numerisk analyse i denne foreslåtte PhD-studien har krevet et fullstendig koblet simulerings- og optimaliserings verktøy som kan inkludere den globale responsen fra den flytende vindturbinen og de hydrodynamiske belastningene på kraftkabler for en flytende havvindpark. Forskningen har resultert i 11 publikasjoner, hvorav 2 er under endelig vurdering, og 2 rene konferanseartikler. Kandidaten har hatt 4 presentasjoner på nasjonale og internasjonale konferanser. Kandidaten er hovedforfatter for 6 av publikasjonene og andreforfatter for 5. Publikasjoner: • “A Comparative Study on Damage Detection in the Delta Mooring System of Spar Floating Offshore Wind Turbines”. 2023, Springer Nature. Second author • “Dynamic Power Cable Configuration Design for Floating Offshore Wind Turbines Using Gradient-Based Optimization”. 2023, The American Society of Mechanical Engineers (ASME). Main author • “Numerical Investigations on Suspended Power Cable Configurations for Floating Offshore Wind Turbines in Deep Water Powering an FPSO”. 2023, Journal of Offshore Mechanics and Arctic Engineering. Main author • “Flow over a step cylinder using partially averaged Navier-Stokes equations with application towards dynamic subsea power cables”. 2023, IOP Conference Series: Materials Science and Engineering. Second author • “Design basis considerations for the design of floating offshore wind turbines”. 2023, Sustainable Marine Structures. Second author • “Fatigue Analysis of Inter-Array Power Cables between Two Floating Offshore Wind Turbines Including a Simplified Method to Estimate Stress Factors”, Journal of Marine Science and Engineering (JMSE), Second author • “An optimisation methodology for suspended inter-array power cable configurations between two floating offshore wind turbines”. 2023, Ocean Engineering. Second author • “Feasibility study on suspended inter-array power cables between two spar-type offshore wind turbines”. 2023, Ocean Engineering. Main author • “Suspended Power Cable Configurations for Floating Offshore Wind Turbines in Deep Water Powering an FPSO”. 2022, The American Society of Mechanical Engineers (ASME). Main author Publikasjoner under endelig vurdering: • “Key constraints for design analysis and optimisation of inter-array power cable configurations in floating offshore wind farms”. (2024), Marine Structures. Main author • “Efficient Global Optimization of dynamic power cable configurations for floating offshore wind turbines”. (2024), Journal of Offshore Mechanics and Arctic Engineering. Main author Kandidaten har videre vært veileder for 3 studentprosjekter. Av direkte relevans for industrien har doktorgradsarbeidet blant annet resultert i to optimeringsalgoritmer for konfigurasjon av strømkabel, som har blitt brukt i CoreMarine offshore vindprosjekter. Kandidaten har jobbet tett med CoreMarine-ingeniører i Norge og spesielt i Spania som har vært involvert i havvindindustrien i nærmere 2 tiår. Kandidaten har hatt et lengre opphold på CoreMarine australske kontor, blitt introdusert til det stigende havvindmarkedet der og støttet prosjektene deres med forskningen hennes. Dette har bidratt til å bringe virkelighetserfaring, kontekst og innhold til arbeidet.

The investigation has focused mainly on dynamic subsea power cables associated with floating offshore wind installations. Initially various case studies were performed and documented to understand cable design and the driving parameters. The ultimate aim with the work though has been to define a standard for- and developing efficient algorithms for optimizing dynamic power cable configurations. To support this, a framework involving design basis considerations and key constraints has been defined to bring clarity to the border conditions for the optimization and maintain the need safety and integrity. The framework defined will as outcome support our company in our work processes for dynamic cable design, in particular for floating wind projects. The framework defined can also impact on workflow and standards for the greater industry and play into the standards of the regulating bodies. The efficient optimization algorithms developed will bring advantage to the business of our company in providing a much more qualified and objective way of defining optimal and cost-effective dynamic cable configurations. The algorithms will be known in principle through publications and can impact the way the greater industry too should they choose to benefit from the principles and findings. For the evolvement of the offshore floating wind industry to reach a low levelized cost of energy (LCOE) and become competitive to other forms of energy, this work is a contribution. The sum of works like this on other aspects of the offshore wind turbines, is what realistically will enable the offshore industry through technical readiness and financial sustainability. This is indeed an important impact.

Over the preceding decades the global demand for electricity has been rising due to social and economic progress. Together with the climate change challenge, a desire for alternative solutions is opening opportunities for renewable energies. One branch of renewable energies is offshore wind technology. It is a rising force on the energy market and its deployment has strongly increased over the last years. Projects can be large, and the wind turbines can work closer to their optimum efficiency due to more consistent wind conditions compared to on land. Bottom-fixed offshore wind turbines have a high level of standardization nowadays but are limited to a certain water depth. Thus, the trend is to go further offshore with floating concepts for even better wind resources and greater social acceptance. Currently, floating offshore wind technology does not reach a low levelized cost of energy (LCOE), meaning cost competitiveness, compared to other energy sources yet, but this is expected to change by further development. Areas for cost reduction are technology and design improvements. The cost of floating offshore wind turbines is dominated by the capital expenditure of which about 10% are mooring and anchoring costs. Apart from the mooring, power cables are also exposed to large loads due to fluid-cable-soil interactions under combined waves and currents conditions. Hence, to reduce costs, the equipment should be designed long lasting, durable, optimally laid out and with the least amount of impact for the environment. Therefore, the primary objective of the proposed PhD study is to optimize the power cable, shared electrical lines and mooring configurations of floating offshore wind turbines. Numerical analysis in this proposed PhD study requires a fully coupled simulation tool that can account for the global response of the floating wind turbine, the hydrodynamic loads on power cables, shared electrical lines and mooring lines for a floating offshore wind park.