Spectral Fatigue and LCOE Assessment of Floating Offshore Wind Turbines
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Typ
Examensarbete för masterexamen
Program
Sustainable energy systems (MPSES), MSc
Publicerad
2022
Författare
Nembach, Björn
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Floating offshore wind turbines (FOWT) are an emerging technology that will contribute
towards a more sustainable energy system in the near future. Some of the
main challenges in an early design stage of floating offshore wind turbines are the
estimation of costs, the site selection and analyzing their fatigue damage. These
challenges are investigated in this work for the WindStar TLP system.
In the first part a LCOE-model from the literature for other FOWT concepts is
adapted for the WindStar TLP system. The model calculates the costs as a function
of the water depth and the distance to the closest shore and puts them in
relation to the annual energy production. By using MetOcean-data as input, the
LCOE for possible site locations on a grid of the North Sea area are estimated. The
results show that the calculated LCOE of the WindStar TLP system is comparable
to the LCOE of other concepts from literature. Furthermore, the results show that,
based on the LCOE, good locations for floating wind farms are north of Scotland
and west of Denmark.
In the second part, four approaches to perform a spectral fatigue assessment using
FAST simulations are studied. With the so-called White-Noise approach the
fatigue damage for every possible sea state can be calculated with just a very limited
number of simulations. The short-term fatigue damage for every approach is
calculated using several spectral approximation methods and correction factors for
non-Gaussian loads. Comparing the results with results obtained with the rainflowcounting
method in the time domain leads to the following main conclusions: It is
necessary to use a non-Gaussian correction factor and, if second order wave effects
are considered, a spectral fatigue approximation method for widebanded spectra has
to be used to get results close to the reference results. It should be noted that wind
effects are not considered in the White-Noise approach for this thesis since the focus
is on proposing approaches for a quick spectral fatigue assessment with FAST, but
not on the detailed estimation of loads.
Beskrivning
Ämne/nyckelord
Floating offshore wind turbines , LCOE , FAST , Fatigue , Narrow band approximation , Spectral approximation methods , RAOs , S-N-curve