Investigation of Soil Effects on the Fatigue Behaviour of an Offshore Wind Turbine

Resumo

Fatigue is a governing limit state for the design of an offshore wind turbine (OWT). The fatigue loads
are not only strongly dependent on the action of waves and wind but also on the site-specific soil properties. The
present article is aimed at investigating the effects of cohesive and non-cohesive soils on the fatigue damage of
a monopile foundation in water depth of 20 meters, using SIMA-RIFLEX for coupled aero-hydro-servo-elastic
simulations and TurbSim for spatio-temporal stochastic wind speed generation. The turbine model is based on the
5-MW reference wind turbine described by NREL (National Renewable Energy Laboratory) and the soil-structure
interaction is simulated by applying p-y curves proposed by API-RP-2GEO (2011) and DNVGL-ST-0126 (2016).
Fatigue damage is estimated with use of rainflow counting (RFC) method, which is used in combination with
Palmgreen-Miner rule and S-N curve proposed by DNVGL-RP-C203 (2016). It was identified that, depending on
the soil type, the degree of fatigue damage can vary as well as the critical region along the monopile.