Abstract
The importance of foundation modelling for the support-structure fatigue damage estimation of a 10 MW monopile based offshore wind turbine is investigated in different operational states and wind-wave misalignment conditions. Three different models are used: (1) a non-linear elasto-plastic model including hysteretic behaviour effects, (2) a linear elastic model and (3) a non-linear elastic model, using numerical simulations with an aero-hydro-servo-elastic computational tool. Depending on the environmental condition, different dynamic processes dominate the responses. For parked states, deviations between models up to 160% were found. For wind wave-misalignment over 30° in operational cases, differences up to 180% were found for low sea states and 119% for high sea sates. Both nonlinear foundation damping and stiffness formulation have considerable effect on the responses, with hysteretic effects becoming crucial when aerodynamic damping is negligible in the direction of the response. Attention is required when comparing the fatigue damage only at the mudline, as larger variations between the models may occur in the embedded part of the monopile, where the absolute maximum is found.
Highlights
The offshore wind industry is growing fast, becoming a mainstream supplier of low-carbon electricity and it is expected to produce 7% to 11% of the EU’s electricity demand by 2030 [1]
The levelized cost of energy (LCOE) has lately been reduced by the use of larger capacity turbines and improved supply chain integration [3], further cost reduction can be achieved by more efficient designs of offshore wind turbines (OWTs)
Results show that different processes dominate the responses depending on the environmental state, with both foundation stiffness and damping formulation affecting the behaviour of the models in different frequency regimes
Summary
The offshore wind industry is growing fast, becoming a mainstream supplier of low-carbon electricity and it is expected to produce 7% to 11% of the EU’s electricity demand by 2030 [1]. Offshore wind farm developments are growing in size, with their average capacity reaching 493 MW in 2017 [2]. The main challenge for future offshore wind farm developments is to reduce the levelized cost of energy (LCOE). The LCOE has lately been reduced by the use of larger capacity turbines and improved supply chain integration [3], further cost reduction can be achieved by more efficient designs of offshore wind turbines (OWTs). With the gradual introduction of higher capacity OWTs (6–10 MW) for deeper water wind farms, large-diameter monopiles are considered to be one of the most promising options, testing various technical and economical limits
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