On the Adequacy of Existing Foundation Schemes for Offshore Wind Turbines Subjected to Extreme Loading

Dictated by the world’s escalating energy demands, offshore infrastructure is moving beyond the immediate continental shelf into deeper waters. Although the monopile solution has proven its reliability for many years, its feasibility in larger depths is questionable, or even limited, and multi-pod foundations, such as jacket structures, could be regarded as viable alternatives. Their main advantage, compared to the monopile alternative, is that they are able to sustain large lateral loads through axial stressing rather than bending at their supports (usually materialized using piles or suction caissons).Recognizing this reality, the present study attempts to compare the performance of a conventional monopile system with that of a jacket foundation when taking into consideration extreme earthquake loading. Although safety fuses do exist to isolate the mechanical equipment from the direct effects of such loading, our focus in this study is on the irrecoverable deformation at the foundation level which, under circumstances, may render the turbine inoperable.To this end, two foundation alternatives supporting an offshore wind turbine in the Mediterranean Sea are comparatively discussed: the conventional large diameter monopile and a jacket foundation supported by smaller piles or suction caissons. Results show that under expected operational loads the performance of the two systems is practically equivalent. However, extreme loading conditions may significantly alter the response and may, in some cases question the common practice.Copyright © 2017 by ASME