Abstract

The study provides insights on the design and seismic response of a novel support structure for large capacity offshore wind turbines. In the proposed scheme, the lateral stability of the turbine tower is provided by a taut mooring system comprising of four pre-stressed tendons anchored to the seabed by means of suction caissons. To facilitate installation, a single pinned connection is implemented at the tower base, which is founded on a circular shallow footing. By eliminating the moment transfer at the tower foundation, the system's design requirements are substantially reduced. Compared to conventional solutions, the proposed system offers the necessary support without resorting to massive and difficult to construct foundations. To demonstrate its efficacy, the system's performance is investigated under concurrent environmental and seismic loading. The NOWITECH 10MW reference wind turbine, installed in a water depth of 50 m in the seismically active region of the North-Western Adriatic, is used as benchmark.

Introduction

According to the Paris Agreement on Climate Change (COP21, Paris, December 2015), at least 27% of the energy consumed in 2030 should come from renewable sources. In this context, and as the energy requirements worldwide are constantly increasing, the offshore wind industry is growing at an exponential rate, accompanied by several technological challenges. Offshore wind turbines are increasing in size and power, and are moving away from the coastline, posing an ongoing challenge for the design and installation of their foundations.

Offshore geotechnical engineering strives to provide new techno-economic solutions that will increase the durability, safety, reliability, and functionality of offshore wind energy systems. And while floating and semi-floating foundation solutions are steadily evolving during recent years, drastic cost reductions are required before these foundations proceed to mass-production (Bulder et al, 2002; Bastick, 2009; Bratland, 2009; Weinstein, 2009). Inspired by this reality, the present study investigates the design specifications and dynamic response of a novel foundation scheme for mega-turbines (8-10MW), suitable for application at intermediate sea depths (30-80 m) - where the applicability of the dominant (in shallow waters) monopile is disputed.

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