Effectiveness of Hybrid Foundations for the Development of Offshore Wind Towers
Installation of wind farms of significant turbine capacities is planned with increasing frequency worldwide and since the availability of onshore locations may be limited, offshore wind parks are nowadays commonly adopted as viable alternatives. The challenge for the design of their foundation is to safely assume large overturning moments under comparatively low vertical loading. In contrast to common offshore structures, such as oil and gas structures, in the case of wind turbines the foundation may account for up to 35% of the installation cost, thus its design may become crucial to the financial feasibility of the project. Among the several foundation types currently implemented in medium depth waters, the monopile option dominates the industry. However, as the installation depth or the turbine size increase, the financial viability of the monopole foundation is questioned.
Motivated by this industrial need, this research project includes numerical and physical modeling in order to identify the limitations of the monopile foundation and highlight the benefit of moving to novel solutions. Apart from the monopile foundation, two new concepts are investigated as to their efficacy in tackling common challenges while remaining economical and constructible. The first alternative comprises of a skirted steel foundation “bolted” to the ground through a central pile. In this case the peripheral footing increases the moment stiffness of the foundation, providing a lateral restraint to the monopile. The second scheme is again consisted of a combination of a central short monopile combined with a peripheral lid that resembles a reversed suction caisson filled with soil.