Study On Multi-footing Foundations For Offshore Wind Turbines

Renewable energy is a strategic choice to solve the problerm of energy shortage. Currently the wind energy is one of the fastest-growing and the most perspectiverenewable energy sources.Significantlymore difficult and cost during the construction of offshore wind turbines than those on land becomes a bottleneck restricting its rapid development. The foundation is the ultimate bearer of the upper load of the wind turbine and an important part of wind turbine design. Asthe large sizeofoffshore wind turbine, suffering complex loads of wind and wave, there are strict requirements of the foundation supporting wind turbine and tower structure.Multi-footing foundation is a highly representative type of all kinds of wind turbine foundations, typically including group piles high cap foundation and suction multi-caissons. The group piles foundation has been widely applied to practical engineering, while a lot of design problems exist. The suction multi-caissons foundation is more innovative in the country with many characteristics yet to be studied. In this paper various studies have been conducted aimed at these two kinds of multi-footing foundations of wind turbines. First, on basis of summarizing methods at home and abroad to analyze the pile-soil interaction, the hyperbolic p-y curve was proposed to calculate the internal force and deformation of piles under the action of horizontal loads. It was verified that this method can not only calculate the small deformation of piles in accordance with specifications in our country, but also consider the large deformation in the horizontal direction of the pile. Secondly, with the unified static and dynamic analysis model for elevated pile group foundations of wind turbines, considering both lateral and axial pile-soil interaction, multi-complex loads analysis, and modal analysis on the natural frequency of the wind turbine were carried out, studying the influence of various parameters on the frequency. Besides, dynamic analysis by setting the damping of the soil around the piles under impact loads was carried out too, and the results were compared with the calculations of domestic and international norms.Model tests of suction multi-caissons under overturning loads were conducted. Variation of the force and displacement of caissons was acquired by data from force sensors and displacement sensors. Then the distribution of axial force, shear force, and bending moment during the overturning was analyzed, so were the changes of negative pressure changes.