Research on the equivalent stiffness of bucket foundations for offshore wind power

Abstract

Natural frequencies and foundation displacements are vital for the safe operation of offshore wind turbines because of their dependence on the equivalent stiffness of foundations. To investigate this dependency, a finite element method based on substructures is proposed for wide and shallow bucket foundations (aspect ratios of 0.25–1). The equivalent stiffness coefficient (ki) is defined to analyze the influences of the relative skirt flexibility, foundation size, and soil parameters on the equivalent stiffness. The results highlight the predominant impacts of the relative skirt flexibility and aspect ratio on the equivalent stiffness coefficients of bucket foundations. Conversely, certain factors, such as bucket diameter, skirt thickness, and soil modulus, have minimal influences on the equivalent stiffness coefficients. The significance of the Poisson's ratio of the soil is particularly notable, especially concerning the vertical stiffness coefficients. Based on finite element calculations, an empirical formula for bucket foundation equivalent stiffness is proposed and effectively utilized for predicting natural frequencies and evaluating foundation displacements.