A macro-element for integrated time domain analyses representing bucket foundations for offshore wind turbines

• Published in: Marine structures 2018-05, Vol.59, p.158-178
• Main Authors: Skau, K.S., Grimstad, G., Page, A.M., Eiksund, G.R., Jostad, H.P.
• Format: Article
• Language: English
• Subjects: Building foundations; Clay; Cyclic loading; Cyclic loads; Data processing; Field tests; Finite element method; Frameworks; Horizontal loads; Load; Materials fatigue; Mathematical models; Motivation; Offshore; Offshore engineering; Offshore oil exploration & development; Offshore operations; Offshore structures; Ratcheting; Serrated yielding; Shallow foundations; Soil; Soil analysis; Time domain analysis; Turbine engines; Turbines; Vertical loads; Wind power; Wind turbines
• ISSN: 0951-8339; 1873-4170
• DOI: 10.1016/j.marstruc.2018.01.011

The paper presents a macro-element model for bucket foundations to be used in integrated time domain analyses of offshore wind turbines. The macro-element has been formulated in the multi-surface plasticity framework, and captures the characteristic behaviour of a shallow foundation subjected to irregular cyclic loading. A numerical study of shallow foundations in clay has been used as basis for the development. In conjunction with offshore wind support structures, bucket foundations can be used as monopod foundations and in multi-leg configurations. This makes almost any combination of vertical, horizontal and moment loads relevant. The macro-element has been developed with the intention of creating an application oriented engineering model with physical interpretable input data. Three examples are used to illustrate the macro-element's performance. These examples show that the macro-element 1) reproduces the response computed in finite element analyses of the soil volume and the bucket foundation, 2) is numerically stable and does not cause numerical ratchetting, 3) produces response in good agreement with a large scale field test. •A macro-element for engineering practise.•A macro-element with anisotropic nonlinear stiffness and a flexible plastic flow rule.•A macro-element adaptable to variations in soil conditions and foundation geometry.•Physical input parameters makes the usage intuitive.•The formulation prevents numerical ratcheting.