B-SDM: A bounding surface stiffness degradation method for modelling the long-term ratcheting response of offshore wind turbine foundations. (February 2023)

• Record Type: Journal Article
• Authors: Gao, Zhiwei; Yan, Luoyi; Whyte, Scott
• Is Part Of: Computers and geotechnics. Volume 154(2023)
• Publication Date: 2023-02
• Subjects: Monopile -- Constitutive model -- Sand -- Cyclic ratcheting -- Stiffness degradation; Engineering geology -- Data processing -- Periodicals; Soil mechanics -- Data processing -- Periodicals; Rock mechanics -- Data processing -- Periodicals; 624.1510285
• DOI: 10.1016/j.compgeo.2022.105157
• Languages: English
• ISSNs: 0266-352X

Abstract

Abstract: Long-term cyclic loading from environmental conditions can lead to excessive permanent rotation of offshore wind turbines (OWTs) due to the ratcheting response of sand. A practical hybrid strain accumulation approach, termed the bounding surface stiffness degradation method (B-SDM), for finite element analysis (FEA)-based design of OWTs under cyclic loading is presented. This method includes a base elastoplastic constitutive model that captures the stress–strain relationship in the first load-unload cycle and a cyclic strain accumulation scheme for modelling the subsequent cycles. The presented approach allows for a versatile overlay scheme that calculates cyclic strain accumulation to be applied to a range of base elastoplastic models. The base constitutive model utilised is established based on the bounding surface concept and considers strain-hardening and plastic volume change before failure. The method has been validated by single element test data on sand and used in finitesingle-element element modelling of monopile response in cyclic loading. When the monopile response is modelled in 3D FEA, the conventional step-by-step modelling approach is used until the end of the first regular cycle. Strain accumulation in subsequent cycles is modelled using the B-SDM, in which the plastic modulus and dilatancy relationship are scaled based on a strain accumulation law.