3D Finite Element Analysis of Monopiles and Its Application in Offshore Wind Farm Design-Paper

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The paper presents three-dimensional finite element (FE) analyses used to design monopile foundations for an offshore wind farm in the North Sea. Using the ICFEP code, the analyses supported the PISA design approach by evaluating soil response, deriving site-specific soil reaction curves and predicting structural forces in monopiles.<br /><br />The site contained stiff clays of varying plasticity and mostly dense sands. Low-plasticity clays were modelled with an enhanced Modified Cam Clay model, which reproduced laboratory test results well. Another clay deposit showed substantial variability in plasticity and behaviour, including strain softening in some samples. It was represented using a simpler Tresca-type model, acknowledged as conservative and limited; the findings underline the need for careful laboratory testing to select suitable constitutive models.<br /><br />Sands were modelled using a strain-softening Mohr–Coulomb model combined with the nonlinear IC.G3S stiffness model. This approach captured key effects of stress state and density, though its parameters must be adjusted for different sand conditions. Calibrated against Dunkirk field tests, it reproduced the overall response of two laterally loaded test piles well. At large displacements, it predicted a slightly softer response than the more advanced sand model used in the original PISA study.<br /><br />Analyses of monopiles at eight wind-farm locations showed that predicted ultimate loads varied by about a factor of two, reflecting differences in soil layering and pile geometry. Initial stiffness also varied, affecting operational performance. Loads and structural forces generally continued to increase beyond a displacement of 10% of pile diameter, although the extent depended on location.<br /><br />Overall, the study demonstrates the value of 3D FE analysis for site-specific monopile design and highlights the importance of robust ground investigations and constitutive models appropriate to each soil type.

Keywords

finite element analysis

monopile foundations

offshore wind farm

North Sea

PISA design

soil reaction curves

stiff clay

Mohr-Coulomb model

Modified Cam Clay

soil-structure interaction