Investigating the effect of monopile dimensions on hysteretic foundation damping of monopile-supported offshore wind turbines

1. Home
2. Publications
3. Online Library
4. Investigating the effect of monopile dimensions on hysteretic foundation damping of monopile-supported offshore wind turbines

Examining the factors that influence the magnitudes of foundation damping ratio is crucial as it allows optimising the dimensions of monopiles to support the fatigue design requirements of offshore wind turbines (OWTs). Given that modern size OWTs are often characterised as slender structures, their low fundamental natural frequency often lies close to the frequency range of environmental and operational loads, thereby increasing the likelihood of resonance. As a result, determining the contribution of energy dissipation from different sources is essential, as the overall damping ratio governs the dynamic amplification of OWT response during resonance. One important source of energy loss is the foundation damping which is due to the nonlinear hysteretic behaviour of soil during cyclic loading. As the soil-structure interaction is influenced by the dimensions of the monopile, the foundation damping ratio varies accordingly. This research aims to investigate the variation of damping ratio with different monopile dimensions using 3D finite element (FE) simulations which incorporate the soil domain, the monopile, and the support structure of a 15 MW OWT. The Hardening soil model with small strain stiffness (HSsmall) is adopted to represent the hysteretic behaviour of soil and is calibrated from cyclic and monotonic laboratory triaxial tests. The foundation damping ratio at different mudline displacement levels is determined using the logarithmic-decrement approach. The results help practice engineers to incorporate foundation damping in the design process to minimise the amount of steel required for the support structure. 

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

8 - Monopile design to lateral monotonic loads