Lessons learnt from back-analysis of offshore monopile lateral response-PPT Presentation

PPT Presentation

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The WINDSOIL project investigates why the measured natural frequencies of Belgian offshore wind turbines (OWTs) differ from their design predictions, using years of monitoring data. This issue matters as Belgium plans to add 3.1–3.5 GW of offshore wind capacity in the Princess Elisabeth Zone.<br /><br />OWT foundations must meet strength and serviceability requirements, but fatigue performance is a key design driver over their 20–25-year lifetime. The study back-analyzed natural frequencies for 73 OWTs using several foundation-design approaches. The PISA methodology matched measurements more closely than the API RP2 GEO and Kallehave methods, with an average relative difference of −1.48%, though it still tended to underestimate frequencies.<br /><br />To improve predictions, the researchers developed a stress-dependent CPT-based correlation for estimating shear-wave velocity and soil stiffness, accounting for increased soil stress. They also examined scour protection, which can stiffen the system both by increasing soil stress and stiffness and by providing additional restraint. Including both effects reduced the average relative difference between modeled and monitored frequencies to −0.51%.<br /><br />The findings support the use of PISA for modeling monopile–soil interaction, while indicating that further improvement may require well-calibrated 3D finite-element models. More research is needed to quantify scour protection’s effects and characteristics. The approach may also be relevant to other geotechnical structures, including onshore wind turbines and retaining structures.

Keywords

offshore wind turbines

natural frequencies

Belgian offshore wind

monopile-soil interaction

PISA methodology

foundation design

fatigue performance

shear-wave velocity

scour protection

CPT-based correlation