Modelling of Offshore Wind Monopile Lifetime Performance-Paper

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The paper presents a computationally efficient method for predicting the lifetime response of offshore wind turbine monopiles under cyclic lateral loading. It combines the PISA design model, which calculates the pile’s monotonic response and provides a backbone curve, with the HARM framework, which models cyclic hysteresis and the progressive accumulation of permanent deformation, or ratcheting.<br /><br />The method is demonstrated for a monopile embedded in layered soil and subjected to a realistic 25-year service-load history followed by an extreme storm. HARM accelerates repeated cycles within load packets while retaining the effects of cycle count and changing load magnitude. The example simulates up to approximately 300 million cycles in around 30 minutes on a standard laptop.<br /><br />Results show that ratcheting can cause substantial permanent deformation during long-term, moderate-intensity loading. In contrast, the pile’s response during the final storm is governed mainly by the largest load event. The approach also tracks residual deformation after unloading and the evolution of pile response over its service life—capabilities not adequately represented by conventional cyclic p-y methods using fixed degradation factors.<br /><br />The authors conclude that the PISA–HARM framework offers a useful tool for assessing serviceability and fatigue performance, investigating load-history effects, and potentially evaluating lifetime extension of existing monopiles. The example uses a simplified zero-dimensional moment–rotation model; future work could incorporate additional interactions and behaviours, such as gapping and rate dependence.

Keywords

offshore wind turbine

monopile

cyclic lateral loading

PISA model

HARM framework

ratcheting

permanent deformation

service-life assessment

cyclic p-y methods

fatigue performance