Numerical evaluation of the dynamic performance of recommissioned offshore wind turbines under service life extension and repowering strategies

Abstract

This study addresses the recommissioning needs of offshore wind farms facing foundation degradation and equipment aging after years of operation. Service Life Extension (SLE) and Repowering, as key strategies to reduce decommissioning costs and enhance asset value, have been successfully applied to multiple wind farms. Based on advanced 3D finite element (FE) simulations, this study systematically analyzes the dynamic response of sand-monopile-offshore wind turbine (OWT) system under long-term service and scour effects, focusing on the impact of recommissioning strategies, including upper structure replacement (Repowering) and cement-solidified soil foundation remediation (SLE). The analysis reveals that long-term service and scour effects significantly reduce the natural frequency of OWTs, increasing the risk of resonance and exacerbating the dynamic response and deformation of the tower. Replacing the upper structure with a lower-power OWT can effectively enhance the tower’s resistance to deformation but may lead to increased dynamic response at the nacelle. When replacing with a higher-power OWT, cement- solidified soil remediation significantly restores the turbine’s service performance by suppressing displacement and strain accumulation in shallow soils, though its effectiveness diminishes as the remediation height increases. These findings provide valuable insights for selecting and evaluating recommissioning strategies for OWTs.