Natural frequency responses of jacket supported offshore wind turbine subjected to cyclic loads considering scour countermeasures

Abstract

Offshore wind turbines are flexible, dynamically sensitive structures; however, marine environmental factors pose significant challenges to their normal operation, as they can lead to the degradation of the foundation performance, thereby increasing operational difficulties and maintenance costs. Local scour poses considerable challenges to the long-term performance of jacket-supported offshore wind turbines. Scour countermeasures with high energy-efficiency indicators, such as preinstalled riprap and solidified soil protection method, contribute to safeguarding the normal operation of turbine's foundation while reducing the carbon emissions and operational costs across the entire lifecycle of wind farm projects. However, the combined factor associated with cyclic environmental loads may introduce uncertainties into the effectiveness of the protection layers surrounding the base-piles. These effects could migrate the natural frequency of the superstructure-jacket foundation-soil system beyond safe limits and increasing the risk of failure. In this study, a series of flume experiments were conducted to investigate the combined effects unidirectional flow-induced scour and cyclic loading on the development of local scour around the jacket foundation under three conditions: no protection, preinstalled riprap layer, and solidified soil grouting. The tests reveal how variations in protection layer performance impact the natural frequency evolution in wind turbine structures. These findings offer insights for optimizing structural design and selecting effective scour countermeasures for tetrapod jacket foundations, and guiding the safe dynamic design of offshore wind turbines.