Structural performance of an HSFD for mitigating wind turbine tower demand under multiple wind load scenarios

Large wind turbines face significant challenges in terms of structural stress due to wind loads. Such severe demand, if not properly managed, can reduce the turbine's service life and/or increase its maintenance costs. In this context, the present study focuses on the validation of a passive vibration control device, the Hinge-Spring-Friction Device (HSFD), designed to reduce the bending moment at the base of the tower against wind loads, thereby mitigating structural loads during turbine operation. The HSFD combines a spherical hinge, springs to provide rotational stiffness, and a friction system that dissipates energy through a rocking mechanism. This approach makes it possible to reduce the bending moment at the base of the tower without compromising the overall stability of the structure. In previous work, the design of the device was carried out by the authors considering two reference wind scenarios. Herein extensive validation is performed, against a wide series of operational scenarios representing different wind conditions. The numerical simulations presented in this study cover 91 wind load cases, divided over 13 wind speed ranges, according to IEC 64100-1. These include moderate, intermediate and extreme situations, even close to the turbine cut-out speed (25 m/s), when the turbine stops operating to avoid structural damage. The analyses provided a comprehensive overview of the control system's capacity, enabling the formulation of highly encouraging conclusions. Specifically, the device consistently enhances the system's performance, with the level of protection increasing as the demand for stress rises, achieving an average reduction of approximately 20%.