Posters
Come meet the poster presenters to ask them questions and discuss their work
We would like to invite you to come and see the posters at our upcoming conference. The posters will showcase a diverse range of research topics, and will give delegates an opportunity to engage with the authors and learn more about their work. Whether you are a seasoned researcher or simply curious about the latest developments in your field, we believe that the posters will offer something of interest to everyone. So please join us at the conference and take advantage of this opportunity to learn and engage with your peers in industry and the academic community.
PO152: Estimation of damping through operational modal analysis for monopile-supported wind turbines
Toke Schäffer, Engineer, Ramboll
Abstract
As the wind industry moves forward towards deeper waters with larger and more powerful turbines, the monopile support structures become softer, shifting the first bending modes closer to rotor and environmental excitation frequencies. This results in a more dynamically sensitive structure with increased idling fatigue damage. Under these conditions, the structural damping - usually comprised of the steel hysteretic, wave radiation and soil hysteretic as main contributors - is key in lifetime prediction and structural optimization. And while analytical and numerical tools are essential for design, measurement-based estimates can provide complementary insights into the current gap between operation & maintenance and design. Operational modal analysis (OMA) is commonly applied on operating turbines, but in this study, conducted between Ramboll, Vestas, and DTU, OMA is applied to measurements from an idling Vestas 8.0 MW offshore wind turbine with no tuned-mass damper, supported by a Ramboll-designed monopile with an outer diameter of 6.5 meters. Five days of accelerometer data recorded just below the hub were analyzed using stochastic subspace identification (SSI). The natural frequencies and damping ratios of the first fore-aft (FA) and side-side (SS) bending modes are then compared with estimates from Ramboll’s finite element method-based foundation design tool. SSI produced consistent frequency estimates across solvers and post-processors, with narrow distributions and values slightly higher than those from the design model, indicating conservatism. Damping estimates were more uncertain, reflecting both the influence of aerodynamic contributions and the known challenges of identifying damping in lightly damped systems. For the FA mode, damping remained nearly constant across excitation levels, while the SS mode showed a stronger aerodynamic contribution. The work demonstrates the potential of using SSI on existing measurement data for design model validation in addition to structural health monitoring.
No recording available for this poster.
