Implicit Floquet analysis of wind turbines using tangent matrices of a non-linear aeroelastic code
Article first published online: 20 MAY 2011
Copyright © 2011 John Wiley & Sons, Ltd.
Volume 15, Issue 2, pages 275–287, March 2012
How to Cite
Skjoldan, P. F. and Hansen, M. H. (2012), Implicit Floquet analysis of wind turbines using tangent matrices of a non-linear aeroelastic code. Wind Energ., 15: 275–287. doi: 10.1002/we.467
- Issue published online: 13 MAR 2012
- Article first published online: 20 MAY 2011
- Manuscript Accepted: 12 FEB 2011
- Manuscript Revised: 7 OCT 2010
- Manuscript Received: 26 JUN 2010
- modal analysis;
- Floquet analysis;
- rotor dynamics
The aeroelastic code BHawC for calculation of the dynamic response of a wind turbine uses a non-linear finite element formulation. Most wind turbine stability tools for calculation of the aeroelastic modes are, however, based on separate linearized models. This paper presents an approach to modal analysis where the linear structural model is extracted directly from BHawC using the tangent system matrices when the turbine is in a steady state. A purely structural modal analysis of the periodic system for an isotropic rotor operating at a stationary steady state was performed by eigenvalue analysis after describing the rotor degrees of freedom in the inertial frame with the Coleman transformation. For general anisotropic systems, implicit Floquet analysis, which is less computationally intensive than classical Floquet analysis, was used to extract the least damped modes. Both methods were applied to a model of a three-bladed 2.3 MW Siemens wind turbine model. Frequencies matched individually and with a modal identification on time simulations with the non-linear model. The implicit Floquet analysis performed for an anisotropic system in a periodic steady state showed that the response of a single mode contains multiple harmonic components differing in frequency by the rotor speed. Copyright © 2011 John Wiley & Sons, Ltd.