Wind turbine structural model using non-linear modal formulations

In this paper a new method to obtain a geometrically non-linear wind turbine structural model based on the full linear finite element model is presented. For this purpose, the wind turbine model is divided into multiple segments, i.e. tower, drive train and blades. For each segment a modal analysis is carried out. Boundary grid points are defined on each segment and loaded by ficticious masses. The modal analysis produces a set of 6 rigid-body modes and elastic modes close to fixed-fixed analysis. For the aeroelastic turbine simulation, the ficticious masses are removed. The elastic modes are used as master modes that describe the deformation, while the rigid-body modes are used as slaves to establish compatibility between the segments. A modal analysis is carried out in the local segment attached reference frame, yielding a local linear solution that is part of a global non-linear analysis. Large rotations and displacements are provided by rigid-body modes in a co-rotational framework.