Reduced order models for wind turbine blades with large deflections

Abstract

Non-intrusive nonlinear reduced order modeling (ROM) techniques have been applied by researchers to obtain computationally cheap and yet accurate structural responses of aircraft panels. However, its application to wind turbine blades is new and challenging due to much larger deflections of wind turbine blades. This study improves a non-intrusive nonlinear ROM method for wind turbine blades going through large deflections. In the nonlinear ROM, the nonlinear stiffness is described by the quadratic and cubic functions, and the secondary motions induced by the primary large deflections are described by the modal derivative vectors in the reduction basis. The non-intrusive nature of the method requires a geometrically nonlinear solver, and HAWC2 is chosen in this study for the computation of nonlinear stiffness terms. Two examples, including a cantilever beam example and the NREL 5MW wind turbine blade model, are used to evaluate the accuracy and computational effectiveness of the nonlinear ROMs. The cantilever beam example shows that the nonlinear ROM can accurately capture the axial displacements due to large deflections reaching 20 % of span length as well as the torsion coupled with flapwise and edgewise motions. The NREL blade example shows that the nonlinear ROM is accurate for the tip displacements more than 5.9 m. Because the size of the nonlinear ROM is much smaller than that of HAWC2 model, a speedup factor of 8.5 for computational time is observed for the NREL blade example.