Modelling of anisotropic beam for rotating composite wind turbine blade by using finite-difference time-domain (FDTD) method

Abstract Most modern large wind turbine blades are made of composite materials which are naturally anisotropic. Modern wind turbine blade design, such as BTC design tends to further enhance the anisotropy of a composite blade. As a result, the modelling of an anisotropic rotating wind turbine blade is an important topic in the wind energy industry. In this paper, the governing equations of an anisotropic rotating beam is derived using Newtonian theory. These governing equations are discretized and solved using a finite-difference time-domain (FDTD) method. This methodology is shown to be highly computationally efficient owing to the fact that the governing equations are solved element by element alternately and explicitly, so only a few operations are required per grid point. The anisotropic beam model developed in this paper is validated using four test cases: (1) modal analysis of an anisotropic box beam; (2) dynamic simulation of a spin-up maneuver; (3) simulation of the NREL 5 MW wind turbine blade; and, (4) simulation of the WindPACT wind turbine blade. The validation is conducted in terms of the predicted natural frequencies and tip displacements for both inertial and non-inertial frames. It is shown that the proposed model can be extended to deal with the case of large rotations.