Design Blades of a Wind Turbine Using Flexible Multibody Modelling

Abstract

A methodology for the application of structural optimization to find the optimal layouts of composite blades, based on a multibody model of a wind turbine, is presented. VABS (Variational Asymptotic Beam Section) is used to compute the sectional constants for a generalized Timoshenko beam model. The gravity and inertia effects are taken into account as well as the aerodynamic force, which are calculated by the aerodynamic coefficients and transferred to the corresponding finite element nodes. The minimum lateral moment component at the blade root is found by using an optimization methodology that finds the optimal values for the fiber orientation of the composite spar of the blade. The computational efficiency and robustness of the optimal process relies on the accurate evaluation of the system sensitivities. In this work a general formulation for the computation of the first order analytical sensitivities based on the direct method is used. The direct method for sensitivity calculation is obtained by differentiating the equations defining the response of the structure with respect to the design variables. The equations of motion and sensitivities of the flexible multibody system are solved simultaneously and therefore the accelerations and velocities of the system and the sensitivities of the accelerations and of the velocities are integrated in time using a multi-step multi-order integration algorithm.