Structural Analysis of Complex Wind Turbine Blades: Flexo- Torsional Vibrational Modes

A. D. OTERO; F. L. PONTA; L. I. LAGO

Advances in Wind Power

InTech

Lugar: Rijeka; Año: 2012; p. 1 - 28

Limitations in the current blade technology constitute a technological barrier that needs to be broken in order to continue the improvement in wind-energy cost. Blade manufacturing is mostly based on composite laminates, which is labor-intensive and requires highly-qualified manpower. It constitutes a bottleneck to turbine upscaling that reflects into the increasing share of the cost of the rotor, within the total cost of the turbine, as turbine size increases.Moreover, while the rest of the wind turbine subsystems are highly developed technological products, the blades are unique. There is no other technological application that uses such a device, so practical experience in blade manufacturing is relatively new. Blades also operate under a complex combination of fluctuating loads, and huge size differences complicate extrapolation of experimental data from the wind-tunnel to the prototype scale. Hence, computer models of fluid-structure interaction phenomena are particularly relevant to the design and optimization of wind-turbines. The wind-turbine industry is increasingly using computer models for blade structural design and for the optimization of its aerodynamics. Nevertheless, several features of the complex interaction of physical processes that characterize the coupled aeroelastic problem still exceed the capacities of existing commercial simulation codes. Changes in structural response due to the development of new techniques in blade construction and/or the use of new materials would also represent a major factor to take into account if the development of a new prototype blade is considered.Hence, a key factor for a breakthrough in wind-turbine technology is to reduce the uncertainties related to blade dynamics, by the improvement of the quality of numerical simulations of the fluid-structure interaction process, and by a better understanding of the underlying physics. The current state-of-the-art is to solve the aeroelastic equations in a fully non-linear coupled mode using Bernoulli or Timoshenko beam models.The goal is to provide the industry with a tool that helps them to introduce new technological solutions to improve the economics of blade design, manufacturing and transport logistics, without compromising reliability. A fundamental step in that direction is the implementation of structural models capable of capturing the complex features of innovative prototype blades, so they can be tested at realistic full-scale conditions with a reasonable computational cost. To this end, we developed a generalized Timoshenko code based on a modified implementation the Variational-Asymptotic Beam Sectional technique (VABS) proposed by Hodges et al.In this chapter we present a set of tools for the design and full-scale analysis of the dynamics of composite laminate wind-turbine blades. The geometric design is carried on by means of a novel interpolation technique and the behavior of the blades is then simulated under normal operational conditions. We obtained results for the displacements and rotations of the blade sections along the span, section stresses, and fundamental vibrational modes of the blades.