A zero torsional stiffness twist morphing blade as a wind turbine load alleviation device

This paper presents the design, analysis and realization of a zero stiffness twist morphing wind turbine blade. The morphing blade is designed to actively twist as a means of alleviating the gust loads which reduce the fatigue life of wind turbine blades. The morphing structure exploits an elastic strain energy balance within the blade to enable large twisting deformations with modest actuation requirements. While twist is introduced using the warping of the blade skin, internal pre-stressed members ensure that a constant strain energy balance is achieved throughout the deformation, resulting in a zero torsional stiffness structure. The torsional stability of the morphing blade is characterized by analysing the elastic strain energy in the device. Analytical models of the skin, the pre-stressed components and the complete blade are compared to their respective finite element models as well as experimental results. The load alleviation potential of the adaptive structure is quantified using a two-dimensional steady flow aerodynamic model which is experimentally validated with wind tunnel measurements

Concept for morphing airfoil with zero torsional stiffness

A morphing wing structure is presented which is designed to have zero torsional stiffness to minimise actuation requirements. The concept consists of carbon fibre reinforced plastic strips which are initially curved prior to being flattened and assembled into a grid-like structure in a heightened state of elastic strain energy. Varying the initial curvature of the strips, material properties and the assembled geometry enables the torsional stiffness to be tailored. A state of zero torsional stiffness can be obtained when there is a balance between the changes in strain energy associated with bending and twist deformations

A non-linear stiffness composite twisting i-beam

A classic structural component of mechanical engineering, the I-beam, is re-designed by adding a morphing twist functionality to the high bending stiffness inherent to the geometry of the component. The beam, as with its conventional counterpart, is made of two flanges separated by a web. Here, bi-stability is introduced from a combination of flange pre-stress, web geometry and material properties, yielding a highly non-linear twist morphing structure while keeping the low weight and the high bending stiffness of the beam. The present case study offers two twisted stable shapes and can be morphed from one stable configuration to the other by applying a snap-through twist moment to the ends of the structure. Correlation is found between tests results, finite element model data and analytical predictions, validating the modelling assumptions. A sensitivity study is also performed to understand the influence of the design parameters of the beam and loading condition on the stability of the structure. As a result, the three conflicting requirements of adaptive structures are met in a single structural entity: low mass, load-carrying capability and compliance

Multi-stable composite twisting structure for morphing applications

Conventional shape-changing engineering structures use discrete parts articulated around a number of linkages. Each part carries the loads, and the articulations provide the degrees of freedom of the system, leading to heavy and complex mechanisms. Consequently, there has been increased interest in morphing structures over the past decade owing to their potential to combine the conflicting requirements of strength, flexibility and low mass. This article presents a novel type of morphing structure capable of large deformations, simply consisting of two pre-stressed flanges joined to introduce two stable configurations. The bistability is analysed through a simple analytical model, predicting the positions of the stable and unstable states for different design parameters and material properties. Good correlation is found between experimental results, finite-element modelling and predictions from the analytical model for one particular example. A wide range of design parameters and material properties is also analytically investigated, yielding a remarkable structure with zero stiffness along the twisting axis

Analysis of spruce photodegraded lignins by thioacidolysis

National audienc

Structure and reactivity of spruce mechanical pulp lignins. Part I : bleaching and photoyellowing of in situ lignins

International audienc

Structure and reactivity of spruce mechanical pulp lignins. Part II : organosol V fractionation of lignins in a flow-through reactor

International audienc