Numerical analysis of connection in wind turbine rotor blade
Sammanfattning: A globally growing population, an increased energy consumption and growing environmental awareness have made the interest for renewable energy sources, such as wind power, higher. As a result of the increased demand the need for new and improved technologies have increased. The energy production of a wind turbine is highly affected by the rotor blade length, which is limited by the massive dead load of the blade. Moreover, rotor blades are expensive and demanding or impossible to transport to inaccessible construction sites. These are some, among many, limitations with wind turbines, which are the premise to a new technology for rotor blades currently being developed. These, innovative wind turbine rotor blades will be longer, cheaper and more mobile than traditional rotor blades. In a lightweight truss-like structure, e.g. the rotor blade investigated, the structural elements must be designed carefully in general and the connections in particular. One of the connections in the blade, where several of the structural elements are joint, was the focus in this project. A number of design proposals were evaluated in numerical analyses using finite element methods. Since stress concentrations were developed in the initial design proposal a new design of the connection, where additional structural elements were introduced, was proposed. By introducing a steel pipe and a thin layer of adhesive material, the stresses were distributed more evenly and the loads were transferred more efficient. It was shown that a soft, highly deformable, adhesive is preferable. Moreover, a design of adhesive such that abrupt changes in stiffness are minimised is favourable. This can be achieved by alternating the stiffness over the lap, either by vary the thickness of the layer or by vary the properties of the material. Furthermore, the main beams of the blade should be made of carbon fibre reinforced composite with a layup that was defined. Moreover, using the designs of the connection element that were considered feasible yet another numerical model was established. This, simplified, model was designed for a defined set up in an upcoming experimental testing. The results from this model can be combined with the results from the experimental testing for proof of concept, to validate the models and to identify sources of errors.
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