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The motivation
Due to the fact that current wind turbine blade designs are not thoroughly optimized with regards to structural strength, large differences occur in the safety against various types of failure modes. The safety against different failure modes including material, structural and buckling failure in current design is illustrated in Figure below. Buckling and structural strength have been separated, even though both relate to the structural aspect. This is done in order to illustrate the difference in the unused capacity.
Illustration of the safety margins for current and future blade designs.
The parameter ‘t’, representing the thickness of the chain links, illustrates the safety against ultimate failure. The figures are estimated based on experience in Find Mølholt Jensen's PhD-project and panel tests prepared by colleagues at DTU-Campus and Risø DTU. The arrows represent the safety of the chain illustrated by unit forces. The optimized chain can carry two times the unit force that can be carried by the existing design of the chain. Hence the optimized chain can carry double the load that can be carried by the chain representing present wind turbine blades. The figure illustrates also that the material strength enjoys a very large safety margin in modern wind turbine blades.
In the Structural Blade Design and Testing Group, the experimental work is combined with numerical analysis to fully address the critical failure mechanisms and thus get the understanding of the complex structural behaviour of wind turbine blades. The aim is to design longer blades that will be respectively lighter and more robust.
The Structural Design Group uses a pyramid concept. The four faces of the pyramid visualize the relationship between the most important research fields considered. It shows multi-scale approach for Experimental Tests and Finite Element Analysis combined with other areas.
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Four facets of the 'Mission Pyramid':
- Experimental tests
- Finite Element Method
- Structural Health Monitoring
- Measurements
Three faces of the 'Invention Prism':
- Failure mechanisms
- Solutions
- New load cases and boundaries |
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For the Structural Design Group one of most important goals is using new innovative solutions in order to optimize future wind turbine blades. One of the most important activities leading to this aim are Experimental Tests. The pyramid presents the multi-scale approach to this area:  Risø DTU and DTU's laboratories test sub components as well as specimens of various sizes. The cooperation between numerous Risø and DTU departments makes is possible to cover all test levels shown in the pyramid presented above.
Innovative wind turbine blades design
At Risø DTU an extensive research has been performed in structural failure mechanisms in wind turbine blades. It has resulted in several inventions to improve present wind turbine. The reinforcements developed support of the blade precisely where it is weakest.  The extent and choice of reinforcements depend on many parameters such as manufacturing process, design, materials, the size of the blade etc. |