Patents

Seven independent reinforcements solutions have been patented, where the first four patents expected to be finally accepted in the end of 2011. The region chosen are U.S., China, India and Europe.

Innovative reinforcements prevent failure


The full scale tests lead to alternative solutions creating stronger blade structure. The ideal would be a total redesign of the blade, but as this is not feasible, improvements are invented.

The extent and choice of applied reinforcements depends on many parameters such as manufacturing process, design, materials and the size of the blade etc.



Seven independent reinforcements solutions have been recently published in seven patents.
Descriptions below consider the patented solutions only. A comprehensive explaination
of the motivation for inventions, the failure mechanisms solved and licence conditions are
given in the presentation "Structural strength optimization using Risø DTU patents".

The reinforcements bring solutions to many structural as well as material problems.

1) Cap reinforcement (Patent A)

PCT/DK2007/000547, submitted December 2006



Cap reinforcement prevents a curved cap from flattening out. In tests conducted in frame of Find M. Jensen's PhD project, wires were used as reinforcement and the out of plane deformation of the cap were reduced by 10-30%. The measured strain has also decreased after the cap reinforcement has been introduced.

For detailed information on this patent see Cap_reinforcement(A).pdf

2) Cap reinforcement of flat laminates (Patent A2)



Left: A different solution reducing the delamination problem (see patent A). Right: FEM-simulation showing the effect of the transverse stiffeners used. For detailed information on this patent see Cap_reinforcement(A2).pdf

3) Web coupling/ floor reinforcement (Patent B)

PCT/DK2008/000017, submitted January 2007
   
   

The main purpose to insert web coupling reinforcement is to prevent ovalisation. Implementing the floor reinforcement in the root section allows to transfer shear loads from the trailing edge to the main structure. Another reason is to minimize the deformation of the aerofoil (to prevent trailing edge fatigue problems and to increase aerodynamic efficiency). The floor panel also prevents overall waving of the trailing edge.

For detailed information on the patent see Floor_reinforcement(B).pdf

4) Shear cross reinforcement (Patent C)

PCT/DK2008/000032, submitted January 2007

   

The cross prevents the blade from distort in transverse shear distortion. The solution shown to the right uses wires/pin, which should be positioned each 2-5 metres, depending on the design, loads etc. Alternatively, a dry fibrermat solution could be used.
The solution depends on the manufacturing techniques which are used. A FE-analysis of a 34m blade from SSP-Technology A/S has been performed with combined flap- and edgewise loading and a full-scale test is also under preparation.

For detailed information on the patent see Shear_cross(C).pdf

A parallel to a bookcase

One “new” failure mode found (see Failure modes) is transverse shear distortion, see figure below.



Sketch of a distorted wind turbine blade profile

If a parallel is drawn between the blade and a bookcase in order to visualize the failure mechanism and the concept of suggested reinforcements, the shelves play role of the caps in the blade.

   

Extreme wind conditions Full-scale test with clamps

Notice, how the clamps commonly used in full-scale tests (see Anchor plates vs. clamps) prevent the failure mechanisms, causing unrealistic test results.

                        

Extreme wind conditions with shear cross reinforcement applied.
The shelves are more stable if reinforced with a shear cross. Even with less material in the caps (“thin” shelves), more stability is obtained.

5) Tilted shear webs (Patent C2)

PCT/DK2009/000150, submitted June 2008



During operation of the blade, transverse shear forces are generated in the blade by the flapwise and edgewise loads. The inventions prevent transverse shear distortion of the profile. This increases the blade’s resistance to crushing pressure and thereby increases the ultimate strength of the wind turbine blade. For detailed information on the patent see Angled_girders(C2).pdf.

6) U-box girder (manufacturer friendly design, Patent D)

   

Sketch of a wind turbine section with U-design concept implemented. Left: Combined solution. Tilted webs (Patent C2) and cap reinforcement (Patent A) are integrated in manufacturer friendly splitted section design. Right: Cap cover design with I-stiffeners integrated in the cap cover part.

This invention is mainly production friendly design, but it considers also structural aspects.It enables manufacturer to integrate stiffeners and to produce the cap with high quality. For detailed information on the patent see U_design(D).pdf

7) Coupling of the trailing edge panels (Patent E)

PCT/DK2009/000149, submitted June 2008

   


The reinforcing members:


  • prevent from urging the two connections away from each other, strengthening the shell against deformation and significantly reducing load of the adhesive joint of the trailing edge 
  • strengthening against deformation increases the resistance of the blade against fatigue failure of the girder and shell as well as in the connection between them 
  • increases the resistance of the blade against buckling of the shell thereby increasing the ultimate strength of the blade 
  • increase the blades resistance to buckling of the trailing edge and thereby increase the safety margin for the general failure load of the blade and also decrease the peeling and shear stresses in the trailing edge decreasing the tip deflection of the blade 
  • the aerodynamic efficiency of the blade is also improved.
For detailed information on the patent see Coupling_reinforcement(E).pdf.

Conclusions

  • Based on studies of different blade designs, it is expected that there is a big unused potential in the materials in present wind turbine blades. The structural failure mechanisms must be solved before larger weight reduction can be performed. The improvements can also be transferred to extra reliability
  • Failure mechanisms which are found relevant for the blade designs which have studied may not be critical to other blade designs. However most of the failure mechanisms and the reinforcements are expected to be relevant for other blade designs as well
  • New design and testing procedures must be implemented if the full potential of the material should be used
  • Non-linear geometric effects must be included in the FE-modelling and a CPU-cluster is recommended
  • Combined load cases with realistic boundary supports result in other failure modes than required by design and testing procedures today
  • Full-scale tests with more (and advanced) measuring equipment supported by FE-results give the optimal values
  • Some of the failure mechanisms may not be critical today but if a blade is scaled up or optimized further then they could become critical (e.g. Brazier forces)
The deliberations on the patented solutions discussed below can be found in Risø-PhD-34(EN). 













Page updated  by   01.03.2011


Find Mølholt Jensen
Researcher
Wind Energy (VEA)
Dir tel+45 46775054