Environmental Engineering Reference
In-Depth Information
CHAPTER 14
Anton W. Hulskamp & Harald E.N. Bersee
Faculty of Aerospace Engineering, Delft University of Technology,
The Netherlands.
Fatigue is one of the biggest issues in wind turbine design. Most of the sources
for fatigue loads are related to changes in the airfl ow around the blades due to, for
instance, turbulence, tower shadow or jaw misalignment. Therefore systems are
proposed that counteract these load fl uctuations, which are both deterministic and
stochastic in nature. The systems aim at infl uencing the lift and drag at different
stations along the blade's length. This way, the aerodynamics along the blade can
be controlled and the dynamic loads and modes can be dampened. This is called
the 'smart' rotor concept. Such systems are already used in aerospace, both with
airplanes and helicopters, although in the latter case mostly experimental. They
aim at reconfi guration of the wing or rotor, fl ight control or vibration reduction.
The concepts are often implemented using adaptive materials such as piezoelectric
materials and shape memory alloys (SMAs). Piezoelectric materials are mostly
implemented for high frequent actuation, in which low strains but high actuation
forces are required. SMAs can exert very high forces and can recover very large
strains, but within a limited bandwidth. At the Delft University of Technology a
series of experiments is conducted in which the feasibility of the concept is proven
and in which several control issues are being addressed. For instance, it has been
shown that the control concept can be based on the structural response of the blade
to the fl ow disturbance and that the presence of natural modes has a large infl uence
on the performance of the system.
1 I ntroduction
Currently, horizontal axis wind turbine (HAWT) manufacturers are facing several
challenges related to both a fast increase in turbine size (see Fig. 1) and market
growth. The trends force manufacturers to rapidly increase production capacity
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