Environmental Engineering Reference
In-Depth Information
offshore turbines) in order to increase platform pitch motion damping, this in its
turn, decreases the demand for the pitch system giving the chance even for the slow
pitch system to follow—to some limit—the controller commands. Therefore, if the
control strategy is changed, and the demands on the pitch system are increased, the
slower pitch system response will fail to respond on time and rotor imbalance will
build up resulting in an increase in structural loading. A good example for such
increased demands on the pitch system is the usage of IBP control strategy to
accommodate the changes in the turbulent wind profile, or to compensate the
vertical wind shear, or even to use the IBP to build up a restoring moment over
the rotor disk that can counteract the pitch moment of the platform due to waves.
Actuator stuck shows a different effect on the turbine structure, starting with the
increased blade root loading of the faulty blade that stuck at angles close to zero and
increases with the wind speed. LSS and tower bending and torsional moments are
also affected by this fault where the moments are increased up to 5 times in some
cases. Furthermore, actuator runaway has substantial effect on the turbine structure,
namely on tower bending and torsional moments, and an LSS bending moments.
The barge platform motion is mainly affected by the actuator stuck and actuator
runaway, while other faults show negligible influence. The actuator stuck excites
the platform pitch motion as a response to the fault-induced increase in generator
power error. However, the excited pitch motion is still small compared to that
caused by the actuator runaway fault. This later fault also excites the platform roll
and yaw motions with amplitudes that depend on the mean wind speed. Other
platform concepts might show different response to these faults due to their own
dynamics, which is different from the studied barge platform; therefore, the pre-
sented results are limited to the barge platform concept.
Finally, in some cases, the process that the fault affects the turbine structure is
explained; in other cases, more work is needed to completely understand the
connection between the introduced fault and obtained result due to the high
complexity of the turbine dynamics and the coupling between the modes in
addition to the aero-structural dynamical interaction where the fault is introduced.
References
1. Musial W, Butterfield S, Ram B (2006) Energy from offshore wind. In: Offshore technology
conference, NREL/CP-500-39450, Houston, Texas
2. Jonkman J, Matha D (2009) A quantitative comparison of the responses of three floating
platforms. In: European offshore wind 2009 conference and exhibition, NREL/CP-500-
46726, Stockholm, Sweden
3. Biester D (2009) Hywind: siemens and statoilhydro install first floating wind turbine (online).
http://www.siemens.com/press/pool/de/pressemitteilungen/2009/renewable_energy/
ERE200906064e.pdf
4. Jonkman J (2007) Dynamics modeling and loads analysis of an offshore floating wind
turbine. Ph.D. thesis, National Renewable Energy Laboratory
5. Jonkman JM (2008) Influence of control on the pitch damping of a floating wind turbine.
National Renewable Energy Laboratory, NREL/CP-500-42589
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