Abstract for a paper submitted for the
World Wind Energy Conference WWEC
November 23-26, 2003, Cape Town, South Africa
Session: Generic R&D:
Load strategies
Load reductions on HAWT's using smart flaps
B.A.H. Marrant, Th. Van Holten
Delft University of Technology, Faculty of Aerospace Engineering
Kluyverweg 1, 2629 HS Delft, The Netherlands
Tel.: +31 (0)15 27 85171
Fax: +31 (0)15 27 83444
E-mail: B.Marrant@lr.tudelft.nl
ABSTRACT
The proposed paper describes the further developments in the smart dynamic rotor
control project. The program on smart dynamic rotor control for large offshore wind turbines
aims to develop new technology capable of considerably reducing the extreme and fatigue
loads on wind turbines – in particular on very large wind turbines for offshore application –
and thereby to reduce the costs of wind turbines. A second aim is to reduce maintenance
requirements and improve reliability by applying condition-monitoring techniques.
The way to achieve these goals is to implement recent advances in control theory,
sensor- and actuator technology, smart structures, etc. taking into account the special
requirements and conditions of offshore wind turbines. An earlier program, called
FLEXHAT, performed in the Netherlands in the nineties has shown that “smart” control
methods may have a significant effect on the various loads [1]. The purpose of the former
project was to decrease loads in the drive train and rotor blades by using passive tip control
and flexibilities in the rotor system. Unfortunately, the techniques used within the FLEXHAT
configuration are not suitable for incorporation into very large wind turbines. Therefore,
different solutions have to be developed.
A preliminary study on smart dynamic rotor control for large offshore wind turbines
revealed the possibility to use smart materials for on the rotor actuation [2],[3]. Smart material
actuator technology has become available and has the potential to overcome the size, weight
and complexity issues of hydraulic and electric on the rotor operation. However, the
feasibility of smart materials for actuation purposes is highly dependant on the kind of
aerodynamic rotor control method1 that is used to obtain load alleviations. Preliminary
calculations made clear that camber control and full-span pitch control are no option when
smart materials are used for the actuation. On the other hand part-span pitch control, active
twist control, MEM-tabs and active trailing-edge flap control are feasible. Based on
preliminary calculations and some qualitative considerations active flap control (see figure 1)
has turned out to be the best option with respect to the required control forces, required
actuation power, high frequency control capabilities and fail safety of the system.
This paper will present the results of an investigation on active trailing-edge flaps for
the reduction of aerodynamic load fluctuations. A dynamic simulation model will be
developed for the wind turbine rotor with active trailing-edge flaps. The model will include
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The possible aerodynamic rotor control options are full- and part-span blade pitch, active twist, camber control,
Micro-Electro-Mechanical tabs (MEM-tabs) and active trailing-edge flap control.
flap, pitch and trailing-edge flap deflections as degrees of freedom. The equations of motion
of the wind turbine will be determined using Lagrange's method. In order to determine the
possible reductions of aerodynamic load fluctuations, open-loop first harmonic cyclic control
inputs of the trailing-edge flap will be analysed. This may essentially improve the somewhat
higher frequencies in the load spectrum, by reacting to wind shear as well as to the very
important rotational sampling loads. The paper will also expand on the implications of the
findings showing better insight in the design of and the requirements on active flaps and the
smart material actuation system.
References:
[1] G.A.M. van Kuik, J.W.M. Dekker, The FLEXHAT program, technology development and
testing of flexible rotor systems with fast passive pitch control, Journal of Wind
Engineering and Industrial Aerodynamics, 39 (1992) 435-448
[2] B.A.H. Marrant, K. Hinnen, Th. Van Holten, G.A.M. van Kuik, Smart Dynamic Rotor
Control of Large Offshore Wind Turbines, Inventory of Present Techniques, Duwind
2002.011, May 2002
[3] B.A.H. Marrant, Th. van Holten, Smart Dynamic Rotor Control for Large Offshore Wind
Turbines, OWEMES conference, April 10-12 2003, Naples-Campania, Italy
Figure 1: Artist's impression of a wind turbine with trailing-edge flaps
CV- ir. Benjamin Marrant :
Benjamin Marrant was born on August 16th, 1977, in Etterbeek a suburb of Brussels, in
Belgium. After completing primary, secondary and high school in Sint Pieters-Woluwe near
Brussels, he started his study at Delft University of Technology, Faculty of Aerospace
Engineering in 1995. After a general study of three years he specialized in "Flight Mechanics
and Propulsion". In 2001 he received the title of "aerospace engineer" after a final graduation
project, which was entitled "Investigation of Rotor Weaving on a Helicopter with a HillerSystem and the Influence of High Coning Angles on Rotor-Fuselage Coupling".
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After graduation he joined the Flight Mechanics and Propulsion Department where he started
working on the preliminary research program "Smart Dynamic Rotor Control for Large
Offshore Wind Turbines" which was an inter-disciplinary project between different faculties
of Delft University of Technology (DUWIND). In 2002 it was decided that this research
program would be the project for his further PhD study.
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