As the size of commercial wind turbines increases, new blade designs become more flexible in order to comply with the requirement for reduced weights. In normal operation conditions, flexible blades undergo large bending deflections, which exceed 10% of their radius, while significant torsion angles toward the tip of the blade are obtained, which potentially affect performance and stability. In the present paper, the effects on the loads of a wind turbine from structural nonlinearities induced by large deflections of the blades are assessed, based on simulations carried out for the NREL 5 MW wind turbine. Two nonlinear beam models, a second order (2nd order) model and a multibody model that both account for geometric nonlinear structural effects, are compared to a first order beam (1st order) model. Deflections and loads produced by finite element method based aero-elastic simulations using these three models show that the bending–torsion coupling is the main nonlinear effect that drives differences on loads. The main effect on fatigue loads is the over 100% increase of the torsion moment, having obvious implications on the design of the pitch bearings. In addition, nonlinearity leads to a clear shift in the frequencies of the second edgewise modes.

References

References
1.
Hansen
,
M. O. L.
,
Sørensen
,
J. N.
,
Voutsinas
,
S.
,
Sørensen
,
N.
, and
Madsen
,
H. Aa.
,
2006
, “
State of the Art in Wind Turbine Aerodynamics and Aeroelasticity
,”
Prog. Aerospace Sci.
,
42
, pp.
285
330
.10.1016/j.paerosci.2006.10.002
2.
Chaviaropoulos
,
P.
,
1996
, “
Development of a State-of-the-Art Aeroelastic Simulator for Horizontal Axis Wind Turbines, Part 1: Structural Aspects
,”
Wind Eng.
,
20
(
6
), pp.
405
422
.
3.
Riziotis
,
V. A.
, and
Voutsinas
,
S. G.
,
1997
, “
Gast: A General Aerodynamic and Structural Prediction Tool for Wind Turbines
,”
Proceedings of the EWEC’ 97
,
Dublin, Ireland
.
4.
Petersen
,
J. T.
,
1990
, “
Kinematically Non-Linear Finite Element Model for a Horizontal Axis Wind Turbine
,” Ph.D. thesis, Wind Energy Department, Risø National Laboratory, Roskilde, Denmark.
5.
Jonkman
,
J. M.
, and
Buhl
, Jr.,
M. L.
,
2005
, “
FAST User's Guide
,” NREL, Technical Report No. NREL/EL-500-38230.
6.
Bossanyi
,
E. A.
,
2003
,
GH Bladed Version 3.6 User Manual, 282/BR/010
,
Garrad Hassan and Partners Limited
,
Bristol, UK
.
7.
Øye
,
S.
,
1996
, “
FLEX4 Simulation of Wind Turbine Dynamics
,”
Proceedings of 28th IEA Meeting of Experts Concerning State of the Art of Aeroelastic Codes for Wind Turbine Calculations
, available through IEA.
8.
Riziotis
,
V. A.
,
Voutsinas
,
S. G.
,
Politis
,
E. S.
,
Chaviaropoulos
,
P. K.
,
Hansen
,
A. M.
,
Madsen
,
A. H.
, and
Rasmussen
,
F.
,
2008
, “
Identification of Structural Non-Linearities due to Large Deflections on a 5 MW Wind Turbine Blade
,”
Proceedings of the EWEC’08, Scientific Track
,
Brussels, Belgium
, Mar. 31–Apr. 3.
9.
Chortis
,
D. I.
,
Chrysochoidis
,
N. A.
, and
Saravanos
,
D. A.
,
2007
, “
Damped Structural Dynamics Models of Large Wind-Turbine Blades Including Material and Structural Damping
,”
J. Phys.: Conf. Ser.
,
75
, p.
012076
.10.1088/1742-6596/75/1/012076
10.
Larsen
,
T. J.
,
Hansen
,
A.
, and
Buhl
,
T.
,
2004
, “
Aeroelastic Effects of Large Blade Deflections for Wind Turbines
,”
Proceedings of the Special Topic Conference “The Science of Making Torque From Wind
,” pp.
238
246
.
11.
Bottasso
,
C. L.
,
Croce
,
A.
,
Savini
,
B.
,
Sirchi
,
W.
, and
Trainelli
,
L.
,
2006
, “
Aero-Servo-Elastic Modeling and Control of Wind Turbines Using Finite Element Multibody Procedures
,”
Multibody Syst. Dyn.
,
16
, pp.
291
308
.10.1007/s11044-006-9027-1
12.
Riziotis
,
V. A.
, and
Voutsinas
,
S. G.
,
2006
, “
Advanced Aeroelastic Modelling of Complete Wind Turbine Configurations in View of Assessing Stability Characteristics
,”
Proceedings of the EWEC’06, Scientific Track
, Athens, Greece, Feb. 27–Mar. 2.
13.
Kallesøe
,
B. S.
,
2007
, “
Equations of Motion for a Rotor Blade, Including Gravity, Pitch Action and Rotor Speed Variations
,”
Wind Energy J.
,
10
(
3
), pp.
209
230
.10.1002/we.217
14.
Hodges
,
D. H.
, “
Nonlinear Composite Beam Theory
,”
AIAA
, Reston, VA.10.2514/4.866821
15.
Hodges
,
D. H.
, and
Dowell
,
E. H.
,
1974
, “
Nonlinear Equations of Motion for the Elastic Bending and Torsion of Twisted Non-Uniform Rotor Blades
,” Report No. NASA TN D-7818.
16.
Chortis
,
D. I.
,
Varelis
,
D. S.
, and
Saravanos
,
D. A.
,
2012
, “
Prediction of Material Coupling Effect on Structural Damping of Composite Beams and Blades
,”
Compos. Struct.
,
95
(
5
), pp.
1646
1655
.10.1016/j.compstruct.2011.12.004
17.
Bottasso
,
C. L.
,
Campagnolo
,
F.
,
Croce
,
A.
, and
Tibaldi
,
C.
, “
Integrating Passive and Active Load Control on Wind Turbines
,” EWEA Annual Event, Copenhagen, Apr. 16–19.
18.
Kallesøe
,
B. S.
,
2011
, “
Effect of Steady Deflections on the Aeroelastic Stability of a Turbine Blade
,”
Wind Energy J.
,
14
(
2
), pp.
209
224
.10.1002/we.413
19.
Jonkman
,
J.
,
2009
,“
NREL 5 MW Baseline Wind Turbine
,” Technical Report No. NREL/TP-500-38060, NREL, Golden, CO.
20.
Politis
,
E. S.
, and
Riziotis
,
V. A.
,
2007
, “
The Importance of Nonlinear Effects Identified by Aerodynamic and Aero-Elastic Simulations on the 5 MW Reference Wind Turbine
,” UPWIND Project, Technical Report No. SES6
.
21.
Voutsinas
,
S. G.
,
Riziotis
,
V. A.
, and
Chaviaropoulos
,
P.
,
1997
, “
Non-Linear Aerodynamics and Fatigue Loading on Wind Turbines Operating at Extreme Sites
,” AIAA Paper No. 97-0935.
22.
Voutsinas
,
S. G.
,
2006
, “
Vortex Methods in Aeronautics: How to Make Things Work
,”
Int. J. Comput. Fluid Dyn.
,
20
, pp.
3
18
23.
Crisfield
,
M. A.
,
1998
,
Non-Linear Finite Element Analysis of Solids and Structures, Essentials
,
John Wiley and Sons
,
London, UK
.
24.
Zienkiewicz
,
O. C.
, and
Taylor
,
R. L.
,
2000
,
The Finite Element Method: Volume 1
,
Butterworth-Heinemann
, Oxford, UK.
25.
Lobitz
,
D. W.
, and
Veers
,
P. S.
,
1998
, “
Aeroelastic Behavior of Twist-Coupled HAWT Blades
,” AIAA Paper No. 98-0029.
26.
IEC 61400-1, IEC 2003, 188184CDV, 2004, edited by TC88-MT1, 3rd ed., May 25–26, pp. 26–29.
You do not currently have access to this content.