WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS
Arturo Rodriguez Tsouroukdissian, PhD
ALSTOM Wind R&D Structural Department
Technical Leader Offshore Substructures
Technical Session: Innovative concepts and support structures for offshore
EWEA 2011Brussels, 16 March, 2011
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 2
Agenda
• Brief Overview
• Damping devices
• Results
• Conclusions & Future Work
• Motivation
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 3
Agenda
• Brief Overview
• Damping devices
• Results
• Conclusions & Future Work
• Motivation
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 4
Modular
Pitch- VS
ALSTOM PURE TORQUE™
Yaw concept
• Over 1,600 wind turbines of different generations are in operation
• Concepts are coming from a track record in challenging sites
• A safe design is ensured by measurements and validated simulations
• Components fully tested
Proven and validated technology
Build on the experience of previous WT generations
Technology ECO 80 ECO 100
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 5
Product portfolio
ECO 100 platformECO 80 platform
Higher energy yield
Power: 3MW
Rotor Ø: 100, 110m
Status:
ECO100: series
ECO110: proto end ‘09
Higher reliability
Power: 1.67 & 2MW
Rotor Ø: 74, 80, 86m
Status:
ECO74/80: >1’200MW
ECO86: Proto 2010
Output MW
1
2
3
1.67
6.5 7.5 8.5
ECO 100 3MW
Site Average
Wind Speed m/s9.5 10.5
Class IClass IIClass III
ECO 74/80 1.67ECO 80/86 1.67
ECO 80 2MW
ECO 110 3MW
Technology ECO 80 ECO 100
Differentiated and Competitive Products
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 6
A unique rotor support concept protecting the gearbox
from deflection loads
• The hub is resting on a large cast frame on two bearings, transferring all wind deflection loads
(red arrows) directly to the tower
• The shaft is connected to the front part of the hub and inserted inside the large casted frame,
transferring only the torque (green arrows) to the gearbox
ALSTOM PURE TORQUE™ concept
Transmitting pure torque to the gearbox for higher reliability
Technology ECO 80 ECO 100
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 7
Agenda
• Brief Overview
• Damping devices
• Results
• Conclusions & Future Work
• Motivation
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 8 P 8
Motivation for damping devices
• Next generation WT’s:
− Longer blades and taller tower
larger loads
need of integrated designs using structural control.
− Offshore WT’s
costly & difficult access in a rough environment.
• Structural damping lighter towers and substructures:− Decrease costs for material, manufacturing and transportation
− Fit to manufacturing, installation and transportation limits (weight and geometry)
− Increase Lifetime of whole turbine
Achieve significant decrease in cost
& reliable, competitive and economical efficient product
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 9
Integrated design of structures with embedded control systems
• State-of-the-practice:
− Tuned Mass Dampers (TMD’s):
− Multi Tuned Mass Dampers (MTMD’s):
− Active Mass Damper (AMD):
CHALLENGING !!!! huge mass, large space requirement, prohibitely costly, among many more.
Wide range of innovation available, so the end product is robust & reliable
Imaging changing some structural components!!!!
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 10
Agenda
• Brief Overview
• Damping devices
• Results
• Conclusions & Future Work
• Motivation
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 11
Technical description.Modal damping.
• The tower is a very stiff structure:
− Small drifts and interstory velocities.
− The system is non-classically damped modal properties require complex Eigenvalue analysis.
• Assumption #1: The mode shapes of the non-classically damped structure are identical to those of an undamped structure (ei. ξnc = ξud = 0.02).
− Non-classically damped structure is not a diagonal matrix due to the complex structure (soil-structure interaction + nacelle & rotor components).
• The frequency (ω), damping ratios (ξ) and mode shapes (Φ) depend on the [M], [K], and [C] matrices.
CT
References
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 12
Technical description.Magnification factor & effective damping.
•The amount of magnification of the damping force depends on the geometry.
•The device displacements are greater than the structural drift.
ufuD
DFfF
tutuCF oD sgn
The device displacement (uD) is proportional to a magnification factor (f) times the structural drift (u).
The force exerted by the damper (F) on the structure is proportional to the force along the axis of
the damper (FD) times a magnification factor (f).
Co is the damping coefficient and is the relative velocity between the ends
of the damper along its axis.
• Assumption #2: The joints can move up to +/-0.3º due to slippage distortion and inelastic action during testing.
• Assumption #3: the damper force is reduced by a relaxation time due to sliding at joints.
DFTheory
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 13 P 13
Damper Geometrical Configurations
Diagonal brace Chevron brace
Scissor jack Lower toggle
cosf
If θ = 37º, then f = 0.799 and
consequently ξD = 0.032 or 3.2%
damping
1ff = 1 and
consequently ξD = 0.05 or 5% damping
costan
f
If θ = 70º and ψ= 9º, then f = 2.16
and consequently
ξD = 0.23 or 23% damping
21
312
cossinsin
f
If θ1 = 32º, θ2 =
43º, and θ3 = 35ºthen f = 2.42 and
consequently ξD = 0.2935 or 29.35%
damping
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 14
Optimal Configuration: Upper-toggle bracing
•Highly efficient configuration that provides high damping.
31321
2 sincoscossin
fIf θ1 = 30º, θ2 = 50º, and θ3 = 40 then f = 2.792 and consequently ξD = 0.39 or 39% damping
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 15
Main characteristics
• The damper can be:
− Passive or active filled with a viscous fluid or − Controllable fluid damper filled with either magnetorheological fluid or electrorheological fluid.
• The damper may be:
− Dependent of the frequency (passive), current (semi-active), fluid pressure (active), and combined (hybrid).
• Advantages:
− They dissipate energy over a wide range of deformations and a broad range of frequencies.− They are velocity-dependent.− Easy manufacturability and assembly on-site.− Long-life or high-cycle resistance.
Polar arrangement to provide damping in all directions of the wind turbine due to: (i)
rotor movement, (ii) nacelle imbalances.
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 16 P 16
Geometrical integration (ECO100 t90m - hybrid)
Upper toggle bracing
Tower Base
Tower Top
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 17
Agenda
• Brief Overview
• Damping devices
• Results
• Conclusions & Future Work
• Motivation
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 18
Control Structure – Feedback Controller + ACTIVE, SEMIACTIVE & HYBRID TOWER DAMPING
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 19
Control scheme
• Semi-active, active, and hybrid control schemes.
• Acceleration and force feedback control.
− Robust.− Optimal.− Adaptive and/or predictive.
• Damper force depends on the tower frequency.
• Available sensors, DAC, and processors.
• Power supply from the wind turbine.
• Command signal depends on the device (ei. For MR damper = current).
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 20 P 20
Passive – Semi-active damping device
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 21 P 21
Tower Weight Reduction – Extreme Loads
Undamped and damped SF for ECO100 T90 steel Adjusted - 31.5t Steel -13.1%
0
0.5
1
1.5
2
2.5
3
3.5
4
0 20 40 60 80 100
Tower Height [m]
Safe
ty F
acto
r [-]
USF baseline
USF damped
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0 20 40 60 80 100
Tower Height [m]
Safe
ty F
acto
r [-]
USF baseline
USF damped
Undamped and damped SF for ECO100 T90 hybrid Adjusted - 19.8t Hybrid -7.7%
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 22 P 22
Fatigue Calculation / DEL
Mxy
Tower Bottom
SN Slope Baseline Damped
Inverse abs. red.
3 22.8865 20.4642 -11%
5 23.4415 21.6052 -8%
9 27.558 25.5454 -7%
Hybrid 90m Tower Steel 90m Tower
All values:
- In MNm
- For 1E7 cycles
- 20 years lifetime
Mxy
Tower Bottom
SN Slope Baseline Damped
Inverse abs. red.
3 23.0334 19.9411 -13%
5 24.0013 21.6556 -10%
9 27.9451 25.6931 -8%
Increase Fatigue Safety Factors Tower:
- Hybrid 7.6% in average, 9% increase of the lowest
- Steel 11% in average, 12.5% increase of the lowest
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 23
Agenda
• Brief Overview
• Damping devices
• Results
• Conclusions & Future Work
• Motivation
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 24
Conclusions
• The impactsignificant tower load reduction, consequently the total tower cost may drop (… similar situation for an offshore support structure & tower).
• The advantages cutting edge technology applied to very high flexible towers and offshore substructures.
• The catch wind turbine towers and support structures account for a large stake in the total wind turbine cost
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 25
Future Work
Damper locationsTower base damper
location
Aerodynamic & Gravitational load
Hydrodynamic
load
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 26
Future Work
• Reduce elevated dynamic loads for water depths above 25m
• Increase fatigue life of transition piece connection
• Don’t discard Monopiles as a feasible and cheap substructure solution
− Cheap manufacturing− Cheap installation compared to its substructure counterparts
Consider as a feasible option the Monopile employing dampers
for water depths between 5m to 35m
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 27
Thank you for your attention!
www.power.alstom.com
Acknowledgements:T. Fischer, B. Kuhnle, M. Scheu (U. Stuttgart)C. Carcangiu, I. Pineda, M. Martin (Alstom Wind)
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 28
WT degrees-of-freedom
FLAP
WIS
E D
ISPL
ACEM
ENT
(OU
T-O
F-PL
ANE)
EDG
EWIS
E D
ISPL
ACEM
ENT
(IN
-PLA
NE)
Return
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 29
External loads
1. Steady:
1. Mass force: Gravity
2. Env. Influence: Thrust on the motor, sea current, temperature.
3. Operational status: Rotational speed
• Transient:
• Mass force: Breaking forces
• Env. Influence: Gusts.
• Operational status: Breaking, grid instabilities
• Periodic:
• Mass force: Mass imbalance
• Env. Influence: Tower shadow, wind shear, etc.
• Operational status: Aerodynamic imbalances
• Stochastic – Random:
1. Mass force: ---
2. Env. Influence: Turbulence of wind, sea condition, earthquake.
3. Operational status: ---
Return
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 30
Global Eigenmodes - Tower
1st Tower transverse mode
1st Tower longitudinal mode
2nd Tower transverse mode
2nd Tower longitudinal mode
Return
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 31
Global Eigenmodes - Rotor
1st rotor leadwise (on plane) modes
1st rotor flapwise (out of plane) modes
Return
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 32
Technical description.Effective damping.
iii
jjrjjk
D m
fCT
2
22
4
T = the period of vibration of the kth mode the structure (either FA or StS for a wind turbine);
Cj is the damping coefficient of the damper j;
fj= magnification factor of damper j;
Wi= is the reactive weight on top of the damping system or at level i;
Φrj= is the relative modal displacement of the damper j of the kth vibration mode;
Φi= is the modal displacement on top of the damping system or at level i.
• Using the Linear Static Procedure (LSP) a velocity-dependent device in a structure may be analyzed.
k
jj
SD W
W
4
i
iik FW 21
222
rjjj CT
W
Work done by the device j in one
complete cycle of loading, where Cj is
the damping coefficient of the damper j
and δrj level is the relative displacement between the ends of the device.
Maximum strain energy in the structure, where δi level displacements
and Fi is the inertia force at the ith level.
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 33 P 33
Elevator Design Restriction
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 34 P 34
Tower Maximal Force
WIND TURBINE TOWER LOAD REDUCTION USING PASSIVE AND SEMI-ACTIVE DAMPERS - 16/03/2011 - P 35
References
• [1] Ashour SA, Hanson RD (1987). Elastic seismic response of buildings with supplemental damping. Report No. UMCE 87-01, Department of Civil Engineering, University of Michigan, Ann Arbor, MI.
• [2] Baz, A. “Active Damping”, Encyclopedia of Vibration, pp. 351-364. San Diego: Academic Press, 2001.
• [3] Constantinou, M. C., Tsopelas, P., Hammel, W., and Sigaher, A. N (2001). Toggle-brace-damper seismic energy dissipation systems. Journal of Structural Engineering. 127(2): 105–112.
• [4] Gluck N, Reinhorn AM, Gluck J, Levy R (1996). Design of supplemental dampers for control of structures. Journal of Structural Engineering. 122(12):1394 –1399.
• [5] Hwang J-S, Huang Y-N, and Hung Y-H (2005). Analytical and Experimental Study of Toggle-Brace-Damper Systems. Journal of Structural Engineering. 131 (7): 1035-1043.
• [6] Milman MH, Chu CC (1994). Optimization methods for passive damper placement and tuning. Journal of Guidance, Control and Dynamics. 17(4):848–856.
• [7] Natke HG, Soong TT (1993). Topological structural optimization under dynamic loads. In Optimization of Structural Systems and Applications, Hernandez S, Brebbia CA (eds). Computational Mechanics Publications: Southampton.
• [8] Shukla AK, Datta TK (1999). Optimal use of viscoelastic dampers in building frames for seismic response. Journal of Structural Engineering. 125(4):401– 409.
• [9] Singh MP, Moreschi LM (2001). Optimal seismic response control with dampers. Earthquake Engineering and Structural Dynamics. 30:553–572.
• [10] Takewaki I (1997). Optimal damper placement for minimum transfer functions. Earthquake Engineering and Structural Dynamics. 26:1113–1124.
• [11] Takewaki I, Yoshitomi S, Uetani K, Tsuji M (1999). Non-monotonic optimal damper placement via steepest direction search. Earthquake Engineering and Structural Dynamics. 28:655–670.
• [12] Ungar, E. E. (2001) “Damping Materials”, Encyclopedia of Vibration, San Diego: Academic Press. 327-331
• [13] U.S. Patent 4644714 and 2004/0098930 A1
• [14] U.S. Patent Nos. 5870863 and 5934028, 1996
• [15] Wu B, Ou JP, Soong TT (1997). Optimal placement of energy dissipation devices for three-dimensional structures. Engineering Structures. 19:113–125.
• [16] Zhang RH, Soong TT (1992). Seismic design of viscoelastic dampers for structural applications. Journal of Structural Engineering. 118(5):1375 –1392.