Experimental investigation of ice mass
detection on a 1 kW wind turbine blade
using its natural frequencies
Sudhakar Gantasala
PhD student
Luleå University of Technology, Sweden
June 13, 2017
Luleå University of Technology
Contents
 Background
 Objectives
 Experimental set-up and modal analysis
 Results & Discussion
 Conclusions
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Ice detection systems #
Clouds
Nacelle based
systems
Rotor based
systems
o
Heated anemometer
o
Power curve
o
Infrared light
(HoloOptics)
o
o
Atmospheric conditions
measurement
Eigen frequency
(Bosch Rexroth
/ Fos4X / Wölfel
SHM.Blade)
o
Changes in impedence
(Eologix)
o
Ultrasonic signal
(Goodrich)
o
Webcams
etc.
# IEA Wind Task 19: Available Technologies report of Wind Energy in Cold Climates, 2016
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Background: Ice detection and removal #

DongFang – Electrical resistance heating (leading edge) + Hot air system
(trailing edge), Labkotec ice detector

Enercon – Hot air system (225 kW for typical 3 MW wind turbines), Power
curve and pitch angle based ice detection

Siemens – Electrical resistance heating, Flexible ice detection sensors
(power curve/Eigen frequency/external ice detection sensors)

Nordex – Electrical resistance heating, Multi sensor approach for ice
detection (power curve + ice sensor + meteorological conditions)

Vestas – Hot air system (105-150 kW for typical 3 MW wind turbine), Power
curve based ice detection
# Wind turbine manufacturers presentations in Winterwind 2017 conference
January 26, 2017
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Impacts of icing on wind turbines
#
 Ice accumulation on wind turbine blades reduces its natural frequencies and each
frequency reduce differently based on the location and quantity of ice mass
 This behavior of natural frequencies can be used to detect and monitor ice growth on the
wind turbine blades
# Brenner, D. Determination of the actual ice mass on wind turbine blades Measurements and
methods for avoiding excessive icing loads threads, WinterWind, Åre, February 9, 2016.
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Objectives

To find information about the location and quantity of ice mass accumulated
on wind turbines based on its first few natural frequencies
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Experimental set-up and modal analysis
Accelerometers
Sensor 1
Sensor 2
Sensor 3
Sensor 4
Wind turbine blade
Data acquisition card
 A 1 kW wind turbine blade (0.97 m in length, 1.26 kg) is rigidly fixed to a stationary support
 Experimental modal analysis (EMA) is carried out on the blade and its vibration
accelerations are measured at four different locations
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o Ice mass in Zone 1
- 40 and 80 g
o 2 EMA tests
o Ice mass in Zone 2
- 40 and 80 g
o 2 EMA tests
o Ice mass in Zone 3
- 40 and 80 g
o 2 EMA tests
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m1, m2, m3
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Direct problem
masses
f1, f2, f3
frequencies
 FEM – definite function
 Experiment
 Unique solution
f1, f2, f3
Inverse problem
frequencies
m1, m2, m3
masses
 Function approximation
 Multiple solutions
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Neural network for inverse problem
f1
m1
f2
m2
f3
m3
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Results & Discussion
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Conclusions

A technique to identify the location and quantity of ice mass is successfully
demonstrated on 1 kW wind turbine blade based on 7 experimental modal
analysis tests with ice masses

The proposed technique identifies ice masses with an average error (WAPE)
of 14.12 % in the eight test cases
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January 26, 2017
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Background: Aeroelastic changes with icing

Structural – Mass increases
Center of gravity location changes

Aerodynamic – Chord length increases
Aerodynamic center location changes
Lift coefficient decreases
Drag coefficient increases
*
Lift
Drag
*
* Wind energy production in cold climate (WECO), (1998)
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Background: Impacts of icing on wind turbines
Reduction in power output #
# Rindeskär, E. Modelling of Icing for Wind Farms in Cold Climate; Department of Earth Sciences,
Uppsala University: Uppsala, Sweden, 2010
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Background: Impacts of icing on wind turbines
Increase in nacelle vibrations #
# Skrimpas et al. Detection of icing on wind turbine blades by means of vibration and power curve
analysis. Wind Energy, 2015, 19, 1819–1832
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Quadratic polynomial fitted between third flapwise natural frequency of the iced NREL 5 MW
wind turbine blade (when ice mass is only considered in Zone 3) and respective ice masses
used in the Zone 3