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Smart Wind Turbine BladesSensor TeamCassel, Fraser, Larsen, McCrummen, Sarrazin
ME 580 – Smart Structures
ME 580 – Smart Wind Turbine Blades – Sensor Team
Objective: • Gather and support development for
sensors in wind turbine blades.• Investigate multiple types of sensors to
allow for monitoring or measuring:– Structural Loads– Tip Deflection– Damage– Environmental Aspects
ME 580 – Smart Wind Turbine Blades – Sensor Team
What to Sense Why to Sense Strain Gage Piezoresistive Piezoelectric Optical
Strain Composite failure X X X X
Monitor blade stress X X X X
Displacement Tip deflection X
Vibration Vibration absorption X X X
TemperatureTemperature effects on
materials X
Pressure Wind pressure X X X X
Air flow X X X X
Natural wind
frequencies/gusts X X X X
Impact Hail/Rain intensity X X X
Natural wind
frequencies/gusts X X X
AccelerationWind loading vs. energy
generation X X
UltrasonicNon-destructive for
delamination X
Humidity/MoisturePrevention of system
degradation X
Piezoelectric Sensing
• 4 Types– Single Crystal
• Original– Ceramic
• Similar to single crystal– Polymer (PVDF)
• Flexible, poor for actuation– Active Fiber Composite
(AFC)• Subset of Ceramic• Flexible• Compromise
ME 580 – Smart Wind Turbine Blades – Sensor Team
ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezoelectric Sensors• Wide frequency range• High voltage output (particularly
PVDF)– No power supply needed
• PVDF has low acoustic impedance, good for adhesives
• High compliance in PVDF• Flexible, thin, easily
manipulated
ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezoelectric Sensor• Drawbacks/Considerations
– Temperature range for PVDF: -40 to 80/100°C (Not as bad for PZT)
– Strong pyroelectric effect
– Inability to actuate large displacements
– Inability to sense static load
– Capacitive effect of unloaded area
– Crosstalk if both driving signal and sensing
Piezoelectric AFC
• Ceramic-Polymer composite
• Advantages: can custom design properties– Tradeoffs– Properties determined by:
• Ceramic type• Polymer Properties• Volume fraction
ME 580 – Smart Wind Turbine Blades – Sensor Team
ME 580 – Smart Wind Turbine Blades – Sensor Team
Impact Sensing• Weather Detection
– Active control– Damage prevention
• Wind Gust Detection– Active control
• PVDF appropriate if surface mounted– Thin– Sensitive
ME 580 – Smart Wind Turbine Blades – Sensor Team
Vibration Sensing• Vibration hurts performance/strength
– Active control
• Most sensors can detect
• Primary considerations: Wide frequency range, Cost
• PVDF good for surface
mount
ME 580 – Smart Wind Turbine Blades – Sensor Team
Ultrasonic/NDT
• Piezoelectric typically used.
• PVDF good if done during operation
• 1/64th in. smallest size
• Depth small for small flaw
Metal Foil Gauges
• Uses wire resistance change to compute strain• Most commonly used gauge in engineering• Can use strain to compute stress, torque, and
pressure
ME 580 – Smart Wind Turbine Blades – Sensor Team
Metal Foil Gauges Advantages
• Strain and Pressure gages• Widely available• Cheap• Easy to apply• Easy to use
ME 580 – Smart Wind Turbine Blades – Sensor Team
Metal Foil Gauges Disadvantages
• Must be properly bonded• Sensitive to temperature changes• Maximum strain limited to foil material
used (3%)• Size limitations• Can change resistance over time
(creep)• Susceptible to fatigue
ME 580 – Smart Wind Turbine Blades – Sensor Team
ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezo-resistive Sensing – Basic Structure
http://www.microsystems.metu.edu.tr/piezops/piezops.html
Piezo-resistive Sensing – Background
ME 580 – Smart Wind Turbine Blades – Sensor Team
• Types of measurement– Pressure– Force
• Higher sensitivity than standard strain gage• Pressure Sensor Calibration• Able to be microfabricated
http://www.ceatec.com/2007/en/visitor/ex_must_detail.html?exh_id=E070209 http://cooperinst.thomasnet.com/Asset/lpm562.pdf
ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezo-resistive Sensing – Pros and Cons
• Pros– Low fabrication cost– Varying pressure levels can be achieved– High sensitivity (>10mV/V)– Good data linearity at constant temp.
• Cons– Requires significant amount of power– Low output signal– Strong drift of offset with temperature
ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezo-resistive Sensing – Conclusion
• Not Recommended– Ideal placement is blade exterior
• Temperature change affects data collection• Possible weather damage to sensor
– Required, potentially bulky equipment• Power source• Data collection device / Wireless emitter
– Uses• Only designed for pressure and force data collection
– Recommendation• Use a sensor that is more versatile
Fiber Optics
ME 580 – Smart Wind Turbine Blades – Sensor Team
Total Internal Reflection• Cladding material
less dense than core material.
• The critical angle is less than the angle of incidence for the core and cladding combination.
ME 580 – Smart Wind Turbine Blades – Sensor Team
Fiber Optic Sensor Pros
• Essentially passive• Immune to Electrical
Interference• Low Weight• Flexibility• Long Transmission
Distances• Low Material
Reactivity
• Electrical Insulation• Electromagnetic
Immunity• Multiple Sensor
Multiplexing• Multi-Functionality• Good in Harsh
Environments• Capable of Fitting in
Small Areas
ME 580 – Smart Wind Turbine Blades – Sensor Team
Fiber Optic Sensor Cons• Expensive
– Need:– Fiber optic cable– Polarized light emitter– Interrogator Unit/Receiver
• Newer Technology• Not time tested
• Limited Availability• Few suppliers
ME 580 – Smart Wind Turbine Blades – Sensor Team
Sensing Capabilities
• Strain• Displacement• Vibration
• Temperature• Leak Detection• Pressure
ME 580 – Smart Wind Turbine Blades – Sensor Team
FBG Working Principle• Sensors created by Fiber Bragg Grating
– An intense UV source “inscribes” a periodic variation of refractive index into the core of an optical fiber. A special germanium-doped silica fiber is used due to its photosensitivity.
– Variations in the fiber change the reflected and transmitted response within the optical fiber. The fiber responds to strain and temperature initially, and different orientations allow for multiple sensing options.
ME 580 – Smart Wind Turbine Blades – Sensor Team
Fiber Bragg Grating
ME 580 – Smart Wind Turbine Blades – Sensor Team
Bragg Grating Configurations
ME 580 – Smart Wind Turbine Blades – Sensor Team
Data Collection and Utilization
• Data Collection Options– Slip Ring– Brushless Slip Ring– Rolling Ring– Liquid Filled Slip Ring– Wireless
ME 580 – Smart Wind Turbine Blades – Sensor Team
Data Collection• Brushless Slip Ring
– Continuous Data Collection Ability– Improved lifespan
• Rolling Contacts reduce friction, reduce wear
– Minimizes wire tanglage– HoneyBee Robotics
ME 580 – Smart Wind Turbine Blades – Sensor Team
RecommendationsTest sleeve made from combination of PVDF film and fiber optic sensors.
•PVDF film senses wind loading.
•Fiber Optic Sensors acquire resulting strains/stresses on blade.
ME 580 – Smart Wind Turbine Blades – Sensor Team
Recommendations• Lab testing
– Cantilever beam distributed load• Include tension and compression
– Consider bank of hydraulic actuators applying load conditions, and perhaps even a cam system to apply concurrent vibration
ME 580 – Smart Wind Turbine Blades – Sensor Team