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

• Current Data and Usage

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 Optic Sensors

ME 580 – Smart Wind Turbine Blades – Sensor Team

Fiber Optics

ME 580 – Smart Wind Turbine Blades – Sensor Team

Types of Cores

• Glass Cores • Plastic Cores

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

Sensing Capabilities

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

Strain Measurement

ME 580 – Smart Wind Turbine Blades – Sensor Team

Bragg Grating Configurations

ME 580 – Smart Wind Turbine Blades – Sensor Team

Types of Configurations

ME 580 – Smart Wind Turbine Blades – Sensor Team

Sensor Multiplexing Multiple Functions

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

ME 580 – Smart Wind Turbine Blades – Sensor Team

Questions?