1. Smart Wind Turbine Blades Sensor Team Cassel, Fraser, Larsen, McCrummen, Sarrazin ME 580 – Smart Structures

2. 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

3. ME 580 – Smart Wind Turbine Blades – Sensor Team Current Data and Usage

4. ME 580 – Smart Wind Turbine Blades – Sensor Team What to SenseWhy to SenseStrain GagePiezoresistivePiezoelectricOptical StrainComposite failureXXXX Monitor blade stressXXXX DisplacementTip deflection X VibrationVibration absorption XXX Temperature Temperature effects on materials X PressureWind pressureXXXX Air flowXXXX Natural wind frequencies/gustsXXXX ImpactHail/Rain intensity XXX Natural wind frequencies/gusts XXX Acceleration Wind loading vs. energy generation XX Ultrasonic Non-destructive for delamination X Humidity/Moisture Prevention of system degradation X

5. 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

6. 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

7. 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

8. 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

9. Impact Sensing Weather Detection –Active control –Damage prevention Wind Gust Detection –Active control PVDF appropriate if surface mounted –Thin –Sensitive

10. 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

11. 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

12. 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

13. 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

14. 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

15. Piezo-resistive Sensing – Basic Structure http://www.microsystems.metu.edu.tr/piezops/piezops.html

16. 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=E070209http://cooperinst.thomasnet.com/Asset/lpm562.pdf

17. 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

18. 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

19. Fiber Optic Sensors ME 580 – Smart Wind Turbine Blades – Sensor Team

20. Fiber Optics ME 580 – Smart Wind Turbine Blades – Sensor Team

21. Types of Cores Glass CoresPlastic Cores ME 580 – Smart Wind Turbine Blades – Sensor Team

22. 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

23. 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

24. 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

25. Sensing Capabilities Strain Displacement Vibration Temperature Leak Detection Pressure ME 580 – Smart Wind Turbine Blades – Sensor Team

26. Sensing Capabilities ME 580 – Smart Wind Turbine Blades – Sensor Team

27. 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

28. Fiber Bragg Grating ME 580 – Smart Wind Turbine Blades – Sensor Team

29. Strain Measurement ME 580 – Smart Wind Turbine Blades – Sensor Team

30. Bragg Grating Configurations ME 580 – Smart Wind Turbine Blades – Sensor Team

31. Types of Configurations ME 580 – Smart Wind Turbine Blades – Sensor Team

32. Sensor Multiplexing Multiple Functions ME 580 – Smart Wind Turbine Blades – Sensor Team

33. 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

34. 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

35. Recommendations Test 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

36. 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

37. Questions?