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REAL-TIME SHAPE ESTIMATION WITH FIBER OPTIC SENSORS DISTRIBUTED IN ROTOR BLADES. Hong-Il Kim 1 , Lae-Hyong Kang 1 , Jae-Hung Han 1* , Hyung-Joon Bang 2 2010.04.23 . 09:00~10:30 1 Department of Aerospace Engineering, KAIST, Republic of Korea

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real time shape estimation with fiber optic sensors distributed in rotor blades

REAL-TIME SHAPE ESTIMATION WITH FIBER OPTIC SENSORS DISTRIBUTED IN ROTOR BLADES

Hong-Il Kim1,Lae-HyongKang1,Jae-Hung Han1*, Hyung-Joon Bang2

2010.04.23. 09:00~10:30

1Department of Aerospace Engineering, KAIST, Republic of Korea

2Wind Energy Research Center, KIER, Republic of Korea

outline

Experiments

Introduction

Conclusion

Numerical Study

Outline
slide3

Introduction- Research Backgrounds (Condition monitoring with Shape estimation)- Why Fiber Bragg Grating sensors? - Shape Estimation based on Measured Strains Using FBG Sensors - Research objectives

condition monitoring for reliability
Condition Monitoring for Reliability

Sense What?

Full-scale Testing

Condition

Monitoring

Appropriate Environmental

Conditions

  • Strains
  • Loads
  • Cracks
  • Dry-spots
  • Voids
  • Operational Dynamics
  • Temperature gradients
  • Lightening

High-Reliability

WT Blade

Accurate Loads-

Design Requirements

O & M

Data Base

Designed-in

Maintainability

Designed-in

Reliability

Reliability

Analysis

Blade shape(Deformation)

Rumsey, 2009, “Condition Monitoring and Wind Turbine Blades,” Wind Turbine Reliability Workshop

why blade shapes are important
Why blade shapes are important?

The “Blades”

  • The shapes of the “Blades” influence the whole systems’ status

Design Validation

Status Monitoring

Active control for blades

Blade Shape Information

- Bending => Flapping motion

- Torsion => Pitching motion

why blade shapes are important1
Why blade shapes are important?

Direct Shape Measurement

Optical image processing techniques

Pattern (NASA Langley)

Marker(DNW)

PMI (Projection MoireInterferometry)

SPR(Stereo Pattern Recognition)

  • It is difficult to directly monitor the shape changes on operation.

Shape estimation On operation

  • The real-time shape estimation techniques based on embeddable sensors
why fiber bragg grating sensor
Why Fiber Bragg grating sensor?
  • Typical embeddable sensors (Strain gauge, accelerometer..)
    • Complex electric-wiring (Slip ring) + Significant measurement noise
  • FBG (Fiber Bragg Grating) sensor
    • Small, lightweight, High sensitivity, Electro-magnetic immunity
    • No hygro-effects and easily installable onto/into host structures.
    • Multiplexing
    • Real time strain acquisition
    • FBG sensors are already applied to the load monitoring

Optical Rotary Joint

Slip ring

[1]

[2]

[1] A fibre Bragg grating sensor system monitors operational load in a wind turbine rotor blade

[2] Advanced Wing Turbine Controls Input Based on Real Time Loads Measured with Fibre Optical Sensors embedded in Rotor Blades

shape estimation based on measured strains using fbg sensors previous works

Discrete strains

Shape Estimation based on Measured Strains Using FBG Sensors – previous works
  • Estimation model using
  • modal approach
  • FEM data

e

State Space

Weighting matrix

Kk

C

[DST]

Integration of the filtering technologies

Real-time shape estimation of the Rotating structures

Real time Shape Estimation of a Two-Dimensional Structure

Error covariances

w

C’F

Fr

full state vectordisplacement field

Output matrix

State matrix

Distributed FBG sensors

research objectives
Research objectives
  • Primary objectives
    • Development and validation of a real-time shape estimation technique for Wind Turbine blades using FBG sensors
  • Research steps
    • Numerical study on the shape estimation method for the rotating beams
      • Rotating beam dynamics are simulated. (displacement fields, a few strain data)
      • Displacement is reconstructed using strains
      • Shape estimation method is evaluated through the comparison between original displacements and the estimated displacements.
      • Sensor location is optimized.
    • Experimental Demonstration of the real-time shape estimation for the rotating structures
      • FBG sensors are used to measure multi-point strains of the beam.
      • Structural deformation shape of the rotating beam is estimated.
      • The estimated shapes are compared with the directly measured shapes using photogrammety.
virtual experiments simulation steps
Virtual experiments – simulation steps

Rotating beam motions are simulated

- Full-field Displacement & strain

Shape estimation

DST matrix constructed

Discrete strains

Sensor location

Optimization

FMD

Full-field Strain & Displacement

Beam model

Sensor

location

Evaluation

Mode shapes

M : # of sensors, N : # of disp. Points, n : # of used modes

simulation results
Simulation Results

Directly Simulated Deflection

  • Rotating beam dynamics are simulated
    • Full-field displacement & distributed strain

Comparison

Full-field Displacement

Discrete strains

  • Strains at a few points are used for reconstruction of full-field displacement via DST matrix.

Estimated Deflection

simulation results1
Simulation Results

Rotating beam displacement at the Tip of the beam

(Numerical simulation vs. Shape estimation results)

Numerical simulation

Shape estimation

Directly Simulated

Reconstructed fromstrains

  • Shape estimation using simulated strains are performed
  • Full-field displacement from numerical simulation are compared with Estimated shape using strains
optimization of sensor locations
Optimization of Sensor locations

Estimated displacement

Measured strain

DST matrix (Displacement Strain Transformation)

Condition number

  • Used as the objective function for sensor location optimization
  • Small condition number indicates good information conservation during matrix operations

Initial Seed

Sensor 1: 0~4cm

Sensor 2: 5~16cm

Sensor 3: 19~31cm

Sensor 4: 33~38cm

Condition Number of DST

Sensor position

CN=19, (4.0,15.0,21,33)

test setup demonstration of the rotating beam
Test setup – Demonstration of the rotating beam

Reconstructed shape (DST)

Photo-grammetry

fbg1

fbg2

fbg3

Images taken by High-speed camera

fbg4

Optical rotary joint

test measurand
Test measurand
  • Measurand
    • Four Strains (FBG sensors)
    • 13 Marker positions (Photogrammety)
    • Angular position

Strain by FBG

60RPM case

Rotating angle

dst matrix
DST matrix
  • Acrylic beam (500mm×20mm×1.9mm) was used for denstrating large deflection in low speed

Optimized sensor locations

fbg1

fbg2

fbg3

fbg4

Marker positions

FBG position

Marker position

DST

matrix

results qualitative aspects
Results – qualitative aspects

30 RPM rotation

60 RPM rotation

results shape comparison between dst vs images
Results -Shape comparison between DST vs. Images

Directly Measured

(High Speed Camera)

Estimated

(from strains using FBG)

results quantitative aspects
Results – quantitative aspects

Time [s]

Pole effect

Skewed

distribution

conclusion

Development of the shape estimation technique for a rotating structure

    • A real-time deflection of the rotating beam is successfully estimated based displacement -strain transformation
    • - Sensor location optimization is executed.
    • - From the test results, it is clear that beam shape estimation of the rotating beam is successfully performed based on DST method and strain data obtained by FBG sensors.
    • FBG(Fiber Bragg grating) sensor is selected as a strain sensor because of many inherent advantages of fiber optic sensors and multiplexing capability.
Conclusion
slide23

THANK YOU!

Hong-Il Kim (hama@kaist.ac.kr)

Ph. D. candidate

Aerospace Engineering, KAIST

Jae-Hung Han (jaehunghan@kaist.ac.kr)

Associate Prof.

Aerospace Engineering, KAIST

Smart Systems and Structures Lab. : Design & Control

Visit our website: http://sss.kaist.ac.kr

  • Acknowledgments
  • This work was supported by the Korea Institute of Energy Research through the research project (grant No. NT2009-0008).