S mart S ystems & S tructures Lab. New concepts and Methods : Hardware 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 :00~10:30 1 Department of Aerospace Engineering, KAIST, Republic of Korea 2 Wind Energy Research Center, KIER, Republic of Korea 1

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Outline Experiments Conclusion 2 Introduction Numerical Study

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Introduction - Research Backgrounds (Condition monitoring with Shape estimation) - Why Fiber Bragg Grating sensors? - Shape Estimation based on Measured Strains Using FBG Sensors - Research objectives 3

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Condition Monitoring for Reliability 4 Rumsey, 2009, “Condition Monitoring and Wind Turbine Blades,” Wind Turbine Reliability Workshop Full-scale Testing O & M Data Base Designed-in Maintainability Accurate Loads- Design Requirements Appropriate Environmental Conditions Designed-in Reliability Analysis High-Reliability WT Blade High-Reliability WT Blade Condition Monitoring Strains Loads Cracks Dry-spots Voids Operational Dynamics Temperature gradients Lightening Sense What? Blade shape(Deformation)

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Why blade shapes are important? 5 The “Blades” The shapes of the “Blades” influence the whole systems’ status Status Monitoring Design Validation Active control for blades Blade Shape Information - Bending => Flapping motion - Torsion => Pitching motion

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Why blade shapes are important? 6 The real-time shape estimation techniques based on embeddable sensors Shape estimation On operation It is difficult to directly monitor the shape changes on operation. Marker (DNW) SPR (Stereo Pattern Recognition) Optical image processing techniques PMI (Projection Moire Interferometry) Pattern (NASA Langley) Direct Shape Measurement

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware 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 Why Fiber Bragg grating sensor? 7 [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 [1][2] Slip ring Optical Rotary Joint

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Shape Estimation based on Measured Strains Using FBG Sensors – previous works 8 [DST] Discrete strains full state vector displacement field Estimation model using modal approach FEM data Distributed FBG sensors Real time Shape Estimation of a Two-Dimensional Structure FrFr KkKk C C’   w State matrix Output matrix Weighting matrix Error covariances State Space Integration of the filtering technologies Real-time shape estimation of the Rotating structures

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Research objectives Primary objectives – Development and validation of a real-time shape estimation technique for Wind Turbine blades using FBG sensors Research steps ① 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. ② 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. 9

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware 10 Numerical Study - Simulation Steps - Simulation Results - Optimization of Sensor locations

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware FMD Virtual experiments – simulation steps Beam model Mode shapes 11 Rotating beam motions are simulated - Full-field Displacement & strain Rotating beam motions are simulated - Full-field Displacement & strain M : # of sensors, N : # of disp. Points, n : # of used modes Discrete strains DST matrix constructed Shape estimation Sensor location Optimization Sensor location Optimization Full-field Strain & Displacement Sensor location Sensor location Evaluation

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Rotating beam dynamics are simulated – Full-field displacement & distributed strain Simulation Results 12 Full-field Displacement Discrete strains Estimated Deflection Strains at a few points are used for reconstruction of full-field displacement via DST matrix. Comparison Directly Simulated Deflection

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Simulation Results Rotating beam displacement at the Tip of the beam (Numerical simulation vs. Shape estimation results) 13 - Shape estimation using simulated strains are performed - Full-field displacement from numerical simulation are compared with Estimated shape using strains Numerical simulation Shape estimation Reconstructed from strains Directly Simulated

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Optimization of Sensor locations 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) 14 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

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware 15 Experiments –rotating beam - Rotating beam test setup - Test measurand/DST matrix - Results

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Test setup – Demonstration of the rotating beam fbg1 fbg2 fbg3 fbg4 16 Reconstructed shape (DST) Photo-grammetry Images taken by High-speed camera Optical rotary joint

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Test measurand Measurand –Four Strains (FBG sensors) –13 Marker positions (Photogrammety) –Angular position Strain by FBG Rotating angle 60RPM case In. Volt.Ang. Vel Case 10.1V15 RPM Case 20.2V30 RPM Case 30.3V45 RPM Case 40.4V60 RPM 17

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware DST matrix fbg 1 fbg 2 fbg 3 fbg 4 pointpt1pt2pt3pt4pt5pt6pt7pt8pt9pt10pt11pt12pt13 [mm] Marker position FBG1FBG2FBG3FBG4 wavelength [nm] [mm] FBG position DST matrix DST matrix Acrylic beam (500mm×20mm×1.9mm) was used for denstrating large deflection in low speed Optimized sensor locations Marker positions

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Results – qualitative aspects RPM rotation 60 RPM rotation

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Results -Shape comparison between DST vs. Images Directly Measured (High Speed Camera) Directly Measured (High Speed Camera) Estimated (from strains using FBG) Estimated (from strains using FBG) 20

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Results – quantitative aspects Pole effect 21 15RPM30RPM45RPM60RPM MAC (median) Skewed distribution Skewed distribution Time [s]

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware 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. 22

S mart S ystems & S tructures Lab. New concepts and Methods : Hardware Hong-Il Kim Ph. D. candidate Aerospace Engineering, KAIST Jae-Hung Han Associate Prof. Aerospace Engineering, KAIST Smart Systems and Structures Lab. : Design & Control Visit our website: 23 THANK YOU! Acknowledgments This work was supported by the Korea Institute of Energy Research through the research project (grant No. NT ).