Motivation. Composite Rotating Structures. SHM Applications. <Composite High. <Composite Fan Blade. < Wind Turbine blade > Speed Rotor (HSCL Lab)>

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1 Noncontact Sensing with Rotary Optical Radial Coupler (RORC) using C-lens Khazar Hayat, Prof. Sung Kyu Ha

2 Motivation Structural Health Monitoring (SHM) of Critical Rotary Components SHM Components Rotating Structure Sensing Mechanism Data acquisition & Management SHM Goals: Condition Assessment Damage Evaluation Service Life Prediction Catastrophic Failure Prevention SHM Advantages: Co osts Cost Savings trend Ensure Structural Integrity Maintenance on demand Lower unscheduled inspections SHM Scheduled Unscheduled Unscheduled (Today) Predictive Predictive < SHM Benefits (Source: Holger Speckmann, AIRBUS)> Time Slide 2

3 Motivation Composite Rotating Structures <Composite High Speed Rotor (HSCL Lab)> SHM Applications <Composite Fan Blade ( Model: GE90-115B)> < Wind Turbine blade > < Hli Helicopter Blades Bld (Source: Sikorsky k Aircraft Corp) > Slide 3

4 Problem Statement Structural integrity can be assessed by monitoring strains Difficult to receive strain data from Rotating Structure Development of a Noncontact Strain Measurement Method using Rotary Optical Radial Coupler (RORC) Slide 4

5 Previous Strain Measurement Methods Strain Gauges with Slip Ring / Telemetry system High signal to noise ratio Data transmission limitation Not applicable to higher speed Need power supply Sensitive to electromagnetic (EM) interference Slide 5

6 Previous Strain Measurement Methods FBG Sensor with Telemetry System Power Supply Problem Imbalance of Rotating Structure at Higher Speed < Wireless signal transmission between Signal Process Unit (SPU) & FBG sensors attached on wind turbine blade> Ref: Kerstin S., Wolfgang E., Jorg A., Elfrum L. and Gerhard L. A fibre bragg grating sensor system monitors operational load in a wind turbine blade. Meas. Sci. Technol. 2006: (17) Slide 6

7 Previous Strain Measurement Methods Fiber Optic Rotary Joint Optical signal transmission Insensitive to EM interference Tight mechanical tolerance for optical alignment Limited speed & durability due to mechanical parts < Working Principle of Fiber Optic Rotary Joint > Ref: Jing W., Jia D., Tang F., Zhang H., Zhang Y., Zhou G., Yu J., Kong F. and Liu K. Design and implementation of a broadband optical rotary joint using C-lenses. Opt. Express: (2004) Slide 7

8 Previous Strain Measurement Methods Fiber Optic Coupler Free-space coupling Require machining of for installation, weakening the Shaft Space Installation Problems in real structures < Arrangements of a rotary optical coupler and FBG sensors > Radial Optical Rotary Coupler (RORC) (Over( come above problems associate with Fiber Optic Coupler) Slide 8

9 Theory Fiber Bragg Grating (FBG) Sensor Reflect particular (i.e. Bragg) wavelength of light and transmits others Strain-included shift = Δλ n 0 : refractive index of the air n 1 : refractive index of the cladding n 2 : refractive index of the core n 3 : refractive index of the grating Strain & Temperature Measurements Slide 9

10 Theory Wavelength Division Multiplexing (WDM) Many FBG sensors on single optical fiber can be address simultaneously Sensing Network < Representation of a WDM interrogation of FBG sensor array > Slide 10

11 Experiment Experimental Arrangement for RORC Feasibility < Sketch of experiment test fixture to show feasibility of rotary optical radial coupler (RORC) > Slide 11

12 Alignment of Collimators Experiment Tedious and Time Consuming (i.e. 06 DOF s ) Use of marked Collimators < 06 DOF manipulation > V-groove block pre-alignment for marking < Optical alignment b/t stationary side and rotary side collimators > < Circumferential marking of C-lens Collimators pair at proper optical alignment position > Final alignment with marked collimator (i.e. mark matching) Slide 12

13 Equipment Specification & Setup Experiment FBG Sensor Spec.: Qty: 01 Central Wavelength: nm < Pair of C-lens Collimators used as RORC > < Experimental setup > Slide 13

14 Preliminary Results & Conclusions Optical signal pike per each rotation of disk appeared on si-425 Optical Sensing Interrogator (as expected ) Wavelengt th As speed increases, the time space between wavelength signal spikes decreases and vice versa (see region A & C ) Increase in speed sometimes causes misalignment that result in missing signal spikes (see region B) Time < Signal spikes appearing on si-425 interrogator > Slide 14

15 Preliminary Results & Conclusions For max. test speed of 1350 RPM, strain modulated wavelength signal was observed Wavelength Signal Strain Measurement < Wavelength signal measurement on si-425 optical sensing interrogator at different rotating disk speeds > Wavelength signal value (i.e nm) remained constant up to 1350 rpm, because negligible deformation / strain of steel disk Slide 15

16 Future Work Multiple points strain signal measurement (i.e.for 0 o ~ 360 o varying strains) High Sampling Data Acquisition System Optical Loss across RORC < signal measurement four times per revolution at required rotation angles > Minimize by precise alignment & use of better quality Collimators Overcome by Higher Laser Source Real-time applications (i.e. on wind turbine blade, composite flywheel rotor, helicopter blade, Composite fan blades etc.) Slide 16

17 Thank You for Your Attention Slide 17