Structural Health and Condition Monitoring for Blades ...
Transcript of Structural Health and Condition Monitoring for Blades ...
Center for Nondestructive Evaluation
Wind Energy Symposium: September 29, 2015
Structural Health and Condition
Monitoring for Blades & Rotary
Machinery
Leonard J. Bond, PhD., F.AAAS, F. Inst.P
Director, CNDE; Professor Aerospace Engineering
Professor Mechanical Engineering
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Outline
• Wind turbines - they can have a bad day
• Allowables – what needs to be detected?
• NDT/SHM/condition monitoring –state-of-art
• Nacelle, blades, tower and base
• SHM – in-situ detection
• Proactive management of degradation
• Prognostics
• Condition monitoring and SCADA
• Failure & failure monitoring
• Future challenges, needs and opportunities
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Wind turbines Can have a bad day.
Gaslamp press, Wind watch,
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Typical development of mechanical failure
Tchakoua et al (2014)
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Current SHM has limited
coverage and flaw size
detection is yet to be
demonstrated at
acceptable POD, but is
near real time
After Jan Achenbach – talk at Stanford (2008)
NDE + SHM &
PROGNOSTICS
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Manufacturing “Allowables” e.g. Composites
• Influence of damage on
structural allowables
• “manufacturing
acceptable features”
criteria – acceptable
“anomalies”
Damage & degradation
• Impacts
• Joints
• Micro-cracks & pores
Cross-section of Sandia CX-100 9m blade
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Blade Damage Type Damage
Type 1 Adhesive debonding between
spar cap and shear webs
Type 2 Adhesive debonding along
leading and trailing edge
Type 3 Adhesive debonding between
core and laminate materials
Type 4 Delamination in the laminate
sections
Type 5 Fiber breakage in the
laminate sections
Type 6 Adhesive debonding due to
buckling
Type 7 Gel coat cracking Ciang et al., “Structural health monitoring for a wind turbine
system: a review of damage detection methods,” Measurement
Science and technology. Vol 19, 2008.
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Rotating machinery – NDT & monitoring
Gear – defect: find with conventional
NDT & Particles found in oil
Figs from NREL Hyers et al (2006)
Cracks in gears
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Intrusive & NDT based condition monitoring
INTRUSIVE
• Vibration analysis
• Oil analysis
• Strain measurement
• Electrical effects
• Shock pulse method
• Physical condition of
materials
• Self-diagnosis sensors
NDT BASED
• Ultrasonic testing
• Visual inspection
• Acoustic emission
• Thermography
• Performance monitoring
• Radiographic inspection
After NREL & Tchakoua et al (2013)
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State-of-the-art – Nacelle monitoring
• Displacement
Monitoring
• Temperature
Monitoring
• Vibration Censors
• Accelerometers Ludeca, Inc
The green arrows indicate sensor
(accelerometer) locations for standard
wind turbines.
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Blades - Current Methods of Detection
• Rope access
technicians
• Blade access
platforms
• Optical - Telescope
and camera
• Thermography
• Ultrasound
Performance Composites
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Current Methods of Detection - optical
• Telephotography
Inspection
• Inspect for damages
and leading edge
erosion
• 3-4 turbines per day
Performance Composites
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Current Methods of Detection - thermal
• Thermography
• Record
Temperature
differences
• Detect de-
laminations, de-
bonding, and
internal structural
problems
Performance Composites
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Current Methods of Detection - ultrasound
• Ultrasonic
• Reveals certain
flaws quickly
• Scattering effect has
a negative impact
• Time consuming for
large areas
National Instruments
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Towers and base
• wind speed, torque,
power, drive train
vibration, tower
vibration
• Base
inspection/minitoring
• Off shore structures
Swartz et al (2008)
Monitoring with Accelerometer
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SHM -- In – Situ Detection Methods
• Methods
• Ultrasound
• Fiber-optic Sensor
• Electric Strain Gage
• Acoustic Emission
• Not yet fully implemented
in service (used in fatigue
tests)
• Not considered to be
economically feasible
• Economics of Scale and
remote locations (off-shore)
may create feasibility
• Must withstand steady
rotations, vibrations,
mechanical shocks, EM-
fields, lightning and temp
changes
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In-Situ Detection Methods - strain gauges
• Strain Gauges • Electrical Sensors
• Require Large Sensor arrays
• Stress Field is required
• Applicable in Operation
• Mature technology
P.J. Schubel et al. / Renewable Energy 51 (2013) 113e123
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• Acoustic Emissions
• Detection
• Crack initiation
• Breaking of Fibers
• Impacts
• High levels of Noise
• Issues with coverage
and # of sensors
• Lightning sensitivity –
conductors!
Integrity Diagnostics
In-Situ Detection Methods – acoustic emission
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Acoustic Emission during Fatigue Testing
“Experimental results of structural health monitoring of wind turbine blades”, Rumsey et al.
3 acoustic emission sensors attached to a 9m blade during fatigue
testing with a crack growing between the sensors.
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In-Situ Detection Methods - fiber sensors
• Fiber Bragg Grating
• Offer physical correlation
between wavelength and
strain
• Long term stability and no
recalibration required
• Lightning Safety and
neutrality to electro-
magnetic interference
• Limited number of sensors
• Prototype: Enercon 4.5MW
• 53m blade
P.J. Schubel et al. / Renewable Energy 51 (2013) 113e123
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Hess (Darpa)
Goal is to proactively address potential future degradation in operating
system to avoid failures and to maintain integrity, operability and safety
Wind Turbine
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A moderate complexity conceptual structure of a
Diagnostics, Prognostics and Health Management system.
Mrad (2011)
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Combine condition and SCADA/performance
Chen (2010) & Tchakoua et al (2014)
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Failure and monitoring techniques
Failure and monitoring techniques
Tchakous et al (2014)
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Needs and opportunities
• NREL – GRC
• Long term plan
• Prognostics research
• Condition based
maintenance
• Cost benefit analysis
for condition
monitoring systems
• Needs & issues
amplified for offshore
operation
ISU activities:
Coble, J.,…, Bond, L.J.,.. (2015)
A review of prognostics and health management
applications in nuclear power plants,
Int. J. Prognostics and Health Management (IJPHM),
Bond, L.J., Doctor, S.R., Jarrell, D.B. and Bond, J.W.D.
(2007) Improved economics of nuclear plant life
management, Proceedings, 2nd IAEA Int. Symp. on
Nuclear Power Plant Life Management
NDT, monitoring & prognostics