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


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


Typical major components in wind turbine


Wind turbines Can have a bad day.

Gaslamp press, Wind watch,

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0CAcQjRxqFQoTCNeQub6plcgCFUEPkgod4rYPRA&url=https://gaslamppost.wordpress.com/2012/04/04/publicly-funded-wind-turbines-only-generate-rebates-for-those-who-can-afford-them-not-much-else/&psig=AFQjCNGizh1KfyNkN0jP9Pr-vsK7hbXQ0Q&ust=1443378256970144

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRxqFQoTCILM6e2plcgCFYuLkgodsA4NjQ&url=https://www.wind-watch.org/news/2014/05/09/second-wind-tower-blade-suffers-structural-failure-at-prairie-breeze-wind-energy-farm/&psig=AFQjCNHEUzaqnHWVWj06UKLkhyOXhREbGw&ust=1443378396202439


“bathtub” curve – reliability of system

Tchakous et al (2014)


Typical development of mechanical failure

Tchakoua et al (2014)


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


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


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.


Rotating machinery – NDT & monitoring

Gear – defect: find with conventional

NDT & Particles found in oil

Figs from NREL Hyers et al (2006)

Cracks in gears


NDT/SHM/Condition Monitoring

AND MUCH MORE!!!


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)


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.


Vibration based monitoring

Sheng & Veers (2011) Nrel


Blades - Current Methods of Detection

• Rope access

technicians

• Blade access

platforms

• Optical - Telescope

and camera

• Thermography

• Ultrasound

Performance Composites


Current Methods of Detection - optical

• Telephotography

Inspection

• Inspect for damages

and leading edge

erosion

• 3-4 turbines per day



Current Methods of Detection - thermal

• Thermography

• Record

Temperature

differences

• Detect de-

laminations, de-

bonding, and

internal structural

problems



Current Methods of Detection - ultrasound

• Ultrasonic

• Reveals certain

flaws quickly

• Scattering effect has

a negative impact

• Time consuming for

large areas

National Instruments


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


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


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


• 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


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.


Acoustic Emission

Hameed et al (2009)


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


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


A moderate complexity conceptual structure of a

Diagnostics, Prognostics and Health Management system.

Mrad (2011)


Combine condition and SCADA/performance

Chen (2010) & Tchakoua et al (2014)


Failure and monitoring techniques

Failure and monitoring techniques

Tchakous et al (2014)


Future challenges [Tchakoua et al (2014)


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

Documents

Structural Health and Condition Monitoring for Blades