Blade model for certification test support and

failure prediction

A G Dutton, M Clarke1, P Bonnet2

Energy Research Unit (ERU)

Rutherford Appleton Laboratory (RAL)

Science and Technology Facilities Council (STFC)(now at 1Oxford Brookes University and 2SAMTECH Iberica)

Supergen Wind Final Assembly

Holywell Park, Loughborough University

25 March 2010

Background: Blade modelling

• Which are the best

materials?

• What is the optimum lay-up?

• What is the best internal

structure?

• What are the size limits for

wind turbine blades?

• What additional stresses do

smart control devices

generate in a blade?

• How should NDT

measurements be

interpreted?

Parametric blade model:

Design strategy

• Parametric processing tool for creation and running of the underlying FE

model

• Suitable for sensitivity analyses, flexibility, documenting, re-usability

Python script front end for automation of the Abaqus FE package

Modular program

Realistic load application, including quasi-static aerodynamic loading

Ultimate strength & fatigue analysis

Developing dynamic implementation

Parametric blade model:

Geometry definition

a b

c d

aerofoil shape

=> parameter sweeps: e.g.

tip

deflection

or

max s

tress

d - shear web offset (mm)

Parametric blade model:

Geometry definition

Parametric blade model:

Lay-up

Parametric blade model:

Fully distrubuted aerodynamic load

Parametric blade model:

Variable mesh density...

... at the push of a button

Parametric blade model

5 MW (61 m) blade model

• Basic lay-up information

• Target mass and stiffness distributions

• Limitations of lay-up information

• Overall mass

• Discretisation of lay-up info

• Required spar-cap stress profile?

• Lay-up modification

• Materials variation

• Static load case (aerodynamic load distribution)

• Fatigue lifetime

5 MW (61 m) blade model:

Spar-cap stress distribution (initial)

5 MW (61 m) blade model:

Spar-cap stress distribution (adjusted)

5 MW (61 m) blade model:

Spar-cap stress distribution (smoothed)

5 MW (61 m) blade model:

Spar-cap stress distribution (lumped load)

5 MW (61 m) blade model:

Materials

Baseline UD

material

Mean value

E1T (GPa) 39.042

E1C (GPa) 38.91

ν120.29058

E2T (GPa) 14.077

E2C (GPa) 14.997

ν210.95036E-01

G12 (MPa) 4.2388

Baseline UD

material

Mean value

XT (MPa) 776.5

XC (MPa) -521.82

YT (MPa) 53.865

YC (MPa) -165

S (MPa) 56.071

5 MW (61 m) blade model:

Static and fatigue failure

kd fFn m

k f

1 F

“Design” load

Characteristic

value of

material

property

Characteristic

load

Partial safety

factors

Loads

Material

Consequences

of failure

Design guidelines:

• ISO 61400-1

• Germanischer Lloyd (GL)

• Det Norske Veritas (DNV)

Range of design load cases:

• Ultimate

• Fatigue

5 MW (61 m) blade model:

Static strength – skins and shear web

Choice of static failure

criteria:

• Tsai-Wu

• Tsai-Hill

• Other (user specified)

5 MW (61 m) blade model:

Static strength – bonding paste

Cohesive element model

•Normal stress component

•Shear stress component

•Linear up to characteristic

value

•Material “softening”

5 MW (61 m) blade model:

Biaxial stress ratio

Biaxial stress ratio is

the ratio between the

two largest

magnitude principal

stress components

5 MW (61 m) blade model:

Uni-axial fatigue properties (R=0.1)

5 MW (61 m) blade model:

Fatigue lifetime

Baseline glass fibre

Uniaxial fatigue

743.9

1

9.1178

nS

Min: 1.3 x 109

593.10

1

2.1250

nS

High performance

glass fibre

Min: 1.6 x 1010

Full scale blade testing

Multi-axial loading validation

Full scale blade testing

Multi-axial loading validation

-8

-6

-4

-2

0

2

4

6

8

-1.5

Tip

Fla

pw

ise

De

fle

cti

on

s (

m)

Tip Edgewise Deflections (m)

Blade model

Experimental data

(courtesy NAREC)

Full scale blade testing

Thermoelastic stress analysis

Blade test: blade with defects

2211

pc

TTIsotropic materials:

Orthotropic materials: 22221111

pc

TT

Full scale blade testing

Thermoelastic stress analysis

Blade test: blade with defects

Blade model: normal blade

Blade model: blade with defects

Conclusions

• Flexible, parametric blade model for assessment of alternative

materials with enhanced static and fatigue properties

• Initial results also available for application to full-scale blade testing,

control of smart blades and interpretation of condition monitoring data

• Future work planned on dynamic loading – operation in wakes from

upstream turbines & “smart” blade devices

Acknowledgements

EPSRC grant no. EP/D034566/1

SUPERGEN Wind Energy Technologies

Consortium

For further information please contact:

geoff.dutton@stfc.ac.uk