Challenges with Wind Blade RoadChallenges with Wind Blade...

Challenges with Wind Blade Road-transportationChallenges with Wind Blade Road-transportation & in-situ Dynamics

July 21, 2010

2010 Wind Turbine Blade Workshop – SANDIA Labs

Presented by

PARI TAHTAVADEKARPARI TAHTAVADEKARValidation Testing & Development EngineerClipper Windpower, Inc.

© 2010 Clipper Windpower, Inc. and subsidiaries All rights Reserved

B k d

OVERVIEW• Background• Objective• Problem statement• Problem statement• Technical approach

• Break-down of in-situ Dynamics• Hybrid approach – Testing and Finite Element (FE) analysis

• Results C l i• Conclusions

• Comments• Acknowledgements• Acknowledgements

© 2010 Clipper Windpower, Inc. and Subsidiaries All Rights Reserved2

Wi d t bi t d t t it th f th

BACKGROUND• Wind turbines are erected at remote sites, therefore, the

wind turbine blades are transported on a variety of roads leading up to the sites (paved roads, sharp bends, dirt g p (p proads, etc.)

• Modern wind turbine blades weigh several tons and far exceed common trailer lengths available for roadexceed common trailer lengths available for road-transportation

• A wind turbine blade is a “pay-load” (should not act as an p y (extension of the shipping fixture/structure) that needs to be isolated, thus protected from any damage during road-transportationtransportation

• The structural-dynamic behavior of “trailer + blade” is complicated and needs attention to ensure blade safety


T th t i d t bi bl d t t d f l

OBJECTIVE• To ensure that wind turbine blades are transported safely

during road-transportation and protected against a combination of static, dynamic, and stochastic loadsy

• To develop a hybrid methodology that can assess blade shipment fixture design against all loads

A l i t t f ll l di h• Analysis – cannot account for all loading phenomena• Measurement – too expensive to prototype all design alternatives

• To identify isolation needs of the blade and subsequent y qdesign requirements


A i d t bi bl d i l t d t di t

PROBLEM STATEMENT• A wind turbine blade is commonly supported at discrete

locations during road-transportation – (1) near the root, and (2) approximately 60-75% outboard along the blade span( ) pp y g p

• A wind turbine blade is subjected to a variety of static and dynamic loads (reaction- forces and moments),

Bl d di t ib ti b b di t t l ti• Blade mass distribution– as borne by discrete support locations• Wind loads – cross winds on the aerofoil during transportation• In-situ harmonic behavior of blade + trailer – a combination of resulting

flap edge and twist motionflap-, edge-, and twist motion• Impact or transient loading caused by road bumps, pot-holes #

• Quasi-static loading (torsion and bending) at low speeds

R ti l d l t h h h bi ti f• Reaction loads escalate when a harsh combination of loads is experienced causing highly concentrated strains in support vicinity

© 2010 Clipper Windpower, Inc. and Subsidiaries All Rights Reserved

# Potentially non-linear loading behavior

5

V i l di h i d ib d i th bl

TECHNICAL APPROACH - Strains• Various loading mechanisms described in the problem

statement cause strain in the wind turbine blade and contribute towards the resultant, Sresres

randomimpactharmonicswindmassres XSSSSS ++++=• Smass can be calculated (FE model) or measuredmass ( )• Swind is stochastic and can be approximated by averaging

blade strains during periods of quiescence (of road induced it ti ) d i th t texcitation) during the test

• “Sharmonics + Simpact” is the most concerning and also the hardest to quantify since the former is caused by severalhardest to quantify since the former is caused by several contributing structural modes of “blade + trailer” and the latter occurs due to random road input

i ll d b f t h t t© 2010 Clipper Windpower, Inc. and Subsidiaries All Rights Reserved

• Xrandom is small, caused by factors such as temperature6

A h b id t h i l h d h th t b th t t

TECHNICAL APPROACH – FE + Test• A hybrid technical approach was used such that both a test

and an FE model were used;• Test

» To measure relative motion between the blade and the support-frame» To measure strains in aerofoil c/s for correlation

• Linear FE modelLinear FE model» To predict detailed stresses/strains in the vicinity of aerofoil c/s» To correlate with the full blade’s in-situ dynamic behavior


Test Set-upNumbers in Red indicateA l t L t

3

56

1 3’

6’

Numbers in Red indicate accelerometer locations

Accelerometer Lay-out

4

6

2 4’

6

Root Section • Multiple blade lengths Salient Featuresp g• Design alternatives to

support all blades

Strain Gauge Lay-out

Salient Features• x-, y-, and z- acceleration

data was collected at various blade sections (locations 1 6)Strain Gauge Lay out blade sections (locations 1-6) on the trailer, the support-frame, and the blade

• Strain gauges were installed• Strain gauges were installed at multiple span-wise sections as shown


Ti hi t f ti f t f d bl d

TECHNICAL APPROACH - Reactive loads• Time history of motion of support-frame and blade were

recorded during the test using accelerometers• Using periods quiescence as the initial condition, support-Using periods quiescence as the initial condition, support

frame and blade motion (therefore the relative motion) were calculated £ (by integrating time data)S i f i l i d k h l i• Spring rates of isolation pads were known, so the resulting discrete forces and moments at the support location were calculated

wvu

xyxzyz

wvu

−−

−

−

1

1

11

11

11

11

0

0

0

01000010

0001• x1-2, y1-2, and z1-2 are global co-

ordinates of frame and blade on two sides of the interface

nn

n

wvu

xyxzyz

y

−−

−=

=

2

2

2

1

22

22

22

110

01000010

0001

ψθϕ

q two sides of the interface£ u1-2, v1-2, and w1-2 are computed

motions from time series


Ref: Rhombus Consultants Group

RESULTS –Support-frame Motion

Translation Frame Twist

10 cm 5.70

• Support-frame motion of 20+ cm was observed in an extreme case caused by a combination of trailer twist andextreme case caused by a combination of trailer twist and blade harmonics

• Frame twist (not blade twist) reached 5.70 in an extreme


case10

RESULTS – Reactive loads

Force (kN) Moment (kN-m)

10 kN

5 kN-m

• From relative motion of blade w.r.t. support, and spring-rates of isolation elements reactive forces and momentsrates of isolation elements, reactive forces and moments acting on the blade were calculated

• Up 53 kN vertical force (Fz) and 10 kN-m of vertical


bending moment (Fz) were reached in extreme case11

St i d b f

RESULTS – Strain Data• Strains were zeroed before

taking data in transit,Smass = 0 µS

1 2

Strain history (30 min) at various strain gauges along the aerofoil

• As predicted, a review of strain history of 30 min showed that strain (at any l ti ) i d b

1 2

location) is caused by;1. Harmonics2. Impact loadingF 64:LE00:428:+Z

F 65:LE45:428:+ZF 66:LE90:428:+ZF 67 SLE 328 Zus

gau

ges

• A particularly harsh loading period of ‘30 s’ was considered for FE analysis

F 67:SLE:328:+ZF 69:PLE:528:+ZF 70:PLB:628:+ZF 72:PTB:728:+ZF 73:LE00:429F 74:LE45:429F 75:LE90:429F 76:SLE:329F 78:PLE:529F 81:PTB:729F 82:LE00:430tra

in a

t var

io

F 83:LE45:430F 84:LE90:430F 85:SLE:330F 86:SLB:230F 88:PLB:630F 90:PTB:730

Time (0-1800 s)

S


S li t F t

FE ModelSalient Features• Linear finite elements• Composite aerofoil c/s with UNI

Aerofoil

pand BIAX layers modeled in detail

• Spring rates of all rubber p gelements were known

• Termination at the support-frame interface considered “rigid”; a glogical assumption since the support-frame is nearly inflexible below 20 HzSaddle including

A design alternative

rubber matRubber Isolator


RESULTS – Aerofoil Strains

LP Side HP Side

Max acute strainsDesign Alternative 1

Stresses/Strains are better diffused and lowered in peak valuesStresses/Strains are better diffused and lowered in peak values

Design Alternative 2


P t d th d l bl d i i i f

CONCLUSIONS• Presented methodology enabled an engineering review of

various design alternatives for shipping fixtures• Results ensured that a design alternative was available (forResults ensured that a design alternative was available (for

all blades) such that aerofoil strains during road-transportation did not exceed the target (i.e. maximum allowable strain)allowable strain)

• A hybrid approach involving test and analysis succeeded such that1. Dynamic motion of the blade and the support-frame and resulting

strains in the blade were measured for correlation with the model2 Once loads (forces and moments) acting on the blade were2. Once loads (forces and moments) acting on the blade were

calculated, multiple design alternatives were analyzed

• Additional valuable information regarding trailer quality needs and blade isolation requirements were obtained© 2010 Clipper Windpower, Inc. and Subsidiaries All Rights Reserved

needs, and blade isolation requirements were obtained15

D i b h i f th bl d d i d t t ti

COMMENTS• Dynamic behavior of the blade during road-transportation

was well replicated by the model but strain correlation was not perfect for all load casesp• Interface between blade and support-frame is modeled one way,

but a greater variation exists in reality• Strains introduced by blade mass and cross-winds were filtered outStrains introduced by blade mass and cross winds were filtered out

of the FE analysis (however considered in decision making)

• Proposed methodology worked very well for comparing design alternatives but the correlation with absolutedesign-alternatives, but the correlation with absolute measured strains can be improved• A non-linear FE model• Trailer shake/harshness measurements in a controlled environment

• An alternative method in structural analysis called Transfer Path Analysis is available to compute reactive loads


Path Analysis is available to compute reactive loads

16

SANDIA L b Alb NM

ACKNOWLEDGEMENTS• SANDIA Labs, Albuquerque, NM• Clipper Technical Team:

• Pari Tathavadekar Patrick Desnoyers Mark Elliott et alPari Tathavadekar, Patrick Desnoyers, Mark Elliott, et al

• TECSIS (blade manufacturer)• Rhombus Consultants Group• LMS North America


Th k Y !Thank You!

This document, or an embodiment of it in any media, discloses information which is proprietary, is the property of Clipper Windpower, inc. & It’s subsidiaries, is anunpublished work protected under applicable copyright laws, and is delivered on the express condition that it is not to be used, disclosed (including reproduction as aderivative work), or used for manufacture for anyone other than Clipper Windpower inc. & It’s subsidiaries without its written consent, and that no right is granted todisclose or so use any information contained therein. All rights reserved. Any act in violation of prior agreement or applicable law may result in civil and criminalpenalties.

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