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
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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
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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
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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
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# 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
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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
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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
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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
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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
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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
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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
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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
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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
© 2010 Clipper Windpower, Inc. and Subsidiaries All Rights Reserved
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
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Th k Y !Thank You!
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