How robust is the simplified load model - Alistair

How robust is the simplified load
model (SLM)
Alistair Mackinnon
Operations Manager Wind Energy
Why……part 1
September 2011
Proven Energy
P35-2 Shaft Failures……
Diaper moment….
Suspended the certification:
Root cause analysis/failure investigation
Agreement of remedial actions
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DECC
MCS Licensee (Gemserv)
RenewableUK
HSE
VG Energy
Kingspan
ETC
Beach marks – crack
propagation signature
Signature indicating the blade
was
passing the tower shadow.
Why……part 2
Hurricane Bawbag….
F1
CoG
A L2
F2
Experience is the comb which
nature gives us when we are
bald…..
BIS – NMS Project
Feasibility study of the scope for
revising the simplified load model in
IEC 61400-2: 2006
FHRE25
Acknowledgements
• Dr John Bingham
• Dr Raymond Boyle
• Dr Wai Kong Lee
• Dean Boyce
• Tom Clark
Project scope
• Objective
• Background to the SLM
• Perceived limitations of the SLM
• Potential areas for improvement
• Recommendations for implementing the improvements
Objectives
• detailed review of the equations in the SLM
• re-assessment of the load cases to determine if there is
sufficient coverage
• GAP analysis of loads not aequately addressed
• technical approach to validating/implementing any proposed
change
• develop a framework for delivering the changes
Background
• DS 472
• 61400-2: 1992 – 40m2 limit
• JOULE 2 Project (ECN/CRES/NEL/DEWI/RISO)
• Field verification programme - NREL/Windward Engineering
• IEA round robin – AOC 15/50
• 61400-2: 1999 – 200m2 limit
• 61400-2: 2006
• Static loading – generally constant
• Cyclic loading – quasi static & dynamic cycling
• Stochastic loading – random variations
• Aerodynamic loading – force of the wind
• Mechanical loading – gravity, yawing, gyroscopic, transient
Load Case A – normal operation
• only fatigue load case
• assumes abnormal loads are rare…
• blade root flapwise bending and rotor shaft bending may be
under predicted by the SLM (NREL/Windward/NEL)
• architecture neutral (up/downwind) compressive or tensile
loading
• omits the fatigue performance of the tail
Load Case B – yawing
• any out of balance gyroscopic moment can give rise to a
fatigue load
• Need for blades to act in a co-ordinated fashion
Load Case C – yaw error
• assumes flapwise bending at 30 deg yaw error
• yaw error assumed to be constant – is a dynamic factor
ignored?
• flapwise bending may be under predicted by the SLM
Load Case D – maximum thrust
• thrust coefficient (0.5) may be in error…by a factor of 2
when the rotational speed at 2.5Vave is high (Edition 3)
• this could affect the buckling capacity of the supporting
structure……
Load Case E – maximum rotational
speed
• 2 equations (33) and (34) – centrifugal load at the blade root
and bending moment (blade imbalance) over the rotor shaft
• if a blade fails……centrifugal and bending moments
become large……fugitive blades can travel over 500m
Load Case F – short at load connection
• 2 equations (35) and (36) – rotor torsion & edgewise
bending – G is assumed to be 2 …..can over or under predict
depending on the rotor/generator arrangement
Load Case G – shutdown (braking)
Load Case H – parked wind loading
• no fatigue assessment….
• stationary rotor
• spinning rotor
• tower loadings……
Load Case I – parked wind loading –
maximum exposure
• no fatigue assessment….
• assumes components are only affected by Vave – rather than
Ve50
Load Case J – transportation, assembly,
maintenance and repair
• probably OK
• but be sensible……
And finally……
• Manufacture …….FPC?
• Welding…….
• No paperclips…….
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IEC 61400-2: 2006 is a minimum requirement for
assessing the design of small wind turbine
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Simplified load model (SLM) is only applicable to HAWT
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It is believed to be very conservative, however it ignores
local stress and a number of operating conditions