london array - windpower · kan fundamenterne optimeres i fase 2 erfaringerne fra london array...
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Kan fundamenterne optimeres i fase 2
Erfaringerne fra London Array
London Array
Jan K Rønberg1Sept. 2011 - Offshore konference - Esbjerg
Jan K Rønberg
Project and Market Director
COWI
Agenda
� Presentation of London Array project
� Geotechnical
� Structural
London Array
Jan K Rønberg2Sept. 2011 - Offshore konference - Esbjerg
Employer : DONG (50%) E.ON (30%) Masdar (20%)
Client : Aarsleff / Bilfinger | Berger JV, ABJV
Designer : COWI,IMS JV , CIJV
London Array
Jan K Rønberg3Sept. 2011 - Offshore konference - Esbjerg
Designer : COWI,IMS JV , CIJV
Certifying body : DNV
Phase 1
• 175 wind turbines
• SWP 3.6 MW -120
• 630 MW
• Water depth: 0-25 m
• Monopiles
London Array
Jan K Rønberg4Sept. 2011 - Offshore konference - Esbjerg
• Monopiles
• No scour protection
MP/TP resultsGlobal scour range
Maximum: 16.90 m
Minimum: 2.00 m
Jan K Rønberg6Sept. 2011 - Offshore konference - Esbjerg
� Two types of MP:
- 4,7 m diameter- 5,7 m diameter
� Five types of TP
� Four types of cages
London Array
Jan K Rønberg7Sept. 2011 - Offshore konference - Esbjerg
� Four types of cages
Geotechnical
� Pile length criteria
� Toe Shear at pile tip
� Large Pile Diameter effect
Jan K Rønberg11Sept. 2011 - Offshore konference - Esbjerg
Case History
zero toe-kick
vertical tangent
rotation criterion
ULS stability?
Jan K Rønberg1311 Nov 2010 London Array
Pile Toe Fixation
Key issues
� The toe-kick should be within the elastic part of the soil response to ensure a stable fixation of the pile toe.
� This gives robustness against accumulating pile inclination due to cyclic lateral loads.
yy ≤
Jan K Rønberg14London Array11 Nov 2010
y
Ptoe
ypl
pltoe yy ≤
Toe-Shear Response
Pile Slenderness
Key issues
� Checking the pile toe response does not cover the overall soil-pile-interaction
� An additional criterion can be defined by use of the critical pile length
� A unique design can be achieved for a certain pile slenderness
Jan K Rønberg15London Array11 Nov 2010
Pile Toe Rigidity
Pile Slenderness
The pile slenderness λ characterises the response of the soil-pile system.
cL
L=λ
0.65
Critical Pile Length
The elastic or critical length Lc gives the length of the pile that is mainly responsible for the pile head deformation.
In layered soils and for piles with differing wall thickness Lc can not be calculated directly. But it can be determined from the pile head rotation vs. length curve.
from Reese & Van Impe, 2001
Jan K Rønberg19London Array
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
λ [-]
Pile head rotation,
α [°]
NC19
ND17
NG14
NG17
NI09
NJ16
insufficient
robustness
11 Nov 2010
from Reese & Van Impe, 2001
� The pile design must fulfil conventional checks of ULS soil and pile strength utilisation, permanent rotation and meet the requirements for upper and lower bound eigenfrequencies.
� In addition CIJV designs for
� a pile slenderness λ equal to or greater than 0.9
� and a soil utilisation ratio at the pile toe less than 0.4 in Clay,
Pile Length Criteria
Jan K Rønberg20London Array
� and a soil utilisation ratio at the pile toe less than 0.4 in Clay, respectively 0.2 in Sand
� a toe-shear response within elastic limits
� Achieved length reduction by advanced model up to app. 2.5 m
11 Nov 2010
P-y curves
� Large pile diameter effect studied
� API p-y curves for soft clay do not portray as strong behaviour as seenin some tests.
� It is understood that DONG has experienced higher stiffness than API soft clay formulation
Jan K Rønberg21London Array
than API soft clay formulation describes
� Conclusion
� stiff clay;– no large pile diameter effect
Geotechnical
� Pile length criteria, λ : Optimization obtained, λ may be relaxed further
� Toe Shear at pile tip : Optimization obtained, could use better curve than bi-linear
� Large Pile Diameter effect: No gain, but observed higher stiffness shouldbe further looked into
Jan K Rønberg
Project information from actual projects could close information gap and increase optimization further
22Sept. 2011 - Offshore konference - Esbjerg
Structural
� Eigenfrequency calculation – Load determination
� Grouted connection
� Appurtenances
Jan K Rønberg23Sept. 2011 - Offshore konference - Esbjerg
Structural
� Eigenfrequency calculation – FLS load dependant on eigenfrequency
Optimization based on FLS load calculations for different lower bound eigenfrequencies for the different load classes. Sensitivity analysis showed that in some cases the design could be optimized by changing the lower bound frequencies for FLS load calculation
Jan K Rønberg24Sept. 2011 - Offshore konference - Esbjerg
MP/TP resultsEigen frequencies – preliminary design
0,29
0,3
0,31
0,32
0,33
0,34
0,35Eigenfrequency [Hz]
eigenfreq_ub
eigenfreq_lb
Lower Limit
Jan K Rønberg
0,25
0,26
0,27
0,28
0,29
0 5 10 15 20 25
Water depth [m]
Eigenfrequency [Hz]
Lower Limit
Upper limit
25
Sept. 2011 - Offshore konference - Esbjerg
Structural
� Eigenfrequency calculation – Load determination
We need to compare the true eigenfrequencies for the structures with the calculated eigenfrequencies to reduce the uncertainty in assessing the upper and lower limits.
WTG supplier to sharpen the upper and lower boundaries for Eigenfrequencies
Jan K Rønberg26Sept. 2011 - Offshore konference - Esbjerg
Grouted connectionModes of Moment Transfer
Jan K Rønberg
three general modes of transferring the momentum
27Sept. 2011 - Offshore konference - Esbjerg
Grouted connection Local Load Application
monopile,
grout
contact gap
Jan K Rønberg
gap
29Sept. 2011 - Offshore konference - Esbjerg
Grouted connection Modes of Moment Transfer
radial forces
µµµµ=0.8
Jan K Rønberg
Σ Fr = 39.2 MN (= 100%)
30Sept. 2011 - Offshore konference - Esbjerg
Grouted connection
� Grouted connection: Conical solution introduced
We need to understand actual behaviour of grouted connections from the projects now being implemented.
Jan K Rønberg31Sept. 2011 - Offshore konference - Esbjerg
Appurtenances
� Boatlanding
� External J-tubes including cages
Jan K Rønberg32Sept. 2011 - Offshore konference - Esbjerg
Boatlanding
Jan K Rønberg33Seminar , COWI 11th November 2010
Optimized Boat Landing Frame for energy absorption
Estimated reduction in steel approximately 20%
Steel Cages
Design Issues Design Issues Design Issues Design Issues –––– External JExternal JExternal JExternal J----tubes on steel cages for deeper turbine locationstubes on steel cages for deeper turbine locationstubes on steel cages for deeper turbine locationstubes on steel cages for deeper turbine locations
Increased hydrodynamic loads because of
- J-tubes
- cages
- anodes
Jan K Rønberg34Seminar , COWI 11th November 2010
Optimization could be attained through keeping cables internal
Would require new anode system, eg anode cluster in seabed.
Summary London Array
� Geotechnical
– λ, soil stiffness, toe shear further looked into
� Structural
– Eigenfreuncy boundaries and actual structural behaviour looked into
– Grouted connection behaviour to be observed
Jan K Rønberg
– Grouted connection behaviour to be observed
– Cages/external J-tubes to be assessed
37Sept. 2011 - Offshore konference - Esbjerg
Summary
All in all we need monitored information from actual projects.
The OWF market is big;
we need to establish the industry before
Jan K Rønberg
we need to establish the industry before we ensure competive edge
38Sept. 2011 - Offshore konference - Esbjerg
Summary
Vi skal have konkret viden fra realiserede projekter ind I design processen
Fra dagens øvrige deltagere:
Henrik Stiesdahl, Siemens:
- 'Vi kan regne alt det vi vil, det er I testen vi ser om det holder'
Jan K Rønberg39Sept. 2011 - Offshore konference - Esbjerg
Anders Søe Jensen, Vestas:
- ' Hvis vi ikke får Cost-of-Energy' ned slår vi hele industrien ned'