london array - windpower · kan fundamenterne optimeres i fase 2 erfaringerne fra london array...

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


Employer : DONG (50%) E.ON (30%) Masdar (20%)

Client : Aarsleff / Bilfinger | Berger JV, ABJV

Designer : COWI,IMS JV , CIJV

London Array


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


• Monopiles

• No scour protection

London Array


MP/TP resultsGlobal scour range

Maximum: 16.90 m

Minimum: 2.00 m


� Two types of MP:

- 4,7 m diameter- 5,7 m diameter

� Five types of TP

� Four types of cages

London Array


� Four types of cages

Overview of weights


London Array


Geotechnical

� Pile length criteria

� Toe Shear at pile tip

� Large Pile Diameter effect


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


� 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


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


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


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


Grouted connectionModes of Moment Transfer

Jan K Rønberg

three general modes of transferring the momentum


Grouted connection Local Load Application

monopile,

grout

contact gap

Jan K Rønberg

gap


Grouted connection Modes of Moment Transfer

radial forces

µµµµ=0.8

Jan K Rønberg

Σ Fr = 39.2 MN (= 100%)


Grouted connection

� Grouted connection: Conical solution introduced

We need to understand actual behaviour of grouted connections from the projects now being implemented.


Appurtenances

� Boatlanding

� External J-tubes including cages


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


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


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'


Anders Søe Jensen, Vestas:

- ' Hvis vi ikke får Cost-of-Energy' ned slår vi hele industrien ned'

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