London Array. Kan fundamenterne optimeres i fase 2. Erfaringerne fra London Array. Jan K Rønberg. Project and Market Director COWI.

Transcription

1 London Array Kan fundamenterne optimeres i fase 2 Erfaringerne fra London Array Project and Market Director COWI 1

2 London Array Agenda Presentation of London Array project Geotechnical Structural 2

3 London Array Employer : DONG (50%) E.ON (30%) Masdar (20%) Client : Aarsleff / Bilfinger Berger JV, ABJV Designer : COWI,IMS JV, CIJV Certifying body : DNV 3

4 London Array Phase wind turbines SWP 3.6 MW MW Water depth: 0-25 m Monopiles No scour protection 4

5 London Array 5

6 MP/TP results Global scour range Maximum: m Minimum: 2.00 m 6

7 London Array Two types of MP: - 4,7 m diameter - 5,7 m diameter Five types of TP Four types of cages 7

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9 Overview of weights 9

10 London Array 10

11 Geotechnical Pile length criteria Toe Shear at pile tip Large Pile Diameter effect 11

12 Case History zero toe-kick vertical tangent rotation criterion? ULS stability Nov 2010 London Array

13 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. y toe y pl P to e Toe-Shear Response y pl y 11 Nov London Array

14 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 11 Nov London Array

15 Pile Toe Rigidity Critical Pile Length The elastic or critical length L c gives the length of the pile that is mainly responsible for the pile head deformation. Pile Slenderness The pile slenderness λ characterises the response of the soil-pile system. In layered soils and for piles with differing wall thickness L c can not be calculated directly. But it can be determined from the pile head rotation vs. length curve. λ = L L c from Reese & Van Impe, 2001 Pile head rotation, α [ ] insuffic ient robust ness NC19 ND17 NG14 NG17 NI09 NJ λ [-] 11 Nov London Array

16 Pile Length Criteria 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, 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 London Array

17 P-y curves Large pile diameter effect studied API p-y curves for soft clay do not portray as strong behaviour as seen in some tests. It is understood that DONG has experienced higher stiffness than API soft clay formulation describes Conclusion stiff clay; no large pile diameter effect 21 London Array

18 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 should be further looked into Project information from actual projects could close information gap and increase optimization further 22

19 Structural Eigenfrequency calculation Load determination Grouted connection Appurtenances 23

20 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 24

21 MP/TP results Eigen frequencies preliminary design 0,35 0,34 0,33 Eigenfr requency [Hz] 0,32 0,31 0,3 0,29 0,28 0,27 0,26 eigenfreq_ub eigenfreq_lb Lower Limit Upper limit 0, Water depth [m] 25

22 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 26

23 Grouted connection Modes of Moment Transfer three general modes of transferring the momentum 27

24 Grouted connection Local Load Application monopile, grout contact gap 29

25 Grouted connection Modes of Moment Transfer radial forces µ=0.8 Σ F r = 39.2 MN (= 100%) 30

26 Grouted connection Grouted connection: Conical solution introduced We need to understand actual behaviour of grouted connections from the projects now being implemented. 31

27 Appurtenances Boatlanding External J-tubes including cages 32

28 Boatlanding Optimized Boat Landing Frame for energy absorption Estimated reduction in steel approximately 20% 33 Seminar, COWI 11 th November 2010

29 Steel Cages Design Issues External J-tubes on steel cages for deeper turbine locations Increased hydrodynamic loads because of - J-tubes - cages - anodes Optimization could be attained through keeping cables internal Would require new anode system, eg anode cluster in seabed. 34 Seminar, COWI 11 th November 2010

30 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 Cages/external J-tubes to be assessed 37

31 Summary All in all we need monitored information from actual projects. The OWF market is big; we need to establish the industry before we ensure competive edge 38

32 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' 39