Design af monopæle til havvindmøller

Transkript

1 Design af monopæle til havvindmøller kan vi gøre det bedre? Christian LeBlanc Thilsted, M.Sc., Ph.D.

2 Agenda 1. Offshore Vind i DONG Energy 2. Historik bag P-Y Ykurver 3. P-Y kurvernes utilstrækkelighed 1. Moment kapacitet 2. Akkumulerede deformationer 3. Dæmpning 4. Stivhed 4. Udvalgte resultater 1. Beregning af akkumulerede deformationer 2. Måleresultater fra Horns Rev 1 3. Dæmpning 5. Aktuelle tiltag i DONG Energy 2

3 Offshore Wind in DONG Energy DONG Energy's Vision DONG Energy Offshore wind farm support structures - a key technology area DKK 1,000 million spent annually on support structures Development of foundations has a high priority Frederikshavn Offshore Tunø Knob Wigtown Bay Horns Rev II Middelgrunden Horns Rev I Vindeby Walney II Barrow Nysted Walney I West of Duddon Borkum Riffgrund II Sands Shell Flat Burbo Westermost Borkum Riffgrund I Rough In operation Gunfleet Sands London Array II Under construction Scarweather London Array I Sands Maturation / Analysis 3

5 Historik bag P-Y kurver P-Y kurver: Simpel beregningsmetode (Winkler model) Fleksibelt kan håndtere et vilkårligt antal jordlag og forskellige typer jordlag. Pålidelig anvendt i vid udstrækning (konstruktionerne vælter ikke) Er P-Y kurverne tilstrækkelige til at designe offshore vindmølle fundamenter? Kan vi gøre det bedre? 5

6 Historik bag P-Y kurver The p y curves for piles in sand described by Reese et al. (1974) and O Neill & Murchison (1983) led to recommendations in the standards (DNV, 1977; API, 1993) 6

8 P-Y kurvernes utilstrækkelighed Moment kapacitet Skala effekter? Effekt af tip resistance? Diameteren på monopæle er ca. 10 gange større end reference pælene Stiv vs. fleksibel Lagdelt jord? Reference pæle er fleksible, men monopæle er stive 8

9 P-Y kurvernes utilstrækkelighed Akkumulerede deformationer Long-term cyclic loading from wind and waves: accumulated deformations and changes in stiffness Excessive deformations reduce fatigue life of support structure, machine components and blades 9

10 P-Y kurvernes utilstrækkelighed Stivhed Initial stivhed er uafhængig af diameter p [MN] D=6m 1.2 D=6m D=5m D=5m 1 D=4m D=3m D=4m D=2m D=3m 0.6 D=1m D=2m 0.2 z=5m y displacement [m] p [MN] p D=1m z=100m y displacement [m] Initial stivhed stiger lineært med dybden 0 5 Depth [m] P Y stiffness [MPa] Christian LeBlanc Thilsted, Design af Offshore vindmøllefundamenter, 12 th 10November 2009

11 P-Y kurvernes utilstrækkelighed Dæmpning Dæmpning fra jorden? 11

12 P-Y kurvernes utilstrækkelighed Cykliske laster? Evolution of stiffness 12

13 P-Y kurvernes utilstrækkelighed Partielt drænede tilstande Partielt drænede tilstande (silt) hvilke P-Y kurver skal vi anvende? 13

15 Udvalgte resultater Beregning g af akkumulerede deformationer A conceptual model, capable of predicting accumulated rotation and changes in stiffness of monopiles Publications: LeBlanc, C., Houlsby, G. T. & Byrne, B. W. Response of stiff piles in sand to long-term cyclic lateral loading. Geotechniqué, Accepted for publication. LeBlanc, C., Byrne, B. W. & Houlsby, G. T. Response of stiff piles to random two-way lateral loading. Geotechniqué, Accepted for publication. Applied to HR2: Worst transient load constitutes 68 % of the total accumulated rotation Christian LeBlanc Thilsted, Design af Offshore vindmøllefundamenter, 12 th 15November 2009

16 Udvalgte resultater Måleresultater fra Horns Rev 1 Above seabed Below seabed 16

17 Udvalgte resultater Måleresultater fra Horns Rev 1 The measured response is 30-50% smaller than the response predicted by the p-y curves developed upon the original soil data. Attempts to increase stiffness: Non-conservative soil interpretation The possible effect of a large diameter is taken into account by increasing k by a factor 2. The stiffness as function of pressure is described by Generally, all attempts to increase the pile response results in larger moments than measured! Publications: i Revisiting monopile design using p-y curves - Results from full scale measurements on Horns Rev, T. Hald, C. LeBlanc, C. Mørch, L. Jensen, K. Ahle, EOW 2009 Christian LeBlanc Thilsted, Design af Offshore vindmøllefundamenter, 12 th 17November 2009

18 Udvalgte resultater Soil damping Current approach assumes e.g. log. decr. δ modal = 6% Measurements from emergency stops at Horns Rev 1 and Burbo, i.e. no aerodynamic damping: δ modal > 10% (δ 2πζ, ζ = damping ratio) 80 m 0.3 Hz δ modal 3%-5% D=4.7 m Publications: 20 m Comparing Sources of Damping of Cross-Wind Motion, N. J. Tarp-Johansen Johansen, L. Andersen, E.D. Christensen, C. Mørch, B. Kallesøe, S. Frandsen., EOW 2009 Christian LeBlanc Thilsted, Design af Offshore vindmøllefundamenter, 12 th 18November 2009

20 Aktuelle tiltag i DONG Energy 1. P-Y kurver for sand EFP Numerical and physical modeling of laterally loaded of pile in sand subject to cyclic loading (AAU, DTU, DONG Energy) 2. P-Y kurver for ler ( ) EPSRC (Engineering and Physical Sciences Research Council) Cyclic Behaviour of Monopile Foundations for Offshore Wind Farms (Cambridge University, DONG Energy) 3. Numerisk evaluering af dæmpning (University of Stuttgart, DONG Energy) 4. Pressuremeter tests in future site investigations (DONG Energy) 20

21 Aktuelle tiltag i DONG Energy 5. Fuld-skala måleprogram i Walney Offshore Wind Farm (2010) (DONG Energy) Strain gauges Optical strain gauges (fiber Bragg gratings) Temperature sensors Inclinometers Accelerometers 21

22 Spørgsmål? 22