Upload
hakhuong
View
226
Download
1
Embed Size (px)
Citation preview
1
DEPARTMENT OF ENGINEERING SCIENCE
September 4, 2013
Foundations for Offshore Wind
Turbines
Byron Byrne and Guy Houlsby SUPERGEN Wind 7th Training Event
Overview
This presentation focuses on foundation design for offshore wind energy applications
Refers to the interaction between the structure and the ground
Loading and structural design also very important
Many turbines for each site (say 30 to 100 or more) over a large site area
Foundation significant fraction of the installed cost
Different problem to bespoke oil and gas foundation design
Site conditions can vary markedly across a site (e.g. factor 10 on
strengths in some areas, layered materials, sand waves etc)
Good characterisation of the site early on very important for
developing realistic designs (but minimal coverage likely)
Page 2
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
2
90m to 120m
90m
to
120m
1MN to 2MN
3MN to 8MN
~6MN
200MN
25MN
Page 3
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Loads on an Offshore Turbine Foundation
(b)(a)
V
H
V
H
V
H
M
H2H1
V2
V1
Page 4
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
3
Foundation stiffness
The main excitation frequencies
are 1P (the rotational
frequency) and 3P (the blade-
passing frequency)
These must be avoided
The flexibility of the foundation
reduces the natural frequency
k
EI
m
L
k
L
EI
Lm
fn 23
3
1
2
1
Page 5
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
frequency
DAF
1P 3P
1.0
Structural Response
Page 6
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
4
Options for foundations
sD
LD
L
(g) (h) (i)(f)(e)(d)(c)(b)(a)
(j)
(k)
Page 7
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
CURRENT DESIGNS PILE FOUNDATIONS
Page 8
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
5
Mono-Pile Foundations
A wind turbine monopile is at least 4m diameter and of the order of 25m long
Driving is at the limits of offshore oil-and-gas experience which typically involves smaller diameter (~2m) and longer piles (~100m)
Large diameter drilling is suitable in certain materials
Options:
drive
drill and grout
composite e.g. drive-drill-drive
Mono-Pile Multi-Pile
L
D
L
D
s
Page 9
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
“Monopile” Foundations
Average 89
hours per pile
at North Hoyle Image/Notes from www.foundationworld.org.uk
Page 10
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
6
Walney Wind Farm
Photos from Dong Energy: Christian LeBlanc Thilsted and Dan Kallehave
Page 11
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Pile Design Issues – Wind Turbine
Stiffness is the over-riding design criterion rather than capacity.
Various offshore design approaches (API, DNV) are based on much more flexible piles and are more concerned with lateral capacity than stiffness.
Typical offshore pile say L/D ~ 30 – 50 or more whilst wind-farm pile L/D ~ 4 – 8.
Are the usual design approaches still appropriate?
Performance under cyclic loading is important
Accumulated rotations?
Stiffness response?
Page 12
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
7
Experiment
Motor
Reaction Frame
Mass
Mass
Mass
Page 13
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Research Results two way
one way
h
L
D
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0 0.002 0.004 0.006 0.008 0.01 0.012
No
rma
lis
ed
Mo
me
nt
Normalised Rotation
Cycle 0 - 10 Cycle 1500 - 1510 Cycle 9050 - 9060
Page 14
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
8
Summary of Research Output
Framework developed for calculating accumulated rotation Results indicate change in pile stiffness with cycle number
Effect on natural frequency of structure and implications for fatigue
Limitations include scaling, cycle numbers, loading direction…
Additional laboratory testing addressing these areas
Ongoing research…
Monitoring of structures in the field
Assessment of actual loading conditions and foundation response
(e.g. moment distribution)
Large scale field tests
Better basis for design methodology development
Page 15
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Basis for developing modified design methodologies
Full Scale Results – Standard Systems
Standard API p-y
formulation
Modified p-y
formulation Data and photos from DONG Energy: Christian LeBlanc Thilsted and Dan Kallehave
Page 16
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
9
Field Monitoring
Data currently being gathered from installed piles
Verify design calculations
Guidance for future designs
Database for the industry?
Data and photos from DONG Energy: Christian LeBlanc Thilsted and Dan Kallehave
Page 17
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Measured Strains
Data and photos from DONG Energy: Christian LeBlanc Thilsted and Dan Kallehave
0 5 10 15 20 25
Time [s]
Page 18
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
10
Large Scale Pile Testing – PISA Project
Figure from Christelle Abadie, PhD student funded by EDF; Photo of field pile load test from Ken Gavin, University College Dublin
Page 19
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Page 20
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
11
Multi-Pile Foundations
Much more like typical oil and gas pile design
…except…
Any cyclic degradation of the axial response must be well understood
Mono-Pile Multi-Pile
L
D
L
D
s
Page 21
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Current designs Alpha Ventus
Bard Offshore 1
Beatrice
Page 22
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
Source: Various websites
September 4, 2013
12
FUTURE DESIGNS? SUCTION CAISSONS
Page 23
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Caisson Foundations
Design Issues
Suction installation
Combined Loading (mono-caisson)
Vertical Loading (multi-caisson)
Research
Laboratory testing
Field scale testing
Theoretical investigations
Numerical modelling
Focus here is on work at Oxford
Mono-Caisson Multi-Caisson
L
Ds
L
D
Page 24
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
13
Suction Caissons
Flow
Pressure differential
W
Flow
Page 25
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
Source: Houlsby, G.T., Ibsen, L.B. and Byrne, B.W (2005) "Suction caissons for wind turbines",
Invited Theme Lecture, Proc. International Symposium on Frontiers in Offshore Geotechnics, Perth,
Australia, 19-21 September, Taylor and Francis, pp 75-94, ISBN 0415 39063 X
September 4, 2013
Mobile met mast application (DONG, 2009)
Source: C.L. Thilsted, PhD Thesis
Page 26
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
14
M
2R
Lt
Research Methodology
Laboratory model tests
Theoretical analyses
Calibrate theory
against tests to
develop design
methods
Field trials
Validated
design
methods
Page 27
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Field Installation - 3m diameter
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30 35
Dis
pla
ce
me
nt (m
m)
Suction (kPa)
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30 35
Dis
pla
ce
me
nt (m
m)
Suction (kPa)
Page 28
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
15
“Hardening Plasticity” Models
Plasticity models require
Yield Surface
Hardening Rule
Flow Rule
Elasticity Expressions
Suitable for coupling with structural calculations
M
V
H
2R
Page 29
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Experimental equipment
Page 30
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
16
Field Testing at Bothkennar
Page 31
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Moment Test Results (Clay)
Page 32
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
17
-100
-80
-60
-40
-20
0
20
40
60
80
100
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
Mo
me
nt
Lo
ad
, M
/2R
(N)
Rotational Displacement, 2Rq (mm)
-100
-80
-60
-40
-20
0
20
40
60
80
100
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
Mo
me
nt
Lo
ad
, M
/2R
(N)
Rotational Displacement, 2Rq (mm)
Comparison of Theory to Experiment
Page 33
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Loads on an Offshore Turbine Foundation
(b)(a)
V
H
V
H
V
H
M
H2H1
V2
V1
Page 34
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
18
Tripod or tetrapod?
Tower
Tower
Tower
(a) (b) (c)
Page 35
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Multiple caissons: Europipe platform
Page 36
Source: Andersen, K.H., Jostad, H.P. and Dyvik, R. (2008) "Penetration resistance of offshore skirted foundations
and anchors in dense sand", Proc ASCE Journal of Geotechnical and Geoenvironmental Engineering, Vol 134, No 1,
pp 106 - 116.
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
19
Vertical Loading Tests (Sand)
Com
pre
ssio
n
Tension
Page 37
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Summary of Research Outputs
Caisson design approaches supported by a range of experimental and field scale data
Installation
Cyclic loading
Monotonic loading
Sand / Clay and layered soils
Stiffness / Capacity
Issues of scalability need to be investigated further
Only by larger scale trial offshore…
Page 38
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
20
Other possibilities - Helical Screw Piles
(a) (b) (c) (d) (e)
Page 39
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Helical Screw Piles Characteristics
Good tension capacity
Applicable to a range of soil conditions
Reusable - piles can be “unscrewed”
Installation
Torque motors smaller than pile drivers
Over water or under water possibilities
Quick and quiet installation process
Design approaches
Pile design verified during the SI phase
CPT correlations with pile design
Further SI during pile installation
Torque data can verify capacity
M
V
H
(f) (g)
Page 40
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
21
Scale of Design for Offshore
Small onshore turbine – 50kW V = 50 kN, H = 60 kN, M = 1.4 MNm 2m by 2m grillage system with 9 screw piles
helical flights approximately 0.5m diameter
installed with torque of 60kNm
Large offshore turbine – 3 MW turbine in 19m water depth V = 6 MN, H = 6.5MN, M = 160 MNm 30m by 30m tetrapod structure with screw piles at each corner
helical flights approximately 2.0m
installed with torque of 1.5MNm
Page 41
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013
Summary
Offshore wind energy will require significant geotechnical design efforts going forward
Monopile designs are currently used though there are concerns about design approaches and the effects of cyclic loading
More innovative suction caisson foundations could be used and the next step is a larger scale offshore trial
Other more radical solutions might involve helical screw piles but this would involve significant upscaling from onshore designs
Page 42
Foundations for Offshore Wind Turbines
Byron Byrne and Guy Houlsby
SUPERGEN Wind 7th Training Event
September 4, 2013