Offshore Windenergieanlagen – Wie baut man das aus

Offshore Windenergieanlagen – Wie baut man das aus

Offshore Windenergieanlagen
– Wie baut man das aus Beton?
Univ.-Prof. Dr.-Ing. Steffen Marx
Dipl.-Ing. Christoph von der Haar
Dipl.-Ing. Boso Schmidt
© DOTI GmbH
ForWind – Zentrum für Windenergieforschung
Oldenburg, 20.02.2014
CONCRETE?!
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 2
Concrete?!

Concrete ships
 First presented in 1855 on the
world fair in Paris
 Saving in steel ≤ 70%
www.schifffahrtsmuseum-rostock.de

Pre-stressed concrete wings
 First examinations in 1949
by E. Freyssinet
 80% lower production period
 15% higher weight
Brocard, M.J.; Bruner, M.G. (1953): Le béton
précontraint matériau de construction aéronautique
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 3
Concrete?!

Oil platforms
 Types of oil platforms
Chakrabarti, S. K. (2005): Handbook of
Offshore Engineering
Minerals Management Service (2000): Gulf of
Mexico Deepwater Operations and Activities
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 4
www.concretesubmarine.com
Concrete?!

Oil platform
 Troll A
Prof. Dr.-Ing Steffen Marx
Building of ballast tanks /
floating bodies
Building of the legs
Towing of the platform
Completed platform
OWEA – Wie baut man das aus Beton?
Slide 5
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 6
Concrete?!

Advantages of concrete towards steel
 Costs are less dependent on world market prices
 Higher durability in marine environment
 Low carbon footprint
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 7
EXPECTATIONS & CHALLENGES
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 8
Expectations & Challenges

Development of wind energy
WindGuard(2012): Status des
Windenergieausbaus in Deutschland
dena(2005):
dena-Netzstudie
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 9
Expectations & Challenges

Development of offshore wind energy
 German wind farms – Baltic Sea
operating
authorized /
under construction
Baltic 1
21 WEA
in authorization process
www.offshore-windenergie.net/windparks
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 11
Expectations & Challenges

Development of offshore wind energy

German wind farms – North Sea
operating
authorized /
under construction
in authorization process
Bard 1
80 WEA
Alpha Ventus
12 WEA
Prof. Dr.-Ing Steffen Marx
www.offshore-windenergie.net/windparks
OWEA – Wie baut man das aus Beton?
Slide 12
Expectations & Challenges

Trends of waterdepth & foundation concepts
RolandBerger(2013):
Offshore Wind toward 2020
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 13
FOUNDATION CONCEPTS
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 14
Foundation concepts

Gravity base foundation (GBF)
 Lower and medium water depths
 Low noise emission
 Self floating or transportation by
installation vessels / barges
 Preparation of the sea bed:
leveling, dreding, gravel bed
 Scour protection, skirt
www.4Coffshore.com
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 15
Foundation concepts

Gravity base foundation – Low water depths
 Wind farm Roedsand 2
(Denmark)
 Build 1991
 Baltic Sea
 Water depth 6 m - 12 m
 Reinforced concrete
 Normal strength concrete
Conical shaft to reduce
the impact of ice loads
© Aarsleff Bilfinger Berger Joint Venture
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 16
Foundation concepts

Gravity base foundation
– Low water depths
Transportation on barges,
as possible more than one
Lowering on the prepared sea bed
by an installation vessel
Openings for ballasting
with gravel
Construction in dry
docks, constr. yards
Prof. Dr.-Ing Steffen Marx
The Concrete Centre (2005):
Concrete Wind Towers
OWEA – Wie baut man das aus Beton?
Slide 17
Foundation concepts

Gravity base foundation
– Low water depths
Transportation on barges,
as possible more than one
Lowering on the prepared sea bed
by an installation vessel
Construction in dry
docks, constr. yards
Prof. Dr.-Ing Steffen Marx
The Concrete Centre (2005):
Concrete Wind Towers
OWEA – Wie baut man das aus Beton?
Slide 18
Foundation concepts

Gravity base foundation
– Low water depths
Transportation on barges,
as possible more than one
Lowering on the prepared sea bed
by an installation vessel
Construction in dry
docks, constr. yards
Prof. Dr.-Ing Steffen Marx
The Concrete Centre (2005):
Concrete Wind Towers
OWEA – Wie baut man das aus Beton?
Slide 19
Foundation concepts

Gravity base foundation – Medium water depths
 Wind farm Thornton bank (Belgium)
 Build 2007
 Water depths ≤ 28 m
 Repower 5M Ø 126m
 Wall thickness: 0.50 m
 Normal strength concrete
 32 post-tensioned tendons
between platform and
lower part of conical section
 Monopile?
Peire, K.; Nonneman, H.; Bosschem E. (2009): Gravity Base
Foundations for the Thornton Bank Offshore Wind Farm
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 20
Foundation concepts

Gravity base foundation
– Medium water depths
Scour protection and sand infill
Construction yard
Transport / layering by installation vessel
Peire, K.; Nonneman, H.; Bosschem E. (2009): Gravity Base Foundations for the Thornton Bank Offshore Wind Farm
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 21
Foundation concepts

Gravity base foundation – Further concepts
Hochtief/ Costain / Arup
Prof. Dr.-Ing Steffen Marx
Vici ventus
Skanska / SMIT / Grontmij
OWEA – Wie baut man das aus Beton?
Strabag / Züblin
Slide 22
Foundation concepts

Concrete filigree substructures (CFS)
 High and Ultra high performance
concrete
 Design of connection points
 Fatigue Design
Lang, M.; Bachmann, H. (2011): Gründung von
Offshore WEA aus filigranen Betonstrukturen…
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 23
Foundation concepts

Concrete filigree substructures (CFS)
 „Hexafix“ designed by
Oevermann GmbH & Co. KG
 Design of brace connection points
© Oevermann GmbH & Co. KG
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 24
www.ngi.no
Foundation concepts

Innovative concrete foundations
 Suction buckets
Institut für Massivbau, LUH
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 25
Foundation concepts

Innovative concrete foundations
 Floating
 Drilled concrete monopile
www.offshorewind.biz
Prof. Dr.-Ing Steffen Marx
© Ballast Nedam Offshore
OWEA – Wie baut man das aus Beton?
© Ballast Nedam Offshore
Slide 26
TOWER CONCEPTS
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 27
Tower concepts

Onshore concrete towers
 Cast-in-place
 Climbing / sliding formwork
Pictures: Nordex SE
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 28
Tower concepts

Onshore concrete towers
 Hybrid tower by Max Bögl
 Pre-cast elements
Horizontal joint: Polished
Vertical joint:
one segment out of two half
shells for transportation
Pictures: Max Bögl Wind AG
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 29
Tower concepts

Onshore concrete towers
 Forces in the joints
compression zone
tension zone
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 30
Tower concepts

Onshore concrete towers
 Primarily post-tensioned
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 31
EXTERNAL CONDITIONS & LOADS
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 32
External Conditions & Loads






Wind
Waves
Current
Sea level
Sea ice
Operating conditions
Herklotz, K. (2013): Oceanographic
Measurements
www.ramboll.com
Prof. Dr.-Ing Steffen Marx
www.fino-offshore.de
OWEA – Wie baut man das aus Beton?
Slide 33
External Conditions & Loads

Rules & Guidelines
 Approval for Offshore Wind Farms is granted by BSH
 BSH requires a certification
GL (2012): Guideline for the
certification of offshore wind turbines
Prof. Dr.-Ing Steffen Marx
DNV (2007): Design of offshore
wind turbine structures
OWEA – Wie baut man das aus Beton?
DIN EN 61400-3 (2009): Design
requirements for offshore wind turbines
Slide 34
External Conditions & Loads

Design load cases
(extract from
GL-2012)
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 35
External Conditions & Loads

Environmental design parameters
 Design parameters of “normal” external conditions in scatter diagrams
 Based on measurements and/or Hindcasts
 Associated design parameters including frequency of occurrence (important for FLS)
Grünberg (2011): Windenergieanlagen in Stahlbeton- und Spannbetonbauweise
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 36
External Conditions & Loads
0,45
0,40
Environmental design
parameters
0,35
Frequency [-]

 No measurements of extreme
design parameters
0,30
0,25
Histogramm
0,20
Gumbel-Verteilung
0,15
0,10
0,05
0,14
0,00
0
1
2
3
0,12
4
5
6
7
8
9
10
11
12
13
Significant wave height [m]
Frequency [-]
0,1
Histogram
 Statistical methods for
extreme events
 Gumbel distribution
approximates extreme wind
speed & significant wave very
well
0,08
Gumbel-Verteilung
0,06
0,04
0,02
0
0
5
10
15
20
25
30
35
40
45
50
Wind speed [m/s]
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 37
External Conditions & Loads

Environmental design parameters
 Design parameters of extreme external Conditions
Parameter
Distribution
mExt
σExt
a
u
[m]
[m]
[m-1]
[m]
Hs (One year extreme)
Gumbel
7,091
1,311
0,979
6,501
Vref (One year extreme)
Gumbel
31,368
4,123
0,311
29,513
Hs50 = 10,49 m (~ 19,5 m max wave height)
Vref = 42,06 m/s
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 38
External Conditions & Loads

Comparison measurements and guidelines
 Wind profile with a return
period of 50 years based
on measurements and
GL-Guideline
 Measured profile runs
steeper compared to the
GL-wind profile
 Adaption of exponent
improved compliance for
the location FINO 1
120
Wind speed by evaluating the
Gumbel distribution
Height [m]
100
80
Wind speed by evaluating the
Gumbel distribution with
regression analysis
60
Wind speed according to the
exponantial function in [GL]
Wind speed according to the
exponantial function in [GL] with
alpha=0,09
40
20
0
0
5
10
15
20
25
30
35
40
Wind speed [m/s]
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
45
Hansen et al. (2012): Probabilistic
Safety Assessment of Offshore Wind
Turbines, Annual Report 2011
Slide 39
External Conditions & Loads

Sensitivity of design parameters
 Extreme value distribution to describe areas of high quantiles
 Decreaising population for extreme value distributions
fu(x)
Distribution of the
population
Distribution of
extremes (Gumbel Typ
1 for maximum values)
Distribution of
extremes (Gumbel Typ
1 for minimum values)
x
Schmidt (2013): Langzeitstatistik von Wellenhöhen am Standort der FINO 1 Messplattform
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 40
External Conditions & Loads
Based on
6h-extremes
Based on
1day-extremes
Based on
4week-extremes
Based on
1week-extremes
12

Sensitivity of design parameters
Based on
1day-extremes
Based on
6h-extremes
Based on
4week-extremes
Based on
1week-extremes
Significant wave height [m]
10
8
6
Mean value and standard deviation
(Gumbel distribution of one year
extreme values)
4
98% quantile of Gumbel distribution
2
60
0
0
100
300
400
500
600
700
800
Number of 1h-extremes per extreme event [-]
50
Wind speed [m/s]
200
 Influence of different
observation periods for
extreme extrapolations
 After a period of more than
one week for determining
extreme values, both mean
values and quantiles run
up against a limit
40
30
Mean value and standard deviation
(Gumbel distribution of one year
extreme values)
20
98% quantile of Gumbel distribution
10
0
0
100
200
300
400
500
600
700
800
Number of 1h-extremes per extreme event [-]
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 41
External Conditions & Loads
2,0
Averages of Hs
1,8
Sensitivity of design parameters
 Seasonal influences (here:
exemplary one year)
1,4
1,2
Hs [m]

1,6
1,0
0,8
0,6
0,4
0,2
0,0
12,0
Averages of Wind speed
Wind speed [m/s]
10,0
Months [-]
8,0
Failures of measurements
6,0
 Design parameter based on winter
months are ~ 10 % higher
 Smaller population
 Design parameter are more uncertain
to determine
4,0
2,0
0,0
Months [-]
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 42
External Conditions & Loads
0,45

Sensitivity of design parameters
0,40
 Local dependence
0,35
Probability density function
of 1 week extreme values at
FINO 1
Frequency [-]
0,30
0,25
Probability density function
of 1 week extreme values at
FINO 3
0,20
0,15
0,10
0,05
0,00
4
5
6
7
8
9
10
11
12
13
Hs [m]
Location
Prof. Dr.-Ing Steffen Marx
Water depth
Distribution
mExt
σExt
V
Hs50
[m]
[m]
[-]
[m]
FINO 3
22 m
Gumbel
6,893
1,227
0,178
10,07
FINO 1
30 m
Gumbel
7,091
1,311
0,185
10,49
OWEA – Wie baut man das aus Beton?
Slide 43
14
External Conditions & Loads

Directional dependence of V and Hs
360°
345°
330°
360°
15°
35
30°
30
315°
345°
330°
45°
25
20
300°
10
300°
75°
60°
6
4
285°
75°
2
5
270°
45°
8
15
285°
30°
10
315°
60°
15°
12
90°
0
255°
105°
240°
120°
225°
135°
210°
150°
195°
270°
90°
0
255°
105°
240°
120°
225°
135°
210°
165°
150°
195°
180°
165°
180°
Directional distribution average wind speed [m/s]
Directional distribution average significant wave height [m]
Directional distribution maximum wind speed [m/s]
Directional distribution maximum significant wave height [m]
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 44
External Conditions & Loads

Temporal correlation of V and Hs
 There are few data
for extreme wind
speeds and wave
heights
 Maximum wind
speed and wave
height do not occur
simultaneously
40
35
VWind [m/s]
30
25
20
15
10
5
0
0
1
2
3
4
5
6
7
8
9
10
Hs [m]
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 45
WAVE LOADS
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 46
Wave loads

Hydrodynamic load determination for offshore structures
 Morison equation widely used
𝒇 𝒕 = 𝒄𝑴 ∙ 𝝆 ∙
𝝅 ∙ 𝑫𝟐 𝝏𝒗 𝒕
𝝆
∙
+ 𝒄𝑫 ∙ ∙ 𝑫 ∙ 𝒗 𝒕 ∙ 𝒗 𝒕
𝟒
𝝏𝒕
𝟐
 Only valid for hydrodynamically transparent cylinder
 Assumption: structure does not affect the wave
© WaveLoads
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 47
Wave loads

Special aspect of the hydrodynamic load determination for compact concrete
structures
 The structure affects the wave
 Diffraction effects are not taken into account by the morison equation
 From a ratio structure diameter (D) / Wavelength (L) > 1 / 5 diffraction
effects become more important
 Effects which significantly increase hydrodynamic loads can even occur for
very small ratios
 CFD-Methods are able to consider diffraction effects
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 48
Wave loads

Wave length in the North Sea
0,030
Frequency [-]
0,025
The Concrete Centre (2005):
Concrete Wind Towers
0,020
Peire, K.; Nonneman, H.; Bosschem E.
(2009): Gravity Base Foundations for the
Thornton Bank Offshore Wind Farm
Histogram
0,015
Weibull-distribution
0,010
0,005
0,000
0
20
40
60
80
100
120
140
160
180
3h-averages of wave length [m]
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
200
 Weibull-distribution well
approximates average
wave length
 A not insignificant
proportionof waves leads
to D/L > 1/5
 Diffraction effects may
also occur in sub sections
Slide 49
Wave loads

Morison and CFD in comparison
 Differences of min. Shear
forces and moments resulting
from diffraction effects
 The structure influences the
wave => less strong restoring
forces/moments
400,00
300,00
Shear force (Morison)
100,00
0,00
0,00
Shear force (CFD)
0,50
1,00
1,50
2,00
2,50
3,00
3,50
4,00
4,50
-100,00
6000,00
-200,00
4000,00
-300,00
-400,00
Moment at top edge
foundation (Morison)
2000,00
Time [s]
 Investigation of a modal wave
 D/L = 1/4
 Good agreement of max.
shear forces
Moment [kNm]
Shear force [kN]
200,00
0,00
0,00
Moment at top edge
foundation (CFD)
0,50
1,00
1,50
2,00
2,50
3,00
3,50
4,00
-2000,00
-4000,00
-6000,00
Time [s]
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 50
4,50
Wave loads

Flow effects at extreme waves
 Wave run up on the front
side
 High bending moments
due to large lever arm
 Flow directed towards
wave direction on the
back side
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 51
Wave loads

Flow effects at extreme waves
 A “normal” extreme wave
 By interaction with the structure
the wave becomes steeper
Nearly breaking wave,
wave run up and
increasing wave loads at
the upper part of the
foundation
 Calculations by Morison not
capture these effects
Prof. Dr.-Ing Steffen Marx
OWEA – Wie baut man das aus Beton?
Slide 52
Offshore Windenergieanlagen
– Wie baut man das aus Beton?
Thank you for your attention!
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