This document discusses the planning of an offshore wind farm in the Mediterranean Sea. Key details include:
- The wind farm would consist of 105 turbines with a capacity of 315-525 MW located 10 km offshore in 20-35 meters of water.
- Site selection considered technical, financial, and environmental factors like seabed depth and distance from coast.
- Energy production is estimated at 919 GWh annually based on wind conditions and turbine specifications.
- Structural, geotechnical, seismic, and metocean analyses were performed to inform the design. A jacket foundation structure was selected.
- The project aims to highlight the role of analysis in decision making for an offshore wind farm in a challenging Mediterranean environment.
Construction Documents Checklist before Construction
7 - Planning of an Offshore Wind Farm in the Mediterranean Sea - Gkoumas
1. PlanningofanOffshoreWindFarmintheMediterraneanSea
Vladimiro Rotisciani1
Salvatore Miliziano2
Franco Bontempi2
Konstantinos Gkoumas2
1ICARIA srl
2University of Rome “La Sapienza”
12th International Conference
ON ENGINEERING, SCIENCE, CONSTRUCTION AND
OPERATIONS IN CHALLENGING ENVIRONMENTS
EARTH&SPACE 2010
MARCH 14-17, 2010 Honolulu, HI
“Planning of an Offshore Wind Farm in the
Mediterranean Sea”
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PlanningofanOffshoreWindFarmintheMediterraneanSea
1
Objective
• To expose the main aspects influencing the
basis of the design of offshore wind turbine
(OWT) structures for an OWF in Central Italy
§ the essential role of the structural analysis
supporting the decisional process is
enlightened
• The project under consideration is characterized
by elevated complexity due to the harsh
environment, and the innovating characteristics,
being, among else, the support structures
placed in elevated depth, in the range of 20-35
meters.EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Presentation outline
• Offshore Wind Farms
• Advantages and trends
• Recent realizations
• Proposed OWF in the Mediterranean Sea: key facts
• Site location
• Energy production
• Geologic and geophysical characterization
• Geotechnical characterization
• Seismic response
• Meteo-marine conditions
• Structural analyses
• Additional aspects
• Conclusions and overview
2EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Offshore Wind Farms
Advantages and trends
• Advantages
• Considerably stronger, more consistent and less turbulent
wind speeds offshore
• increased power production.
• Reduced visual impact as they are placed far away from the
coast
• Future trends*
• Cumulative Offshore Europe: 1.9 GW-40 GW (2008-2020)
• Offshore wind share: 3.9% (2008), 25% (2020)
• It can be expected that total offshore wind capacity will
exceed onshore capacity at some point beyond 2030
*Pure Power: Wind energy targets for 2020 and 2030:
A report by the European Wind Energy Association - 2009 update
3EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Recent realizations of OWF’s
4EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
Commissioned:
September 2009
Location:
15-30 km / 10-20 miles
off the westernmost
point of Denmark,
Blåvands Huk
Installed capacity:
209 MW
Turbines:
91 Siemens SWP 2.3-93
Water depth:
9-17 meters
Foundation:
monopile
Horns Rev 2
Photograph: MEDVIND/BENT SOERENSEN
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Recent realizations of OWF’s (2)
5EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
Operation:
2010/11
Location:
100 kilometres (62 mi)
northwest of the isle
Borkum, in Germany
Capacity:
400 MW
Turbines:
80 BARD 5.0
Water depth:
about 40 meters
Foundation:
BARDTM triple
Demonstration turbine at Hooksiel
Bard Offshore 1
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PlanningofanOffshoreWindFarmintheMediterraneanSea
6
Nominal power of a single turbine 3.0÷5.0 MW
Number of turbines 105
Hub height 100 ÷ a.s.l.
Nominal power of a the farm 315 ÷ 525 MW
Minimum distance from the shore 10 Km
Surface of the farm area 67.20 Km2
Water depth 20-35 m
Life span 29 years
Offshore wind farm: key facts
6EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Site location
• Choosing the OWF site location was the result of a
series of technical, financial and environmental
considerations
– the seabed morphology (seabed depth of 35 meters or
lower);
– the large minimum distance from the coast (10 km),
something that influences positively the visual impact;
– the absence of environmental, territory or archeological
issues;
– the anemometric conditions;
• In the vast area other (inshore) wind farms are sited, a
factor that identifies it as a key area for wind energy
production
99EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Energy production estimation
• On the basis of the anemometric survey and the performed
simulations, it was possible to estimate the energy production
of the OWF.
• For this aim the utilization of Vestas V90 wind turbines with a
3.0 MW nominal power has been
• The energy produced of each of these turbines results being
between 7000 and 9100 MWh (the maximum value
corresponds to the maximum distance from the shore).
• A layout in 7 rows of turbines, with 15 turbines at each row, for
a total 105 turbines has been considered. The orientation is on
the South-East/North-Ovest axis (prevalent wind direction)
10
Emin [GWh] Emax [GWh] Etot [GWh] Range [Km2]
8.66 8.94 919.99 67.20
10EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Wake effect losses
• Wake effect: “the aggregated influence on the energy production
of the wind farm, which results from the changes in wind speed
caused by the impact of the turbines on each other”.
• On the basis of models found in literature, the wake effect losses
have been estimated for three different turbine types:
– Vestas V90 (3.00 MW)
– GE Energy 3.6r (3.6 MW)
– Repower 5M (5.00 MW)
11
Turbine Ø (m) ØP ØO PL estimation (%)
Vestas V90 90 ØP = 11 ØO = 9 ≤ 8.7 %
GE Energy 3.6r 111 9 < ØP < 10 7 < ØO < 8 ≤ 8.7 %
Repower 5M 126 ØP ~ 8 6 < ØO < 7 8.7% ≤ PL ≤ 10.0%
11EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Meteo-marine conditions
• Available historical data of direct measurements of the
surface waves have been gathered, and following
analysis and numerical elaboration, the boundary
conditions forming the basis for the wake propagation
modeling have been set. On the basis of such
propagation model, the maximum wave heights have
been calculated.
• In order to obtain the proper combination of wind and
wave characteristics, a prognostic model has been
applied on a finer mesh (local area model), on the basis
of wind profiles on the points of a coarse grid in the area
of interest obtained from a global forecasting model.
– Manenti, S. and Leuzzi, G. (2010). “Wind-wave hindcasting on
offshore wind turbine through combined atmospheric and spectral
models”.
1212EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Geologic and geophysical characterization
• The OWF site is part to the eastern margin of the Apulia
Platform, consisting in a succession of substrates of carbon-rich
facies and fine-grained sea limestone
• From the surface towards the inner substrates, the following
stratigraphic sections can be identified:
– A depository of holocene clay soil, for a substrate of 20-40 meters;
– A depository of Plio-Pleistocene clay with sand intercalation, for a
substrate of 300-500 meters;
– An Oligo-Miocenic depository, consisting in marl, clay and white
limestone, for a substrate of 800-1000 meters.
– A mesozoic carbon depository
• The OWF site is situated near the Gondola Fault, essentially
inactive since the Pliocene; the sea area is characterized by an
earthquake activity of mild intensitythe, something also
documented on the national earthquake map.
1313EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Geotechnical characterization
• In order to design the foundations of the OWT and of the service
platform, a geotechnical model has been implemented, with the
following stratigraphy:
– Substrate 1- Holocen depositories, normally consolidated (from the seabed
and up to -30.00 meters below): soil of fine granulometry, essentially
normally consolidated clay of recent depository;
– Substrate 2- Pleistocene depositories, over consolidated (beginning at -
30.00 meters below the seabed): over-consolidated layer of slimy clay of
better mechanic resistance.
14
Substrate z (m) γγγγ (kN/m3) suk (kPa) Eu (MPa) Es (MPa)
1 0-30 17 0 ÷ 42 0.45 ÷ 12.5 0.84÷ 25
2 > 30 17 90 ÷ 145 27 ÷ 44 54 ÷ 88
Where, γ is the unit weight of the soil, suk the undrained shear strength, Eu is
the undrained Young’s Modulus and Es the secant operative Young’s Modulus
14EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Geotechnical characterization
15
Where, OCR is the over consolidation ratio, suk the undrained shear strength, sud
the design shear strength, Eu the undrained Young’s Modulus and Es the secant
operative Young’s Modulus
1 1.5 2 2.5 3
OCR
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
z(m)
0 50 100 150 200
suk/sud
(kPa)
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
z(m)
suk (hp.OC)
(characteristic values)
suk (hp.NC)
(characteristic values)
sud (hp.OC)
(design values)
0 20 40 60 80 100
Eu/Es
(MPa)
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
z(m)
Eu=300suk
Es_working
15EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Seismic response
• The principal seismotectonic features and the information
obtained from the geological and geophysical features of the site,
lead to the characterization of the area seismicity
• The significant seismogenetic areas (in terms of magnitude-
distance relationships) were defined, leading to the selection of
the appropriate natural accelerograms to be used as an input for
the local seismic response
• Results obtained by the geotechnical model, allowed defining the
seismic action to be implemented in the design process, in terms
of time histories of the acceleration and of response spectra.
• For the reference seismic action, the prescriptions from the
Italian building code have been implemented (NTC, 2008).
– Specifically, the design seismic action has been identified with reference to a
return period of 475 years, in accordance with international codes and standards
(DNV, 2004). This return period corresponds to a “rare” seismic event, defined
as an event with a 10 % probability of exceedance in 50 years.
1616EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Design meteo-marine conditions
• A Meteo-marine study has been carried out, aiming at
extreme event characterization and definition of the off-
shore wave conditions.
• The extreme event statistic analysis performed, lead to
the individuation of the design waves in two sectors for
a return period of 100 years.
• Successively, the design waves were propagated in
the area, and four points of observation (corresponding
to the vertices of the area) were considered.
• For these points, the maximum wave height, direction,
and length have been calculated.
• Manenti, S. and Petrini, F. (2010). “Dynamic Analysis of an Offshore Wind Turbine:
Wind-Waves Nonlinear Interaction”.
1717EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Structural analyses
Support structure (1)
• Structural analyses have been performed, after a structural
system decomposition, implementing different structural schemes
and FEM models of increasing complexity
– Bontempi, F. (2010). “Advanced Topics in Offshore Wind Turbines Design”
18
Foundation
Transition
Immersed
Emergent
18EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Structural analyses
Support structure (2)
• Numerical analyses carried out on different support structures
and their variations, led to the adoption of a jacket structure
1919EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
Motivation:
• Vibrations
• Displacements
• Weight (similar)
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Structural analyses
Support structure and foundations
• On the basis of specific performed preliminary analyses, and
considering the stratigraphy of the seabed, the foundation type
chosen is a four-leg jacket structure.
– This is also in accordance with literature for similar cases (for a sea depth of
15-35 meters).
• Numerical analyses have been performed for both the 3 and the
5 MW turbines.
– The four-leg jacket is founded on four tubular steel piles, each having a
diameter of 2 meters, and with a variable thickness
21
Depth (m) d (mm)
< 24 26 (3 MW) - 28 (5 MW)
24-36 18
36 -48 16
>48 14
21EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Structural analyses
Foundations – stress and displacements
22
Turbine type N (compression) N (traction) T M
[kN] [kN] [kN] [kN*m]
3 MW 17500 9250 2170 6440
5 MW 23800 14350 2580 7840
Turbine type N (compression) N (traction) T M
[kN] [kN] [kN] [kN*m]
3 MW 13450 7115 1670 4950
5 MW 18300 11040 1990 6030
Turbine type Vertical. displ. Pile length 1,2Assumed vertical load
[cm] [m] [kN]
3 MW 3.01 57 13713
5 MW 4.52 68 18288
Maximum stress (singe pile – SLS)
Maximum stress (singe pile – ULS)
Vertical displacement and pile length - SLS
22EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Additional aspects
23
• Electrical installations
• Among the aspects addressed are the connection between the
offshore wind turbines and the offshore substation, the
connection between the offshore substations, and the transfer of
energy to the onshore substation, with successive connection to
the national energy transfer network.
• Navigation safety in the confining area
• The marine traffic of interest for the nearby ports has been
assessed and the possible routes that could intercept the site
have been designated. The impacting force of the vessels has
been evaluated.
• Environmental impact
• The visual impact of the OWF to the landscape, the acoustic
impact, the electromagnetic interference and the impact of the
farm to the marine biology have been assessed.
23EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Conclusions and overview
• In this presentation, fundamental aspects from the
design procedure adopted for an offshore wind farm in
the Mediterranean Sea are exposed in a crisp manner.
• The wind farm presents unique characteristics, being,
due to the particular environmental conditions and the
seabed level, the first of its kind in the Southern Europe.
• The adopted design choices, the approach used, and
the performed analyses, can be of particular interest for
future similar projects.
• The project will be further refined with the advancement
from the “design” to the “construction” status
24EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE
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PlanningofanOffshoreWindFarmintheMediterraneanSea
Thank you for your attention
1 info@icariasrl.it
2 salvatore.miliziano@uniroma1.it
3 franco.bontempi@uniroma1.it
4 konstantinos.gkoumas@uniroma1.it
The scientific contribution in the design process of the offshore wind farm of
University Professors Marcello Bernabini, Giuseppe Lanzo, Alberto Noli, Corrado
Ratto and Maurizio Sciotti is greatly acknowledged.
V. Rotisciani 1, S. Miliziano 2, F. Bontempi 3 and K. Gkoumas 4
25EARTH & SPACE 2010, MARCH 14-17, 2010 Honolulu, HI Konstantinos Gkoumas, PhD, PE