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Design of Offshore Wind FarmsPrepared by Flemming Jakobsen & Andrass Ziska Davidsen

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Types of Foundations

Overview of selected supportstructure and foundation types.

From top left:

1. Monopile;

2. Tripod;

3. Jacket;

4. gravity based; and

5. SPAR platform

Bucket:

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Existing WTG Foundations

Type Nos Water depth

Concretegravity

~ 247 Up to 27 m

Steel monopiles ~ 900 Up to 30 m

Steel tripods ~ 12 Up to 30 m

Steel jackets ~ 30 Up to 45 m

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Existing Monopile Foundations

Project Year No Water

Depth

Maritime

Condition

Turbine

(MW)Horns Rev 2002 80 14 m Offshore 2,0

North Hoyle 2003 30 11 m Offshore 2,0

Scroby Sands 2004 30 10 m Offshore 2,0

Kentish Flats 2005 30 8 m Offshore 3,0

Barrow 2006 30 20 m Offshore 3,0

Egmond 2006 30 10 m Offshore 3,0

Burbo Bank 2007 25 8 m Offshore 3,6

LID 2008 54 11 m Offshore 3,6

Princess Amalia (Q7) 2008 60 24 m Offshore 2,0

Rhyl Flats 2008 25 13 m Offshore 3,6

Robin Rigg 2009 60 9 m Offshore 3,0

Gunfleet Sands 2009 48 10 m Offshore 3,6

Baltic 1 2010 21 19 m Inland waters 2,3Thanet 2010 100 25 m Offshore 3,0

Greater Gabbard 2010 140 32 m Offshore 3,6

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Existing Gravity Based FarmsProject Year No Water Depth Maritime Turbine Size

Vindeby 1992 11 4 m Inland waters 0,45

Middelgrunden 2000 20 6 m Inland waters 2,0

Rdsand 1 2003 72 10 m Inland waters 2,3

Lillgrund 2007 48 10 m Inland waters 2,3

Thornton 2008 6 24 m Offshore waters 5,0

Rdsand 2 2009 90 13 m Inland waters 2,3

Middelgrunden ~1800 tons Thornton Bank ~3000 tons

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Parameters to ConsiderTopic Parameter

Site specific: Water depthWindTides, Waves and CurrentIce conditionsSoil conditions (soft mud, sand, boulders, rock a.m.)Sand waves and bed changes

WTG and tower: Frequency bandOther requirements by WTG supplierMass and inertia of WTG, RNA and tower

Design Complexity of designCables

Proven technologyReliability of conceptFabrication of support structureand foundation

Numbers of weldsComplexity of jointsMass of primary steel

Installation Transportation inlandTransportation offshore (distance to land)LiftingFoundationConnectionsCable installation

Maintenance Scour protectionCorrosion protectionAccess

Decommissioning DisconnectingFoundation removalEnvironmental impact of remains

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Water Depth

Evaluation results from theProject Upwind.

The higher the qualitativescore the more suited thesolution is.

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Northwind Offshore Wind Farm

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Generalarrangement

Interface at flangein +19 m LAT.

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Generalarrangement Mass 1200 mT

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Codes / Design Basis and Design Briefs / CertifierThe Design Briefs are: 3-1 Design Brief - Geotechnical Data Interpretation 3-2 Design Brief - Extreme Operational Event 3-3 Design Brief - Fatigue Analysis 3-4 Design Brief - Natural Frequency 3-5 Design Brief - Grouted Connection 3-6 Design Brief - Ship Impact 3-7 Design Brief - Transportation 3-8 Design Brief - Installation 3-9 Design Brief - Dismantling

3-10 Design Brief - Design Primary Structures 3-11 Design Brief - Design Secondary Structures 3-12 Design Brief - Design Provisional Structures 3-13 Design Brief - Design Elastomeric Bearings 3-14 Design Brief - Corrosion and Cathodic Protection 3-15 Design Brief - Scour Protection 3-16 Design Brief - Fabrication 3-17 Design Brief - Operation & Maintenance

3-18 Design Brief - Quality Control (Fabrication and installation) 3-19 Design Brief - Hydrodynamic Coefficients 3-20 Design Brief - Driveability and Driving-Induced Fatigue

Analysis 3-21 Design Brief - Damping Ratio

The design basis for the project consists of PartsA, B and C:

The Design Basis Part A includes: Part A.1: General design requirements Part A.2: Hydrodynamic and morphological

design basis Part A.3: Geophysical and geotechnical

factual data reports Part A.4: Site specific wind dataThe Design Basis Part B consists of:

Part B: Northwind OWFThe Design Basis Part C consists of: Part C: Integrated data for detailed design

INTERFACE REPORTS:to WTG SUPPLIER

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Wind (Interface)

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Load Table!!!

3 pages with more table! In total 4014 load cases!

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Northwind Offshore Wind Farm

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Northwind Offshore Wind Farm

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Northwind Offshore Wind Farm

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Northwind Offshore Wind Farm

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Northwind Offshore Wind Farm

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Grout (elastomeric bearing)

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Toe-Kick

Total movement

SLS

ULS

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Damping ratio big savings!

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CablesInternal:

Corrosion Vibration

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Cables real life

Internal:

Vibration

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Ladder big science!

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Ship impact

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Ladder real life!

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SlammingLINK:

Wave

http://localhost/var/www/apps/conversion/tmp/scratch_6/Wave%20run%20up,%20blger_billeder.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_6/Wave%20run%20up,%20blger_billeder.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_6/Wave%20run%20up,%20blger_billeder.pdf

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Limits for Monopile Foundation

The present limits for the monopiles are:

1. Wall thickness of 100 mm. It is difficult to weld the cans together for a wall thicknessabove 100 mm;

2. Diameter of 6000 mm. No hammer and anvil exist that can drive a monopile with adiameter of more than 6000 mm;

3. Weight of about 900 mT. It is not possible to handle monopiles weighing more than 900mT with todays cranes; and

4. Length of about 100 m.

Boulders may cause that some piles cannot be driven.Local buckling also put some limits on the combination of diameter and wall thickness.

These limits are reached in about 35 m water depth with an about 4 MW turbine at thisstage the monopile diameter is about 6000 mm and the wall thickness about 100 mm at themudline and the total weight of the monopile up to about 900 mT.

As the turbine is increased (and requested stiffness of support structure made moredemanding) the limits will be reached at an even shallower water depth.

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The near and not so near FUTURE