Offshore Wind Turbine Design

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Offshore Wind Turbine Design



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Renewable Energy Goals

Why Wind Energy?

Countries turning to renewable energy sources to cut carbon emissions andreplace depleting oil supplies.

UK – 10% now and 15% by 2020

Denmark - 20% now and 30% by 2020

Germany – 18% by 2020 and 60% by 2050

USA – produce 20% of all electrical needs through wind power by 2030



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USA - Offshore Wind/Population Map

Offshore Wind Resource EstimatePopulation Density



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Wind Energy Activity - USA



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Wind Energy Activity - Europe

Largest operational wind farmsProposed wind farm development



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Wind Power – Top 10 Countries

Countries with the most wind powercapacity (onshore & offshore).



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Cost of Wind Energy (NREL 2006)



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Offshore Wind Turbine Foundation Concepts

Monopile 0<30m Jacket 30m<60m Floating 60m+

SACS 35+ years experience indesigning offshore jacket structures



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Existing Wind Farms With Jacket StructureFoundation

Beatrice (Demonstrator) Wind Farm – 2 Jacket Structures

Alpha Ventus - 6 Jacket Structures

Ormonde Wind Farm – 30 Jacket Structures



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Offshore Wind Turbines

Turbine

Tower

Substructure/Jacket

Foundation

Typical offshore wind turbine consists of a turbineand tower which are attached to a partiallysubmerged substructure (jacket).

The substructure is fastened to the ocean floorusing foundation piles.



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Main Turbines ComponentsRotor : Blades, Hub

Nacelle : Drive Shaft, Generator, Gearbox

Most modern turbines are direct drive and do not contain a gearbox.



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Top 10 Wind Turbine Manufactures



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Wind Turbine Size

VESTAS V164 7.0MW : 164 m diameter, 80 meter blade lengthtip height =187m , hub height = 105m

2011-2015

H 187m

Vestas

V164 7000 kW

Ø 164m



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SACS - Life Cycle Applications for Analysisand Design of Wind Turbines Platforms

FABRICATION

INSTALLATION

INPLACE

CONDITION



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Fabrication

• Bent Roll Up - Jacket manufactured in portionswhich are then rolled over using slings and joinedtogether.

•Design structure to resist sling forces



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Transportation Analysis• Jacket structure is designed to resist inertial resulting from vessel motions

• Seafastners designed to resist inertial loads.• TOW, SEASTATE: modules used to generate inertia loads

• COMBINE: module used to combine static & dynamic common solution file



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Installation Lift Analysis• Design Jacket to resist lift forces and buoyancy loads as its lowered into the

water

• FEMGV: Detailed FE analysis of lift padeyes



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Inplace Design with PSI

•Structure Analyzed and designed to resist maximumoperational and storm wave, wind and current loading -typically from eight directions.SEASTATE : Used to generate environmental loads



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Inplace Design - Non Linear Soil Behaviour PSI:

• API P-Y / T-Z Soil

• API Adhesion Soil

• User Defined P-Y / T –Z Soil

• User Defined Adhesion Soil

Pile

Mudline



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Member Code Check Design

POST:



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Detailed Joint Design

JOINT CAN:



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Earthquake AnalysisDYNAMIC RESPONSE:

•Spectral•API response spectra built in•User defined spectra•Modal combinations via SRSS or CQC methods•Generate Equivalent Static Loads

•Time History•Variable Time step Integration•Nonlinear fluid damping•Linear, quadratic or cubic interpolation betweentime history input values



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•Design wind turbine jacket structure to withstand impact from a servicevessel.

•Use the SACS COLLAPSE module to account for both geometric andmaterial non-linearity's resulting from a ship impact event.

•Automatically mesh impact points to account for local indentation effects.

•Both quasi-static and dynamic impact analysis possible in SACS

Non-Linear Ship Impact Analysis



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• Low Energy (Operational Impact)

Jacket Bracing Designed to Survive Operational Impact (partial yielding at pointof impact).

• High Energy (Accidental Impact)

Jacket Legs Designed to Survive Accidental Impact.

Face and leg joints designed to survive accidental loading.Jacket Bracing allowed to fail – Structure designed to survive loss of bracemember.

For an Impact Design Consider both Low Energy and High EnergyImpact Events

Non-Linear Ship Impact Analysis



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Member Impact

•Automatic 3D meshing of tubular members

•Seamless integration into SACS model

•User controlled mesh density

PRECEDE:



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Automatic Tubular Member Meshing



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Joint Impact

•3D Mesh of tubular joint in seconds

•Automatically identify chord and bracemembers

•Seamless integration into SACS model

•User controlled mesh density

MESH JOINT:



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Automatic Joint Meshing



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DYNAMIC RESPONSE / COLLAPSE:

Non-Linear Dynamic Ship Impact Analysis



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Wind Turbine Fatigue AnalysisWind Turbine Fatigue Loading

Wind load on Turbine

Wind load on Structure

Wave Load on Structure

Dynamic Response of Structure



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Wind Turbine Fatigue AnalysisWind Loading on Tower & Jacket

Wind

Spectrum

Wind Velocity Time History

Wind loading can be represented in terms

of a wind spectrum or by a wind velocitytime history.

Von Karman

HarrisKaimal

t

V



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Wind Turbine Fatigue AnalysisWave Loading on Jacket Structure

Wave Spectrum

Pierson-Moskowitz

JONSWAPOchi-HubbleUser defined

Wave Surface Profile Time History

Wave loading can be represented either asa wave spectrum or time history of thesurface profile.

η

t



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Wind Turbine Fatigue Analysis

Wind load on Turbine

Wind Loading On Turbine

The wind loading on the turbine causes the rotationof the wind turbine, which in turn generatesaerodynamic and mechanical forces on the top ofthe tower, which can be represented by a force timehistory.F

t

Force Time History



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Aerodynamic and Mechanical Turbine Forces

Aero Elastic Programs

GH Bladed

Garrad Hassan, UK

Flex 5

Stig Øye at Department of Fluid Mechanics at The Technical University of

Denmark.

FAST

National Renewable Energy Laboratory (NREL), USA

www.nrel.gov

http://www.nrel.gov/

http://www.nrel.gov/



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FAST : Fatigue, Aerodynamic, Structure & Turbulence

A comprehensive simulation software capable of predicting both fatigue loads

and extreme loads for two and three bladed horizontal axis wind turbines.

Wind Turbines modeled as a combination of rigid and flexible bodies.

Rigid bodies: Earth,Nacelle, Hub, Tip Breaks (point masses).

Flexible Bodies: Blades, Tower and Drive Shaft.



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Wind Turbine Fatigue AnalysisSACS to FAST Interface (WAVE RESPONSE)

1. Includes multiple modal response required for jacket fatigue analysis

2. Hydrodynamic modeling for wave loading

3. Allows users to conduct a fully coupled dynamic response analysis resulting from wave, wind

and turbine forces.



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Wind Turbine Fatigue AnalysisSACS Fatigue Analysis

Time history fatigue analysis for the structure is possible if the followingfatigue load sources are available:

1. Turbine Mechanical and Aerodynamic Force Time History

2. Wind Spectrum or Wind Velocity Time History

3. Wave Spectrum* or Wave Surface Profile Time History

*For a given wave spectrum, a random seastate profile can begenerated by assuming the random sea to be comprised of an infinitenumber of waves with a random phase angle, but with heights andperiods defined by the spectrum.



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• For a fatigue analysis resulting from a random wave and a force time history. A

stress range counting method such as the rain flow method is used to determinethe fatigue lives.

There are different variants of the rain flow counting method:

• SACS uses method recommended by ASTM (American Society for Testing andMaterials) E 1049-85. (Reapproved 2005). Standard practices for cycle counting infatigue analysis. ASTM International

Rain flow count: Largest cycle extracted first. Smaller cycles considered to besuperimposed on the lager cycles




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Fatigue Analysis

SCF: Efthymiou, Kwang andWordsworth, Smedley andFischer, Marshal, DNV

FATIGUE:

S-N : API, HSE, AWS, NORSOK,ISO, USER DEFINED



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• Typical Simulation:

For each wave in scatter diagram, use six tenminute random seastate profiles

Analyze structure every 0.05 seconds

Total number of load cases to analyze perwave = 6 x 600 /0.05 = 72000




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• Standards for Offshore Wind Turbines:

IEC – 61400-3 : Design Requirements for offshore wind turbines.

DNV-OS-J101 : Design of offshore wind turbines

Germanischer Lloyd IV Part 2 : Guidelines for the Certification ofOffshore Wind Turbines

Offshore Wind Turbine Standards



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Parvinder JhitaProduct Manager SACS2113 38th StreetKennerLA 70065

[email protected]

www.bentley.com/sacs

Telephone (504) 443 5481

mailto:[email protected]

http://www.bentley.com/sacs

http://www.bentley.com/sacs

mailto:[email protected]

Offshore Wind Turbine Design

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