oe4604 2014 offshore wind energy

8/10/2019 OE4604 2014 Offshore Wind Energy

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Introduction to Offshore Engineering OE4606

Offshore Wind Energy

Eliz-Mari Lourens




Offshore Wind:

Two parent industries

• loading:

• + (dynamic) wind

• + rotor harmonics

• single structure vs serial

production

• optimization gains!

• loading:

• + hydrodynamic

• foundation considerations

• maintenance!




Why Offshore Wind?

Onshore:

• Land is increasingly occupied

• Resistance against visual ‘pollution’ is growing

• Wind turbines are getting larger-> requires more space

-> visible from greater distance

Offshore:

• No obstacles more & steadier wind

• Space

But: remote & tougher conditions!




Offshore wind farms

• Primary function: convert wind power offshore into electric

power onshore

• Main challenge: reducing the cost per kWh

• Main area of development: NW Europe(shallow seas & favorable wind conditions)

• Fast growing industry sector

• Lack of trained engineers!




Lecture content

1. Offshore Wind Energy: A Short History

2. Statistics and Trends

3. Offshore Wind Farm Components

4. Overview of courses

5. Support Structures and Installation




(Offshore) Wind Energy

A Short History




Persian deserts




Windmills




Power from wind 1888

• Brushmill

• 12 kW

• Auto control




Poul la Cour (DK) 1891

• Step forward:

aerodynamics

• Tests in wind tunnel

• Produced hydrogen




MW size, 1941, Vermont

• 1.25 MW

• Largest wind turbine ever built

until 1979

• Steel blades

• Fatigue of blade only 1100 hours operational




Gedser: test turbine in Denmark

• 1957

• By J. Juul

• 200 kW

• 24m rotor diameter

• “The Danish Concept”: domination of the market well

into the 1980’s




70’s-80’s: NASA program

• Boeing

• General

Electric

• Purpose:develop

technology

and support

emerging

market.• Largely

unsuccessful




Offshore idea’s 1970-80

• Heerema

• RSV

• Boskalis

• Fugro

Studying offshore wind




Offshore: detailed

plans

• Copy offshore structures

• Adapted to be produced in large

numbers

• Conclusion: bigger turbines needed




• Installed 1990

• Decommissioned 1996• 1 Wind World 220 kW turbine

• Rotor diameter 25 m

• Water depth 6 m

• Distance to shore 350 m

Test facility to study influence of

offshore wind turbines on:

• Birds

• Fish and fishing

• Shipping

• Public opinion

• Operation & maintenance

Nogersund




Vindeby

• Installed 1991

• 11 Bonus 450 kW turbines• Rotor diameter 35 m

• Max. water depth 5 m

• Distance to shore 2.5 km

• Total Power 5.0 MW

• Gravity-based foundations




Lely

• Installed 1994

• 4 NedWind 500 kW turbines• Rotor diameter 37 m


• Distance to shore 750 m

• Total Power 2 MW

• 2-bladed turbines

• First driven monopiles




Tunø Knob

• Installed 1995

• 10 Vestas V39 500 kW turbines• Rotor diameter 39 m


• Distance to shore 6 km


• Gravity-based foundation




Bockstigen

• Installed 1998

• 5 WindWorld 500 kW turbines• Rotor diameter 37 m




• Monopile foundations




Blyth

• Installed 2000

• 2 Vestas V80 2.0 MW turbines• Rotor diameter 80 m




• Drilled monopile foundations




Middelgrunden


• Public involvement/investment

• Installed 2001

• 20 Bonus 2.0 MW turbines• Rotor diameter 72 m







Yttre Stengrund

• Installed 2002

• 5 NEG-Micon 2 MW turbines• Rotor diameter 72 m








Horns Rev

• Installed 2002

• 80 Vestas 2,0 MW turbines• Rotor diameter 80 m




• First large offshore wind farm

• Driven monopile foundations

• Helicopter access




Samsø

• Installed 2003


• Water depth 18 m







Nysted

• Installed 2003


• Water depth 9 m







Arklow Bank

• Installed 2004

• 7 GE 3.6 MW turbines• Rotor diameter 104 m




• Monopiles




North Hoyle

• Installed 2005

• 30 Vestas 3.0 MW turbine• Rotor diameter 90 m

• Water depth 5 m







Scroby Sands

• Installed 2005

• 30 Vestas 2.0 MW turbines• Rotor diameter 80 m








• Installed 2005


• Water depth 5 m




Kentish Flats




• Installed 2005





• First Dutch offshore wind farm• Monopile foundations

Egmond aan Zee




Beatrice

• Installed 2007

• 2 REpower 5.0 MW turbines• Rotor diameter 126 m




• Jacket structure

• Most expensive so far




Princess Amalia (Q7)

• Installed 2008





• Deepest monopile foundations

when constructed




Thornton Bank

• Installed 2008

• 6 REpower 5.0 MW turbines• Rotor diameter 126 m




• Deepest gravity-based

foundations

• OWF to be built in 3 phases




Alpha Ventus

• Installed 2009/2010

• 6 Repower 5M turbines• 6 Areva Multibrid M5000 turbines

• Rotor diameter 126 m




• Demonstration project

• Tripod & jacket foundations

• Extensively used for research

(RAVE)




Hywind

• Installed 2009

• Floating

• 2.3MW Siemens turbine

• Test project

• Water depth: 100m

• Distance to shore: 10km




London Array

• Fully operational April 2013

• 175 3.6 MW Siemens turbines

• Area: 100 km2

• Maximum water depth: 23 m

• Distance to shore: 20 km

• World’s largest offshore wind

farm

• First with about the same size as

a large coal or nuclear plant




Statistics and Trends




Key Statistics by the end of 2013

• 2080 Offshore Wind Turbines installed and grid connected

• Totalling 6562 MW

• 69 Wind Farms

• 11 European countries

• Average offshore wind turbine size is 4 MW

• 2 Full-scale grid connected floating turbines




Trends in the Industry

• Installed in deeper water






• Larger turbines






• Larger turbines

• Larger wind farms




2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 20200

5

10

15

20

25

30

35

40

year

i n s t a l l e d c a p a c

i t y [ G W ]

Total installed capacity

Will the target of 40 GW in 2020 be met?




Offshore Wind CapEx




Offshore Wind Farm

Components




Offshore Wind Farm Components

Wind Turbine





Support structure

• Monopile

• Gravity-based

• Jacket

•

Tripod

• Floating?





MET mast

• Placed 2-3 years before OWF

•

Map environmental conditions• Wind

• Waves

• Current

use for detailed design





Electrical infrastructure

• Infield transmission cables

• Substation

• Shore connection cables

•

Onshore substation/tie-in




OE5662 Offshore Wind Farm Design

(Q3)

• Offshore Wind within Offshore Engineering• Design Considerations• Economics• Environmental Impact• Development Aspects

• Environmental Conditions• Wake effects / layout design• Electrical Infrastructure• Aero- & Hydrodynamic Loads• Support Structure Design• Installation

• Operation & Maintenance

?

air

sea

soil

wind

waves &

current

air

sea

soil

wind

waves &

current

air

sea

soil

wind

waves &

current




OE5665 Offshore Wind Support

Structures (Q4)

Focus on design of bottom-

founded steel structures with

piled foundations

• analysis of environmental data

• preliminary design of monopile andmulti-member structure

• concept selection

• detailed design of monopile/multi-

member structure




Other courses

• Introduction to Wind Energy AE3W02TU (Q1)

• Wind Turbine Design AE4W09 (Q3)

• Site Conditions for Wind Turbine Design AE4W13 (Q3)

• Design and Manufacturing of Wind Turbine Blades

AE4ASM509 (Q3)• Wind Turbine Aeroelasticity AE4W21 (Q4)

Interfaculty organization for research on wind energy(5 faculties, 13 groups)




Support Structures and

Installation




Support structure types

• Monopiles

• Gravity-based

• Jackets

• Tripods

• Tripiles

• Floating

Source:h ttp://bildarchiv.alpha-ventus.de/ Source: http://www.siemens.com/Source:http://bildarchiv.alpha-ventus.de/




Share of substructure types

Source: The European offshore wind industry – key trends and statistics 2013 , EWEA, January 2014.




Definitions

• Hub height:Elevation of hub above sea level

• Interface level:Elevation of bottom tower flange abovesea level

• Support structure

Entire structure holding RNA in place• Tower

Tubular structure spanning distancebetween interface and RNA

• SubstructurePart of the structure spanning distance

between interface level and seabed• Foundation

Part of structure in direct contact withsoil

Support

Structure

Foundation

Sub-

structure

Tower

Support

structure

Hub height

Interface level




Design objectives – support

structure

• Survival

• extreme loads

• cyclic loads

• Operation• deformations

• accelerations

• Optimization for cost reduction

• Secondary aspects

• export of energy

• access and repair




Sources of excitation: wind

• 1P = rotational frequency of rotor

• 3P = blade passing frequency




Sources of excitation:

wind

Siemens 3.6 MW

Minimum rotor speed: 5 rpm

Nominal rotor speed: 13 rpm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

0.08 0.22 0.25 0.65

1P 3P

Frequency [Hz]

1P 3P

soft-soft soft-stiff stiff-stiff




Sources of excitation: waves

• Generic wave spectra• Pierson-Moskowitz

fully developed sea state

• JONSWAP (JOint North Sea WAve Project)

fetch limited situations

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 0.2 0.4 0.6 0.8 1 1.2

PM

JONSWAP

Frequency [Hz]




Other harmonic sources?

• Mass imbalance rotor

• Tower shadow

• Yaw misalignment

• Aerodynamic imbalances due to

•

wind shear• blade pitch errors




Transformation to loads

• Waves

• Currents

• Wind BEM

Morison

= +




Dynamic interactions

• Aerodynamic damping induced by operating rotor

• Hydrodynamic forces and structural response

• Soil and structure

• Interactions between dynamics of different OWEC

components

il




Monopile support structure:

components

• Foundation pile

• Transition piece

• Tower

Boatlanding J-tube

M il





Installation

• Seabed preparation / scour

protection installation

• Drilling or driving of pile

• Transition piece options...

• Tower sections bolted Source: http://www.dongenergy.com/anholt

M il





Foundation pile

• Dpile ~ 4.0 - 6.5 m

• t ~ 45 – 110 mm

• D/t ~ 80 - 90

M il t t t





Transition piece

• Grouted joints – settlements...

• Conical grouted joints with

shear keys

• New concepts:

•

hammering on flange• slip joint

inclination correction?

secondary steel?



G it b d F b i ti




Gravity-based: Fabrication

• Constructed (hollow) on land- crane lifting capacity

G it b d T t ti d




Gravity-based: Transportation and

installation

G it b d B ll t d




Gravity-based: Ballast and scour

protection

M lti b t t




Multi-member structures

Jacket Tripod Tripile

Wh lti b t ?




Why multi-member systems?

• Deeper waters, larger turbines

and increase

natural frequency decreases

• For same environmental loading, we require: increase in EI, without significantly increasing (mass

of support structure per unit length)

place material as far away from the neutral line as

possible

Large diameter piles

OR

Multi-member structuresf =

3,04

4( + 0,228)

mtop

L EI

Neutral line

E l il




Example: monopiles

Becomes more impractical and less economic

Solutions required with higher stiffness for equal mass

Multi-member structures

V90 in 20 m water depth

Diameter ~ 4.0 m

RE5M in 35 m water depth

Diameter ~ 7.0 m

1 Jackets




1. Jackets

Jackets: definitions




Jackets: definitions

Leg angle (Batter)

Pile sleeve

Foundation pile Horizontal brace

Diagonal brace

Leg

Transition sub-structure to tower

Panel / bay height

Base width

Disadvantages




Disadvantages

• fabrication and welding of many geometrically complex joints

expensive

• weld details susceptible to higher stress concentrations/fatigue

extra material requirements

• step down in width necessitates provision of substantialtransition section heavy!

• piles needed to attach jacket to seabed

2 Tripods




2. Tripods

Tripod: definitions




Tripod: definitions

A A’’

Leg angle

Foundation pile

Leg

Mud brace

Inner brace

Main Column

Pile sleeve

Fabrication & Installation




Fabrication & Installation

Example: Alpha Ventus

Source: DOTI

Jackets

Tripods

Fabrication of tripod elements (NL)




Fabrication of tripod elements (NL)

Source: DOTI

Fabrication of tripods in Norway




Fabrication of tripods in Norway

Source: DOTI

Load oat




Load oat

Source: DOTI

Transport of tripod foundations





Source: DOTI






Source: DOTI

Lifting and landing




Lifting and landing

Source: DOTI

Pile driving




Pile driving

Source: DOTI

Turbine installation




Turbine installation

Source: DOTI

Jacket load out




Jacket load out

Source: DOTI

Pile driving




Pile driving

Source: DOTI Source: DOTI

Transportation




Transportation

Source: DOTI

Installation




Installation

Source: DOTI

3. Tripile




3. Tripile

• Higher lever arms...

• Developed by BARD

(1st installation 2008)

• 3 grouted transition pieces

• Weight comparable to that of

Alpha Ventus jacket (similar

water depths)

Source: http://creativecommons.org/licenses/by-sa/3.0

Concept selection?




Concept selection?

• Consider:

• structural design (strength and fatigue)

• fabrication (onshore)

• transportation to offshore site

• installation in-situ

• Keep operation & maintenance firmly in mind

Support structure optimization?



Support structure optimization?

Computer-aided (vs manual) optimization widely used in

automotive and aerospace industry, but not for the design of

offshore wind turbine structures

Why?

• Large number of parameters

• Complexity of working with many engineering disciplines,

often using different assumptions

• Uncertainty about soil conditions

• Simplified models required (large number of load cases)

• etc.

oe4604 2014 offshore wind energy

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