Floating Support Structures

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Floating Support Structures Enabling New Markets
for Offshore Wind Energy
Andrew Henderson Garrad Hassan
European Wind Energy Conference, Marseille, March
2009
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About us

• Founded in 1984 in UK
• Now have 26 offices worldwide 300 staff
• Local understanding informs global perspective

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Offshore Wind at GH
? First offshore wind work 1987 ? 200
commercial contracts ? 5,000 MW offshore OM
studies ? 8,000 MW offshore energy
assessments ? 8,000 MW of Technical Due
Diligence ? 1,500 MW of FEED Studies ? 50
Offshore Windfarms ? 20 UK ? 10 Germany ?
Also NL, FR, DK, SE, ES, BE ? Rest of the world
(USA, China, Korea) ? Team now boasts gt80
engineer-years in offshore wind
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Contents

• Introduction
• Benefits and challenges
• Technology
• Class of Foundations Spars / TLPs / Framework
• New Markets
• Countries with large areas of shallow-water
  suitable for lowest cost technology are the
  exception
• Conclusions

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Benefits of Deepwater Wind

• greater choice of sites countries
• Mediterranean (France, Spain, Italy), Norway, US
  (east and West coast), East Asia (China, Japan,
  Korea)
• greater choice of concepts
• evidence see variety of proposals
• cost probably similar to fixed structures in
  medium depths
• Loads are dissipated in to the water rather than
  being transferred rigidly to the ground
• costs do remain to be demonstrated
• greater flexibility of construction
  installation procedures
• easier removal / decommissioning

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Challenges of Deepwater Wind

• minimising turbine and wave induced motion
• additional complexity for the design process
• understanding and modelling the coupling between
  the support structure and the windturbine
  (moorings control)
• the electrical infrastructure flexible cable
• the construction, installation and O M
  procedures

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Design Drivers
Primary

• turbine thrust (mean dynamic)
• waves (dynamic)
• cost

Secondary

• turbine torque
• upwind yaw stability
• waves (mean drift)

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Floating 3 Classes of Concepts

• Method of achieving stability
• Tensioned moorings
• Ballast
• Hydrostatic (surface area)

Tensioned Leg Platform
Floating Jacket
source TU Delft
Spar
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know your way around the Spar Buoy
Heels over when turbine is operating
Narrower section at water-plane (reduces wave
loads and improves motion behaviour generally)
Three lines lower cost but may lose position, if
one breaksbuoy is inherently stable (i.e. When
without moorings)
Ballast at base of spar provides stabilityIf
this is a fluid, stability can be adjusted
Slack mooring
Choice of anchors (depends on ground)
Flexible export cable
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Design Drivers
Conflicts
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Design Optimisation
Design-Space Exclusion

• Balancing contradicting design objectives
• Viable design space is small
• Improved situation for larger turbines, however
  the minimum water depth increases

Stability
Vertical Motion
Pitching Motion
Cost
Fatigue Loading
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Spar Challenges

• Size of Structure
• Strengthened tower
• Assembly (turbine on to spar)
• In vertical but sites limited where this can be
  done (Norway)
• Horizontal tow-out and upending (conventional
  approach but may induce high loads)
• But
• Spar concept can be compared with the monopile
• Somewhat larger but similar simple steel tube
  structure

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know your way around the TLP Floater
Turbine always vertical
Legs provide stability during tow-outonce legs
submerged, vessel has no stabilityvarious
possible solutions including buoyancy sacks and
collars (shown)
Small structure hence long term prospects for
costs appear good
Tensioned mooring limits vertical movement
If one mooring line (group) fails, structure will
flip over (i.e. total loss)
Flexible export cable
Choice of anchors (depends on ground)
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Existing Candidate Offshore Structures
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Wind Turbine Issues Control

• Key challenge regarding the wind turbine is
  control
• how can it be demonstrated that the controller
  will be able to function successfully?
• Spar Buoys pose a greater challenge than TLPs
• yaw control
• A well designed controller would be able to damp
  out
• wind driven vessel motion
• some high frequency wave driven vessel motion
• but not low frequency wave driven vessel motion
  (i.e. due to drift forces)
• Need for advanced modelling capabilities
• Multi-body integrated model
• See Slides about BLADED in Annex at end of
  presentation
• Other potential issues surrounding inclination
  during installation and operation

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Opening New Markets

• Northern Europe benefits from large areas of
  shallow waters unusual topology
• Other markets typically have sufficient sites for
  only a limited shallow-water bottom-mounted fleet
• In deeper waters, choice of support structure is
  costly jackets/tripods/tripiles are considered
  but floating should be too

Water depth 50m resolution (source NOAA)
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Opening New MarketsMethodology

• Review some key countries
• Indicative estimate of potential resource within
  40km of the shore
• Presume that this will be developed first
• Water depth constraints
• Classic offshore wind 0 50m
• TLP-class offshore wind 50 300m
• Also suitable for floating-jacket class
• Spar-class offshore wind 150 500m
• Other details
• GEBCO 2min bathymetry dataset
• 25 multiplier factor to account for constraints
• But
• No wind data used (data quality is too variable
  for global assessment ?)

Water depth 50m resolution (source NOAA)
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Southern Europe
Marseille
Barcelona
Madrid
Water depth 50m resolution (source NOAA)
Water depth 50m resolution (source NOAA)
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China

• First offshore wind farm being built (off-grid
  turbine already installed)
• Very large regions of shallow waters in East
• indicative capacity 40GW, predominantly TLP class
  sites in the South

Beijing
Shanghai
Pearl River Delta
Water depth 50m resolution (source NOAA)
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Japan

• Japan was an early adaptor of wind energy but
  onshore progress has been limited due to
  mountainous terrain etc.
• indicative capacity 275GW both TLP and Spar
  class sites
• Generally stronger winds in North

Tokyo
Kyoto
Water depth 50m resolution (source NOAA)
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Other Selected Countries

• Norway 125GW both Spar and TLP technologies
• Other countries (which also have good sites for
  classic technology)
• United Kingdom 125GW, predominantly TLP
  technology
• Ireland 40GW, predominantly TLP technology
• Sweden 40GW, predominantly TLP technology
• South Korea 25GW predominantly TLP technology
• USA 1500GW total (source NREL different
  criteria)
• Relaxing distance constraint to 100km typically
  doubles the potential resource for most counties

Water depth 50m resolution (source NOAA)
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Current Situation

• Interest in deep-water offshore wind is growing
• With commercial groups playing an increasingly
  active role
• Funding now also being provided by non-government
  sources
• The current focus a fully-functional prototype,
  costs millions /
• A Barrier of Entry
• High cost of grid connection
• New technologies flexible cable, subsea
  switchgear, low cost moorings
• Of course cost is the key issue, as for classic
  offshore
• beyond 30-40m, cost increases can be expected to
  be small since new concepts become possible

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Challenges / Future Prospects

• Resolving wind turbine performance issues
• Requires fully functional modelling capabilities
  (wind turbine as well as offshore aspects)
• Developing robust installation and repair
  procedures
• It isnt sufficient if the structure is stable
  during all operation conditions it must be
  stable through-out the entire tow-out and
  installation procedure
• mooring TLPs more challenging
• Demonstration of Fully Functional Prototype
• i.e. full size turbine supplying power to the
  grid
• Hywind prototype spar under construction at
  Technips Pori yard in Finland turbine to be
  supplied by Siemens
• Others expected to follow Arcadis (DE state
  support promised) Blue H (off-grid floater
  demonstration prototype installed)
• Extension of Offshore Wind Market to new
  Countries
• Spain, Portugal, Italy, Greece, Norway, Japan
• Expansion of sites elsewhere such as France, USA

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Thank You for Your Attention Andrew Henderson -
Garrad Hassan Please contact myself Or Jerome
Jacquemin in Paris
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Integrated in GH Bladed

• All the features of GH Bladed which have proved
  successful for modelling onshore and bottom
  mounted offshore wind turbines
• Modal representation of tower and rotor
  structural dynamics.
• Validated methods for rotor aerodynamics and
  hydrodynamic loads.

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Rigid Body Modes

• Structural modes superposed on translations and
  rotations of the whole structure about its centre
  of mass.
• Allows the modal representation to cope with
  large displacements.
• Mooring line forces applied as an external load
  rather than a modal stiffness.

Surge Sway Heave
Pitch Roll Yaw
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Mooring line forces

• Mooring line forces implemented by definition of
  a 6x6 matrix of non-linear force-displacement
  curves.
• Any number of sets of stiffness matrices can be
  defined and used at multiple locations.
• Additionally, damping and mass matrices can be
  defined.

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Offshore Code Comparison Collaboration

• Garrad Hassan is a leading partner in this
  project, coordinated by NREL under IEA Annex
  XXIII (Subtask 2).
• Testing the capabilities of GH Bladed against
  other codes including multi-body, finite element
  and codes coupled to specialised mooring line
  codes.
• Identical model and selection of load cases mean
  that differences due to modelling can be
  identified.