Offshore Vindmller Udenoms faciliteter
Offshore Wind TurbinesDesign Standards
ByJan Behrendt Ibs
DNV Global Wind Energy
DNV Global Wind Energy
DNV Global Wind Energylocated in Denmark
Network with DNV offices: UK, Germany, Spain, US, the Netherlands, Taiwan and India
Wind turbine type certification, wind farm project certification, State of the art rules for off-shore windturbine structures
25 employees in Denmark and growing
Technical co-operation with Ris Research Laboratory
DNV history of Offshore Wind Farms - Denmark
Frederikshavn, 4 prototype WTInstallation Year: 2002/2003Elsam
Horns Rev, 160 MWInstallation Year: 2002/2003Elsam/Eltra
Rdsand, 165 MW Installation Year: 2002/2003Energi E2/SEAS
DENMARK
Vindeby, 5 MW, Installation Year: 1991SEAS/Bonus
Tun Knob, 5 MW, Installation Year: 1995Elsam/Vestas
Middelgrunden 40 MW.Installation Year: 2000SEAS and Bonus
Sams, 25 MW Installation Year: 2002 Hydro Soil ServicesProject Certification.
DNV history of Offshore Wind Farms - Germany
GERMANY
Wilhelmshaven, 4.5 MWInstallation Year: 2004Enercon/Bladt Industries
Borkum West, 60 MWInstallation Year: 2004Prokon Nord
SKY 2000 150 MWInstallation Year: 2004EON
Butendiek, 240 MWInstallation Year: 2005Offshore Brgerwindpark Butendiek
Arkona Becken SdostAWE (EON)
AdlergrundUmweltkontor
Pommersche BuchtWinkra
North SeaWSD
DNV history of Offshore Wind Farms UK
UKNorth Hoyle, 60 MWInstallation Year: 2003Vestas Celtic Ltd
Kentish Flats, 90 MWInstallation Year: 2004GREP
Rhyl Flat, 60 MWInstallation Year: 2005National Wind Power
Barrow Offshore Wind Farm, 110 MWInstallation Year: 2005Vestas Celtic Wind Technology Ltd.
Teeside Offshore Wind Farm, 110 MWInstallation Year: 2006LPC.
Lynn + Inner Dowsing, 250 MWInstallation Year: 2004AMEC.
NETHERLANDSEgmond an Zee, 100 MWInstallation year: 2004BCE
Site Specific Integrated Structural System
Site specific, e.g.:
- Wave height- Water depth- Tide and Current- Soil Conditions- Wind+Wave Loads- Optimised project
specific support structure design
The Integrated Model
Definition of integrated model for offshore Definition of integrated model for offshore wind turbines:wind turbines:An An aeroelasticaeroelastic model that includes the model that includes the dynamic influence of wave loads and dynamic influence of wave loads and foundation/soil stiffness and damping. foundation/soil stiffness and damping.
New topics when moving offshore New topics when moving offshore Stiffness and dampingStiffness and damping
Soil stiffness and deflection, uSoil stiffness and deflection, u Wave spectre and 1st tower/pile Wave spectre and 1st tower/pile
bending frequencybending frequency Movements at tower top Movements at tower top du/dtdu/dt Structural analysis of the foundation Structural analysis of the foundation
and soiland soilLoad casesLoad cases
Traditional load cases are Traditional load cases are combined with wave loads combined with wave loads
How offshore wind farmsaffect support structure design
Support Structures (tower + foundation) reaches 30-40 % of the total investment. This has the following impact:
Design- Differentiated foundation types and or sizes- Further offshore i.e. harsh environment yielding high requirements to strength- Large water depth resulting in significant dynamic influence of foundation to the WT- High requirements to installation phase as critical when far out to sea- Simple and robust solutions in favor to high-tech non-proven solutions.
Insurance Investors- Requirements to reliable investments, thus independent project certification
Critical issues during project- e.g. procurement of steel, sea transport, installation vessels, installation
Design Standards Key Areas
New key areas for design standards for offshore wind turbines
including support structures as compared with onshore:
- Geotechnical modeling and analysis
- Aerodynamic modeling and analysis
- Hydrodynamic modeling and analysis
- Structural modeling and analysis
- Corrosion aspects
- Practical issues such as procurement, manufacturing and installation
- Combination of the above
Standards and Codes Offshore Wind Turbines
Currently no national nor international Standard/Codescovering Offshore Wind Turbines as an integratedSystem:
IEC 61400-1 and IEC WT01 covers onshore wind turbines but not foundationIEC 61400-3 (not finalised) covers offshore wind turbines but not foundationsEurocodes cover onshore buildings (High Safety Class) not wind turbines IS0 19902 and API covers offshore oil-and gas fixed structures(High Safety Class (wind turbines not covered) Danish Recommendation for Offshore Wind Turbines, December 2001 Offhoresupport structure design not covered specifically and based on DS codes
DNV Offshore Wind Turbine Standards
DNV-OS-J100: Offshore Wind Turbines
- DNV-OS-J101: Offshore Wind Turbine Structures- DNV-OS-J102: Wind Turbine Blades, Nov. 2004- DNV-OS-J103: Offshore Wind Turbine Electrical Systems, 2005 - DNV-OS-J104: Offshore Wind Turbine Gear Boxes, 2005
DNV Offshore Standard DNV-OS-J101
Special new topics covered in the DNV Standard:
Minimum soil investigations Determination of design waves Combined loads (wind-waves and wind-ice) State-of-the-art fatigue design of tubular joints Grouted connections in mono-piles Grouted connections - pile to jacket sleeve Composite design - steel tubular in concrete shaft Suction bucket foundation
DNV Offshore Standard DNV-OS-J101
New design standard for design of support structure for offshore wind turbines
Basis for new DNV rulesDNV standard is based on experience from more than 24 offshore wind projects & general rule development from maritime and offshore industries for decades
StatusInternal and external hearing finalised 16 April 2004 Will be published in June 2004
DNV Offshore Standard DNV-OS-J101
The standard focuses on structural design manufacturing installation follow-up during the in-service phase
for the support structure i.e. all structural parts below the nacelle
including the soil
DNV Rules for Offshore Wind Turbine Structures
DNV-OS-J101 Standard covers:Site specific design of wind turbine,support structure and foundationconsidered as an integrated structure.Site specific parameters e.g.: Soil conditions Wind conditions Water depth Wave height Current Combined Wind-Wave,Wind-Ice Corrosion Structural stiffness
DNV Rules for Offshore Wind Turbine Structures
Content of DNV Rules
Design principles Safety levels Site conditions Loads Structural design Materials
Life cycle approach
Corrosion Manufacturing Transport Installation Maintenance Decommissioning
Foundation Solutions
Various foundation design covered
Focus on Gravity foundation Mono-piles Tripods
Other concepts included: Jackets, Hybrids, Floating foundations, Suction buckets etc.
DNV Rules for Offshore Wind Structures
Design Principles DNV-OS-J101
1) Design by the LRFD Method (linear combination of individual load processes)
2) Design by direct simulation of combined load (direct simulation of combined load effet of simultaneously acting load processes)
3) Design assisted by testing
4) Probability-based design
Design Principles Target Safety Level
The rules are an offshore standard, providing an overall safety level corresponding to low to normal safety class:
The target safety level for structural ultimate limit state (ULS) designs is to the lower end of normal safety class corresponding to an annual probability of failure in the range 105-104 with 105 (=4.2) being the aim for designs to the normal safety class and104 (=3.7) being the aim for designs to the low safety class. This range of ultimate limit state (ULS) target safety levels is the range aimed at for structures, whose failures are ductile with no reserve capacity.
Target Reliability Index
Limit state Target reliabilityindex (design working life)
Target annualreliability index (one year)
Ultimate 3,1 (EC:3.8) 3,7 (EC:4.7)
Fatigue 1.2-3,1 (EC:3.8) *) -
*) Depends on inspectability, reparability and damage tolerances.
)1
DNV Offshore Standard DNV-OS-J101
The rules are an offshore standard, providing an overall safety level corresponding to low to normal safety class.
The DNV-OS-J101 account for the fact that the structures are unmanned and the risk for pollution of the environment is limited.
Fatigue Design of Offshore WT Structures
In order for offshore wind turbines and their support structures to be economically feasible, optimisation of the design, including the fatigue design needs to be carried out.
Local Joint Flexibility (LJF)
Spring characteristics may be found from Buitrago.
Rotational and/or axial LJF spring
Stiff offset elementBeam element
Application of joint flexibility will give a more correct distribution of member forces.
Influence from mean stress (crack closure)
Welded structural details:
Fracture Mechanics Fatigue Calculations
K = FS FE FT FG S c
FS = 1.12 0.12 bc
FE= 2/165.1
25945.41
+
bc
FT = ( )tc 2/sec
c/b = 0.2
Fracture Mechanics Fati
