update on design standards for offshore wind turbines j. f. manwell, prof. wind energy center dept....
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Update on Design Standards for Offshore Wind Turbines
J. F. Manwell, Prof.Wind Energy Center
Dept. of Mechanical & Industrial Engineering
Univ. of Mass., Amherst, MA 01003
Massachusetts Wind Working GroupJanuary 30, 2013
Why Are Standards Necessary?
• Without proper design standards, failures are much more likely
• Offshore presents particular challenges!2
Parts of an Offshore Wind Turbine
• OWT defined here• Includes:
– Rotor/nacelle assembly (RNA)
– Support structure• Tower
• Substructure
• Foundation
s u b - s t r u c t u r e
p i l e
f o u n d a t i o n
p i l e
p l a t f o r m
t o w e r t o w e r
s u b - s t r u c t u r e
sea floor
s u p p o r t s t r u c t u r e
rotor-nacelle assembly
seabed
water level
RNA
Substructure
Foundation
Tower
3
Common Types of Support Structures
• Monopiles
• Gravity base
• Jackets
• Others – Tripods– Suction bucket
http://www.theengineer.co.uk/in-depth/the-big-story/wind-energy-gets-serial/1012449.article
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Floating offshore wind turbines outside scope of current standards; guidelines for FOWTs being considered separately
Relevant Offshore Standards/Topics
• International Electrotechnical Commission’s IEC 61400-3 (2009)
• IEC 61400-3, 2nd edition (in preparation)• American Petroleum Institute Recommended Practice for
Fixed Offshore Structures (API RP2A, 1993)• AWEA’s Recommended Practices for Design,
Deployment, and Operation of Offshore Wind Turbines in the United State (2012)
• Referenced documents, e.g. ISO 19000 series• Validating, Testing, Certification (application of standards)
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IEC 61400-3 Process
• Prepare preliminary design (PD)• Develop structural dynamic model of PD (SDM)• Specify external design conditions (EDCs)• Specify design load cases (DLCs)• Using SDM with EDCs and DLCs determine
structural loads, deflections and stresses• Check that stresses etc. are acceptable, given chosen
material • Adapt design if necessary and repeat
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External Design Conditions
• Wind conditions
• Marine conditions – Waves, sea currents, water level, sea ice, marine
growth, seabed movement and scour
• Other environmental conditions
• Soil properties at the site– Including time variation due to seabed movement,
scour and other elements of seabed instability
Meteorological /oceanographic or “Metocean” Conditions
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Occurrences of External Conditions
• Normal – Recurrent structural loading conditions
• Extreme– Rare external design conditions of greater than
normal magnitude or effect
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Design Load Case Situations
1. As in 61400-1– Power production– Power production plus occurrence of fault– Start up– Normal shut down– Emergency shut down– Parked (standing still or idling)– Parked and fault conditions– Transport, assembly, maintenance and repair
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DLCs for Various Situations …
• Wind conditions
• Waves
• Wind and wave directionality
• Sea currents
• Water level
• Other conditions
• Type of analysis
• Partial safety factor10
IEC 61400-3, 2nd Ed. Changes Likely
• General corrections
• Wave models
• Hurricanes/cyclones
• Wind shear as affected by waves
• Floating ice
• Boat (service vessel) impact
• Soil characterization
• Vortex induced vibrations11
Issues for US
• Wind/wave conditions (e.g. hurricanes)– 100 yr vs. 50 yr events
• Role of API, other US standards
• Role of BOEM
• Other standards referenced by 61400-3 – US vs. European or international– English units vs. metric (SI) units
• Should IEC 61400-3 2nd ed. supercede AWEA’s Recommended Practice?
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