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Update on Design Standards for Offshore Wind Turbines. Massachusetts Wind Working Group January 30, 2013. J. F. Manwell, Prof. Wind Energy Center Dept. of Mechanical & Industrial Engineering Univ. of Mass., Amherst, MA 01003. Why Are Standards Necessary?.
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Update on Design Standards for Offshore Wind Turbines Massachusetts Wind Working Group January 30, 2013 J. F. Manwell, Prof. Wind Energy Center Dept. of Mechanical & Industrial Engineering Univ. of Mass., Amherst, MA 01003
Why Are Standards Necessary? Without proper design standards, failures are much more likely Offshore presents particular challenges!
Parts of an Offshore Wind Turbine RNA Tower • Substructure Foundation • OWT defined here • Includes: • Rotor/nacelle assembly (RNA) • Support structure • Tower • Substructure • Foundation
Common Types of Support Structures http://www.theengineer.co.uk/in-depth/the-big-story/wind-energy-gets-serial/1012449.article Floating offshore wind turbines outside scope of current standards; guidelines for FOWTs being considered separately • Monopiles • Gravity base • Jackets • Others • Tripods • Suction bucket
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)
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
External Design Conditions Meteorological /oceanographic or “Metocean” 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
Occurrences of External Conditions • Normal • Recurrent structural loading conditions • Extreme • Rare external design conditions of greater than normal magnitude or effect
Design Load Case Situations • 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
DLCs for Various Situations … • Wind conditions • Waves • Wind and wave directionality • Sea currents • Water level • Other conditions • Type of analysis • Partial safety factor
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 vibrations
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?