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 Massachusetts Wind Working Group January 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 RNA Substructure Foundation Tower 3

Common Types of Support Structures Monopiles Gravity base Jackets Others –Tripods –Suction bucket story/wind-energy-gets-serial/ article 4 Floating offshore wind turbines outside scope of current standards; guidelines for FOWTs being considered separately

Relevant Offshore Standards/Topics International Electrotechnical Commission’s IEC (2009) IEC , 2 nd 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 series Validating, Testing, Certification (application of standards) 5

IEC 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 6

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 7

Occurrences of External Conditions Normal –Recurrent structural loading conditions Extreme –Rare external design conditions of greater than normal magnitude or effect 8

Design Load Case Situations 1.As in  –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 9

DLCs for Various Situations … Wind conditions Waves Wind and wave directionality Sea currents Water level Other conditions Type of analysis Partial safety factor 10

IEC , 2 nd 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 11

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 –US vs. European or international –English units vs. metric (SI) units Should IEC nd ed. supercede AWEA’s Recommended Practice? 12