DNVGL-ST-0437 Loads And Site Conditions For Wind Turbines

STANDARDDNVGL-ST-0437Edition November 2016Loads and site conditions for wind turbinesThe electronic pdf version of this document found through http://www.dnvgl.com is the officially binding version.The documents are available free of charge in PDF format.DNV GL AS

FOREWORDDNV GL standards contain requirements, principles and acceptance criteria for objects, personnel,organisations and/or operations. DNV GL AS November 2016Any comments may be sent by e-mail to rules@dnvgl.comThis service document has been prepared based on available knowledge, technology and/or information at the time of issuance of this document. The use of thisdocument by others than DNV GL is at the user's sole risk. DNV GL does not accept any liability or responsibility for loss or damages resulting from any use ofthis document.

Changes – currentCHANGES – CURRENTGeneralThis is a new document.Standard, DNVGL-ST-0437 – Edition November 2016DNV GL ASPage 3

CHANGES – CURRENT . 3Sec.1Sec.2Sec.3Introduction . 81.1General.81.2Objectives .81.3Scope and application .91.4Normative references .91.5Informative references.101.6Terminology .111.7Acronyms, abbreviations and symbols .121.7.1 Acronyms and abbreviations. 121.7.2 Symbols . 131.7.3 Greek symbols. 16External conditions . 182.1Fundamentals.182.1.1 Relevant types of external conditions. 182.1.2 External conditions for turbine types and wind farm sites . 182.1.3 Consideration of external conditions in the design . 182.2Wind turbine classes .192.2.1 Wind data for turbine classes. 192.2.2 Wave data for offshore wind turbine classes . 202.2.3 Wind turbine classes. 202.3Wind conditions.222.3.1 General . 222.3.2 Offshore normal turbulence model. 222.3.3 Offshore extreme turbulence model . 242.4Marine conditions for offshore wind turbines .242.4.1 General . 242.4.2 Wave climate . 252.4.3 Wind-wave misalignment . 252.4.4 Reference sea states and wave heights . 252.4.5 Wave modelling . 262.4.6 Wave theories and wave kinematics . 312.4.7 Breaking waves . 312.4.8 Sea currents . 322.4.9 Sea level, bathymetry . 332.4.10 Sea ice . 342.4.11 Marine growth . 352.5Other environmental conditions .362.5.1 General . 362.5.2 Other environmental conditions . 372.5.3 Extreme temperatures . 372.5.4 Atmospheric ice formation. 372.5.5 Earthquakes . 382.5.6 Wind farm influence . 382.5.7 Soil properties . 382.5.8 Risk analysis . 392.5.9 Sea bed and scour . 392.5.10 Electrical power network conditions . 39Determination of site specific design conditions . 40Standard, DNVGL-ST-0437 – Edition November 2016DNV GL ASPage 4ContentsContents

Sec.4General.403.1.1 External conditions. 403.1.2 Wind farm location data . 413.2Methods for determining site specific meteorological designconditions .413.2.1 General . 413.2.2 Meteorological data bases . 413.2.3 Meteorological measurements. 413.2.4 Numerical methods . 423.3Determination of meteorological data .423.3.1 General . 423.3.2 Turbulence intensity . 433.3.3 Extreme wind extrapolation . 433.4Site specific marine conditions .443.4.1 General . 443.4.2 Wave data . 453.4.3 Current data . 463.4.4 Water level data . 463.4.5 Sea ice . 463.4.6 Marine growth . 463.4.7 Seabed movement and scour. 463.5Determination of other environmental conditions .463.5.1 Foundation/soil properties . 463.5.2 Influence of earthquakes. 473.5.3 Complex terrain . 473.5.4 Corrosive and/or abrasive effects . 483.5.5 Electrical network conditions . 483.5.6 Weather window and weather down time . 48Calculation of loads . 494.1Fundamentals.494.1.1 General . 494.1.2 Assessment documents. 494.1.3 Design methods. 514.1.4 Safety classes . 514.2Calculation of loads .514.2.1 General . 514.2.2 Loads . 524.2.3 Operational loads . 524.2.4 Inertia and gravitation loads. 534.2.5 Aerodynamic loads . 534.2.6 Hydrodynamic loads . 544.2.7 Hydrostatic loads . 594.2.8 Sea ice loads . 594.2.9 Seismic loads . 604.2.10 Boat impact loads . 604.2.11 Combination of external conditions . 624.2.12 Combination of loads . 624.2.13 Load impact due to extreme temperatures . 624.2.14 Variation of support structure natural frequency and operationwithin the resonance range . 624.2.15 Load-relevant control and safety system functions. 624.2.16 Other loads . 634.3Partial safety factors for loads .63Standard, DNVGL-ST-0437 – Edition November 2016DNV GL ASPage 5Contents3.1

4.3.24.3.34.3.44.3.5Sec.5Partial safety factors for the loads in the analysis of the ultimatelimit state/ultimate strength . 64Partial safety factors in the analysis of the fatigue limit state/fatiguestrength . 64Partial safety factors in the analysis of the accidental limit states. 64Serviceability limit states . 64Special partial safety factors. 654.4Load case tables for onshore and offshore loads .654.5Design situations and load cases for wind turbines .694.5.1 Power production (DLC 1.1 to 1.7) . 694.5.2 Power production plus occurrence of fault (DLC 2.1 to 2.5) . 704.5.3 Start-up (DLC 3.1 to 3.3). 714.5.4 Normal shut-down (DLC 4.1 and 4.2) . 714.5.5 Emergency shut-down (DLC 5.1). 724.5.6 Parked (DLC 6.1 to 6.5) . 724.5.7 Parked plus fault conditions (DLC 7.1 and 7.2) . 734.5.8 Transport, installation, maintenance and repair (DLC 8.1 to 8.5) . 744.5.9 General influences . 754.5.10 Operational influences . 764.6Design load cases for extended design situations .764.6.1 Drifting sea ice (DLC 9.1 to 9.5). 794.6.2 Temperature effect (DLC 10.1 and 10.2) . 794.6.3 Earthquakes (DLC 11.1 to 11.3). 794.6.4 Wind farm influence (DLC 12.1) . 794.7Evaluation of loads .794.7.1 General . 794.7.2 Evaluation of load cases applying deterministic gusts . 804.7.3 Evaluation of load cases applying turbulent wind . 804.7.4 Evaluation of DLC 1.1 and DLC1.3 . 804.8Site specific evaluation .814.8.1 Site specific evaluation through comparison of site wind conditionsand design class conditions . 814.8.2 Site specific evaluation through load calculations. 82Measurements. 845.1General.845.2Requirements for the wind turbine to be tested .845.3Power curve measurements .855.4Load measurements .855.4.1 Measurement of mechanical loads according IEC 61400-13. 855.4.2 Verification of design loads via model verification by comparingsimulation and measurement results . 85App. A Coordinate systems. 87App. B Statistical extrapolation procedure . 91App. C Evaluation of the loads. 93App. D Generator short-circuit. 97App. E Design parameters for the description of an onshore wind turbineclass S . 98App. FDesign parameters for the descriptionof an offshore wind turbine andwind farm. 100App. G Directional distribution of waves in a sea state . 103App. H Wake and wind farm turbulence. 104Standard, DNVGL-ST-0437 – Edition November 2016DNV GL ASPage 6Contents4.3.1

Load assessment relevant data . 106Standard, DNVGL-ST-0437 – Edition November 2016DNV GL ASPage 7ContentsApp. I

SECTION 1 INTRODUCTION1.1 GeneralThis DNV GL standard provides principles, technical requirements and guidance for loads and site conditionsof wind turbines. For the first time, the requirements for onshore and bottom mounted offshore windturbines are defined consistently and concisely in a single document. The definition of offshore turbulenceclasses has been revised significantly to include turbulence distributions adapted to the offshoreenvironment. In addition marine parameters have been included to define offshore type classes which maybe used for the type certification of an offshore rotor-nacelle assembly (RNA) and sub-structure.Based on more than three decades of experience as standard setter and certification body in the windindustry, this standard fills gaps and provides clarity and additional guidance, where existing standards lacksuch guidance. The requirements of this standard focus on reaching the intended safety level in an economicway. Where the intended safety level could have been reached in several ways, the requirements of thisstandard have in general been aligned with requirements of other international standards, in particular withthe IEC 61400 series of standards.This standard has been developed and updated by DNV GL and undergoes external hearing by thecommittee of experts and other external stakeholders prior to publication as part of the quality assuranceprocess. This standard is checked regularly to ensure its content is in accordance with the state of the art.It will be updated to keep it current and to ensure appropriate coverage in areas of ongoing technologicaldevelopment.The standard has been written for world-wide application. National and governmental regulations mayinclude requirements in excess of the provisions given in this standard. The DNV GL wind turbine standardsas listed in Table 1-1 have been aligned technically, regarding the provided safety level and theirrequirements. Along with the DNV GL service documents as listed in Table 1-1 they form the mostcomprehensive basis for the design and certification of wind turbines and wind farms.The standard contains five sections:Sec.1 gives an introduction and provides context towards other DNV GL standards and service specificationsand towards other existing loads standards.Sec.2 covers external conditions relevant for the loads of wind turbines. External conditions for onshorewind turbines are identical to those in IEC 61400-1, whereas marine conditions are covered in depth in thisstandard and refer partly to IEC 61400-3.Sec.3 covers site conditions and requirements for determining site specific design conditions as part of thedesign basis.Sec.4 covers the calculation of loads, including different sources of loading, safety factors, load casedefinitions and evaluation of loads.Sec.5 covers requirements for type testing, in particular regarding verification of design loads throughcomparison of simulations and measurements.Guidance note:The present DNV GL standard will cover the technical requirements to be applied for the DNV GL certification schemes according toDNVGL-SE-0190 and DNVGL-SE-0441, and it is also intended to cover the requirements implied when using IEC 61400-22 relatedcertification schemes.The latest revision of all DNV GL documents may be found on the DNV GL website n-c-e---n-o-t-e---1.2 ObjectivesThe objectives of this standard are to:— provide an internationally acceptable level of safety by defining minimum requirements for thedetermination of loads of wind turbines (in combination with referenced standards, recommendedpractices, etc.)— serve as a design basis for designers, suppliers, purchasers and authorities— specify requirements for wind turbines and wind farms subject to DNV GL certification.Standard, DNVGL-ST-0437 – Edition November 2016DNV GL ASPage 8

wind turbines are identical to those in IEC 61400-1, wh ereas marine conditions are covered in depth in this standard and refer partly to IEC 61400-3. Sec.3 covers site conditions and requirements for determin ing site specific design conditions as part of the design basis.