Wind Turbines Guidelines for Design

Guidelines for  Design of  Wind Turbines

A publication from  DNV/Risø

Second Edition

Guidelines for Design of Wind Turbines 2nd Edition  Det Norske Veritas, Copenhagen ([email protected]) ([email protected]) and Wind Energy Department, Risø National Laboratory ([email protected]) ([email protected]) 2002. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronical, mechanical, photocopying, photocopying, recording and/or otherwise without the prior written permission of the publishers. This book may not be lent, resold, hired out or otherwise disposed of by way of trade in any form of binding or cover other than that in which it is published, without the prior consent of  the publishers. The front-page picture is from Microsoft Clipart Gallery ver. 2.0. Printed by Jydsk Centraltrykkeri, Denmark 2002

ISBN 87-550-2870-5

Guidelines for Design of Wind Turbines −  DNV/Risø Preface

The guidelines for design of wind turbines have been developed with an aim to compile into one book much of the knowledge about design and construction of wind turbines that has been gained over the past few years. This applies to knowledge achieved from research projects as well as to knowledge resulting from practical design experience. In addition, the various rules and methods required for type approval within the major  markets for the wind turbine industry form a  basis for the guidelines, with emphasis on the international standards for wind turbines given by the International Electrotechnical Commission, IEC. The objective is to provide guidelines, which can be used for design of different types of wind turbines in the future. The guidelines provide recommendations and guidance for design together with application-oriented solutions to commonly encountered design problems.

The guidelines can be used by wind turbine manufacturers, certifying authorities, and wind turbine owners. The guidelines will also be useful as an introduction and tutorial for new technical personnel and as a reference for experienced engineers. The guidelines are available as a printed  book in a handy format as well as electronically in pdf format on a CD-ROM. The development of the guidelines is the result of a joint effort between Det Norske Veritas and Risø National Laboratory. The development has been founded by Danish Energy Agency, Det Norske Veritas and Risø National Laboratory. These guidelines for design of wind turbines have been thoroughly reviewed by internal and external experts. However, no warranty, expressed or implied, is made by Det Norske Veritas and Risø National Laboratory, as to the accuracy or functionality of the guidelines, and no responsibility is assumed in connection therewith.

Guidelines for Design of Wind Turbines © 2002 Det Norske Veritas and Risø National Laboratory

Preface

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Guidelines for Design of Wind Turbines −  DNV/Risø Contents

1. WIND TURBINE TURBINE CONCEPTS CONCEPTS ......... 1

1.1 I NTRODUCTION............................ ................................. ..... 1 1.2 CONCEPTUAL ASPECTS ..................... ..................... 1 1.2.1 Vertical axis turbines .................... .................... 2 1.2.2 Horizontal axis turbines.......... turbines ................ ...... 2 1.2.3  Number of rotor blades................. 3 1.2.4 Power control aspects aspects ........ ............ ........ ....... ... 3 1.3 ECONOMICAL ASPECTS ..................... ..................... 5 1.4 POWER PRODUCTION ........................ ........................ 5 1.4.1 Power curve ............................ .................................. ...... 6 1.4.2 Annual Annual energy production production ........ ............ .... 7 1.5 CONFIGURATIONS AND SIZES ......... ........... .. 7 1.6 FUTURE CONCEPTS ........................... ........................... 8 REFERENCES ......................... ....................................... .................. .... 9

2. SAFETY SAFETY AND RELIABILITY........ RELIABILITY........ 10

2.1 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.3.6 2.3.7 2.3.8 2.3.9 2.4 2.5 ii

SAFETY PHILOSOPHY ...................... ...................... 10 SYSTEM SAFETY AND OPERATIONAL RELIABILITY .......... ............ .. 11 Control system........... system ....................... ................. ..... 12 Protection system........................ system........................ 13 Brake system system ........ ............. ......... ......... ......... ........ .... 14 Failure mode and effects analysis ......................... ...................................... ............... 15 Fault tree analysis ....................... ....................... 16 STRUCTURAL SAFETY ..................... ..................... 18 Limit states ........................ ................................. ......... 18 Failure probability and other  measures of structural reliability. 18 Structural Structural reliabil reliability ity methods methods ..... ..... 19 Code format, characteristic values, and partial safety factors factors.. 19 Code calibration.......................... calibration.......................... 20 Example – axially loaded steel tower......................... tower................................... .......... 22 Example – fatigue of FRP  blade root in bending .................. .................. 24 Tests and calculations for  verification.................................. verification........................ .......... 26 Inspection and inspection intervals ..................... ..................... 26 MECHANICAL SAFETY .................... .................... 27 LABOUR SAFETY ............................ ............................ 28

2.5.1

Transportation, installation and commissioning ..................... ..................... 28 2.5.2  Normal operation........................ operation........................ 29 2.5.3 Service, Service, maintenanc maintenancee and repair repair . 29 2.6 CODES AND STANDARDS ......... .............. ....... .. 30 REFERENCES .......................... ....................................... ............... .. 30

3. EXTERNAL EXTERNAL CONDITIONS............ CONDITIONS............ 32

3.1 WIND CONDITIONS ......................... ......................... 32 3.1.1 10-minute 10-minute mean mean wind speed speed ....... ....... 32 3.1.2 Standard deviation of  wind speed ............................ .................................. ...... 34 3.1.3 Turbulence Turbulence intensity intensity ......... ............. ........ ...... .. 36 3.1.4 Lateral Lateral and vertica verticall turbulence turbulence ... 37 3.1.5 Stochastic Stochastic turbule turbulence nce models models ..... ..... 37 3.1.6 Wind shear.................................. shear.................................. 40 3.1.7 Wind direction ......................... ............................ ... 42 3.1.8 Transient Transient wind wind conditions conditions ........ .......... .. 43 3.1.9 Extreme winds – gusts gusts............ ................ .... 43 3.1.10 Site assessment .......................... ............................ 46 3.2 OTHER EXTERNAL CONDITIONS ...... ...... 48 3.2.1 Temperatures ........................... .............................. ... 48 3.2.2 Density of air .......................... .............................. .... 49 3.2.3 Humidity................................... Humidity..................................... .. 50 3.2.4 Radiation Radiation and ultravi ultraviolet olet light light .... 50 3.2.5 Ice ............................. ........................................... .................. .... 50 3.2.6 Rain, snow and and hail ........ ............ ......... ........ ... 50 3.2.7 Atmospheric corrosion and abrasion........... abrasion ........................ ..................... ........ 51 3.2.8 Earthquake............ Earthquake .......................... ...................... ........ 51 3.2.9 Lightning ........................... .................................... ......... 53 REFERENCES .......................... ....................................... ............... .. 53

4. LOADS...................... LOADS.................................... ......................... ........... 55

4.1 LOAD CASES ............................. ................................... ...... 55 4.1.1 Design Design situations situations ........ ............ ........ ........ ........ .... 55 4.1.2 Wind events .......................... ................................ ...... 55 4.1.3 Design Design load cases ........ ............ ........ ........ ....... ... 55 4.2 LOAD TYPES ............................. ................................... ...... 58 4.2.1 Inertia Inertia and gravity loads loads ......... ............. .... 58 4.2.2 Aerodynamic loads ..................... ..................... 59 4.2.3 Functional loads............. loads.......................... ............. 60

Contents

Guidelines for Design of Wind Turbines −  DNV/Risø 4.2.4 Other loads.................... loads.................................. .............. 60 4.3 AEROELASTIC LOAD CALCULATIONS ............................ .............................. .. 60 4.3.1 Model elements................ elements........................... ........... 61 4.3.2 Aeroelastic models for load  prediction ........................... .................................... ......... 70 4.3.3 Aerodynam Aerodynamic ic data assessment assessment .... 70 4.3.4 Special Special considerati considerations ons ........ ............ ........ .... 72 4.4 LOAD ANALYSIS AND SYNTHESIS ... ... 76 4.4.1 Fatigue loads.................... loads............................... ........... 76 4.4.2 Ultimate loads............................. loads............................. 82 4.5 SIMPLIFIED LOAD CALCULATIONS .. 86 4.5.1 Parametrise Parametrised d empirical empirical models... 86 4.5.2 The simple simple load basis ........ ............ ........ ...... 86 4.5.3 Quasi-static method .................... .................... 87 4.5.4 Peak factor approach for  extreme loads............ loads ......................... .................. ..... 88 4.5.5 Parametrise Parametrised d load spectra spectra ........ ........... ... 89 4.6 SITE-SPECIFIC DESIGN LOADS ......... ......... 92 4.7 LOADS FROM OTHER SOURCES THAN WIND ............................ ..................................... ......... 93 4.7.1 Wave loads ............................. ................................. .... 93 4.7.2 Current Current loads ......... .............. ......... ......... ......... ....... ... 99 4.7.3 Ice loads........................... loads...................................... ........... 99 4.7.4 Earthquake loads.............. loads......................... ........... 99 4.8 LOAD COMBINATION ...................... ...................... 99 REFERENCES ......................... ...................................... ............... 101

5. ROTOR............... ROTOR............................. ........................... ............... .. 104

5.1 BLADES ........................... ........................................ ............. 104 5.1.1 Blade geometry......................... geometry......................... 104 5.1.2 Design Design loads ........ ............. ......... ......... ......... ....... ... 105 5.1.3 Blade materials ........................ .......................... 105 5.1.4 Manufactur Manufacturing ing techniques techniques ........ ........ 108 5.1.5 Quality assurance for blade design design and manufacture manufacture ........ ............ .... 109 5.1.6 Strength analyses ...................... ...................... 110 5.1.7 Tip deflections ........................ .......................... .. 113 5.1.8 Lightning Lightning protection protection ........ ............. ......... .... 113 5.1.9 Blade testing ......................... ............................. .... 114 5.1.10 Maintenanc Maintenancee ......... ............. ........ ......... ......... ....... ... 116 5.2 HUB ........................... ......................................... .................. .... 116 5.2.1 Determinat Determination ion of design loads loads .. 117 5.2.2 Strength Analysis...................... Analysis...................... 117 5.2.3 Analysis of bolt connections..... 118 5.2.4 Hub enclosure ........................ ........................... ... 118

5.2.5 Materials............. Materials ........................... ...................... ........ 118 5.2.6 Standards ........................... .................................. ....... 119 REFERENCES ......................... ...................................... ............... 119

6. NACELLE NACELLE ......................... ...................................... ............... 120

6.1 MAIN SHAFT ............................ ................................. ..... 120 6.1.1 Determinat Determination ion of design design loads.. 120 6.1.2 Strength analysis....................... analysis....................... 120 6.1.3 Fatigue Fatigue strength strength ........ ............ ........ ........ ........ .... 121 6.1.4 Ultimate Ultimate strength strength ........ ............ ........ ........ ...... .. 125 6.1.5 Main shaft-gea shaft-gearr connection connection ...... ...... 126 6.1.6 Materials............. Materials ........................... ...................... ........ 126 6.1.7 Standards ........................... .................................. ....... 127 6.2 MAIN BEARING ........................... ............................. 127 6.2.1 Determinat Determination ion of design design loads.. 129 6.2.2 Selection of bearing types......... types......... 130 6.2.3 Operational and environmental conditions.......... 130 6.2.4 Seals, lubrication and temperatures.................... temperatures....................... ... 130 6.2.5 Rating Rating life calculations calculations ........ ............ ...... 132 6.2.6 Connection Connection to main shaft ........ .......... .. 133 6.2.7 Bearing housing............ housing ........................ ............ 133 6.2.8 Connection Connection to machine machine frame... 133 6.2.9 Standards ........................... .................................. ....... 133 6.3 MAIN GEAR .......................... .................................. ........ 133 6.3.1 Gear types............. types .......................... .................... ....... 134 6.3.2 Loads Loads and capacity ........ ............ ........ ....... ... 137 6.3.3 Codes and standards standards ......... .............. ........ ... 141 6.3.4 Lubrication Lubrication ........ ............ ........ ......... ......... ........ ...... .. 141 6.3.5 Materials and testing................. 142 6.4 COUPLINGS .......................... .................................. ........ 145 6.4.1 Flange couplings....................... couplings....................... 145 6.4.2 Shrink fit couplings couplings ........ ............ ........ ...... .. 146 6.4.3 Key connections connections ........ ............ ........ ......... ....... .. 146 6.4.4 Torsionall Torsionally y elastic couplings. couplings. ... 146 6.4.5 Tooth couplings ....................... ......................... 146 6.5 MECHANICAL BRAKE ......... .............. ......... ...... 146 6.5.1 Types of brakes......................... brakes......................... 146 6.5.2 Brake discs and brake pads....... 148 6.5.3 Brake torque sequence.............. 148 6.6 HYDRAULIC SYSTEMS ........ ............. ......... ...... 149 6.6.1 Arrangement .......................... ............................. ... 149 6.6.2 Accumulators............................ Accumulators............................ 149 6.6.3 Valves............. Valves ........................... .......................... ............ 149

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Guidelines for Design of Wind Turbines −  DNV/Risø 6.6.4

Application in  protection systems .................... .................... 150 6.6.5 Additional Additional provisions provisions ........ ............ ....... ... 151 6.6.6 Codes Codes and standards standards ......... ............. ........ .... 151 6.7 GENERATOR ........................... ................................. ...... 151 6.7.1 Types of generators generators ......... ............. ......... ..... 151 6.7.2 Climate aspects ......................... ......................... 153 6.7.3 Safety aspects aspects ........ ............ ........ ........ ........ ....... ... 153 6.7.4 Cooling Cooling and and degree degree of sealing sealing .. 155 6.7.5 Vibrations .......................... ................................. ....... 155 6.7.6 Overspeed ........................... ................................. ...... 155 6.7.7 Overloading ........................... .............................. ... 155 6.7.8 Materials ........................... ................................... ........ 156 6.7.9 Generator braking ..................... ..................... 156 6.7.10 Lifetime .......................... .................................... .......... 157 6.7.11 Testing Testing of generators generators ........ ............ ........ .... 157 6.8 MACHINE SUPPORT FRAME ........ ........... ... 157 6.9  NACELLE ENCLOSURE .................. .................. 158 6.10 YAW SYSTEM ........................... ............................... .... 158 6.10.1 6.10.1 Determinati Determination on of design design loads.. 160 6.10.2 Yaw drive ......................... ................................. ........ 161 6.10.3 Yaw ring ........................... ................................... ........ 162 6.10.4 Yaw brake..................... brake................................. ............ 162 6.10.5 Yaw bearing.................. bearing.............................. ............ 163 6.10.6 Yaw error and and control............... 166 6.10.7 Cable twist ......................... ................................ ....... 166 6.10.8 Special Special design considerat considerations ions... ... 166 REFERENCES ......................... ...................................... ............... 167

7. TOWER .......................... ....................................... ................. .... 169

7.1 7.2 7.3 7.3.1 7.3.2 7.4 7.4.1 7.4.2 7.4.3 7.4.4 7.4.5 7.4.6

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LOAD CASES ........................... ................................. ...... 170 DESIGN LOADS ............................ .............................. 170 GENERAL VERIFICATIONS FOR  TOWERS ........................... ........................................ ............. 171 Dynamic response and resonance .......................... .............................. .... 171 Critical blade deflection analysis ....................... ....................... 172 TUBULAR TOWERS ....................... ....................... 173 Loads and responses ................. ................. 173 Extreme loads .......................... ............................ 174 Fatigue loads............................. loads............................. 174 Vortex induced induced vibrations......... vibrations......... 174 Welded joints............. joints .......................... ............... .. 175 Stress concentrations near  hatches and doors...................... doors...................... 176

7.4.7 Stability analysis....................... analysis....................... 177 7.4.8 Flange connections connections ......... ............. ........ ...... .. 178 7.4.9 Corrosion protection ................. ................. 179 7.4.10 Tolerance Tolerancess and specificati specifications ons... ... 179 7.5 ACCESS AND WORKING ENVIRONMENT .......................... ............................. ... 180 7.6 EXAMPLE OF TOWER LOAD CALCULATION ........................... .............................. ... 180 7.6.1 Loads and responses ................. ................. 180 7.6.2 Occurrence of extreme loads during normal power production.......... 181 7.6.3 Extreme Extreme loads loads – parked parked turbine turbine 182 7.6.4 Fatigue loading ......................... ......................... 183 REFERENCES ......................... ...................................... ............... 186

8. FOUNDATIONS........................ FOUNDATIONS............................. ..... 187

8.1 SOIL INVESTIGATIONS ........ ............. ......... ...... 187 8.1.1 General ........................... ..................................... .......... 187 8.1.2 Recommendations for gravity  based foundations ..................... ..................... 188 8.1.3 Recommendations for pile foundations ......................... ............................... ...... 189 8.2 GRAVITY-BASED FOUNDATIONS ... ... 189 189 8.2.1 Bearing Bearing capacity formulas formulas ........ ........ 190 8.3 PILE-SUPPORTED FOUNDATIONS ... ... 193 193 8.3.1 Pile groups .......................... ................................ ...... 194 8.3.2 Axial pile resistance.................. resistance.................. 195 8.3.3 Laterally loaded loaded piles.............. piles................ .. 197 8.3.4 Soil resistance for embedded  pile caps ........................... .................................... ......... 200 8.4 FOUNDATION STIFFNESS ........ ............ ....... ... 201 EINFORCED 8.5 PROPERTIES OF R EINFORCED CONCRETE ........................... ................................... ........ 206 8.5.1 Fatigue .......................... ...................................... ............ 206 8.5.2 Crack-width ......................... .............................. ..... 207 8.5.3 Execution.................................. Execution........................ .......... 208 8.6 SELECTED FOUNDATION STRUCTURE CONCEPTS FOR 

........ ............ ...... 208 8.6.1 Introduction Introduction to concepts concepts ........ ........... ... 208 8.6.2 Monopile Monopile ........ ............ ........ ........ ........ ......... ......... ...... 209 8.6.3 Tripod ........................... ....................................... ............ 215 REFERENCES ......................... ...................................... ............... 221

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OFFSHORE APPLICATIONS

Guidelines for Design of Wind Turbines −  DNV/Risø 9. ELECTRICA ELECTRICAL L SYSTEM............... 223

9.1 ELECTRICAL COMPONENTS ........ ........... ... 223 9.1.1 Generators....................... Generators................................. .......... 223 9.1.2 Softstarter Softstarter ........ ............ ......... ......... ........ ......... ........ ... 225 9.1.3 Capacitor bank............. bank ......................... .............. 225 9.1.4 Frequency Frequency converter converter ........ ............ ........ ...... 226 9.2 WIND TURBINE CONFIGURATIONS 227 9.3 POWER QUALITY AND GRID CONNECTION .......................... ................................ ...... 229 9.4 ELECTRICAL SAFETY .................... .................... 230 9.5 WIND FARM INTEGRATION ........ ........... ... 231 REFERENCES ......................... ...................................... ............... 232

10. MANUA MANUALS LS ........................... ...................................... ........... 233

USER MANUAL ............................ .............................. 233 SERVICE AND MAINTENANCE MANUAL .......................... ....................................... ............. 233 10.3 I NSTALLATION MANUAL ......... .............. ....... 233 REFERENCE ......................... ..................................... ................ .... 233

A.7

MINIMUM DEPTH OF THREADED HOLES ......................... ......................... 244 A.8 BOLT FORCE ANALYSIS ........ ............. ........ ... 245 A.8.1 Stiffness of bolts ....................... ....................... 245 A.8.2 Stiffness Stiffness of the mating mating parts parts ..... ..... 246 A.8.3 Force triangle............................ triangle............................ 246 A.9 CONNECTIONS SUBJECTED TO SHEAR  ........................... ..................................... .......... 247 A.10 BOLTS SUBJECTED TO TENSILE LOAD ......................... ......................... 248 A.11 BOLTS SUBJECTED TO TENSILE LOAD AND SHEAR ......................... ......................... 249 A.12 EXECUTION OF BOLT CONNECTIONS ........................... .............................. ... 249 A.13 CODES AND STANDARDS ......... ............. ...... 249 REFERENCES ......................... ...................................... ............... 249

10.1 10.2

11. TESTS AND MEASUREMENTS.. MEASUREMENTS.. 234

11.1

POWER PERFORMANCE MEASUREMENTS ........................... ........................... 234 11.2 LOAD MEASUREMENTS ......... ............. ........ .... 236 11.3 TEST OF CONTROL AND PROTECTION SYSTEM .................... .................... 237 11.4 POWER QUALITY MEASUREMENT . 237 11.5 BLADE TESTING ........................... ............................. 237 11.6  NOISE MEASUREMENTS ........ ............ ........ .... 237 REFERENCES ......................... ...................................... ............... 237

A. BOLT CONNECTIO CONNECTIONS................. NS................. 239

A.1 A.2 A.3 A.4 A.5 A.5.1

BOLT STANDARDIZATION ......... ............. .... 239 STRENGTH ............................ .................................... ........ 239 IMPACT STRENGTH ....................... ....................... 239 SURFACE TREATMENT .................. .................. 239 S-N CURVES ........................... ................................. ...... 240 S-N curves in structural steel codes..................... codes................................. ............ 241 A.5.2 Allowable surface pressure....... 242 A.6 PRETENSION ........................... ................................. ...... 242 A.6.1 Safety Safety against against loosening loosening ........ ........... ... 244

B. RULES OF THUMB.............. THUMB....................... ......... 250

B.1 LOADS ........................... ......................................... ................ 250 B.1.1 Rotor loads.................. loads............................... ............... 250 B.1.2 Fatigue loads............................. loads............................. 250 OTOR  .......................... B.2 R OTOR  ........................................ ................ 250 B.3  NACELLE ............................ ...................................... .......... 251 B.3.1 Main shaft............ shaft .......................... ..................... ....... 251 B.4  NOISE ............................ .......................................... ................ 251 REFERENCES ......................... ...................................... ............... 251

C. FATIGUE FATIGUE CALCULATI CALCULATIONS ONS ....... 252

C.1 C.2 C.3 C.4 C.5 C.6

STRESS RANGES ........................... ............................. 252 FRACTURE MECHANICS ........ ............. ........ ... 252 S - N   N CURVES ............................ ................................. ..... 253 THE PALMGREN-MINER RULE ...... ...... 254 FATIGUE IN WELDED STRUCTURES 255 CHARACTERISTIC S - N   N CURVES FOR STRUCTURAL STEEL ........ ............ ....... ... 256 C.7 CHARACTERISTIC S - N   N CURVES FOR FORGED OR ROLLED STEEL .... .... 256 256 C.8 S - N   N CURVES FOR COMPOSITES ...... ...... 257 C.9 OTHER TYPES OF FATIGUE ASSESSMENT ........................... ................................ ..... 258 REFERENCES ......................... ...................................... ............... 258

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Guidelines for Design of Wind Turbines −  DNV/Risø D. FEM CALCULATION CALCULATIONS.............. S................. ... 260

D.1 TYPES OF ANALYSIS ..................... ..................... 260 D.2 MODELLING ........................... ................................. ...... 261 D.2.1 Model............................ Model........................................ ............ 261 D.2.2 Elements ........................... ................................... ........ 262 D.2.3 Boundary conditions................. 264 D.2.4 Loads ........................... ........................................ ............. 265 D.3 DOCUMENTATION ........................ ........................ 265 D.3.1 Model............................ Model........................................ ............ 265 D.3.2 Results .......................... ...................................... ............ 267

E. MATERIAL MATERIAL PROPERTIES PROPERTIES .......... 268

E.1 STEEL ........................... ......................................... ................ .. 268 E.1.1 Structural steel ......................... ........................... 268 E.1.2 Alloy steel..................... steel................................. ............ 269 E.2 CAST IRON ............................ .................................... ........ 269 EINFORCED PLASTICS ...... E.3 FIBRE R EINFORCED ...... 269 E.3.1 Glass Glass fibre reinforced reinforced plastics plastics .. 269 E.4 CONCRETE ........................... ................................... ........ 270 E.4.1 Mechanical properties............... properties............... 270 REFERENCES ......................... ...................................... ............... 270

F. TERMS AND DEFINITIONS DEFINITIONS ....... 271

REFERENCES ......................... ...................................... ............... 276

G. TABLES TABLES AND CONVERSIONS CONVERSIONS ... 277

G.1 G.2 G.3 G.4

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E NGLISH/METRIC CONVERSION .... .... 277 277 AIR DENSITY VS . TEMPERATURE .. 277 277 AIR DENSITY VS . HEIGHT ........ ............. ....... 277 AYLEIGH WIND DISTRIBUTION .... R AYLEIGH .... 277 277

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