Page 9 - Wind Energy Handbook

CONTENTS ix

5.4 Extreme Loads 214
5.4.1 Non-operational load cases – normal machine state 214
5.4.2 Non-operational load cases – machine fault state 215
5.4.3 Operational load cases – normal machine state 215
5.4.4 Operational load cases – loss of load 217
5.4.5 Operational load cases – machine fault states 218
5.4.6 Start-up and shut-down cases 218
5.4.7 Blade/tower clearance 218
5.5 Fatigue Loading 218
5.5.1 Synthesis of fatigue load spectrum 218
5.6 Stationary Blade Loading 219
5.6.1 Lift and drag coefficients 219
5.6.2 Critical configuration for different machine types 219
5.6.3 Dynamic response 220
5.7 Blade Loads During Operation 228
5.7.1 Deterministic and stochastic load components 228
5.7.2 Deterministic aerodynamic loads 228
5.7.3 Gravity loads 236
5.7.4 Deterministic inertia loads 236
5.7.5 Stochastic aerodynamic loads – analysis in the frequency domain 239
5.7.6 Stochastic aerodynamic loads – analysis in the time domain 249
5.7.7 Extreme loads 252
5.8 Blade Dynamic Response 255
5.8.1 Modal analysis 255
5.8.2 Mode shapes and frequencies 258
5.8.3 Centrifugal stiffening 259
5.8.4 Aerodynamic and structural damping 262
5.8.5 Response to deterministic loads—step-by-step dynamic analysis 264
5.8.6 Response to stochastic loads 268
5.8.7 Response to simulated loads 271
5.8.8 Teeter motion 271
5.8.9 Tower coupling 276
5.8.10 Wind turbine dynamic analysis codes 282
5.8.11 Aeroelastic stability 286
5.9 Blade Fatigue Stresses 287
5.9.1 Methodology for blade fatigue design 287
5.9.2 Combination of deterministic and stochastic components 288
5.9.3 Fatigue predictions in the frequency domain 290
5.9.4 Wind simulation 292
5.9.5 Fatigue cycle counting 293
5.10 Hub and Low-speed Shaft Loading 293
5.10.1 Introduction 293
5.10.2 Deterministic aerodynamic loads 294
5.10.3 Stochastic aerodynamic loads 296
5.10.4 Gravity loading 297
5.11 Nacelle Loading 298
5.11.1 Loadings from rotor 298