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Wind Turbine Broadband + Deterministic Fatigue

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Presentation on theme: "Wind Turbine Broadband + Deterministic Fatigue"— Presentation transcript:

1 Wind Turbine Broadband + Deterministic Fatigue
Nigel Barltrop University of Strathclyde

2 Nature of Stress History
Broadband stochastic: Low frequency gusting Rotational sampling of gusts at multiples of rotor frequency Natural frequency resonances Deterministic: Moment from blade weight reverses in plane (1P) Blades sample high winds at height and low wind speeds near ground Cyclic load from any yaw error Tower shadow

3 Fatigue Analysis Options
Usual method for design Time domain Calculate all effects together Rainflow count Simplified check Frequency domain for stochastic effect Rainflow count using Dirlik distribution Add in deterministic damage

4 Methods of adding Stochastic & Deterministic Damage
Assume Linear or Quadratic (SRSS) addition of proportion (p) of stresses at lowest frequency Add additional damage from higher frequencies (Stress to D1/m, m = 3 to 5, 3 assumed here (corrosive environment)) Linear suggests direct addition of stress ranges (likely when frequencies very different) Quadratic suggests random addition (seems more reasonable when frequencies close)

5 Comparison of methods with rainflow count
Safe Unsafe Linear: safe but sometimes perhaps too safe, Quadratic: generally unsafe but a closer estimate

6 Deterministic Stress: Phase Angle Sensitivity

7 Conclusion In this case:
Linear addition of stresses is as expected pessimistic (safe) Quadratic (SRSS) addition is slightly unsafe


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