Fatigue Design of Wind Turbines - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 677

The log-normal curve-fit equations for the two modes are as follows:

2

ln( L F ) - m

1

Mode 1: (12-4a)

n 1 = 4, 876exp - 0.5

s

1

2

ln( L F - 12.3) - m

Mode 2:

2

(12-4b)

n 2 = 235exp - 0.5

s

2

n = n 1 + n 2

(12-4c)

(12-4d)

PDF = n /0.5

where

n 1 , n 2 = bin cycle counts in Modes 1 and 2, respectively (cycles/hr/bin)

m 1 = 0.20, natural logarithm of median edgewise blade cyclic load L F in Mode 1

s 1 = 0.90, natural logarithm of standard deviation of L F in Mode 1

m 2 = 2.00, natural logarithm of median edgewise blade cyclic load L F in Mode 2

s 1 = 0.39, natural logarithm of standard deviation of L F in Mode 2

Using these log-normal curve-fit parameters, the median sizes of the edgewise cyclic loads
are 1.2 kN-m for Mode 1 and 19.7 kN-m for Mode 2. The 98 th percentile cyclic loads are 14.1
and 28.4 kN-m for Modes 1 and 2, respectively.