Final report for WP4.3: Enhancement of design methods ... - Upwind

Table 5.16 shows the required FDF values for different values of the α∆σ(U) function, namely the function
in Figure 5.2 and one where α∆σ(U) is constant. It is seen that almost the same FDF values are obtained.
Table 5.16: Required FDF and corresponding partial safety factors γf γm in ( ) for different values of COV∆. ∆βmin,FAT
= 3.5.
α∆σ(U) Mudline
Figure 2
moment, Constant
FDF (γf γm) 2.27 (1.31) 2.24 (1.31)
If a bi-linear SN curve is used then the required FDF values are shown in Table 5.17. Also shown are the
decreases in design values using a bi-linear SN-curve instead of a linear SN-curve. It is seen that compared
to a linear SN-curve larger FDF values are required, but at the same time smaller design values are
obtained.
Table 5.17: FDF and corresponding partial safety factors γf γm in ( ) and given ∆βmin,FAT (∆PF,max,FAT). Bi-linear SNcurve.
Wind turbine in wind farm
∆βmin,FAT (∆PF,max,FAT) 3,1 (10 -3 ) 3,5 (2 10 -4 ) 3,8 (10 -4 )
FDF 2.45 3.96 5.62
z Bilin / zlin
0.84 0.84 0.84
The stochastic model shown in Table 5.2 is used with model uncertainty on wind load, XWind and model
uncertainty on wake effect model, XWake LogNormal distributed with expected values = 1 and coefficient of
variations COVWind = = 0.10 and COVWake =0.10. This stochastic model is considered as representative for
a fatigue sensitive detail where consequences of failure are large, partly on [39], [40] and [41] and partly
based on engineering judgment. It is assumed that 5 wind turbines are close to the wind turbine considered
with distance between wind turbines di = 4 rotor diameters.
Table 5.18: Required FDF and corresponding partial safety factors γf γm in ( ) for given ∆βmin,FAT (∆PF,max,FAT). (–)
indicates that FDF ≤ 1.
P(COL|FAT) 3,1 (10 -3 ) 3,5 (2 10 -4 ) 3,8 (10 -4 )
1.0 1.80 (1.22) 2.54 (1.37) 3.26 (1.48)
0.5 1.49 (1.14) 2.17 (1.29) 2.81 (1.41)
0.1 1.0 (1.0) 1.40 (1.12) 1.95 (1.25)
0.01 1.0 (1.0) 1.0 (1.0) 1.0 (1.0)
If a linear SN-curve with m = 3 is used then Table 5.18 shows the required FDF values for PF,max = 10 -4 , 2
10 -4 , 10 -3 and for P(COL|FAT) = 1.0, 0.5, 0.1 and 0.01. In brackets is shown the corresponding values of the
product of the load and material partial safety factors γf γm. For a minimum annual reliability index equal to
3.5 FDF = 2.3 (and partial safety factor 1.31) is obtained if the consequence of the fatigue failure is large.
Table 5.19 shows the required FDF values for different values of COVWake. It is seen that the required FDF
is not sensitive with respect to COVWake.
Table 5.19: Required FDF and corresponding partial safety factors γf γm in ( ) for different values of COVWake.
COVWake 0.05 0.10 0.15
FDF (γf γm ) 2.54 (1.36) 2.54 (1.37) 2.55 (1.37)
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