Fatigue damage calculation method of monopile supported offshore wind turbine
Jian-bin ZHAO1(),Yi-bo XI1,Zhen-yu WANG2,*()
1. School of Civil Engineering, Shenyang Jianzhu University, Shenyang 110168, China 2. College of Civil and architecture, Zhejiang University, Hangzhou 310058, China
The applicability and influence of different calculation methods were evaluated, in order to improve the accuracy of the fatigue damage calculation of offshore wind turbine foundation. The fatigue evaluation of a monopile supported offshore wind turbine was studied. The full time domain dynamic analysis model and the frequency domain fatigue damage calculation process based on power spectral density function were established. The influence of aerodynamic damping, combined wind and wave loads and stress range probability distribution model on the fatigue damage were studied. Results show that the fatigue damage is easily affected by the aerodynamic damping, and the wind-induced fatigue damage is more sensitive to aerodynamic damping than the wave-induced fatigue damage. Since the combined wind and wave loads has great influence on the foundation fatigue damage, the result of simply superimposing wind-induced and wave-induced fatigue damage is less than the result of combined wind and wave loads. It is necessary to determine an appropriate stress range probability distribution model. The wind-induced and wave-induced fatigue damage calculated by Dirlik model and inverse fast Fourier transform (IFFT) in frequency domain method is respectively close to the results by time domain method, but the total fatigue damage of superimposing wind-induced and wave-induced fatigue damage is less than that of combining wind and wave loads by time domain method.
Fig.2Flow chart of frequency domain method fatigue evaluation analysis
风况
Δu/（m·s?2）
u/（m·s?2）
P/%
海况
Hs/m
T/s
P/%
W1
2.5~4.0
3
10.52
S1
0.5
2
5.93
W2
4.0~6.0
5
20.11
S2
0.5
3
36.59
W3
6.0~8.0
7
21.94
S3
1.0
3
16.05
W4
8.0~10.0
9
18.42
S4
0.5
4
8.05
W5
10.0~12.0
11
12.28
S5
1.0
4
19.79
W6
12.0~14.0
13
6.59
S6
1.5
4
6.76
W7
14.0~20.0
16
4.13
S7
1.5
5
2.45
W8
<2.5
?
5.93
S8
2.0
5
3.18
W9
>20.0
?
0.08
S9
2.5
5
1.20
Tab.1Division results of wind cases and sea cases
Fig.3Occurrence probability of wind and sea combined cases
Fig.4Comparison of time and frequency domain stress PSD
Fig.5Influence of aerodynamic damping on fatigue damage in wind case IV
Fig.6Influence of aerodynamic damping on fatigue damage in sea case IX
Fig.7Influence of aerodynamic damping on fatigue damage in combined wind case IV and sea case IX
风况
Dwind
K/%
海况
Dwave
K/%
注：Dtotal=Dwind+Dwave=4.70×10?1
W1
3.80×10?6
0
S1
2.09×10?5
0.25
W2
4.87×10?4
0.11
S2
1.33×10?4
1.56
W3
7.89×10?3
1.71
S3
1.87×10?3
22.00
W4
3.87×10?2
8.39
S4
1.20×10?5
0.14
W5
9.03×10?2
19.59
S5
9.44×10?4
11.11
W6
1.37×10?1
29.72
S6
2.45×10?3
28.82
W7
1.87×10?1
40.56
S7
2.38×10?4
2.80
W8
0
0
S8
1.30×10?3
15.29
W9
0
0
S9
1.53×10?3
18.00
Dwind
4.61×10?1
100.00
Dwave
8.50×10?3
100.00
Tab.2Foundation fatigue damage of each case with wind or wave loading alone
Fig.8Foundation fatigue damage of each case with combined wind and wave loads
Fig.9Fatigue damage under combination of sea case II and each wind case
Fig.10Fatigue damage under combination of wind case VII and each sea case
计算方法
Dwind
Dwave
时域方法
0.461
8.50×10?3
频域方法
IFFT方法
1.94
9.70×10?3
Dirlik模型
0.523
?
BT模型
4.35
?
Tunna模型
1.21
?
Rayleigh模型
?
0.461
Tab.3Foundation fatigue damage with different calculation methods
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