Research on Dynamic Characteristics of Monopile Offshore Wind Turbine Tower Under Different Wind Speed Conditions

doi:10.12096/j.2096-4528.pgt.22153

Abstract

Abstract:

Based on the ANSYS finite element software, the NREL 5 MW monopile offshore wind turbine tower system was modeled in 3D. The influence of different wind speeds on the dynamic characteristics of the tower structure was simulated and analyzed under the full consideration of the soil structure coupling effect and the impeller rotation. The six average wind speeds and the corresponding impeller speeds in the interval between the cut-in wind speed of 3 m/s and the cut-out wind speed of 25 m/s were selected as simulation conditions. The analysis results show that, with the increase of wind speed and impeller speed, the modal frequency of the tower structure gradually increases, and the first two modal frequencies change most obviously. Moreover, the peak value of the tower displacement increases as the wind speed and impeller speed increases, but the amplitude decreases. The displacement shows a non-linear growth trend. The equivalent stress value of the tower increases as the wind speed and impeller speed increases, but the change trend is different from the displacement, which is roughly linear. The fatigue life of the tower decreases sharply, but they are far more than the actual working hours, the fatigue damage and safety factor hazard values are mainly distributed at the bottom of the tower and at the single pile, consistent with the maximum equivalent stress distribution position.

Key words: offshore wind turbine, tower, wind speed, blade rotation speed, soil-structure interaction, dynamic characteristics

CLC Number:

TK 83

Ang FAN, Luping LI, Rui LIU, Minnan OUYANG, Shangnian CHEN. Research on Dynamic Characteristics of Monopile Offshore Wind Turbine Tower Under Different Wind Speed Conditions[J]. Power Generation Technology, 2024, 45(2): 312-322.

Figures/Tables 20

Fig. 1 Three-dimensional solid model of monopile offshore wind turbine

Tab. 1 Structural material properties of wind turbines

结构名称	密度/(kg/m³)	杨氏模量/GPa	泊松比
叶片	1 850	38	0.3
塔筒	7 850	210	0.3
单桩	7 850	210	0.3

Tab. 2 Main parameters of NREL 5 MW mono-pile offshore wind turbine

项目	参数	数值
基础描述	额定功率/MW	5
	切入、额定风速/( $m · s - 1$ )	3、11.4
	额定转速/(r/min)	12.1
	转子配置	3叶片
叶片	转子直径/m	126
	轮毂高度/m	100
	轮毂直径/m	3
	叶片长度/m	61.5
塔筒	塔筒高度/m	90
	塔顶、塔底外径/m	3.87、6
	塔顶、塔底壁厚/m	0.027、0.054
单桩	单桩长度/m	75
	单桩外径/m	6
	单桩壁厚/m	0.054

Tab. 2 Main parameters of NREL 5 MW mono-pile offshore wind turbine

项目	参数	数值
基础描述	额定功率/MW	5
	切入、额定风速/( $m · s - 1$ )	3、11.4
	额定转速/(r/min)	12.1
	转子配置	3叶片
叶片	转子直径/m	126
	轮毂高度/m	100
	轮毂直径/m	3
	叶片长度/m	61.5
塔筒	塔筒高度/m	90
	塔顶、塔底外径/m	3.87、6
	塔顶、塔底壁厚/m	0.027、0.054
单桩	单桩长度/m	75
	单桩外径/m	6
	单桩壁厚/m	0.054

Tab. 3 Six simulation conditions

参数	工况1	工况2	工况3	工况4	工况5	工况6
平均风速/( $m / s$ )	3.0	7.2	11.4	16.0	20.4	25.0
叶轮转速/(r/min)	6.9	9.6	12.1	12.1	12.1	12.1

Tab. 3 Six simulation conditions

参数	工况1	工况2	工况3	工况4	工况5	工况6
平均风速/( $m / s$ )	3.0	7.2	11.4	16.0	20.4	25.0
叶轮转速/(r/min)	6.9	9.6	12.1	12.1	12.1	12.1

Fig. 2 Curve of relationship between average wind speed and impeller speed

Tab. 4 Measured soil quality parameters of offshore wind farms

参数	淤泥质粉质黏土	粉砂	粉质黏土
有效重度/( $k N · m - 3$ )	7.6	9.6	9.9
剪切波速/( $m · s - 1$ )	110.0	190.0	210.0
剪切模量/MPa	21. 7	70. 8	97. 2
弹性模量/MPa	56. 4	184	252. 7
泊松比	0.3	0.3	0.3

Tab. 4 Measured soil quality parameters of offshore wind farms

参数	淤泥质粉质黏土	粉砂	粉质黏土
有效重度/( $k N · m - 3$ )	7.6	9.6	9.9
剪切波速/( $m · s - 1$ )	110.0	190.0	210.0
剪切模量/MPa	21. 7	70. 8	97. 2
弹性模量/MPa	56. 4	184	252. 7
泊松比	0.3	0.3	0.3

Fig. 3 Schematic diagram of the internal cross-section of the soil and monopile model

Tab. 5 Meshing division scheme

参数	方案1	方案2	方案3	方案4
机组网格尺寸/mm	1 000	750	500	500
土体网格尺寸/mm	2 000	2 000	2 000	1 000
总单元数	359 320	408 432	534 033	2 794 423
总节点数	515 230	593 260	805 936	3 868 600
平均元素质量	0.824 9	0.803 03	0.851 31	0.878 21
平均Skewness值	0.232 54	0.263 09	0.209 1	0.188 38

Fig. 4 Mesh independence verification results

Fig. 5 100 s distribution diagram of fluctuating wind speed when the average wind speed is 11.4 m/s

Fig. 6 100 s time history curve of fluctuating wind load at the top of the tower under rated wind speed

Fig. 7 100 s wave load time history curve

Tab. 6 Modal frequency values of the tower structure under the first three simulation conditions

模态阶数	叶片静止工况/Hz	工况1计算值/Hz	变化率/%	工况2计算值/Hz	变化率/%	工况3计算值/Hz	变化率/%
一阶频率	0.154 92	0.159 51	2.966	0.163 74	5.697	0.169 28	9.27
二阶频率	0.158 08	0.162 62	2.869	0.166 67	5.431	0.172 36	9.03
三阶频率	0.643 33	0.646 74	0.531	0.648 99	0.880	0.649 57	0.97
四阶频率	0.735 98	0.740 37	0.597	0.742 10	0.832	0.743 50	1.02
五阶频率	0.890 43	0.902 10	1.310	0.911 10	2.321	0.954 75	7.22
六阶频率	1.364 94	1.410 45	3.334	1.421 00	4.107	1.437 70	5.33

Fig. 8 Cloud diagram of the total displacement of the transient response of the overall unit under different simulation conditions

Fig. 9 Variation curve of tower transient response displacement with average wind speed

Fig. 10 Equivalent stress cloud diagram of tower structure transient response under different working conditions

Fig. 11 Variation curve of equivalent stress value of tower transient response with average wind speed

Fig. 12 Tower sructural material S-N Curve

Fig. 13 Variation curve of fatigue life of tower structure with average wind speed

Fig. 14 Fatigue damage distribution and safety factor cloud map of tower structure

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