Analysis of the influence of scour depth on the dynamic response of offshore wind turbine towers under earthquake action
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摘要: 基于某海上風電塔進行現場監測、有限元模擬及室內振動臺試驗研究，考慮樁-土相互作用并對結構進行精細化數值模擬分析，研究了不同沖刷深度下結構自振周期的變化及不同沖刷深度對結構地震動作用下動力響應的影響規律.現場監測結果表明：6#風機結構受海水沖刷嚴重，與同時期建造的15#風機相比振動幅度明顯，說明沖刷深度對結構的影響不可忽略.數值模擬分析表明：沖刷深度主要影響結構高階振型，使結構自振周期變長，增幅最大達33%.由于沖刷致使土層對高柔性結構約束減弱，結構將產生大的振動進而導致風機停擺；在遭遇7度罕遇地震時，應立即停止發電工作.室內縮尺振動臺試驗與數值模擬所得結果的變化曲線較為均勻，趨勢上較吻合，充分驗證了數值模擬的準確性.Abstract: The operational environment of offshore wind turbine towers is complex, and the harsh service environment makes them more vulnerable to damage under conditions of complex stress such as sea water scouring. The scouring pit has a great influence on the vibration of wind turbine towers. It is of great importance to study the dynamic response to earthquakes of wind turbine towers under scouring depths. The research object of this study was a wind turbine tower at a wind farm in Jiangsu Province, which had a seven-degree seismic fortification in the area. Based on finite element simulation, on-site monitoring and a shaking table test of the offshore wind tower, and considering pile-soil interaction in a refined model, variation in the natural vibration period of the structure under different scouring depths and the influence of different scouring depths on the dynamic response of the structure under seismic excitation were studied. On-site monitoring results show that the #6 wind turbine structure is seriously eroded by sea water, and the vibration amplitude is clear compared with the #15 wind turbine built in the same period. These aspects indicate that the influence of scouring depth on the structure could not be ignored. Analysis of numerical simulation show that scouring depth has a great influence on the high-order mode of the structure, which lengthen the natural vibration period of the structure by a maximum of 33%. On account of scouring, constraints of the soil layer on the highly flexible structure were weakened, and the structure produced considerable vibration, which could lead to damage of structures such as wind towers. Results also indicate that when encountering a seven-degree rare earthquake, power generation should immediately be stopped. The variation curves of the shaking table test and the numerical simulation results were more uniform, and the trend coincided well, which fully verified the accuracy of the numerical simulation.
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圖 2 自由振動衰減動力特性傅氏頻率. (a) 6#風機；(b) 15#風機
Figure 2. Fourier frequency of free vibration attenuation dynamic characteristic: (a) wind turbine tower 6#; (b) wind turbine tower 15#
圖 3 各土層不同深度P-y關系曲線. (a)粉砂層；(b)粉土層
Figure 3. P-y curves at different soil layer depths: (a) silty sand; (b) silty soil
圖 4 不同沖刷深度的計算模型示意圖及細部模擬示意圖. (a)不同沖刷深度計算模型示意圖；(b)細部模擬示意圖
Figure 4. Calculating models and detailed simulation sketches for different scouring depths: (a) calculation models of different scouring depths; (b) detailed simulation sketches
圖 6 3種地震波加速度反應譜
Figure 6. Acceleration response spectra of three types of seismic waves
圖 7 不同沖刷深度條件下風電塔結構模態頻率對比圖
Figure 7. Comparison of modal frequencies of wind turbine towers under different scour depth conditions
圖 8 不同沖刷深度下結構動力響應峰值. (a)位移峰值；(b)加速度峰值；(c)應力峰值
Figure 8. Peak dynamic response of structures under different scouring conditions: (a) displacement peak value; (b) acceleration peak value; (c) stress peak value
圖 9 不同沖刷深度支撐結構頂部節點時程曲線. (a)位移時程曲線；(b)加速度時程曲線
Figure 9. Time-history curves of the top node with different scour depth support structures: (a) displacement-time history curve; (b) acceleration-time history curve
圖 10 振動臺試驗模型. (a)試驗振動臺；(b)傳感器布置(單位：mm)；(c)振動試驗示意圖
Figure 10. Shaking table test model: (a) shaking table; (b) sensor arrangement(unit: mm); (c) schematic of the vibration test
圖 11 試驗與模擬對比. (a) ILA049；(b) ILA004
Figure 11. Comparison of the experiment and simulation: (a) ILA049; (b) ILA004
表 1 現場急剎車試驗自振頻率
Table 1. Natural vibration frequency of field braking test
測試工況 6#風機 15#風機 自振頻率/Hz 自振周期/s 自振頻率/Hz 自振周期/s 第一次急剎車試驗 0.319 3.135 0.331 3.021 第二次急剎車試驗 0.318 3.145 0.327 3.058 
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表 2 土層及地質參數表
Table 2. Soil layer and geological parameter
編號 類型 深度/m 有效重度, γ/(kN·m-3) 極限側阻力標準值, qsik/kPa 地基抗力比例系數，m/(kN·m-4) 內摩擦角, ?/(°) 不排水剪切強度, Cu/kPa 1/2最大應力時的應變, εc 極限抗力側移值，yc/mm 1 粉砂 4 9.8 15 1400 32 / / / 2 粉土 3 10 30 1600 30.7 / / / 3 粉砂 6 10 60 4000 32.6 / / / 3-夾 層狀粉土 6 8.2 32 2000 28.5 / / / 4 粉質黏土 3 9.5 52 4500 / 32 0.009 112.5 6-3 粉細砂 12 10 84 6000 34.1 / / /
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表 3 沖刷前后風電塔支撐結構振動模態比較
Table 3. Comparison of vibration modes of wind turbine tower supporting structures before and after scouring
模態階數 無沖刷結構/Hz 沖刷5 m結構/Hz 降幅/% 沖刷10 m結構/Hz 降幅/% 1 0.306 0.301 1.6 0.291 4.9 2 0.311 0.305 1.9 0.295 5.1 3 0.916 0.906 1.1 0.890 2.8 4 1.225 1.205 1.6 1.172 4.3 5 1.460 1.406 3.7 1.361 6.8 6 3.095 2.942 4.9 2.715 12.3 7 3.223 2.985 7.4 2.774 13.9 8 7.017 5.819 17.1 5.683 19.0 9 7.061 6.560 7.1 6.002 15.0 10 8.186 6.597 19.4 6.124 25.2
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中文字幕在线观看表 4 不同沖刷深度結構在不同地震動作用下的動力響應結果
Table 4. Dynamic response of structures with different scouring degrees under different ground motions
地震動名稱 峰值調整/(cm·s-2) 最大響應加速度/(m·s-2) 加速度放大率/% 最大響應位移/m 最大響應應力/MPa 沖刷5 m 沖刷10 m 沖刷5 m 沖刷10 m 沖刷5 m 沖刷10 m 沖刷5 m 沖刷10 m Imperial
Valley-06220 9.623 10.267 9.6 17.0 0.443 0.477 68.7 71.3 400 17.610 18.788 10.3 17.7 0.811 0.873 125.8 130.5 1000 44.170 47.125 11.8 19.3 2.512 2.723 312.2 327.4 T1-Ⅲ-1 220 5.724 6.240 1.2 10.3 0.413 0.461 56.8 60.5 400 10.400 11.286 2.1 10.8 0.749 0.838 103.1 109.9 1000 26.043 28.262 6.1 15.1 2.199 2.430 260.9 275.3 T2-Ⅲ-1 220 4.151 4.396 1.1 7.1 0.231 0.240 34.5 45.6 400 9.473 10.050 1.7 7.9 0.418 0.434 67.3 82.6 1000 21.199 22.617 3.2 10.1 1.228 1.274 169.4 206.7
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