海上风电吸力桶基础地震分析

Seismic analysis of a suction caisson foundation for offshore wind turbines

为进行海上风电吸力桶基础地震安全评估,选取欧洲北海砂质海床中典型的吸力桶基础,基于三维砂土液化大变形统一本构模型,通过OpenSees有限元开源平台进行三维动力计算,分析了吸力桶基础的地震变形和倾覆转角。吸力桶基础的地震变形具体如下:基础产生一定的水平位移震荡,最终累积发展为大变形;桶基发生严重的不均匀沉降,桶基后部出现一定程度的上移;倾覆转角不断增加,最终达0.8°以上,远超过规范规定的安全稳定运营值,后期无法运营;基础转动中心在地震过程中不断调整;地震中海床孔压上升,桶基内出现一定的负孔压,可以提高抗倾覆承载力,地震结束时负压区消散。海床液化深度约3m,桶基前部产生刺入海床破坏。海床地震液化加剧了吸力桶基础的变形和倾覆,严重影响着海上风机的安全运营。

The stability of suction caisson foundations during earthquakes is evaluated for a typical suction caisson foundation of an offshore wind turbine located in a sandy seabed in the North Sea. The analysis was a unified plasticity model for the large post-liquefaction shear deformation of the sand and a three-dimensional dynamic finite clement analysis to predict the seismic deformation and overturning probability during an earthquake. The analysis shows that the foundation experiences horizontal oscillations that lead to large deformations. The caisson slants with the rear moving up. The overturning probability keeps increasing and the angle eventually reaches more than 0.8°, which exceeds the safety limit. The rotation center constantly changes and the seabed pore pressure increases. Negative pore pressures can develop inside the caisson which enhance the overturning probability, but then dissipate. The seabed liquefaction depth is about 3 m, so the front of the caisson pierces into the seabed. Consequently, seabed liquefaction aggravates the deformation and overturning probability which affects the system operation.