Offshore wind turbines are often built on large-diameter monopile, which are exposed to lateral loads and overturning moments from wind and wave action, which is cyclic in nature. In this work, an attempt was made to examine the influence of embedded length on monopile behaviour using finite-element analysis (Plaxis 3D). The developed model was validated using a centrifuge test conducted on monopile embedded in sand. Numerical studies were conducted on a 6 m diameter monopile by varying the load amplitude and embedded length ratios. The monopile was subjected to both one-way and two-way symmetric lateral cyclic loading with an amplitude of 30%, 40% and 50% of the pile monotonic ultimate capacity. The effects of embedded lengths and load amplitude on the accumulated displacements and the cyclic stiffness were studied. It was found that the rate of accumulated displacement increased by a factor of 0.3–0.7 when the load amplitude increased from 30% to 50%. An increase in load amplitude was also observed to cause a linear increase in accumulated displacements. The slope of the attenuation value was found to be higher for an increase in the L/D ratio from 4 to 5 as compared to an increase from 5 to 6.

中文翻译：

---

单桩单向和双向横向循环荷载的有限元分析

海上风力涡轮机通常建造在大直径单桩上，承受风浪作用产生的侧向载荷和倾覆力矩，其本质上是循环的。在这项工作中，尝试使用有限元分析 (Plaxis 3D) 检查嵌入长度对单桩行为的影响。使用对嵌入沙子的单桩进行离心测试来验证开发的模型。通过改变荷载振幅和嵌入长度比，对直径 6 m 的单桩进行了数值研究。单桩承受单向和双向对称横向循环荷载，振幅分别为桩单调极限承载力的30%、40%和50%。研究了嵌入长度和载荷幅值对累积位移和循环刚度的影响。研究发现，当载荷幅值从30%增加到50%时，累积位移率增加了0.3-0.7倍。还观察到负载幅度的增加导致累积位移线性增加。我们发现，与 L/D 比从 5 增加到 6 相比，L/D 比从 4 增加到 5 时，衰减值的斜率更高。