Abstract

The large-diameter monopile, as one of the most used foundations of offshore wind turbines, is subjected to severe sea conditions, such as the cyclic lateral loads induced by wind and waves, as well as the scour induced by the flushing currents. The combined cyclic lateral loads and scour introduces additional complexity and is encountered in offshore wind turbines as well as other offshore structures.

In this study, the experimental tests and numerical simulation methods are adopted to investigate the behavior of monopile subjected to the combined cyclic lateral loads and scour. Firstly, the static and one-way cyclic lateral load tests are conducted to investigate the influence of scour conditions and the characteristics of cyclic lateral loads on the lateral displacement and bending moment of monopile. Subsequently, the three-dimensional numerical model is established by employing the stiffness degradation material model, reasonable comparisons between the numerical results and the experimental results suggest that the numerical model can be used as a reliable complement of the model tests. Finally, a series of parametric studies are carried out to investigate the effect of cycle numbers, scour conditions and cyclic load ratio on the accumulated deformation and lateral bearing capacity of monopile. It is found that the accumulated deformations are dependent on the cyclic load characteristics and scour depth, the one-way cyclic load and scour have opposite effects to the lateral capacity of monopile. A framework to predict the accumulated deformation of monopile subjected to the combined scour and long-term cyclic lateral load is developed, which can be served as a basis for the practical design of monopile.

摘要

大直径单桩作为海上风电机组最常用的基础之一，承受着风浪引起的周期性横向载荷以及冲水流的冲刷等恶劣海况。联合循环横向载荷和冲刷引入了额外的复杂性，并且在海上风力涡轮机以及其他海上结构中遇到。

本研究采用试验试验和数值模拟方法研究单桩在联合循环侧向荷载和冲刷作用下的行为。首先进行静力和单向循环侧向荷载试验，研究冲刷条件和循环侧向荷载特性对单桩侧向位移和弯矩的影响。随后，采用刚度退化材料模型建立了三维数值模型，数值结果与实验结果的合理比较表明，该数值模型可以作为模型试验的可靠补充。最后，进行了一系列参数研究来研究循环次数的影响，冲刷条件和循环荷载比对单桩累积变形和横向承载力的影响。研究发现，累积变形取决于循环荷载特性和冲刷深度，单向循环荷载和冲刷对单桩侧向承载力的影响相反。建立了单桩在冲刷和长期循环侧向联合荷载作用下的累积变形预测框架，可为单桩的实际设计提供依据。