Dynamic stiffness of monopiles supporting offshore wind turbine generators
Dynamic stiffness of monopiles supporting offshore wind turbine generators
复制标题
DOI：
10.1016/j.soildyn.2016.04.002
复制
发表时间：
2016-09
影响因子：
4
通讯作者：
M. Shadlou;M. Shadlou;S. Bhattacharya
中科院分区：
文献类型：
--
作者：
M. Shadlou;M. Shadlou;S. Bhattacharya
超大直径钢管桩（直径达10米，称为XL或XXL单桩）和沉箱目前被用作支撑海上风力发电机（WTG）的基础，尽管实践规范的指导有限。API/DnV等现行规范建议分析长柔性桩的方法（通常没有任何修改），用于分析大直径单桩，结果不令人满意。因此，人们对深地基的长径比（L/D）的大范围嵌入不同类型的土壤的分析很感兴趣。本文利用哈密顿原理进行了一项理论研究，分析了埋在三种类型的地面剖面（均质、非均质和分层连续体）中的深地基（L/D≥2），这是海上风力涡轮机行业感兴趣的。对于在所有3种地基剖面中表现出刚性和柔性行为的桩，已经提出了阻抗函数（静态和动态）。通过分析得出，传统的基于Winkler的方法（如p-y曲线或Bean-on-Dynamic Winkler地基）可能不适用于长径比小于10 ~ 15的桩或沉箱。结果还表明，在相同的无量纲频率下，大直径刚性桩的阻尼比高于长柔性桩，约为材料阻尼的1.2 ~ 1.5倍。研究还表明，基于winkler的柔性桩方法不能准确预测刚性桩的刚度，从而也不能准确预测WTG系统的固有频率。来自四个不同的欧洲风力发电场的四个风力涡轮机基金会被认为可以获得进一步有用的见解。
Very large diameter steel tubular piles (up to 10 m in diameter, termed as XL or XXL monopiles) and caissons are currently used as foundations to support offshore Wind Turbine Generators (WTG) despite limited guidance in codes of practice. The current codes of practice such as API/DnV suggest methods to analysis long flexible piles which are being used (often without any modification) to analyse large diameter monopiles giving unsatisfactory results. As a result, there is an interest in the analysis of deep foundation for a wide range of length to diameter (L/D) ratio embedded in different types of soil. This paper carries out a theoretical study utilising Hamiltonian principle to analyse deep foundations (L/D≥ 2) embedded in three types of ground profiles (homogeneous, inhomogeneous and layered continua) that are of interest to offshore wind turbine industry. Impedance functions (static and dynamic) have been proposed for piles exhibiting rigid and flexible behaviour in all the 3 ground profiles. Through the analysis, it is concluded that the conventional Winkler-based approach (such as p–y curves or Bean-on-Dynamic Winkler Foundations) may not be applicable for piles or caissons having aspect ratio less than about 10 to 15. The results also show that, for the same dimensionless frequency, damping ratio of large diameter rigid piles is higher than long flexible piles and is approximately 1.2–1.5 times the material damping. It is also shown that Winkler-based approach developed for flexible piles will under predict stiffness of rigid piles, thereby also under predicting natural frequency of the WTG system. Four wind turbine foundations from four different European wind farms have been considered to gain further useful insights.