Numerical Modelling of large diameter monopiles supporting OWT-Head stiffness assessment in Nonhomogeneous Soils

A. Hemza, Amar Bouzid Djillali
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Abstract

Many countries are now planning to build new wind farms with high capacity up to 5MW. Consequently, the size of the foundation increased. This kind of structures are subjected to fatigue damage from environmental loading mainly due to wind and waves as well as from cyclic loading imposed through the rotational frequency (1P) through mass and aerodynamic imbalances and from the blade passing frequency (3P) of the wind turbine which makes their behavior dynamically very sensitive. That is why natural frequency must be determined with accuracy in order to avoid the resonance of the system. This paper presents a numerical procedure which combines the finite element method based on the 2D discretization in the radial plane and the Fourier series based on expansion of displacements and forces in the circumferential direction. Firstly analytical expressions of stiffnesses of foundations with large diameter embedded in soils with different stiffness profile are established. Secondly and in order to check the accuracy of the proposed formulas, a mathematical model approach based on nondimensional parameters is used to calculate the natural frequency taking into account the soil structure interaction (SSI) compared with measured frequency in five wind farms selected from the litterature. Keywords—Offshore Wind Turbines; Semi-analytical FE analysis; DNV/Risø; Monopiles foundations; Natural frequency.
非均质土中大直径单桩owt头刚度评估的数值模拟
许多国家现在都在计划建造新的风电场,容量高达5兆瓦。因此,基础的规模增加了。这类结构受到环境载荷的疲劳损伤,主要是由于风和波浪,以及通过旋转频率(1P)施加的循环载荷,通过质量和气动不平衡以及风力机的叶片通过频率(3P),这使得它们的动态行为非常敏感。这就是为什么必须准确地确定固有频率,以避免系统的共振。本文提出了一种将基于径向平面二维离散化的有限元法与基于周向位移和力展开的傅立叶级数相结合的数值计算方法。首先建立了不同刚度剖面下大直径埋置地基的刚度解析表达式;其次,为了检验所提公式的准确性,采用基于无量纲参数的数学模型方法计算考虑土壤结构相互作用(SSI)的固有频率,并将从文献中选择的五个风电场的实测频率进行比较。关键词:海上风力发电机组;半解析有限元分析;DNV / Risø;Monopiles基础;自然频率。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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