海上风电结构地基土动应力变化规律研究

Numerical Study on Stress Change within the Foundation of Offshore Wind Generators

以承受水平荷载为主的海上风力发电机在风、浪等荷载的共同作用下其结构—地基系统具有复杂的受荷特性,使得基础周围的地基土表现出复杂的应力变化特性。本文通过数值计算分析了海上风机上部结构所受水平荷载与波浪荷载的作用方向夹角以及荷载频率对地基土应力状态的影响,揭示了海上风机单桩结构地基土的典型应力时程变化及分布规律。结果表明海上风电结构地基土的应力幅值大小和主应力方向角都在发生变化,上部水平荷载与波浪荷载间的夹角以及二者的频率都对地基土的应力状态,特别是主应力方向角的旋转产生了很大影响。

As a clean energy, offshore wind power has attracted increasing attention and invest- ments. Offshore wind generators with pile foundations are mainly subjected to horizontal loading coursed by wind, waves, ice, ocean currents, and earthquakes. Such complex loading that acts upon the structure-foundation system leads to complex stress changes within the foundation. Mo reover, extremely strict requirements for the deformation behaviors of offshore wind generator foundation structures and adjacent soils are controlled in their design and usage. However, knowledge of the actual stress changes and the deformation laws are very limited. This paper sys- tematically investigates the stress-time histories of typical points in the foundations around a typi- cal offshore wind generator and the amplitude distribution of the stress-changing induced by wind and waves through three-dimensional {3D） finite element method （FEM） numerical analysis. The effects of the angle between the directions of horizontal wind loading acting on the structure and the waves and frequency of the two loading types are studied. The results indicate that the ampli- tude and the principal stress direction of the wind generator foundations are both changing. The angle and the frequencies of the two loadings significantly affect the stress state, particularly the principal stress rotation. 3D cyclic rotation of the principal stress axes within a limited rotating angle is determined to occur always in the foundation soil adjacent to the foundation structure of an offshore wind generator. In particular, it is shown to become a two--dimensional （2D） cyclic rotation of principal stress axes when two directions of the wind load and the wave propagation remain the same. However, the stress paths become more complex when the frequencies of the two cyclic loads differ.