Abstract

Monopiles are popular solutions as the foundation to support offshore wind turbines (OWTs), which suffer from various amplitudes of continuous lateral cyclic wind and wave loading. The accumulation of tilt and change of the natural frequency of OWTs under cyclic loading have become crucial issues for OWT design. Hence the monopile-tower-soil system was established at the small-scale level based on similarity laws with a suit of constant-amplitude and multi-amplitude tests in dense sand. Two sets of gear-driving assembly were successfully set up to achieve the application of cyclic loading to the model OWT. The amplitude and symmetry of cyclic loading were specified as three indicative regions according to those of real wind farms. On the basis of test results, the two-way loading was found to be the most hazardous situation and the preloading condition led to a high accumulation of tilt. The change of natural frequency was controlled by the load magnitude and tended to increase during cyclic loads, while a sharp decrease was observed when sand subsidence was generated. The post-cyclic lateral capacity seemed to be a slight increase compared with the static capacity. The relevant analyses based on test results can provide practical recommendations for OWT design.

摘要

单桩作为支撑海上风力涡轮机 (OWT) 的基础是流行的解决方案，这些风力涡轮机遭受各种幅度的连续横向循环风和波浪载荷。循环载荷下 OWT 的倾斜累积和固有频率的变化已成为 OWT 设计的关键问题。因此，基于相似定律，在密砂中进行了一系列等幅和多幅试验，在小尺度上建立了单桩-塔-土系统。成功地设置了两组齿轮驱动组件，实现了循环加载到模型 OWT 的应用。循环载荷的幅值和对称性根据实际风电场的幅值和对称性被指定为三个指示区域。根据测试结果，双向加载被认为是最危险的情况，预加载条件导致倾斜的高度积累。固有频率的变化受荷载大小控制，在循环荷载期间趋于增加，而在产生砂土沉降时观察到急剧下降。与静态容量相比，循环后横向容量似乎略有增加。基于测试结果的相关分析可为OWT设计提供实用建议。