海上风机支撑结构动力特性模型试验研究

Scaled Model Test Study of the Dynamic Behavior of an Offshore Wind Turbine Support Structure

摘要:

海上风机是一种高柔性海洋结构物，其支撑结构动力响应受风、浪、流等环境因素，风机荷载及基础刚度的影响异常敏感。本文在结构动力特性试验平台上，建立了以基础-塔架-顶部集中质量为一体的风机简化分析模型，并利用新型循环加载装置，在砂土中开展了4组针对风机模型长期动力特性变化规律的试验。主要研究在一定的加载频率下，支撑结构一阶自振频率在不同幅值的循环荷载作用下的变化规律，并从土体力学行为特性及循环荷载下土颗粒运移规律角度对试验现象进行分析。通过该模型试验所获得的结论，并基于一系列的相似性准则，在一定程度上可以揭示长期循环荷载下，海上风机支撑结构动力特性的变化规律，并对今后实际工程中有关基础选型及支撑结构设计上给出了相关建议。

Abstract:

Offshore wind is a safe，clean, and stable source of renewable energy，which is a strategic option for overcoming the problems of energy shortage and environment contamination. Because of their high，slender，and flexible nature，accompanied with mass and stiffness distribution，offshore wind turbines are dynamically sensitive structures in which their dynamic behavior is strongly affected by environmental loading and the stiffness of their foundations.The first natural frequencies of these structures are very close to the forcing frequencies imposed by the environment and the onboard machinery.Changes in the foundation stiffness under cyclic loading will ultimately result in changes to the natural frequency of the structure.However，little is known about the long-term dynamic behavior of the entire offshore wind turbine structure.Therefore，the design of foundations and prediction of long term performance remain challenging.In the design work of offshore wind turbines，the soft-stiff type is usually chosen under general circumstances in which the natural frequency is between 1P and 3P bands.This study establishes a simplified wind turbine model based on the dynamic model test platform at the University of Surrey.The model system includes a foundation，tower，and top mass.On the basis of the novel cyclic loading provide system，four groups of tests were conducted to study the long-term dynamic behavior of a wind turbine model supported on a pile foundation.This investigation focused on changes of the model turbine’s first natural frequency and studied the influence from the amplitude of cyclic loading.For the observed tests results，detailed analysis was performed on the basis of soil behavior and its migration pattern.The test results and a series of similitude relationships reveal the dynamic behavior of an wind turbine structure. Moreover，suggestions for foundation and structure selection for a prototype wind turbine are given.