考虑土-斜桩相互作用的近海风机支撑结构动力行为研究

Offshore wind turbines (OWT) have a rapid development in the east coasts of China where is an active seismic region. As an efficient way to resist horizontal loads, inclined pile groups have been widely used in OWTs of China. The influence of soil-inclined pile interaction on OTWs becomes a key problem for the seismic fortification and long-term stable operation of OTWs. Therefore, this project would take the “stiffness degradation of soil-interaction between soil and inclined piles-system dynamic model” as the main line to study the dynamic behavior of an OWT with the consideration of soil-inclined pile interaction effect. Firstly, horizontal cyclic load test of a scaled OWT model supported on an inclined pile group, together with the cyclic triaxial test of soil, will be performed to establish a mathematical model for the description of the soil cyclic degradation; Secondly, the impedance of the inclined pile group which is embedded in layered saturated half-space with a degraded area, will be derived based on the theory of saturated porous media. Thirdly, the dynamic conventional governing equation of the soil-inclined pile-support structure system can be established based on the substructure method. The time history analysis and natural frequency of OWT can be obtained by employing the step-by-step integration method and the complex model theory, respectively. The validity and efficiency of the present procedure will be verified by the results obtained by shaking table test and cyclic loading test of the OWT system. The dynamic mechanism of OWT effected by the soil-inclined pile interaction would be demonstrated based on the parametric analysis. The achievements from the present project will provide both theoretical interest and engineering value for the seismic design and natural frequency prediction of OWTs.

我国风电场迅速发展的东部沿海地区属地震活跃区，为了更好的抵抗水平环境荷载，斜桩承台基础在国内风机设计中得到了广泛应用。考虑土-斜桩相互作用对风机支撑结构的动力行为影响，是实现风机结构抗震设防和长期稳定运行要解决的关键问题。鉴于此，本项目以“土体弱化效应—桩土相互作用—系统力学模型”为主线，进行了以下研究：(1)开展饱和土循环三轴试验以及风机支撑结构模型水平循环加载试验，建立描述桩周土循环弱化规律的数学模型；(2)基于饱和多孔介质理论，推导埋置于含有弱化域饱和土中的斜桩承台基础阻抗函数；(3)采用子结构法建立土-斜桩-风机支撑结构系统的半解析动力学模型，参数化分析影响风机支撑结构地震响应及其动力特性演变的关键因素及其影响规律，揭示土-斜桩相互作用对风机支撑结构动力行为的影响机理。本项目的研究成果为近海风机支撑结构的抗震设计及其服役期内的自振频率演变预测提供理论依据。

近海风机支撑结构长径比大、侧向刚度小，属于典型的长周期结构，土-斜桩动力相互作用效应对风机支撑结构的动力行为有着显著的影响。本项目提出了研究地震作用下土-斜桩-风机支撑结构系统动力响应的半解析方法，参数化分析桩、土参数对动力相互作用的影响规律。主要工作包括：1）基于弹性半空间理论以及连续梁振动理论，推导了考虑桩周土扰动效应的桩基振动阻抗及相邻斜桩动力相互作用因子；2）基于切比雪夫多项式建立了描述斜桩群基础阻抗频率依赖性的递归集总参数模型；3）基于上述递归集总参数模型，建立了考虑土-斜桩-风机支撑结构耦合的半解析动力学模型，利用逐步积分法求解地震作用下风机支撑结构的时程响应。该方法程序简单，计算量小，参数确定方便，具有较强的实用性，为解决地震作用下风机结构的动力学响应分析奠定了理论基础。