运行状态下海上单桩风机系统自振频率分析

系统自振频率限制是海上风机结构设计中的一个关键因素。运行状态下风机动力荷载会引起基础的水平侧移,较大的水平侧移会导致基础刚度的降低,进一步影响风机系统的自振频率。该文基于有限元软件ABAQUS平台,建立单桩式海上风机结构系统的自振频率数值模型,并讨论运行状态下基础水平侧移对大直径海上风机系统自振频率的影响。模型中考虑了塔筒的变截面特性;桩-土相互作用通过p-y曲线方法模拟;桩和塔采用梁单元模拟;通过Pushover分析汇总出水平侧移引起的桩顶水平刚度。研究结果表明:桩基侧向位移会降低风机结构体系的自振频率;桩基侧向位移对基频的影响较小,对高阶频率的影响显著;大直径海上风机的频率计算中可忽略风机运行状态对体系自振频率的影响。

Effect of Operating State on the Natural Frequency of an Offshore Wind Turbine Founded on Monopiles

Restriction of system frequency is one of the key points in the design of offshore wind turbines. The dynamic loads of operating offshore wind turbines can cause the horizontal displacement of the monopile foundation, which will decrease the stiffness of the pile-soil system, so that the natural frequency of the offshore wind turbine system will be further influenced. Based on the software platform ABAQUS, a numerical model is developed to analyze the system natural frequencies of offshore wind turbines supported on monopiles. Effect of the horizontal displacement of the foundation in the operating state on the natural frequencies of the offshore wind turbine system is further investigated. The numerical model considers the variation of the cross-sectional geometry of the wind turbine tower; the pile-soil interaction is simulated by a p-y curve method. The tower and monopile are modeled using beam element, and the pushover analysis is used to obtain the equivalent springs providing the foundation response at the pile-cap level. Results indicated that the lateral displacement of the monopile will reduce the natural frequency of the system. It has little effect on fundamental frequency, but has a significant effect on higher frequencies. In general, the influence of the operating state of the wind turbine on the natural frequency of the wind turbine system can be neglected.