长期循环荷载作用时单桩式海上风力机结构自振频率的影响规律研究

基于FLAC^3D有限差分计算平台,建立风力机结构自振频率数值计算模型,并与工程监测的自振频率数据进行对比验证模型的有效性;然后通过嵌入土体刚度衰减模型（DSM）,考虑长期循环荷载对地基刚度的影响;探讨不同大小的循环荷载、不同的循环加载次数对海上风力机结构体系自振频率的影响规律,提出自振频率衰减公式;最后结合既有的风力机结构体系自振频率简化计算方法,建立单桩式海上风力机长期自振频率简化评价方法。结果表明,循环荷载的增大、加载次数的增加会导致海上风力机结构体系自振频率较小;风力机结构体系的设计自振频率应偏移3P,以保证海上风力机的长期运营安全。

INFLUENCE STUDY OF NATURAL FREQUENCY OF MONOPILE SUPPORTED OFFSHORE WIND TURBINE STRUCTURE UNDER LONG-TERM CYCLIC LOADS

A numerical calculation model is established to obtain the natural frequency of wind turbine structures by employing FLAC^3D software. This model is verified by comparing with the engineering monitored data. The degradation stiffness model （DSM） is embedded into the numerical model to consider the effect of long-term cyclic loads on foundation stiffness. Influences of different amplitude and number of cyclic loads on the natural frequency of the offshore wind turbine structure is explored by using this developed numerical model. Finally, the natural frequency attenuation formula is put forward, and an evaluation method is proposed to evaluate the effect of the long-term cyclic loads on the natural frequency. The results show that the natural frequency of the offshore wind turbine structure decreases with increasing the amplitude and number of cyclic loads. The natural frequency design of the wind turbine structure should be offset towards 3P to ensure the long-term operational safety of the offshore wind turbine.