二阶波浪载荷作用下张力腿型浮式风力机高频谐振响应与疲劳特性研究

Tension leg-type floating wind turbine is vertically constrained by tendons and thus has small wave frequency response. However, the second-order and higher-order wave loads can induce significant low-frequency resonance and high-frequency resonance, which in turn increases the structural and tendon load fluctuation and reduces its fatigue life. At present, both domestic and foreign researches were carried out from the numerical point of view, and the numerical model was not verified with the model test results, so the accuracy of the calculation results were not guaranteed. In addition, the previous studies on structure fatigue damage only involved in part of the typical loading conditions, and less consideration was given to structural fatigue damage caused by second-order wave loads under full-wave spectrum conditions. In view of this situation, this project intends to use the method of theoretical analysis, numerical simulation and model test to systematically study the high-frequency resonance response and fatigue characteristics of tension leg-type floating wind turbine under second-order wave loads with quantification of the influence of the second-order wave loads on the extreme tendon tension and structural fatigue damage. The outcomes of this study are expected to provide a theoretical basis and technical support for future works regarding the design and analysis of floating offshore wind turbines.

张力腿型浮式风力机通过采用垂直张紧式系泊系统，使其运动固有频率避开了波浪能量集中的频率范围，具有较小的波频运动响应。然而，在二阶和更高阶波浪载荷的作用下，张力腿型支撑平台会发生低频谐振和高频谐振，继而显著地增大结构以及筋键的载荷波动幅度，减小其疲劳寿命。目前已有国内外相关研究均从数值计算角度进行展开，并未结合试验结果对其数值模型进行验证，因而难以保证计算结果的准确性。此外，已发表的结构疲劳特性研究仅考虑了部分典型工况，较少考虑全波浪谱工况下的二阶波浪载荷所导致的结构疲劳损伤。针对这一现状，本课题拟采用理论分析、数值模拟和模型试验相结合的方法对二阶波浪载荷作用下张力腿型浮式风力机的高频谐振响应与疲劳特性进行系统性研究，揭示其作用机理和影响规律，量化二阶波浪载荷对筋键张力极值与结构疲劳损伤的影响程度，为我国系统掌握张力腿型浮式风力机设计分析关键技术提供理论依据和技术支持。

海洋风电开发正致力于向远海深水区域发展。张力腿型浮式风力机是目前开发远海深水风能最具潜力的核心装备之一。我国深远海浮式风电系统研发起步不久，自主设计评估核心技术匮乏，对高海况下张力腿型浮式风机耦合动力学响应机理及结构疲劳特性的认识欠缺。本项目通过理论分析、数值计算和模型试验的技术途径，开展了二阶波浪载荷作用下张力腿型浮式风力机的高频谐振响应与疲劳特性研究。主要研究成果如下：基于时域耦合分析方法建立了张力腿型浮式风力机全耦合动力学模型，并利用前期开展的水池模型试验结果验证并完善了该耦合数值分析模型，明晰了不同工况下的系统耦合动力特性；揭示了二阶和频波浪载荷对张力腿型浮式风机纵摇运动、机舱纵荡方向加速度、塔筒载荷和张力腿载荷波动高频响应影响规律。针对浮式风力机的极限载荷统计外推方法以及时域疲劳载荷计算方法进行了系统研究，改进了极限载荷分析中局部最大载荷的提取方法，预报了关键部件的极限载荷；考虑一阶和二阶波浪载荷后的张力腿张力的数值计算结果与试验结果吻合较好，能够有效地模拟由垂荡和纵摇运动引起的张力腿张力高频响应；揭示了二阶波浪载荷引起结构疲劳损伤加剧机理。项目研究成果可为研发张力腿型浮式风机系统及其复杂海况下的结构安全性评估提供技术支撑。