基于 HHT 方法的非稳定工况风力机结构动态响应时频特性分析

摘要

The typical non-stationary operating conditions,such as,turbulent inflow of wind speed changing dramatically,starting up,yawing motion,and emergency shutdown enhance nonlinear aero-elastic responses of a wind turbine,its structural dynamic responses in time domain and frequency domain both have obvious non-stationary characteristics.The turbulent inflow with velocity and direction both varying intensely was built based on its spectral model and coherent structure.The dynamic characteristics of the wind turbine under non-stationary operating conditions were computed with the aerodynamic-servo-elastic software called FAST.The numerical calculation results were compared with those of GH Bladed to verify the results'validity.The dynamic characteristics in time-frequency domain for blades and tower deflections were analyzed based on Hilbert-Huang Transformation (HHT)method.The results showed that the deflections of tower and blade tip fluctuate within a narrow range of about 40 s and then increase rapidly in starting up,but they fluctuate wildly about 20 s and return a steady state after emergency shutdown;yawing motion leads to a clearly rise of tower tip deflection in lateral direction;the fluctuation of tower tip deflection is concentrated at the first order vibration frequency and its amplitude increases in yawing motion;the fluctuation of blade tip deflection in plane is mainly caused by the rotor rotating and blades'the first order shimmy frequency is affected by coherent structure;the negative aerodynamic damping makes amplitudes rising during emergency shutdown,enlarging structural damping should be considered in the design of blades to depress their amplitude rising due to aerodynamic damping rapidly dropping.%风速变化剧烈的湍流风场、开机启动、偏航以及紧急停机等典型非稳定运行工况均会增强风力机非线性气动弹性响应，时域和频域的结构动力学响应具有十分明显的非平稳特征。为此，基于湍流风谱和相干结构，建立了速度和方向均剧烈波动的湍流风，在气动－伺服－弹性仿真软件 FAST 中计算了风力机非稳定工况下的动力学特性，并与 GH Bladed 计算结果对比，验证了结果的有效性。使用 HHT 方法分析了塔架和叶片位移的时频特性，结果表明：开机启动阶段塔架和叶片位移均小幅振荡约40 s 后急剧增加，紧急停机均剧烈振荡约20 s 后恢复平稳，偏航导致塔尖侧向位移明显上升。塔架位移响应频率主要集中于一阶振动频率，偏航时幅值增大明显。风轮旋转频率为叶尖摆振的主要谐振动频率，叶片一阶摆振频率受到相干结构影响，紧急停机时由于负气动阻尼影响而使得幅值增大，叶片设计时应适当增大阻尼以减小气动阻尼迅速降低带来的振幅急速增加现象。