风电叶片低阶频率识别的近似解法及试验

Approximate solving method and test for lower order natural frequency identification of a wind turbine blade

风电叶片截面具有不规则特征,采用传统的Bernoulli-Euler Beam模型求解其低阶固有频率非常困难。提出一种风电叶片低阶固有频率识别的新方法—矩阵传递算法。沿叶片展向将其离散为若干个二节点梁,对每个二节点梁段求出段矩阵,将总传递矩阵等效为若干个段矩阵之积。通过引入边界条件,编制程序对aeroblade3.6-56.4风电叶片的低阶固有频率进行数值计算。最后以该叶片为研究对象,构建一套大叶片模态参数识别试验系统,采用单点激励中的"不测力法",加速度信号经过有限脉冲滤波器(FIR)和快速FFT变换后,得到最大挥舞、摆振方向(Max flapwise、Maxedgewise)的低阶固有频率值。将计算结果与试验结果作对比,验证了矩阵传递算法应用于大叶片低阶固有频率识别的可行性。模态参数识别试验得到的频率值,也为后续的风电叶片疲劳加载试验打下基础。

It is very difficult to solve the lower order natural frequencies of a wind turbine blade using the traditional Bernoulli-Euler beam model because its cross-section has irregular features. A new identification method for lower order natural frequency of a wind turbine blade, a transfer matrix method, was proposed. The blade was diseretized into several beam segments with two-node along its span and the transfer matrix of each segment was obtained. The transfer matrix of the whole blade was the multiplication of the transfer matrices of the beam segments. The lower natural frequencies of aeroblade3.6-56.4 wind turbine blade were calculated using the transfer matrix derived with introducting boundary conditions. Finally, a modal parameter identification test system was setup. The lower order natural frequencies for the Max flapwise direction and the Max edgewise direction were obtained with the ＂unmeasured strength method＂ of single-point excitation using accelerator signal passing FIR filter and FFT. The calculated and test results were compared and the feasibility of the transfer matrix method used to calculate lower order natural frequencies of a wind turbine blade was verified. The modal parameter identification test results laid a foundation for several beam segments with two-node wind turbine blade fatigue loading test.