Research on Vibration Suppression of a Wind Mill

随着风力发电的发展，振动和噪声成为一个严重的问题。然而，大多数关于风力米尔斯的研究都是与发电有关的，例如，叶片的形状、叶片的数量等。有些风力米尔斯的叶片长达近50米。因此，出现了在普通旋转机械中观察不到的非常独特的振动问题。例如，在叶片的顶部位置和底部位置处的风力是不同的，并且这种差异形成周期性的激振力。当叶片靠近磁极时，压力脉冲起作用。这种激振力可引起叶片的各种振动。我们澄清了以下几点。(1)由于周期性激振力，发生谐波共振。(2)由于在顶部位置和底部位置的恢复力不同，该系统成为一个受激系统。(3)重力作用下的参数激励与风力作用下的周期激励共存，引起了各种形式的超谐共振。(4)随着叶片刚度的减小，参数激励的影响增大。(5)不稳定区域是指在周期性激励下，叶片的刚度小于一定值时出现的区域。从该研究可以看出，即使没有制造误差，风力发电机也有可能引起振动。

As the development of wind mil generation, vibrations and sounds became a serious problem. However, most of the research on wind mills are those related to the generation of the electric power, such as, the shape of blade, number of blades, etc. Recently, the size of the blade becomes large. Some wind mills has a long blade of almost 50 meters. Therefore, very unique vibration problems which are not observed in the ordinary rotating machinery occur. For example, the wind forces at the top position and the bottom position of the blade are different and this difference makes a periodic excitation force. When a blade passes near the pole, a pressure impulse works. Such excitation forces may cause various kinds of vibrations of the blades. We clarified the followings.(1) Due to the periodic excitation force, a harmonic resonance occurs. (2) Since the restoring forces at the top position and the bottom position are different, this system becomes a periodically-excited system. (3) The coexistence of the parametric excitation due to the gravity and the periodic excitation due to wind force causes various kinds of superharmonic resonances. (4) As the stiffness of the blade decreases, the effect of parametric excitation increases. (5) Unstable zone appears when the stiffness of the blades becomes smaller than a certain value due to the periodic excitation.From this research, it became clear that wind turbines has a potential to cause vibrations even if they are made without manufacturing errors.