环境激励下二滩拱坝拍振机理的研究

在二滩拱坝泄洪振动时程曲线中，可以看到波形的包络线随时间增大或减小的现象，波形非常像振动中的“拍”现象。通过对原型观测数据的分析，研究二滩拱坝拍振机理。首先引入自然界中“拍”的概念，论述了初相差、频率比和振幅比对“拍”的影响以及多列波合成拍的特性；然后应用随机子空间方法(SSI)和频谱分析方法，对二滩拱坝的模态参数进行识别；最后结合实测拍振现象的自身特点，对泄洪激励下二滩拱坝拍振现象的机理进行研究。结果表明，拱坝工作频率相近的前两阶振型振动是形成拍振的主要原因，此外，一个频带在1.27~1.39Hz的振动分量也参与了拍的合成，初步认为这一分量是由坝段间接触非线性引起的。

Beat vibration of ertan arch dam under ambient excitation

On the vibration time history curve of Ertan arch dam under flood discharge excitation,the phenomenon that the wave envelope rises or reduces along with the time can be observed.The effects caused by initial phase difference,frequency ratio and amplitude ratio were discussed.The dominant frequency of measured data was collected and analyzed with the auto regressive model,and the first four vibration modes were obtained based on SSI.Considering the special features of beat vibrations,the beat vibration of Ertan arch dam under discharge flow was investigated.The result shows that the main cause forming beat vibration is the first two orders of vibration modes whose frequencies situate closely.In addition,a vibration component with the its frequency band at 1.27 ～1.39Hz also gives rise to forming "beat".The component is considered to be caused by nonlinear contact between dam sections.