二维晃动自然频率与阻尼比系数的试验识别

液体的晃动模态（自然频率、振型与阻尼比系数）是贮液结构设计以及振动控制的重要参数。在液体晃动的模态试验中，需要激发液面的模态运动，但液面的对称模态运动一般比较难以激发出来，使得对称模态参数（特别是阻尼比系数）难以精确识别。本文采用参数激振的方法对矩形、U形和圆形截面容器进行竖向激振，可容易激发出液体表面的前四阶模态(包括对称模态)运动，撤除激励后液体表面按某一特定的振型作自由衰减振动，通过激光测量液体表面波高的自由衰减曲线，从而精确得到液体晃动的自然频率与对应的阻尼比系数，测得晃动频率与理论频率结果吻合良好，表明本文试验识别方法有效。

An experimental identification for the natural frequencies and damping ratios of two-dimensional sloshing

The modal parameters of sloshing fluid are essential for the design of liquid tanks and vibration control. In the modal experiment of fluid sloshing，the modal motions of free liquid surface should be aroused. However the symmetric-mode motions of free surface are difficultly stimulated, therefore the modal parameters (especially for the damping ratios) of the symmetric modes cannot be accurately measured. This paper applied parametric vibration method to excite the two-dimensional (parametric) sloshing in the rectangular, U-shaped and circular tanks. The first four mode motions (including the symmetric-mode motions) of free surface are easily aroused. After stopping the external excitation, a free damped vibration response of a certain mode on the free liquid surface can be obtained, and measured with the laser displacement sensor. The sloshing natural frequencies and the corresponding damping ratios are precisely obtained. The experimental and theoretical frequency results agree well, which verified the validation of present experimental method.