Self-Excited Vibration of a Flexible Shell Caused by Fluid Discharge

在法国Super Phenix LMFBR的试运行中，观察到了一种由于流体放电而产生的新型自激振荡现象。观察到两种失稳模式：一种是晃动模式，其含义是与进料和恢复集热器有关的堰的振动；另一种是水弹性模式，其含义是与流体壳模式有关的堰的振动。在本研究中，从理论和实验两方面讨论了这两种模式的激发机制。在实验中，设计和制造了矩形和环形水箱，研究了落差高度和供给流量对失稳的影响。在矩形水池中观察到了晃动和水弹性两种模式。在另一波段，环形水箱中只观察到了晃动模不稳定性。为了建立能够解释这种不稳定性机理的理论，提出了理论模型。在该理论中，基本方程由下游液舱晃动的动量方程和供给流量守恒方程组成。采用动量理论，建立了流体与自由表面碰撞的数学模型。最后，我们成功地推导出了这种不稳定性的简化控制方程。理论结果表明：(L)这种不稳定振动的频率几乎等于下游水舱晃动的一阶固有频率；(2)在一定的落差高度范围内可以发生不稳定振动；(3)这种不稳定振动的范围随着供水流量的增加而变窄。这些理论结果与实验结果吻合较好，证实了理论的正确性。

A new type of self-excited osillation due to the fluid discharge was observed during test operations of the Super Phenix LMFBR in France. Two types of instability modes were observed : one is the sloshing mode the meaning of which is the oscillation of a weir associated with both feeding and restitution collectors ; the other is hydroelastic mode the meaning of which is the osillation of a weir associated with fluid shell modes. In this investigation, the excitation mechanism of both modes is discussed both theoretically and experimentally. In the experiments, rectangular and annular tank were designed and manufactured to investigate the effect of fall hight and supply flow rate on the instability. Both sloshing and hydroelastic modes were observed in a rectangular tank. On the other band, only asloshing mode instability was observed in an annular tank. To establish the theory which can explain the mechanism of this instability, theoretical model was proposed. In this theory, basic equations are composed of the momentum equation of the downstream tank sloshing and conservation of supply flow rate. To formulate the fluid force colliding with free surface, momentum theory was employed. Finally, we succeeded in deriving the simplified governing equation of this instability. Theoretical results show the following ; (l)the frequency of this unstable oscillation is almost equal to the first natural frequency of the downstream tank sloshing, (2)unstable vibration can occur at the range of certain fall height, (3)the range of which becomes narrow with increasing supply flow rate. These theoretical results agree well with experimental results and the validity of the theory was confirmed.