MECHANISM OF VIBRATION SUPPRESSION EFFECT FOR CONNECTED CANTILEVERED STRUCTURE OSCILLATING IN-LINE DIRECTION IN CROSS FLOW

这项研究是关于快中子增殖堆文州的一个热井在液钠横流中经历的自激在线振动。虽然日本在热井失效后对悬臂圆柱体的顺列振动进行了大量的研究，但对振动的原因还没有作出明确的解释。特别是对只有一口特殊热井破裂的原因还没有给出解释，目前仍在调查中。从学术兴趣的角度来看，这是一个激动人心的话题，因此，我们决定利用CRIERI Abiko研究中心的水洞，在小强迫幅值的外部激励下，对振动圆柱体上的流体动力进行精确测量。在一系列实验中，我们通过改变激励幅值、来流速度和激励频率来检验这种依赖关系对柱体振幅和折合速度的影响，结果发现流体作用力是由与振动圆柱的加速度、速度和位移成正比的分量组成的。我们还发现，决定不稳定性的激发参数强烈依赖于柱面的振幅。另外，附加质量系数随折算速度的不同而变化，质量比对减振稳定性判据的影响较小。最后，我们收集了非定常流体动力学数据作为进一步研究的数据库。

This study is related to self-excited in-line vibration of a thermo-well in liquid sodium cross flow experienced in Fast Breeder Reactor Monju. Although quite a large number of research on the in-line oscillation of a cantilevered cylinder have been conducted in Japan after the failure of the thermo-well, clear cut explanation of the cause of the vibration has not yet been done. Especially, the explanation on the reason why only single particular thermo-well was broken is not yet given and is still under investigation. From the viewpoint of academic interest, this is an exciting topic.Therefore, we decided, to conduct precise measurement of fluid dynamic forces acting on the vibrating cylinder by using water tunnel at CRIERI Abiko Research Center under small forcing amplitude external excitations. In a series of experiments, we changed forcing amplitudes, oncoming flow velocities and excitation frequencies to check the effect of the dependency on the amplitude of the cylinder and reduced velocity.As a result, we found the fact that fluid force is composed of the component proportional to acceleration, velocity and displacement of the vibrating circular cylinder. We also found that excitation parameter which determines the instability is strongly dependent on the cylinder amplitude. In addition, added mass coefficient varies depending on reduced velocity and the stability criteria of reduced damping is slightly affected by the mass ratio. Finally, we collected unsteady fluid dynamic data as a database for further studies.