Study on Flow Induced Vibration Mechanism and Its Critical Velocity of Tube Bundle

明确了各管束在非定常流体动力作用下的运动方程。应用多自由度振动计算流致振动的临界速度，并推导出计算方程。因此，在已知结构特征和非定常流体动力学的情况下，可以计算出尼尼无管束的临界速度。非定常流体动力由两种力组成，一种是由其自身运动引起的力，另一种是由另一管运动引起的力。这些流动的力量是建立在一个稳定的支撑上的。通过实验获得了应变片。在实验中，一个圆柱体安装在振荡器上，另一个圆柱体安装在每个支撑杆上，以获得作用在管子上的流体动力。应变片的信号有很大的噪声，这是由振荡器或其他运动部件产生的。对如何在早期消除噪声进行了考虑，并尝试了几种方法。然而，我们没有找到任何有用的方法，然后用数字滤波和傅立叶展开来去除计算中的噪声。一根管子有两种自由度，流体动力也有两种分量。需要知道随折减速度变化的8种流体动力。通过实验得到了所有的流体动力，并计算出了启动振动的临界流速。结果表明，该估计方法对判断是否会发生振动具有一定的实用价值。

Equation of motion of each tubes in bundle which is forced by unsteady fluid dynamic forces was cleared in this study. Vibration with Multidegree of freedom was applied to calculate the critical velocity at which flow induced vibration starts and equation for calculation was induced. So that, critical velocity of ninni no tube bundle can be calculated if structural characteristics and unsteady fluid dynamics are know.Unsteady fluid dynamic forces are consist of two kind of forces, one is induced by its own moving and the another is by moving of the other tube. These fluid forces were set on a steady support. Strain gages were obtained by experiment. On experiment, one cylinder is mounted on oscillator and the other cylinders were put on each support bar to obtain fluid dynamic forces acting on the tube. Signal from the strain gages had great noise which was generated by the oscillator or other moving parts. It was considered how to remove the noise in early stage and several method were tried. However, we could not fined out any useful method and after that, digital filter and Fourie expansion were used to remove the noise in calculation.One tube has two kind of freedom and fluid dynamic force also has two component. It is necessary to know 8 kinds of fluid dynamic forces which vary with reduced velocity. All fluid dynamic forces were obtained by the experiment and critical flow velocities at which vibration will start were calculated. It was cleared that the method of estimation is useful to judge whether vibration will occur or not.