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

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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.