Fundamental Study on Self-Excited Vibration of Concentric Tubes Subjected to Double Axial Annular Flow

Abstract

This study investigates the self-excited vibration of concentric tubes subjected to double axial annular flow. Recent designs in nuclear reactor components involve a long circular cylinder containing an elastic hollow tube, which in turn houses an elastic solid bar. Axial flow through the annulus between these components can induce vibrations of tubes. While previous research has extensively examined vibration in concentric tube systems subjected to single annular flow, research on concentric tube systems subjected to double annular flows are not seen. In this research the equations of motion for a concentric tube system subjected to double annular flows are shown and the stability of self-excited vibrations using complex eigenvalue analysis are investigated. The coupled vibration modes of the hollow tube and solid bar are derived by superpositions of vacuum modes. Based on this theory, the simulation studies are performed. Simulations are validated by comparing the results with those of concentric tube systems subjected to single annular flow. In addition, this study investigates how the Young's modulus and length of the tubes affect the critical flow velocity. It is found that the smaller the Young's modulus and the larger the length of the structure, the smaller the critical flow velocity. The coupled modes are also displayed, and it is confirmed that the modes are distorted at the critical flow velocity.