NUMERICAL-ANALYSIS OF THE FLUIDELASTIC VIBRATION OF A STEAM-GENERATOR TUBE WITH LOOSE SUPPORTS

The vibration and wear of U-tubes has been observed in PWR steam generators, especially in the U-bend region where the tubes experience two-phase cross-flow. In this region the tubes are supported by anti-vibration bars (AVBs); however, clearances can exist between the tubes and AVBs so that flow-induced vibration can cause impacting and sliding to occur between the two components, leading to fretting wear. A method is described for analyzing the impacting behaviour of a steam generator tube which has one or more loose supports and is fluidelastically unstable. The method uses a fluidelastic instability model to predict the damping (positive or negative) of all the modes of vibration of the tube and uses this information in a nonlinear transient analysis computer code, which includes the effects of impacting at loose supports. A comparison is made between numerical predictions and experimental results obtained from a cantilever tube array in cross-fly. The predicted changes in frequency of vibration with flow velocity agree well with the experimental values, giving some confidence in the accuracy of the method. The method is then used to analyze the fluid-elastic vibration of a steam generator U-tube with a single loose AVB support point. © 1992.