Analysis of the flow-induced vibration characteristics of U-tubes in steam generators based on the 14-equation model

Steam generator U-tubes are essential components of nuclear power plants, and fluid-induced vibrations in these tubes can cause fatigue damage. To examine the vibration characteristics of fluid-filled U-tubes, this paper develops a three-dimensional vibration analysis model based on the transfer matrix method and a 14-equation model that accounts for fluid-structure interaction. The overall system transfer equation is constructed by discretizing and combining field transfer and point transfer matrices, allowing for the efficient estimation of natural frequencies and mode shapes. Using the Type 55/19 steam generator U-tubes as the subject, this paper examines the modal features under various bending radii and elastic support conditions, comparing the results to those produced by the finite element method for validation. The results show that the TMM and FEM computations are highly consistent; the error in the first six natural frequencies is less than 1% across all operating conditions, and the mode order stay consistent, confirming the model's accuracy and stability. Furthermore, the bending radius and support stiffness significantly affect the system's dynamic characteristics, and the TMM achieves a computational efficiency that is around two orders of magnitude higher than FEM, all while preserving engineering correctness. Results indicate that the constructed model combines accuracy and computational efficiency, providing an effective tool for dynamic characteristic analysis, vibration-resistant design, and safety assessment of steam generator U-tubes.