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基于POD方法的EPR燃料棒流致振动特性分析

FLOW-INDUCED VIBRATION CHARACTERISTICS ANALYSIS OF EPR FUEL RODS BASED ON POD METHOD

  • 摘要: EPR (European pressurized reactor)燃料棒相比M310燃料棒的棒长更长, 导致其频率降低、幅值增大, 在冷却剂的作用下, 会加剧格架与棒束之间微动磨损(grid-to-rod fretting, GTRF), 进而造成放射性物质的泄漏. 将EPR燃料棒简化为3D梁模型, 将刚凸和弹簧对燃料棒的约束等效为弹性约束, 将带格架的燃料棒简化为多跨连续简支梁模型, 然后基于ANSYS-APDL建立了EPR燃料棒的有限元模型. 阐述了湿模态分析和湍流激振响应分析的基本原理, 整理了12个格架失效工况, 系统地研究了格架失效对湿模态和湍流激振响应的影响. 针对EPR燃料棒流致振动问题, 提出了采用本征正交分解(proper orthogonal decomposition, POD)原理分析EPR燃料棒流致振动特性的方法, 通过对快照矩阵进行POD分解生成投影子空间, 将湍流激振响应投影到子空间进行模型降阶, 最后在物理空间快速地重构湍流激振响应. 结果表明: 格架失效会导致频率降低, 且湍流激振响应的幅值会在格架失效处增大; 当格架失效使得EPR燃料棒模型成为悬臂梁结构时, 湍流激振响应最大; 前2阶POD降阶模型基本能快速重构燃料棒的湍流激振响应, 且误差非常小. 文章的研究将有助于核反应堆工程的优化和设计.

     

    Abstract: The length of the EPR (European pressurized reactor) fuel rod is longer compared to the M310 fuel rod, resulting in a decrease in frequency and an increase in amplitude compared to the M310 fuel rod. Under the influences of the coolant, grid-to-rod fretting (GTRF) wear may be exacerbated, potentially leading to the leakage of radioactive materials. Here, the EPR fuel rod is simplified as a 3D beam model, where the constraints of dimples and springs on the fuel rod are treated as equivalent elastic constraints. Additionally, the fuel rod with a spacer grid is further simplified as a multi-span continuous simply supported beam model. A finite element model of the EPR fuel rod based on ANSYS-APDL is established, and the fundamental principles of wet mode analysis and vibration response analysis are explained. 12 grid failure conditions have been sorted out, and the influences of grid failure on wet mode and vibration response have been systematically studied. A method for analyzing the vibration characteristics of the EPR fuel rod using the proper orthogonal decomposition (POD) method is proposed, targeting flow-induced vibration (FIV) of the EPR fuel rod. The snapshot matrix is decomposed by POD method to generate the projection subspace, and the responses are projected onto the subspace for model reduction. Finally, the response is reconstructed in the physical space. The results show that the amplitude of vibration responses would increase at the location of grid failure; When the grid structure fails and causes the EPR fuel rod model to become a cantilever beam configuration, the maximum response to turbulent excitation is achieved; For the analysis of response, the first 2 orders POD reduced order model (ROM) can basically reconstruct the response of the fuel rod. The research in this paper will help to the optimization and design of nuclear reactor engineering.

     

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