FLOW-INDUCED VIBRATION RESPONSE ANALYSIS OF A HELICAL CRUCIFORM FUEL ROD BASED ON TRANSFER MATRIX METHOD

The helical cruciform fuel (HCF) rod is a novel fuel rod, which exhibits favorable thermal-hydraulic performance and a self-supporting structural configuration. However, conventional Workbench-based fluid-structure interaction analyses of flow-induced vibration (FIV) are computationally expensive and often require substantial effort to achieve numerical convergence. To address these limitations, an efficient analytical framework integrating the transfer matrix method (TMM) and modal superposition method (MSM) was developed based on Euler-Bernoulli beam theory. First, the cross-sectional moment of inertia at different axial positions of the HCF rod was determined using the parallel-axis theorem. The transfer matrix of the HCF rod was then derived to calculate its natural frequencies and mode shapes, and the modal results were verified against those obtained using the finite element method (FEM). Subsequently, the turbulent excitation forces acting on the fuel rod were obtained through large-eddy simulation, and the FIV response was calculated using the MSM. The results show that the first three natural frequencies predicted by the TMM agree closely with the results by FEM. The relative difference in the root-mean-square displacement at the midspan is approximately 0.01%, and the predicted mode shapes, time- domain and frequency-domain responses, and vibration trajectories are in close agreement. For the cases and computational configurations considered, the total computation time of the proposed framework is approximately one quarter of that of the referenced Workbench-based method, while the structural response calculation requires only about 4.5 min. The proposed framework improves computational efficiency while maintaining high accuracy and provides a practical approach for the FIV analysis of large-scale fuel rod bundles.