The fatigue damage and lift force caused by vortex induced vibration occur very often in the core of the Pressurized Water Reactor (PWR) [1] It is extremely complex to illustrate the mechanism of vibration which induced by Cross-flow. With the spacer grids and wings, the flow direction which in axial direction at the inlet will change and create swirls, so there are many flow directions in the nuclear fuel component. Assumed the tube endure cross-flow only in this article to simplify the fluid model. Most researchers in this field often ignore the displacement of structure induced by the cross flow because the value is so small that not enough to change the fluid region. In truth conditions, the motion of the cylinder caused the wake oscillation and strengthen the vortex shedding, in turn, the vortex shedding will aggravate the vibration amplitude. According that, one way FSI (Fluid Solid Interaction) can’t capture the influence from the cylinder vibration. In this article, Two-way FSI method was executed to get the vibration in time history in order to get the random vibration induced by the cross flow more close to the actual project. Using Finite Volume Method to discrete the fluid control equation and finite element method to discrete structure control equation combined with moving mesh technology. An interface between the fluid region and the structure region was created to transfer the fluid force and the structure displacement. Coupling CFD code and CSD (Computational Solid Dynamics) code to solve the differential equation and obtain the displacement of the cylinder in time history. A Fast Fourier Transfer (FFT) has been done to get the vibration frequency. An Analysis of the vortex shedding frequency and vibration frequency to find the correlation between the vortex shedding and the vibration frequency has been done. A modal analysis for the cylinder without water has been done to get the natural frequency. Results shows the cylinder has different response to the vortex shedding at different position of the cylinder in the same condition. There are more works need to be done aim to get the vibration mechanism in tandem tube and parallel tube to get clearly mechanism of vortex induced vibration in nuclear fuel assembly. The research of the vortex induced vibration in this article is a key to get on the follow research in more tubes array in different methods.

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