Local modified mesh deformation based on radial basis functions for fluid solid interaction in reactor core

Abstract

In reactor core, the fuel assembly immersed in the coolant will vibrate under the action of fluid pressure, the vibration of the fuel assembly will also change the distribution of the coolant in space, thus forming a typical fluid structure interaction. In numerical simulation, the interaction between the fluid domain (coolant) and the solid domain (fuel assembly) is reflected in the change of the mesh, and the change of the solid domain will directly affect the spatial position of the fluid domain mesh. Consequently, the displacement caused by such change should be mapped to the fluid domain, and the spatial position of fluid domain mesh should be updated accordingly. To improve the efficiency and accuracy of mesh deformation in the fluid domain, we propose a local modified mesh deformation based on radial basis functions (LMMD-RBF), which realizes local mesh deformation for the fluid domain. It first estimates a deformation degree for each local area of the fluid domain. If the deformation degree is too large, it will calculate the displacement and update the position for each node in this local area based on an incremental modified scheme. The local area is obtained by dividing the fluid domain into multiple sub-areas of similar size, and it employs a maximum deformation and a threshold to evaluate the deformation degree of each local area. Furthermore, the whole deformation calculation can be further accelerated by a designed two-level hash mechanism. LMMD-RBF is proved to be efficient and accurate by six “flow channel-fuel rod” numerical examples, and the efficiency and accuracy are greatly improved compared with other RBF-based methods. Experimental results show that the deformation mainly occurs in the flow channel near the outer surface of the fuel rod, and the deformation near the wire winding of the fuel rod is more obvious.