Study on the added mass of the double-fixed constrained flexible coaxial cylindrical shells with liquid in the narrow gap

There are many coaxial cylindrical thin-wall structures with a narrow fluid gap in the reactor block of the pool type sodium cold fast reactor (such as primary pump support and its thermal shield). The fluid-structure interaction (usually represented by added mass) of shells and the fluid gap changes the structure's dynamic characteristics under seismic conditions. Therefore, it is significant to calculate the added mass of the coaxial cylindrical shells. At present, there are few studies on the vibration modes and added mass of flexible shells with double-fixed constrain. For the flexible coaxial cylindrical shells model, due to the coupling of the inner and outer shell, the vibration modes of the inner and outer shell in the same and opposite directions are generated. In this paper, the added mass of two vibration modes in the same direction and in the opposite direction are investigated. The finite element models (with water and without water) of the coaxial cylindrical shells were established using ANSYS software, and the vibration modes and added mass were calculated by FEM. Further, the effect of different outer shell rigidity on the added mass of coaxial cylindrical shells was studied by changing the material parameters of the outer shell.