Study on fluid-structure interaction characteristics for coaxial cylindrical shells with liquid in the annular gap

There are many coaxial cylindrical thin-wall structures with narrow fluid gaps in the reactor vessel of the pooltype fast reactor. The fluid-structure interaction characteristics of such structures are important for the reactor's safety in an earthquake. However, the fluid-structure interaction characteristics of coaxial cylindrical shells with different boundary conditions and the inner-outer-shell coupling remains to be explored. In this paper, we study the added mass for the shell-type vibration of single-end-fixed coaxial cylindrical shells by vibration experiments and the finite element method (FEM). Then, we study the influence of the outer shell's rigidity and different boundary conditions (single-end-fixed and double-end-fixed cylinder) on the modal frequency and the added mass by the FEM. It shows that different boundary conditions cause a 50% difference in the added mass with modes with small circumferential wave numbers. This work provides a benchmark for strong fluid-structure interaction for flexible double shells with small fluid gaps.