  The aim of this study is to develop a semi-analytical method to investigate
fluid-structure coupling of concentric double shells with different lengths and
elastic behaviours. Co-axial shells constitute a cylindrical circular container
and a baffle submerged inside the stored fluid. The container shell is made of
functionally graded materials with mechanical properties changing through its
thickness continuously. The baffle made of steel is fixed along its top edge
and submerged inside fluid such that its lower edge freely moves. The developed
approach is verified using a commercial finite element computer code. Although
the model is presented for a specific case in the present work, it can be
generalized to investigate coupling of shellplate structures via fluid. It is
shown that the coupling between concentric shells occurs only when they vibrate
in a same circumferential mode number, n. It is also revealed that the
normalized vibration amplitude of the inner shell is about the same as that of
the outer shell, for narrower radial gaps. Moreover, the natural frequencies of
the fluid-coupled system gradually decrease and converge to the certain values
as the gradient index increases.
