Theory and experiment of two concentric submerged cylindrical shells coupled by the entrained fluid

Abstract

In this paper theory and experiment for the coupled vibration of two concentric cylindrical shells (double shell) are described; the inner shell contains air, the outer shell is surrounded by water, and water exists in the annular space between them. A point force is applied to the inner shell, whose displacement produces acoustic pressure in the annular space and in turn this pressure wave drives the outer shell. The nature of acoustic field in the annular fluid and its coupling effect on the shells is investigated. Using Flügge's shell equations and the Helmholtz equation, the normal modes of an infinite double shell are calculated. The theory includes the effect of initial prestress (uniform axial compression). The results of these numerical calculations in wave‐number space will be compared with the results from generalized near‐field acoustical holography (GENAH) experiment on a simply supported finite double shell. The wave‐number/frequency representation of this double shell will be also compared with that of a single submerged shell.