Theoretical and experimental studies of effects of non-axisymmetric inner structures on vibration signatures of axisymmetric submarine hulls

A unified hybrid analytical-numerical method is proposed for vibration analysis of stiffened hulls coupled with non-axisymmetric internal structures. The coupled system is firstly de-composed into the submarine hull and internal structures. Then, the stiffened hull is fur-ther divided into ring stiffeners, bulkheads and shell segments, including conical and cylin-drical shell segments. The shell strips and axisymmetric reinforcements are uniformly de-scribed by the Flugge formula and power series method. For non-axisymmetric interior structures, finite element method is utilized to establish the motion equations owing to their irregular shapes. To synthesize the shell and non-axisymmetric internal structures, the receptance functions at coupling nodes are respectively deduced by condensing the global stiff matrices of the hull and interior substructures. A precise coupling method fully considering all 6 DOFs at coupling nodes, rather than just 3 or 4 DOFs in previous lit-erature, is proposed to synthesize the receptance functions. To verify the validity of this approach, a stiffened conical-cylindrical-spherical shell coupled with two foundations is manufactured and the forced vibration characteristics of this coupled model subjected to multiple types of excitations are tested. Results obtained by semi-analytical method are simultaneously compared with the ones measured from this experiment and calculated through finite element method (FEM). Effects of the inner structures and different exter-nal excitations on forced vibrations are discussed by experiment. Furthermore, how non-axisymmetric internal structures modify wave propagation and conversion characteristics of axisymmetric hulls is investigated through the present method. (c) 2023 Elsevier Inc. All rights reserved.

Automated summary

A unified hybrid analytical-numerical method is proposed for vibration analysis of stiffened hulls coupled with non-axisymmetric internal structures. The method decomposes the coupled system into the submarine hull and internal structures, and further divides the stiffened hull into ring stiffeners, bulkheads, and shell segments. The non-axisymmetric interior structures are analyzed using the finite element method, while the shell strips and axisymmetric reinforcements are described using the Flugge formula and power series method. A precise coupling method is proposed to synthesize the receptance functions at coupling nodes, considering all 6 degrees of freedom. The method is verified through experiments and compared with results obtained from the finite element method.